Guest Blog: About the Author Stuart Elmes is CEO of Viridian Solar, a UK based manufacturer of both solar heating and solar photovoltaic panels. He also writes online as the solarblogger.
Stuart has published a more detailed assessment of how the new calculation impacts solar heating and solar photovoltaic (pv) energy as a briefing document available from the Viridian Solar website, but here's a quick round up of the headlines:
New postcode-based irradiation data (PV&Thermal)
The UK average irradiation remains the same, but the value varies depending on location with northern Scotland around 10% below the average and southern England around 10% above. This change directly impacts the solar pv energy with variations of similar scale, but results in a smaller +/- 5% change across the country for solar heating. (See maps)
Updated fuel carbon emissions factors (PV&Thermal)
Carbon savings from solar electricity reduce by 2%, carbon emissions avoided by solar thermal replacing natural gas increase by 9%. In previous versions of SAP, electricity generated on site qualified for a higher carbon emissions rate than electricity used on site. In SAP 2012 all electricity used or generated has the same emissions factor.
Addition of hot water use factor (Thermal only)
If no electric showers are present in the home, there is a 29% increase in the hot water volume taken from the hot water cylinder in the solar thermal calculation, and a corresponding reduction of 36% if only electric showers are present. This produces a 20% increase in solar heating energy in SAP Appendix H compared to the previous version for homes without electric showers. Since it’s never a good idea to combine solar heating with electric showers (which use a cold feed), this change should encourage good design and boost solar heating energy.
Reduction in solar pump electricity consumption (Thermal only)
Solar heating systems use an electric pump to circulate fluid through the solar panels, and this consumes electricity. SAP takes this into account with a flat rate penalty in electricity used. In SAP 2012, the 75kWh flat rate for the solar pump electricity consumption has been reduced to 50kWh.
So What Does it Mean for Housing Design?
Taken together, the changes result in a modest change in the carbon benefits from solar pv (around 2% drop on average), and a very strong rise in the carbon benefits from solar heating (around 25% increase on average).
Energy Assessors will need to select solar technologies with the location of the house in mind, and are likely to be taking a fresh look at solar heating for driving carbon reduction in homes.