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Solar hot water

5235 Views 9 Replies 6 Participants Last post by  g60vwr
Ok I'm looking to get/build one.. and all of the diagrams online I come across
Shows a mixing valve Which leads me to believe that solar hot water
can get fairly hot But I can never find out how hot it typically gets..

And how hot can I keep the water? I would like to use it for both potable
and for my house Heat... good thing is I live in the valley of AZ..

Thanks in advance,
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solar heated water gets around 200+° so you'll need to study up a bit on temp/pressure release valves, etc.
there are different ways to do solar water too. here's one simplified way that i am building now.
arizona would be great for solar powered anything!



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I would like to use it for both potable
and for my house Heat... good thing is I live in the valley of AZ..
70 gals/person/day is normal, maybe 1/3 of this is hot water.
This link will tell you your heating degree days
but I haven't been able to find a link that gives you continuous days of cloud cover (one determinant of the size of the tank).
This link tells your solar energy input

1 BTU raises 1# of water 1°F; this link lets you convert between different units for energy and power.
Awesome thanks I might somewhat over size it use a mixing valve
so no one gets scalded. This way I hope to also use less of the stored
hot water per person. Also might use a heat dump just in case things start
to get to hot.
I have a solar water heater for my pool
When water 1st starts to pass thru the setup on a hot day the water coming out is 130+
I oversized my system (and only use it for hot water), and live in cloudy New England. I have three 4x8 FP's heating a 120 gallon tank. Mine has heated the water in my tank to 160F (in AZ I'm guessing you may get 200F+ in the tank). Where I live 2/3rds of the days are cloudy and honestly we use hot water all the time. We've not left for vacation and had 6-7 days of sun and seen how hot it can really get.

Mixing valves I think are required regardless solar or not (plumbing code or could be a state thing where I live). It keeps things consistent, you don't want 160F water heading to your shower one day and 120F another. You don't want visitors being unware when they turn on the faucet to wash their hands it will get to 160F+ before they know it (in summer)!

The tanks are the bottleneck to how hot you can get it, they have an upper limit. In the manual that comes with your tank it will tell you what temp not to exceed. My tank is a solar tank and the specs say the max temp is 180F. Some non-solar tanks I've seen say not to exceed 140F.

You may want to pay extra $ for a solar controller that handles excessive heat. My solar controller (made by Radiantec of Vermont) when my tank exceeds a temp I set it opens a solenoid that dumps hot water down the drain. Cold water comes into the tank to replace the hot water it's dumping and cools the whole tank & solar loop. In that way I don't exceed my tanks 180F limit. I never have to worry about going on vacations and the like. You don't want the kind that simply shuts the system off so it stagnates, nor depend on pressure/temp valves that will blow hot water/glycol all over the floor (usually there isn't a drain nearby). My system has them as well incase there's no power but it's not the first method my system uses to relieve of excessive heat.

Do you have radiant floor heating? In winter my system on a clear sunny day heats my 120 gallon tank to 110F... good enough for showers. If I doubled my system and used half for heating 110F is fine for radiant floor heating but ain't gonna cut it if you got baseboards (which want 150F-180F water). Around here people w/out radiant floor heating accept solar heating can be used for late winter - early winter but not dead winter. There's about 6-8 weeks out of the 7 months of heating it's just too darn cold and the sun doesn't last long enough (obviously around Dec 21st) for baseboards. People usually burn wood or turn on other forms of heating. If you aim for 100% your system has to be like twice the size over one aimed for 85% (radiant floor heating is more like 95%). Your insurance company requires you to have a form of heating other than wood or solar so it's good not to aim for 100% solar letting you give your regular heating system some use once and awhile else it'll rot.

Glycol has to be drinkable and there's 2 types. The cheap $5/gallon kind which prevents heating systems from freezing and the more expensive kind which is designed for heating systems & cars. I used the Sierra brand radiator fluid that goes into cars (which is drinkable glycol), found locally at my NAPA autoparts store.
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I hope the pictures attach in order.

The Glycol picture is me filling the system with glycol. My system took 11 gallons, I had buckets filled with a 60/40 mix of glycol & water and buckets for when I was flushing the system with straight water before filling it with the mix. You can see my solar loop exchanger goes into the middle of the tank and comes out the bottom, heating the bottom of my tank (better for FP's). For tips on filling
  • Trick the solar loop pump to kick on while also adding that inline pump to build enough head to fill the system.
  • To help build up pressure, close the fill valve slowly when you want to disconnect the fill pump.
  • Put a mix of 60%+ glycol/40% water. You'll have a hard time trying to get decent pressure in the loop unless you have access to a high head pump. My 2 pumps in series couldn't do it they couldn't get more than 16psi. I had to attach a garden hose from my city water & pressure (65 psi I think) to the loop and add it directly to get it up to the 25 psi I needed. However, that added straight water... but if you start with a 60% glycol/40% water you're fine diluting it a little as long as it doesn't dilute below 50/50.
  • Even after running both motors purging air for 2 hours, still the automatic air valve burped air out for weeks to follow. I had to repeat attaching the garden hose to city water to get pressure back in the loop until all the air was gone. My system pressure needed to be 25psi (cold), in the beginning a good day of solar and it'd burp enough air to drop the system to 5psi when it cooled, and what I found out was my pump couldn't pump unless the system was at least 12psi else it would just spin.
One is my wife hugging the panels on my roof. I installed them flat and low so they wouldn't be seen from the front of my house. That was a mistake cause outside high temp solar insulation is $6/foot. Could I do it again, I'd have them upright and all 3 in the same row/series instead of 2 in the back and 1 in front. You have to cover them until the piping is done, they get real hot real fast in sun.

One is my controller, I think the solar loop is 153.3F and the water in my tank (the bottom that is) is 141F. That was in mid February after a couple sunny days and we didn't use much hot water. Oh, my system uses a 3 speed pump which works better with FP systems you want the heat transferred out of the loop and into the tank as fast as you can with FP's. When the temp difference is 8F it goes to low speed, at 12F or so goes to medium speed, and over 16F difference kicks into high speed. This controller also controls the solenoid valve which dumps hot water down the drain when things get too hot for the tank.

One is my PMP (or plumbing package). It has a pressure gauge, temp gauge, fill valves with a ball valve in-between, pressure/temp blow valve (you can't see), the expansion tank is screwed into the automatic air bleeder (the automatic air bleeder is a must), and a check valve.


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Very nice, I'm just South of Boston
Hoping to get a solar hook-up in the next 2 years
I built a small greenhouse & the temp in the spring was up to 110 :eek:
Im thinking of a solar HW system. Im leaning more toward the closed /drainback system as we do freeze here in winter. Does anyone have a kit or brand that they would reccomend?
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