The number of patents for renewable energy products and systems filed worldwide has fallen by 42per cent in the last three years, suggesting that global investment and innovation in green energy is stalling, it has been claimed.

Research by commercial law firm EMW found the number of patents for solar power, wind energy, biofuels and waste-generated energy fell from 35,590 in 2012 to 20,655 worldwide last year.

It says the fall has been principally driven by oversupply in the solar panel market thanks to Chinese mass production hitting profit margins. Solar-related patents accounted for two-thirds of total patents last year.

EMW adds this has been exacerbated by subsidy cuts for renewables in many countries, including the UK, as well as the dramatic fall in oil prices that has widened the price differential between low carbon and conventional energy.

The firm's energy head James Geary said: "The boom in green energy innovation that we have witnessed in recent years has peaked for now, suggesting that investment in R&D is tailing off across the renewables sector".

He added: "This is not good news for the green lobby and could well hamper efforts by governments around the world to meet their carbon reduction targets."