Don2222 said:
mayhem said:
So thats about $30 or so a month, right? Fantastic. I'm strongly leaning towards getting one of these things myself. Even conservatively I think I use about 20 gallons a month in oil for my hot water. If this new tank uses $40 a month in electricity year round and oil remains stable where it is, it looks like a 4 year return on investment of $1500.
Hello mayham
I just roughly calculated 22 gallons of oil per month for DHW since I use a pellet stove for heat now. However I am considering a DHW solar panel system. There is a new German drain back system that prevents pressure build up and the Solar Panel is the latest in reflective heat technology. New England Solar sells it but the parts are probably much cheaper if you buy and install it. There are still really good tax breaks on Solar and the savings can be alot more than the Electric. Electric rates go up too but Solar is Free!!
http://neshw.com/residential/benefits-of-solar-hot-water/
So Don, I looked at solar too....and I will still be going with the HP.
I got a quote for $13k for a small solar DHW (two panels) or $15k for a three panel system with a 50 or 80 gal storage tank, installed, pre rebate (brand was Velux). Solar rebates in PA right now are 70% as a tax credit (!!) so my cost would be $4-5k. While the pre rebate price seems like a lot, these were very spiffy, well engineered systems, an experienced installer in the area, and, um, I don't think DIY installs get rebates.
I had several tech concerns, which the installer confirmed:
--I checked out my insolation using this tool: (broken link removed) and what I found out was pretty cool, my annual energy output would be about 1000 hours * my maximum output, and my output in the dead of winter would be ~0.4 times my summer output. The tool is for PV, but I can use it for solar thermal if you assume a different eff, it is basically telling you solar input. The conclusion is that if I sized my system for fall/spring, I would have to dump some excess heat in the summer, and use some backup in the winter.
--The tank temp has to 'swing' a lot to store the solar heat--you can compute the BTUs, but to store a days input the bottom half or more of tank has to be cold at the beginning of the day. The backup controller fires the elec coil when the top half of the tank gets cold, and shuts it down when the top half is heated. So, when you are in backup, your DHW capacity is ~half of your tank volume (25 or 40 gallons).
Taken together, if our house used more than than half of what the tank stored daily, then we would be firing the backup a little all year round, and a lot in the winter. So while a conventional 50 gal tank would suffice for my family, if I got a 50 gal solar system, solar would likely only provide 50-60% of my needs, with the rest backup, and we might run out a lot. The bigger system would do better, at a cost, but was still unlikely to provide more than 70% of our needs on the solar.
In comparison, I computed that I could get either a 50 or 80 gallon HP water heater, and it would use 50-60% less elec than a conventional elec tank, and thus about the same amount as the **conventional elec backup** in the solar systems I was considering. This year there is a $300 rebate for these guys, and I suspect that my installed cost will be about the same or less than the after rebate solar cost.
I would love hear from anyone with a actual solar DHW system to see if my logic/estimates are off base!