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The Great Microinverter Debate April 9, 2012

Posted by Maury Markowitz in solar.
Tags: ,

It was only a couple years ago that Enphase released the M175 onto the market. The follow-up release of the M190 really got the ball rolling, capturing a large part of the California inverter market. The M190 was the first “micro-inverter” to really succeed.

And with that success came the slings and arrows. Traditional big-iron inverter companies started pooh-poohing the upstart, stating that there was no way the product could ever be competitive. Enphase fought back, unleashing Raghu Belur on an unsuspecting market. His argument about scaling factors following the computer market model, a Moore’s Law of inverters, struck a chord.

The debate quickly grew heated as Enphase sales continued to ramp up. The competition became increasingly frustrated, launching a variety of attacks against both the product and the company. I’ve had representatives from major inverter and panel companies badmouth them right to my face, apparently oblivious of that damage this does to the market as a whole (it’s a small sandbox kids, play nice).

And in spite of looking really closely at all of this, I still can’t make up my mind about who’s got the best argument. And when I say I’ve looked really hard, the readers that know me will understand exactly what that means. So, in lieu of any strong conclusions, I’m going to spend some time -well, a lot really- simply laying out what I’ve learned so far.

Note: I’ve published a market update you might want to read. You can click it now, it will open in another tab/window.

The basics

Solar panels produce DC power, like a battery. Your house, and most everything else, runs on AC power, what comes out of a wall socket.

Systems that convert one to the other are generically known as “converters”, but we don’t use that term all that often in practice. Instead, we call AC-to-DC converters “power supplies” (or “rectifiers”, inaccurately), and the DC-to-AC versions “inverters”. There’s a whole class of devices that convert DC-to-DC in order to change the voltage, which go by a variety of names. There’s no equivalent AC-to-AC circuit, because that task is easily handled by a transformer – that’s why we use AC for everything, transformers are cheap and efficient.

You can buy an inverter at Canadian Tire that you plug into your car’s lighter socket that lets you power small devices like TV sets or radios. They’re cheap and not that bad in efficiency terms. In the case of solar, though, these devices are missing two very important features.

The first is the accuracy of the output power. Most devices will work fine if the power is “AC-like”, where “like” varies from something entirely unlike the grid to increasingly accurate approximations. The power company will not accept this, and they demand far more accurate renditions of their power. Not only does the waveform have to look like a clean sine signal, but the signal has to match the voltage, frequency and phase that the company is using. We talk about 120V power at 60Hz as the basis for the North American grid, but in practice this can vary a whole lot in the field, and the inverter needs to match it in real-time.

The other issue is specific to solar. PV systems deliver their power efficiently only when they are presented with the proper “load”. The relationship between incoming sunlight, temperature and load is complex. This is handled by a system known as a “MPPT“, a DC-to-DC converter that loads the panel as conditions vary, and converts the output voltage so it matches what the inverter wants.

Traditional PV inverters consist of three basic parts: the DC-to-DC MPPT, the DC-to-AC inverter, and control electronics that tune the operation of both. The electronics also watch for various fault conditions in the system and on the grid, and cuts power when certain red flags come up. This is known as “anti-islanding”, and it’s intended to protect the electrical workers when they come out to fix the wires in the event of a blackout – they don’t want to face your live wire, so the inverter turns off if the grid is down.

The inverter market

For most of the history of PV inverters they’ve been based on a basic circuit design known as “PWM high-frequency conversion”. We won’t get into the technology here, but suffice it to say that practically everyone – SMA, Xantrax, Fronius, everyone – produced designs based on this concept. That’s designs, as opposed to design, for a reason…

Inverters are only really efficient when they work near a specific design power. In addition, generally speaking, the higher the voltage the better. You can get higher voltage from your panels by stringing them in series like Christmas tree lights, each one adding about 30 to 40V. There’s an upper limit due to the cabling, which normally tops out at 600V, which gets you about 15 panels or so in a “string”.

Ok, so let’s make an inverter that’s tuned for 600V and 7 kW of total power, two string of 15 panels. Ok, fine, but now I ship it to a customer with a small home that can only fit 12 panels on the roof. His efficiency goes to hell.

It’s possible to design your inverter so a single chassis can have the parts inside swapped to produce models at different sizes. In most cases you don’t even have to change that much, because the controller electronics and cables and things all stay the same. Ahhh, but that’s not true for the transformer. It’s a big block of iron wrapped in very expensive copper, and its sizing is part of the fundamental efficiency criterion. At a minimum you need to change the transformer for the different models, and when you do, a bunch of other components end up changing too.

Building small number of different things is generally not a good idea. It means you have small production runs and all sorts of inventory issues, both of which drive up costs. That’s a problem with any mass produced product, but in the case of solar there’s a more subtle problem as well. We can design our line to minimize what needs to be changed for different models, like cables and electronics. In a large inverter this might represent only a fraction of the cost, so changing from the 5 kW model to the 7 kW one scales pretty smoothly – the parts you’re swapping are the real value. But when you start scaling down that falls apart – the parts in the 1 kW model might be pretty much the same price as the 1.5 version. The price is no longer scaling with size.

This isn’t trifling matter, it means that small systems will always be less cost effective than large ones.

And once the customer has selected a model, if they want to add a panel they have to buy a new inverter. Generally both the customers and installers want to get the price and efficiency maxed out. The best way to do that is put every panel you can onto a given inverter… got a 5 kW model that says it can actually handle 5.5 kW of panels? Put 5.5 on it! But now when you buy two more panels and try to make it a 6 kW system? Ka-blooie!

It’s all bad.

It would be much better if we had a single inverter model that could be used across a wide variety of installations and different power levels, from one panel to one million.

The microinverter concept

So all of this naturally gives rise to the concept of an inverter specifically designed to work with a single panel. Panels generally come at about the same power ratings, modern ones all fall between about 235 and 260 Watts for instance. If I have a small range of power settings to worry about, it becomes possible to make an inverter that works with any “system” out there. One panel? Fine, obviously. Two panels? No problem, just wire them in parallel. Five? Ten? 100 panels? Go nuts!

There’s huge advantage that this exposes. Solar panels are funny things. When you shade them, they produce less power. No surprise there. But they also increase their resistance to power flowing through them. It’s a problem because when you string those panels together in series to feed them into your inverter, a shadow on any one panel drives down the production of the entire string. If you use single-panel inverters wired in parallel, this problem is eliminated. Sure, the shaded panel will lose power, but that will have no effect on anyone else.

