Solar Powered Water Heater

[Mark Blatter]

I am looking at building a new shop which I will heat with under slab radiant heating. My original plan was to bring in natural gas or use propane. However, as I am also looking to add solar panels to my house, I realized that adding them to the shop would be pretty easy. The roof will be sloped to the southwest and could take quite a few panels.

In considering this, the idea of using an electric water heater, instead of gas, was pretty natural. Has anyone done the same thing? Naturally, heating at night would be impossible using solar, so the grid would take over. I haven't even started looking at the costs/rewards yet, so it simply may not be worth doing.

Love to hear from others if it works or not.

[Bill Dufour]

gas is way cheaper then electric. Not sure if you can even use resistance electric for over 30 gallons. I think at 40 gallons it has to be heat pump. I would run the solar water into a demand instant heater. How much snow will shade the collectors in the heating season?
Bill

[Art Mann]

I have a 50 gallon electric water heater. They are more common where I live. Heat pump water heating technology hasn't caught on yet due to the high cost and long payback time.

[Adam Herman]

Electric hot water heaters are around 4kw? We have 4500 watt peak solar array that covers about 350 square feet. Our array covers our houses total electicity usage You are looking at around 20k installed for such a system, owned by you. You can also lease, but i do not know the cost associated with that.

In the summer we make around 300 kwh per month and, in the winter, we don't make a whole lot even in sunny Colorado. We just got a meter that allows us to track this a few months ago.

[Benjamin Miller]

Why would you take all of the sun's energy, convert it to electricity (at 25% efficiency, if you're lucky), and then convert that energy back into heat for water?

For a lot less money, you could install a closed-loop solar water heater. Basically, water and antifreeze flow through a black greenhouse box on your roof and then coil around in your water heater.

https://energy.gov/energysaver/solar-water-heaters

[Mike Heidrick]

I am using a 23kw instant electric hot water heater to do my radiant floor at 2560sq. I will change to gas as money allows. I dont think your solar idea will heat much. Three 40amp circuits for my boiler. You do not want open air potable water in your radiant loops. You would use a heat transfer panel if ypu use a non sealed system. Radiant sytems with one boiler like Naven for the floor and for sink and tub use have two water circuits. The floor is not exposed to atmosphere and is treated to prevent microbial growth in the lines. Folks doing it with reg water heaters have not studied any science and professional installs

[Mike Henderson]

Use natural gas. In this area, natural gas is pretty cheap.

I have a solar array on my house and it basically zeros me out for electricity cost for the year. But part of that is the way the charges are calculated. We are on a time of day charge, where electricity is more expensive during the day than at night so, during the day, when rates are high, I'm putting electricity into the grid and being paid the higher amount. At night, I take lower cost power from the grid. I have 14 panels.

Regarding solar water systems, my only observations is that those systems have been around for many years (a LOT more years than solar) and yet you don't see many on houses. I expect there's something about them that's a problem. Either they don't work very well, or they require a lot of maintenance, or the economics just don't work. They get the same energy rebates as solar so if they were the greatest thing since sliced bread you'd see a lot of them installed.

Mike

[Mel Fulks]

They work well. Many came down for roof problems or just to move on to new electricity systems. They are pretty simple ,what's to not work?

[Mark Blatter]

[QUOTE=Benjamin Miller;2732475]Why would you take all of the sun's energy, convert it to electricity (at 25% efficiency, if you're lucky), and then convert that energy back into heat for water?

For a lot less money, you could install a closed-loop solar water heater. Basically, water and antifreeze flow through a black greenhouse box on your roof and then coil around in your water heater.

https://energy.gov/energysaver/solar-water-heaters[/QUOTE

Excellent question and one that I had pretty much realized killed the idea. As others have noted, nat gas is pretty cheap where I live so no reason not to use it. I will give some thoughts to using the solar water heater. Thanks for the idea.

[Art Mann]

In some parts of the country, electricity is 3 or 4 times as expensive as it is where I live ($0.10/KWH). More often than not, location determines whether solar power makes economic sense.

[Benjamin Miller]

I wasn't suggesting Mark roll his own solar water heater -- there are many manufacturers selling engineered solutions.

[Bill Dufour]

You do mean solar hot water panels don't you. PV panels to an electric water heater will lose roughly 90% of the energy. Theoretical maximum efficiency panels will lose like 77% in conversion to electric power. In summer you can run the system at night to provide cooling during the day.
If you are serious about PV panels to heat water just put $100,000 or so in the bank and use the interest to pay the gas heat bill.
Bill D