Author Archives: john4150

About john4150

Advisor, Consultant, Writer, Editor and Teacher on Energy and the Environment. Consulting Editor, African Wildlife & Environment magazine. Past Associate Professor of Energy Studies, University of Johannesburg. Currently Visiting Associate Professor in the School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg. Sole Proprietor, Gauteng Solar Solutions, Agents for On-Sun South African designed and built solar geysers. Suppliers of PV systems, inverters, batteries and load-shedding solutions.

Welcome to 32 Years of Solar Water Heating


It is with a very heavy heart that I advise our readers and supporters that after being in the solar geyser business for 32 years, my dear friend Willi Suremann has decided to close down his operation. This means that the wonderful On-Sun product is no longer available. We will continue to support On-Sun owners in Gauteng who require servicing and spares for their solar geysers. Many of the units that I have installed in Gauteng, starting about 18 years ago, are still going strong, only needing some maintenance to keep them in good shape.

Why have things come to this sad ending? There are a number of reasons, main among them being the rising costs of materials and transport , making it very hard to produce the On-Sun at a cost that justifies keeping the factory open, while remaining competitive in the market place. Willi has not grown any younger, and the strain of running the business has taken its toll on his health. And finally, despite having created jobs for a number of people in his factory for many years, some of these beneficiaries of Willi’s initiative have been stealing materials and equipment from the factory for their own selfish benefit. This is extremely disheartening, and nobody can blame Willi for cutting his losses and hoping to retire to a life with less stress.

The business is available for purchase by any seriously interested entrepreneurs.

I am going to leave this blog site on the Internet for the interest on On-Sun owners and solar energy historians.

Best wishes

John. 12 October 2022

Greetings from John Ledger and Gauteng Solar Solutions!

Venter 12.05.09 007 LR LR

Introducing the On-Sun solar geyser – neat, functional, practical, freeze-resistant, made in South Africa by South Africans, using South African materials and skills. Strong and reliable in sun and snow for THIRTY TWO YEARS – since 1990.


“To give you feedback, so far we are delighted. Water piping hot, the element has never been switched on so far, everything hunky dory and although early days, I do not anticipate any problems.”

Mike and Sue,

“The solar system is working fine – yesterday it went up to 72 degrees. I’ve switched the geyser on for only an hour this week.”

“By the way, after the first month of installation, my electricity bill was reduced by 50%”

RC, Garsfontein, PRETORIA


Elephant Toy

 We know the On-Sun is freeze-resistant, and has been working in the icy regions of the Free State and Lesotho for 32 years, but now we can add another attribute to our proudly South African solar geyser – elephant-resistant! A problematic elephant bull in the Madikwe Game Reserve (near the Botswana border) attacked the On-Sun and flung it to the ground from its stand, causing extensive damage. The owner was convinced that he would have to buy a new On-Sun, but we persuaded him to bring it in and we sent it back to our factory, where it was named the ‘Elephant Toy’ by our amused workers. They straightened the bent pipes, fitted new fins and put the working parts into a new casing to make it as good as new again, at a fraction of the new cost. When we say the On-Sun is fully repairable, we mean it! The photo shows the On-Sun factory team with the innards of the unit before repainting the collector and putting everything inside the new casing

Contact me
Mobile 083-650-1768


We market and instal the South African designed, patented and manufactured On-Sun solar geyser in 150 and 300 litre models. Our standard model is the 150 litre system, which can be doubled up to 300 litres by connecting two matching 150 units in series.

Summary of current prices

Standard 150 litre is R14,750. Installation is R4,000 plus materials used. Average installed price is usually around R19,500 depending on the amount of plumbing material used. A 300 litre system involves two 150 units, but the installation charge would be R5,000 rather than R8,000. Prices are subject to change without notice. Contact me for latest prices.

Is this a fair price? We think so, but as a potential buyer, your money has been hard-earned, and you must look at whatever else is on the market and make your own decision. When comparing prices, ask whether a particular product has a proven track record in South Africa? Is it made in South Africa or in China? Can you get spare parts from your local plumbing store?

We recommend and can supply a remote temperature display that tells you how hot the water is in your On-Sun, and this in turn informs you about how to manage your hot water system for the best economy. This display unit can be mounted next to your electricity distribution board, or anywhere else in the house that is convenient for you. The price is R400, plus the cost of the twin ripcord used to connect the sensor in the SWH to the display unit..

We recommend and can supply a South African manufactured CBI electronic timer to control when your hot water system might require boosting to ensure you always have hot water. The timer works in conjunction with the thermostat in your electric geyser or solar geyser, and helps reduce your electricity consumption for water heating to the minimum. It has a battery backup so keeps time during outages.

