How did you decide? Microinverter vs Optimizer & PV Inverter

[ButchDeal]

Well they had some layoffs, have introduced storage which is getting a huge response, and are coming out with the S300 which brings cost par with strings (main reduction is in the case which is a significant component of the case). Their projection is that they have a roadmap to bring the micros below string cost and they believe the strings won't be able to lower costs equivalently.

where do you get the AC battery has a huge response? They have barely opened any markets with it, and it is lacking in the primary feature that people want with a backup system, BACKUP.

[Engineer]

I have noticed a few people saying that they have compared the financials of Enphase to SolarEdge in their purchase decision. ..

Well they had some layoffs, have introduced storage which is getting a huge response, and are coming out with the S300 which brings cost par with strings (main reduction is in the case which is a significant component of the case). Their projection is that they have a roadmap to bring the micros below string cost and they believe the strings won't be able to lower costs equivalently.

People on this board should be cheering for Enphase/Micros. It's not a good thing actually that the industry is facing cut-throat end pricing, it can ultimately be bad for the market. What you want is several competitors who all have good profit margins - that's where new R&D funding comes from which delivers better products. If SolarEdge was the only choice they'd cut R&D funding to nearly zero*. Generally when the companies are forced to cut costs to the bone by the end customer you get bankruptcies and mergers that result in less innovation and choice, not more.

I don't know how it will turn out in this industry but I lived through the same process in a different industry (semiconductor test). It's not fun, but more importantly is often ultimately bad for the customers.

* A point first made clear to me early in my career when I complained that we had competitors. An older engineer said "yeah, and if they didn't exist you wouldn't have a job"

[HWD]

I have noticed a few people saying that they have compared the financials of Enphase to SolarEdge in their purchase decision. For those doing this, make sure you look at the most recent quarters. My concern is that people may be checking the last reported full (fiscal) year for both companies – the 12 months to Dec’15 for Enphase, and the 12 months to Jun’15 for SolarEdge.

As a quick summary – Enphase lost $19m in full year 2015. But if you look at 1Q16 (to Mar’16) and 4Q15 (to Dec’15), it made losses of $19m and $15m respectively each quarter. i.e. its current runrate means they are losing >$60m per year. This is for a company that had just $13m cash as of the latest quarter (versus $28.5m at the end of 2015)

SolarEdge made a profit of $19-20m in the last two quarters – i.e. run-rate profit of almost $80m versus $28.2m in its last fiscal year. It has net cash of $171m. Its average price per watt is less than Enphase’s COGS per watt.

Basically – either Enphase changes something drastic soon or it’s going bankrupt

[J.P.M.]

To a first approximation, when A is close to B, A⁴ - B⁴ is proportional to 4(A-B) (Average)³
As the temp difference gets very large the heat transfer becomes proportional to the fourth power of the higher temperature. In between, it is messier.

Which is easier on a calculator ?

[inetdog]

To a first approximation, when A is close to B, A⁴ - B⁴ is proportional to 4(A-B) (Average)³
As the temp difference gets very large the heat transfer becomes proportional to the fourth power of the higher temperature. In between, it is messier.

[J.P.M.]

Whilst solar panels run hot (say 60C max or so), that is relatively cool in the semiconductor world and that's why they can live almost forever. If an inverter living under said solar panel reaches similar temps, then its internal components will be much hotter (because they are generating heat), especially if one considers integrated circuit thermal resistance to die temps along with all of the other components, caps, etc. It would be best to decouple the inverter from solid contact with the panel and have it live on the rail where at least convective heat transfer can carry heat away better. Radiative heat transfer goes as T cubed and is probably not a factor. It's all about convection.

I agree it's probably better to separate the panel from the inverter and give more available area for convective heat transfer. How much separation and in what ways can be an interesting design activity.

However, and contrary to what you write, the total emission of radiation from a body is proportional to the 4th power of its absolute temp., not the cube. The 4T^3 approx. may work when temps. are close, but it's an unnecessary approx. since the advent of calculators with a power function button. The radiant exchange between two surfaces is actually proportional to the difference in the 4th power of the absolute temp. of the two surfaces that can "see" one another in radiative exchange, not the third power of the average of the two. View factors and the idea that nothing is a perfect blackbody radiator (emissivity <1.0 and f(wavelength)) as well as other things also need consideration.

