During the middle of April, the UK achieved a significant milestone: the country ran for three days without coal-fired generation and with renewables contributing about one-third of the generation mix (the balance being primarily gas and nuclear).
On a day in March, wind power had achieved an almost 36% contribution to the national electricity supply. Then over the early May holiday weekend, another record was made, with solar power reaching over 28%. In both cases, these levels were greater than any other energy source.
Such record figures are going to be achieved and exceeded increasingly frequently as renewables continue to grow. But that growth also adds to the challenges of integrating those renewables. In particular, the challenge will be to manage the frequency on the grid, which must be maintained at 50Hz in the UK (±1% according to the licence obligation), as unlike the traditional thermal power stations, renewables typically do not provide inertia.
In addition, as the frequency is more volatile when the system inertia is low, faster response services are required for frequency containment.
Enhanced frequency control
Recognising the emerging challenge, the UK’s system operator National Grid launched the ‘Enhanced Frequency Control Capability’ (EFCC) project in November 2014, supported with £6.9m from Ofgem’s Network Innovation Competition.
The goal of the project is to identify ways to control frequency in low inertia transmission systems, using technologies such as demand side response, solar PV, wind and different ways of operating the combined cycle gas turbine (CCGT) plants.
The project is trialling a novel phasor measurement unit-based wide-area monitoring and control system, which obtains frequency data at a regional level, from which the required rate and volume of very fast response can be calculated and initiated. By doing this at a regional level it is intended to provide control room operators with the accurate, real-time information they need to react much faster to changes to the grid.
Other participants in the project include solar power expert Belectric, which is providing response from PV plants and storage facilities; multinational utility business Centrica, which is providing response from both large-scale generation and wind farms and demand-side management provider Flexitricity. Ørsted and Siemens are collaborating on fast frequency response delivery from wind farms, GE Grid Solutions has developed the monitoring and control system, and the Universities of Manchester and Strathclyde are the academic partners.
Wide-area network monitoring
With the three-year project well into its second half, much of the recent focus has been on demonstrating GE Grid Solutions’ monitoring and control scheme.
Site acceptance tests at Flexitricity’s demand response client site, a chemicals plant in north-east England, and at South Humber Bank CCGT Power Station, have been underway to deliver a demonstrable but secure solution to provide learning for a business-as-usual approach.
Flexitricity, along with the other commercial project partners Belectric and Centrica, also have been performing technical field trials for solar PV, battery, CCGT and demand side fast frequency response.
According to the latest project update, a key learning is that the configuration settings of the monitoring and control scheme need to be defined carefully. An effort has been devoted to establishing a realistic baseline for future deployment.
As the project now enters its closing stages, the focus is on bringing together the learnings and experiences in order to develop a commercial framework to encourage the widest participation in the new market for fast frequency response.
This will be tested in an auction trial to be launched in Q4 and running through 2019.
Lilian Macleod, EFCC Project Manager from National Grid, comments: “The EFCC project will provide greater visibility of the grid system performance by using real-time data. By working together with industry partners, we can lead the transition to a new energy future. Not only will this help to deliver greater value to consumers by running the system more efficiently, it will also evolve and future-proof the grid.”
Support for renewables
Other learnings from the project, which has been shortlisted for the Renewable Energy Association’s British Renewable Energy Awards in the innovation category, pertain to its technical complexity and the need for industry-wide collaboration. More work is needed to understand how it will interface with existing systems and the roles, responsibilities and impacts for both National Grid and the emerging system operators require further clarity.
The business impacts also need to be understood and a cost-benefit analysis is underway by consultancy Baringa Partners.