Our On-Sun solar geyser has been built by South Africans for 32 years, since 1990, using local materials and components. It is a practical, strong, reliable, durable, fully repairable and, above all, proven solar geyser for South African conditions.

Our promise to our customers

The On-Sun is built in a small factory with excellent quality control. We have full confidence in our product and believe that our track record is your assurance of quality and durability. We also undertake to remove our system and pay you back in full if you are not happy with our product, within three months of the installation.

The On-Sun 150 SWH was successfully tested at the SABS for compliance for the Eskom rebate scheme, and passed with flying colours, but we never participated in that programme, and our prices have always been based on a fair, non-subsidized cost for a good, durable, locally made product. We will continue to do business on this basis.

The Eskom subsidy scheme has come to an end, and has not been replaced. Many solar suppliers went bankrupt as a result, and numerous installers have lost their jobs. The Eskom rebate scheme was supposed to stimulate demand for solar geysers, but in the end it only stimulated supply. The result is now rather sad history.

Thank you for visiting this site. Please browse the information below – I hope you will find it interesting. Please call or e-mail me if you have any queries. I enjoy talking about solar water heating to interested people!

Best wishes to all our clients and readers.


Updated 19 January 2022


The On-Sun DIRECT solar geyser was first designed and built in 1990, and has now been in service for 32 years! DIRECT means that no heat exchange fluid is involved in this system, making it simpler and more efficient.

I have been marketing and installing the On-Sun for nineteen years, and I am happy to offer you my experience and time to consult, discuss and conduct a free site visit to assess your solar water heating requirements, within reasonable distances around Gauteng. When you buy an On-Sun system from us, I will personally be on site with my team to install and commission it. When you buy our South African On-Sun solar water heating system, you own the system and you make the savings in electricity. Every year you save more as the cost of electricity goes up. With an expected lifespan of at least 35 years, and quite likely even longer, this is an excellent long-term investment. If necessary, old systems can be refurbished at a fraction of the new price. This involves returning the unit to the factory for professional attention.

We also offer a preventive maintenance service to our clients. After about five to seven years, there may be some small patches of rust on the casing, and the rubber sleeves over the pipe connections will have taken a beating from the sun. We can address these issues and make your On-Sun like new again at a very reasonable cost. Please look at our Facebook page to see an example of our maintenance programme: 

Most of our installations involve fitting the On-Sun 150 as a pre-heater in series with your existing electric geyser. Used correctly, this combination should reduce your geyser’s electricity consumption by between 60 – 80%. Such an installation will also increase your hot water storage capacity by 150 litres. Please read our item below about the rationale of installing the On-Sun as a pre-heater to your existing geyser.

There is no such thing as ‘FREE HOT WATER’! You either have to pay for the solar equipment to harvest the energy from the sun, or you have to pay for the fuel to heat your water, in different proportions, according to the technology you employ. Remember that in life, as in nature there are NO FREE LUNCHES!

You can buy a cheap electric geyser and then pay for expensive electricity during the lifetime of the geyser. Or you can buy a relatively expensive solar geyser and pay almost nothing for the solar energy it will employ to make hot water. But when there is no sun, you will always need some kind of back-up for warming your water. You can make warm water by using electricity, gas, wood, coal or solar. Solar provides an elegant solution, and once your equipment is paid for, the recurrent costs of the solar energy are free.

We always do a site visit before providing our clients with a written quotation, to make sure that we identify any problems beforehand and that our installation will go smoothly.


We promote, market and instal On-Sun South African Solar Geysers in Gauteng Province, the vibrant business and economic hub of South Africa. I am a professional energy practitioner, past Associate Professor of Energy Studies at the University of Johannesburg, and current Visiting Associate Professor at the University of the Witwatersrand. I have taught post-graduate courses in energy, notably the BSc Honours programme in Energy Studies at UJ and the Energy and Environment module for the MSc programme in Environmental Science at Wits.



We concentrate on only one product , the remarkable On-Sun solar water heating system, designed by Willi Suremann 32 years ago in 1990 and built by hand in his small factory in Ladybrand, in the Free State province of South Africa. We devote all our efforts to placing these ‘personal power stations’ on as many South African roofs as we can, to harvest the abundant energy of the African sun.

