What Happens to Your Energy Bill When the Wind Doesn’t Blow

Low wind periods can add 30–50% to UK electricity spot prices in under 24 hours.

In January 2025, the UK experienced four consecutive days of unusually low wind generation. Offshore wind output dropped to less than 4% of installed capacity. Gas-fired power stations stepped in to fill the gap. Wholesale day-ahead electricity prices moved from approximately £80/MWh to over £130/MWh within 48 hours.

Business owners on fixed contracts didn’t notice. Their unit rate was locked. But businesses on flexible contracts, pass-through pricing, or out-of-contract tariffs paid the spike. The UK now generates approximately 30% of its electricity from wind on an annual average basis. On calm, anticyclonic days — which tend to coincide with winter cold snaps — it can drop to single digits. The gap between peak and trough is a structural feature of the renewable energy transition, with direct implications for how UK SMEs should think about energy procurement.

How the UK electricity market prices wind intermittency

The UK electricity market operates as a marginal pricing system. The price for all electricity in a given half-hour period is set by the most expensive generator required to meet demand. Gas-fired generation frequently sets the marginal price — particularly when renewable output is low. When wind is high, a greater proportion of demand is met by zero-marginal-cost generation, wholesale prices fall. When wind is low, gas plants move up the merit order. More gas is burned. On the coldest, calmest winter days — the “dunkelflaute” — electricity prices can reach several times the annual average.

The direct business impact by contract type

Fixed-price contracts: You are fully insulated from day-to-day price movements. The supplier has already priced the expected wholesale cost — including modelled intermittency risk — into your unit rate. For the vast majority of SMEs, this is the appropriate structure.

Flexible or half-hourly settled contracts: You are buying energy against actual market prices for each half-hour settlement period. When wind is low and prices spike, you pay the spike. The net effect over a year depends on whether your consumption pattern aligns well with low-price periods — which requires active management.

Pass-through contracts: The wholesale element may be fixed, but charges that respond to grid stress events — including Triad avoidance — can move. High-demand, low-wind periods trigger Triad periods, which attract surcharges. Missing Triad avoidance on a larger site can cost thousands.

The Triad system and why low-wind days matter most

Triad charges (TNUoS Triad charges) are assessed on the three half-hours of peak UK electricity demand between November and February each year. Cold, calm winter evenings — when heating demand peaks and wind generation is minimal — are exactly when Triad events occur. A business consuming 500 kW during a Triad half-hour can face a Triad charge of £10,000–£25,000 for that year, depending on TNUoS rates and location.

Businesses that understand this can reduce Triad exposure by curtailing consumption during forecast Triad windows — typically 4–7pm on cold, calm weekday evenings in winter. This requires nothing more than awareness of when to switch off non-essential loads.

What SME owners should take from this

• If you’re on a fixed contract, your supplier has built intermittency risk into your rate. You’re paying for certainty. That’s usually the right trade.
• If you’re on a flexible contract, make sure your adviser is actively managing your exposure — not just billing you against market prices.
• If you have a half-hourly meter, review whether you’re managing Triad exposure actively. If you don’t know your Triad history, you should.
• If you’re a larger energy user with flexible processes, demand-side response and embedded generation can convert intermittency risk into revenue opportunity.

Telnergy reviews contract structure, Triad exposure, and non-commodity charge profiles as standard. If you’re currently on a contract that leaves you exposed to intermittency without knowing it, that’s a conversation worth having before your next renewal.

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