And since every system from one to a million panels uses the same model of inverter, your production line is building a large number of a single basic design. That’s great for driving down the prices. And since there’s one on every panel, instead of one on every string, you’re producing maybe 10 to 20 times as many of them in total. And that can really drive the prices down. It’s kind of like what happened with computers; as soon as the microprocessor came on the market, the price of all electronics fell because you could use a single chip design to punch out all sorts of different products. And thus the microinverter was born, a great example of marketing driving the terminology.

There are drawbacks.

One is a production issue. Earlier we noted that there’s a problem with the pricing as you scale down. In the case of a micro, you can imagine that even the smallest parts like the case and wiring becomes a huge percentage of the total cost. Consider just the panel wiring connectors; and they might cost $5 in a product you hope to sell for $150. Well a 10kW inverter has the same two connectors, but it might sell for $4000. So, as a percentage, these basic parts represent a tiny fraction of the cost of a string inverter, but a major portion of the cost of a micro.

Another problem is technical. Any given wire can carry a certain amount of current. Power is current times voltage. So if I raise my voltage, I can carry more power on the same cable. In the case of common household 14-gauge wire, that limit is 15A. 15A times 120V is 1,800W, enough to run the biggest hair dryer you can buy (that’s not a coincidence). Now if I used that same cable, but bumped the voltage to 600V, that gets me 9,000W, enough to run my entire house. Since inverters pump out AC deliberately matched to the local grid, they normally operate at 120 or 240V. So, generally, micros have to use heaver gauge wire to carry the same amount of power. And copper is freaking expensive these days.

And so, there’s the rub. Micros are, by any basic measure, more expensive than a conventional string inverter. You may, as proponents suggest, be able to overwhelm those inherent disadvantages through huge production runs – after all, that’s why the cost of solar panels is so low these days. But “maybe” and “reality” are two different things, and the proof is always in the pudding.

The Enphase story

The introduction of the PWM high-frequency inverter in the 1980s/90s made for highly efficient string inverters, and it also allowed for them to be scaled down as far as you might need. It was this invention that made the microinverter possible. But facing the price pressures outlined above, this didn’t happen overnight.

The first real microinverter was the Mastervolt Sunmaster 130S from 1993, but it simply couldn’t compete with conventional designs and disappeared from the market fairly quickly. A more aggressive attempt was made with the OK4 product, but after a run of some 200,000 or so, production ended for reasons that are not well recorded (rumours of huge failure rates).

And then came Enphase. Started by ex-telecoms people from California, Enphase was able to tap into the local talent pool and vast reserves of venture capital, and came out of the gate flying. Their original M175 model was released in 2008 and followed quickly by the improved M190. At the time, the M190 sold for about $190, or in the lingo of the industry, “one dollar a Watt” ($1/W). This was definitely higher than string inverters of the same era, which were around 65 cents/W, but with panels selling at over $2/W and another $1 for all the little extras, the effect of that 40 cents on the overall system price wasn’t enormous.

For smaller projects, say up to two dozen panels, the higher price of the M190s might work out to a few hundred dollars in total. This was more than made up for by the fact that the installers could stock a single inverter design for every one of their projects. Installation was way easier too; no need to design the layout and select the right inverter, you simply stuck the micro to the back of the panel, plugged it in, and moved onto the next one. And for small projects, the 240V/20A limit of the Enphase wiring meant that systems up to 4,800 W could be run off a single wire, which encompasses a huge chunk of the residential market.

So for a while Enphase had a run at the residential rooftops that left the other inverter companies gasping. Arguments from the cost side simply didn’t gain any traction with the installers, who were perfectly happy with the value proposition of the simplified design and inventory control. In spite of the best efforts on the part of the big iron companies, Enphase’s portion of that market just grew and grew.

So then it got nasty…

A little bit about reliability

I’m sorry to have to do this, but to understand the arguments that did stick we need to delve a little into the topic of reliability. And to do that, we need to start by considering the difference between the failure rate, and operational lifetime.

The tires on your car might have a tread life warranty for 100,000 km, which is a pretty good indication that the company expects them to last that long. It’s reasonable to expect that the tires might make it to 150,000 km, because if there’s one thing Goodyear doesn’t like, it’s handing out free tires. So when you notice that one tire is worn out after 125,000 km, that likely means they all need to be replaced.

Now there’s also the chance that the tire will simply fail, blow out for some random reason. But this happens rarely, maybe once every million km or more. That’s what’s known as the “Mean Time Between Failure”, or MTBF. But that’s just one tire, your car has four. According to Lusser’s Law, the chance that a system will fail is the MTBF for a part times the number of parts. So if we stick with the numbers above, you’ll have to go about 250,000 km before one of your tires fails.

If the MTBF was lower, say 200,000 for each tire, then you’d expect to lose one around 50,000 km, long before they reached their operational life. In that case, the rest of the tires would still have lots of tread, so you’d just fix the broken one and keep going. A failure doesn’t imply anything about the other tires.

Normally these numbers are expressed in terms of years, so I’ll convert. The average car is driven about 25,000 km a year – so the warranty is 4 years, the operational lifetime is 6, the MTBF is 20 years, and your chance of having a blow-out is 1 in 10 years. All good?

Finally, I want to touch on the different types of failures, because this is an important part of the microinverter story that is often overlooked. Lusser’s Law states that having more of something means more failures. So then wouldn’t an airplane with two engines have twice as many engine failures as a single engine plane? Indeed, they do. So then, why do airliners all have more than one engine? That’s because engine failure on a single engine plane means you’re that night’s leading news story. An engine failure on a twin engine plane is a lot less interesting. One of these is a critical failure, the other isn’t.

This “critical failure mode” is an important consideration in any design.

Let the games begin

So back to micros. You’re at year ten in your PV’s system’s life, and one of your inverters stops working. Ok, did it fail, or did it wear out? If it failed, who cares? After all, it’s wired in parallel, so you don’t even have to replace it if you don’t want to, everything else is still going. But if it wore out, well, that’s different, because that means you’re going to have a bunch of other ones go soon too.

So which is it? Well if the Enphase is really just a conventional inverter in a smaller box, why should it last any longer than a conventional inverter? And those only last 10 to 12 years, something the manufacturer will be happy to tell you. But here’s one difference… microinverters are attached under the panels… on the roof. Which means that when they start to go, you need to take the entire system apart to replace them.