The On-Sun South African Solar Geyser embodies all Willi Suremann’s experience and skills acquired over a lifetime of working with renewable energy. Forty two years ago, in 1980, Willi established a business to instal photovoltaic systems and solar water heaters for farmers, schools, clinics, hospitals and mission stations in the Eastern Free State and Lesotho, where the high altitude, intense solar radiation and freezing winters resulted in a very high failure rate of the various water heating products that he bought from other suppliers. The only product that worked consistently well was the Van Leer direct system (no heat transfer fluid), manufactured with special machinery as a stainless steel ‘envelope’ that could withstand freezing by flexing to accommodate the increased volume of ice inside. There are still many Van Leer direct systems working in freezing conditions in South Africa.

Below is one that Willi installed in Ladybrand in 1980. In April 2007 he removed the system for refurbishing. Although the old fibreglass covers were almost completely opaque, the system was still working and making hot water. After cleaning the panels and fitting new toughened glass, the 27 year old system was as good as new again! And that was 15 years ago!

Van Leer panels before refurbishing                  

Van Leer panels 2 - 1980-2007 LoRes

Restored Van Leer system

Van Leer panels 3 - 1980-2007 LoRes

You will hear and read a lot of propaganda from people who only market indirect systems about why direct systems cannot be used in areas that experience frost. The Van Leer collector is a direct system, many of which are still functioning in South Africa after more than 40 years. It is often said that ‘direct systems’ must not be installed in areas that get frost in winter – most direct systems cannot, but the On-Sun is another direct system that has been exposed to frost, ice and snow for 32 years!

The Dutch Van Leer company decided to withdraw from South Africa because of the country’s apartheid policies. The machines used by Van Leer to make their unique collectors were bought by a competitor who changed the design, resulting in collectors that failed on a massive scale during a particularly cold winter in the mid 1980s that saw temperatures in Johannesburg drop to -7 degrees C. This resulted in a setback to the solar water heating industry that persisted for over 30 years. It is only fairly recently that ever-rising electricity costs and reliable solar geysers are creating the renaissance in harnessing the power of the sun once again.

Having lost his only supply of reliable, freeze resistant, Van Leer direct solar geysers, Willi then set about designing his own system that would work equally effectively in this very tough environment. His design challenge: how to build an efficient, durable, practical and aesthetically acceptable solar geyser that would operate at the extremes of very high solar radiation at high altitude, coupled with extremely high temperatures in summer, and freezing winter temperatures with ice and snow in winter? Add to that Willi’s philosophy that:

• the system had to be built by hand by unskilled but trained workers, to create jobs for poor people in an impoverished part of South Africa
• the factory must use hand-operated bending, pressing and cutting machinery to minimize the risk of injury to the workers
• the solar geyser could be installed by any DIY enthusiast or competent handyman, and be easily repaired using ordinary tools
• it would incorporate standard water pressure and electrical components available throughout South Africa and neighbouring countries from plumbing and hardware outlets
• the system had to be resistant to both hail and freezing and be simple to instal and maintain.
• the system would have a clean and neat appearance when installed on the roof
• the system would have a reliable working life span of at least 25 years

The result: The On-Sun South African Solar Geyser!

Today the On-Sun is the only freeze-tolerant, flat plate, direct system (no anti-freeze, pumps or valves) solar geyser made in South Africa!

What are the Advantages of the On-Sun system?

• Direct, freeze resistant On-Sun system is very efficient and reliable
• Fully compliant with all SABS tests required by Eskom during its solar water heater campaign
• On-Sun copper tank and piping has a virtually unlimited lifespan
• On-Sun has no pumps or valves to cause problems
• On-Sun will never boil – stagnation temperature is rarely above 80 degrees C
• No anti-freeze to worry about with On-Sun direct system
• No regular servicing required by On-Sun system – only fix when something fails – and that is very rare! Preventive maintenance only recommended to address small corrosion issues on galvanized steel tray every 5-7 years
• On-Sun is fully South African built with locally available components
• On-Sun provides South Africans with employment and skills
• No import duties payable on the On-Sun system, made in South Africa
• On-Sun solar geysers are easily repaired using local parts and skills
• On-Sun has a track record of 31 years of reliable service in Lesotho and the eastern Free State under extreme climatic conditions – a true test of quality!
• On-Sun is a unique product, unlike any other solar geyser on the market

Here is a system that was installed on the ablution block of the Sehlabathebe Farm Training Centre in Lesotho in April 1992, and that is still going strong 30 years later!

Sehlabathebe installation 1992 LoRes

Lesotho has one of the harshest climates in Africa. A solar geyser that can work in this climate has to be tough!

JK LEE 5 copy LRes

We design and make steel frames for fitting the On-Sun to any roof. Here is a system installed on the west-sloping roof of a house in Ladybrand.

