House Extension and Modification. 1. Have Combi, want to add thermal store.

[mjolnir]

I had to start somewhere so first things first. I have a SolarPV setup 4.8kWp and use some of the excess to charge a Nissan Leaf. The car is not always there and a lot of energy goes back to the grid. We are planning a house extension and I want to take the opportunity to use more of this and less gas for heating water.
I also want to replace our wood burner with one which has a boiler.
I currently just have a combi boiler. If I install a thermal store will this work with the  ImmerSun and the wood stove boiler AND the combi boiler as a backup ?