One of the biggest power guzzlers in our domestic homes is the hot water geyser. It is reported to use between 40 and 60% of your electricity consumption. This of course depends on how much hot water you use, how hot you’ve set your thermostat and whether you keep it on all the time. It also depends on other appliances in your house, for example whether you have an electric or gas stove.
So why don’t we all have our solar geysers in place yet, enjoying free sun energy for the future and vastly reducing our electricity bills? Why is it that even when Eskom’s rebates were increased considerably, there was hardly any impact on the rate of purchases in our country? Yet, when load shedding started, sales jumped up?
There are many reasons for the reluctance in the market, or the slower than planned implementation of solar geyser targets. Let’s consider 2 possible answers to this.
- Lack of clarity or understanding of exactly what’s available, what the difference is, how they work and what the different benefits and drawbacks to the various systems are.
- A clear and proven link to economy: how is this going to benefit my pocket?
- The news of collusion amongst the manufacturers, who shifted up their prices in line with Eskom’s increased rebates, has of course shocked us all. And we are waiting for this issue to be resolved, hopefully benefiting our pockets, at it should.
- The entire system is geared towards supplying a specific solution (a standard electric geyser to supply hot water). The geyser is hidden and most people don’t think about it as long as it’s working. The builder or insurance company (in the event of geyser failure) often takes the decision.
Over the green bridge
Mean time I discovered that if I am to convince my man that we need to cross this essential bridge now, I’d need to understand it all much better and fully be able to play the numbers game, something which doesn’t come naturally to a creative soul like myself. Could it also be that there is a measure of intentional mystification of the exact details regarding how these essentially simple systems work?
My friend Karin Kritzinger, who has just completed her MPhil degree in Sustainable Development on this topic, is adamant that they’re easy to understand and kindly explained this to me woman to woman. So this story covers the bare basics, as in solar geysers 101 for dummies. We hope to turn this into a series, but this story will be followed up by pieces written by experts. I will however always help to translate technical details into ordinary language so we can all understand enough to make the move.
Flat plates or evacuated tubes?
A solar hot water system consists of a geyser and a solar collector. The collector is that dark flat plate on your roof, which captures radiation from the sun, transforms it into heat and feeds it to the geyser water. (This is not to be confused with solar PV, which is a source of solar electricity for the home. More about this in a future story.)
There are 2 different types of collectors. The sun’s radiation can be captured by either glass tubesor copper pipes, turned into heat and transferred to the water circulating through them. The glass ones are called evacuated tubes and are similar to the glass insides of the old vacuum flasks.
The evacuated tube panels are all imported from overseas, mostly from China or Europe. The thickness of the glass of course impacts on the price. This type seems to be ideally suited to the colder northern countries, where the sun is at a premium, as it’s very effective…
Most systems are designed to supply hot water 70% of the time. The rest is done through an electrical back-up. If it’s designed for 100% of the time, then it’s over-engineered for most of the year. 70% is optimal.
The flat plate system consists of copper pipes, which are also imported, but the systems are manufactured locally. In fact Solardome in Stellenbosch have been manufacturing them for 40 years. There are many other local manufacturers of flat plates too. The tubes are covered in a flat plate of thick glass and here solar radiation is converted to heat, and trapped in the water inside the pipes.
Thermosyphon or pumped?
As hot water is less dense than cold water, it rises. The thermosyphoned way of getting the hot water to the geyser relies on this natural process. As the water in the solar collectors heats up, it starts a natural process of circulation and pulls the colder water from the storage area into the collectors to be heated. Of course it means the geyser must always be higher than the collector, hence we see the geysers sitting right on the roof above the solar collector.
Some people want the geyser out of sight as they don’t like what it looks like out in the open. Or some neighbours complain! I have heard of a family who had to pay a higher levy in a complex because of their system on the roof, can you believe it?
