The UK’s National Energy System Operator (NESO) is preparing for significant solar surpluses this summer, as rapid growth in solar generation threatens to overwhelm the electricity grid during peak midday hours.

NESO, which runs Great Britain’s electricity system, expects periods this summer where solar (and wind) generation could exceed demand—especially on sunny, low-demand weekends or bank holidays. This is driven by record solar output (GB broke two maximum solar power records just last week), growing rooftop and small-scale solar, warmer weather reducing overall demand (less heating/lighting), and the transition away from large traditional power stations.

Electricity grids must balance supply and demand second by second. Solar is “variable” and peaks midday when many people are out, creating what engineers call the “duck curve”—a midday dip in net grid demand that can turn into oversupply as solar scales up. The UK is seeing more of this as renewables grow under net-zero policies.

NESO is clear: These surpluses are “normal features of a modern electricity system with increasing levels of clean power.” They’ve been planning for it since at least 2019, and the system has handled similar (though less frequent) events before.

The Telegraph’s framing (and similar coverage in GB News/Express) highlights risks like potential instability or the need for new measures, tying it to Energy Secretary Ed Miliband’s push for more solar/wind farms.

But NESO itself stresses no threat to supply security—they’re confident the system is “secure, resilient, and well prepared.”

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Solar power threatens to overwhelm electricity grid

Households could be paid to use excess electricity for the first time, energy bosses say

Energy chiefs are drawing up plans to stop the electricity grid being overwhelmed by solar power this summer. The Telegraph has the story.

The National Energy System Operator (Neso) said it would be forced to use “more tools, more often” to keep power networks stable when sunny weather caused surges in energy generation.

This would include paying households and factories to consume excess power for the first time, as well as potentially issuing unprecedented orders to switch off large power stations.

Neso issued the warning as Rachel Reeves travelled to Washington, where she is expected to urge a gathering of world leaders to “follow her plan” to combat the energy crisis caused by the conflict in the Middle East.

At the International Monetary Fund summit, the Chancellor will call for “collective action” while urging countries to embrace net zero to boost energy security.

She will also pledge to “do all in her power to keep costs down for the British public”, warning against “knee-jerk decisions that are unaffordable and deepen economic pain”.

As Donald Trump threatened to blockade Iranian vessels attempting to pass through the Strait of Hormuz on Monday, oil traders warned that the price of crude risked hitting $150 per barrel – up from around $100 today.

Ministers said their priority was to support diplomatic efforts to reopen the strait, but that they were drawing up “contingencies” to guarantee crucial fuel supplies such as red diesel for farmers.

In its summer outlook, published on Tuesday, Neso said war in Iran would push prices higher because of Britain’s dependence on gas, but that it had no concerns about the security of electricity supplies this summer.

However, it warned that gluts of solar power and “low demand” periods were making the grid more difficult to manage as Ed Miliband, the Energy Secretary, rolled out swathes of new wind and solar farms to hit net zero.

Grid instability occurs when energy demand is low but renewables still generate large amounts of power. If not counterbalanced, this can trigger blackouts.

But many onshore solar and wind farms are not directly connected to the main transmission system and cannot be managed by Neso, which is tasked with keeping electricity networks stable.

Read the full story here.

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The duck curve

The duck curve is a graph that illustrates a key operational challenge in electricity grids with high levels of solar power. It shows net load — total electricity demand minus generation from variable renewables (mainly solar, sometimes plus wind) — over a 24-hour period. The resulting line often resembles the profile of a duck: a low “belly” in the middle of the day followed by a steep “neck” ramp-up in the evening.

The term was popularized in 2013 by the California Independent System Operator (CAISO), though similar concepts appeared earlier in research from the National Renewable Energy Laboratory (NREL) around 2008. CAISO created charts projecting how growing solar capacity would reshape the grid from 2012–2020, focusing on a typical spring day (e.g., March 31) when solar output is strong but overall demand is moderate (mild weather, no heavy air conditioning or heating).

The curve is most pronounced in spring and sometimes summer, when solar irradiance is high but temperatures aren’t extreme enough to drive heavy cooling loads. It has deepened in California over time: midday net load has dropped significantly (sometimes below 10,000 MW or even lower on extreme days), while evening ramps have steepened to 13,000–17,000 MW or more in just 2–3 hours.

Challenges the Duck Curve Creates

Oversupply and Curtailment (Midday Belly): When solar exceeds what the grid can absorb, operators may curtail (reduce or shut off) solar and wind output to prevent frequency/voltage instability or equipment damage. This wastes clean energy and can lead to negative wholesale prices (generators pay to offload power). Curtailment acts as a short-term “safety valve” but reduces the economic and environmental value of renewables.

Steep Evening Ramp (Neck): Grid operators must quickly bring online fast-ramping resources to replace fading solar. Traditional coal or nuclear plants ramp slowly and aren’t ideal for this; older systems may struggle, increasing reliance on flexible (often gas-fired) peaker plants, which can raise costs and emissions if overused.

Grid Stability Issues: High inverter-based solar/wind reduces system inertia (the “flywheel” effect from spinning turbines in conventional plants), making frequency control harder. Rapid changes can also strain transmission lines and voltage management.

Economic and Reliability Pressures: Extreme swings complicate market pricing, forecasting, and planning. Without mitigation, it risks higher bills, more blackouts in edge cases, or slowed renewable deployment.

Real-world examples show this isn’t theoretical. California has seen deep dips and large ramps, with actual data sometimes exceeding early projections. Similar patterns appear in Texas (ERCOT), Arizona, Australia, Germany/Europe, and increasingly the UK (where NESO notes growing solar-driven low-demand periods in summer).

In the UK context, rapid solar growth (including rooftop) combined with mild summer days can create surpluses, prompting more use of demand flexibility tools.

The duck curve is typically modeled mathematically as the difference between gross electricity demand (D(t)) and variable renewable generation (primarily solar) (S(t)), over a 24-hour period

$t in [0, 24]$t in [0, 24]

(hours from midnight).

A simple yet realistic analytical model uses Gaussian functions for the peaks, which are smooth, differentiable (useful for calculating ramp rates), and capture the bell-shaped daily profiles observed in real grid data (e.g., CAISO). These are parametric approximations—real operators use empirical time-series data—but this form is widely used in research for simulation, optimization, and forecasting studies.