Know Your Solar

Solar radiation, the earth’s most abundant energy supply, comes free from the sun every day. There are many ways to make use of this energy: for example, we already use it to illuminate our buildings, grow our plants and even obtain a suntan. But solar radiation can also be used to provide both hot water and electricity to supplement more traditional energy sources.
 

The equipment designed to collect solar radiation is fixed on to the outside of our buildings, either flat (horizontal) or more often pitched up to best face towards the sun. The two main forms of collectors found on roofs are for water heating (solar thermal) and photovoltaic (solar electricity). It sounds simple; but when you try to fit all the many different components together into a working system, and then to predict the value of that system, things get rather more complicated. Cowboy installers are a major problem in the industry. A recent Which? probe found that 10 out of 14 solar water heating installers exaggerated potential savings, used questionable sales tactics and hugely over-stated the potential benefits of installing a system.

 
According to the Which? report, none of the 14 companies tested managed to identify all important technical challenges before providing a quote. Key checks they missed included inspecting the roof from the ground as well as the existing gas boiler, the cold water tank in the loft, and the hot water cylinder; and checking the water quality and whether the washing machine and dishwasher could use solar-heated water. Five companies even gave a quote over the phone without bothering to visit the property and only one company was given a favourable report. So the most important first step anyone interested in solar can take is to make sure they’re getting accurate, reliable information on how the technology actually works.

• Gather information. Before talking to installers, you need to gather reputable information about what you’ll need to look out for. The Which? guide found that many of the companies were delivering false information using hard-sell techniques, which could confuse and pressure customers into making possible wrong decisions. Earthscan have produced a series of well-regarded books which help plan, design and install renewable energy systems including solar domestic water heating and solar photovoltaic.

• Find an installer. Customers need to find a reputable, accredited installer, preferably via referral from someone else. A considerate installer will take care to prepare a quote using the steps outlined in the books, using simulation software to deliver accurate information where required.

• Size and position. A good installer will thoroughly check sizing and positioning before preparing a quote. Inconsiderate installers reduce accuracy and safety by attempting to design a system without visiting buildings where they already exist. There is no substitute for an internal on-site visit to reassure the customer they have received a thorough inspection.

Shading has a particularly strong effect on solar collectors, with even small shadows causing significant losses on photovoltaic modules. Shading can occur from other roof objects or nearby buildings, trees or hills. These are particularly prominent when the sun is low in the sky, such as morning and evening or during winter. In order to correctly position solar collectors, consideration must be given to the daily sun-path between sunrise and sunset. This sun-path also alters seasonally according to the latitude of the location. There are also local climatic conditions to consider, where perhaps morning mists or afternoon thunderstorms occur. Professional solar engineers now use computer simulation software, such as T*SOL for solar thermal or PV*SOL for solar photovoltaic, to work out the best use of this technology.
 
These programs allow their users to calculate accurately what returns on their investment customers can expect. Customers can then be given information such as CO₂ emissions avoided, expected savings on traditional heating costs, and the number of years before all money spent will be made back.
 
The accuracy of any simulation model depends on the accuracy of the data entered into the program. To increase confidence in simulation results, any engineer should be prepared to reveal their assumptions for scrutiny to allow double-checking. The key is to gather as much reliable information as possible from a trustworthy source, to allow customers to make an informed decision.