Energy produced by the UK’s renewable sector outpaced fossil fuel plants on a record 137 days in 2019 to help the country’s energy system record its greenest year.

The report by the Carbon Brief website found that renewable energy – from wind, solar, hydro and biomass projects – grew by 9% last year and was the UK’s largest electricity source in March, August, September and December.

The rise of renewables helped drive generation from coal and gas plants down by 6% from the year before, and 50% lower from the start of the decade. Meanwhile, the number of coal-free days has accelerated from the first 24-hour period in 2017 to 21 days in 2018 and 83 days last year.

The report’s findings come after National Grid confirmed that “low-carbon” electricity – including energy from renewables and nuclear plants – made up more than half the UK’s energy mix for the first time last year.

Although the UK’s low-carbon electricity production doubled over the last 10 years and despite the 2019 record, growth slowed sharply in the last year of the decade because of a string of outages at the UK’s ageing nuclear power plants. Carbon Brief warned this could slow progress in the years ahead.

Simon Evans, the author of Carbon Brief’s report, said: “Our analysis shows that rapid gains in decarbonising the power sector can’t be taken for granted and won’t just continue to magically happen forever.

“The government’s seemingly ambitious target to roll out 40GW of offshore wind by 2030 won’t happen without policies to back it up – and it may not be enough on its own to meet UK climate goals, without contributions from onshore wind, solar or further new nuclear.”

Audrey Gallacher, Energy UK’s interim chief executive, said the report was a “stark reminder” that the energy industry must go “much further and faster” to help meet the UK’s climate target.

Britain has set a legally binding target to create a carbon-neutral economy by cutting emissions to net zero by 2050. This means the UK must only emit as much carbon as it is able to capture and store.

The target will require a huge increase in low-carbon generation to help meet the UK’s rising need for clean electricity for transport and heating. However, the government’s delayed energy white paper is yet to emerge.

“The amount of low-carbon power produced has doubled over the last decade but we need to go above and beyond that to keep pace with our climate change targets, especially with overall demand set to increase, rather than falling as it has done in recent years,” Gallacher said.

“This underlines the urgency of increasing all forms of low-carbon generation – and why we need to see [the government’s] energy white paper as soon as possible, with action and policies that can enable the required investment and innovation to make this happen.”