The On-Sun 150 has complied with all four SABS Tests for the South African National Solar Water Heater Standards required by Eskom. SANS 1307 is the standard for exposure, rain penetration, hail resistance, freeze resistance, marking and the 250 000 pulsation test. SANS 6211 is the standard for thermal performance (Q factor) and heat loss. The Q factor for the On-Sun 150 is 16.412 Megajoules at 16 MJ. SANS 151 is the standard for fixed electric water storage heaters. SANS 60335-2-21 is the standard for the safety of household and similar electrical appliances. Part 2 covers the particular requirements for storage water heaters.

ON-SUN solar geyser fitted as a pre-heater to your existing electric geyser

If you have an existing electric geyser in good working condition, we recommend that you leave it in place, keep it insured under your household policy, and instal the On-Sun solar geyser in series, to supply the electric geyser with water heated by the sun. Not only will this save you significant amounts of electricity, it also increases the total capacity of your hot water system.

In such an installation the heating element of the On-Sun is not connected to the mains. This has the advantage that no new electrical work is required and therefore no new Certificate of Compliance needs to be issued by an electrician, which saves you money on the installation.

On its own, an electric geyser of 150 litres with the thermostat set to 55 degrees C (recommended temperature for household sanitary hot water storage) will use 6.1 kilowatt hours (kWh) to heat the water from say 20º (the incoming temperature) to 55º. By the way, a comfortably hot shower is around 42 degrees C.  Here is the calculation: 150 litres x 35º = 5 250 kcal / 860 = 6.1 kWh

In winter the incoming water might only be at a cold 10ºC, in which case the geyser will use 7.8 kWh to reach 55ºC. That’s a lot of energy!  Here is the calculation: 150 litres x 45º = 6 750 kcal / 860 = 7.8 kWh

But if the incoming water is at a warm 40ºC, the geyser will use only 2.6 kWh to warm it to 55º C.  Here is  the calculation: 150 litres x 15º = 2 250 kcal / 860 = 2.6 kWh

THESE CALCULATIONS DO NOT ACCOUNT FOR THE STANDING LOSSES OF THE ELECTRIC GEYSER, WHICH MAY BE AROUND 2.6 kWh/24 hours, depending where you live, and how well the geyser is insulated..

So you can see that any warming of the water supplying your electric geyser always reduces the use of electricity. The warmer the incoming water, the less electricity required to raise the temperature to 55ºC

Once the incoming water is at 55º C or higher, the thermostat will not switch on at all.

This is how the On-Sun installed as a pre-heater works. On a warm, sunny day hardly any electricity will be consumed by the geyser because the On-Sun will feed it with water above 60ºC.

We always insulate the piping carrying hot water from the solar water heater to the electric geyser with foam rubber sleeves. We recommend that your electric geyser should be fitted with a suitable insulating blanket, and that the hot outlet pipe of the geyser be fitted with a one  metre insulating sleeve to reduce thermal loss. The TPS (temperature and pressure safety) valve should also be insulated. The radiative heat losses from exposed piping is significant, particularly in winter months in the interior of South Africa. If your electric geyser does not already have insulation fitted, we will do this for you at no charge at the time of installation.


We can offer you advice about the supply and installation of a suitable timer to control your geyser automatically. This way you can ‘fine tune’ your hot water system to ensure that the geyser only switches on for a limited time each day to ‘boost’ your hot water in case it has been overcast and there has been insufficient solar energy to get your solar system above 55 degrees. We recommend the South African CBI electronic timer with inbuilt battery backup, which will ensure that your timer keeps time during municipal or Eskom power failures.


OnSun 011 Cr LR

The On-Sun has a very clean and neat appearance, as all the water controls are contained within the tank cover. The standard tank cover is galvanised steel, which can be painted to match the roof if required. Tank covers can be painted to match the roof colour by the owner, and are also available in stucco aluminium or stainless steel by special arrangement and extra charge. This is a standard 150 litre model, fitted flat on a north-facing pitched roof.

March 06 009 LRes

This On-Sun 150 litre unit is mounted on a steel frame on a flat roof, to achieve the correct orientation (true north) and tilt (35 degrees from horizontal at a latitude of 25 degrees South).  We can make up computer-designed frames for any roof pitch or orientation.The unit can also be mounted on the ground if required, as below.

Copy of Vision energy Sol 001

On-Sun mounted on the ground in 300 litre configuration

Here we use a matched pair of standard 150 litre units that are closely connected in series. A cover over the connections makes for a very neat appearance, with no piping visible.

