We have 2.25 kW (9 x 250w panels) of solar taking up almost the entire roof space of a 60 fter.
No way could we get another 7 panels up there.
What? You don't have 29 m2 (>300sf) of unobstructed roof space?
I love these theoretical table-top exercises. They sound so wonderful until you break-down the numbers:
A 210kwh battery bank has a potential of about 715,000 Btu. What does a 210kw battery bank look like and what does it take to charge it?
- if traditional Flood Acid GC T105s, There are over 150 of them, cost almost $20,000, weigh over 7-tons, and occupy a space of over three cubic yards. Swapping them out every 5-years would likely take a week and a couple bottles of Ibuprofen.
- If you had a 200A alternator on each of two engines (400A total), it would take two full days of running to charge
- If you used the 16-panel array, it would take 10-full days to charge
- If you wanted to charge using a generator running a 250A charger, would likely take a 12KW generator and would take over 3.5 days. Or you could go to some sort of industrial 3-phase setup and get 500A of charging, but that's well beyond my pay-grade.
And for all that, you avoid burning the equivalent of around 15 gallons of diesel. ((715k Btu / 125K Btu per gal diesel) / 0.33 efficiency))
BTW - this line of thinking is very active in the sailing community. Jimmy Cornell, of World Cruising Routes fame, recently abandoned a solar-only project for a sailing cat, presumably due to some of the harsh realities of the above. Maybe he should talk to some of the new-breed of trawler builders. Sounds like they've cracked the code on a battery-powered trawler - apparently the sails on Cornell's cat inhibited efficiency.
Peter