Andy Lester from AROCHA says he is "disappointed but not surprised" that the UK is falling short.
Under European Union (EU) goals, the UK needs to have 15 per cent of energy come from green sources by 2020, including 30 per cent of electricity, 12 per cent of heat and 10 per cent in transport.
Britain's set to outstrip its renewable electricity target by 2020, but it is not yet halfway to the heating goal, and the proportion of renewables in transport fell last year, a report from the Energy and Climate Change Committee (ECC) said.
Speaking on Premier's News Hour, Andy Lester said: "It's time to look again at the alternative energy sector and renewable sector and say we'll have to do something different if we're going to make a meaningful difference to energy use and consumption in the UK."
The ECC committee report said that while the 2020 targets were set by the EU, they had been adopted by the UK and still had many merits even as Britain prepared for Brexit.
MPs said if the UK misses its commitment to the targets it will undermine confidence in its determination to meet other long-term goals, including its legally-binding target to cut greenhouse gas emissions by 80 per cent by 2050.
A Government spokesperson said: "Our priority's providing secure, affordable and clean energy for families and businesses.
"Renewable energy already makes up around 25% of our electricity and we're on track to hit our overall targets.
"The latest Climate Change Performance Index shows the UK is the second best country in the world on tackling climate change."
Listen to Premier's Hannah Tooley speak to Andy Lester from AROCHA here: