How Does It Work

The mechanics of a solar pool heating system are quite simple. Cold water from your pool is pumped through the filter up to the solar panels — often called low-temperature solar collectors — usually installed on your roof. While the water circulates through the solar collectors it is heated by energy from the sun and then returned to the pool. This process continues until the desired temperature is reached in the pool and the pump automatically turns off.

The following descriptions go into detail about specific parts of a solar pool heating system in addition to how to determine the size of the system and the limitations of the solar pool heater.

Solar Pool Panels: Unglazed vs. Glazed

There are two basic types of solar pool heating panels: unglazed and glazed.

An unglazed solar pool panel consists of an absorber which is typically manufactured of heavy-duty polymers, metal or even rubber. They are effective in moderate climates, like the weather we experience here in Los Angeles and Orange Counties, and are affordable due to the inexpensive parts and straightforward design.

A glazed solar pool panel has a transparent plastic or glass cover that is applied over the top of the absorber to reduce convective and radiative heat loss. Usually a glazed collector is insulated to enhance its ability to operate in cold air conditions. While the additional cover and insulation increases the production in cooler weather, it also increases the cost of a solar panel making it a more expensive option.

Many of our customers choose to heat their pool water with unglazed solar panels, which can provide moderate pool temperatures (75º F to 85º F) for a maximum swimming season of April through November. Since unglazed collectors are influenced by air temperatures, they are not expected to heat the pool effectively during the offseason from November to April. However, a pool blanket will help retain the heat that is produced by the unglazed solar panels on warmer winter days, which could potentially extend the swimming season into the colder months.

Glazed solar panels have their own set of advantages. Because glazed collectors are insulated, they can operate on cold days when the sun isn’t shining and extend your swimming season nearly year-round. In addition to the improved performance, glazed solar panels are more aesthetically pleasing and will look more like skylights on your roof. If you are heating water for a spa, hot tub or a pool for therapeutic use, we recommend installing glazed collectors since they can more easily meet the higher temperature requirements. We also suggest glazed solar panels for large commercial swimming pools since they are typically heated for the entire year.


Solar Pool Pump and Controls

In almost all cases where the filter pump is currently keeping the pool clean, it is not necessary to change it or to add a pump for the solar pool heater. The existing pump is usually capable of circulating pool water up through the solar panels on your roof.

Solar heating is completely automatic in a properly designed system. When your pool requires heat, the automatic control diverts the water coming from the filter to the solar panels (also known as collectors). This process continues until the desired temperature is reached or until no more solar energy is available. The solar collectors will preheat the water before it gets to the gas heater and the gas heater will only use the fuel needed to make up the difference.

Flow through the solar collectors should occur only during the daylight. Since the panels normally receive water from the existing pool pump, the solar system will not require any additional electricity usage. For this reason, it is important to size the system in order to gather enough energy during the pump’s normal operating schedule.


Solar Pool Heating and Your Roof

To get the full benefits of a solar pool heater, you must have an area on your roof that is large enough for the solar collectors. Typically, the solar module will need to cover about 60% of the area of your pool surface. You can find the square footage by multiplying the length of your pool by the width, and then multiplying that number by .6. For example, an average pool size in California is about 400 square feet. Based on the formula, the pool would need about 240 square feet of solar collectors to heat it properly.

The roof area needed for the solar system also depends on the following factors:

  • Desired water temperature
  • Surface area of the swimming pool
  • Amount of exposure the pool has to sun and shading
  • Direction that the solar collectors will face (south facing is optimal)

Depending on the factors above, the size of the solar pool heating system will vary. For instance, if the solar collectors are facing south on a pitched roof and you’d like to swim comfortably from June through September, then you will only need a solar system that is about 50% of the surface area of the pool. However, if your roof faces west and you would like to swim from April to November, then you will need a solar system that is 94% of the surface area of the pool. During your solar evaluation, our experts will assess your pool, roof and swimming needs to determine the size of your solar pool heating system.


Solar Pool Heater Limitations

Though solar pool heating is extremely efficient (especially in comparison to other pool heating options), there are some limitations you should be aware of before purchasing. Unglazed solar pool heating panels cannot keep up the temperature when it’s heavily overcast or raining. If you would like to swim during the winter months, you may need to operate your gas heater to make up the temperature difference. Even if you need to use your conventional gas pool heater on dreary days, the solar heater will still supply a large amount of free energy during most of the year and will save you money on your monthly costs of heating the pool. Also, solar pool heaters do not warm a pool as fast as a gas or electric unit. It usually takes a few days for the pool to reach the desired temperature — but it will be heated with free solar energy!


Learn More About Solar Pool Heating

Our website offers much practical information about solar pool heaters. Learn the basics of a solar pool heating system or get into the more technical side by reading about the theory behind solar pool heating.

Some of your questions might already be answered on our solar pool FAQs page, but if you still have questions feel free to contact us. If you are interested in installing a solar pool heater, fill out a brief form to request an installation and we will be in touch with you shortly.