June 2026 was the UK's hottest June on record. For the first time, The Met Office issued three consecutive Red Extreme Heat Warnings, with temperatures reaching at least 39°C. It was the second record heatwave inside a matter of weeks, following an equally unusual spell in May.

If you run an anaerobic digestion (AD) site, none of that will be news. But heat wasn't the only reason sites went down this summer. That changes what resilience should look like on site and how outages get reported from here.

Heat doesn't stop at the gate

Digester tanks, the vessels in which the process happens, run on a live population of microbes breaking waste down in stages. Those microbes are fussy: a change of just a couple of degrees can throw the whole process off.

The roofs of these tanks conduct outside heat straight in, so once ambient temperature climbs, substrate temperature climbs with it, and the biology can tip out of balance within days. It's a bit like an upset stomach. There’s no quick fix. The biology needs to be nursed back to a stable state, and that takes weeks, with gas production and revenue down in the meantime.

Yet the biggest problem this summer didn’t arrive through the rood, but through the gate. Commercial refrigeration is built to hold temperature up to around 32°C. As June temperatures soared, cooling systems failed across supermarkets in at least six regions. Food Standards Agency rules require chilled food above 8°C to be pulled from sale, so retailers withdrew stock in bulk. That stock was sent to AD plants.

The surge landed on a sector with little room to absorb it. Defra's mandatory weekly household food waste collections, rolled out under Simpler Recycling from March 2026, had already taken up much of the sector's spare capacity. Gate fees, what AD plants charge to take feedstock, rose 75% between January and mid-July, reaching £15 a tonne. The Environment Agency ended up phoning operators directly to find who had spare headroom and redirected tonnage by hand.

This summer made the heat chain clear: refrigeration fails, waste surges, plants that look adequately sized on an annual basis run out of room over a few days.

What that means for maintenance

The Environment Agency's response, ringing round operators to find spare capacity, worked, but it was improvised. There was no standing protocol for what is becoming a recurring event. A July 2026 briefing from the Parliamentary Office of Science and Technology found the UK's AD sector needs to grow roughly tenfold by 2050 to meet demand, while the Climate Change Committee has called the UK's wider adaptation planning "not fit for purpose." Two record heatwaves inside a few weeks in the same year is becoming the new baseline.

As heatwaves cluster, the sites that cope best will be the ones that planned for them. That means buffer tank space you can really use on a hot night, clear limits on what you'll accept before the gate backs up, and cooling systems sized and monitored like winter heating.

Heat wasn't the only cause

At one AD site, a battery that should have been sorted out from incoming food waste wasn't, and took the plant offline for half a day. It's not the only kind of outage that has nothing to do with the weather. Across the sites tem works with, this summer's unplanned downtime also came from a fault on a high-voltage connection and a blockage in an ash system. Add DC cable and string faults, and inverter outages on solar sites, and the same holds: none of it is unusual. It's what running generation assets looks like, heatwave or not.

Whatever breaks, the sequence is the same: output drops, and someone has to notice it, understand it, and pass it on.

Why reporting matters

tem routes more money back to UK businesses by balancing our generation portfolio against business demand. That's money back in the pockets that goes towards keeping the lights on at a rugby club, hiring another teacher at a primary school or securing new kitchen equipment at a community pub.

The earlier we know about an outage, the sooner we can update our forecast of a generator’s output, so the portfolio stays balanced and we create more value for generators and businesses. Outage reporting is one thing within your control to make sure more of that money finds its way back to those businesses.

How reporting works with tem

As soon as you’re aware of an outage, email outages@tem.energy and include:

• your Meter Point Administration Number (MPAN)

• the outage's start and end dates

• if the outage was planned or unplanned

• how much output is affected (percentage or megawatts)

Every generation site goes offline sometimes. Digesters need buffer tanks emptied and cooling systems checked. Engines and inverters need servicing. That's a site being looked after properly.

After this summer, we want more of that, not less: sites that invest in maintenance and resilience will handle the next heatwave better than sites that don't. We'd rather you took the downtime to do it properly than push it until something fails.