The big iron companies smelled blood in the water.

The fight started in earnest in 2010. Every other inverter company started hammering Enphase – a string inverter was mounted in a convenient location on the wall or in your basement, so it could be easily replaced in 10 to 12 years when it was expected to fail. But how much would it cost you to replace the Enphase kit on your roof? Ten times as much? And, of course, they’re going to fail.

Enphase fought back, but not convincingly. They started listing MTBF in the hundreds of years, but have failed to make a single statement about their expected lifetime. They were somewhat more successful in pointing out that a single Enphase failure isn’t critical, but that’s where the argument about the product’s real-world lifetime came in.

Much of this became academic in 2011. The continuing massive downward price pressure in the solar market was particularly notable on the panel side, with prices dropping roughly in half between 2010 and 2012. Panels are now widely available around $1/W, which made the $1/W of the M190 harder and harder to swallow. If that wasn’t enough, traditional string inverters were also falling in price, down to about 40 cents/W today.

During the same period the average panel’s normal power started to creep upward, from around 220W when the M190 shipped, to 245W by late 2011, and 250 to 260 was common by 2012. The 190W M190 simply wasn’t well matched to newer panels. When you consider that the inverter was the limiting factor in production, buying higher-rated panels didn’t get you any more power. But if you took those same panels and connected them to a slightly larger string inverter, presto, more power out.

The M190 was in trouble.


Enphase responded to all of these issues with one sweeping product upgrade, the M215. Among many changes, the M215 was best matched with panels around 245W, cost as about 60 cents/W, and came with a 25 year warranty. That should have been enough to silence the arguments against the product.

But everything got worse.

In order to hit the new prices points, Enphase had to address those fixed costs we talked about earlier. They introduced a smaller and simpler case, shortened up the connectors and made other basic changes. But the big change was to remove the cables that ran in parallel from inverter to inverter. Instead, the M215 had a single short cable that ended in a new connector, and they were connected to their neighbours with a separate “trunk cable”. In theory this made installation even easier, because you could attach the inverters anywhere you wanted, and then just pull the trunk cable along and click them together.

In reality it was a disaster. The connectors were so expensive that they completely offset any price advantage in the design – the branch cable general sells for $15 to $20 per connector. When you add that on, *poof*, there goes any major price advantage over the M190. Worse, since the branch cable came in a long spool, you had to cut it to length to wire up the branch, and then you have to close with all the loose ends with manually-wired plastic caps. In comparison, the M190 daisy-chained together, so there wasn’t any cutting at all. And as if that weren’t enough, because you could install panels either upright (“portrait”) or sideways (“landscape”), you needed two different types of cables so the connectors would be in the right place.

So much for simple inventory!

That might have been enough to sink the product right there, but it got a lot worse. Sure, the M215 came with a 25 year warranty, but there was little change to the internal workings. If the M190 was only going to make it to 15 years, its warranty, why should we expect the M215 to last any longer? In particular, its use of a particular part inside, the electrolytic capacitor, become a rallying cry for its opponents. These are generally expected to last 10 to 15 years.

So if they have components in there that just won’t last 25 years, yet they still offer a 25 year warranty, what’s the story? That’s when people started really nasty stories about the company, all apocryphal of course. If that wasn’t enough, I had people start telling me I was the bad guy for installing them – one audience member at the SMA booth in Toronto went so far to say I was “damaging the solar market”. Yeah, sure.

But most worrying of all these developments is the lack of major downward movement on the price. Enphase’s whole argument was that once production ramped up the price would start coming down to the point where you didn’t even think about the delta. The M215, the 3rd generation product, was their chance to demonstrate this in action. But the difference in pricing was minor. By any measure, the drop in price considerably less than the drop in pricing in string inverters over the same period.

Opportunity knocking?

In spite of all the comments from the big iron companies, or perhaps because of it, Enphase has convinced the market that the micro is a good idea. And so there’s a bunch of companies jumping into the ring.

Primary among the new entrants is Enecsys, a UK company that took work from Cambridge to produce a 220V/50Hz product for the local market. The tech was licensed to investors in the US, and re-launched in a 240V/60Hz version for North America. Enecsys’ main claim of superiority is the replacement of those electrolytic capacitors with film capacitors, which have a much longer expected lifetime. There are some interesting changes to the internal construction too, but I don’t understand it well enough to comment. They also use a different cabling system that is sort of a hybrid between the one on the M190 and the one on the M215… they have a single cable coming out of the inverter, but it ends in a T that you daisy-chain extension cables into. They offer a 20 year warranty, and come in at about the same price as the M215.

A more amusing entrant is SMA, king of the big-iron string inverters. They bought the technology from OK4 and have been claiming they’ll launch an improved version of it any day now – which they’ve been saying for two years now. They really don’t offer any arguments why their technology is better, other than to stress that SMA is a “real company” and they’ll “stand behind their product” – the implication being that “other companies” might not. But what’s odd is that they can’t stop bad-mouthing it at the same time they’re trying to pitch it, continually stressing that string inverters are cheaper and you’d only want micros in certain installs. With friends like these…

Beyond that there’s dozens of smaller companies all over the world trying to break into the micro space. Most of them boast one or two features they claim make them so much better than Enphase, but in most cases it always boils down to the use of film capacitors. And there’s a definite downside to those – they’re larger, more expensive, and you need more of them to get the same effect as one electrolytic cap. There’s a serious question as to whether or not any of these companies can get their prices down, because their parts count goes up even if the individual parts price doesn’t go up – and it does.

Lightning strikes SPARQ?

The reason I wrote this article is SPARQ Systems. Sparq is a startup out of Queen’s University in Kingston, right here in Ontario, so I’ve been watching them more closely than normal. I’ve seen their product a couple of times at the Toronto shows, but they haven’t been shipping anything (yet), so I never put too much effort into studying it in depth. But if there’s ever a time to launch a micro, this is it.

What makes Sparq interesting is that it works on a totally different principle from other inverters. Most models use the “pulse-width modulation” technique, or PWM. Basically they switch the DC power from the panels on and off really quickly in a particular pattern that, once it makes it through the rest of the circuits, looks close enough to a sine wave that only minor modification is needed to match the grid. The problem with this approach is that the rapid switching puts a whole lot of strain on the electronics, regardless of what sort of capacitor they use. Don’t get me wrong, using film caps helps a lot, but it just means some other part becomes the critical failure point.

