Solar Questions

Ask Your Solar Questions Here

Using the sun to heat water may sound simple, but it has the capacity to generate a lot of unanswered solar questions.

And since I specialise in measuring the performance of already installed solar water heater systems worldwide, I might be able to answer some of them for you.

To save time, cast your eyes over the frequently asked solar questions below that I have already dealt with just in case your issue has been resolved in the past.

If not, then contact me and I will try and answer you.

What is the useful life of a solar water heater and how can it be used to heat water on a cloudy day? Does cloud cover cause the system to stop working and if so, what can be done about it?


Glad you asked these questions Charan because they are ones that many people wonder about.

The life expectancy of a solar water heater depends on the quality of its construction and design. So some of them will only last five years and others can reach the ripe old age of 25 years.

Keep in mind that the separate components of a solar water heater have different life expectancies too. So the pump might only last four years and the heating fluid might need to be replaced every second year.

The best is to buy a system with a generous guarantee because that shows the manufacturer is confident their system will last. As can be expected, the longer the guarantee the more expensive the SWH will probably be.

Regarding performance in cloudy conditions, it definitely does suffer in that the water will reach lower temperatures than when the sun is out. So it does still work, just not as well. The backup booster will have to kick in to get the water temperature up to where it should be, but it will still be a lot warmer than ambient temperature.

The only thing you can do about it is increase the size of your water storage tank so that it stays warmer for longer without additional heating. But 2 or 3 days of cloudy weather in a row will mean lower water temperatures no matter what you do.

Take a look at how this evacuated tube solar water heater performed in the cloudy weather conditions of Wellington, New Zealand.

Why do your recommended companies on the top 3 solar water heaters list change according to the capacity of the water storage tank? Why is the company that is best in the 100 litre category not also the best in the 300 litre category?


This is a fantastic question Anjanie, very perceptive on your part to see the distinction there.

It's not impossible for the same company to rank at the top for different capacity storage tanks but the reason it doesn't happen more often is due to the design characteristics of each system.

If you were to take a design that is very efficient for a 100 litre storage tank and use the exact same design for a 300 litre storage tank, it will likely perform worse than another companies system that was designed specifically to heat 300 litres of water.

The reason for this comes down to the fact that the amount of water to be heated (the storage tank size) is a very important factor in the efficiency of a solar water heater.

In fact there are several factors that affect a solar water heaters efficiency. Take a look at a list I've developed of the ten major performance factors here.

So you need a specific design for all the different storage tank sizes. If you keep it the same, they will still be efficient, but another one designed specifically for that size storage tank would probably be more efficient. The larger the difference in size of the storage tank the more true this is.

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