Solar Photovoltaic Electricity Generation for Dairy Farms

Gelli Aur Solar PV A5_13605 Practical sheep breeding 16/07/2012 09:02 Page 6
Electrical installation issues
PV panels produce direct current (DC) so they use inverters to convert the output to
mains voltage - alternating current (AC). The inverter is connected in parallel with
the mains supply and energy generated either
displaces that which would normally be
CASE STUDY
purchased, or is exported when on-site
generation is greater than site demand. A
‘protection’ system is required to prevent the
system back-feeding into the grid should the
grid fail.
The electricity supply should be at least 1.5
times larger than the maximum PV array output
i.e. 15 kilovolt-ampere (kVa) for a 10 kilowattpeak
(kWp) system. For systems over 15kWp
the electricity supply will probably need to be
three-phase. If you have to upgrade the supply,
the distribution network operator will charge
you for the upgrade and this can be expensive.
Energy generation
PV cannot be regarded as a means to energy
self-sufficiency as it only operates during
daylight hours and its output is dependent on
the elevation of the sun and cloud cover.
Roughly speaking a typical photovoltaic system
will produce an average of about 9% of its
theoretical maximum output in the UK. There is
a published Standard Assessment Procedure
(SAP) which will estimate the likely output of a
system depending on its rating, latitude and
Mr and Mrs Price from Brecon installed a
solar PV system on the roof of one of their
farm buildings in March 2012.
Mr Price said: “We knew that we wanted to
install some form of renewable technology
and solar PV fitted our needs. A local
company did the installation and they were
very professional. To date we have
generated almost 1,700kWh of electricity
which has reduced our electricity bill by
around £105. We are very pleased with the
system and are happy with the investment
that we have made.”
Income plus savings for the period March –
July 2012 generated through FITs:
Generation tariff = £736
Export tariff = £26
Electricity bill savings = £105
Total income & savings to date = £867
orientation. Please visit the following webpage address for further information:
http://www.decc.gov.uk/en/content/cms/emissions/sap/sap.aspx
Output from panels will fall over time, at a rate of approximately 0.8% a year or 20%
over their 25 year lifespan.
6 Solar PV electricity generation for dairy farms