Wind generation was the largest contributor to Britain’s power mix for a record 28 successive hours in May – the first time this trend has exceeded 24 hours. However, data recorded for the first week in June by EnAppSys, indicates the value of developing an energy storage complement.

Over the second May bank holiday weekend, wind farms set a new record by providing the highest contribution to the overall fuel mix for a period in excess of 24 hours for the first time. The longest such run previously had been exactly 24 hours on 14th to 15th March 2018, but this record has now been breached.
“Over the 28-hour period when wind provided the largest share of generation, wind farms generated approximately 233GWh of power (including estimates for embedded wind generation), which amounted to 31 per cent of the power being generated or imported throughout the period,” Rob Lalor, senior analyst at EnAppSys told Power Engineering International.

“These strong levels of wind generation combined with relatively high levels of solar energy output ensured that 52% of power generation during this period came from renewable sources; with an additional 25% coming from nuclear plants.”

“This trend came to an end at 6pm on 27th May 2018 as gas generation was turned up for the evening peak, but the period saw less than one fifth of power come from fossil fuel plants, with the balance coming from interconnector imports. During this period coal plants generated only 2.5GWh, which amounted to just over 1% of the levels of wind generation achieved over the same period.”

Following the period, levels of wind generation backed off heading further into summer, with Bloomberg reporting on the low generation over the seven days from 30th May to 5th June 2018.

This period saw a reversal of fortunes, where wind farms provided on average less than 1GW of power. This was a key reason why levels of renewable generation fell to just 18 per cent of total power generation over this seven-day period. The impact was a climb in levels of gas-fired generation to provide just under half the overall fuel mix over this timespan, but coal activity remained very low due to the very high carbon prices.

Wind farms are highly seasonal and tend to generate power mainly in the first and last quarters of the calendar year. This is why May 2018 also saw the lowest average monthly wind generation of the year so far. However, with demand also dropping away over the summer months, it still becomes possible for wind to set generation records during this period.

“With the UK set to focus on wind as a primary source of renewable power, periods of low generation do highlight the future value of high-volume storage projects, with Coire Glas being the most high-profile example,” says Lalor. “These projects focus on having the ability to deliver large volumes of power for days at a time, filling any gaps in the market as required.”

“The case for these projects becomes stronger as levels of wind output grow and this will be aided by improved interconnections that are being finalised between England and Scotland via the Western Link interconnector. However, this will be offset by the reduced number of import-export cycles versus short-duration fast-acting storage.”

In terms of using current battery technology to increase the viability of subsidy-free wind farms, the current cost of grid scale batteries does not support the case for building them in the UK to provide ‘time shifting’ of power output from a wind farm without government support.

“Currently the cost of a battery is £450/kWh of energy stored and has a life of 3,000 to 10,000 cycles. To recover the cost of the battery investment would therefore require more than 45p/KWh gross profit for each cycle of operation. Over 2017 the average daily spread between the peak price and the lowest price was 37p/kWh. Allowing for efficiency loss and cost of capital, a project would struggle to achieve payback. If renewable build out increases, the spread between low and high prices will also rise, providing a better economic case for batteries to be installed alongside renewables.”

“It is likely that the cost of batteries will continue to fall, improving their economic case, but for time shifting the use of flow batteries will become part of a grid scale storage solution as they offer the potential for greater £/kWh installed capital cost saving.”

During the initial peak wind period, the combination of high renewables and low demand made conditions tricky for thermal generators, but by managing imbalances between supply and demand via the Balancing Mechanism, average system prices for the day were exceeded for the following nine days, according to the energy monitoring specialists.

“This suggests that the system and National Grid are dealing well with the challenges being posed by renewables, although as offshore wind capacity continues to climb and if nuclear capacity remains high via new builds, the share of generation from fossil-fuelled sources could fall to critical levels.”

“This activity highlights the on-going changes being seen in the market and starts to indicate future potential activity as renewable levels continue to grow, with the market falling back upon its levels of gas supply during periods when wind farms are unable to deliver.”