Sparq’s inverter is based on a technology known as “resonant conversion” that’s been around for about a decade, but only recently started to become really popular. This is really a fairly simple change to the design, so instead of switching on and off rapidly, the switch is slowly flicked (sorry, bad metaphor) from on to off using a signal that itself looks more like a sine wave. This doesn’t really directly change the output, and the rest of the inverter circuit is pretty much the same. But what it does is dramatically reduce the stress on the main switching elements. So much so that they are expected to last decades.

Now when you’ve got a system that has a potential lifetime out that long, then it becomes important to make sure all of the components you use can make it. Sparq uses film caps, sure, but it also eliminates optocouplers, and thyristors/IGCTs. Those are items one, two and three on the list of things that don’t last very long. So they expect their inverter to last decades, like four or five of them. And just to be sure, they offer a 25 year warranty.

That’s not all. In a traditional inverter, you have three basic parts, the MPPT, inverter and controller. In the Sparq, the MPPT and inverter are the same thing, and they are largely implemented in the controller. The inverter isn’t so much hardware as software, software that outputs such a smooth signal that you don’t need to clean it up. So, yes, they have film caps, but they don’t have nearly as many, and their overall parts count is way less. This bodes well for scalability. And since the output is from a program, they can simply change the program to deliver any sort of output you need – 230, 240, 600, single-phase, three-phase, you name it. That bodes even better for scalability, because you can sell a single box around the world. According to their engineers, they can scale to price points that compete with the string inverters – of course, Enphase said that too.

So stop and consider the entire suite of arguments against Enphase – it really boils down to the operational lifetime being too short. Too short? Well, to be exact, anything shorter than the lifetime of the panels. Panels are warranted for 25 years and are expected to last 35 to 40.  So if Sparq can deliver, they have a product where the lifetime issue simply goes away – they not only outlast micros, they outlast the strings too, and maybe even the panel. That changes the entire ballgame.

Should we believe them? Well let’s put it this way, resonant conversion is already used in a number of applications where super-high reliability and long lifetimes are needed. Like on the Space Station. And when they tested their prototype unit, it scored between “space” (the highest) and “aerospace” (the second highest). I don’t know where the other products score, but it still gives me warm fuzzes. In comparison, Enphase, SMA, they’re all just string inverters in a small box. String inverters last about 10 to 12 years. That’s not warm and fuzzy.

Of course Sparq is a Canadian start-up, not a US one, so there’s a lot less VC and a lot more bootstrapping. Time will tell if they can pull it off, but as always, I’ll be rooting for the home team.

As if that weren’t enough…

Earlier I said that a conventional inverter consists of three basic parts, the MPPT, the inverter, and the controller. Much of the performance advantage of the micro concept is due to each panel having it’s own MPPT, which allows the micro to pull power from the panel independently of the rest.

So what if you put just the MPPT on the panel? You get all the same advantages as the micro, and the output – still in DC form – goes right into a conventional inverter. This is the “power optimizer” approach, pioneered by Tigo and now offered by a number of companies, notably SolarEdge.

One thing I’ve noticed is how much smaller and lighter an optimizer is compared to a micro. The Tigo is about 1/3rd the size of a M190, and considerably lighter. Much of this is due to the lack of a transformer, the heaviest component in a typical inverter. But the Tigo is also made entirely of plastic, and gives off little heat. That lack of heat implies high efficiency of the conversion process, and to a lesser extent, less stress on the components. This can be interpreted to suggest a very long lifetime, which is how Tigo puts it. But here’s the thing I’ve failed to wrap my head around…

The main complaint against the micro concept is that you have a distributed system and have to replace all those parts at some point. OK, but in the case of the optimizer, you still have all of those distributed components, even if their lifetime is longer. In addition, the optimizer still has the string inverter, which we know is not going to last. So you still have the minor failure modes of the micro approach, and the catastrophic failure mode of the string approach.

Maybe I’m over-thinking this, but it seems to me this approach is compounding the chance of failure. At best, you can ignore the optimizers on the panel, assuming very long life, and so it’s the same thing as if you didn’t have an optimizer. At worse, you’ve increased the chance of a failure. I’ve tried my best, and I still can’t come to a strong conclusion one way or the other.

The no-conclusion conclusions

So, like I said way back at the beginning, its tough to draw any firm conclusions from all of this.

The classic inverter’s argument is simple – yeah, it’ll fail, but it will be cheap and easy to replace. Everything else is unimportant.

The microinverter’s argument isn’t so simple – we’ll get you more power and greatly simplify your design and installation. And don’t worry about all that reliability stuff.

And then there’s the power optimizers – we’ll get you all the advantages of the micro with all the advantages of a string. Unless we get you all the disadvantages of a micro with all the disadvantages of a string!

Sadly, the only way we’ll know how this really shakes out is to sit back and wait. In the meantime I’ll be watching the Sparq story very closely. Cha Gheill!


1. Dennis Klingele PE - May 15, 2012

WOW, So well stated. Thanks for the effort to write the best wrap up of the industry position that I have seen.

Maury Markowitz - May 15, 2012

Aww shucks. 🙂

2. Herb Aarons - May 15, 2012

I very much liked your fully comprehensive review of the overall advantages/disadvantages of each technology. The lack of conclusions is probably a function of cost/benefit analysis. The technical analysis is awesome, however,

If you cost out each technology using your assumptions on component life, efficiency, reliability and made a posited a range of capital costs and operating costs. It would be revealing. It seems that you might also do some predictive analysis as to how each technology might scale in volume production. You would have to measure both production cost scaling and what economist call elasticity on the demand side of the equation–how many more units sold as each increment of price drop.

I was looking at the Enphase IPO and was wondering why they are not yet profitable at high production levels and prices. I think you hit it–component count and electrolytic capacitance.

So a few questions that I would have:

1. The Sparq technology–which is evidently not proprietary uses resonance conversion. Why not more interest from established companies in Micro inverters? It sounds like the holy grail

2. The MPPT, TIGO approach seems to have higher efficiencies than does the Enphase and other mico inverters. They claim so on the website. The Enphase people claim that an “independent study” they get 16% greater efficiency advantage over DC strings with conventional inverters–this is in “real world tests”.

So can Tigo do better than this, Tigo unit costs on Amazon are about $60 for a 300 watt unit–not including controllers, wiring, etc. Lets say it cost $.05/watt–with inverter prices falling that is quite a bargain.

