TW9

If you want to manage the electricity used by heat pumps you wouldn't do it by cutting all the power. That risks causing all sorts of problems. You'd do it by remotely connecting to the controls.

It seems to be mostly oil companies promoting hydrogen, not environmentalists.

Different chemicals depending on the time of year? Red flames for Christmas. Green for St Patrick's day. A cheery yellow in summer.

Energy Catapult showed that heat pumps can work in all types of property (assuming there's space to fit one) - https://es.catapult.org.uk/news/electrification-of-heat-trial-finds-heat-pumps-suitable-for-all-housing-types/ The Fully Charged Show did an episode on hydrogen. The expert they talked to explained why hydrogen is not a good option in pretty much every situation (particularly home heating) - https://youtu.be/MgmBkvrO0Dg

We use it. We shift as much load as we can into the cheap periods (water heating, washing machine, dishwasher, car charging). We also adjust the settings on our battery to limit our use of the grid during the expensive period. Our heat pump is controlled by a Tado so we have made small adjustments to the timings to try and push use away from the peak period. It's harder to do this with most heat pump controls. Without an EV or a battery I think you might struggle to save more than pennies. If you're already on Octopus there's an app called Octopus Compare that tells you how much you would pay each day on different tariffs. So you could see if it's worth going for without actually moving it.

I read that as a 12kW hybrid inverter with 11.6kWh of batteries. No solar panels.

That's a recipe for neighbourhood discontent. There will be arguments about who is using more than their fair share.

Yes, it's normal for the tank to gradually lose heat. How much it loses will depend on where it is and how well the pipework is insulated (I'm assuming it's a modern tank with built in insulation so there isn't much you can do to improve that). We heat ours to 50 degrees, which is hot enough.

I suspect the radiators aren't able to put out enough heat because they're too small. Did you have a heat loss assessment done on the house before the heating system was specified? This will tell you how much heat each room needs so you can check this against the radiator specifications. Make sure you check the spec at the correct flow temperature.

https://www.ebay.co.uk/itm/203546625381?hash=item2f64530565

One thing to add to Nick's excellent advice, the application you need is a G99 (not a G98) as your inverter is over 3.68kW. It doesn't matter that it's export limited. As Nick said, this has to be approved before connecting the system to the grid.

My Ecodan heats to 55 degrees so there's no reason yours shouldn't be able to. What happens when you try to increase the temperature on the controller?

What would happen if you put the CT clamp for the iboost on the inverter output? Would that result in the iboost attempting to divert to the immersion whenever you're generating electricity? The immersion will take as much of the solar electricity as it can leaving the rest to go to the house. Or is that utter nonsense that won't work?

How would you avoid DNO approval? I thought as soon as you connect any generation to the grid they need to know about it.

Unless you build a system that is entirely off grid you can't avoid DNO approval. The DNO are interested in the export capability, not in what it actually exports. So if you add more panels on a separate inverter and/or a battery they need to know.