02-07-2020, 11:27 AM
If you are putting in a solar PV system panels are now cheap enough to add a few more and run an electric resistance water heater. Depending on the wattage and voltage used the rate of heating can be pretty anemic unless you have installed an extra 4kw of panels (enough to run the typical electric water heater). At about $1 per watt that would bee too expensive just for hot water but here in Puna our sun is so variable that I for example am planning on increasing my panels from 3kw up to 5 or 6kw, just to have adequate electrical power during those cloudy periods. Most of the time my batteries get full by 10 or 11 am and I could potentially send a couple of kw to a water heater for 3 to 4 hours. That's what I am doing now with the 3kw of panels I've got. With the stock heater elements I've got I heat at 700 to 800 watts for 3 to 6 hours and put maybe 4kwh of heat into a big 120 gallon electric water heater on a good day. O
n a bad day and even on every other good day I heat with propane. If I add more panels I can get all my hot water from solar PVusing a standard hot water heater and simultaneously have halfway decent electric power output on cloudy days. Of course on those days electric power generation takes precedence and you must use a backup propane system for hot water.
If you are not already committed to solar PV for electricity the economics are not so favorable but for me if I don't make enough electricity I end up burning gas in a generator which costs money and is inconvenient. If I invest in more panels I get smoother power generation and lower generator costs. During summer all my hot water needs would be covered for "free". I don't think it would pay to install enough panels to cover all power and hot water needs all the time. Just hunting for that elusive sweet spot which is very subjective. Ease of use is part of it and going with PV instead of solar thermal collectors makes things lots easier.
Is this for Eden Roc or somewhere on the mainland?
n a bad day and even on every other good day I heat with propane. If I add more panels I can get all my hot water from solar PVusing a standard hot water heater and simultaneously have halfway decent electric power output on cloudy days. Of course on those days electric power generation takes precedence and you must use a backup propane system for hot water.
If you are not already committed to solar PV for electricity the economics are not so favorable but for me if I don't make enough electricity I end up burning gas in a generator which costs money and is inconvenient. If I invest in more panels I get smoother power generation and lower generator costs. During summer all my hot water needs would be covered for "free". I don't think it would pay to install enough panels to cover all power and hot water needs all the time. Just hunting for that elusive sweet spot which is very subjective. Ease of use is part of it and going with PV instead of solar thermal collectors makes things lots easier.
Is this for Eden Roc or somewhere on the mainland?