Solar PV Vs Solar Thermal: Which is Better?

The basic difference between solar PV (photovoltaic) and solar thermal is that PV produces electricity while thermal produces hot water. But which is the better option for Irish households?

Solar thermal panel with hot water tank on a roof; Array of solar PV panels on a roof.
Solar thermal (left) versus solar PV (right). Credits: ResoluteSupportMedia licensed under CC BY 2.0 (solar thermal); trochej licensed under CC BY 2.0.

Potential Savings are Higher With Solar PV

Forgetting to turn off the immersion is the nightmare of every Irish householder. And it’s true that it takes a lot of electricity to heat a full water cylinder. So heating water with solar thermal instead of an immersion heater can give you significant savings on your electricity bills. However, solar PV gives you even more savings. This is because – in addition to giving you hot water – solar PV can help power every electrical appliance in your home.

Solar PV Requires Almost No Indoor Space

Solar thermal systems require significant plumbing. In particular, you might have to get a bigger hot water tank. This makes people with solar thermal complain they “have no room in their hot press any more”.

In contrast, a solar PV power diverter can give you hot water with no change to your plumbing. Overall disruption is minimal with solar PV because it takes up only a tiny amount of indoor space. Better still, PV hardware can be located out of the way in your attic or garage.

Solar PV is More Reliable

Solar thermal systems require a pump to move fluid through the system. Unfortunately, this means pump failures and pipe leaks can be a problem. You will have to maintain these parts periodically. On the other hand, solar PV systems have no risk of leaks and require little or no maintenance.

Solar Thermal Requires Less Roof Space

Solar PV systems start with as little as 3 square meters, but 10-30 square meters is more common. In contrast, solar thermal systems generally need much less roof space. 2-7 square metres is usual for solar thermal. Because of this, solar thermal can be the winner if don’t have much roof space.

Solar thermal provides hot water.  The savings are moderate and the panel area required is small.  The maximum grant amount is €1,200.  Solar thermal will not bring the opportunity to sell surplus electricity to the grid.Solar PV provides electricity and hot water.  Savings are large.  The roof area required is large.  Grants are up to €3,000 and you will soon be able to sell your surplus solar PV electricity to the grid.
Solar thermal vs solar PV. CC:BY energyd.ie

Higher Grants for Solar PV

You can get grants for both solar PV and solar thermal. However, solar PV grants are significantly higher (up to €3,000) than solar thermal grants (€1,200).

Make Money Selling Surplus Solar PV Electricity

From June 2022, you can sell your surplus solar PV electricity to the grid in Ireland. This could be a nice extra income solar PV owners. You can’t sell surplus hot water unfortunately!

Conclusion – Solar PV vs Solar Thermal

For most people, solar PV is a better option than solar thermal. However, if you’re short of roof space, then consider a solar thermal system.

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Installers generally don't offer quotes for timeframes longer than 6 months. So here are guide prices (before grants):

  • 2kW (S): ~€5,500
  • 4kW (M) + myEddi: ~€8,500
  • 6kW (L) + battery: ~€12,500