Reverse cycle AC units are air to air heat pumps.

Efficiency is variable and depends on outside temperature; there are also water to air versions.
This gets very technical very fast.

The standing charge is variable and depends on the power that you wish to be able to consume, so if you need an extra few kW to run your aircon you have to pay a higher standing charge, all year round, as well as the electricity when you actually use it. Like a gas cooker, a log burner side-steps this standing charge problem for those on a tight budget.

However, a log burner does not heat much of our house, hence the night storage heaters in the kitchen, dining room, study and bathrooms which only need to consume electricity at the lowest tariff.

We have a large thermal store for hot water (and partial under-floor heating, so it doesn't heat much of our house either) but not large enough to transfer enough of our energy requirements from night to day. If only we could have affordable heat pump powered storage heaters, powered by solar voltaic and/or off-peak electricity.

If only the electricity generating companies would pass on the savings they now make by using PV solar farms. I suppose they need to recoup the huge capital outlay they have made. Large scale investment in solar farms is the way ahead in Portugal, not individual households trying to produce their own electricity.

If there's too much solar generated electricity we might eventually be faced with paying a premium price after dark.

That's a good point. What does EDP do with all that spare electricity? No doubt there will be too much generated during the hot summer days in the Algarve and that's my worry with a home-based PV setup. My pool does not need any more heat and nor does the house. My mains water from the kitchen cold tap is 28 degrees Celsius in the summer and that's a problem with bread-making if I forget to chill some water.

Air conditioning and refrigeration demands obviously go up in high summer but we all still want electricity at the flick of a switch day or night. Managing that supply efficiently is probably harder than we think.

Ah well, back to the garden and this wonderful weather.

The generators can turn off the expensive oil fired power stations and the wind turbines if solar production increases.

Not directly related but this is interesting about the UK power consumption/generation

Live monitoring of the UK electricity National Grid