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How do most people heat water with solar panels and batteries?

WorldwideDave

WorldwideDave

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We have gas tankless on demand hot water heaters. One is at and of life. Considering options.
Do most people with solar install big 240v tank hot water heaters?
Or do they do on demand tankless electric hot water heater for whole house?
Or do people do smaller 120v point of use on demand tankless heaters?
Or what about the 8 gallon point of use hot water tanks?

When I look at some of the specs they all seem to use a lot of power, but the big tank ones at 4.4kWh seem to be the most. That’s like a day of production for me right now.

I’d prefer to do 120v stuff vs 240v if possible.
 
I'm in France so no 120V.

Currently I use an electric tank water heater. I changed the previous one due to a leak, so I picked a model with a 1800W three phase heating element, ie it has three 600W heaters. I'm going to switch them independently to follow PV production. Another solution is to use a dimmer, but these have terrible power factor and inject a lot of noise in the grid.

Tankless heaters use way too much power to be any use with PV.
 
WorldwideDave said:
do they do on demand tankless electric hot water heater for whole house?
Click to expand...

Those are the worst. They do save energy, but they pull easily 30kW, so they would need a dedicated inverter-- for something that runs 10 times a day 10 minutes each.

The opposite technology is a heat pump water heater. Ours runs up to 10h a day, but pulls only 300W. That doesn't stress the inverter. And also saves energy.

The conventional resistance w/h pulls 20A @240v = 5kW. A heavy load, but manageable with a big enough inverter. These are rather wasteful.
 
I use wood for 2 months during the winter.
When the day length gets longer, I wait for charge parameters met for the battery. Then turn the hot water heater breaker on after 9:30 am .
(240 volt 4500 watt heater elements). Turn off breaker after 4:30 pm. The water stays hot for showers at night.
Works for me.
I have 8kw of panels and 8kw inverter.
With as cheap as solar panels have gotten, I recommend having enough panel wattage to match the Max inverter output. That way the batteries for an off-grid system maintain close to 100% state of charge through out the day.
 
CaliSunHarvester said:
Those are the worst. They do save energy, but they pull easily 30kW, so they would need a dedicated inverter-- for something that runs 10 times a day 10 minutes each.

The opposite technology is a heat pump water heater. Ours runs up to 10h a day, but pulls only 300W. That doesn't stress the inverter. And also saves energy.

The conventional resistance w/h pulls 20A @240v = 5kW. A heavy load, but manageable with a big enough inverter. These are rather wasteful.
Click to expand...
Link to your heat pump water heater please
 
For the last 2 years I used a 30gal water tank that I switched out the 4500W 240vAC elements with 2000W 120vAC elements. It was on a switch so that when I wanted hot water and there was extra solar I would turn it on. From cold it would take about 2.5hours to heat up. Provided me with plenty of water to shower and do a load of laundry. Not everyday but for me plenty sufficient.

I just 2 days ago switched to 3000W-240vAC (due to upgrades to my PV setup that now allows split phase to home) elements. I installed a hot water timer box and it is programed to operate from 9:30am to 2:30pm. With the water in it kept warmer I noticed it takes just about 1/2 hour to reach temperature in the morning.
 
Just me and the wife, been using Solar with RV style 10gal water heater for about 2 weeks, can keep on 24x7 with heating cycle pulling 1350w.. this ends up 3-4kwh a day… now testing with cycling it for washing hands and dishes .. then scheduled full heating for shower times… could reduce need to 1-2kwh …

But if I was in house or fixed non RV location … I might do something like this
Amazon description:

GE Appliances 10 Gallon Electric Water Heater, Versatile Plug and Play with Adjustable Thermostat, Easily Installs Where You Want It, 120 Volt​

 
CaliSunHarvester said:
Those are the worst. They do save energy, but they pull easily 30kW, so they would need a dedicated inverter-- for something that runs 10 times a day 10 minutes each.

The opposite technology is a heat pump water heater. Ours runs up to 10h a day, but pulls only 300W. That doesn't stress the inverter. And also saves energy.