As for it being all about convection, often not. For example, and disregarding the relatively small amount of conduction through the racking, when doing a heat balance on the PV array sitting on my roof when under something like a full sun, depending on wind velocity and dew point (often used to estimate the effective radiant sky temp), about 40-60% of the heat rejected to the surroundings is from convection. The rest is from thermal radiation - or, the other way around if a dry day with little wind. Often, in heat transfer calcs.,the radiant heat transfer is expressed as a heat transfer coeff. per degree of temp. diff. between the body and the surroundings and then added to the convection coefficient to approximately linearize the overall heat transfer rate per degree. For a lot of work, heat exchanger design, process work, etc., where radiation heat transfer is relatively small, that's usually not a problem. For other work such as terrestrial solar or in space, or other places where thermal radiation becomes important. An example, heat loss through a single glazed window: 70 F. inside, 20F. outside, say 5 MPH wind outside. Convection coeff. ~ 1.0 BTU/hr.ft.^2/deg. F. radiation loss ~~ 44 BTU/hr. ft.^2, or ~~44/50 = ~ 0.7 BTU/hr. ft^2/deg. F. when linearized per deg. F and a .88 emissivity is considered.

The two mechanisms, convection and thermal radiation, or all 3 heat transfer mechanisms including conduction, need to be considered separately and treated as such if warranted, but it ain't a slam dunk, thermal radiation doesn't matter type situation.

[DaveDE2]

Whilst solar panels run hot (say 60C max or so), that is relatively cool in the semiconductor world and that's why they can live almost forever. If an inverter living under said solar panel reaches similar temps, then its internal components will be much hotter (because they are generating heat), especially if one considers integrated circuit thermal resistance to die temps along with all of the other components, caps, etc. It would be best to decouple the inverter from solid contact with the panel and have it live on the rail where at least convective heat transfer can carry heat away better. Radiative heat transfer goes as T cubed and is probably not a factor. It's mostly all about convection imo. This all assumes that the rail is cooler than the panel which I think it probably is and that the inverter will be more exposed to air flow if it's not integrated with the panel.

[J.P.M.]

The solar panel is likely to be hotter than the inverter, or at best, they will be the same temperature. I don't see a significant advantage in the thermal behavior for either one. I would guess most of the heat transfer will be radiative in either case.

FWIW, and if interested: For two bodies with flat surface that have a common plane, any heat transfer between them will be totally radiative in nature if the surfaces are not in contact.

If in contact or clamped/screwed with no "visible" gap, the heat transfer between two bodies will be mostly conduction heat transfer, but not as much as if, say, glued via thermal contact cement, or, for metals, welded/soldered/braised/etc. While clamping leads to a relatively poor heat transfer (not entirely unlike increased electrical resistance for loosely/poorly connected electrical contacts), heat transfer in the small micro to panel gap case will still probably be conduction governed because the effectively zero air gap will prevent convection cooling between the two facing surfaces, effectively (assuming the panel is warmer than the ambient surroundings, and the micro is cooler than the panel) increasing the micro temp. While smaller than bonded surface conduction, the conduction that is present in the simple clamped case is still likely to be an order of magnitude or so greater than any convective heat transfer from the back/sides of the micro (unless the micro has fins on it). That will tend to get the two surfaces closer in temp. For a standard (say, no fins, clamped, and little air gap) scenario, the micro and the panel will probably be closer in temperature to one another than if an air gap exists between them. If so, radiation heat transfer between the two bodies will be less than if there is a, say, a 1 cm. gap or so between them.

That, however, is a somewhat different discussion than micro inverter temperature. IF there is an air gap (say, a cm. or so) between the inverter and the panel, convective cooling, either natural (gravity driven and probably relatively minor), or wind driven (and larger), such cooling will reduce the temp. of the micro. That will increase the radiative heat transfer due to the increased temp. diff. - panel to micro. Under steady state conditions, the relative amounts of heat transfer between the two bodies via radiation and conduction will be such that the amount of entropy increase due to each will be equal.

[sensij]

The solar panel is likely to be hotter than the inverter, or at best, they will be the same temperature. I don't see a significant advantage in the thermal behavior for either one. I would guess most of the heat transfer will be radiative in either case.

