"[Wood composted with urine could generate temperatures] high enough to be useful for heating buildings and, with a bit of a boost, perhaps for providing hot water as well. To commercialise the idea would mean designing a suitable reactor and heat exchanger, but the waste-wood fuel would be cheap. How you would go about gathering the necessary urine in bulk, given the expense of installing a network of suitably dedicated collection points, is not clear."

Paywall, so I couldn’t read the whole thing. But this reminds me of rural areas in India, where they use dung for heating. Quite a lot less hygienic than urine, given that urine starts out sterile.

The usual concern with these alternative energy systems is whether they provide more energy than they use. There have been plenty of cases of businesses that sell expensive recycled products under the guise of being eco-friendly, but it turns out that the recycling process actually ends up being more harmful than just disposing of the materials.