Solar Panel choices: SunPower E20 vs Solaria PowerXT vs Hanwha (QCell)

Sunpower is good stuff, but not any better than other quality equipment. Believe it. Their prices are coming down but are still overpriced. the power output warranties are unverifiable. The smart money knows this as do those who've been around the block once or twice. I own a Sunpower system and it's fit for purpose, but nowhere near as cost effective as other stuff for the same output and reliability, but I didn't buy Sunpower for its cost effectiveness or superior quality. It has neither of those attributes. Long story.

At the end of the all the analyses, all equally (electrical) sized systems in the same location, orientation and duty, when installed in a safe and professional manner by a competent and ethical vendor, will have about equal annual electricity production for as long or longer than you're likely to own such a system, Sunpower or anyone else's equipment, provided it's reasonable quality stuff from known mfgs. Equipment failures seem rare (with the exception of micro inverters it seems - and lately with some higher of Sunpower micro failures) with infant mortality being the most common occurrences.

Pay more attention to vendor quality than equipment quality. Forget yelp and those sites where people who know less than you do about solar and less about vendors rate their experience. A case of the blind leading the one eyed. Go by experience, length of time in business and only interview vendors who have been in business at least 10 years, sold PV for at least 5 of those years and are established general or electrical contractors who have other lines besides solar to survive on after the bloom is off the solar rose - as it seems to be heading these days.

Everything's negotiable. Counter offer the Sunpower at $2.65/STC W and see if they bite. If not go to $2.70. If still not, walk away and offer Solaria or some other vendor $2.65/STC watt. And whatever you do, unless you like screwing yourself, under all circumstances keep all vendor pricing to yourself, and don't fall for the price matching scam.

Why micros? Multipoint failures with all the electronics in a hot, harsh, sometimes wet environment. Some think that unless you've got shade (in which case you may have a poor solar access area and thus not cost effective), a string inverter makes more sense. To be fair, others just as or more knowledgeable than me don't agree with my opinion on micros.

Buy and read a copy of "Solar Power Your Home for Dummies" 20 bucks cheap and a good primer. Get your annual load and some idea of the rate structure and options for rates from your POCO (POwer COmpany). Download and get familiar with PVWatts. Read the help/info screens a few times, use 10 % system losses instead of the 14 % default value. Then, do a few runs for practice and aftyer you get familiar, size your own array to what you think is your best (and now better informed) judgement. Then, call the vendors back and negotiate a better system for a sharper but still fair price.

Lastly, get your roof inspected and serviced. PV on a roof can last a long time. Chasing a leak on a roof is never fun or easy. Finding one under an array is a double PITA, very expensive and may never work out will even for all the toil and treasure expended. Consider roof maint. as cheap insurance. You can thank me when you get your first leak free rainstorm and sleep well.

Welcome to the neighborhood and forum of few(er) illusions.

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

what is best construction type of panel for a northern climate with lots of cloudy days ,but not a very cold winter ,average winter temp of +3c
and summer high temps of high 20,s

If you're referring to PV panels, pretty much any decent panel on the market is fit for service for most climates including Scotland. If you are referring to mounting methods, racking from one or two different mfrs. is pretty standard not unlike erector set methods and probably quite suitable. If snow is common, or to the degree it is a regular occurrence, roof mounting is not as easy to make productive/cost effective, can and often is a PITA to keep clear of snow, and maybe ought to be avoided in favor of a ground mount which will cost more and likely require some design work for at least the foundation.

YES PV -- solar thermal i,m confident with
no very little snow -- so mono crystalline type or what?

Mono has several advantages over poly - better efficiency which will mean smaller arrays, probably longer service life with less performance deterioration as f(time).

Although some poly cell panels will work better in low light then a Mono cell panel.

Of course it will depend on the panel manufacturer.

There's probably no one size fits all answer to this, but overall, with poly efficiencies generally being less than mono, but poly $/W being generally less, at least for the panels and not talking BOS costs which often go up because of the greater physical array sizes required of poly cell arrays for the same output, it's probably more application sensitive as to which to use with several variables coming into play, some of them economic, some practical ("do I have room for lower efficiency"), some weather.

