Letter: But how much power does this thing produce?

From Sam Edge, Ringwood, Hampshire, UK

You say that a hygroelectric generator based on graphene produces 1.5 volts and that this is equivalent to an AA or AAA battery (1 December 2018, p 20). But I want to know what current it delivers, and so its power in watts.

The editor writes:
• The experimental device produced of the order of a microamp – and an AA cell may deliver 1 amp for an hour or so. What was interesting was that it was possible at all.