solar pool heating Systems

Heating swimming pools is rapidly becoming one of the biggest areas of application for solar energy.  Using the sun's thermal energy to heat swimming pools is very similar to using the sun to heat hot water for other types of domestic use.  Typically solar flat plate collectors are used to heat the water. These are described in our section Solar Hot Water Systems.   The collectors can be mounted on the roof of your house, on a patio roof near the pool, or on mounts alongside your pool.  Under typical weather conditions a solar water heater can raise your pool temperature by 10-15 degrees.  This can greatly extend how long you can use your pool each season.

Design of Solar Pool Heating Systems

 Most solar pool heating systems include the following:

• A strainer— this is filter for straining out large matter such as leaves.
• A pump — which circulates water through the filter and the solar hot water collector. From there it may go back into the pool or to a conventional pool heater for further heating. 
• A filter — removes finer debris before water is pumped through the collector
• A solar collector — the device through which pool water is circulated to be heated by the sun.  These are often mounted on a south facing roof near the pool.
• A check valve - The check valve between the pool heater and solar panels prevents water from backing up into the panels when flow control valve is in the non-solar position.
• A flow control valve — an automatic or manual device that diverts pool water through the solar collector.

Optionally there may be a conventional pool heater used to further heat the hot water.  When used in this way the solar collectors act as a pre-heater which reduces the load on the pool heater. Another feature you may see in some systems are heat sensors which are combined with an automatic flow control valve.  What these systems will do is divert the water automatically once the water in the solar collectors is of significantly higher a temperature than the pool water.  This can be a good energy saving feature in that the pump doesn't end up pumping water through the system until it has had time to come up to an adequate temperature. 

If you live in a cooler climate where freezing can occur it often does not make sense to take water directly from the pool and pump it through the solar collectors. If the water froze in the pipes they could be damaged. One option is to drain the pipes when cool weather sets it but this can be a bit of a hassle and there is sometimes a risk that you will not be able to get all of the water to drain out. For these situations another design is often used which is to pump antifreeze rather than water through the pipes. This is often referred to as a closed loop design. The antifreeze is warmed by the sun just like the water would be and then that heat is transferred to the pool water through the use of a heat exchanger. Because it is antifreeze and not water in the collectors there is no risk of freezing and the pool can be heated longer into the fall and winter season.

Construction of Solar Collectors

Solar pool collectors are made out of different materials depending upon the climate you live in.   In warmer climates the most cost effective solution is probably an unglazed solar collector. Unglazed collectors don't have a glass covering (glazing). They are generally made of heavy-duty rubber or plastic which is often treated with an ultraviolet (UV) light inhibitor to cut down on damage from the sun's ultraviolet rays. By eliminating the glass the overall cost and weight of the collector is reduced making it a good choice if budget is a concern.

By contrast, a glazed collector is usually made of copper tubing on an aluminum plate with an iron-tempered glass covering. One advantage of a fully glazed collector is that it tends to perform better in colder climates.  These types of collectors can be designed either to circulate the pool water directly or a glycol antifreeze solution which is then used in combination with a heat exchanger.

Types of Solar Collectors

Solar collectors can be classified into two types, rigid collectors and flexible collectors.  The rigid flat panel type are the most common. Rigid collectors come in different sizes the most common being rectangular panels about 4 feet by 12 feet.  Like solar panels you can combine these modules together to form a large collector bank.  Most rigid collectors are designed to be placed on the roof but there are some which can be ground mounted beside the pool.  The ground mount collectors are often used in conjunction with large above ground pools as show in this picture. One advantage of these types of collectors is that they can be easily stored or taken down during winter when the pool may not be in use.

Flexible style collectors are basically black integrated flexible tubing and can be used to accommodate the wavy clay tile roofs that are so common in the southwest.  These types of collectors can come in any length up to 88 feet and are on headers that are 12.5" each. They glue down horizontally on wavy tile roofs where a rigid flat panel would be more difficult to install.

Factors to Consider

There are a number of factors you should consider before investing in a solar heating system.  Here are a few:

Age of Your Roof - When considering a roof mounted pool heater you need to consider the age of your roof.  It is a similar issue with PV solar panels.  If the roof is on its last legs and is going to need replacing in a few years you probably don't want install a roof pool heating system until you have replaced the roof.  If your roof has another 10 or 20 years then this is not a problem. 

Climate - Running water directly from your pool through a solar system makes sense if you live in a warm climate like California or Florida.  If you live in a colder climate where freezing occurs it is a bit more difficult.  One option is to thoroughly drain the collectors before a freeze can occur. However, freezes can sometimes be hard to predict so take that into account.  Another option is to use a system that circulates an anti-freeze type of solution rather than water.  In this type of system the antifreeze solution once heater is run through a heat exchanger which transfers the heat to the water from the pool.  These types of systems are a bit more expensive than water circulating systems but can be quite effective even in a cooler climate.

Leaks - A solar collector is one of those products where you need to go with strong quality.  The collectors are painted black and will expand and contract significantly with temperature changes.  The system you choose needs to be designed to handle this temper variance or leaks can occur. 

Weight - If you are putting in a number of heating panels and the panels use larger diameter tubing or pipes, then they will add significant weight to your roof when filled with water.  If your roof is in good shape this should present no problem but if it has any potential structural issues then these should be addressed before installing it.  One metric to get from the solar contractor is the weight of the system per square foot or meter once it is full of water or antifreeze.

Conserving Heat - Solar pool heaters should always be used in conjunction with a pool cover which you can put over the pool when it is not being used.  Otherwise much of the heat you generated during the day will be lost. There are many types of pool covers on the market.  One of the more convenient types is placed on a roller which makes it easy to put on each night.