Even though you say your analysis is inconclusive, its getting close to it. I don’t think the philosophy question (distributed vs centralized, AC vs DC) is as important. Your article made me a lot more skeptical of the mico-inverter claims.

Herb Aarons

Maury Markowitz - May 16, 2012

Hey Herb, good questions. I’ll try my best:

1) I think this technology has been limited largely to those customers willing to pay for the development of what is still a not widely used technology. Certainly the aerospace field seems to have many examples (google it some time) but beyond that it’s not so common. The guy doing Sparq originally started another company in the field, CHiL Semi, in the same field. So it *may* be nothing more than a non-mainstream tech be applied.

2) The Tigo and Enphase claims are both based on non-standard conditions, non-standard in that there is really no standard on how to test these things. If Tigo assumes 5% shading and Enphase assumes 2.5%, bingo. If both use field-sampling for their numbers, then it all depends on the installs.

There is one subtle thing to consider with Tigo. The Tigo box is basically an MPPT that attempts to tune the output current so that the array is all at the same voltage (or did I reverse that?!) However, this might not be the right voltage for the array as a whole. It has to average it out. And then there’s the same circuitry in the inverter itself, fighting with all the Tigos. I can’t help but *postulate* that this can’t be as efficient as the same process in the Enphase case. Right?

Which brings up the other part I’m not yet clear on. A Tigo is basically a DC-DC converter in a box. A DC-DC converter is effectively a DC-AC and AC-DC converters places back to back. So if that’s the case, an Enphase should be 1/3rd larger than a Tigo, and one might expect it to run 1/3rd hotter. But it’s not, an Enphase is well over twice the size and weight, and dissipates much more heat. I *assume* this is because the last step in the Enphase is down to 240V/60Hz, whereas the Tigo is high-frequency from one end to the other. And if this is the case, one might be inclined to grant the Tigo a longer lifetime, as (in my limited experience) lifetime is strongly related to heat dissipation. But I have trouble trying to put any numbers to this, I simply don’t know enough about power electronics to say.

Which of course leads to the SolarEdge approach. MPPT on the panels, all the AC on the wall. Keep the long-lived low-power parts on the roof where they do the maximum good, and put the short-lifetime part on the wall where it’s easy to replace.

3. Herb Aarons - May 15, 2012

OOps…not $.05/watt for the Tigo unit, say $.25/watt in volume, including controller.


4. John Patrick - May 16, 2012

Hi, thanks for the write up, I found it very interesting. I am having a little difficulty in understanding current string inverter pricing in the less than 10KW range. In the Sunshot vision paper they quote Goodwin 2012 and come up with a residential inverter cost of 42 cents/watt but looking at that reference is pretty much a dead end in terms of methodology. In the Solarbuzz survey of retail pricing Jan. 2012, they say that average inverter prices are $0.71/watt. I have gone on several discount web sites, looked min and avg. for the major manufacturers at each KW level. I get min. at about 51cents/watt and average over range of about 60cents/watt. Can you give me background on your statement that string inverter prices have fallen to 40cents per watt. I am lookng at this smaller KW range because that is where microinverters play. – Thanks

Maury Markowitz - May 16, 2012

So this is one of those oddities of the solar market.

In most industries, distributers buy in bulk, add a markup, and then sell to dealers. Dealers then add a markup and then sell to users. That last step is normally the big jump in price.

In order to ensure end users don’t get wind of the “real price” and then demand it, the manufacturer has a “[manufacturer’s] suggested retail price”, or SRP. That’s set very high, allowing dealers a lot of wiggle room to choose their markups.

But, unlike most industries, in the solar industry the dealers don’t resell, they install. The SRP never really applies because you’re not going out and buying your own inverter, you’re getting someone to install it. As a result, the “real” cost of the inverter is the distribution cost.

Normally you can’t find the real cost, and what you’ll find on dealer’s web pages is something closer to the SRP. If you average over those, you’ll get a high price that’s not indicative of what you’d actually pay. But if you poke around a bit you’ll find the realistic price without too much trouble. For instance, a little Google-fu turned up this:


Look for the Power-One 5k inverter as it scrolls by – $2,419 CAD, or about 48 cents *after* markup. And then compare that to the M215, $175 or 80 cents a watt. The “real” cost of these is somewhat lower, I’ve seen M215s listed at CAD$150 on Google.

5. Frank Shefman - June 1, 2012

Wonderful write up. I am in the process of purchasing a small 5- 6 kw system, having a contract in Ontario and have to decide whether to go with the Enphase 215 or a string inverter (tbc). Your blog is great in discussing the issues but I am still treading through the swamp still trying to come to a decision. Although you have discussed failure rates, what wasn’t discussed and would definitely have an impact, is whether Enphase will be around in 25 years…a warranty is only as good as the company it keeps. From what I gather it only raised 50% of the capital it wanted when it went public recently. As well, the costs of labor to replace the inverters could be a factor if the failed inverter is at the back of the array requiring a bit of expensive labor to get at it. The last factor would be the ultimate efficiency of the energy harvest. If your not in an area where there is a shading issue would string inverters provide a higher return?

Maury Markowitz - June 1, 2012

The warrantee issue is a problem with any vendor these days. I think you can feel safe if the product says “Apple” or “General Electric”, but beyond that, who knows?

As to the harvest, micro’s always outperform strings on small systems. That’s because there’s no DC runs, so the line losses are much smaller. There’s also some advantage because there’s always a little difference from panel to panel that a string inverter serializes into the worst-case, whereas a micro will get the best possible from every individual panel. Enphase suggests 5% better harvest, and that matches my experience with my system (I have 12 Enphase on my roof) – and check out greentoronto.me for some detailed numbers and analysis.

For your own install, what’s the time frame? If it’s a month out, at least consider the Sparq, we should be getting the first examples this month.

6. Joe - June 14, 2012


Why would “no DC runs” outperform string inverters on harvest?
Somehow you need to run cables to the same service entry point.

If you combine AC on the roof you only have 240Vac and therefore a higher current. For a 5 kW system: 20.8 A.
Combining DC at lets say 400Vdc for a 5 kW system, the current is only 12.5 A. The inverter is likely downstairs, close to the service entry.

Now do the math. Cable losses are calculated: P=R_cable * I^2.

And I am not even talking about the cost of standard cable compared to pre-configured special cables from the micro inverter company.

