Category Archives: Solar Thermal

Information about our research into Solar Thermal water heating systems


20 Aug 2015

Going from the data that Tim got of the 3.3 kWh/m^2 day, we have discovered it will give us about 840 kWh per year.

3.3 x .7 efficiency x 365 days per year ~ 840 kWh/year

Now all we need is the amount of energy from TESC’s pool to know how much space we need.  Going from the Gustavus Adolphes example of a 572 m^2 surface area taking 51,100 kWh per year, we know we would need 61 m^2 of solar thermal.

Adding 25% to our needs to incorporate the diving pool:

64,000 kWh would need 76 m2 of solar thermal.  This is a very small estimate so either the efficiency is too high or the power needed to heat the pool is quoted as extremely.  

Using a process found on Engineer’s Toolbox:

Heat Loss through Evaporation Tutorial

Evaporated water per second


Heat Supply for pool evaporation

Using this example and plugging in our own value of 608m^2 for our surface area (swim and dive pools) we get a evaporation rate of .069 kg/s.

Our heat supply must provide 156 kW to compensate for the heat lost through evaporation.  To calculate the kWh/year, we multiply by the hours and days:

156 kW x 24 hours/day x 365 days/year = 1,372,078 kWh/year

at $.08 a kWh, this costs Evergreen roughly $110,000 a year.  Using our estimate of 840 kWh/year m2 from solar thermal panels, we need an array of a size:

1,372,078 kWh/year  /  840 kWh/Year m^2 = 1640 m^2 of solar thermal panels.


21 Aug 2015


This site gave us a request of about $140,000 with an array of 3500ft2 ~ 315m2


25 Aug 2015


Found a site with another calculation of about $87,000 (before tax) for a 1500m2 solar thermal array for the swimming pool.


These price differences are pretty disconcerting at the moment.  from $87k for 1500m2  to $140k for 300m2.


The lower estimates assume we have pool covers that are used nightly and throughout the winter months.  Without the pool cover, you have to double the estimates from the online calculators.  It’s worth taking note that the use of a pool cover can dramatically decrease the amount of energy it takes to heat the pool.


Using an efficiency of 80% and an insolation of 1000W/m2


800 W/m2 * 1000 hours/year = 800 kWh/m2 per year.


1,400,000 kWh’s needed / 800 W/m2 = 1750 m2


Solar Direct can supply the 350 panels we would need for $92,000 (before tax I”m sure)

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