Flexible energy storage systems

Peter Taylor outlines the growing need for energy storage and the variety of potential options.

Most renewable sources of energy have one key drawback – they are not very predictable. For example, wind power cannot be turned on and off with the flick of a switch, a fact that runs counter to the core principle which energy providers the world over must adhere to on a 24/7 basis.

Most people are used to working with energy storage systems. The common battery is a case in point. But powering a flash lamp when required is not the same as ensuring that an entire country’s electricity requirements can be met in full on an ongoing basis.

For its part, the European Commission believes that energy storage will play a key role in enabling the EU to develop a low-carbon electricity system. According to Brussels, energy storage can supply more flexibility and balancing to the grid, providing a back-up to intermittent renewable energy.

Locally, it can improve the management of distribution networks, reducing costs and improving efficiency. In this way, it can ease the market introduction of renewables, accelerate the decarbonisation of the electricity grid, and improve the security and efficiency of electricity transmission and distribution. In other words: reduce unplanned loop flows, grid congestion, voltage and frequency variations and stabilise market prices for electricity, while also ensuring a higher security of energy supply.

Currently, there is limited storage in the EU energy system – around 5 per cent of total installed capacity. This is almost exclusively from pumped hydro-storage, mainly in mountainous areas. Other forms of storage – batteries, electric cars, flywheels, hydrogen, chemical storage – are either minimal or at a very early stage of development.

This ‘feast or famine’ dimension to renewables brings into focus the need for energy storage systems, the use of which would help even out the supply: requirement conundrums that are so associated with wind, tidal, wave and solar energy sources. This was an issue discussed in some detail by Professor Peter Taylor (pictured at left), from Leeds University’s Centre for Integrated Research at the Energy Ireland conference.

“We now know that there will be a significant increase in renewable energy production to meet targets,” he explains. “The drivers here are the tackling of climate change and the need to improve energy security at national level. For example, in Ireland’s case, there is a commitment to generate 40 per cent of the country’s total electricity requirement by 2020.”

“There will also be an increased electricity demand expected in many countries, for example, from electric vehicles and heat pumps. This, in turn, will lead to an increased requirement for energy system flexibility and the need to cope with events that may cause an imbalance between supply and demand. Energy storage is one option that can help provide this increased flexibility.”

Professor Taylor went on to point out that the development of suitable energy storage systems will help optimise utilisation of renewable electricity assets by minimising curtailment. They will also make renewable electricity output more predictable.

He continued: “Storage systems will also make it easier for energy suppliers to match supply with demand. Grid connection costs can also be minimised by peak shaving and time shifting. Efficient storage will also allow for electricity delivery at specified peak times, so maximising revenue.

“Fundamentally, we need to increase energy system flexibility so as to allow us to cope with events that can cause an imbalance between supply and demand. And these can be both long-term and short-term issues. And, of course, it is often overlooked that fossil fuels are very easily stored.”

Balance

Taylor added that the key determinant at all times is to ensure that the energy equation involving supply and demand is in balance at all times. Energy storage is “an important component of this mix” as is the use of interconnectors in tandem with flexible energy production mechanisms, centred on the use of fossil fuels. In addition, educating consumers on how to best utilise the energy sources available to them is another component within the mix.

Taylor added: “Where storage is concerned, we need to understand what types of storage are needed, how much and where it should be deployed in the energy system. There is also a fundamental requirement to develop a coherent policy approach to energy storage, thereby stimulating governance and business models to enable rapid implementation.”

Professor Taylor then reflected on the range of flexible energy storage options currently available and where they kick in along the energy supply-demand chain. Energy can be stored in mechanical, electrical or chemical devices and in the form of heat. The place of deployment of different technologies is likely to be at city, region, home and personal or domestic device level. Very large-scale storage capacity is likely to be associated with industrial operations or at points of generation and distribution.

As delegates were also informed, the role of the distribution network and its flexibility is an essential component in the delivery and overall cost and viability of any storage scheme. Significantly, Professor Taylor also pointed out that there is little bespoke legislation which addresses energy storage across Europe.

“This raises fundamental issues, particularly in the context of a regulated market for energy,” he commented. “Given this backdrop, staff from Leeds and Birmingham universities recently joined forces to survey key stakeholders within the UK’s energy sector in order to gauge their views on the need for energy flexibility, the future priorities for storage systems, how they should be implemented and the possible requirement for future government support.”

The results of this survey have identified a number of interesting trends. Significantly, the projected increase in renewable energy sources was identified as a key driver pushing forward the need for increased energy system flexibility. The key technologies identified as being most capable of delivering this greater flexibility were additional storage and back-up fossil fuel generation capacity with the required storage capacity located at the point of generation. The availability of interconnectors between different member states of the EU was also regarded as significant in this context.

Perceived barriers affecting the implementation of future storage systems included the associated costs and an uncertainty regarding their future value. With regard to government involvement in this area, the main drivers cited were the need for effective regulation and the demonstration of relevant new technologies.

Peter Taylor remarked: “It is a fundamental fact [that] increased renewable energy generation will require additional system flexibility. And storage could be an important source of flexibility. But the implementation of the various technology options currently faces technical, regulatory and market barriers in many countries.”

He concluded: “The drive to secure more energy from renewable sources is already a reality and is one that will gather considerable momentum over the coming years. This, in turn, puts a more than significant onus on energy suppliers to put systems in place to ensure that renewables are used in the most efficient way possible, both from a generation and utilisation point of view.”

Peter Taylor is Professor at the Centre for Integrated Energy Research at the University of Leeds.