So you can have what’s called a ‘split’ system with the geyser inside the roof, but now the hot water needs to be pumped down to the geyser with a little pump. This takes very little energ; as much as a garden water feature or a fish tank, I’m told. This system must have some kind of heat measuring in it to make sure that the water is only pumped when in fact the water in the collectors is hotter than that in the tank This all adds to the cost. Some people also complain that the pump can be noisy. Both evacuated tubes and flat plate systems can either use thermosyphon or a pump. Some cheaper evacuated tube systems, where the tubes come directly out of the tank, only work on thermosyphon.
All systems with an electric back up come with a timer. Some systems come with a ‘geyserwise’ or other similar meter which sits in your house and indicates the temperature of your geyser’s water. This way you can switch your system off when you don’t need it.
Most systems come with an electric back-up system in case there’s not enough solar radiation around to satisfy the needs of the household. This is why all systems that are SABS approved need to have a timer. The timer ensures the element doesn’t come on during peak time and that the element doesn’t heat the water after your morning shower. If it should come on then, the sun’s radiation later in the morning will be wasted as the geyser’s already hot.
Direct or indirect?
In the direct system the water that is circulated in the collector runs into the geyser and you use this to shower or bath. The hot water goes in at the top, and the cold water leaves the geyser at the bottom and flows back through your tubes in the collector for heating. However, this water could collect sediment and corrode your geyser. All metal geysers have what’s called a ‘sacrificial anode,’ which prevents the geyser from rusting. This needs to be replaced every 3 years.
Then you get the indirect system, where you can add antifreeze to the pipes and the circulating water never mixes with the geyser water. Inside the geyser are coiled pipes with hot water inside, which runs through the cold water already in the geyser and so heats up your geyser water. Now the water quality is not so important, and water quality can be a problem in our country. In places where you get low temperatures, it is essential that an indirect system should be used to protect the system from freezing.
Now for your investment
What holds back most of us at the moment is the initial capital outlay of between 10 to 25 grand (after Eskom subsidy). However, talking to the experts who have done the math, I am beginning to realise how silly we are. Many companies have now arranged financing for us to pay off our geysers, or you could purchase yours on your credit card, or you house bond. I’ve even heard that one can access money from your life insurance policy for home improvements.
Many installers now offer ‘green credit,’ which means they’ve already made an arrangement with a bank and can lend you the money directly. They even deduct the rebate up front and you start paying off your investment to the tune of R500 to R600 per month, depending on the size of the geyser you select. These payments happen over 48 months, while you electricity bill shows a considerable reduction. After this period you’re scoring big time, and for the next 10 to 2o years you’re capturing free solar heat.
Makes a lot of sense? Some people worry about how long they will still be living in their current house. I have no doubt that selling a house with a good, guaranteed solar geyser will add to the attraction of the house. Wouldn’t you like to buy a house which includes free hot water? If you move you could even take your SWH with you, then you only need to pay the installation costs at the new house.
Start saving now
Currently we’re paying about R1 per kWh, including VAT and this is increasing by 25% in July to R1.25. And next year it’ll increase again. Apparently we use about 70 litres of hot water per person per day, which comes to about 4 kW per person per day if the heater is heated from 20 degrees to 70 degrees. 70% of this could be saved by using a solar geyser.
Building more fossil fuel power generators is going to be frightfully expensive and shove the planet over the tipping point in terms of global warming. We simply have to go solar, now.
To my mind it’s a no brainer to see how clever such a green investment will be all the way round for the pocket, for mankind, for the planet.
Karin Kritzinger has just handed in her thesis for an MPhil in Sustainable Development at the University of Stellenbosch. Her thesis topic is: ‘Exploring the possibility of the insurance industry as a solar water heater driver in South Africa.’ (The insurance industry purchases 50% of all standard electric geysers in our country). Karin has kindly provided most of the information for this story. She works as a sustainability consultant.
Here are some solar providers to contact about products and installation: