An efficient version is a photovoltaic tube, they get so hot you would only need a tiny one but either way you need a heat dump to get rid of excess heat.
You can buy simple black hollow mats with a matrix inside for small pools, just slow flow in and out with the mat in the sun.....works a treat on my friends pool.
You can buy simple black hollow mats with a matrix inside for small pools, just slow flow in and out with the mat in the sun.....works a treat on my friends pool.
