Current sweet spot for residential roof arrays?

[DanKegel]

For somewhat space constrained 4-10kw residential rooftop arrays
with nonzero shading, my impression is that the sweet spot
as of January 2015 is roughly 270-280 watt 60-cell panels
with Enphase microinverters.

(More cells -> too high a voltage for enphase;
non-enphase -> too small a player;
non-microinverter -> poor shade performance;
less than 270 watts -> wasting roof space;
more than 280 watts -> price per watt crazy high)

Is that about right? What's your take on the market? Where
do you go for this kind of information?

[foo1bar]

For somewhat space constrained 4-10kw residential rooftop arrays
with nonzero shading, my impression is that the sweet spot
as of January 2015 is roughly 270-280 watt 60-cell panels
with Enphase microinverters.

(More cells -> too high a voltage for enphase;
non-enphase -> too small a player;
non-microinverter -> poor shade performance;
less than 270 watts -> wasting roof space;
more than 280 watts -> price per watt crazy high)

Is that about right? What's your take on the market? Where
do you go for this kind of information?

I am using solaredge optimizers to deal with shade, rather than microinverters. From what I can see they give similar benefits for shading but cost less.

280W 60-cell panels are what I bought. 72-cell possibly would have been better if available at same efficiency and same $/watt. (20% more power with same costs in racking and not much increase in inverter/optimizer costs) But question is whether 72-cell fits in the space on your roof. (For my biggest roof section, 72-cell would have not worked well - would have been 1.5 rows instead of 2 and therefore fewer watts)

FWIW, 300W panels came out very similar in price per watt to the 280W, for the whole system when I priced it out.. It was more per panel, but savings in fewer optimizers and less racking. Depending on labor costs, 300W 60-cell could be cheaper. (with $0 for labor I think it was within 10% )

[J.P.M.]

For somewhat space constrained 4-10kw residential rooftop arrays
with nonzero shading, my impression is that the sweet spot
as of January 2015 is roughly 270-280 watt 60-cell panels
with Enphase microinverters.

(More cells -> too high a voltage for enphase;
non-enphase -> too small a player;
non-microinverter -> poor shade performance;
less than 270 watts -> wasting roof space;
more than 280 watts -> price per watt crazy high)

Is that about right? What's your take on the market? Where
do you go for this kind of information?

Since you ask, I think I think it's a bit simplistic.

As to the market, IMO it's mostly driven by peddlers and opportunists capitalizing on the solar ignorance of crowd following sheeple mostly (but not entirely) of three stripes: those who often have more money than brains and throw that money at self inflicted high energy bills; those who have a deficit of both and lease stuff falling into the buy nothing, own nothing and pay for it for 20 years hole, and self absorbed tree huggers who do more harm than good for the "cause" of renewable energy that they more often use as a delineator between the elite (them) and what they often imply to be the great unwashed masses. In the end, the residential solar market will adjust some in a couple of years, but since human greed, lack of foresight and selfishness seem to be with us always, the market will go on.

As to where to go for information, start with a good book on the basics of residential solar energy. Then, use the knowledge gained to read prior threads on this forum.

Your one size fits all attempt probably covers some situations, but I'm of the opinion that trying to find a quick resolution and cost effective solutions to high residential energy bills can be tempting but counterproductive. One example: Your description leaves out string inverters altogether, which in the opinion of many, are usually better choices than micros. Your post also at least implies that any roof situation can be made a good one by using micros. Sometimes, and more often than peddlers will probably tell you, some roofs are simply not candidates for a cost effective solar installation. That little factoid that some roofs are simply crappy applications for solar is often conveniently forgotten. The silt purse out of a sow's ear analogy applies.l

If an application needs micros to work, maybe it's not a good application for solar in the first place. Or, perhaps, since the end goal is a lower energy bill rather than solar for its own sake the, other, more cost effective measure(s) such as conservation could be investigated. Solar is about the most costly way to reduce an electric bill. Therefore, it might just be better placed further down the list, if at all, ratherthan knee jerking it as the first, last and only solution.

Take what you want of the above. Scrap the rest.

My apologies to ethical peddlers and sincere, dedicated environmentalists whose job is only made tougher by the scumbags.

[DanKegel]

280W 60-cell panels are what I bought. ... 72-cell would have not worked well - would have been 1.5 rows instead of 2 and therefore fewer watts)
FWIW, 300W panels came out very similar in price per watt to the 280W, for the whole system... (with $0 for labor I think it was within 10% )

Thanks for the data points. Which brand and model did you end up getting, what was system wattage, and what was final system price per watt installed?

Your one size fits all attempt probably covers some situations, but I'm of the opinion that trying to find a quick resolution and cost effective solutions to high residential energy bills can be tempting but counterproductive. One example: Your description leaves out string inverters altogether, which in the opinion of many, are usually better choices than micros. Your post also at least implies that any roof situation can be made a good one by using micros. Sometimes, and more often than peddlers will probably tell you, some roofs are simply not candidates for a cost effective solar installation.

I used a plain old inverter on my first solar retrofit, since that's all there was at the time,
and it was fine... but time marches on, and it's possible that microinverters
would have helped that system cope with the shadow of a palm tree that
wanders across the array part of the day. Also, individual monitoring
really appeals to me; I like the idea that if one panel starts failing
(heck, or even had more birdcrap on it than the others?), the system would tell me.
So I'm looking at them as I plan my second solar retrofit.

