Solar Pool Covers

In response to the recent water restrictions we have had a large number of enquiries regarding solar pool blankets. There are a number of issues both for and against solar covers and many of these have not been adequately raised.

The following table shows the average predicted temperatures of water in an open swimming pool in Sydney exposed to full sunshine and a wind velocity equal to 1/3 of the mean monthly values.
A – unheated and uncovered pool
B – covered with double layer clear plastic cover
C – uncovered and heated with solar collector

Pool JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
A 24.3 23.5 22.8 19.0 15.1 12.3 11.9 13.7 16.9 20.2 22.6 23.7
B 29.9 28.2 27.4 22.3 17.8 14.6 14.5 17.0 21.1 25.6 28.7 29.5
C 28.8 28.2 27.4 25.3 19.5 16.2 16.4 18.4 22.0 24.9 27.5 28.3

This table is reproduced from the report “Swimming Pool Heating By Solar Energy” by J.T. Czarnecki, CSIRO Division of Mechanical Engineering Report TR19.

As the table illustrates, like solar, solar pool covers help extend the length of your swimming season by up to 3 months a year, however the differences are only minimal and the real benefits are achieved when used in conjunction with pool heating.

Sealed Air (formerly known as Rheem) commenced production of solar pool blanket material in 1976. The specially formulated polyethylene film contains UV absorbers and quenchers together with tougheners to minimise the effects of Solar and Chemical degradation. The material is manufactured at the Sealed Air Plant at Alexandria NSW and is exclusively used byDaisy Pool Covers in the manufacture of all commercial blankets.

Owning a solar pool cover will cost you about $2.00 per week forever (or $80 to $120 per annum). The pool solar covers are limited life products and will only last between 50%-125% of their rated life. A number of grades of solar blanket are available with a life expectancy ranging from 2-3 years up to 6-8 years.

When a solar pool cover is on the pool ensure the chemical balance remains correct (never allow chlorine over 3ppm) as this can remarkably shorten the life expectancy of a cover. Running your filter during the middle of the day will help disperse the heat through the pool and protect the cover however this may require some adjusting of your chlorinator to ensure only the appropriate amount of chlorine is produced..

Solar pool covers are not recommended for pools with lots of leaves and will affect automatic pool cleaners. As most pool cleaners operate using a partially submerged hose to randomly manoeuvre around your pool they are easily affected by the floating cover which restricts movement of the hose. This will force your cleaner to only clean one area of the pool or tangle. We recommend removing cleaners when using solar covers. Leaves is another issue. As you will not have a cleaner in your pool you will still get the same amount of debris. While a lot of material will land on the cover it is not easy to remove. In most cases it will fall down the sides of the cover due to the wind or on removal of the cover. As the cover is partially submerged in water this material often ends up partially submerged and is difficult to brush or remove from the floating cover.

You will lose less water from evaporation however there are a few important pointers to consider. Water and air temperature, humidity, wind level and the wind speed at the waters surface all affect evaporation rates. In dry and/or windy conditions, the evaporation rate of the pool increases, so it becomes beneficial to use a solar pool cover during daylight hours. In warm humid conditions, however, the evaporation rate decreases and it may be more energy efficient to leave the cover off during the daytime. While we are currently going through an extended period of dry weather and low humidity, Sydney is normally a warm city with medium to high relative humidity, which is why covers have never been a necessity. In the middle of summer evaporation can cause a pool to lose up to an inch or about 1000 litres of water per week.

If you are using covers to save on heating costs then the benefits can be significant, however, in terms of filtrations and chemical costs they do not lead to major savings.

Solar pool blankets must never be left in the sun while folded, even for a few minutes. This can lead to the covers breaking down very rapidly. If the air temperature exceeds 35 degrees Celcius then the cover should be removed and placed in a protected cooler storage area. Even covers stored on a roller should be protected from these conditions.

The final issue is accessibility. Having a cover on your pool can make it less easily accessible when you want to use it. Will your kids remove the cover? In some cases we know of covers not being used because the kids would swim dangerously under them rather than removing them. If you do not purchase a roller can you, or will you, remove the cover to use the pool? What times of year will you cover the pool? Solar pool covers will heat the water considerably if used in summer, however because the pool is used heavily at this time of year, they are often removed. They can help extend the swimming season, as shown in the table above, but only if they are used for extended periods to maximise heat gain and minimise heat loss. If you use the cover early or late in the season will you remove it? These questions may sound simple and obvious but they are often the questions never asked when discussing pool covers.

Solar covers are available to suit any size or shape pool. They are made oversize to allow for shrinkage when first used.

For those with leaf problems and automatic cleaners, or those looking to cover their pool in winter to minimise maintenance, you should consider debris covers. These are a sewn mesh material that is custom fitted to your pool and attached to the surrounds through a number of tie-downs. These covers stretch across the pool above the coping and are tied to the ground. They are tensioned so they do not touch the surface of the water allowing your cleaner underneath, and they also allow leaves to be blown or broomed cleanly off the top without getting into the pool. They are however much more cumbersome and difficult to fit and remove.

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