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Summer Outlook 2019: Solar PV stable but whole system approach now critical

Image: Getty.

Image: Getty.

National Grid expects minimum summer transmission system demand in 2019 to fall broadly in line with last year’s, owing to a collapse in new solar deployment.

The Electricity System Operator (ESO) has also paid testament to its advanced, machine-learning forecasting tools, but said whole system thinking will need to become far more prevalent as the country’s energy mix continues to change.

Today National Grid’s ESO function released this year’s Summer Outlook report, its annual summary of the grid balancing challenges the ESO expects to encounter as demand on the transmission system changes.

National Grid expects transmission system demand to fall broadly in line with last year’s figures, owing principally to a collapse in new solar PV deployment.

Peak electricity transmission demand is forecasted to be 33.7GW while minimum demand is expected to be around 17.9GW, both figures down 100-200MW in comparison to last year’s expectations.

Deployment of new solar PV capacity, seen as a fall in transmission system demand due to its location on the country’s distribution grid, has fallen in line with the retreat of subsidies.

And National Grid’s understanding of and ability to forecast solar generation has also improved. It has developed a machine learning-based national solar power model, implemented last September in association with Reading University, whichhas reduced the ESO’s absolute solar forecasting errors by around 33%.

The need for such tools was brought into sharp focus just last weekend, when unseasonably bright weather conditions sent PV generation to more than double its seasonal average and some 700MW above forecast which, when combined with significant quantities of wind generation, sent the country’s wholesale market into negative pricing for an “unprecedented” six hours straight.

Based on its current data, National Grid has said in its outlook report that levels of inflexible generation on the grid plus flexible wind will exceed minimum demand during some periods this summer, requiring intervention.

As well as utilising the country’s pumped storage fleet, flexible wind output at a national level may need to be curtailed via the Balancing Mechanism or direct trades, and interconnector imports may need to be reduced.

However, the ESO has also said that whole system thinking is to become increasingly important as trends related to decarbonisation and decentralisation drive the country’s gas and electric grids together.

Writing in the outlook’s foreword, National Grid’s director for UK system operator Fintan Slye said there would be “increasing interactions” between gas and electricity markets and operations as new energy challenges emerge.

The ESO has illustrated this my showing how renewable and gas-fired generation mirrored each other throughout last summer, creating additional volatility that requires more hands-on management.

Image: National Grid.
Image: National Grid.

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