Renewable energy on farms

Following on from the Farm Environmental Link Project article in the last Farming and Wildlife, Adviser Adam Lockyear from Somerset takes a brief look at four ways for producing energy on your farm.

Sustainability is the word of the moment and energy supply is a market which receives particular attention.  The UK has ambitious targets to cut 60% of its Carbon Dioxide emissions by 2050, based on the 1990 level.  In 2006 the UK's Carbon Dioxide emissions had fallen 5.3% from the 1990 level.  There is still a long way to go and there are many different ways this target can be met, the use of renewable energy is one of the key ways.

Existing renewable energy in the UK
From a survey by RegenSW (the South West renewable energy agency) -

• 4.55% of the UK's energy comes from renewable sources.
• There are 215 renewable electricity projects connected to the national grid. This is approximately 137MW of energy a year (~3% of the regions demand).
• The South West has a target to produce 597MW of renewable electricity by 2010 (11-15% of the regions energy requirements).
• It has identified 419 renewable heat projects generating 27.85MW of heat energy.

How does this fit with Agriculture?

As fuel and energy costs rise, improving energy efficiency and investing in renewable energy on your farm can become a more feasible option as the payback on your investment decreases.

The Energy Savings Trust (EST, 2006) estimates that by 2050 up to 30-40% of the UK's electricity generation could be produced by small and microgeneration technologies.  This is a large market which farm businesses could be well placed to access, with opportunities to sell surplus energy and generate an additional income.

Matching the correct technology with the existing resources on the farm is vital to ensure the right technology is installed to get the maximum efficiency of the installation.
Wind

Being an island Britain has its fair share of wind, and according to the Met Offices 30yr trend, the average wind speed in the south west is approximately 6m/s.  Most turbines are designed to operate efficiently at average wind speeds of ~5m/s.

The British Wind Energy Association (www.bwea.com) estimates 6% of the UK's electricity could be generated by small wind energy by 2050.

Why are farms well suited to wind energy?

• Modern small scale turbines vary in size, many being not much bigger than a hedgerow tree up to around 15m tall.
• Their impact on farm operations is small as they can be farmed right up to the base of the turbine and they don't disturb livestock.

• There are a number of different manufacturers of farm scale turbines ranging from 5kW to 50kW.

General example:

• Proven Energy is one company that produces small turbines they build two models suitable for agricultural sites the Proven 6 and 15 which produce either 6kW or 15kW (www.proven-energy.co.uk).
• E.g The Proven 15 is able to produce 15kW enough to supply six three bedroom houses.
• Dairy Farms use between 200 - 400 kWh of energy per cow per year. A 15kW turbine in the right location could produce 15,000 - 30,000kWh of electricity a year.
• Therefore for a farm using 300kWh a year per cow, a single 15kW turbine could produce enough electricity for 80 cows.

• Payback can be around 10yrs on installations depending on the site and existing energy costs.

Biomass - Woodfuels

Woodfuel has been used as a source of heat and energy for thousands of years.  Until the industrial revolution and the development of coal technology it was the major source of energy for industry.  Woodfuel technology has developed over the last 30yrs in other parts of Europe particularly in Scandinavia. 

Energy in the form of heat makes up a large proportion of the UK's energy requirement, needed for heating water, industrial processes and space heating.

What are the advantages of woodfuel:

• Relatively stable fuel price
• Decentralised fuel supply - supports local employment and economy
• Adds value to low grade timber
• Can promote management of small woodlands

• High efficiency 90% is possible

There are a wide range of systems available, from fully automated woodchip systems to hand fed log boilers.  One of the important advantages for many agricultural units is that there is a potential cheap source of timber already available on the farm, either in woodlands or large hedges.

Energy is generated through a two stage burning process.  The wood first undergoes combustion which produces heat and gas. Then there a second burning process of the gases called gasification. This is when most of the heat is generated.
The hot air then passes through a heat exchanger, which heats the water to up to around 85oC.  This heat can then either be used directly, if there is a constant demand, or stored in an accumulator tank or heat store for later use.

General Example

• The simplest woodfuel systems burn whole logs these systems are well suited to agricultural sites.
• A well set up system would require loading 2 or 3 times a day in winter and as low as once every few days in the summer if the boiler is combined with an accumulator tank.
• A 40kW boiler can cost around £3,500 and an accumulator tank can cost an extra £2,000. The additional cost of installation and plumbing will vary greatly depending on the site (Dunster Woodfuels, www.dunsterwoodfuels.co.uk).

Anaerobic digestion

Anaerobic digestion (AD) uses bacteria to breakdown organic waste into three components: Biogas, Fibre and Liquor.  This occurs in a sealed container under anaerobic (without oxygen) conditions.  The Biogas produced is a mix of Methane and Carbon Dioxide, which can be burnt to generate heat or electricity.

This system is well suited to Dairy farms where as much as 50% of the farms energy is used for heating water.  Waste from the food processing can also be incorporated with the waste from livestock.

Benefits of an AD systems:

• Income can be generated from the sale of surplus electricity.
• The fibre and liquor produced has a value as a fertiliser, which if used efficiently can offset costs of importing fertiliser.

• AD provides an integrated Waste Management System for farm businesses.

General cost: 

• A small digester that produces 10 kW of electricity would require the waste from around 100 cattle or 1,000 pigs and would likely cost between £50,000 and £70,000.
• The capital cost per kW is around £3,000 to £7,000
• Other costs to develop a project will vary greatly with each project. These include the cost of consultants, licenses for transporting waste, training costs for operating the plant and annual running costs, which could range from £7,000 to £10,000 per year
• Running costs include transport costs for waste, annual fees for licences, maintenance and operating costs.
• A plant is likely to require 2 staff days a week.

(Source: Devon County Council Renewable energy guide for land based industries, 2004, www.devon.gov.uk). 

Small Scale Hydro

• Hydro power produces around 40% of the UK's renewable energy and around 13% of Europe's total energy requirement.
• In Norway Hydro produces 99% of the countries electricity. (EC, 1998, Small Hydro handbook)
• In the UK there are an estimated 20,000 disused water mills

• These sites could produce 1000 MW. .(University of Southampton)

The basic requirements for a successful hydro system are a large enough head of water and a reliable flow.  The head is the height water drops from upstream to the turbine.  The flow is the volume of water usually measure in m3/sec.  The flow and head need to be measured and there are a number of different deigns of turbine which suite different flows, for example 50 kW of electricity can be produced from a flow rate of 1 m3/s dropping 6 m.

Some key benefits are:

• Systems can be 70-90% efficient.
• The supply of energy in the form of water is reasonably predictable.
• There is only a gradual variation in output from day to day.

• Systems have a long lifespan compared to other technologies, often 50yrs or more.

General cost:

• The cost of installations is variable depending on the site and the infrastructure required but can start from £1,000 to £4,000 per kW.
• UK sites with old water mills are very suitable.
• The payback on investment is good compared to other technologies because of the lifespan of installations and the high efficiency.  A 10 kW turbine could generate 50,000 kWh a year which at 6p/kWh is £3,000 worth of electricity a year (www.british-hydro.org).

• Renewable energy on farms (PDF 532KB)