Power Storage is considered as an integral part of National Grid, the stored electric power is helpful in offsetting power interruptions in the energy that is derived from an onsite generator, or a utility. Customarily, common capacitors were used for filtering and for temporary storage; cells were used for transitional power storage, while the diesel fuel is applied in long-term power storage.
Advances established in the use and application of technologies affecting each of the power storage intervals has been debated. In the present work specific attention is focused on the power storage technologies that are in use in the UK; their roles in National Grid; and their future development in the energy system in the UK.
The Vision 2050 for the United Kingdom development blueprint supports realization of a supply of green electricity in meeting the national energy consumption scheme. However, this calls for dramatic transformations in the process of energy demand and supply in the light of renewable power generation with strong seasonal electricity consumption.
To ensure that there is a reliable security of the energy supply and meet the energy demand, the challenges for the power system are unprecedented, but manageable with appropriate preparation. Power storage stands an advantageous position in meeting these challenges. Alternative options include flexible energy generation, efficient power distribution network, and demand-guided response. However, the outcomes of attaining the Vision 2050, beyond the deployment targets should be understood to ensure a possible transition to green energy (Kruger 2006).
The current paper is an attempt to present a tactical perspective of the opportunities for electric power storage, and outline the scale and nature of the challenges that will be faced towards actualization of green energy. The present work provides a description on how power storage should be implemented towards facing the future demand and supply challenges in the UK National-Grid.
The low-level carbon generated electricity in the UK is projected to play a significant role in the achievement of emissions goals. Currently, there is an increase in generation of renewable energy coupled with the electrification of transport and heating facilities. The impact on this development will be an oscillating peaking of power demand and variability of the power supply from recurrent power generation (Kruger 2006).
Power storage has been identified as the means of providing elasticity in the energy system, which if fully exploited, may reduce the need for new power generation while allowing greater application of low carbon generated/emitting power. In addition, during the power network revitalization, power storage may use the already established infrastructure. Presently, rechargeable power storage is economically challenging as compared to the fossil fuel. Nevertheless, electrical power storage is a field experiencing continuous technical advancement. In the UK, this may be partly attributed to the deployment of the EV (electric vehicles) powering battery advancement, and to some extent, by the fact that power market is in the need of energy storage technologies to handle the intermittency of the renewable energy generation. Power storage is expected to lower the power cost, while improving the efficiency of technology (Kruger 2006).
The current work assumes an integrated view of power storage in the United Kingdom, with the aim of highlighting the current and future technological advancement and their impacts on the UK’s National Grid.
Need for Storage in the Electric Power System
The financial value for the time-shift (electric energy time- shift) may be derived through the use of storages to establish multiple electric energy buying low/selling high financial transactions. For the utility, the financial benefit may assume a form of profit (where energy is sold) or may lower the cost of energy. For the energy stakeholders it will mean the raise of their profit. To approximate the benefit from the time-shift, a storage dispatch algorithm is applied. The algorithm has the logic required for the determination of the period for charging and discharging the storage so as to improve the financial benefit (Twidell 2006).
The time-shift is applied to determine the best time to buy or to sell the electric energy in terms of price. The dispatch algorithm assesses the time series of the prices to come up with all the possible transactions over a given time with improved net benefit. The algorithm is helpful in evaluating the net benefits from the financial transactions over a given time (Kruger 2006).
Electric Supply Capacity
In the UK regions with low electric energy generation capacity, the energy storage may be used as a means of off-setting the need to install or to buy new generation capacity, or to compensate the need to rent energy generation capacity in the electricity market. The avoided cost becomes a benefit associated to the energy storage that may be used for the energy supply capacity. The other option for accrediting a financial aspect to this storage benefit is the price-based, where the energy price is determined by the designated energy agency or by the electricity market (Kruger 2006).
It is significant to observe that, in most electricity markets, the generation capacity cost may not be separated from the cost of energy. In such marketplace, the energy generation capacity cost should be embedded in the price per the unit of energy traded. Thus, there is no explicit capacity charge that may be avoided, nor are there means of trading the generation capacity. However, there are capacity charges that are related to the electricity consumers, notwithstanding how the net cost may be recouped (Kruger 2006).
Frequently, the possible types of the modern generation facilities are clean, effective natural-gas-driven combustion turbines using power facilities that may be operating for between 2000 and 6000 hours a year.
The electric energy generation cost has the element of the marginal cost and that of the capacity cost. The energy generation marginal cost entails the element of fuel and maintenance cost. This cost may be reduced where the generation may not be done to provide the load-following service since the power storage is used for that purpose. The generation marginal cost lowers relatively to the part load operation reduction. By avoiding the part load, the generation wear, air emissions and fuel consumption are reduced (Kruger 2006).