I have been marketing and installing the On-Sun South African Patent Solar geyser in Gauteng, South Africa, for 19 years now, and I have learnt to appreciate the very special qualities of this unique product. By the way, I also own four On-Sun 150 units that are in daily use at home and office, so I am a practicing On-Sun user who walks the talk every day! We have installed On-Sun systems in Greylingstad and Nelspruit in Mpumalanga, Ventersdorp, Klerksdorp and Lichtenburg in North West, Pretoria in the north, and Meyerton in the south of Gauteng. We prefer to work in Gauteng, but remember that the On-Sun is easily installed by any plumber or handyman, so you can always pick up a unit from us and DO IT YOURSELF!


Kirsh 009LoRes

When a satisfied client orders a second On-Sun because the performance of the first is so good, we really feel proud of our product! Mrs Kirsch installed an On-Sun 150 litre system for her kitchen, scullery and outbuilding. It worked so well that she ordered a second one for her bathroom. We installed an On-Sun 150 202 split system close to the first. This house is now harvesting a significant amount of thermal energy from the sun, and cutting electricity costs!

Merand C 028 LRes
Merand B copy 014 LRes

We installed three systems for a client in Houghton, Johannesburg. One standard 150 litre On-Sun was mounted on a frame on a horizontal concrete roof (left) as a stand-alone supply with electric backup to a flat (we removed the existing geyser). A 150 litre 202 split system (right)  was installed on the main house as a pre-feed to the electric geyser.

A 100 litre system was fitted onto the roof of a patio next to the swimming pool, to supply hot water to an outdoor shower and a hand basin. The tank covers of the latter two systems were painted by the client’s handyman to match the terracotta colour of the tiled roofs. He did a really great job!

Godsell 019 LR

14 Roxburghe Road, Craighall Park, Johannesburg

Godsell 062 LR

Two On-Sun 150 units were installed, one on the main house and the other on the outbuilding. The main house system was mounted flat onto the slate roof, while the system for the outbuilding was mounted on a steel frame to get the best inclination for year-round performance.

SSA40792 CR LR LRes

Denton Place, Mondeor. Johannesburg

On-Sun 150 system installed on a steel frame on a back-sloping IBR roof with loose tiles on top.

Chamfuti Street 007 LRes

17 Chamfuti Street, Sharonlea, Ransburg

This On-Sun 150 has been painted to match the green tiled roof of the house. Water-based primer and roof paint from Prominent Paints was applied, after the tank cover and tray were thoroughly cleaned with galvanized steel cleaner and the fibreglass end-caps sanded with water paper. The paint is guaranteed for seven years and the On-Sun can be touched up whenever the roof is repainted. The green solar water heater blends well with the roof, the awnings and the greenery of the garden. Because all the water controls, including the vacuum breakers, are housed inside the tank cover, we do not have unsightly pipes projecting above the system.

The On-Sun is the only flat-plate, freeze-resistant, direct solar geyser, without special pumps or valves, on the South African market. The SABS test for freeze tolerance requires the system to be cooled to minus 20 degrees C and held there for 14 hours. With its 32 year pedigree in the snow and ice of Lesotho, the On-Sun had no problem with that particular challenge!

Remember, if you are not satisfied with your On-Sun solar geyser, let us know within three months and we will remove the system, make good any structural impacts made by the installation, and refund your money in full. No arguments, no lawyers, no harsh words. That is just the way we want to do business with you!

With best wishes to all our readers and customers for 2022!
19 January 2022

Copy of On-Sun sticker 001


(in alphabetical order of location)

Bethlehem – Crezco Steel & Hardware Traders – 058-303-4035

Bloemfontein – Radio SOS cc – Pieter & Christa Lategan – 051-436-2084

Gauteng – Gauteng Solar Solutions – Dr John Ledger – 083-650-1768

Ladybrand – Free State Utilities – Fanie Terblanche – 082-568-5387

Lesotho –  Thabang Tjabane +266 58 777 138

Welkom – SolarSafe, Welkom – Bernard Olivier 083 385 2650.

The On-Sun factory is in Ladybrand, Free State. If you have any questions for the most experienced solar water heating expert in Southern Africa, you can call Willi Suremann at 051-924-3038. He designed and patented the On-Sun 32 years ago, and thousands of these wonderful solar geysers are operating effectively and reliably through sun and snow all around Southern Africa. This is a very special product in this age of plastic and mass production, built by hand with craftsmanship and care, using copper, one of the most useful and durable metals known to humankind.