When people take an interest in a solar air heater, the first question is almost always the same: how much does it really heat? The answer lies in one figure: the temperature rise. In this article we explain what it is, what we measured with our collector in the middle of winter, and how you can work out your own savings.
What is temperature rise?
Temperature rise is the difference in temperature between the air entering the collector and the air leaving it. If air enters at 5 °C and leaves at 30 °C, the temperature rise is 25 °C. The higher it is, the more heat the sun is adding to your home.
What we measured
We tested our collector on 20 January 2024 in Valladolid city, at 13:30, on a sunny winter day:
- Outdoor feels-like temperature: 2 °C
- 100 m³/h fan
- Air temperature at the collector outlet: 40 °C
- Temperature rise: 38 °C
In other words, on a bitterly cold morning on the Spanish plateau, the collector was delivering air at 40 °C into the home.
What the outlet temperature depends on
- Solar radiation: the rise is highest in the middle of a clear day and drops with clouds or early and late in the day.
- Orientation: the collector performs best facing south and free from shade between 10:00 and 16:00.
- Fan airflow: with lower airflow the air spends longer inside the collector and leaves hotter. Solar air collectors can reach about 70 °C at the outlet with low airflow; with higher airflow the air leaves slightly less hot but more volume is moved.
How much it costs to run
The sun provides the heat. The only thing that uses electricity is the fan. To work out the cost, remember that your electricity supplier doesn't charge by the hour but by the kilowatt-hour (kWh):
- Power (kW) × hours of use = energy (kWh)
- Energy (kWh) × price per kWh = cost in euros
A 14 W fan running for 5 hours uses 0.014 × 5 = 0.07 kWh. At €0.18/kWh, that's just over 1 cent a day.
You can use the same formula to see what your current heating costs. A 1,200 W electric heater switched on for 5 hours uses 1.2 × 5 = 6 kWh, which at €0.18/kWh costs €1.08. Every hour the solar heater takes off that heater is money you don't pay.
Where does it pay off most?
- Homes, village houses and second homes heated with electric heaters or stoves.
- Rooms with a south-facing wall or roof and no shade in the middle of the day.
- Garages, workshops, sheds, greenhouses or premises used mainly during the day.
- Inland areas with cold but sunny winters, such as Castile and León, Castile-La Mancha, Aragon or Madrid.
What it doesn't do
It doesn't heat at night or on overcast days, and it doesn't replace your main heating. Its role is to reduce the hours your conventional heating runs, at practically zero running cost and with no emissions.
Want to know how much you would save in your home?
Tell us where you live, which way your wall or roof faces and how you currently heat your home, and we'll work it out for you with no obligation. You can also check the prices of our solar heaters.
Get my savings estimate or call us on +34 686 227 287.