Not GP but I assume the fixed prices have to be fairly high to account for people using lots of power during peak demand when most people use lots of power?

Exactly.

For me I'm happy to avoid big power draws during the peak times, as I'm 'compensated' for it outside of those periods with a little planning. Downside is when the wind is not blowing AND disruptions to global energy markets - I'm exposed to that, warts and all, there's definitely been an increase in prices over the past 4 weeks, although there has been a few days (including today) where the wind has basically made the energy free and my average unit rate is dropping again.

It's not only that, you also need reserve for the intermittent sources like wind and solar.

I live on an island, we have big batteries that can supply up to 15 MW of power for a period. In the Netherlands we have natural gas plants that are called up when the wind or sun output decreases, lest the grid frequency drop.