Frequently Asked Questions
How does evacuated tube technology work?
Evacuated Tube Technology works on the same principle as a thermo flask. The tube is designed to capture as much sunlight as possible but then to maintain the stored heat and not conduct it away to the surrounding air. It consists of two layers of borosilicate glass with a vacuum layer between them. Sunlight is transmitted through the vacuum and its energy is transferred to the heat pipe inside. A small amount of evaporative fluid in each tube transfers this heat to the manifold above. This in turn heats the geyser water which is being circulated through the manifold. The efficiency means that more than 90% of the sun’s energy which hits the collector is transferred to the water.
How do evacuated tubes compare to flat plate collectors?
With regards to efficiency:
- On a very hot, clear day there is very little difference in performance between conventional flat plate panels and evacuated tubes. However, on cooler days, evacuated tubes have a clear advantage. The reasons for this are:
- The vacuum greatly reduces the conductive and convective heat losses. As a result wind and cold temperatures have less effect on the efficiency of the evacuated tube.
- Due to the cylindrical shape of the tubes, they passively “track” the sun during the day by presenting themselves perpendicular to the sun throughout the day. Flat plate collectors generally only experience perpendicular exposure around midday.
- Averaged over a whole year output of an evacuated tube collector is between 20 to 30% greater than that of a flat plate collector
Other advantages of evacuated tube collectors:
- Due to their modular nature, they are easier to install.
- They are less susceptible to being blown off your roof in high winds.
- They can be serviced without shutting down the system.
- If a tube breaks the whole panel is not lost. A broken tube is easily rep
How long have evacuated tubes been around?
Evacuated tube technology has been used in Europe, USA and China for over 15 years. Evacuated tubes are relatively new to South Africa for the simple reason that in the past our electricity has just been too cheap. This resulted in very limited incentive to bring advanced technology to the country.
Why is it advisable to have a controller?
First generation solar systems didn’t have the technology to allow a user to monitor just how the system was performing. There was no control of the time of day at which the electrical backup heating would operate or to what max temperatures a geyser would get to. Due to technological advances, second generation solar systems now provide a user with full control and monitoring of the system's performance. A controller performs the following functions:
- Full monitoring of system performance
- Timer control of the time of day at which the electrical backup operates
- Limits maximum geyser temperatures on high-gain solar days (to prevent scalding!)
- Limits minimum geyser temperatures on low-gain solar days (switches on electrical back-up)
- In frost areas the controller will prevent the collector from freezing by maintaining its temperature above 5 degrees
Will my system heat water during a power outage?
No. Split systems (geyser in roof) almost always have to be pumped systems due to the fact that the geyser is below the height of the panels. The pump and controller need a small amount of electrical power to operate. Some systems employ solar driven pumps to circulate the water through the collector. We have experimented considerably with this option but have found that solar driven pumps are weak, sensitive to impurities in the water and have trouble bleeding air out of the circulation system.
Solar pumps have to be driven by an additional photovoltaic panel which is a lot more sensitive to cloud shadows which stop the pump from being powered. This leads to an inefficient system as the tubes are still being heated by the sun on even moderately cloudy days – but due to the pump not working, the hot water is not circulated to the geyser.
Doesn’t an electric pump negate going solar?
No. Solar water heating should not be seen as a solution to South Africa’s electricity supply problem. Solar water heating is a long-term investment in the future of our planet since it uses a renewable energy source (the sun) to heat water (in place of environmentally unfriendly sources such as: coal / nuclear energy). Added benefits are the resultant decrease in electricity consumption and long-term cost savings. The pump uses less than 45W when in operation and is maintenance free and extremely efficient. By monitoring the temperature difference between the collector and the geyser, the controller only operates the pump when it is beneficial to the system.
Does Evacuated tubes get too hot in South Africa?
Here, once again, the SunScan collector is superior. Our collectors have a stagnation temperature of less than 203 degrees which is equivalent to that of quality flat plate panels. Other evacuated tube collectors have stagnation temperatures in excess of 250 degrees (some up to 280 deg!). This creates problems for any components in the system which are not designed for these high temperatures
Why should water be less than 55 degrees?
Water hotter than 55 deg can result in serious scalding. This is particularly problematic for children and the elderly. In the UK and Australia a tempering valve is a legal requirement on any geyser installation.
How long does an installation take?
A team comprising a plumber and an assistant can carry out most installations in a day