We've just bought somewhere in Portugal and the gas prices are very expensive.

Portugal gets a lot of sun, so we figured let's see if we can heat with solar.

We ideally do not want to be adding things to the roof right away and started researching alternatives, but having never done anything like this we have no starting point.

Is heating via solar realistic, and if so what is the best method...

Convert to electricity and power electric heating? or/ Capture the heat in a liquid and pump it around the property? or/ Something completely different :) ?

[I'm a software engineer by trade so this is all 100% new to us :) ]

  • Google can be your friend. Would search for solar heating Portugal, and you should find pages of information, including if there are any government programs/rebates/loans you might use.
    – crip659
    May 8, 2022 at 11:34
  • 1
    Step zero is likely to be insulating the building properly, if (as it sounds) it's an existing house in an area where that might be "unusual" (at least based on some other questions from Portugal) e.g diy.stackexchange.com/q/217480/18078
    – Ecnerwal
    May 8, 2022 at 11:57
  • This is very interesting, but not particularly well-suited to this site. Can you refine your post to a single, specific question (or two) to fit with how things generally work here? Do some basic research and come back to ask specific, focused questions that can be answered factually.
    – gnicko
    May 11, 2022 at 14:42

2 Answers 2


I'd recommend an energy audit of the house first: in winter, how much energy comes in as heating, how much comes out as losses. And in summer, how much unwanted energy sneaks in, making the house too hot.

Only when you've done that and put numbers can you make informed choices, otherwise it's all guesswork.

This heavily depends on how the house is constructed, where it is located, and its orientation. I know some places in Portugal are pretty hot, but others get rather chilly winters.

As for solar heating, I did a study on the house, but it turned out installing more insulation was a better option. Basically, if you want solar heating, then you need to store heat from sunny days and keep it over the short term to heat during the night, and over the longer term for overcast days where the solar system won't work. This storage can use quite a lot of water volume, and it requires oversizing the solar collectors, so one day of sun will recharge the storage enough to last for 1-2 overcast days. This means diminishing returns, decisions to make, and an auxiliary system for long overcast periods.

If your house was built in a time where energy was plentiful and cheap, and in a climate where a lack of insulation wouldn't result in too much expense, it is likely its insulation is going to be terrible. This means this should be investigated first, as it would be the low hanging fruit, with the highest potential for improvement.

Basically, if you live in a sunny place where winters seldom go below 0°C, with a good amount of insulation and south-facing windows, you should barely need any heating.

Note you don't need solar collectors for solar heating. My house faces south, and it has large windows. So, I installed a large awning on top, with vine growing on it. The leaves provide shade in the summer, so no direct sunlight gets into the house. Then in autumn they fall off, and the sun is lower on the horizon, so I get a lot of sun inside the house in the winter.

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Start by knowing the size of the task. define the load, ie how much heat you need. check out "Degree Days" to calculate load for year.

If you design the building from scratch then no need for a boiler or woodstove - ex-wife & kids live in a house with solar water heating for heating and domestic hot water.

Once you know the load then you can start sizing the equipment. A rule of thumb for DHW (domestic hot water ie showers etc) is 1m^2 of panel per person. Then for heating more area is required.

Tanks based on water use, start with 200 litres per person, but types of solar collector needs different tank minimum volumes. Tank on the house mentioned above is 1300 litres as it does heating and hot water. Use underfloor heating as it matches well with winter water temperatures.

This is to give you ideas of what to research - not going to do endless questions, there are so many websites with good information available.

Make sure you include the safety valves so you don't get scalded by hot water - tanks can easily get to 90 deg C plus.

  • 90deg+ on the tanks is incredible... Thank you so much! This is exactly all the keywording I was hoping to find!
    – John
    May 8, 2022 at 10:10

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