Estimating the minimum area of the solar collector needed to heat your pool isn’t as difficult as you may think. Because almost all of the heat that’s lost from pool water is lost from the surface of the pool, the optimal area for the solar collectors is proportional to the surface area of the pool.
To determine your pool’s surface area, just multiply the length by width for a rectangular pool. For an oval pool, use length by width multiplied by 0.9. For a circular pool, it’s simply the diameter of the pool, squared, and multiplied by 0.79. If your pool is an odd shape, then try dividing it up into rectangles, circles and ovals, estimate the area in parts, and add them together.
A solar collector that has the same area as the pool will almost always be adequate. However, if there’s an issue with the area of north-facing roof you have available, a collector with an area of as little as 60% of the pool area can work in the northern states, and in the southern states, you can generally make do with a collector that occupies 80% of the pool area. If you’re planning to order your collectors in a colour other than black in order to match the colour of your roof, then add 20% to the minimum area.
Now, you have the minimum size for your solar collector. However, if you have a lot of roof space available, then take advantage of it! The larger the solar collector, the more time you’ll have in your comfortably heated pool.