# Payback on Simple Pool Heating Collectors

 Costco.com currently has one of these simple solar pool heating collectors for \$99.99 (including shipping).  It is a 40 sqft collector and is said to include everything you need to hook it up to your current pool. So how long would it take for the collector to pay for itself compared to heating with natural gas?

According to this calculator, each square foot of collector will receive about 2300 BTU of solar radiation on a sunny summer day.

When the pool water temperature is 80F and the air temperature is 80F, the efficiency of this type of collector is about 80%.(1)

So, the heat generated on a sunny day would be:

(40 sqft)(2300 BTU/sqft)(0.8 efic) = 73600 BTU  heat to the pool per sunny day

If you provided this heat with an 80% efficienct pool heater that burns natural gas (the cheapest fuel), the amount of natural gas needed would be:

(73600 BTU)/(0.8 efic) = 92,000 BTU, or 0.92 therms.

If your natural gas costs \$1.60 per therm, this is worth about \$1.50 saving per sunny day.

So, the payback period is roughly  67 days  --- just over 2 months of sunny weather.

You would also be reducing CO2 emissions by about 15 lbs for each day of use.

When the price of natural gas doubles again the payback time will be even less :)

Note 1: These simple unglazed collectors achieve this high efficiency because pool water is usually as cool or cooler than the air temperature during the collection period.  This means that no glazing is needed to prevent heat loss from the collector absorber to the air.  Glazing typically absorbs 10 to 15% of the incoming solar -- without the glazing, all of the solar radiation gets to the absorber.

This is one reason why solar pool heating collectors are such a good deal -- they are simple and cheap, but still very efficient.

Gary May 4, 2008