This house has a steeply sloped roof, and the panels must be invisible from
the street (HPOZ restrictions), so I get to use the southwest crumb of
the roof, with one small west-facing section and one largish south-facing
section. My WAG at a layout, from playing with google earth and
some crayons the warder let me borrow, is

http://kegel.com/energy/net-zero-retrofit/layout.png

(No, I'm not sure I'm meeting the three-foot setback yet, need to check that.)
I suspect I'd need six strings to optimize this properly,
which may explain why I didn't even think of string inverters
when I posted. And then there are those pesky trees poking
their heads up on the west side. I can only trim them back so
much, and I suspect microinverters would get me another
few percent in the evening.

I know of three problems with microinverters: the warranty issue (when they blow,
they're expensive to fix, partly because of finger-pointing problems),
they add a little labor time when installing, and the common ones aren't
compatible with all panels. My cloudy crystal ball suggests that,
several years from now, the reliability problems will be fixed,
and panels with pre-integrated microinverters built right into them will
solve the other two. (There's already one, but I'm not sure it's cost-effective yet:
http://www.lg.com/us/commercial/MonoXACe Seems to be priced to
just barely pencil out when you include savings on labor and external inverter?)

I agree, there's plenty of crazy out there, and it pays to think clearly when
planning / pricing / buying a system.

[sensij]

It looks like you've hit on most of the points to consider when choosing inverter technology. One other aspect to keep in mind is that if you have wire runs to the array of any significant length, the microinverters will output at 240 VAC (in the US), while SolarEdge is at 350 VDC, and a string inverter can operate close to 500 VDC. The higher voltage would allow selection of a smaller (cheaper) wire size for the same loss, or less loss if the conductor size is fixed. The difference in losses / costs for typical residential rooftop systems is probably not much, but for some ground mounted or large house arrays, it might be worth considering.

[foo1bar]

Thanks for the data points. Which brand and model did you end up getting, what was system wattage, and what was final system price per watt installed?.

Still working on the install.
Will be 9kW panels (32*280W) but 7.6kW inverter (expect only slight clipping due to inverter because of some pointed east, some pointed west and some south, and some shadow issues)
Costs not including labor I had estimated $19-20K. ~$17k is panels, racking, inverter. Looks like it might be more than $20k - haven't totalled everything up yet. Some things (like replacing main panel and meter) are expenses that many people won't have)

[DanKegel]

9kW panels (32*280W) but 7.6kW inverter (expect only slight clipping due to inverter because of some pointed east, some pointed west and some south, and some shadow issues)
Costs not including labor I had estimated $19-20K. ~$17k is panels, racking, inverter. Looks like it might be more than $20k - haven't totalled everything up yet. Some things (like replacing main panel and meter) are expenses that many people won't have)

Sounds like a close twin to my planned system, except we're doing a total reroof, and my shading may be worse than yours.
(The reroof will use energy star shingles, so the whole thing will be eligible for both hero financing and federal tax credits, I think.)

[J.P.M.]

Sounds like a close twin to my planned system, except we're doing a total reroof, and my shading may be worse than yours.
(The reroof will use energy star shingles, so the whole thing will be eligible for both hero financing and federal tax credits, I think.)

What interest rate(s) are you getting on HERO financing ? Spread the info around some maybe ?

[sensij]

Sounds like a close twin to my planned system, except we're doing a total reroof, and my shading may be worse than yours.
(The reroof will use energy star shingles, so the whole thing will be eligible for both hero financing and federal tax credits, I think.)

I had been looking into getting the roof (with energy star) and solar done on one contract as well. I did find one respected company that gave a good price for the combination. Are you looking at Certainteed shingles, or perhaps Ecoasis? Maybe something else? There aren't that many to choose from, and 2013 was the last year for the residential energy star roofing credit.

[DanKegel]

I had been looking into getting the roof (with energy star) and solar done on one contract as well. I did find one respected company that gave a good price for the combination. Are you looking at Certainteed shingles, or perhaps Ecoasis? Maybe something else? There aren't that many to choose from, and 2013 was the last year for the residential energy star roofing credit.

d'oh. ok, maybe no energy star roofing credit, then http://energytaxincentives.org/ appears to have recent info on that.

http://www.certainteed.com/resources...olaris-TDS.pdf is the best I've found, but I haven't really looked hard, and I don't know if the colors they have will pass the wife test.

Only thing we have a bid on so far is chimney repair. Bid coming for energy efficiency retrofit shortly. Haven't asked for a bid on roof or solar yet.

Hero financing isn't available yet in the City of Los Angeles, but supposedly it's starting up in the next month or so.

[J.P.M.]

d'oh. ok, maybe no energy star roofing credit, then http://energytaxincentives.org/ appears to have recent info on that.

http://www.certainteed.com/resources...olaris-TDS.pdf is the best I've found, but I haven't really looked hard, and I don't know if the colors they have will pass the wife test.

Only thing we have a bid on so far is chimney repair. Bid coming for energy efficiency retrofit shortly. Haven't asked for a bid on roof or solar yet.

Hero financing isn't available yet in the City of Los Angeles, but supposedly it's starting up in the next month or so.

Check it out. The hero program might be worth a sniff or worth waiting for. It can have some real advantages and probably a few drawbacks depending on your situation. All in all the program seems on the up & up.

[orangechen]

solar panels

For a home solar power plant, the guarantee of adequate roof area is paramount, but there will always be some obstruction, causing some shade, faced with such a problem, I think can be used to improve the efficiency of micro-inverters, but also facilitate the management, omnik micro solar inverter is a good choice.