It also found that in several parts of Scotland, homes fitted with solar PV panels had enough sunshine to generate more than 100% of the electricity needs of an average household.
Wind turbines provided 863.5 gigawatts (GW) of electricity to the National Grid during May, an increase of almost 20% compared to May 2016 when wind energy provided 692.9GW.
Overall the data showed that wind generated enough output to supply 100% or more of Scottish homes on 11 of the 31 days in May.
Homes with solar power panels generated more than 100% of average household electricity needs in Aberdeen, Dumfries, Edinburgh, Glasgow and Inverness.
The sunniest place was Lerwick on the Shetland Islands, which generated 114% of an average household electricity demand, followed closely by Dundee with 112%.
In contrast, there were nearly four months when solar power supplied less than 10% of installed capacity to the UK grid, according to the GMB trade union.
GMB Congress in Plymouth was told that in the year from 1 June 2016 every 1 in 3 days has been a low solar day when solar produced 10% or less of the installed capacity to the National Electricity Grid.
The days of low sunshine were 1 day in June 2016, 1 day in August 2016, 5 days in September 2016, 7 days in October 2016, 18 days in November 2016, 24 days in December 2016, 26 days in January 2017, 21 days in February 2017, 8 days in March 2017 and 3 days in May 2017.
Justin Bowden, GMB National Secretary, said: “We have to face up to the fact that the UK’s wind and solar fleets combined produce no electricity for more than half the time – and that they are a part of a balanced energy mixm not a panacea.
“Over the last 12 months there were 144 days when solar was supplying 10% or less of installed capacity to the national electricity grid.
“In the real world of the here and now we have to keep the lights turned on, homes heated and the economy functioning on the days when the wind doesn’t blow and the sun doesn’t shine.
“This means having a base load electricity capacity we can rely on until there is a breakthrough in large-scale, economically viable and reliable solar or wind power storage.
“The renewable energy suppliers cannot just shrug their shoulders on cloudy, windless days, or when it is dark, and pretend that wishful thinking will keep the lights on.
“Until there is a scientific breakthrough on carbon capture or solar storage, then nuclear and gas are the only reliable shows in town which those advocating a renewables only energy policy have to accept.”