I'm going about measuring that now. Some of those panels are 30 years old and not putting out spec (the smaller light blue ones). The newer ones are beating spec, but there's enough capacity that it can be hard to measure in winter (which is coming on here) since some are shaded and by the time they get out of the shade, they're at a bad angle -and my house and car are both charged anyway. In theory, what we have here goes like this:
Those on the far right on the roof - 12 total, are shcott panels and rated at 240w each. They are making spec at least, so call that 2880 w
The black ones are BP Solar, new production (they shut down their plant, though, darnit) are 175w and making spec, 14 of them, so another 2450w
The light blue sparkly ones are the older BP solar, rated at 120w. 13 of those, lets say they make 100w, so another 1300w.
So, 2880+2450+1300 = 6630w, or thereabouts. In general, I'd call it "enough" as on a sunny day, I can not only charge my car (13kwh) but also run A/C if I want.
In winter, I can charge the car most days (40 miles or so range from a charge, depending, like any car, how you drive etc). And in either case, keep up the house batteries, which have a 24kwh theoretical rating. I'd never know as I never run them down even halfway - it shortens their life and they were not cheap - submarine battery quality there. The electronics might as well be 100% efficient as far as can be told.
Most of these panels are hooked in series-parallel at voltages around 60 to 90v at peak power output, and this is "impedance matched" to the house batteries by a series of efficient switching supplies, which gives perhaps 30% better net output than a straight connection. Solar panels are a kind of constant current device up till near their open circuit voltage, where their diodes (each cell is a diode) start to turn on.
This of course varies with temperature like any diode. The batteries in turn are '"wherever they are", so a variable DC "transformer" really helps, and the wire losses are cut by higher voltages and lower currents in the wires.
The older sparkly looking panels are by far the best on cloudy days. Due to that sparkly nature, straight on light, which is what the spec for testing/rating demands, isn't their strong suit, and so they had to make them bigger for a given rating. When the light is coming from all directions - we get the one case I know of where specs-man-ship helps the end user, which is why I haven't ditched them for a later model.
Where I live, effective noon-equivalent sun hours average 4.5 a day so 5930*4.5 is 29.835 kwh a day. The reality is that we have some days with nearly "nothing", and in summer, have some almost 10 hour days.
The trick there is - you adapt to what nature is willing to hand you - drive more in summer, take more showers (the one thing I heat with other than propane or wood), use the machine shop more and so on.
Strangely, the refrigeration is one of the biggie loads, since it draws power at night (with a round-trip loss in the battery system) and you can't turn it off. But what I did do is put a top loader chest freezer in an unheated building in the shade, so it draws almost no power in the winter. My best power time is actually spring - we get the most sun, but it's not hot yet so the reefers don't draw much. Worst is right now - sun hours already short, but things are still warm. As the system grows and I get better at using what's there, I am smoothing out the peaks and dips with things like air conditioning, electric heat for water and air, water distillation, and other things like that. Because once the car and house batteries are "up" - you may as well use any extra power rather than let it fall on the ground unused.
I will gain about 20% net out of those big black panels leaning one the wall when I put them up on the roof, like the two sets on the right, and rejig the light blue guys already up there with the two-slope approach too. As it turns out, I have one good spare so that three panel rack will be filled to 4 by that time, should be all good, and I'll be done with this for the foreseeable future. There is a row of trees to the south of me, some on land I don't own, so I have shade issues in winter at low sun angles. I'm willing to work with that, but the more of this that makes it to the roof, the better for me.
A side benefit, which I had planned, is that when I used those wood 2x8" to support the two slope racks, I get one heck of a convection current - it will even overwhelm a fairly stiff wind coming from behind and blow out a cigarette lighter. This keeps the roof (there's no attic, I'm on the second floor right under these) and panels cooler in summer - more power and less need for A/C. In winter, I'll try plugging up that channel with foam rubber to see if I can trap more heat in here. I have a skylight on the backside of the roof that serves as a door to get up there from inside easily to do things like that. I'm also hoping the new arrangement will shed snow on the steep parts, but provide some heat to melt it off the top, flatter ones, which I used to have to go up and scrape after every snow - not fun on a slippery roof.
Here is a typical curve of solar panel output vs voltage under standard conditions:
- Solar panel curves
Another benefit no one seems to mention is that in very low light, a 30v nominal panel may still be willing to make some fairly decent power at say 19v. So hooking a bunch in series with an automated max power point regulating controller gets you about another half hour at each end of every day of at least some useful output.
In my system, both battery and panel temperatures are monitored to keep everything as happy as it can be. Batteries especially will be ruined by overcharge when they are hot and "want" a lower terminal voltage.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.