Question regarding solar hot water heating

jp1maui · December 2016

new guy here. I've got a solar water panel 4x10 and a solar 80 gallon tank. Live in Hawaii in sunny Kihei Maui. Still, we need more than just solar heating of water. About five years ago I bought a Craigslist propane water heater and plumbed it downstream of the solar tank and left the electric element off in the solar tank. It worked good. My wife was happy to have full time hot water. But I bought a lot of propane. Anyway the propane tank has rusted out finally. I often felt that propane heaters with their annular doughnut shape, aren't the best storage tanks of hot water, cooling it at night. I wonder what to do. So far, I've suggested to my wife to turn on the element at the breaker just when needed. But, that's unreliable. Likely the element will get left on all day. I've also thought of buying a propane tankless heater to top up the water from the solar tank. Does that work well for anyone? Can propane instant heaters handle warm or hot water input? I also think about getting a second panel. Maybe also a larger solar tank. But I want a practical solution. Any thoughts about the best type of water heater after solar preheating?

mike95490 · December 2016

I do that. I have a solar tank heater on the roof, and it preheats water for my tankless. Summer, I get 120F water, winter only about 50F
I do have a Caleffi mixing valve at the inlet of the tankless so as to not confuse it's brain, The less work the tankless has to do, the less propane is used, Look for a multi-stage burner.

Image: https://us.v-cdn.net/6024911/uploads/editor/fv/3c03mjy40mn1.png

Dave Angelini · December 2016

Is it possible the 80 gallon tank was too large for just you and your wife? Are you open or closed loop?
Where you live should really be pretty easy for solar hot water.
I would use a 50 gallon tank for 2 people with one collector. There are better ways to heat the water on bad solar days but again where you live should not need anything but a gas heater tank. All the other things in a good solar installation like a short run, well insulated pipe, and a decent controller. The gas heater pilot should only be on a few months where you live.

jonr · December 2016

> Can propane instant heaters handle warm or hot water input?

They have a minimum fire rate that makes them cycle (very irritating) with low flow rates that need minimal amount of temperature rise.

Burning too much propane - consider adding insulation to the tanks and increasing the solar heaters storage and/or capacity.

It will help some to put a timer on the 80 gallon tank's electric element. Say 6pm to 6am. And install a 1 GPM shower head.

BB. · December 2016

The "simple" ones (maybe older style?) may have one fire rate--Too warm of water on the inlet will not work out well.

-Bill

Dave Angelini · December 2016

BB. said:

The "simple" ones (maybe older style?) may have one fire rate--Too warm of water on the inlet will not work out well.

-Bill

Definately agree and even thought there good applications like Mikes above, there is something wrong with the OP's system.
In Hawaii where I have some clients, solar hot water is so easy to do with just a 50 gallon tank, a large collector, and gas back-up burner or electric if grid tied. Why make it complicated. I do the same thing up here in snow country for 10 months so I know it is done easily!

Marc Kurth · December 2016

In my previous home in So California, I piped an 80 gallon water tank upstream, in serious with a 60 gallon gas fired hot water heater. Three old school glazed flat plate collectors on the roof heated the first tank directly via a small circ pump and modulating valve to maintain temperature. Typical tank temp was 100-120+ deg F by sundown on clear warm sunny days, higher on hot summer days and of course lower during cold rainy weather. But I was always amazed at the temperature rise during cold sunny weather.

I kept the temperature setpoint on the gas water heater at 105 deg F on a bottom mounted sensor. Our 5 five daughters were younger and living with us at the time, and the gas bill was near the minimum connection charge 9-10 months of the year. I was more than happy with the performance.

I eventually added a little 1/4" circulation line to furthest sink to preheat the HW pipes during the hours that the kids were home. I saw a big difference in water usage when they quickly realized that they didn't have to wait for hot water upstairs.

solar_dave · December 2016

I have one 4X10 panel with a 80 gallon tank and a 50 gallon gas heater to carry us in late Dec and early Jan. It uses a Goldmine controller and is a open loop I guess as it pumps water direct to the panel. I have trouble getting more than a couple a therms a month being paid for, The attachment fees are much more. We do use NatGas for cooktop, fireplace(rarely run) and the hotter backup. Probably will switch out the electric clothes dryer for NatGas when the electric one dies.

Question regarding solar hot water heating

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