Air Source Heat Pump: Electricity bills have tripled since having solar installed - any advice?

Without any more to go on this is what I suggest you do: 

Turn the hot water down to 50 degrees C. Make sure you’re only heating it on a schedule, not on ‘reheat’. I heat our hot water at night during my cheap rate hours and again in the afternoon when the outside temperature is warmest. The space heating (ie radiators) won’t get any heat when the hot water cycle is running so do it at a time when you won’t notice it missing. Mine takes about 45 mins. If you have a ‘legionella’ or disinfectant’ cycle enabled you can disable it. It’s reckoned to be unnecessary in a domestic setting where you’re using and refreshing the contents of your hot water cylinder every day.

Next, rather than have the radiators on for a few hours at a time (generally an inefficient way of running a heat pump) run it at a lower temperature for longer hours. Without knowing what heat pump you have it’s a bit difficult to explain the changes you need to make. Mine is a Daikin Altherma 3 and I have a Madoka room sensor. I’ve set the controls to Weather Dependant, which means the radiators are cooler when it’s warm outside and warmer when it’s cool outside. You may have been set up with a fixed flow temperature which is not an efficient way to run it. Open all your radiator valves (the adjustable ones) fully so they all receive heat at the same time. The heat pump needs a good flow of water pumped around and there’s no benefit closing some off here and there. If that sounds extravagant then don’t worry, you’ll save by the hp running at tickover rather than having to burst into life every time a change of heat is called for, as it is currently. You can turn the overall temperature down to use less electricity rather than turn it off. This does all sound involved I know. With more info on your system I might be able to explain better how you can do all this.