This article is about “solar pool” - the term which is confusing sometimes. Here I will explain the fundamentals you need to know about ‘solar pools’ and how they operate, so you will have basic knowledge about them when you decide to build or to buy one.
What it is and what it’s for
In simple words, the term “solar pool” means that you use solar energy to heat the water in your pool (a swimming pool or a spa). The main reason to have a solar pool is to extend your swimming season into a few spring and autumn months and also to have more “swimming hours” during the day: the water gets warmer earlier in the morning and stays warm longer in the evening.
Obviously, there are more reasons to use solar energy: it is environment-friendly, it is absolutely free (as we don’t have sunshine taxes yet 
) and it reduces dramatically or even eliminates your pool heating costs.
You pool was quite an expensive investment; why not get the most out of it?
How it works
Generally, a modern solar pool heating system includes a water pump, a filter, a valve system, a solar collector, a control computer system, lots of pipes …and, of course, you have to have a pool itself .
Please see the drawing below for details.
The heating system operates under the control of computer (I would not recommend manual systems as they eat up your time and are less effective). The process starts at a solar detector located near the collector and is connected to the computer. When the detector decides that there is enough sun heat to operate, it sends a signal to the computer to turn on the pump. The pump starts sucking water from the pool through the filter (where it gets cleaned) into the valve system and the solar collector.
Basically, the collector is a set of tubes and pipes exposed to the sun. The water inside of the collector warms up naturally under the influence of the sun heat as it flows though it. (Please read “Solar collector types” article for more information on types of collectors, their locations, size and etc.)
The valve system can operate in two modes - it either passes the water through the collector once and returns it to the pool or it makes the water circulating through the collector until it reaches certain temperature before it goes back to the pool.
Please note that the heating system can be plumbed into the existing pool filtering system.
How hot will it be?
The temperature difference between the water in a solar pool and a pool without any heating system depends on the pool’s size mostly. The bigger the pool is the more water you need to pump through the collector during the day. The rough estimate is about 3 - 5 degrees Celsius for big pools and 5 - 8 degrees Celsius for small ones and spas. Obviously, even 5 degrees can make a big difference for swimmers.
How much is a solar pool?
Thus, the most important question - the price. It depends greatly on the size of your solar pool because the bigger the pool is the bigger solar collector you need to build.
From this point of view, there are two types of solar pools - simple do-it-yourself kits when you need to buy all parts and maintain such system independently (or even make-it-yourself solutions when you assemble a solar pool out of various things lying across your backyard) and systems developed and maintained by professionals.
The former is cheaper, ranging from zero up to few hundred dollars or maybe a thousand dollars if you decide to buy solar pool collectors which are the most laborious part of the system. The latter will cost from $2,000 to $5,000 for a typical 300 to 400 square feet surface area of a residential pool. If it sounds somewhat expensive to you - there are also…
Good news
For simple do-it-yourself kits which may cost a couple hundred dollars and which are suitable for small pools about 30-40 sq ft, the pay back period is as short as three or four months! Large solar pools pay back for themselves with energy savings in 2-3 years of use which is a pretty short period of time. Taking into account that an average life span of the system is about 15-20 years (and you should always ask for a warranty), solar pools is a worthy investment.
As for your expenses - the only one is your pump bill. If you are inspired with the solar energy, you can make your pump solar as well and the whole system will work for free.
..and this is it ! Please read the article about solar pool covers as they are very important if you want to reduce heat losses. Solar covers can help you save money! In addition, there are articles about other things you can do with your heating system and more info about solar pool collector types.
