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How Do High-Efficiency Evacuated Tube Solar Collectors Work?

House at sun setAn evacuated tube solar collector absorbs and converts UV rays into free thermal energy. Each solar collector contains 20 double-walled evacuated glass tubes about 2” diameter and about 70 inches long.
Each evacuated tube is made of two layers of very strong borosilicate glass sealed at one end with a small gap between the glass layers. Solar UV rays pass through the transparent outer tube and are absorbed by an aluminum nitride (AIN) film on the inner glass tube. This special coating absorbs more than 92% of the UV rays that incident the tube and heats the space between the inner and outer glass tubes. Like a double-pane window, this heat generates a vacuum and forms a high efficiency heat insulating barrier between the glass tubes.

Because the evacuated tubes absorb both UVA and UVB rays, they work efficiently all day long and even on cloudy days to absorb lower levels of solar radiation to heat your pool.

How a Solar Thermal Pool Heating System Works?

Your existing pool pump is used to circulate the pool water through the solar collector system and back to your pool. Each system has two water temperature sensors, one near the pump, and one up beside the roof-mounted solar collectors.  When the pool water temperature at the pump falls about 4°C below the owner’s temperature setpoint, a digital control system activates an automated 3-way valve to divert water up to the solar collectors for additional heating.
Water is pumped through the collector tubes and the heated water is returned to the pool. The low ferrous glass tubes can withstand up to 134 kg (295 lbs). of external force.
Every square meter of an evacuated tube solar collector will generate over 2,500 Btu of energy per hour. So a solar thermal pool system not only extends your swimming season by up to one month in the spring and one month in the fall, it provides up to 90% of your annual heating without worrying about rising electricity or natural gas rates.House at sun set

Minimize Heat Losses with a Pool Cover

In midsummer, most average pools lose up to 50 mm (2 inches) of water per week from evaporation, with higher losses due to dry or windy weather. This not only removes expensive pool chemicals but accounts for 30-50% of all the heat lost from a swimming pool. Using a pool cover can reduce your heat loss by up to 50% from evaporation, night-time heat losses, and convection losses from swirling water. While a pool cover helps retain heat collected on sunny days, your evacuated tube solar collector will still absorb lower levels of solar radiation even on cooler cloudy days to heat your pool.

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Solar Thermal FAQ

Pool Heating ROI


Savings and payback of solar pool heating

To compare the payback and savings of pool heating systems, let’s assume we are using a
20’x20’, or a 400 square foot pool, for 10 years:

Total Installation and
Operating Costs

Gas Pool
Heating System

Solar Pool
Heating System

Initial Investment


$5,000 - $8,000.00
(including installation)

Operating Costs
After 10 Years (est.)


$0 (maintenance)

Total Costs


$5,000 - $8,000.00

It is very clear that a solar heating system for this pool can be paid back in 3 years and the savings over a 10 year period are over $7,000. There can be much higher savings with a heating a larger pool, or one that is used frequently for an extended season. You can do an annual inspection and cleaning yourself, or you can have your solar company do it for you a small annual fee.

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