The electric energy capacity-related cost involves the cost that is incurred in the addition of the generation capacity. The requirement for the additional generation capacity for the load following tends to be zone- and time-specific, where it may range from no additional load following capacity required to the need for significant increments. Likewise, the form of generation preferred for the new load following capacity tends to be specific in a given region. The form of the load following capacity added ranges from the hydro-electric generation capacity to the simple cycle or cycles of generation capacity (Rosen 2012).
Different types of power storages may respond by rapid change of charging and discharging process. The power generation capacitors such as, flywheel and most types of batteries tend to have fast response. Additionally, generation-based hydroelectric storage facilities respond faster than most generation-based regulation facilities. For these reasons, energy regulation from these rapid-responses power storages can double the benefit as a regulation from the generation.
Unlike the generation applied for the area of regulation, the efficient power storage may provide double kW of service for every kW of the rated power output. This becomes possible since the power storage provides power regulation while charging and discharging, in a similar manner as in the storage applied for the load following (Twidell 2006).
Electric Supply Reserve Capacity
The power storage that is used as an electric power supply reserve capacity reduces the cost and demands for the reserves that are supplied by the power generation plant. In most cases, the price for the reserves tends to be market-based, where prices result from the hourly bidding. The electric power supply reserve capacity benefit tends to be small since generation-based reserves are not expensive. However, it is a significant aspect of a better value proposition since providing power reserves a reduced cost. During charging, the power storage may provide the double capacity as reserves. When charged, the storage may provide the reserves by being available for power discharge (Rosen 2012).
The power storage provides the voltage support that offsets the requirement for central/large generation to generate and provide reactive power to the grid whenever there is a regional voltage emergency. The competing alternatives to the power storage may include, enduring the cost of extra outrage and the risk of possible outrages; buying insurance policies to cover possible outrage-related responsibilities, and adding a central power generation capacity for voltage support (Rosen 2012).
The power storage increases the load transmitting capacity of the power transmission system, thereby; a significant benefit is realized avoiding the transmission outrages. This benefit is realized when an additional load transmission capacity requires supplementary transmission capacity or extra transmission equipment (Brunet 2011).
The Power Storage and Its Improvement to the UK National Grid
Electric power storage plays a significantly important role in the United Kingdom electric power production and distribution structure. Power storage assists in the streamlining the irregularity of the renewable energy production systems and ensures uninterrupted supply to the national grid. According to the current work, various technologies that have been or are being developed are discussed. Currently, the UK national electricity sector is under the most significant transformation. There is an urgent need to diversify the generation sources while introducing nuclear and advanced fossil fuel generation facilities. With important integration of new and previous technologies in the storage and distribution network, these sources will contribute significantly to the National Grid. The development of intelligent electrical appliances and smart grid will allow power demand to vary according to the coast and the availability of power over a given time. The United Kingdom energy demand by 2050 is predicted to have 7-59GW of the entire grid-linked electric power storage capacity. The first reason for this need of energy storage to the National Grid is the increased volume of the renewable sources of electric power (Rosen 2012).
Considering the seasonality of wind and sea waves, it is important to store the additional electric power that is generated during the high seasons fot its further supply during the low seasons. Though the tidal waves may be predictable, they do not necessary correspond with the electric power demand.
The second and equally important reason on the importance of electric power storage is the current rise in the demand for electric power. With the increased electrification of the transport and heating systems the demand of readily available electric power is projected to rise sharply. The increased demand may cause considerable degradation to the electric power generating system, hence, the rise in the cost of integration of systems; to this effect electric energy storage provides a potential reduction of the operation costs (Twidell 2006).
To advance the energy storage in the United Kingdom various technologies at different levels of development are used. In the UK, the major National Grid-connected storage schemes use the pumped storage, where the extra energy generated is used in pumping more water from the low level dams to the high-level reservoirs. When electric power is needed in the national grid, the water in high reservoirs is used to generate the extra power. The Dinorwig facility that is located in the Snowdonia is the UK’s electric power marvel. The facilities that are tunnelled through the Welsh mountains are estimated to have cost of £425 million and it is considered to be the largest man-made cavern ever. Equipped with six 300W power generators, the facility supplies an output capacity of about 1.6GW. Though there are some other pumped power storage facilities located in Scotland and with the proposed plans to transform some hydroelectric stations to pumped power storage facilities, it is still unlikely that the pumped storage will meet the UK National grid-connected power storage demands (Rosen 2012).
