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The wide range of low and zero carbon solar water heating technologies
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The planners want 10% of my new building’s energy to come from “onsite renewable sources”. Is this achievable? Usually, yes and usually easily. How to establish a 10% renewables capability goes like this... First identify your renewable energy resources. Ask precisely what renewable energies, such as solar and wind, are available on site. Then list the technologies (such as turbines) which could realistically harvest some of this energy. Next, ask how much energy is available. Then choose your renewable energy technology or technologies, if you are going for a mix. Now you need to “size” each technology appropriately. Then you need your costings. On the basis of a “lifetime costing” (usually mainly installation costs plus say 20 years running costs) you can then examine the costs-benefits - usually net money in, compared to net energy out. In more detail, your first step is to list the renewable energy resources available in quantity. For example for a new-build government office building in a city, these might be wind and solar. If it were in the country, there might be other available energies such as geothermal (hot rocks) or hydro available from a stream nearby. Now you have your list of energy resources. Step two, identify the collection technologies for each energy resource. For example, within the wind technologies there may be a choice between one large turbine or several smaller ones, with differing planning or cost implications for each. Within the solar technologies, options include electricity or hot water. Since, besides being lower cost, solar hot water systems are often 4 times more efficient per square metre than solar electric systems, solar hot water tends to be a worthwhile technology to examine. Please also do a “seasonality analysis”, by asking, for example: does the wind, sun (or whatever resource) actually arrive when the building is occupied, and when there is a demand for its energy? You may also need to examine backup fuel options, such as gas, electricity or wood chips. Step three is system sizing. Work backwards from the building’s estimated total annual energy demand. Say you are considering solar hot water as an option. Say the designers of the project estimate that the building will use 400,000 kilowatt-hours of energy a year. 10% of this is 40,000 kWh. But how much energy can one Solartwin panel deliver? This depends on a range of factors but is typically in the range of 600-1200 kWh per year. If we estimate its delivery as being 800 kWh per year, then by calculation, 50 solar panels would be required. Reality checks: What would an installation of 50 panels cost? Typically £150k (i.e. £3k per panel) +/- 20% depending on issues such as how the panels are attached to the roof, scaffolding costs and the type of plumbing required to pipe and to store the hot water once you have collected it. How much roof or wall area would this require compared to how much have you got? To allow for unused edges of roof, ready-reckon on 5 sqm of roof per panel provided the roof is pitched and in the range of E, S or W facing. Or you may use S (+/- 30 degrees) facing walls. Say you have 500 sqm of available roof. This could hold 100 panels, so with 50 planned, you fit the comfort zone. Now pass all your figures / assumptions to your financial / technical bean-counters for cross-checking! They will usually confirm that 10% onsite generation of energy is easily achievable, and that solar hot water wins on costs-benefits. |
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