Solar Photovoltaic Electricity Generation for Dairy Farms

Gelli Aur Solar PV A5_13605 Practical sheep breeding 16/07/2012 09:02 Page 1
Improving the Welsh Dairy Supply Chain
Solar Photovoltaic Electricity
Generation for Dairy Farms
www.ddc-wales.co.uk

Gelli Aur Solar PV A5_13605 Practical sheep breeding 16/07/2012 09:02 Page 2
Dairy Development Centre
Gelli Aur
Carmarthen
Carmarthenshire
SA32 8NJ
Telephone: 01554 748570
E-mail: ddc@colegsirgar.ac.uk
www.ddc-wales.co.uk
July 2012
The Dairy Development Centre (DDC) acknowledges the contribution made by
Farm Energy to the technical content of this booklet.
This project has received funding through the Rural Development Plan for Wales 2007-2013 which
is funded by the Welsh Government and the European Agricultural Fund for Rural Development.
No part of this publication may be reproduced or transmitted in any form by any means without the prior
written consent of the Dairy Development Centre.
Whilst all reasonable care has been taken in its preparation, no warranty is given as to its accuracy, no liability
accepted for any loss or damage caused by reliance upon any statement in or omission from this publication.

Gelli Aur Solar PV A5_13605 Practical sheep breeding 16/07/2012 09:02 Page 3
Contents
What is the Feed-in Tariff scheme? 4
Panel positioning 5
Electrical installation issues 6
Energy generation 6
Other costs 7
Financial considerations 7
Application to dairy farming 8
Solar PV electricity generation for dairy farms 3

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Generation of electricity from renewable sources has become more financially
attractive since the introduction of generation subsidies called ‘Feed-in-tariffs’
(FiTs).
Photovoltaic (PV) panels are an attractive technology for farmers with buildings or
areas of land suited to the installation of arrays. Installation is straightforward and
they are, for the most part, a ‘fit and forget’ solution to renewable energy generation.
What is the Feed-in Tariff Scheme?
A FiT is paid for each kilowatt-hour (kWh) of renewable electricity generated from
an eligible renewable scheme. Rates are technology and size specific. Since the
scheme started in 2011 the rates have been reviewed several times and further
changes are expected in the future. The FiT rate is fixed at the time of project
registration, index linked and are currently paid over a 25 year term, although this is
likely to be reduced to 20 years in August 2012 to bring it in line with other
renewable technologies.
4 Solar PV electricity generation for dairy farms

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Panel positioning
PV panels can be installed on a building roof - ideally south east to south west
facing, with a 20 to 50 degree tilt. Ground-mounted systems are also available,
which can be ideally placed and orientated. An area of approximately 8 m 2 per kW of
peak capacity is required. So for example a 50 kW system would require 400 m 2 to
accommodate between 180 and 250 PV panels on a roof. Panel weight is
approximately 15 kg/m 2 . Any building older than 10 years may be rejected by an
installer as not being robust enough to bear this load.
The map represents the
yearly sum of irradiation on
horizontal and optimally
angled panels, over a 10
year average [kWh/m 2 ]. The
same colour legend also
represents potential solar
electricity [kWh/kWp]
generated by a 1kWp
system per year with
photovoltaic panels mounted
at an optimum angle and
assuming system
performance of 75%.
For a system to be
successful there must be no
overshadowing, for example
from trees or other
buildings.
PVGIS European Communities, 2001-2008
Solar PV electricity generation for dairy farms 5

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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

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Other costs
Operation and maintenance costs are usually estimated at between 1% and 2% of the
total installation cost per year. Although PV panels can last 25 years, the lifetime of
the inverters (converts Direct Current to Alternating Current and are vital components
of any PV system) will be shorter, possibly only 10 years.
Financial considerations
You should consider the energy related income that comes from the generation tariff
(FiT); the excess energy that is exported to the national grid (export tariff) and the
energy savings from not having to purchase as much energy from your dedicated
energy supplier.
The basic economics of a 49kW system installed in April 2012 are as follows:
Installation costs £73,500
Likely costs (2012) are £1,500
per kW installed
Average energy generated per year
38,631kWh
9% of theoretical maximum
generation (average for the UK)
Average annual income from FiT £8,460 Generated kWh at 21.9p/kWh
Average annual income from power
sold
£898
Assumed 75% export at
3.1p/kWh
Offset electricity value £1,060
Average maintenance cost £1,600
Annual value to the farm £8,818
Assumed 25% own use at
11p/kWh
Cleaning, repair and system
checks
(FIT income) + (export) + (offset)
- (maintenance)
Payback 8.3 years (Install cost)/(annual value)
Solar PV electricity generation for dairy farms 7

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Application to dairy farming
Even at peak annual generation times, normal dairy farm energy use doesn’t suit solar
energy production. On a typical dairy farm energy demand will be at its peak during
morning and evening milking, where as solar energy production is at its peak around
the middle of the day. Nevertheless, returns on investment can still be acceptable.
It is possible to alter the operation of equipment such as water heaters and ice
builders to make the best use of the PV generated electricity. By doing this the return
on investment will be quicker as electricity used on farm from the PV is worth more
than selling any unused energy back to the electricity supplier.
Application of solar PV on dairy farms
- normal energy use
Electrical energy (KWh)
00:00
01:00
02:00
1st milking
Milk collection
2nd milking
03:00
04:00
05:00
06:00
07:00
08:00
09:00
10:00
11:00
Un-used
solar energy
13:00
14:00
15:00
12:00
Time
16:00
17:00
18:00
19:00
20:00
21:00
normal energy use
solar PV generation
22:00
23:00
20:00
Application of solar PV on dairy farms
- revised energy use utilising solar PV
Electrical energy (KWh)
00:00
01:00
02:00
1st milking
Un-used
solar energy
Milk collection
2nd milking
03:00
04:00
05:00
06:00
07:00
08:00
09:00
10:00
11:00
In order to maintain the best performance from the PV array, it is likely to need
cleaning on a regular basis especially in the summer when dust can be an issue.
Reference
Šúri M., Huld T.A., Dunlop E.D. Ossenbrink H.A., 2007. Potential of solar electricity generation
in the European Union member states and candidate countries. Solar Energy, 81, 1295–1305,
http://re.jrc.ec.europa.eu/pvgis/.
8 Solar PV electricity generation for dairy farms
13:00
14:00
15:00
12:00
Time
16:00
17:00
18:00
19:00
20:00
21:00
normal energy use
solar PV generation
22:00
23:00
20:00
Graphs for illustration purposes only.