Maury Markowitz - June 14, 2012

*good question*

All micro systems, in effect, work at line voltage. Say 240V.

DC systems work at what you might call “ambient”. Sure, that might be 400V in theory, but what is it in reality? And what do you do when you’re putting up four panels?

When you average out all the use-cases, the voltage in the DC case is a lot more variable. That said, I suspect it’s growing, on average, every year.

Joe - June 15, 2012

I think we can agree here.

My position is that a PV system in general makes most sense on a nice, big enough roof without significant shading-issues. The larger, the better, to become more cost effective compared to other energy sources.
In that case you can fit a good string-length on the roof. A string inverter is definitely in favor here.

For small systems (e.g. 4 modules) or with shading issues, a micro is very likely the better choice.

BTW, the average capacity of U.S. grid-connected
residential PV installations is close to 6 kW_dc according to IREC.


7. Lee Lindquist - January 8, 2013

I believe you meant Thyristor / IGBT in your description of the resonant conversion technology, unless there is an IGCT technology that I’m not familiar with.

Maury Markowitz - January 8, 2013

Yup, typo 🙂

8. Michael - January 25, 2013

So… These ? http://www.sparqsys.com/215inverter.html

have you played with them? how did they go?

Maury Markowitz - January 25, 2013

Hey Michael, shortly after writing the article I changed jobs, and never had a chance to try them out. They are selling into the local market, so I’m sure I’ll have more to report at some point.

9. Jon - January 25, 2013

Great article, I really found it informative. I’m trying to research the history of the pv inverter industry and what is currently driving the market as far as technology or supply constraints. do you have any suggestions as to where I could find some more information? Thanks!

Maury Markowitz - January 25, 2013

That’s a good question Jon, and to be honest I can’t point to a single good article on the industry in its current state. There has definitely been a decrease in microinverter mindshare since I wrote the article, but I believe most of that is price related and the negative campaigning I mentioned. Larger vendors like SMA and P1 continue to talk about their micro products, but I haven’t seen one yet. In terms of the larger industry, it appears some consolidation is underway. Satcon is bankrupt, which surprised me. There are any number of new entrants from China, but they seem to have little penetration in North America at least. The one outlier has been SolarEdge, who seem to be doing very well. Perhaps their mix of per-panel MPPT and single inverter really is the way to go.

10. Michael - January 25, 2013

I very much look forward to your results…

just a quick glance over their specs and one standout thing is only 93% efficiency vs 98/99 of the Solaredge, they also only seem to have a 215w version where a good portion of the market panels are 250w, that’s just looking at specs though, I look forward to your analysis Maury

Maury Markowitz - January 26, 2013

Yes, the efficiency is an issue with any micro, in general.

Any power conversion circuit’s efficiency has some basic limit based on the difference between that start and end voltages, and stepping up is generally more difficult than stepping down. A string inverters is stepping down from 400 to 600 to 240, while a micro is stepping up from 30 to 40 to 240.

Enphase manages to pull off their 96% rating through the use of “burst mode”, which stores up energy in large capacitors and then releases it through the converter in a single burst. This both improves efficiency and also improves performance in low light situations. SolarEdge fixes their DC side to 350 and steps down from there.

But I should warn you not to fixate on these numbers, they are useful only to compare one string inverter to another. The whole idea of a micro is to put an MPPT on every panel and thereby improve *collection* in spite of any efficiency number.

11. Michael - January 27, 2013

question for you then, where is a good place to get this unbiased information for enthusiasts ? I hear references to a photon magazine, however generally a lot of big publications are so slow to publish info on what they test that the industry has moved on by the time you figure out what you should be spending your money on!

Maury Markowitz - January 27, 2013

Photon is an excellent mag. But like any dead-tree resource, their publish cycle takes months, and that’s after the months-lone test cycles. And this market has change so rapidly that by the time the review comes out, the panels in question don’t even exist any more.

For instance, the panels on my roof are only three years old, but they’ve gone from 230 to 260W, and changed frame design twice during that period.

More commonly, the suppliers of the parts change monthly, so the panel they tested may have little in common with the one you buy today. For instance, Siliken here in Ontario boasted about their Photon ratings, but not one piece of the panel was the same as the European model – except the label perhaps, and I’m not even sure about that!

But there’s some good news too. The simple fact of the matter is that one panel is pretty much like another these days. It’s so utterly commoditized that as long as it’s not a complete off-brand, you can expect at least some basic parity with other panels out there.

So where do you turn? Right here! And other places like it, especially forums. Google is your friend. I have SolarWorld and Enphase on the roof, and I wouldn’t hesitate to do it again.

12. Jack - May 2, 2013

Good article, Pity there was no conculsion. One point you hit on was inverters life span, lets say 10 years, Enphase is a micro version of your standard inverter. Optimsers are they seperating the parts that fail quicker? I think the Opmisers will have a longer life span.
Enphase in europe is nearly double the price of solaredge.
Solaredge wins.

Peter - May 4, 2013

I have two Enphase roofs and one Tigo roof. The Tigo roof has been a point of frustration for me. The strings have to be very carefully balanced or strings will do weird things and Tigo doesn’t seem to be able or eager to fix them. My Enphase systems don’t have these problems, there’s not much design required there. I’ve had many string-balancing problems with Tigo.
You can see my latest problem at http://www.tigoenergy.com/site.php?4planeroof. On many days, say May 2, 2013, the B string decides to shut down at 13:40. I know it’s not shading because the panels will recover periodically for a short few minutes after that point. On their homepage they advertise “uneven strings on multiple orientations” and “design in shade without compromising strings”, two statements that don’t ring true for my system.
Ok I think I’m done venting!

Peter - May 4, 2013

Another few points I like to make (sorry I’m currently biased to Enphase based on my system experience):
Let’s compare a 20-panel Enphase to a 20-panel Tigo. If our only variable is the MTBF of the microinverter for the Enphase, and the MTBF of the single inverter of the Tigo system, then the Enphase microinverter MTBF would have to be 20 TIMES higher than the Tigo single inverter MTBF. Again the only variable being MTBF, meaning that an inverter on either system would be repaired just as quickly. This is probably obvious now, but the TIgo inverter knocks out every panel and the Enphase just the panels its inverting. I had only of my Tigo Power-One’s fail in July, pretty the worst month for that to occur.

