Striking the right balance

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Selling surplus energy to a transmission system operator (TSO) is an important source of income for many operators of renewable energy systems. However, as Paul McClean of embedded monitoring system specialist eMS explains, this income can be usefully augmented – provided monitoring requirements are met – by delivering balancing services, such as fast/firm frequency response (FFR).

TSOs like Eirgrid and SONI in Ireland, and National Grid in Great Britain, face a dual challenge. They must increasingly accommodate energy from non-traditional sources, but they must also satisfy their obligations to ensure the stability of the networks they operate and to maintain supply frequency and voltage within prescribed limits.

These challenges are not new, but they were easier for TSOs to meet when almost all energy was produced by generating plant, over which they had considerable – if not complete – control. Today the picture is very different. In 2017, renewables accounted for 29% of total installed generating capacity on the island of Ireland. The figure for Great Britain was around 28%. These percentages are growing, so relying solely on traditional generating plant alone to ensure grid stability is no longer possible.

For this reason, TSOs are now encouraging operators of renewable energy sources, energy storage facilities and companies with standby power plants to help maintain the stability of the supply system by providing “ancillary services”. These include offering a fast response to frequency dips by bringing additional generating capacity online. The TSOs pay energy source operators for providing these services. The payments include an amount for making the facility available and an additional amount when the service is provided. Payments depend on the amount of power offered, the time it is available for, and the speed it can be brought on line.

These payments make providing ancillary services an attractive option but life is never completely straightforward, and there are a couple of caveats. The first is that TSOs are usually only interested in signing up larger energy suppliers – typically with generating capacity of 10MW or more. The second caveat is that the TSOs lay down stringent requirements for the energy supplier’s monitoring systems.

To satisfy the first caveat, energy suppliers can work with an aggregator that combines the capacity of several small suppliers to reach a TSO’s minimum. The second caveat may seem onerous, but it is in fact perfectly reasonable because without monitoring, TSOs can’t confirm that they are receiving the ancillary services they’re paying for!

The details of the monitoring required differ between the various TSOs, but information is readily available online. For Eirgrid and SONI, the relevant document is ‘DS3 Performance Measurement Device Standards for Fast Acting Services’, while for National Grid it is ‘Frequency Response Monitoring (Ancillary Services Business Monitoring).’ These two sets of requirements have much in common.

They both stipulate that the monitoring system must provide data acquisition and data storage facilities, as well as network connectivity. The system must monitor and record parameters such as voltage, current, apparent power, real power, reactive power, power factor and frequency. It must offer high accuracy and the measurements must be precisely timed. For data delivery, however, requirements differ. SONI and Eirgrid want data in a defined layout using CSV format, whereas National Grid requires direct access to data via a webserver built into the monitoring system.

How can operators of renewable energy sources meet these monitoring requirements to enjoy extra income from providing ancillary services? Fortunately, well proven web-enabled multifunctional monitoring systems with all of the necessary facilities are now available, and the best of these have been confirmed as satisfying the stipulations of Eirgrid, SONI and National Grid. In fact, the systems do even more. The data they record and analyse is a powerful aid for optimising plant operation, determining supply quality, analysing performance under normal and fault conditions, and for fault finding.

What can users expect from a monitoring system? 

It should be physically compact and robustly constructed. It should accept inputs from standard current and voltage transformers, and it should feature powerful analytical facilities to generate the derived parameters required by the TSOs. Further, as TSO requirements will undoubtedly continue to evolve, provision for customisation is essential. 

The system should provide consistently high accuracy in acquiring, analysing and recording data, and the data storage media should be static, non-volatile and offer large capacity. Measurements must be precisely timed, which is best achieved by using GPS data to synchronise the timing of the monitoring system. Finally, the system must support the TSO’s favoured data delivery method.

Ancillary services are of enormous value to TSOs in helping them to maintain the stability of the supply grid while meeting statutory requirements for supply voltage and frequency. Offering ancillary services is a valuable source of additional income for energy providers and the key to unlocking these benefits is flexible and dependable high-performance monitoring. 

This is readily achievable, but to guarantee success it is vital to consult with an experienced supplier that fully understands the often complex issues involved, that offers proven technology and that provides solutions tailored to meet the exact requirements of each application. eMS is such a supplier.