electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Some of the regular users will recall my solar system. I did a little write up of it here. https://forums.mikeholt.com/threads/my-solar-system.148865/ Basically I used solar panels as the roof for an outbuilding. For some time I have been planning on building a shed roof addition off the back, the north side, at about 16 feet wide, and the length of the building, about 50', but probably with a little overhang on each end so maybe 54 feet. I had always assumed I would use metal roofing, probably for this just the cheap thru fastener stuff. Today I got thinking about it more (and distracted from the stuff I should have been doing but it was more fun to think about this). I thought about using the ribbed clear polycarbonate panels that I used on part of the north side wall of the building (pictures in the link). Metal roofing is about $1.50/ sq ft now. Those polycarb panels are only a little more at $1.66. Then I got thinking.........Why not use solar panels as the roof like I did for the main south facing roof? Ok so I already have a surplus of power, usually about 3500 KWH/year AND if you dont recall I have a 2400V step up step down electrical system using 15 KVA transformers so I cant send infinite amounts of power. I am at 14KW AC now, and I already planning to add another few rows to the south side on a 5KW inverter I already have, so lets just say it will be 19KW AC of PV generation when that is installed. The system is "over-paneled" so that is ACTUAL AC KW that the system makes from about 10:00-2:00 solar time and the transformers will see it (maybe not during hot summer days). I am ok making the transformers run at 19KW for a few hours some days, they are in the shade and Im in the northeast where its not too hot. Ok so its seeming quite absurd to add more PV right? Don't worry about that, I will find a use for the electricity - think sauna, hot tub, lumber drying kiln, heat in the shop, air conditioning.......Well Ive been looking at cheap used modules and it looks like they can be had for about 25 cents/watt delivered, or $3.40 sq/ft. So say ONLY $1500 over the polycarb panels or $1650 over metal roofing. I dont want to buy more inverters (nor would I want to push more than 19KW thru the 15 KVA transformers anyway) so I would string this potential north facing new stuff into the current 3 inverters (7+7+5 KW). They are sunny boy inverters and have 3 MPPT inputs. I havnt run any numbers yet or thought much about stringing yet. I suppose the first thing to do is see how much power north facing mostly shaded panels will produce . Thoughts? Yes I am insane, but any other thoughts?