Secondly if you are on a multi-year tariff contract then you obviously have to amortize system cost over the length of the contract. So a component that costs 2x but produces 1% more energy over the contract’s lifetime may actually be far cheaper. Given this, I wish I would have bit the bullet and completely maxed out panel wattage when I created my systems. It would have been worth borrowing more money to do this.

Maury Markowitz - May 5, 2013

Hope you don’t mind a 2-in-1 reply…

One of the big selling points for Tigo is that they should *not* have strings go down if a panel goes down – just like a micro. But as you note, this *does* happen.

I’m not sure why, but I suspect it has something to do with their communications and setup. The controller, which handles the MPPT, only talks to the optimizers every 15 minutes or so. Moreover, if something goes wrong in the comms, they might get bad updates and then you’ll get nothing.

This is, I think, one of the strengths of the micro approach over the optimizers. Micros really are completely isolated. You can put up a single panel, or two, or two million. There are some “string failure modes”, but they’re rarer. They generally require mechanical damage to the cabling, or for the box itself to fry to the point where the circuits are ruined. I’ve seen *one* such example, ever.

You also touch on another advantage. Tigos don’t do anything to the voltage, so from the inverter’s perspective it’s like they’re not there. Micros, and SolarEdge optimizers, boost the voltage first. This means that they turn on earlier and off later, and thereby gather more energy in a day. I’ve *definitely* noticed this on my system (it turns on before dawn!) and although that might only be a percent or two… well, it’s a percent or two!

13. Joe - August 13, 2013

Hi Maury, do you have any updates on the sparq inverter and what you think of them since you initially wrote the article? Also, my concern is after the installer warranty is up, if I have to pay someone to go on my roof to start replacing micro-inverters it will quickly eat up any savings that the system provided me in the first place. I am about to buy a 13.0 system I have very little to no shading and even though micros are not necessary if they are going to really last 25 years then it will be cheaper than having to replace 2 6k sma inverters at the 15 year point. I would appreciate any insight you may have and your thoughts on the best way to proceed. Thank you.

Maury Markowitz - August 13, 2013

Nothing to report, unfortunately. They are up and running and I know there are some installs going in out west especially. I believe Heliene is also offering them pre-installed on some panels.

Your second portion is precisely the problem that everyone is trying to figure out. Enphase uses a church metaphor – when a lamp burns out on the roof you don’t do anything, you wait until a bunch are dead before it’s worth putting up the scaffolding. The same logic applies to micros, losing a single panel simply isn’t worth doing anything about. I agree with this logic – I have a panel with a blown diode and I can’t be bothered to swap it.

But there’s a bit of slight of hand there… it’s not really about a couple of panels going bad, but whether or not *all* of the inverters will die before the panels. We can’t really say for sure one way or the other, because none of this stuff has been around long enough to get good numbers. We do know that Enphase claims a 0.2% failure rate so far, but what this tells us about 15 years from now, who knows?

14. bill joerg - November 4, 2013

Maury (or anyone else),

I am trying to decide between a 5.5 sma string system and a 5.5 solaredge. My 10/12 pitch roof is oriented southwest but a little bit more south than west with no shading (except clouds). The solaredge guy tells me this is what solaredge was made for and that the sma system will produce much less energy. The sma guy tells me that with my orientation and no shading the productions differences will be minimal and the roof part of the system will be trouble free whereas the 22 power boxes on the solaredge may not be and would cost big labor bucks to replace after the labor warranty is up . I can’t find anything online comparing solaredge to sma on SW facing roofs with no shading. The sma system is $17700 and the solaredge is $18800. Both offered 5 yr labor warranties. What do you think.

Maury Markowitz - November 4, 2013

Hey Bill, thanks for posting!

So in your case with a single roofline and no shading (are you *sure*?!) the main advantages of using a micro or SE system will be a slight reduction in line losses, elimination of inter-panel differences (which tends to be small these days) and a slight increase in efficiency. I would disagree that the SMA would produce “much less” energy, but wouldn’t be surprised if it was in the 2 to 5% range.

Did the SE guy offer any reasoning for the “much” figure?

As to the lifetime issue, remember that the whole idea in the SE system is that boxes don’t really have that much inside them to go wrong. It’s the inverter that is going to go, and the SE inverter is less expensive. I suspect total lifetime costs will be about the same in the end, if not a little in the SE favour (assuming two replacements over the system lifetime).

The real difference, and I can not stress this enough, is the per panel monitoring. Some day a panel will go, like one of mine did (blown diode). If this happens on your SMA, you’ll never know. You’ll just get a little less power forever, but such a small amount you might never notice. With SolarEdge you’ll get an alert (maybe even a email).

Don’t get me wrong, you’re comparing two of the best products money can buy. Either one is going to give you decades of worry-free service and should easily pay for themselves long before then.

I hope you’ve selected panels that will do the same?

But if it were my roof, I’d go SolarEdge every time. I’m a data junky, blinking lights impress me and SE gives me the edge in that regard.

15. IJsselzon - January 8, 2014

Excellent and intelligent post. I have a enphase m215 system myself, sofar no problems at all. I live in The Netherlands so my inverters are not under a lot of temperature stress. Lets see how well they work out after 10-12 years.

I used to be an ambassador for the Enphase systems, specially for their excellent monitoring posibilities.
Unfortunatelly, Enphase decided that ‘customers are not looking for per-panel overview’ and removed it from their monitoring software. Now.. only installers and older owners can see the production per panel. The new owners can only see the per panel production when they ask their installer to hand out a user key.
As per 15th of januari, the installer needs to put up a fee of 248 dollar per user to give them per panel overview (and yes per system does that add on the mandatory 500 dollar Enphse Envoy)
Odd.. looking at the competition: every single one of the microinverter producers give their customers per panel overview.

I have used the Ephase forums to ask for their rationale behind this descision, but it seems that to much stress was put upon their suport desk of customers not understading the monitoring.. so.. they removed it.
Posts on their forums are being deleted, discussions closed, emails to their board of directors ignored.

Cutomers now have a fancy string overview of their enphase microinverters, also on every public system, making Enphase systems less and less attactive.
What is Enpahse thinking on archieving???

(latest thread that is not closed yet: http://community.enphaseenergy.com/enphase_energy_community/topics/enlighten_fee_for_customers_that_are_not_installers)

Maury Markowitz - January 17, 2014

I was astonished when I read your post. I couldn’t believe it was true. But it is! I am flabbergasted.

