Running water heater off gas or electricity

[MamaBear7a]

We have a boiler that warms the water in a tank for showers etc.
We also have an element within the tank so we can run it off electricity instead.
Currently our gas price per kWh is pretty much the same as our electricity per kWh (with about 0.3p).
My brain says that as the unit is the same 1kWh of gas will warm the water up as much as 1kWh or electricity but I have nagging doubts I've made too many assumptions. Maybe one is more efficient than the other?
Also if I knew which was better it may influence whether I go for a fixed tariff in the near future.

Any ideas?

Go solar to heat the water in your tank. You may have to top up with the boiler over winter, but in the summer should save you a fortune. We're central southern, and our panels face SW, we turn the boiler off from March to September/October.

Currently our gas price per kWh is pretty much the same as our electricity per kWh (with about 0.3p)

Are you sure about that?

Standard price for gas is around 8 p per kWh, electricity about 30 p.

But you have to spend thousands of pounds to 'go solar'. It takes many years to recoup the investment.

Yes we are on solar and grid, hence our prices being so similar. We have a battery, but the weather has been so bad recently it sees us through a basic day combined with the PVs but we still have to run washing machines/ dishwashers at night. In the better weather of June we did use mainly solar with the occasional top up of gas but that won't be feasible in autumn/winter.
This will be our first winter with the current set up and I'm trying to do the maths in advance.

We have this:
https://www.marlec.co.uk/product/solar-iboost/
About £330 plus fitting.

When you're generating 0.2kw above what you're actually using, the excess generated energy diverts to heat your water via an immersion heater. Should pay for itself within 2-3 years.