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Storing up a problem

Arup's director of energy business discusses the next steps to delivering a balanced energy portfoli

The right to flick a switch for instant illumination or click the thermostat to feel the heat is seen as unalienable; increasingly though the picture is changing. Energy prices are climbing evermore, fuel supplies are challenged and the easy wins of maintaining our carbon reduction trajectory are stretched.  Achieving the balance of maintaining supply and demand in a low carbon world will require innovative solutions and incentive structures.

With this in mind, this piece is intended to outline the factors shaping the current question of energy and the role of electricity within this, the range of energy storage measures available to spearhead change and the next steps to delivering a balanced energy portfolio.

A changing mix: the drivers impacting energy and electricity

The litmus test of a well developed energy system is one which provides secure, low carbon, affordable energy, while taking into account the need to flex with our varying demands and respond to unforeseen circumstances.

We often hear that there are multiple pillars to the development of an effective energy strategy serving industrial, commercial and domestic users; and this is a sensible approach. Combining a wide range of energy sources with a resilient energy transmission network and demand reduction is crucial, while an increasing switch to electrical transport systems and electric heating, together with the dynamic balance between supply and demand afforded by Smart energy systems, also needs consideration.

A resilient electricity mix should be sourced from various means of generation. Included within this are efficient and flexible gas power plants topping up a foundation of constant low carbon nuclear and carbon sequestered coal, together with both intermittent and predictable renewable forms of generation such as wind and biomass. These sources of electricity each have unique features in terms of developer attraction, capital cost, operational variability, as well as different positions in the secure, affordable, low carbon triumvirate.

Our electricity transmission networks are gradually evolving in response to the need to accept a changing mix, to channel remote renewable electricity from the north of Scotland or nuclear power from Somerset. For example, at a local level, distribution networks are evolving to accommodate local renewables and combined heat and power plants, while recognising the future charging needs of electric vehicles.

A particular focus is on improving the characteristics of our building stock through initiatives such as the ‘Green Deal’. Looking ahead, we see the many advantages which will be provided by a fully integrated Smart electricity network, where both electricity demand and its generation can be more closely matched in real time through tariff-driven dynamic demand response.

At any point in time, the amount of electricity entering the network through generation must be exactly balanced by the amount that we use. Every second of the day, careful management of the system ensures that predictable and less predictable variations alike are accommodated. The collective kettle dash after Coronation Street, favourable winds spinning turbines to full capacity or the automatic shutdown of a power station all require a response.

The here and now: available energy storage measures

In keeping with the notion that a strong, resilient electricity system derives from a broad mix of supply, network and demand measures, a crucial absentee from the UK armoury is significant energy storage. Although we do benefit from large scale pumped storage hydroelectricity, such as the 1,800MW Dinorwig facility in the mountains of North Wales, we are not taking full advantage of the many benefits which energy storage can deliver throughout the energy chain.

There are a whole range of energy storage measures which can be effectively deployed. In essence their features and applicability are defined by two basic parameters; the first is the amount of energy which they are ultimately capable of storing, while the second is the rate at which they can accumulate or release the stored energy. By way of analogy with a car, the former can be compared to the mileage range, while the latter can be equated with the engine output.

Large scale technologies

•    At the high storage and capacity end of the scale, pumped storage hydro (PSH) schemes such as Dinorwig can store hours of scalable, flexible energy. With the ability to fill a supply gap in tens of seconds, and recharge at times of limited demand, this means that major coal or nuclear plants can operate at their most efficient constant output while storage takes up the slack
•    Compressed air energy storage (CAES) is a developing technology using off-peak electrical energy to compress air into underground caverns. As increased electricity demand dictates, the air is released from the cavern directly into the intake of a natural gas fuelled generator, greatly improving the efficiency a power plant can achieve. However, CAES requires an underground cavern, natural gas supply and connection to the electricity grid all at one location, so its application can be limited.

Small scale technologies

•    Liquid air storage systems are in advanced stages of development. These have the scalability, and the amenability to an industrial estate setting, to support local distribution level electrical storage needs. Here, liquefied air is stored in near-atmospheric tanks, ready for expansion by a factor of 700 times through an air turbine, which generates electricity
•    Another scalable form of energy storage comes in the form of battery technology. The modularity of batteries lends them to a whole range of applications, but characteristics including physical size, charge/discharge rate and operational sensitivity and hazard all need to be factored-in when reviewing their storage potential
•    Superconducting magnet energy storage (SMES) lies at the cutting edge of energy storage. They store energy by generating strong magnetic fields within a superconducting coil and are able to instantly discharge electrical energy at a constant rate. Current SMES materials require energy intensive super cooling but, as this requirement diminishes with the advent of new superconductor materials, it is becoming an increasingly viable option

The necessity of commercial return

The challenge faced by energy storage is that it helps to solve numerous energy system challenges, but not all of these are recognised or rewarded. In order for energy storage to achieve wide scale deployment it needs to deliver demonstrable value and service and to be rewarded by predictable revenue streams. Some of these revenue streams are already monetised. Within the National Grid, for example, the UK transmission system operator contracts short term operating reserve (STOR) for rapid electrical supply in the event of loss of generation capacity. Other potential revenue streams for power quality also exist.

As the energy mix is influenced to a greater extent by large, constantly operating baseload fossil and nuclear plants (together with intermittent renewables), a greater reliance on electricity for transport and heating, electrical storage will become increasingly important.

Rather than sizing our distant electrical transmission networks to accommodate the maximum output of a wind farm, a proportion of the electricity could be stored at the wind farm itself, smoothing out the peaks and troughs so that a less expensive and invasive transmission network can be provided to accommodate the average, rather than peak, output.

Large thermal and nuclear power plants operate most efficiently and cost effectively at a constant output. Wind renewables operate on a less predictable basis and little can be done to change their output, other than shedding, in any case. Gas power generation takes up the slack, either as efficient combined cycle plants or their much less efficient open cycle counterparts. Consumer demand varies diurnally, weekly and seasonally. A consequence of this is the fact that electricity prices vary depending upon the degree of impending imbalance between supply and demand. By storing electricity during low price periods and releasing it again at peak times, this ‘time shift’ energy storage can deliver revenue. The end result? A large commercial organisation could store off-peak energy to offset its peak demand.

Thousands of batteries in individual homes (or electric vehicles in the garage) could be controlled remotely to deliver significant electricity as a ‘virtual power plant’. As well as providing a service to balance the overall supply and demand, this approach could also be used to increase the resilience and reduce the redundancy required in the electrical distribution network. In the event that part of the network is damaged or fails, sufficient energy could be delivered from the section downstream of the damage. The resulting reduction in system redundancy represents a cost saving in terms of capital expenditure and ongoing maintenance.

Combined heat and power plants deliver electrical energy as well as heat energy. They achieve high levels of efficiency and perform optimally when their full output of heat and electricity is required by consumers. At times, there will be a demand for heat, perhaps for an ongoing manufacturing process, but the required electrical output and associated revenue is depressed due to lack of demand. By maintaining the heat output while storing the electricity until a more beneficial time slot, both the efficiency and the commercial position can be retained.

Making it a reality

Storage is an integral part of the solution of decarbonising energy networks but cannot be viewed in isolation. Rather, adequate reward for energy storage should be a key pillar of a future energy policy.

These issues are by no means limited to the UK. A visionary, holistic strategy needs to be taken to ensure new and immature technologies are aligned with governments and European investment across the board. Delivering a balanced, effective energy portfolio will require a sustained, integrated effort from Europe – one looking ahead to future generations and the impact of years to come.

Alan Thomson is the Director of Energy Business, Arup.