My Solar PV-based Electrical + Gas-based Water Heating System

[afro-solar]

Heating water is one the biggest energy considerations I've had to think about. On average, 30% of a traditional energy bill can be attributed to heating water.

So I came up with a plan that guarantees I don't have to use the grid to heat water, anymore.

1. 10x 445W LONGi solar panels.
2. 1x dual-heating GeyserWorx control unit (really, is an inverter, but heats water instead of charging a battery).
3. Solar panels are wired in series below 300V (GeyserWorx MPPT input limitation).
4. Solar panels are wired in parallel to bump amperage up to 25A.
5. Each inverter in the GeyserWorx can achieve at least 12A when both are running, or 25A when one is running.
6. GeyserWorx heats traditional water tanks, fitted with a special thermostat.
7. 2x Dewhot tankless, on-demand gas heaters.
8. The gas heaters are electrically powered (to light the pilot flame).
9. The gas heaters are piped into the house's main plumbing.
10. An automated solenoid valve is used to choose between the gas heater or the traditional heater.
11. This choice is automated using a Shelly 1 wi-fi relay switch (on-demand, or time-of-day).
12. Solenoid valves that switch between the traditional tanks and gas heaters, based on the Shelly 1's instructions.

With this setup, the gas heaters are used in the early morning or on cloudy/rainy days.

The traditional tanks (which are heated by the PV-based GeyserWorx system) are used for late morning, afternoon or evening showers, on days when we've had good solar yield (which, in Johannesburg, is at least 73% of the time, per year).

The GeyserWorx system went in first, and on cloudy/rainy days, it supplemented from grid energy to heat water (it is grid-tied). But since we brought in the tankless gas heaters, we have not had to call the grid in for any water heating (going on 3 years now). As a result, I have disabled the breaker that feeds power from the grid to the GeyserWorx. All of its energy now comes purely from solar PV.

I'll share some pictures.

 

[WindWizard]

I have two ways of heating my water.

1- Solar direct vacuum tubes
2- Wood

I use solar panels to provide electricity.

Your system will probably work but sounds complicated.

 

[afro-solar]

I have two ways of heating my water.

1- Solar direct vacuum tubes
2- Wood

I use solar panels to provide electricity.

Solar thermal tubes are very common in South Africa, actually. I considered them, but in addition to having to do a lot of work on my plumbing to get them installed, I figured they utilize ambient heat from the sun to heat water. In our winter, this might not work well for a house of 5 people who each shower 2 times a day, remembering that dishes are also washed with hot water during winter.

Despite clear-sky winters in most of South Africa, there is still not enough sunlight to generate enough heat throughout the day for this type of heating load. But there is enough sun to turn light into electricity, especially with the efficiency of PV generation in cold temperatures.

Also, we require less hot water in the heat of summer, which is when thermal solar tubes make the most heat. And at the same time, they don't work as well for a load of our size in the winter, when we need hot water the most.

I suppose if you lived alone or with one other person that was relatively frugal with hot water, a solar thermal system would be perfect.

Your system will probably work but sounds complicated.

My system has been working for 3 years now. It is actually very simple, and runs itself. The only work I have to do is:

1. Swap out the gas canisters every couple of months.
2. Rinse the solar panels twice during winter, as there is no rains to clean off the dust in that season.

 

[WindWizard]

In our winter, this might not work well for a house of 5 people who each shower 2 times a day, remembering that dishes are also washed with hot water during winter.

The thermal tubes do not supply enough hot water in the winter due to the low sun angle and the snow. They need to be supplemented with an additional heat source. It works well for us with a wood boiler. The boiler heats the house and also the hot water tank. In the winter, if the sun shines, I can usually get an 80 gallon tank to 130 deg f.

We purchase 8 cord of wood tree length. I cut, split and stack it and then we burn it for the heat for the house or for hot water. 8 cord is enough wood for a year. Occasionally the temperature does dip to around -30 deg f.

 

[afro-solar]

The thermal tubes do not supply enough hot water in the winter due to the low sun angle and the snow. They need to be supplemented with an additional heat source. It works well for us with a wood boiler. The boiler heats the house and also the hot water tank. In the winter, if the sun shines, I can usually get an 80 gallon tank to 130 deg f.

We purchase 8 cord of wood tree length. I cut, split and stack it and then we burn it for the heat for the house or for hot water. 8 cord is enough wood for a year. Occasionally the temperature does dip to around -30 deg f.

I guess if you need a major heat source for your rather harsh winters, it does make sense to use some of it to heat water too.

Our South African winters are not as bad as those of the northern hemisphere. The lowest we would see is -1c to -7c in the very early hours of the morning, but the daytime would settle at between 10c - 15c.

During winter, we do get the odd cold snaps that would last a week or two, where ambient temperature is between 3c - 7c during the day (much lower at night), but the clear skies give the illusion that it's warmer than it really is.