You are working on a complicated way to:
- Convert solar radiation (aka sunlight) to electricity, typically at a rate of around 15% efficiency
- Use the electricity to heat water at a low rate (i.e., much lower than the design capacity of the water heater)
Now if all this was essentially "free", it would be well worth it. But we're talking inverters, converters, batteries, capacitors, etc. Not free by any stretch. Plus the electricity generated is not available to run other things that require electricity - computers and other consumer electronics, fans, lights, etc.
On the other hand, if you use the solar radiation to directly heat the water, it is far more efficient. This does require some additional equipment - the solar collector and piping from/to the water heater. But it works. In fact, Israel (and I think some other countries too) use this for residential hot water on a regular basis. Then your solar panels are free to provide electricity for everything else.
This problem is not unique to solar energy. For example, "ordinary" electric heat (aka "giant toaster") is 100% efficient at converting electricity to heat, but the electricity is, in many places, generated very inefficiently from fossil fuels. In that situation, using natural gas to directly generate heat is much more efficient. (Leaving out the "heat pump" issue for the moment - that changes the equation in other ways.) This is especially the case if you use a generator for backup power - a home generator will generally be less efficient overall than a utility-scale generator, so using a generator to run electric heat will go through your gas a lot faster than the same gas burned to generate heat (with electricity just used for fan, controls, etc.).