Can you run an electric water heater with solar panels? (What to expect)

Yes, you can use solar PV panels to supply electricity to heat water in a conventional electric heater.

Whereas, using such as set up may result in some energy savings, it is not as reliable as it depends on available sunlight.

Also, the heated water cools quite fast because the conventional water heaters are not built to keep the heated water hot for several hours.

How to heat water in an electric heater with Solar PV panels

What you need:

  • Solar PV panels wired to provide enough power (watts) to match the power rating of the electric element in the water heater.
  • Conventional Water heater fitted with a DC heater element. These elements are usually rated 12V, 24V, 36V or 48V. Power ratings for these element are usually 300W, 600W, 900W,1,000W or 1,500W.
  • High voltage wire that can carry the current (amps) from the solar panels
  • Circuit breakers that can handle the DC voltage and current switched from the solar panels

Steps to heating water with solar panels

#1. To heat water, make sure that the heater element voltage matches that of the Solar PV panels.

For example, if your solar PV panels are connected in either series or parallel combined to supply 12V, 24V, your heater element should be rated to 12V or 24V respectively.

#2. Select and wire the solar panels such that the combined power rating matches as close as possible that of the heater element (W) for optimal heating performance.

#3. Fill the water heater with water

#4. Wire the solar panels through the circuit breaker to the heater element, switch on the breaker to begin heating the water.

You can use the online calculator below to work out how much water (gallons) you can expect to heat for a given solar panel size (W) and average number of hours of sunshine.

Frequently asked questions

# 1. Calculating how many solar panels you need to run a hot water heater?

The number of solar panels and their voltage rating needed to heat water depends on the power rating of the heater element in the heater.

To work out the number of panels, take the power rating of the heater element and divide by the wattage of available solar panels with the same voltage.

For example, if you have a 1,500W/ 24V heater element and 300W/ 24V solar panels, you need 1,500/300 = Five pcs. of 300W/24V solar panels.

Note: Connecting more panels risks damage to the heater element resulting from excessive current from the panels.

Too few panels take a longer time to heat the water.

# 2. How long a 12V battery can run a water heater?

To work this out, you need to know:

  • The battery capacity (Ah)
  • The power consumption of the water heater (W)

You can use the calculator below to get an estimate of how long the water heater (watts) will run on battery. Enter the heater’s power consumption as the appliance wattage (w) in the calculator.

Note: water heater electric element typically hundreds of watts of power. Given that batteries have limited storage,
a water heater element depending on wattage can drain a battery in a minutes.

Other ways of heating water using solar

Instead of powering a water heater with Solar PV, you can also use solar thermal (flat panel heaters and or evacuated tube collectors).

Solar thermal water heating and Heating Water with Solar PV are compared below

 Heating with Solar PVHeating with Solar thermal
AdvantagesCan use an already available solar panels and  electric water heater (may need to be retrofitted with another electric element)Better heating performance  

Takes up less space.  

Better insulated water storage tanks that keep water hot for longer   Generally have the electric heater backup option for use  during cloudy or rainy weather
DisadvantagesHeating is slower  

Panels take up a larger area to generate sufficient heating  

Water cools quite fast. You typically need to shower early evening otherwise the water will be cold later.

All in all heating water with solar thermal is heater is a more efficient solution

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