[entgegnen]

[QUOTE=sensij;n320402]

Sunpower's approach to installing microinverters is no different than Enphase's. Neither is more integrated than the other. Your comparison here is erroneous.

I am always happy to be corrected. But here is the thing - when you google search images of an enphase micro inverter installations and compare those photos to the Sun Power module, there is a difference. I've looked at various diagrams (from the respective companies) and numerous photos (on google images) to reach my conclusion that the physical integration of the Sun Power module onto the actual frame of the panel/module means that there is likely going to be more heat transference on account of actually being mounted to the frame (right below the wafer). By contrast, the Enphase is first attached to the rails... and based on it mounting height, it is usually .5 to 1-inch below the module frame (or at least the wafer). Heat doesn't transfer through air well. Hence, I think the boiling pot of water - making the pot handle hot as well - is an appropriate analogy.


I bet you didn't meet the person actually working on your roof until the day of the install. The slick sales guy or even the company owner is rarely the one who actually does the work, sub-contracting or not.

Tough audience. But hope springs eternal. I'll be sure to let you know what ends up happening.

[ltbighorn]

My reasons for getting 38 Enphase S280 inverters on my LG315 panels

• I live near Enphase headquarters and know many of the engineers (indeed used to work with them) who are over there now; these guys are the best. So I trust the engineering and the company, plus would like to support a local business.

Technically they're both fine but I think micros have the lead, and I just like them better anyhow.

I must admit I considered this a small but non-zero influence as well. When a US and in particular local manufacturer makes a quality, competitive product, I like to support it. That said I went with LG panels, though SolarWorld/Suniva were my secondary choices/quotes, even though neither is local.

2. I think at the end of the day, all three can be terrific options (string, optimizer, micro) depending on site survey, budget, usage needs, reliability, future adaptability, etc.
3. Two of the best comments I've received (on this and another thread) have been to (a) do a quick energy audit and see if I might benefit more cheaply from a few common sense economizing measures before jumping all in; (b) to understand that year over year there will be incremental improvements in the types of systems... but that the latest and greatest tech may not be the best value purchase $/watt... the more important thing is to jump on the train instead of always waiting for the "next" train.

Absolutely and I agree that they're all excellent options, it really does come down to your specific preferences and situations.

Energy audit is definitely a good idea. The cheapest energy is the energy not purchased..

4. So I've settled on an installer, a system, and a final cost. The installer didn't have the "lowest price" but was hands and away the most knowledgeable of the contractors I've spoken to and didn't steer me towards any one system over any other. (While not the lowest, the price was competitive-reasonable). I am also confident that he will be good to my roof. (And no sub contractors was a big plus). I've researched his contractor's license and I didn't find anything adverse. 5. I'll come back in a few weeks after everything is up and running to provide more details. But again, big thanks to Sensij, ButchDeal, and others who have shared their insight.

Sounds like a good move - best price you can get from an installer you trust to do high quality work. No need to hold off on the details though, I don't think anybody's feelings are going to be hurt regardless of your choices.

I feel similarly about sub-contractors, but for different reasons. To me it's not so much about meeting them, but rather each layer of bureaucracy slows communication and response, which allows more chances for mistakes or subpar work to creep in. The installer you contract with may have a solid reputation for making things right, but I'd rather see things done as best as possible the first time, as sometimes mistakes aren't discovered for some time, and each time I have to deal with an issue again (and the complexity of that resolution) takes away from my life enjoyment. It's part of why I'm paying a small premium to have my roofer (in business for 35+ years) doing all the penetration sealing and guarantees.

While I certainly see this point, I had a different perspective. My goals are not exactly in-line with the utility or in-line with the (economize first, then go solar approach)... I want to approximate my system "output" with my usage at the median life of the system. Assuming a 25 year system life, and a certain fractional percentage of panel degradation year over year, if my system outputs 90-93% at year 12.5... I want to be in the position of NOT buying 7-10% of my electric needs from the utility (at that time in 12.5 years).
...And all environmentalism aside, this is all about the Benjamins.

These two statements are somewhat at odds. Overproducing today so that you're completely offsetting in 12.5 years will probably produce a worse financial return than simply buying a small amount of utility power down the road. If you just want it for environmental or psychological reasons, fair enough, but if the goal is to save the most money, then buying a system that meets your needs today, but requires you to buy some kWh down the road, is probably more cost effective. Obviously it depends on the details, but typically purchasing small amounts of power from the grid is not terribly expensive. Moreover, many utilities do or will require certain minimum fees, so the optimal production may actually be for a less than 100% bill offset, since they literally won't let you zero out your bill.