Given that the United Kingdom is endowed with predictable strong winds, the wind power generation and storage should not be focused on improving individual wind facilities, but should be focused on ensuring the entire system has sufficient back-up to deal with the variations in wind power generation and storage for the national grid (Huggins 2010).
According to Philipp Grunewald, better outcomes from the wind power would be attained through smoothening of the supply by connecting different wind farms. He further indicates that it would be cheaper to develop power distribution network from a central point than to construct storage facilities for individual farms. The electric power storage issue should be addressed to the power demand, but not towards the supply. If the power demand would be met by the power supply through the intelligent appliances, smart grids and industrial appliances that can adjust their power intake according to the demand, hence, there may rise no point of building additional power storage (Huggins 2010).
Nevertheless, as it is with most operations, the actual situation may never attain the projected one. The development of smart grids and improvement of electrical equipment and appliances may balance out the power demand to a significant extent, but the national grid will still remain in need of power storage. The key aspect that needs to be addressed to bring about the development of these storage facilities, is the responsibility of constructing the storage facilities. According to the electric power generators their responsibility is limited to power generation, while provision of storage facilities remains the function of the network. On the other hand, the power network operators have left this responsibility to the government regulations since they have not been allowed to own both the generating and the storage capacities (Boyle 2004).
The only challenge in linking the individual power generators to a common storage facility is that there is no single organization that can negotiate among all the stakeholders. However, negotiations are underway by the Scottish and Southern Energy (SSE) that is behind the construction of power storage facility in Orkney. Scottish and Southern Energy is providing approximately 10kW power network access point. The SSE has also invited potential power storage providers to establish the power storage capacity alongside the Kirkwall Power Station. Power storage facilities in the UK are designed to allow power generators to have recurrent production capacity and to use their equipment fully. However, without a principal oversight, there are chances that power supply problem is likely to outweigh the available solutions (Twidell 2006).
Throughout the current work, the flexibility in the generation and supply of electric power and other related ancillary services have been deemed to be of significant value. The National Grid supports that advanced storage technology will play an important role in maintenance of transmission networks by ensuring the efficient usage of the renewable energy production, and providing significant balancing services. The storage of electric power is possible in different forms (Brunet 2011).
In the UK constitution regarding the power sector, several power storage technologies acts have been highlighted, which include such technologies as Compressed Air Energy Storage, well known Pumped Storage, and Flywheels technology. Other means of electric power storage are also developed from heated water storage as well as chemical means, such as batteries. This additional storage means play an important role in balancing the power storage and supply systems. The most of the Combined Heat Power (CHP) is realised by the sale of the heat and, therefore, the electric power generation from CHP is associated with the heat demands by the consumers as opposed to being adjusted against the electric power demand and the cost of consumption. One way of ensuring CHP meets the electricity and heat demands is by introducing the power storage system. Such systems enable the generation of electric power to be decoupled right from the heat process. Further, this would allow the generators to generate the heat energy at the best time from a financial perspective and the use of the power storage to manage power demand, this could also maximise heating processes by tapping electric power from the National Grid during the high generation time and storing extra energy as heat (Rosen 2012).
Current Power Storage in the UK
Power storage has been indispensable in the provision of reliable electric power supplies over the centuries, from the piles of uranium and coal, to the reservoirs of water and natural gas. Advances in the materials technologies are currently providing intense electric power densities that are stored. The rechargeable power storage decouples the generation and demand of the energy in place and time. Power storage may take different forms ranging from: chemical, thermal, mechanical, gravitational, electromagnetic field, and mechanical, prior to the conversion to the final application power form. Thermal and electrical rechargeable power electric power storages are already in existence in the UK (Twidell 2006).
Pumped Hydro Storage (PHS)
The grid-scale PHS for the electricity power production in the Great Britain is estimated to have a volume of about 27GWh. In UK the main scheme for production of PHS is Dinorwig found in Wales that is the most recent to be established. Dinorwig has PHS volume of approximately 10GWh and a maximum output of about 1.7GW. In the world, PHS contributes about 99 per cent of all the storage capacity, which is estimated at 97GW operation capacity, 20GW being developed, and approximately 45GW proposed. The UK National Grid Seven Years Statement for 2010 has not put into consideration any new PHSs until 2017 (Kruger 2006).
Nevertheless, SSE has put into consideration two 30GWh projects estimated to be commissioned by the year 2018. These schemes are proposed to have an installed power generation capacity ranging between 300MW and about 600MW, with capacity of storing and discharging more than 1000GWh per annum (Brunet 2011).
