Open Letter to the Solar Pool Cover Industry

I’ve been banging on about a certain issue for a while but I wanted to write a more prominent article after the recent release of Australia’s National Climate Risk Assessment report, and after becoming aware that the problem has become significantly worse recently, not better.

Solar pool heating blankets (covers) are great way to warm a swimming pool. We try to promote them and urge customers to use them whenever they can. However, there seems to be a lack of understanding in the way they work. Specifically, pool blankets with a silver backing (and now there are outright black backing covers) will block a lot of the suns energy and prevent deep transmission into a pool.^* This means that a lot of that energy impinging on a dark solar pool cover will simply heat up the plastic and dissipate to the atmosphere very quickly, resulting in a MUCH cooler pool and more energy usage.

Since approx 80-90% of the sun's energy falling onto an uncovered pool is absorbed into the pool, the pool's surface area itself forms the largest source of heat energy for that pool; in fact it provides more heat than a 100% coverage solar pool heating system. By covering the pool with a silver-backed or dark/opaque cover we're shooting ourselves in the foot, for almost no reason whatsoever - as it can't even be argued that they look better visually as these solar blankets typically are blue on the topside which is similar to more transparent blue solar blankets.

The industry is installing more heat pumps which while better than gas units still use a lot of energy, and these darker covers are no doubt greatly increasing the energy requirements to heat a pool, without the pool owner even being aware.

I urge the industry to stop selling these darker blankets as they have no doubt created cooler pools and a large increase in pool energy usage for people (in a cost of living crisis) and greater greenhouse gas emissions.

CO₂ Emission Impact from Dark Solar Pool Cover - a Back of the Envelope Calculation

Firstly, for an average representative pool in Australia, let's calculate the heating loading scenario for a 32 m² in Sydney, using a transparent and dark solar pool cover.

Let's heat the pool to 27°C from Sep to May. Assuming an average wind exposure, no shading and a transparent pool blanket - heat loading calculations show an annual thermal energy requirement of approx 15MWh to heat the pool.

If we change to a dark pool cover, this adds approx 60% extra shading on the pool as a conservative estimate, and our thermal energy requirements more than doubles to 34MWh annually for that particular average pool.

There are 1.2 million or so swimming pools in Australia, if we assume 40% use a solar blanket and 1/2 of those were to use a silver-backed or dark pool cover, the energy impact is (34-15) x 1,200,000 x 40% x 0.5 ~ 4,500,000 MWh extra thermal energy required.

To generate 4,500,000 MWh thermal energy using a heat pump with say an average 5.3 COP factor we need 4,500,000 / 5.3 = 840,000 MWh worth of electricity, which in terms of CO₂ is 500,000 t CO₂-e or 0.5Mt of CO₂-e.

0.5Mt of CO₂-e is equivalent to the annual CO₂ required to power ~145,000 homes (assumes ~5.8 MWh/home on the national grid), or the CO₂ produced from ~2.5 billion car-kms traveled or the CO₂ offset by installing ~90,000 roof top solar PV 6.6kW systems.

Conclusion: phasing out dark silver-backed solar blanket is a major win all around for very little pain and we call on the industry to take action.

Contact: info@EcoOnline.com.au

* J.T. Czarnecki. Swimming Pool Heating by Solar Energy. CSIRO Division of Mechanical Engineering. Tech. Rep. No. TR19. (1978)