16. wewa - February 1, 2014

Great article.
Should be reprinted in the solar publications!
Many in the industry do not go thru these thought processes when selling or recommending inverter technologies.
Like anything else, one size does NOT fit all, and you have to ‘match’ the inverter solution to the project, to get the best chance of long term reliability and power production.
Take care.

17. Tee Cee - May 30, 2014

Thank you for this tremendously informative article. It gave me a better understanding of Solar Panels than did Wikipedia. We are in the process of incorporating a PV system into a new build. I was hearing so much rhetoric from the salespeople who were vehemently against those not in their camp (micros vs. string). This is an install on a two story home with excellent S and SW exposure in sunny Southern California with no trees, so truly no shade. Thanks to your article, I’m educated and ready to make an informed decision!

18. Ian Rowberry - September 13, 2014

Hi Maury,
Very interesting couple of pieces on micro-inverters. I am an SE owner, and had some issues in the first couple of years, no problems for about two years now.
Are you M190s still all good? I’m hearing tales from our local installers about M190 and particularly D380 failures.

Maury Markowitz - September 15, 2014

We installed maybe 500 M190’s and M215s over the period from 2009 to 2012. During that time we had two M190s fail, both very early. Since then, nothing.

I suspect the same will be true for most micros and optimizers. The failure modes *should* be either off-the-line due to QA issues upstream in the components, or much slower degradation. Time will tell, of course!

19. Wilbert - March 7, 2015

Hi Maury (or anyone else who has experience in this area),

From a local distribution company’s (LDC) perspective, what kind of things do LDCs have to consider when deciding whether or not to allow solar system developers to use single-phase micro inverters on 3-phase projects connected to the grid?

If you could provide some background on this issue, reasons to allow or not this, costing and operational impacts to consider.



Maury Markowitz - March 7, 2015

Great question! Sadly it depends entirely on the LDC. Here in Ontario they originally allowed three split-phase micros to be twist-wired into a three-phase circuit. But they changed that at some point and now you either need a load balancer or a pure three-phase inverter. Since Power-One was the first with the later, and that eliminated the need for extra boxes (and cash) they ran away with the market for years. So, sadly, you’re going to have to ask your LDC to find out. The good news is that a balancer is about the same price as a transformer for the same load, so you might be looking at 10 cents/W.

20. Wilbert - March 8, 2015

Thanks Maury!

I live in Ontario.

What is the reason why utilities in Ontario won’t allow single-phase micro inverters in 3-phase systems?
Is there some provincial code or standard preventing this or does each utility have there own reason?

Maury Markowitz - March 8, 2015

I believe it’s province-wide. The “problem” is that if one of the phases does down you can have an imbalance in the lines. On a large array, you might end up feeding power back though the distribution transformers (which is unlikely under 10k which will be used locally) and that results in imbalances up the line. A converter fixes all of this.

21. Pablo - April 2, 2015

Thanks for the great post Maury! In the 3 years since your post was written, do you think there a definitive winner has emerged in the duel between microinverters and power optimizers? I’ve spoken to a few industry professionals and it seems like they are preferential to optimizers these days but given your experience in this area I wanted to vet these opinions against what you’ve observed / heard.

Appreciate your help!

Maury Markowitz - April 2, 2015

Still hard to say. Emphases continues to do well but most other players are gone, notably Enecsys while Soars is relaunching. SolarEdge, on the other hand seems to be doing very well indeed.

22. Akshay Patni - July 15, 2016

I have been doing a similar research on this topic ! Thanks for a brilliant post Murray.
Can you share your viewpoint on Enphase’s continoulsy dropping prices, and how would this affect the micro inverters and entire MLPE market.

Maury Markowitz - July 16, 2016

I haven’t tried pricing them recently, do you have some recent examples?

bpmcrae - November 29, 2016

I’m in Australia, so prices below in A$

6.090 kW system
Fronius Primo 5.0 International version
Fronius Smart Meter
21x290W JA Solar mono precium panels

5.880 kW system
Enphase Envoy-S metered
21 x Enphase S270 micros
21x280W Canadian Solar Quintech mono panels

I’m in Queensland and apparently Enphase seems to like Australia and Qld in particular. Still, I was a bit surprised that there is so small a price difference.

I have a great north facing roof (that’s the ‘right’ way in this hemisphere) with no shading issues, so I don’t ‘need’ micros. We only get a 10-yr warranty on the micros here, but the cost is basically the same as it would be for a string inverter, so any time I get beyond warranty is a bonus. While labour for replacement will be higher, this is offset in my mind by better power capture and maybe longer life and/or only having to replace some micros, rather than the whole system. I also like the per panel monitoring (price above doesn’t include the software, about $260 additional, but there are also apparently some 3rd party options). The SE is quite a bit more expensive here – add $1-2k. For the small price difference, we’re figuring it’s worth the gamble to go for the micros.

Great articles (part 2 as well). You didn’t mention whether the micro might put less stress on the panel and thereby possibly extend their life. One sales rep mentioned this, but not sure I can recall the theory, but I think it stems from managing each panel essentially as a separate system. Can you see any possible basis for this?

Maury Markowitz - November 30, 2016

According to Google, that’s USD$4873 for the first system, or $0.80 a watt. That is freaking amazing! The second is $5209, so 0.88/W, which is hardly bad. Wow, those are seriously better than what I can get on a similar system here in Toronto.

As to the stress, I never heard that before. But I can see the point – in the case where you have a shaded panel, all the power from all the other panels goes through it even though it’s in a high-resistance mode. This causes them to heat up, which you don’t want. Since the panels are isolated with micros, this is not an issue. Is this a real effect that you might be able to measure? That I cannot say.

23. bpmcrae - November 30, 2016

We have a government incentive that basically covers the cost of the panels (it is based on power generation). This scheme, and generous FIT (higher than retail pricing in the early days – no longer) are no doubt part of why we have such a high take-up of residential solar. Those prices are not the lowest quotes I got — one works out to about 0.63/W (USD) and that’s still using a german inverter, so could go cheaper with Chinese.

There is a legislated target of 20% of Australia’s total energy production from alternative sources by 2020. A speculative question is what will happen then. It can be hard to remove a government incentive. Some attempts a while back failed due to public backlash and ultimately lack of political will.

I’m guessing we might see a transition in the incentive scheme, from generation to storgae, as battery prices fall (and stimulating more competition). That would relieve some of the pressure on the big energy generators, but it would also arguably benefit the early adopters with panels over those who haven’t jumped in yet, which could be politically problematic.

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