I have heard that generally speaking solar power ends up not being worthwhile. This is part of why I wanted to run the numbers for this project beforehand. Looking at other options such as http://www.amazon.com/gp/product/B00MNAWMHE?ie=UTF8&ref_=de_a_smtd&showDetailTechData=1#technical-data as the external battery the #charges drops to around 500, but the cost drops as well. It is still not at break-even (even ignoring the cost of solar panels), however the numbers get rather close...
Is that sarcasm or an actual comment about the Tesla Power Wall (which this is the first I have heard of it)?
Part of the thing is that (from the limited experience I have) batteries do not have a good scale.... The price goes up in direct relation to the amount of storage you need generally speaking. Actually, in some ways they scale badly as once you pass a certain point you need to worry about extra things such as eye-wash stations and ventilation.
That being said, the first part of your reply makes me think you agree that the project would have a negative $ return.