In its future energy scenarios report network operator, the National Grid, said even its most optimistic scenario suggests the UK will miss the 15% energy consumption from renewable sources target by two years.
"While we believe the electricity sector can achieve its contribution to the 2020 renewable target, we believe the progress required in the heat and transport sector is beyond what can be achieved on time. As a result, none of our scenarios achieve the 15% level by the 2020 date. Our [most optimistic] Gone Green scenario is the earliest to reach this, meeting the target by 2022," the report said.
"The sector requiring most development is heating. To meet the 15% target, renewable heat needs to increase by around 60TWh from 2016 levels. Over the past four years there was an increase of less than 10TWh, therefore the pace of change needs to increase significantly," according to the National Grid.
Scottish Renewables chief executive Niall Stuart criticised the UK government for cutting support for onshore wind and solar before the 2020 target was met.
"The irony is that there are a huge number of renewable power projects, which could provide cheap and clean electricity before 2020 and make up the shortfall from heat and transport," he said.
"However, onshore wind and solar — the two cheapest forms of clean electricity generation — are unable to bid for long-term contracts for power, and other technologies cannot access support until 2021 at the earliest," Stuart said.
Dr Jenifer Baxter, head of energy and environment at the Institution of Mechanical Engineers, said: "This confirms that the recent cut in renewable energy subsidies, as well as the lack of clear policy to encourage low-carbon technologies, has led to a drop in investment in renewable energy.
The National Grid put forward the case for repowering onshore projects, as the earliest sites will begin to reach the end of their operational lives in the next decade.
"In the event that repowering is not a viable option and wind farms decommission after 25 years, between 2016 and 2030 only an estimated 1GW will come off the system. However, in the following decade, 7GW of capacity will be lost. This would increase the dependency on alternative new low-carbon projects to achieve the 2050 carbon reduction target," National Grid said.
"Repowering in this way exploits the benefits of the much larger capacity that current turbines have compared to those of the 1990s. This level of increased productivity can be expected to continue until the mid-2020s. At this point, due to a marked increase in the capacity of turbines deployed post-2000, the benefits are not expected to be quite as significant (assuming no major step change in onshore wind turbine capacity).
"Provided that two thirds or more of existing onshore wind farms repower, and at the same time increase their capacity by at least 50%, the current 8GW of onshore wind capacity currently on the system will still be available in 2040," National Grid's report read. The operator also said more modern projects might opt for partial repowering to extend the life of the projects.
The report is optimistic however about the growth of interconnectors in the UK, even its lowest "no progress" scenario predicts an increase of interconnected capacity from 4GW to 11GW by 2030, with a possible 23GW in its most optimistic picture.