My understanding is that efficiency "improvements" of poly cells under low light is mostly due to a lower rate of decrease of their efficiency relative to their efficiency under full sun as f(less temperature tolerance). The poly efficiencies will see less of a relative decrease in efficiency under low light vs. full sun than will mono panels (but will still see a large decrease in output simply because less solar energy is available. Whether or not that lower rate of decrease as f(temp.) for poly cells is enough to overcome the mono's generally better STC efficiency but greater efficiency penalty as f(temp.) vs. the other design tradeoffs is probably quite application sensitive.

Overall, if low light conditions are the norm, that is, where the daily clearness index < , say ~ 0.35, or so is common for maybe half the year or more, making any PV application cost effective can be a real challenge. That said, I kind of doubt collecting 15 % of available energy under 20 % irradiance with a mono system vs., say, collecting 20 % of the available energy under the same 20 % light conditions for a poly equipped array, if that solar climate was common, would be the determining factor in a go/no go economic study. Overall and in general, cloudy climates make solar economics a real challenge, making the choice between poly and mono something of a moot point - probably neither will be cost effective in such a solar climate which often delegates solar applications in such places to the province of the solar ignorant, treehuggers and eccentrics like Bruce and me.

Yes sliding far down that irradiance efficiency is generally going to kill the game for any
technology. I am waiting to see ACTUAL CURVES released for competing technologies.

That said, with rainy days for a couple weeks now, I have still managed to collect surplus
energy over HVAC needs every single day. Bruce (not a treehugger) Roe

thank you for the reply --will see if i can find a solar chart for south scotland /northern Ireland

The German forum https://www.photovoltaikforum.com/ is very active (at least 100 posts a day) and even has a section for non German speakers. The regulars there are very knowledgeable and usually very helpful. For a start the suggestion is to check PVGIS for your PV potential. Choose SAF as a database and set losses from 14% to 10%. Enter slope and azimuth and you'll get a number to work with.

John: As mentioned in my first post to this thread on 09/05/18 to Moviefan, try PVWatts. Use 10 % system losses. No registration necessary. Read all the help screens first. After that, it's pretty straight forward. It's got several locations for the Scotland/U.K. I believe you'll find that each STC kW of PV on a roof tilted at local latitude and facing south, in most parts of Scotland will produce about 800-900 kWh/yr. in electricity. Not a whole lot.

that will be about right as most quotes i looked at worked on 3600kw per year from a 4kw system and pay back is 7 years at that rate

I'd respectfully suggest you verify what anyone gives you for suggested modeled output (even and maybe even particularly me), particularly if they have skin in the game - which I do not. My SWAG was for south facing, tilted at about local latitude with no shading. Your situation will be different which will skew the results.

BTW, if optimum cost sizing is one goal of the exercise, and if that 4 STC kW size was suggested by some vendor(s), know that you may or may not want or need a 4 kW size. FWIW, my guess is you may not be able to get PV generated electricity at a long term cost that will be less than the long term cost of simply paying for grid power, particularly at 800-900 kWh/yr. per installed STC PV kW, but that depends on a lot of things I'm not privy to for your particular situation. A lot of that adequacy depends on the assumptions about a lot of things that lead to that 7 yr. "payback", however that's defined, probably by whoever or whichever PV vendor is trying to get into your knickers. Even the 7 year time is a choice you make, not some vendor or "what everyone uses." If so, you may (gasp - oh no - he's saying it !!) be better off without PV, even though it's the darling of the tree hugger set at this time. Caveat Emptor. If it was me (and it ain't), I'd be putting my efforts into lowering usage and conservation efforts as better returns on my investment.

Doing your own preliminary system design using both simple (but not moronic) time value of money analysis tools and your own preliminary PV sizing based on your expected (lower) use with PVWatts are two easy tasks to learn and do. Taking the 20 min. or so to read the help screens for limitations and then an hour or less to get some facility with the model is a small price for what you get back in the way of knowledge and self help. I and lots of others have found it to be fit for the purpose of modeling for preliminary design purposes. There are many other models around and I've run and own my share of them, but PVWatts is adequate for most preliminary design purposes.

even the government renewable energy site suggest same pay back time and they have no axle to grind ,and new houses have to have some solar PV installed no option ,
but yes I take all you say, cut down usage is always first plan ,
new house will be far more energy friendly to start with
4kw is the max size system you can claim a grant for --over that you do not get any RHI payments ,just FIT from what you produce --as that is alot less than what it costs to buy better to use it all
If possible --not convinced battery systems are right price yet
no my location +orientation is as perfect as it gets --