Needs For New Storage Assets In The Bulk Power Systems
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- Jul 28, 2020 10:17 am GMT
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Needs For New Storage Assets In The Bulk Power Systems
On August 8,2019 two UK’s power plants shut down almost simultaneously in London’s first major blackout for a decade. This event was rare and unfortunate, but compared to recent events across the world it was restored much sooner. Hornsea 1 Offshore Wind farm, and Little Barford CCGT trip, and due to high wind condition, the system inertia was low and the system frequency drops even faster to 48.8Hz. Therefore, Low Frequency Demand Disconnection (LFDD) kicked in which caused the power losses across the country.
LFDD is very painful for those affected but 5% suffered so that 95% stayed connected to a functioning grid. Trains were left waiting on the tracks for hours. Tunnels on the London Underground went dark. A backup generator at Ipswich Hospital failed to start, leaving some to struggle down stairs after the lifts ground to a halt. In total, nearly a million people faced blackouts. This was the last defense measure which ensures grid frequency will return to normal. This triggered a storm of questions about how to avoid another failure.
London Blackout 2019 Experience
Within seconds of problems hitting the grid, a fleet of batteries dotted around Great Britain were able to pump power into the system, preventing a rapid drop off in transmission frequency.Upside Energy is one firm that lent a helping hand by supplying six megawatts (MW) from five large lithium-ion batteries located on a solar farm near Luton Airport. Those batteries responded immediately – actually it was sub-second. Six megawatts may not sound like much. It’s about the same capacity as a single medium-sized wind turbine, but in the context of national electricity supply that can make a difference. The big advantage of batteries is they are not hampered by stalling frequency. They just switch on and send electricity straight out, at 50Hz.
In recent years, more companies that manage battery storage have signed up to provide National Grid with a stand-by service. If there is a sudden fall in electricity supply, the batteries are ready and waiting to switch on.
Another company that manages battery assets is RES. It provided 80 megawatts of power at the critical moment. And Limejump had 91 megawatts’ worth of battery power at its fingertips. Most of those batteries were only installed in the last two years.
Battery supplies provided a much-needed safety net that held the fort while heftier power sources came online, such as the pumped-storage hydroelectric station at Dinorwig in Wales. Batteries alone couldn’t replace all of the lost generation , but they did help to prevent the downward cascade of frequency loss tumbling out of control.
Fail-safes have always been important to the grid. But in the past, operators had to rely on generators or power plants able to boost their generation at short notice. Such sources of electricity have one major drawback versus batteries: they don’t come online as quickly.
Plans and Cost Impact
As National Grid Plc, the regulator (Ofgem) and plant operators investigation underlined the need to bolster an electricity grid increasingly fed by intermittent flows from renewable such as wind and solar. One way is by encouraging construction of new storage assets such as hydro power and batteries that can be called upon almost instantly.
Investors suggested that to improve the power system’s ability to cope with plant failures, the government should change its capacity backup system market, by guaranteeing prices for storage assets for 10 to 12 years to help attract institution investors. That would unlock “huge orders of capital” to fund storage projects for renewable energy sources.
An analyst saw that National Grid does have plans in place to pick up the slack when one source goes down, but there may be a limit to what’s practical. The company could pay for enough capacity in case two power stations go out in a few minutes, but that cost would fall to the consumer. And then what if a third goes out?
Another analysts at Aurora Energy Research Ltd. wrote in a note that the price tag might not be too painful. Doubling the current spending on frequency response, which helps balance supply and demand in the grid, would add about 2 pounds ($2.4), or about 0.4%, to an average annual household bill for electricity.
Motivations for deploying hybrid generator-plus-battery storage
Variable renewable energy (VRE) technologies, such as wind and solar photovoltaic (PV), have proliferated world wide with the help of technology improvements, cost reductions, and policy support. Although many storage technologies exist , declining battery costs have helped stimulate interest in integrating batteries onto power grids at an unprecedented scale.
Such battery capacities could be physically sited at various locations within a grid system; it need not be co-located with VRE technologies or other generator types to provide benefits. Siting choices depend on various considerations including, but not limited to, effective VRE integration. However, project developers have demonstrated increasing interest in “hybrid” projects that co-locate generation with batteries at the point of interconnection.
The concept of hybridization can encompass various technologies and configurations ,such as PV co-located with geothermal or wind , concentrating solar power with thermal storage, wind with pumped hydro storage, combined-cycle plants, and combined heat and power systems. Hybrid systems can also consist of elements that are not co-located; virtual hybrids can employ distributed combinations of demand-side response, generation, and batteries to participate in whole sale power markets.
pros and cons
The economic arguments for hybridizing plants focus on opportunities to (1) reduce project costs, and (2) increase project market value.
- Opportunities to reduce project costs arise from policy incentives, construction and operational synergies, and transaction cost mitigation. Hybridized project construction synergies include shared permitting and siting costs, shared power electronic and general power plant equipment, and shared interconnection agreements.
- Market value benefits from hybridization involve design and operations optimization as well as market participation rules.
Hybridization also poses challenges.
- First, coupling a battery system to a generator behind a point of interconnection might result in operational constraints that reduce the battery’s ability to provide maximum value during critical times. These constraints will depend on the nature of the coupling—e.g., alternating current(AC) vs. DC—as well as the size of the shared interconnection.
- Second, hybridization could result in sub-optimal system siting. When developers site their conventional or VRE plants, they typically optimize based on fuel (or renewable resource), capacity factor, and cost considerations, but for hybrid systems these considerations might result in sub-optimal battery siting, away from areas of congestion and load. Finally, the regulatory uncertainty surrounding direct financial incentives and rules for market participation designs could result in conditions that promote or hinder hybridization.
Hybrid resources pose new technical challenges that must be addressed to enhance participation in energy assets, and capacity markets while clarifying the associated market efficiency and reliability implications. Some of these are:
- Forecasts are needed to ensure reliable operations of VREs.
- Resource plans are conducted through a combination of integrated resource plans (IRP).
- Operational simulation tools (i.e., production-cost models) are also used to evaluate operational and production-cost impacts on future systems given a number of different scenarios.