[joshvm]

Have a look at Dave Jones' EEVblog video about his solar install, it include numbers from a year on his roof. He exported around $185 worth of power at 6c/kWh. The price of buying from the grid is 25.5c/kWh. In principle with a battery system that would be a saving of $786, assuming optimal charge/discharge (it's about 80-90% efficient I believe).

If you run the numbers, the battery slightly decreases the payback time for that system to ~7 years vs 7.5 with the panels alone. However, once its paid off, it could save almost $1000 a year if you live in somewhere like Sydney. This does make the big assumption that you store the electricity and use it optimally, but it's not unreasonable.

I would argue that in this case, it's definitely worth buying.

http://www.eevblog.com/2015/03/16/eevblog-724-home-solar-pow...

[jacquesm]

It's all about pack life and capacity decrease over time. Those you really need to factor in otherwise the calculations make no sense. Storing and retrieving a KWh from a battery pack has a cost associated with it in terms of wear on the pack.

[sliverstorm]

Even if it is worth buying, the capital costs are steep.

Chris's main allegation seems to be that you have to have a hell of a lot of cash to even hope to make it worthwhile- and considering it's $5k for the cheapest battery setup, plus anywhere from $5-30k for your panels, I think he's not wrong, no matter what your electricity prices are.

[joshvm]

Dave's 3kW system apparently cost $5k (Australian) and that included the inverter and decent panels. So call it $10k which puts in on par with a cheap new car or a nice kitchen makeover.

You can think of it as an investment which will take 5-10 years to mature with a secondary benefit of backup power if the grid goes down. Not everyone can afford it, but that's the nature of investment.

Also in Chris' scenario, he's using America as the model. Electricity costs there are just over half those in Australia.

[toomuchtodo]

> Chris's main allegation seems to be that you have to have a hell of a lot of cash to even hope to make it worthwhile

Or cheap financing. Other examples of assets that are extremely useful that can be inexpensively financed would be housing or a car. Why would solar be different?

[lotsofmangos]

Here in the UK, you can get free solar panels installed in return for cheaper electricity bills, with most of the funding coming from pension companies.

[toomuchtodo]

Solar City is using the same model in the US:

https://solarbonds.solarcity.com/