The Hot Water Storage (HWS) cylinders estimated to be in more than 13 million UK homes. A 100 litres hot water cylinder that has hot water at 50oC, has a capacity to store approximately 6kWh. The authentic measurements have estimated an average HW consumption to be 120 litres per day, which has electric energy content of 4.7kWh. If applied across the UK, it would accumulate approximately 65GWh per day. Nevertheless, there has been a new trend in the penetration of the combination boilers in the households over the last two decades (Brunet 2011).
Other than from the reduction in the actual electric power storage capacity available in the UK, it may be a sign that the domestic use of Hot Water cylinders has a greater value in itself. This, if not evaluated, may become a barrier to the future deployment of the domestic electric power storage. Several district heating projects in the United Kingdom apply thermal storage that allows efficient generation of the electric power from CHP facilities in case where heat demand is minimal. The Pimlico District Heat Undertaking project in the UK has an accumulator with a capacity to store about 2500m3 of hot water, just below the boiling point. With this capacity, Pimlico serves more than 3000 households and about 40 business premises. In the United Kingdom, CHP is supplying about 472MWth heat for the buildings and households (Rosen 2012).
Electrical Storage Heaters
The heated brick storage heaters are the main heating system in the 7 per cent of the United Kingdom household energy stock. This number has remained constant over the last two decades. In 2008, the electricity used for the space heating was estimated to be 17TWh, contributing about 13 per cent of the overall electric power consumed by the domestic sector (Huggins 2010).
Fossil Fuel Storage
Wilson et al., estimated the electric power storage capacity of the fossil fuel in the United Kingdom at 47TWh of the natural gas and about 30TWh for the coal in reference to the generation of the electrical power. It should be clear that whenever the term “energy storage” is used, it refers to rechargeable electric power, that is, stores that can be recharged thermally or electrically from another source with different form of energy (Brunet 2011).
Future of the Power Storage Technologies in the UK
To evaluate the potential role played by the energy storage in the United Kingdom, the current work has approached the issue by assessing the areas where it may face with the power system challenges. This evaluation is helpful in highlighting the value of storage and the scale of technology needed to attain significant contribution from storage. With this scope of knowledge it becomes easy to assess the level of technology alternatives and to appreciate the cost and performance enhancement needed for the electric power storage to be deployed widely (Boyle 2004).
Space Heating Future
The space heating demand in the United Kingdom tends to have significantly strong periodic profile. Considering that the space heating is predominantly done with the natural gas, the variability is coordinated through modulation of the gas supply through the import or local production. If there would be a substantial way of heating space using electricity, seasonal electric power generation facilities along with permanent power storage would be established . Considering the domestic space heating demand of about 1.9TWh, the mean electric power generation to supply this penetration would be about 5GW.Nevertheless, the actual volume needed ought to be higher considering the increased power demand during the winter. Therefore, there would be a need for the additional capacity to supply the daily peaks to mitigate the power storage (Brunet 2011).
To this effect, by the year 2030, an extra 10GW electric power generation capacity is needed to supply the domestic space heat, leading to a shift from the gas boilers technology to the heat pump technology. According to DECC, total penetration of heat pump technology in the UK is predicted to be realized by 2050. As of 2050, the generation facility, that could just supply periodical heat requirement from the heat pump, will have the load factor less than 50% (Huggins 2010).
Significant seasonal variation possesses a chance for the energy storage to lower the demand profiles of the electrical power production and lower the capacity needed to supply heat during the winter peaks. Nevertheless, power storage of heat/electricity will be needed at an increased level than is presently attainable so as to have a minor impact (Rosen 2012).
Currently, several UK-initiated projects have demonstrated heat storages located below ground. These projects apply solar energy to charge the power stores. With challenge of electric power storage to supply the seasonal demand, and the consequences for increased electric power production, it is worth to consider the alternatives for the space heating, which include heat networks (Rosen 2012).
Power Storage Development Opportunities
Considering the present position of the different energy storage technologies, the capacity of the potential and current UK manufacturers and taking into account the UK goals for the network improvement in support of increased spread of renewable energy production and distributed resources, the following opportunities should be evaluated (Rosen 2012).
Flow cells are of significant interest as they provide the prospect of high electric power rating with a reduced initial consumption cost, along with a low cost for the extra “hours” of electric power storage. These features make flow cells an optimal theoretical choice for the integration with renewables on the National Grid and in different integrations of electric power rating and the storage capacity. The present interest in the flow cells is at the MW level, though a 3MW power system has been developed and used in Japan over the last decade. Flow cells are made of electrochemical cells, separate electrolyte and pipework, power control and conversion systems (Brunet 2011).
