Solar Photovoltaic Electricity Generation for Dairy Farms

ddc.wales.co.uk

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.

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