Solar power currently accounts for about 4% of the UK's electricity. After a period of rapid growth - much of it encouraged by various subsidies such as the Feed In Tariff (FIT) - increases in solar generation have recently slowed. The National Grid figures for solar have been reduced recently, but future growth to up to 4 times the current level of power is still expected.
The National Grid "best case" outlook for maximum solar power is just over 50GW in the Consumer Transformation scenario, which should generate a little over 50TWh in 2050, which would be about 13% of the UK's needs at that time.
Solar power is intermittent. None is generated when it is dark at night - which in winter months includes the period of peak demand - and on dull days generation can be significantly reduced.
Solar power can offset some some fossil fuel usage, but only when the sun is shining.
Solar power is at its most helpful when it can also be stored, preferably at a location close to its source. Typical examples include home "packages" comprising solar panels and batteries for storage.
There are some larger scale "solar parks", such as Shotwick in Flintshire, which has a maximum power of 72.2 MW.