What the Government's new Calculation Means for Solar
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Credit: Viridian Solar |
Ahead
of the announcement of the new Building Regulations later this summer, BRE has
published the accompanying energy calculation, the Standard Assessment
Procedure, or SAP.
If
you think this document is only relevant to the new build sector, you would be
wrong. SAP is also the basis for Energy Performance Certificates (EPCs), and
therefore is also highly influential in the refurbishment of existing homes,
for example under the Green Deal. SAP Appendix H is also used by the
Microgeneration Certification Scheme (MCS) for installers of solar heating to
provide customers with an estimate of their likely energy savings. Finally,
whichever of the proposed routes to calculate payments under the forthcoming
incentive scheme for renewable heat, the domestic RHI, is chosen, SAP lies
behind it somewhere.
This
document is not for the faint-hearted, comprising a thick booklet of dense
calculations and notes. Fortunately the solarblogger has done the heavy
lifting, so you don't have to...
A
detailed assessment has been published 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&T)
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 feeds directly into the solar pv estimate, but results in a smaller +/- 5% change across the country for solar heating.
► Updated fuel carbon emissions factors (PV&T)
Carbon
savings from solar electricity reduce by 2%, carbon emissions avoided by solar thermal
replacing natural gas increase by 9%
► Addition of hot water use factor (T)
There is a 29% increase in hot water used from the hot water cylinder in the solar thermal calculation if no electric showers are present, and a 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
► Reduction in solar pump electricity consumption (T)
The 75kWh
flat rate for the solar pump electricity consumption is reduced to 50kWh for mains powered solar pumps, based on evidence
from EST solar thermal field trials submitted by EST and Solar Trade
Association
► Addition of second order coefficient for thermal panel efficiency (T)
Creates
a level playing field (for more information see my paper on this issue here)
So What Does it all Mean?
Photovoltaics
For
solar PV, the main impact will be on new build housing. Here the
changes are relatively neutral, being a 2% drop in carbon savings on average
due to the lower emissions factor for solar electricity. Of course, compared to
the previous version of SAP, which used a single figure for irradiation for the
entire country, some areas have increased significantly while others have
fallen. (See map, below)
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Credit: Viridian Solar |
For
retrofit PV the recent MCS PV installation Guide has already implemented a new
energy calculation based on a different set of irradiation
data. This produces slightly higher energy outputs than SAP
2012. The discrepancy could be explained by the different uses of
each calculation, with the MCS method taken to predict year one energy (with
solar panel performance degradation taken into account later for any financial
forecasts). By contrast, SAP is more aimed at producing a whole life
average estimate.
Solar Thermal
For
solar heating, the calculation impacts both new build and retrofit, and in a
really positive way. (See map, top of post)
In
new build, carbon savings will increase significantly for almost all homes with solar heating. The new adjustment factor for electric showers
rightly produces a disincentive to install these alongside solar
heating. I reckon that overall the boost to solar heating carbon
savings from all the changes is worth between 17% and 31% depending on where
the house is.
In retrofit situations, the MCS installer will perform an energy calculation for the customer using SAP Appendix H. The new version of SAP will an average of a 20% boost to the
solar energy estimate, again differing depending on the location of the installation.
Further changes are
coming down to road to improve things even more in MCS, more on this soon....