The United Kingdom held a dominant position with the designing of a polysulphide bromide flow cell. The cell was designed by the UK National Power a decade ago. Specific expertise was established in the design of flow batteries modules, designing of the hydraulic flow and current flow bypass and in the electrochemistry. The scheme has been stopped, the steering team has been dispersed, and its properties have been disposed. Though the technology is still sound, a substantial investment would be required to resume the project and attain commercialisation level (Boyle 2004).
To resume the flow cell project, there would be expenditure in the management of processing plant and stack designing. Currently, there are two recognised manufacturers of the flow cell stacks globally. Sumitomo manufacturer in Japan produces stacks intended for the vanadium power systems, while Cellenium Corporation in Thailand manufacture stacks of varying designs. On the other hand VRB Power in USA, recently announced the commencement of manufacturing of vanadium stack in the US. Stacks are hand-manufactured and designed to meet a given requirement. There has been a considerable issue in scaling-up the flow cell modules to develop larger sizes with successful flow cells modules, since it is predicted to be marketable in the UK (Rosen 2012).
A significant manufacturing proposal for the generic flow cell system will challenge the existing flow battery manufacturers and suppliers while creating a market for other cell systems such as cerium zinc and zinc bromine. A UK-based firm (RE Fuel) is estimated to have a flow cell stack system of between 5Kw and 9Kw that has a potential of developing to a point of commercialisation. This firm supports vanadium flow cell manufacturers via technological contracts transfer. RE Fuel has previously researched on the use of the flow cells for electric cars, although this project is yet to develop fully, the firm is still developing electric products for stationary uses (Brunet 2011).
Hiltech is another UK R&D manufacturing company that has significantly invested in the development of small scale flow cells. There are chances that there would be residual UK ownership of the parts of zinc bromine scheme, though the details are not available for the current work. Apart from the few manufacturers mentioned, there are several institution groups, commercial firms, and research organizations with direct or indirect experience in manufacturing of flow cell R&D. Some of the known universities developing flow batteries are Newcastle University, Bath University, and Southampton University. From the above mentioned and many other universitie, specific groups have entered into contract with the US manufacturers of flow batteries (Twidell 2006).
The UK firm Urenco has invested in manufacturing and distribution of the flywheel system, also referred to as the Kinetic Energy Storage System, to several railway lines that are applying it in the reduction of the effect of starring power on their local electric power network. The application of flywheels in the railway line is a demonstration that the application of such power systems on other power networks has rapid generation and varying load capacity. The company offers advanced skills and intensive experience in flywheel development technology as well as in the integration of their appliances with the power system. In is expected that the company will advance its production to sustain a head start status in the production and manufacturing of the Kinetic energy storage facilities (Huggins 2010).
Supercapacitors are moderately a new electric power storage technology that is being established by several groups globally. However, it is only a few developers who have commercialized the production. The main technologies that are required in the development of supercapacitors are currently applied in universities and research groups, such as Newcastle University, under the electrical science department. The future market for the supercapacitors is on rise as their performance improves and their cost lowers. Though it is unlikely to be appropriate for storing significant electric energy, over a lengthy time, with advancement, the supercapacitors will be useful for the electric power storage and distribution network (Rosen 2012).
A consortium and consolidation of the universities and some other research institutes in the United Kingdom, should be established to oversee the advancement work on capacitors applying the advanced intellectual resources that are readily available in the United Kingdom. The objective of the research groups should be focused on the development of marketable power storage devices. This should take into account the requirements of integrating the power storage devices with power control and conversion structures. Apart from the R&D in the electric power storage system, future developers should focus on the knowledge of volume manufacturing (Huggins 2010).
Power storage in the UK has the potential to subsidise the process of overcoming the challenges of development of a low-level carbon power system, however, it has been ignored while attention has been given to the energy generation technologies. Electrification of transport and heat in the wake of considerable deployment of irregular generation will lead to difficulties for the supply to meet future power demand. To supply the rising demand the development of both heat and electrical storage systems will alleviate against an unwarranted extra investment in conservative production.
The periodical demand of heat should be translated to electricity demand in the United Kingdom and the rest of the world is to move towards the development of heat pumps to replace gas boilers. The part played by the rechargeable power storage to meet the increasing demand is limited.
The United Kingdom research and development technological capacity is of significant importance. The globally renowned expertise in supercapacitors and battery research should be supported for the future power storage development. Nevertheless, the connection between R&D and technological development is weak. Therefore, an integrated power storage research and development should be conducted to strengthen the link between the research and technological development of power storage system in the United Kingdom.