Storage Battery

In 2013, Scottish Hydro Electric Power Distribution (SHEPD) installed a 2MW lithium ion battery at Kirkwall Power Station, and connected it to Orkney’s electricity distribution network. This pioneering trial, the first of its kind in the UK, aims to establish the viability of large scale batteries for electricity storage.

The 2MW lithium ion battery was provided by Mitsubishi, and has been integrated into the existing energy storage system within Orkney’s Active Network Management network. The battery, which has already been trialled for two years in Japan, should make it easier to smooth out intermittent power generation from renewable sources by allowing the operator to store clean energy and release it when required. This ability to balance a variable energy output from renewable sources will become increasingly important as the world moves towards a decarbonised electricity generation mix.

Although the installation of the battery has not provided an immediate solution to constraints on the Orkney distribution network, it is hoped that the results of the study will help demonstrate that batteries could provide a cost effective way of freeing up capacity on the network and facilitating new connections in the long term.

There are a number of ways of storing energy and in a number of forms. Examples are:

  • Hydro – Pumping water to an elevated level for later release to generate electricity.
  • Heat – Heating up a substance to store heat energy for later release usually as heat energy but possibly for conversion to other forms of energy.
  • Electrical energy storage – usually in a battery of some form.

This section focuses on the last 2 examples.

Home Heat Battery

Heat batteries contain materials that can absorb much more heat energy than water alone. A battery the same size as a 200lt hot water tank can absorb 14kwh of energy and cost £4k – £6k installed. The basis upon which the heat battery is founded is that most of a home’s energy consumption is heat energy so why not store the energy as heat

This energy can be provided from a variety of sources:

  • Electrical energy from:
    • A solar array
    • A wind turbine
    • Cheap night time electricity
    • An electric battery
  • Heat energy from:
    • A heat pump (air sourced or ground sourced)
    • Any central heating boiler

The stored energy in the heat battery can be released at a later time to produce hot water or to run your heating system. The process is very energy efficient (ie not much energy loss) and a heat battery does not degrade over repeated cycles of heat / cool.

The economics of Heat Batteries – A 14kwh capacity unit cost around £5k to install. If the best case is used and all 14kwh is used every day and each kwh is valued at 32p then the potential annual savings are:

£0.32 x 14 x 365 = £1635 saving per year.

However the level of saving depends upon what you use as the energy source. In a recent house energy assessment where the house had a 4kw solar array and Air to Water (A2W) heating system then the savings were estimated at £900 / year giving a payback of 5.5 years

Home Electrical Battery

A home electric battery was originally a large bank of Lead Acid type batteries and was typically used in conjunction with an off grid wind turbine. The advances in Lithium Ion technology means that most home batteries are now of this form. Currently capacities of up to 20kwh are available and they can be combined to even greater capacity.

Costs depend on manufacturer and are around £15k for a 20kwh capacity unit installed.

The electrical energy can be supplied from a number of sources:

  • Wind turbine
  • Solar
  • Cheap rate electricity from Grid
  • Transfer from another battery (such as an EV battery)

Usually the electricity stored will be consumed at a time to avoid taking peak time electricity from the grid (morning on early evening)

The economics of an Electrical battery – Again taking the best case if the electricity is supplied free of charge and avoids the use of peak rate electricity at 32p / kwh then the annual savings are:

£0.32 x 20 x 365 = £2336 saving per year.

However the level of saving depends upon what you use as the energy source. In a recent house assessment where the house had a 4kw solar array and Air to Water (A2W) heating system then the savings were estimated at £1500 year giving a payback of 10years

Note – Any cost / benefit calculations contained in this article are for illustration only and must not be assumed as accurate for any physical installation. Each individual installation should be assessed for costs and benefits as part of its financial justification


Commercial use of Electric batteries

The use of commercial electric batteries is certain. They should not be used for long term storage (unlike Hydro) but for the following:

  • To provide electricity capacity in times of a grid network failure. Tesla has installed a large battery in Australia for this very purpose     
  • To provide a way to better balance supply and demand on the grid. The battery would be charged at a time of low demand and discharged at times of high demand. This will help prevent having to activate high cost and environmentally unfriendly forms of electricity generation to meet these periods of high demand. This would usually be within the timespan of a day (or two). With the rapid increase of Renewables generation on the grid this will become even more important as Renewables generation is not constant (no solar after dark, no wind on still days)