I mean, it's a difference of policy; spend on solar rollout isn't a significant part of either country's GDP.
GDP PPP is probably the more appropriate comparison here, by the way (a big part of the cost of solar isn't buying the actual panels), and China's GDP PPP is 10x the UK's.
GDP PPP is probably the more appropriate comparison here, by the way (a big part of the cost of solar isn't buying the actual panels), and China's GDP PPP is 10x the UK's.