Great reasoning and agree with the points although I ended up with a sunnyboy with the sps. Same points just different weights.
Very cool.

Indeed. People can truly see all the same considerations and come to a different conclusion about what's best for them, and that's great. Lots of good options out there.

[ltbighorn]

A small sampling over on an EV forum (~4000 inverters with ~11000 device years) confirms some problems with the M190s, but almost zero with the M215s and M250s. Additionally, the M190 problems tended to be clustered on particular installs, suggesting either bad batches or site-specific issues. Both sets of products are relatively young and it's hard to say what the long-term (10+ year) reliability of any will be. The most info we really have is on how long central inverters tend to last.

[sensij]

3. While SunPower appears to have very nice and cutting edge products... I was personally bothered about "heat" transference. Now I am not an engineer of any sort. But since SunPower integrates the micro converter into the panel, it seemed that there would be a likelihood of heat transference from the already "cook a fried egg" panel heat. At least with the Enphase approach, there is an "air gap" between the panel and the microconverter to disallow heat transference. (how many times have you boiled water on the stove and found that the pot handle got hot as well?) But if the pot handle isn't actually touching the boiling pot of water... it doesn't get hot. Perhaps this is an erroneous comparison.... but it was one I made.

Sunpower's approach to installing microinverters is no different than Enphase's. Neither is more integrated than the other. Your comparison here is erroneous.

5. I am not a big fan of subcontractors. If the person you use will ultimately bid out the labor... well, when did you get a chance to meet them? On installation day? Too late. I like to know who I am dealing with in advance. I look up their license numbers. I see if anyone has filed against their contractor bond or filed complaints. Hard to do if you don't know up front.

I bet you didn't meet the person actually working on your roof until the day of the install. The slick sales guy or even the company owner is rarely the one who actually does the work, sub-contracting or not.

Also, a plan in which you size the PV system to cover 100% of consumption is often not the most cost-effective choice, for those who seek to maximize their benjamins. No one knows what the tariffs will be 12.5 years from now, or where you will be living. At least in southern CA, today and for the next few years, leaving a small amount to be paid to the power company may be more optimal.

[nomadh]

I was debating the same decisions (along with string inverter). For my size array, all options were pretty much a wash cost wise. The reason I ultimately went with the Enphase microinverters:

1. Space is at a premium here in SF, and I didn't want the inverter taking up space in my garage (particularly since it's deeper than anything else I have wall mounted, and thus cuts down on walkable space). Outside isn't a better option as it's a narrow access path to the neighbor's front door, and also very visible from the street (neighbors would be very irritated).
2. Having the inverters within 10 feet of the array removes the need for the external cut-off switch in my area, I believe, so one less box on the exterior wall (especially with all the big red labels now).
3. I personally prefer the safety situation of running AC from the roof rather than DC. Not a big deal though.
4. I can expand without having to make decisions today about how much excess inverter capacity to purchase.
5. Doesn't lock me into SolarEdge -- I haven't pre-purchased extra central inverter capacity that only works with SolarEdge optimizers. With Enphase microinverters, if there's a better product out there in 5 years or whenever I want to add, I can use it without discarding excess pre-purchased capacity. I can feed additional AC on one of the existing branches without modifying or interfering with the Enphase setup.
6. 25-year warranty and expected lifetime is longer than central inverters.
7. I build redundant/reliable systems for a living, and I work very hard to avoid single points of failure. A central inverter is a giant single point of failure. Microinverters are lots of points of partial failure. Optimizers are single point of failure + lots of points of partial failures, worst of both worlds. It just doesn't sit well with me. I realize that the failure rate of the optimizers is likely to be much lower, but there's still the inverter. It may be a wash, but psychologically I'm more comfortable with multiple points of partial failure, given the next two items. Similarly I build arrays of systems, servers, devices, etc. with the expectation that some will fail, but the system as a whole keeps on chugging.
8. With microinverters, the incremental cost to do replacements or maintain spares out-of-warranty is low. With a 25 year warranty, I'm already ahead, but should Enphase go out of business, I can pickup spare micros on ebay quite cheaply. Even if there are failures, I think it unlikely that all the micros would fail early. In the unlikely situation SolarEdge goes out of business (or no longer makes a compatible product), because of the higher cost to keep cold spare inverters, I'm less likely to have one on hand, or have more capital tied up in them. If optimizers fail too, then I'm in a nasty lock-in cycle of having to keep buying more of what's not serving me well, because more money is sunk into replacements that only work with more SolarEdge stuff.
9. My roof is flat and only requires me to climb a 1-story ladder. My panels are being installed in separate rows with a good tilt. Should my installer not be around to honor their 15-year workmanship guarantee, I'm confident that I could do replacements myself without risking life and limb. I can get up there easily in 10 minutes.
10. Allows me to combine house consumption monitoring (Envoy-S Metered) and integrated that into the same dashboard overview as my production data.
11. I can take advantage of the Enphase AC battery should it become cost effective. I feel like Enphase's approach/product is more likely to bear fruit for my approach than Tesla's.

