The UK’s solar farms may require additional upgrades to ensure they can ‘ride through’ system faults, instead of acting in a way that exacerbates the system fault, as happened during August’s blackout. The upgrade would require a change to inverter settings.
At the time of the August blackout the industry was gearing up for a long-planned programme to adjust protection settings on all distribution-connected generation to ensure it does not self-disconnect too quickly in response to network conditions. Changes have to be made to up to 50,000 generation sites with capacity totalling 15GW, in a programme that began in May and is currently due to be complete by April 2022.
That change programme focuses on relays, at the site boundary or on specific equipment such as individual wind turbines. Inverter changes would add to the burden of work for solar farm owners.
Previously, the industry change group did not believe that many inverters had specific settings that would disconnect in the event of fast changes in system frequency. However, the rollout programme received feedback that “significant numbers” of inverters have discrete settings. Programme managers have asked for further information, saying, “We now know that many, but not all, inverters do have these settings.”
A request for information has now asked inverter manufacturers about how they addressed loss of mains protection in their devices, and particularly:
- What settings are included as factory defaults? Specifically do these include either or both RoCoF and VS settings, and what are the default values used?
- How new settings can be applied quickly and easily to units that are commissioned.
A stakeholder event in April set out the change programme for the originally-planned relay upgrades. The upgrades are expected to cost £1,00-1,500 for the simpler sites and £2,500-4,000 if more complex work is required. Owners must make the change, but will be able to claim compensation for the cost – but only if they act early enough, as the funding pot is limited. The payment programme is intended to be an incentive to make the changes quickly.
It has taken seven years to agree a modification to the Grid Code and develop an implementation plan, although few disagreed with the need to make the change. Scottish Power Renewables raised concerns over whether smaller power plant would be damaged if they had to ‘ride through’ faster frequency changes and it wanted the new rule to be applied on a ‘case by case’ basis. And it raised concerns over the speed of implementation, saying “owners of existing old generating plant will need to investigate further if these old generators are able to withstand the new RCOCOF setting.” But a working group on assessing the proposed change said it had not found evidence that damage was likely.
It was clear that costs would vary from site to site. Some would require a one-off change in setting levels. SSE Generation pointed out that some wind farms would require changes at individual turbines as well as at site level.
There were also questions over who pays. Because of the shift towards decentralised generation the need for upgrades fall not only on large specialist power generation plant owners but also many other types of owner. UK Power Reserve said, “The upfront cost may deter smaller generators and hinder engagement, …
“The cost of implementation should be socialised across as the industry as security of supply is an industrwide benefit. Socialisation of the cost should also avoid any market disturbances for smaller parties.”