Rising sun – focussing on solar thermal energy
Keith Wilkinson, General Manager, Sundwel Solar Ltd outlines the potential for solar powerOnly a decade or so ago, new house buyers would have been unlikely to demand, or even expect, high-quality insulation and double glazing. Years of rising fuel prices and a growing understanding of ecology and the need to save energy have changed all that. What were once “extras” have become standard on most new properties.
The overall solar energy falling on the Earth’s surface is 10,000 times greater than the world’s current energy requirements. It’s a fact already recognised by our European neighbours. At present Britain lags seriously behind other countries in embracing solar energy; not just the hotter, Southern European countries but Germany, Sweden and Holland, which have climates very similar to our own. This automatically debunks the myths that “solar panels don’t work in Britain”, or “only work when it’s hot and sunny”.
Types of system
The most successful solar system for use in the UK is solar thermal – which uses the sun’s rays to heat water. These can provide up to 70 per cent of a household’s annual domestic hot water requirements, and have a service life of more than 20 years. A high quality solar water heating collector can produce five times more energy than the equivalent area of electrical solar panel (photo voltaic).
So what should the architect or building engineer be taking into consideration?
One square metre of high-quality solar panel will provide approximately 50 litres of water per day heated to 50 degrees centigrade. A “rule of thumb” is to design a system with at least one square metre of solar collector per person in the household. On this basis, a typical energy saving for a standard domestic property with two adults and two children would be 1,500 kWh and just as importantly, more than half a ton of CO2 (carbon dioxide).
When it comes to building design, some early thought to solar energy can pay huge dividends later on. Inevitably, collectors work better the more light they get so a south-facing roof is ideal although alternatives, such as A-frames, and split systems are available. The collectors are designed in specific sizes to work at their most efficient; one recent request from an architect for a triangular panel had to be declined! High-quality panels are aesthetically-pleasing too.
As with most building services, solar collectors are easier and cheaper to install when a building is under construction, when scaffolding is in place and alternative systems don’t have to be removed. The ability to use on-site plumbers and roofers reduces the cost of installation significantly.
Solar thermal heating is at its most efficient when water is being heated from low temperatures. Therefore it’s extremely efficient in public or large buildings where water is being constantly used, and cooler water pulled into the storage cylinders. Two good examples of this kind of system have been installed for Hannover Homes and The Guinness Trust. Both organisations have used Atlas® solar collectors and both are situated in the North East – not an area renowned for its sunshine!
Hannover Homes has installed 39m ² (square metres) of panels to pre-heat the water for three, 45-bedroom extra-care homes. Because residents are drawing water all the time, this is a very efficient use of the system. The extent of pre-heating achieved at any given time depends on usage, and on the weather.
Similarly The Guinness Trust has installed a 29m² system at its development in Blyth, Northumberland. That should meet a major proportion of the residents’ hot water requirements.
What to look for
If a solar collecting panel is to work at peak efficiency over many years, then the materials used in its construction are extremely important.
Systems should have a control regulator that turns on a pump when the temperature on the collectors is sufficiently higher than that in the cylinder; in other words, when there’s a heat benefit. Pumps should be mains voltage, since solar pumps are likely to run haphazardly and will often fail to take full benefit of the UK’s cloudy weather.
The materials used in the collector manufacture should be of high quality; typically a selectively coated copper plate to absorb the heat, which is continuously attached to the tubes carrying the fluid. The insulation material should be high-quality foam, and very importantly the cover should be of toughened glass.
The future of solar energy
Designing and constructing environmentally-efficient buildings is no longer a question of choice. Not only will energy efficiency become a requirement of purchasers, as double glazing has, but the Government is increasingly putting in place strategies to drive the industry in this direction.
It’s a clear decision to make, and for the building engineers and architects who embrace this free, renewable source of energy, the future looks very sunny indeed.
By Keith Wilkinson, General Manager, Sundwel Solar Ltd
Standard Assessment Procedure (SAP) Ratings for new dwellings.