When comparing for yourself, to keep it apples-to-apples, make sure to include the $250 fee for Enlighten Manager access needed for per panel monitoring.

I'm by no means advocating that any particular option is &quot;THE BEST&quot;, just sharing what influenced my decision. Hope it helps.

EDIT: I should also add, I live in cool sometimes foggy climate, where no one has AC. So with good ventilation on the tilts, I think the microinverter reliability can only benefit from the milder conditions vs say, someone in Phoenix AZ.

Great reasoning and agree with the points although I ended up with a sunnyboy with the sps. Same points just different weights.
Very cool.

[entgegnen]

Hi Versailles79-

1. Nothing wrong with adding your question to this thread - but if you created your own thread, you may get more feedback.... just an open ended suggestion for you. (I've found that as threads carry on.... the number of different people viewing drops off to only those few that are talking back and forth).

2. It appears you have limited roof space. Do you also have a limited budget? I've got a number of children, so $1000 bucks saved on my project is $1000 in their college fund, 2-3 trips to Costco, etc. I only say this because of your mention of SunPower. I did engage with SunPower. They were going to cost me about 70-cents per watt more. And drive back my "break-even/pay-off" a few years. Since electricity is electricity... and a utility company is a utility company... i could not justify the premium to myself. (It isn't like you can make the "premium gasoline" arguments.)

3. While SunPower appears to have very nice and cutting edge products... I was personally bothered about "heat" transference. Now I am not an engineer of any sort. But since SunPower integrates the micro converter into the panel, it seemed that there would be a likelihood of heat transference from the already "cook a fried egg" panel heat. At least with the Enphase approach, there is an "air gap" between the panel and the microconverter to disallow heat transference. (how many times have you boiled water on the stove and found that the pot handle got hot as well?) But if the pot handle isn't actually touching the boiling pot of water... it doesn't get hot. Perhaps this is an erroneous comparison.... but it was one I made.

4. If space is limited, you may want to look at the new Panasonic 330w panels (Panasonic HIDs). If you could do that set up for less than SunPower... you may want to think about it....?

5. I am not a big fan of subcontractors. If the person you use will ultimately bid out the labor... well, when did you get a chance to meet them? On installation day? Too late. I like to know who I am dealing with in advance. I look up their license numbers. I see if anyone has filed against their contractor bond or filed complaints. Hard to do if you don't know up front.

6. I found myself gravitating towards bids with good size local companies, but with not too much corporate bureaucracy. Unfortunately, I had a sad experience with a major brand. I called a call center to book an appointment - with essentially a sales man. Then the salesman "no showed" having not been made aware of the appointment from the call center. Then when he called to reschedule, he no-showed on his reschedule! Then he emailed an apology and offered a gift card. I emailed him back, accepted his apology, and said "lets cut to the chase." Can you offer me a system below a certain price per watt? (based upon the 9 quotes I had received from one of the auto-solar-marketplace websites). I never heard from him again. I guess there just wasn't enough ignorance or profit in dealing with me... such is life.

So look at your systems above. What is your cost per watt? Assuming al things equal (quality of equipment, quality of installation, confidence in the guys going up on your roof and not messing everything up - or leaving you with a leaky roof - are you willing to pay more for an electron traveling across the grid from one quote than another?

Good Luck!