The conventional resistance w/h pulls 20A @240v = 5kW. A heavy load, but manageable with a big enough inverter. These are rather wasteful.
Click to expand...

Yeah I have a tankless on demand and it’s not the best for solar. It pulls between 8-15kw depending on the flow rate. But I also have an ev charger that pulls 12kw so I had to size for both.
 
I left the propane water heater in place and added a hybrid heat pump water heater in series ahead of the propane water heater. This gives twice the gallons of hot water. I run the heat pump water heater at a higher temp so the propane won't kick in unless I turn the heat pump water heater off using the app.

Come winter and we get days forecast with limited sun, the heat pump water heater is turned off and we rely on the propane water heater only. If there is plenty of sun, the heat pump water heater provides all the hot water. I prefer choices as solar is not always available and the battery bank needs to last. I intended to use the element in the hybrid heat pump water heater for a dump load but have yet to turn it on. Only time it ever was on was initial startup, I presume automatically to check operation.
 
MattMan119 said:
Just me and the wife, been using Solar with RV style 10gal water heater for about 2 weeks, can keep on 24x7 with heating cycle pulling 1350w.. this ends up 3-4kwh a day… now testing with cycling it for washing hands and dishes .. then scheduled full heating for shower times… could reduce need to 1-2kwh …

But if I was in house or fixed non RV location … I might do something like this
Amazon description:

GE Appliances 10 Gallon Electric Water Heater, Versatile Plug and Play with Adjustable Thermostat, Easily Installs Where You Want It, 120 Volt​

Click to expand...
When you run this device do you shower and do laundry only when the sun is up, or have large battery bank?
 
Regular 4500W 240V 40 gallon electric hot water heater connected to a EG4 18kPV. Would love if there was simple straightforward replacement conversion to 48V DC to bypass inverter but went down that rabbit hole too long. Kept with the standard simple regular tank type water heater was simplest solution for 2 adults.

Edit: this is completely off grid as well with over 100kWh of battery capacity.
 
We are in 220V land but have two 6kW on-demand heaters (one in each bathroom). They run on the grid side of our 3 x Deye 5kW hybrids (running parallel with zero export but grid tie).

Most of the time the inverters don't even blink with the bedroom mini-split A/C and one water heater running. When we do have family over any shortfall from the inverters is seamlessly topped up from the grid.

It works for us but of course YMMV :)
 
Related, although it wasn't solar-powered.

A German friend here in Thailand (sadly now passed) had an indoor pool.

Being German, he liked his pool warm and his rooms set to arctic!

He had a stainless-steel heat-exchanger made by a local fabricator so he could warm the pool using the waste heat from the aircon. It worked well as his pool was invariably like a sauna.

I'm afraid I have no details whatever about the heat exchanger arrangements :(
 
I have one of these babies...

1740704672264.jpeg


Trick is to keep the fire small enough its always making a little heat and then when you need a little more you open the draft and heat water.
 
I've used about five switchback runs of black polyethylene pipe on top of a 20-meter-long roof (nearly 100 meters of 3/8" pipe). When it's sunny, the water is hotter than one could take straight--must be mixed with cold at the faucet. At night, it's a cold shower. But when the sun shines, it's an awful good feeling knowing that the hot water cost nothing. Total investment for the system was about $60, with half that being the hot-and-cold faucet (rare for Thailand). The pipe is inexpensive.

Hot water run into a 5-gallon bucket would stay warm for several hours, for dipper baths.

While the 3/8" pipe heats quickly, I'd recommend the next larger size (or longer length) for a little more capacity. My pipe would give about five minutes of hot shower before starting to cool.
 
I would like to add that our resistance water heater consumed 12.5kWh a day. I measured over a few weeks.

I put it on a timer which let us have hot water from noon to midnight only and it cut consumption in half (6.5kWh).

With the heat pump w/h it's slightly below 3kWh a day. Some days under 2kWh. Hot water 24x7, no more cold water in the late mornings.

9.5kWh savings a day is worth $4 to $6 in our area, let's call it $5. In a year, the savings recover the purchase price, that's without the $700 rebate.
 
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