This has been my latest project. An automatic spa pool cover I made from an old trampoline frame, metal bed frames, old pipe clothes line, used automatic gate opener, two garage door springs and a few other bits.
It has a remote control to open and close, with another button inside the spa. Runs on 12 volt car battery so can still operate if the power goes off.
Solar panels on the roof heat the pool, water is pumped through panels using a dishwasher pump and a hot water thermostat.
The lid can be stopped in any position, so it acts as a roof when it is raining. Still have to finish off the stand for the panels and fit PLC to control water temp.