Wood pellets

It was good to see the fuel for WWT's Slimbridge reserve coming from a renewable resource, but, as the supplier admits:

Until recently, it was not easy to source good-quality, consistent, reliable, well-priced wood pellets in the UK. [...] most of the European pellets available for the UK market come from northern Europe - particularly Scandinavia (primarily Sweden and Finland), the Baltic countries (Latvia, Lithuania and Estonia) and Russia. The Swedes and Finns are particularly advanced in trading pellets internationally, both their own and those produced by their north-European neighbours.

So at present there is a non-renewable penalty to pay in the form of transport costs.