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Solar pool heating generally refers to the process of using the passive solar heat of the sun to warm up a swimming pool. Solar pool heating may also, however, refer to large-scale solar ponds, being heated up to store energy that can be used for a number of purposes. While this first use is something most people have access to, larger-scale solar pool heating is generally undertaken by industry, although it may have applications for homesteads looking to generate their own power.
A solar pond is a large pool of salt water, which sits in a natural gradient, with high salt water at the bottom, and low salt water at the top. Sunlight strikes the water and goes down to the bottom, heating up the lowest layer of salt water, in turn causing the water to expand and become less dense. If it were fresh water, this lower level would rise to the surface, and a convection current would form, but since it is part of a salt water gradient, it remains at the bottom and continues to increase in heat, often with temperatures reaching nearly 200 degrees Fahrenheit (93 Celsius). This heat can in turn be used to power generators, producing a great deal of electricity. Solar pool heating electricity is particularly attractive to developing areas, as a solar pond can be set up for very little cost.
Personal solar pool heating, on the other hand, has nothing to do with salt water, and is not intended for large scale power generation. Instead, it is a way to heat an indoor or outdoor pool without using a non-renewable source of energy. In this sense solar pool heating makes use of passive solar energy collection to heat up the water in the pool using only the light of the sun.
Water is pumped from the pool and makes its way into a series of solar collectors. These solar collectors are essentially just large panels, which run the water into tubes that are often black, to absorb the heat of the sun and become hot. As the water heats up, it makes its way to the top of the tubes, and once hot enough it returns to the swimming pool, to heat up the mass of water.
Using solar pool heating means that little to no electricity is needed to keep a pool warm, but it does mean the temperature of the pool is dependent on peak sunlight. For most people, their desire to use a pool coincides with hotter days, so it works out quite nicely. For those who often want to take dips in a warm pool in the middle of a cool night, however, some sort of electric backup may be ideal.
Even in these cases, however, solar pool heating can still be a good option. With a suitable pool cover, enough heat can be absorbed during the day to keep the pool warm through the night. And even in the coldest climates, solar pool heating will generally keep the average temperature of the pool much higher, requiring much less electricity to bring it up to an ideal temperature.