It’s 2024, and there’s no getting around it. Grid energy is expensive. [Darrell] realized that a lot of his money was going on water heating, and he came up with a neat solution. What if he could hack in some solar power to slash his bills at a minimum of fuss? It worked so well for him, he’s whipped up a calculator to help others do the same.
[Darrell]’s idea was simple enough. He hooked up solar panels to just the bottom heating element of his hot water heater. This cut his power bill in half. His calculator is now up at pvh20.com, and it’s designed to help you figure out if it’s feasible for you. It takes into account your location, local power prices, and the amount of sun your area tends to get on a regular basis. It also takes into account the solar panels you intend to use and your water heater to determine how many panels you’ll need for properly hot water. Key all that in, and you’re well on your way to speccing a decent solar hot water setup. From there you’ll just need to buy the right stuff and wire it all up properly.
If you live in an area where the sun shines freely and the power is more expensive than printer ink, this could be a project well worth pursuing. Cheaper hot water is a grand thing, after all. [Darrell’s] calculator is really only the first step, and it doesn’t deal with the practicalities of installation, but that’s half the fun of a good project, right? Happy hacking!
Nice! Now use solar electricity to power a heat-pump hot water heater and multiply the benefits.
And also, cool the solar panels with cold water that preheats the water going into the water heater. Yeah, this will need a pump, but it also increases the efficiency of the solar panels.
What’s the efficiency cost of the extra layer of transparent material to keep your water in a contained area free of bird poop though
bird poop is a feature, not a bug.
correct. bird poop WAS a bug. now it’s just poop.
If you cool the PV panels only from the back side, the efficiency cost is zero. Really all you have to trade off is the power required to get the warm water back up to service pressure, since you need low pressure water on the panels.
I did just that! My heating bill went from 1000EUR per month to 100EUR!
Wow!
Tankless heater.
This, but get a gas one. Electric ones use an insane amount of power.
A friend got a gas thankless heater, the flue ran dangerously hot. It heated the laundry room. Not very efficient! I hated the cold then hot then cold again with slow flow. In months it burned out what a scare they had. Thankfully no fire spread out of it. A tank of hot water is a very cheap energy storage solution and can even get controlled by the grid provider where a thankless heater would pay extra.
How is that better? They have an insane peak power usage. Energy is energy, so the gains would be the same, but a tankless water heater would require some sort battery as energy storage rather than using the water itself for energy storage.
Energy is energy… Yes a tautology, very nice.
A tankless heater doesn’t have to keep the tank hot 24 hours a day. The heat is still trickling out at the same rate every minute, it’s far more efficient to heat it as needed.
Peak power? Use natural gas stored on-site.
Funnily enough, here is Aus grid energy used to be cheap as chips till the state started chasing unreliable “renewables”.
Everything is insanely expensive until you try to complain about it, then you get told that not only is it not expensive and it’s all just in your head, but also if you vote the right way then the same people who made it expensive will magically fix it
Thanks again!
Careful with supplying DC voltage directly to a thermal switch, just absolutely make sure it’s rated for the DC voltage as there’s no zero crossing like AC. The failure mode could be welded contacts and possible relief valve or explosion. DC is a whole different animal than AC.
But low voltage from panels is definitely enough to bring the temperature of a tank up during a day.
I sure learned this the hard way. I was testing a 120VDC battery setup I was going to use with a special inverter design. I needed to load-test the batteries to see how much voltage droop there would be at high current, so I rigged a clothes iron to it as a load. Which worked fine until I tried to turn it off with the iron’s temperature control. Green fire that didn’t stop until I yanked a wire out. When I took the iron apart to see what had happened, I saw a solid chunk of metal that had originally been two separate contacts. This was only about a 10 Amp load. Lesson learned.
Irony!
Keep in mind you will want to heat your water above 50c occasionally to prevent Legionnaires disease.
Another good reason not to keep it sitting around hot all day.. Although why doesn’t it happen in the pipes? Are you sure the chlorine (or chloramine) doesn’t prevent that anyway?
Well, our water supply is a well.
Ergo, no chlorine.
Water isn’t normally chlorinated where I am. Except in swimming pools. Don’t drink those.
I guess you’ve read too many IoT security stories when your first thought on seeing the phrase “Hot Water Heater Hacked” is “Dammit! Another security breach?”
How about getting rid of the electric part all together. We know the conversion efficiency sucks. What is the maximum conversion efficiency for heating water? I suspect it is going to be higher.
It’s called solar hot water and it’s quite popular here in Australia. You circulate cold water into black panels with embedded piping and it comes out hot at the other end.
Still needs a gas or electric backup for cloudy days.
https://www.rheem.com.au/rheem/products/Residential/Solar/c/solar
Common and effective in the desert southwestern US as well.
Maximum efficiency? Yep, that’s electric.
Can’t beat heat pumps
I’ll just leave this here…
https://www.builditsolar.com/Projects/WaterHeating/water_heating.htm
PV is simple to deploy.
A thermal system adds complexity, needs an electric pump and is surprisingly expensive. Also, it can only heat water.
Why would you heat hot water?
Exactly the comment I was going to make. It’s just a water heater, unless you have two water heaters in series then the second one would be a hot water heater.
The -Hot- Water Heater thing bugs me also.
I use a propane tankless water heater, and I use a 20lb tank to run it. The tank refills are normally $14, but when Countrymax gets their tank filled they have a sale and it’s $10. The 20lb tank lasts 6 months, I think $20 per year is pretty reasonable. And the heater was only $80.
Wow, $10! Are you referring to a 20# tank?
Oh – I thought that dynamic load adjustment for a full PV system is already standard today
If you need only water heating, just use a solar thermal system directly. But that is even on the edge of being superseeded:
– I’ve got one, it still helps, you have too little heat in winter and too much in summer
– if it were PV + water heat pump instead, it would be more efficient, Capex is approaching parity
Typical problem: let’s say you have a regular PV system. if you use your electricity yourself, this saves you from buying from the grid (so the value of a kWh is e. g. 35ct/kWh) But if you give the excess to the grid, you will only get a fraction (6ct/kWh). Even when putting the excess electricity into a direct resistive water heater (no heat pump) this is cheaper than gas/oil/pellet heating!
I understand that you can buy ready made solutions that use the excess electricity to control the wallbox, or electric water heaters. They adjust the power to use only the excess, and if I turn on the oven, that gets priority. One colleague mentioned raspi with evcc, and another one had a commercial solution installed for the water heating…
Come to Europe where they pay you too much for the electricity and you can use it for free.
I was about to tell “this is nonsense, just use the sun to heat the water” but I stopped to think.
Guy already have water heating infra in place, house is already in use, not in construction, and he wants to reduce the heating bill. It’s cheaper to run wires down the roof than pipes, installing a solar panel is cheap and easy.
It’s the optimal solution when you don’t want to cut the walls to pass piping down the water tank. It’s cheap, easy to maintain, and mostly maintenance free as long as the proper protections are in place for the electrical part of it.
Using PV to heat water reduces the complexity and cost significantly. No regulator, inverter, grid tie etc. Just panels, cable and resistor. Think of the water tank as a battery, storing the solar energy until you need it.
Sure it’s not optimal and you’re not eliminating grid power, but the barrier to entry is very low