There is more than transmission between generation and the customer
Posted on May 05, 2003
Just under 3 per cent of the electricity generated in the US comes from pumped hydro energy storage. The pumped hydro generating plants are the unsung heroes of the industry, moving water up and down hills so that demand on the power network can be effectively and efficiently managed. Owners and operators of pumped hydro have access to a very useful asset in their plant portfolio. They have bought themselves an option to generate hundreds or thousands of megawatts at very short notice, without concern over fuel availability, emission limits or long warm up and shut down times. Their “fuel” is off-peak electricity, the lowest cost electricity.
At the flick of a switch, a pumped hydro unit can go from pumping to discharging. It might take a minute for the flows to reverse but the effect is enormous. Pumping at 400 MW and discharging at 500 MW means a system change of 900 MW. That can provide reserve across large parts of the system.
But reserve is only part of the story. There are other ancillary services too. Storage plants, like many other generating assets can maintain frequency and provide long-term reserve. Some conventional hydro plants have a storage component, holding water back until the system demand requires it. Their response time is an asset that can and should be valued.
Of course, hydro plants are becoming increasingly difficult to site – the opportunities to find two lakes separated by hundreds of vertical feet are limited and there are very few sites close to where the transmission system would benefit. This call to the engineers and scientists has been answered by the development of a number of other technologies that can store energy – as electrical energy in the case of supercapacitors and superconducting electromagnetic storage; or as kinetic energy in flywheels, or electrochemical energy in many types of batteries. An energy storage system is breaking the otherwise continuous chain between generation and use of electrical power – other examples are compressed air and thermal energy systems.
Many electricity storage devices are already in widespread use throughout the US and indeed around the world. The Electricity Storage Association estimates that the market for batteries used on power systems is around $1 billion each year. Many of these batteries are used solely to provide back up to conventional generation or the power grid. Batteries, and also high performance flywheels, are being installed to supply uninterruptible power supplies (UPS) for installations where a reliable power source is vital. Energy security can benefit from electricity storage. These end user applications are typically in the size range of 10 kW to a few MW or more.
There is a gap in the middle. Some UPS are in the multi MW range (perhaps 10 or 20 MW) but there are few multi functional electricity storage systems being developed in this range. The exceptions are worth noting: Golden Valley Electric Authority, Fairbanks, AK is building a 40 MW battery system to provide reserve and ancillary services to the local power system and TVA is building a 12 MW flow battery system in Columbus MS. These two projects will demonstrate the remarkable range of benefits that storage can bring – storing energy, matching supply and demand; balancing unexpected fluctuations and waiting in reserve until required.
Where the transmission network is straining, storage can help. Distributed superconducting magnetic energy storage can inject reactive power into transmission zones and improve power flows at a fraction of the cost of other solutions. Battery storage can smooth the output of renewable generators such as wind and solar. Flywheels can improve power quality near to railroads and metro systems. System planners, utilities and customers should start demanding the services that electricity storage pants can provide. A first class transmission system requires nothing less.
Anthony Price is a consultant with many years’ experience of working on electrical energy storage projects with a major international utility company. He has also worked with large and small engineering consultancies on infrastructure projects. He is an elected Director of the Electricity Storage Association, the international trade association that promotes the development use and adoption of electricity storage. Anthony Price may be contacted by email at: email@example.com