Describe how the model works, and how it could be improved.

Optimise the PV array size for the ‘stay at home’ load and no battery.
Add a 14kWh Tesla Powerwall (enter “14” in the battery size cell).
Re-optimise the PV array, then find what the battery needs to cost for this to be a sensible investment.
Repeat this process for different demand profiles, battery sizes, feed in tariffs, costs of capital and any other input assumptions you’d like to test. What do you learn about the range of costs that batteries need to get to?

Use graphs, tables. Shouldn’t be much need for references, but as usual, cite any reference material you use.