Solar Geyser

Solar geysers: what they are and why you need them

Last Updated: January 18, 2024By

People looking to save on their monthly energy bill should consider installing one or more solar geysers.

Solar geysers use the heat energy from the sun to warm water during the daytime.

Our recent solar installation has been going great and we have discovered that water heating accounts for most of our energy use.

Our house has 3 geysers and 2 of these are fitted with a GeyserWise system so we can control when the geysers are on. The third is a very tiny geyser in our outside cottage and doesn’t account for much energy use.

The GeyserWise system allows us to be more efficient with how we use our geysers.

After some experimentation the main geyser (which supplies the kitchen and spare room bathroom) is only on from 2pm to 4pm. The other geyser in the house supplies the main bedroom and is only on from 10am to 12pm. These settings allow the geysers to be fully powered by the electricity from the solar panels and not from the mains (Eskom) or battery.

We have also set the temperature of the water in our geysers to max out at 55 degrees Celcius.

We are still able to have warm showers or baths for both bathrooms even though the geysers are only on for 2 hours a day each. We will adjust the temperature and timings in Winter because the geysers will likely need more energy to keep the water at an acceptable temperature.

Why would we consider solar geysers in the future?

Our goal is to reduce our energy consumption as much as possible. Geysers powered by electricity are the largest energy consumers in our house (except for the oven) and as a result we could reduce our energy use even further by moving to solar water heated geysers.

What is a solar geyser?

A solar geyser uses the thermal effects of the Sun to heat water and doesn’t rely on electricity.

We have excellent conditions for solar geysers in South Africa, especially during the hot summer months. We should therefore rely more on solar thermal heating than electricity.

How does a solar geyser work?

Solar geyser systems include a geyser tank to store water and a Solar Collector. You will find a large variety of solar geysers and kits on the market and each has different features and benefits.

Solar Collectors are usually either flat plates (these look similar to the solar PV panels) or evacuated tubes.

You can convert an existing geyser to a solar geyser.

Water is stored in the geyser tank which has an inlet for cold water and an overflow outlet for any overflow requirements.

A small circulation pump circulates water through the tank and into the solar collector system (flat plates or tubes). The solar collector heats the water and hot water then enters the geyser tank from the collector and is regulated by a number of valves. Hot water can then be accessed through a hot water pipe connected to the tank and which leads into the house.

A circulation pump is not needed if the system has been designed to rely on the natural process of convection. Hot water rises (like hot air rises) and as a result hot water moves up from the solar collector to the water tank above. Cold water flows downwards from the tank into the collector system and this results in natural circulation.

Some solar geysers use indirect heating which transfers heat from a solar collector through a special fluid such as anti-freeze. This fluid moves through a heat exchanger and heats up the water which surrounds it. In this way the water absorbs heat from the anti-freeze but never mixes with it.

What is the difference between a low pressure and high pressure solar geyser?

Low pressure geysers supply the house below with no more than 100kpa of pressure and this is done naturally through the effects of gravity.

You will often find low pressure geysers systems in remote areas or in areas where water is scarce (such as farms).

High pressure systems exist when normal municipal water is used at any pressure above 200kpa. This type of water is usually pumped through the municipal water systems at a high pressure using powerful pumps.

Now that South Africa is implementing water-shedding, the government will most likely reduce the pressure in the taps to limit the amount of water people use.

Your geyser will be rated as either low pressure or high pressure.

Hot water in a high pressure system has a higher pressure than cold water and is usually about 400kpa.

Is a solar geyser worth it?

Yes, a solar geyser will save you energy costs in the long run. If you think about it, it’s quite silly to heat water using electricity during the day if there is such an abundance of thermal energy available from the Sun, especially in South Africa.

How long does it take for a solar geyser to heat up?

This depends on the time of year and the temperature on the day but on average a large geyser will take 4 to 5 hours to reach a good temperature of 55 degrees Celcius when you’re relying on thermal energy.

Electric energy will do the job in about 2 hours.

Does a solar geyser work in Winter?

Yes, it does, but less effectively than the hot summer months. Where you live also makes a massive difference: Joburg Winters are a lot colder than other parts of South Africa like Durban or the Northern Cape areas.

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About the Author: Tony Lopes

Tony is the founder and editor of CleanVolts.co.za. He has completed solar certifications and courses through Green Solar Academy. Tony's goal is to see solar panels on every roof-top in South Africa and the adoption of EVs and renewable technology across the African continent.