It might sound like wasting power but the reason the price is negative is that there is too much production or to put it another way not enough load on the grid. OP is doing exactly what the grid wants, though I think I would try and use it for productive means if I could.
So far the highest I’ve seen is 46p. 12p over my old rate. But these only seem to last for an hour at most. You can view public data on various sites like: https://agileprices.co.uk