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Design

Simulation software sheds light for clients


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 multifarious 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 overstated the potential benefits of installing a system. Thanks to this report, customers are beginning to actively seek out installers who will provide accurate advice and a comprehensive evaluation of their property and load profile.


But how can installers gather accurate, reliable information on what customers will be able to exsystem pect from their system? 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 are
simple-to-use, allowing details to be entered about the site and customer requirements. Components and climate files can then be chosen from extensive databases. The program will then calculate the different returns the systems will be able to provide.


Precise information
This allows installers to quickly create professional client reports with precise graphics and data, providing customers with 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.


Good quality programs allow for comparison between different brands of equipment and system configurations in order to ensure that the best system is being designed for each customer. Separate simulation programs are used for solar water heating and photovoltaics because they are two fundamentally different technologies.


For example, the conversion efficiency of solar radiation to thermal energy occurs at a much higher rate than conversion to electricity. Also, heat is usually stored in water, whereas electricity is either sold straight to the utility grid or stored in batteries. It is vital to account for the effect of changing loads on domestic hot water heating, such as during holidays, or the existence of feed-in tariffs for electricity and heat. Professional simulation software can visualise each of these situations and present a clear interpretation to clients, including financial analysis. Shading has a strong effect on solar collectors, with even small shadows causing significant losses on photovoltaic modules.


An on-site hand-held tool, such as a solar site selector, is used to anticipate shading as an ideal accompaniment to computer simulations. These allow for realtimeanalysis of any site using a template and viewfi nder, the results of which can then be recorded digitally.The accuracy of any simulation model depends on the accuracy of the data entered. To increase confidence in simulation results, any engineer should be prepared to reveal all their assumptions for scrutiny to allow for double-checking.


Chris Laughton’s latest book, Solar Domestic Water Heating: The Earthscan Expert Handbook for Planning, Design and Installation, was published by Earthscan last
month. See page 44 to win a copy.

Chris Laughton is managing director of The Solar Design Company