Heating water with solar power: PV or thermal?
A solar powered water heater can mean two different setups. Solar thermal collectors heat the water directly, while solar PV panels make electricity that runs an ordinary electric or heat pump water heater. Each can work in Canada, and the better choice depends on roof space, budget and how the house is already heated.
What are the ways to power a water heater with the sun?
Three routes cover most cases.
- Solar thermal. Collectors heat a fluid that warms a storage tank. Efficient at turning sunlight into heat, but it makes only hot water and needs plumbing, pumps and freeze protection. See solar water heaters in Canada.
- PV with an electric tank. Panels feed the house, and a controller sends spare solar power to the tank's element, so the tank stores the extra as heat instead of exporting it.
- PV with a heat pump water heater. The same idea with a more efficient heater, which needs less electricity per litre. See heat pump water heaters in Canada.
The head-to-head comparison for the whole house is in solar thermal versus solar PV.
Why would PV panels heat water?
Panels have an advantage in flexibility. The same array powers the lights and appliances, charges a car and feeds the grid when the house does not need it, whereas a solar thermal collector can only warm water. Solar PV also has no pumps or glycol in the roof loop, and it is easier to add to a house later.
The catch is conversion. Electric element heating turns each kilowatt-hour of solar electricity into about one kilowatt-hour of heat, while a heat pump turns it into several. A thermal collector delivers heat straight from the sun and can beat a plain element on roof area. Where exported power is paid at a low rate, storing solar power as hot water can be worth more than selling it. Rules differ by province, so ask your utility about its net metering or microgeneration terms. The Alberta rules are explained in Alberta net metering.
How much solar power does hot water need?
A rough check helps. A household using about 10 kWh a day to heat water with an electric element would need roughly the output of 2 to 3 kW of panels in a sunny spell to cover that heating alone, depending on conditions and shading. In winter the panels may produce a small fraction of that, and snow cover cuts output further. See how many solar panels a house needs and solar panels in winter.
The figures here are assumptions for illustration. A heat pump water heater would cut the electricity need to a fraction, so the panel requirement falls in step. Always size from your own hot water use and a modelled estimate for your roof.
Can a solar powered water heater work off the grid?
It can, with care. Off-grid homes often pair solar thermal for hot water with PV for electricity, because a thermal system makes hot water without taxing batteries. A water heater is a large electrical load, so running one from batteries needs a bigger system. The wider picture is in off-grid solar in Canada and grid-tied versus off-grid solar.
Drake Landing Solar Community used solar heat only, with no PV. Its 800 flat-plate collectors fed a district loop. The DLSC solar collection page describes the field. Costs and rebates for either route change by province, so check the Government of Canada energy-efficiency pages and your utility for current programs.
Quick answers
Can solar panels power an electric water heater?
Yes. A controller can divert surplus solar electricity to the tank's element so that it stores the energy as hot water. Check the wiring and controls with a qualified electrician.
Is solar thermal or PV better for hot water?
Solar thermal gets more heat from a given roof area, while PV is more flexible and simpler to add. The better fit depends on your roof, budget and existing equipment.
Do I need a battery to heat water with solar panels?
No. The tank itself acts as the store, and heating can be timed for sunny hours. A battery is optional.