The Short Answer
The short answer is that, for a standard 32 m2 pool, from a cold water standing start at the beginning of the swimming season, solar heating can heat your pool to a swimmable 28ᵒ C in just a few days.
Exactly how many days is “a few” depends on whether you have a pool cover or not. It also depends, in no small part, on where you live: potentially just 3 days if you live in Brisbane; the better part of a week or more if you live in Melbourne.
That’s because, in more tropical locations, solar pool heating collectors are capable of yielding around 8kwh per square meter per day. In more temperate locations, however, the figure falls to nearer 4 kwh per day. As a result, solar heating can warm a 32 m2 (42,000 litre) pool in Darwin by around 5.5ᵒ C in a day. The same size pool in Melbourne, however, will only be warmed by a little under 2.5ᵒ C in a day.
Of course, this is a lot slower than the more instant heat on demand offered by either traditional gas heaters or by pool heat pumps. But, once you’ve paid for the installation, solar heating is essentially free.
The Longer Answer
The longer answer, however, is that it depends on a whole variety of different things. Obviously, two of the most crucial factors are climate and geography; solar heating needs sunshine – and the more of it the better.
But there are a range of other factors that will affect how long a solar heating system will take to heat up your pool.
General Factors That Influence How Much Your Pool Water Warms Up
Prime among these are the size of your solar collector area: it should be at least 80%, and ideally 100% that of the area of your pool – if it’s not big enough, it’s going to underperform. Equally, it’s going to underperform if it’s facing in the wrong, or at least less than ideal, direction: the optimum orientation is north, although 45ᵒ east or west of true north will not significantly affect its heating performance.
Also, if the solar collector is mounted on the roof of your house, the roof construction material and colour will have an effect: metal and fibro roofs conduct heat more efficiently than tile or slate roofs; dark coloured roofs are better than light coloured roofs.
Likewise, is the solar collector affected by shade? If so, it will heat the water more slowly.
Starting Water Temperature
Geography and climate don’t just determine the amount of sunshine your solar heating system gets and, therefore, how many kwh it can deliver to heat your pool. They also determine how cold your pool water is before you start to heat it.
Average Water Temperatures of Unheated Pools –Without Pool Covers (ᵒ C)
Average Water Temperatures of Unheated Pools – With Pool Covers (ᵒ C)
Pool Heat Loss
Solar heating might be capable of warming your pool by approximately 2.5ᵒ to 5.5ᵒ C per day, but the time required for it actually to warm your pool to a pleasantly swimmable temperature depends on the daily rate at which your pool is losing heat at the same time.
Through evaporation alone, an uncovered 32 m2 pool in summer will lose heat at a rate of around 1.2ᵒ C or more per day. Indeed, more than that if your pool is located in a windy area; in fact, even a gentle breeze of around 10km per hour will significantly increase the rate of heat loss.
Additionally, in spring and autumn, the cooler nighttime temperatures cool the pool’s surface water. The net effect is that, especially in more temperate locations, your pool water temperature may only be benefitting from around half of the actual warmth that is being delivered by your solar heating system.
That’s why a pool cover is so important. It’s all very well to heat the pool, but it’s equally important to retain the heat. On a daily basis, a good pool cover will retain at least 75% of you pool’s heat loss.
Approximate Daily Heating Effect of Solar Heating
|Location||Without Pool Cover||With Pool Cover|
|Brisbane||2.0ᵒ C||3.2ᵒ C|
|Sydney||1.8ᵒ C||2.9ᵒ C|
|Perth||1.6ᵒ C||2.6ᵒ C|
|Adelaide||1.4ᵒ C||2.4ᵒ C|
|Melbourne||1.2ᵒ C||2.2ᵒ C|
How Long Solar Heating Will Take to Heat You Pool – Region by Region
So, depending on where you live, and presuming your solar collector area is the right size for your pool, is oriented in the right direction, not bothered by shade etc., the following tables show the approximate length of time that solar heating should be expected to heat an average 32 m2 backyard pool to a pleasantly swimmable 28ᵒ C – with and without a pool cover.
Approximate Number of Days to Heat Pools to 28ᵒ C – With Pool Covers (ᵒ C)
Approximate Number of Days to Heat Pools to 28ᵒ C –Without Pool Covers (ᵒ C)
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