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Energy storage technologies are currently seen as the means by which a greater reliance can be placed on renewable energy generation as part of the overall energy mix on the national grid network and by which the increasingly varied energy demands of consumers can be met.

Speculators have been identifying suitable sites for large scale storage facilities which would supply storage and grid balancing services to the network operator and to large scale consumers and generators. In time as “smart grid” commercial arrangements are rolled out this market may open up to smaller players, although at present, bankable contracts for grid services are difficult to secure. “Behind the meter” energy storage, or in other words, storage of energy within a farm business, is worthy of consideration for businesses with renewable assets and energy demand profiles that do not match their output. The principle of this is that technologies such as batteries, act as a fuel tank which is filled up when surplus generation is available and depleted when demand outstrips production. Most renewable installations currently use the grid itself as the store. However, energy is fed to the grid at a low rate (wholesale price or export tariff) and purchased back at a higher retail price. To assess the viability of storage technology a calculation needs to be made of the potential savings from avoiding this price difference over the cost and life expectancy of the storage technology. In order to do this a reasonably accurate audit of the on-site energy usage profile is necessary.

Undertaking an energy audit should not be seen purely as a means to justify investment in a particular energy storage technology. Many managers who have carried out this exercise have found substantial savings from changes in operational procedures without any investment in new equipment. The objective is to actively manage your on-site demand to better match the profile of energy production. Demand management is a tool that network operators also use to balance their networks. At peak demand times they may pay large consumers to reduce energy consumption to maintain supply elsewhere on their system. Consumers contracted to supply this service will receive payments for doing so. In this article, we are looking at the opportunities for managing demand “behind the meter” within your own business to reduce as much as possible the need to import energy from the grid.

Water heating – where hot water is a daily requirement such as on a dairy farm, heaters are often controlled by time switch and water stored in insulated thermal stores to ensure that suitable quantities of water are available when required. This can result in grid electricity being used, even where a farm has renewable assets if the sun isn’t shining or the wind isn’t blowing when the time switch clicks on. Fairly simple additions to control circuits can be introduced which will divert any renewable energy to heat cool tanks whenever it is available, irrespective of time switch settings. With high levels of insulation on the tanks and if necessary an increase in thermal store capacity, energy can be stored as heat until required and mains power will only be used when the time switch and temperature sensor signal that insufficient hot water will be available. Other thermal storage devices such as “heat batteries” employing phase changing salts provide efficient means of storing heat in smaller spaces.

Ice-building – Where cooling is required, similar control systems can be used to build ice using on-site energy for use when demand exceeds the available generation.

Other less regular tasks can be programmed to take better advantage of local generation and these do not necessarily have to be automated.

Slurry pumping – Where slurry has to be moved periodically from a cellar to an above ground tank by an electric pump, this could be initiated on a windy day to take advantage of wind turbine output. A certain amount of planning is necessary to minimise the times where cellars become too full and mains power must be used.

Feed milling – can similarly be carried out on windy days, as would have been the case in times gone by when windmills were used for this purpose.

After implementing steps such as these, the installation of battery storage may still be justified and in such cases where batteries are subsequently installed the same principles will improve their effectiveness. Optimum performance will be achieved by programming tasks to take full advantage of the extra facility that storage provides. The ultimate goal should be to supply the maximum amount of your sites demand directly from renewable assets or indirectly through storage technology.

A technical note on energy storage and demand management is available here.
A practical guide on making the most of on-site generation is available on the Farming for a Better Climate website;.

Jim Campbell,
Team Leader – Environment, SAC Consulting

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