Solar Heating for Swimming Pools

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Solar Heating for Swimming Pools

Solar thermal systems have been available for swimming pools for over 40 years, typically as flat panels placed to collect heat energy from the sun. There are now several different types of panels and systems, which vary in cost and efficiency.

Solar Panels generally come in two main technology types, they both collect energy from the sun, but do it in different ways. Thermal ones extract heat energy and transfer it either directly or indirectly into the water. Photovoltaic or P. V. Units work differently in that they convert light energy into an electric current which can then be stored or used immediately to perform many tasks, including heating.

P. V. systems are rarely used to heat pools as a standard 1.6m² panel will deliver less than 200 Watts of energy and even the smallest pool heaters will provide 3,000 Watts.Therefore the smallest of pools would require a minimum of fifteen panelsto match this heat output and at a very high initial cost.

Thermal Panels that are just designed to heat water come in different types too. The most simple ones are called ‘Flat panels’ and are made of a sandwich of two sheets, the top one is clear and the bottom one is insulating and theycontain a battery of water pipes connected to a header and return pipe. These systems can use a heat transfer fluid that is treated to work efficiently (and can last untouched for months) which then uses a heat exchanger to transfer the heat to the pool water. Alternatively, the solar panel uses the pool water passing directly through the heating panels.

Evacuated tubes are used in a slightly more sophisticated design, which tends to have a more extended season. As the name implies, the panel consist of several glass tubes with a central heat collector running down the length of each. Again, different systems can be designed so as to heat via a metal heating element, or heat transfer fluid or directly into the pool water. These indirect systems can allow the transfer fluid or medium to rise to a much higher temperature when the conditions allow for it.

Outside of these typical examples, there are also other solar devices that are round or curved and use reflectors and other construction methods to collect and focus the free energy coming from the sun. With all these types and alternatives there is a trade-off between efficiency, reliability and cost all of which should be carefully considered.

A high degree of the efficiency is also determined by the intelligence of the control system used. If the panels are hotter than the pool water then the pool water will get hotter, but the opposite applies in the middle of the night when the water is hotter than the panels and the air around them. Consequently, the panels will just as efficiently cool the pool water down if the circulation continues. The flow can be controlled as easily as manually diverting the pool water when the sun is shining, or can be automated and controlled by a more complex system of thermostats, electric valves and electronics.

Sizing and positioning of the panels is also of great importance. Generally in the UK, a south facing panel set at 35˚ from horizontal will be the best for efficient summer use. A steeper angle will favour the very beginning and end of the season when the sun arcs lower. More importantly, neither the panels nor the air temperature thermostat should be sited in the shade! Automatic or manual adjustment of the angle of the panels will again add to the cost, complexity and cost of the installation.

With either Domestic or Commercial installations, the major installation factor is space in the right position.

Commonly, the solutions used in the UK to heat pools are the simplest direct thermal solar panel as they work most efficiently in the middle of the summer, are more cost effective and are in little danger of overheating.

Solar energy is a relatively young energy form to be brought to the general public and so there are new developments and improvements happening all the time. Reliable up to date information can be sourced from independent groups such as The Carbon Trust and Department of Energy & Climate Change .

SPATA reminds its Members that no responsibility can be taken by SPATA, its employees or agents in respect of any errors or omissions from this factsheet.

This version of M83 dated 13th March 2014