Possibly the most complex issue our industry must resolve is to help make the grid successfully ‘Smart’; a situation where supply and demand is harmonised, through intelligent electronics, and flexibility in energy consumption at the consumer end.
To realise the importance of achieving a ‘smart grid’, we need to be aware of the variations to be managed, between generators, consumers, and changing climatic conditions.
The Electric Insights Dashboard illustrates the complex mix of supply and demand. The illustration shows the electrical grid receiving contributions from nine different energy sources, and grid managers would ideally try to match supply with demand at all times. The goal of a smarter grid is to manage the peaks and hollows in supply and demand, and although this has always been a difficult task, it is confused further by trying to deal with the varying inputs of wind and solar generators.
Ideally, a ‘Smart’ result would see the above graph as a flat line, where supply and demand are harmonised, but a robust result can only be achieved with the assistance of energy storage in front of, and behind the meter. Ongoing advancements in electrical storage continue, but costs are high and growth in the number of installations is still quite small.
However, there are other useful and affordable ways to store energy, depending on the industry and application. If energy is used to power freezing or heating processes; e.g. hotel air conditioning, dairy cooling, freezing processes, etc., then a thermal store will be the most cost effective technology.
When choosing any storage battery, it is important to consider the ‘round trip efficiency’. Round trip efficiency is quantified by the amount of energy used to charge the store, compared with the quantity of energy delivered at the time of discharge. By comparison, ownership of a low temperature thermal battery will cost around one quarter the price of a lithium battery, and return over 90% round trip efficiency.
Thermal battery technology continues to develop, driven by an overwhelming global need for affordable energy storage, and development work is currently taking place with various ‘phase change materials’, (PCM). Phase change materials rely on latent heat capacity to provide storage with a high energy density, occupying a smaller space. To store thermal energy at high temperature, (HTES), special salts are used, designed to phase change’ at pre-determined temperatures of around 45°C and above, although research continues for an ideal solution.
Low temperature thermal energy storage (LTES) is however significantly more advanced and commercially available. Displaying an energy density > 55kWh/m³, LTES is effective in supporting cooling loads for varied temperature ranges from around +12°C for A/C systems, to processing of frozen foods requiring temperatures below -20°C.
Unless consumers can store some part of the energy need, they will continue to live with high-cost penalties at peak times. When energy can be taken more flexibly, high tariff periods can be avoided while production rates are maintained, and this flexibility comes from LTES. To contribute to a smarter grid, energy users must be flexible in their demand, and by having on-site energy storage, have the ability to vary their energy consumption according to information coming from the Smart-Grid.
Typical thermal battery support example
For minor variations the grid operator has a number of extra power sources available such as kinetic flywheels, pumped-hydro energy storage, and a small amount of electrical battery storage, but the capacity available is a small fraction of the storage actually needed.
As the growth of non-relentless energy sources (wind/Solar) join the mix, this fraction does not improve, and the problem of supply and demand increases proportionately.
In the next parts of his series, Bob will look into the various low carbon technologies and what they mean to our industry. Bob, is on hand to answer any questions you may have, so please do use the comment form.