Capitol Hill Blue Forums Misc. Topics The Energy Forum Splar Hot Water System

I am exploring some self-sufficiency ideas to go along with our solar electric system. A big one apparently has been using propane to keep a 40 gallon water heater running. I installed a 7 KWatt flash heater a while back and shut down the gas water heater. This heater will raise 1.5 GPM (enough for one shower) by 40 degrees F. This is actually enough for comfortable 105 F showers during spring, summer, and fall in San Diego. In fact I had to turn the flash heater current down in the summer time, or it got too hot. That problem was solved recently by installing a replacement Black and Decker flash heater that has a thermostat you can set to a maximum temperature.

But it still has a problem getting hot enough during the winter. So I am building a solar water preheater system for it. The goal is to store enough heat so tap water gets up to at least 70 F as it passes through a heat storage tank. Then the flash heater can do the rest. If I can preheat the tap water to 105 F, that would require no more energy from the flash heater.

Even now, with no solar input, I am still running a surplus on my grid power usage, but we are going to be switching from propane cooking to electric and I would like to keep generating a surplus. So the plan is to use a DIY 24 square foot panel constructed with CPVC, aluminum fins, polyisocyanurate foam insulation (R 7-8), and an old sliding glass door as glazing. It all gets painted black as it goes into service. That feeds by thermosyphon into a 250 gallon IBC heat storage tank. A submerged coil of copper tubing will transfer heat into tap water as it makes it's way to the flash heater. There is no direct contact between the tank water and the tap water, All that gets transferred is heat, and even if the tap water only gets 10 degrees hotter, that will be enough.

I've got the panel built, minus the plumbing. I've got all the needed parts. including the IBC and enough PEX to hook it all up. I have some chain link fence panels I can use to build a fence around and it and keep it "helpful" dog free, .like my solar electric array. As you may be able to tell, I enjoy DIY engineering projects like this. Hours of hot water every day is just a bonus.

Most of us hillbillies get an old water heater tank, paint it black, and put it in a box mostly filled with sawdust with an old window on the front side.

I got a Rinnai high-efficiency tankless gas water heater.

Our basic workhorse for hydronic heating and domestic hot water is a Triangle Tube high efficiency on-demand boiler plumbed into an 80 gallon solar storage tank. It's easy to add supplemental hot water like the hillbilly solar water heater.

Some day I'll get my own biochar making boiler, but the shoemaker and his kids' shoes...

The state of Florida has had a whole lot of rooftop solar water heaters for decades. These are basically just a horizontal tank with a solar water heater panel attached. You mount it with the tank upslope of the panel, and it doesn't require pumps or even electricity. It's not quite as sunny here, so that's why I am using a 250 gallon heat storage tank. And I have a bunch of IBCs my wife used to store rain water. I also have some old sliding glass doors, so I just needed a sheet of plywood, a sheet of insulation, and some plumbing to hook it up.

A lot of DIYers build these systems, but they put the panel above the tank. So they have to use pumps to keep water in the panel or use copper tubing so the panel pipes don't melt. Then they need a PV panel to run the pump if the grid power fails. Thermosyphon is much more reliable for keeping the plumbing a safe temperature and costs nothing to run being inherently solar-powered.

BTW, the thread should be "Solar Hot Water System" but I couldn't figure out how to fix that without a lot of hassle.

Back in my "homesteading" days in northern Idaho, we had an outdoor shower for about six months (no indoor plumbing at all - in fact, not really any indoors of any kind). Through the month of August we bathed in the nearby creek, but it started to get too cool for that as Fall came on, so I decided we needed a heated water shower. The shower stall was four posts set in the ground with a floor and three walls made of roughsawn white pine (I had a Foley-Belsaw sawmill powered by a 1952 International H tractor). It was open to the spring area where the chickadees could watch. The solar water heater was a 55 gallon drum painted black, on the roof in a box with glass on the south side. I eventually learned that the drum was too big and the limited surface area exposed to the weakening suns rays couldn't quite get shower-level warm by evening. By November, it wasn't even getting up to cool...

So, I scrounged up a 2-1/2 gallon electric water heater and plumbed it into the pipe from the barrel. That much hot water mixed with the appropriate amount of cold is just enough for a shower if you run about 30 seconds to get wet, then lather up at leisure with the flow turned off (25 degrees out), and rinse off in about 45 seconds before the water got cold. The big danger was slipping on the ice that formed on the shower floor...

F*ck that. The only ice that needs to be in my world is the ice in my drink as the sun warms the lake up before I take a swim. In December.

Nobody has much used those old rooftop water heaters since the seventies. They never really caught on except among a few cheapskate DIYers. Seems like they were leaky and not terribly reliable. Butt ugly too.

I pay 3-5 Bucks a month for the natural gas to heat my water. It's doable. Better brains than mine have taken efficiency to new levels.

Out in the swamp I used LP gas and a 40-gallon tank, it cost me $62 a month there.

We live just beyond the natural gas lines, so ours was delivered propane. That costs about the same as electricity for cooking, hot water, and heat, just because they can charge that much. What are you going to do? Use wood? So when solar electric got cheap, lots of folks converted to electric since it was electricity they generated. But solar water panels are much cheaper than PV panels, and much much more efficient. If you have room for them. We do. If you can store and make use of that low level heat, it's about 1 KW per square meter at sunny noon. And it averages 5 KWhrs per day per square meter. For me, every KWhr I can harvest is one less KWhr I need from the power company or the propane people.

Yeah, I was pretty thrilled to have a natural gas pipeline right in my front yard. I pay more to be a member of the Lake Apopka Natural Gas District than I do for the metered gas. But my bill is still under $20 a month.

I pay less for internet here too and the speed is about 200 times faster. I don't need to scrimp on my power bills, my HVAC systems are new. Windows are new, a metal roof with 2 inches of insulation was added 9 years ago, Rinnai tankless hot water is new. Everything is state of the art. Every lightbulb is LED. I won't know until June what the AC will cost in the summer but most power bills should be well under $100. In the summer we tend to turn our houses into iceboxes and only crawl out once a day to eat and sh*t. It's pretty brutal and cooling bills are up to the individual and their thermostat settings.

We run multiple ACs as needed, but that lets us leave large portions of our house unconditioned. We also have fantastic insulation. Usually we can just open windows at night and close them in the early morning, and the house stays cool enough without any AC. We have limited South-facing windows, and we usually keep them blocked and insulated. This is why we can run our 1700 square foot house with only 5 KW of solar panels.