Well, here it goes.
Wife and I are finally making the jump to installing solar ( mainly we want the 30% credit in Cali before it runs out and/or diminishes ) and I'm trying to figure out if installing batteries ( cuz I'll get 30% PLUS $250/kWh rebate if I do it ) makes any sense at all.
Some background: We will be on a grid tie system. Batteries - if purchased - will be used simply as storage from pv system during off peak to sell back to the grid during on peak. There is no plan to try and turn the battery system into a blackout system. I have plans to install a generator for that down the road.
We are fairly heavy power users - live near Modesto, Ca - and so use lotsa a/c during the summer. Our typical yearly consumption is around 11,000kWh/year. I've already consulted with one sales guy, and asked him about the viability of using electric radiant heaters to heat during the winter, rather than forced air, so he added on another 2,000kWh/year to size the system, making it 13,000kWh/yr, or a 8.85kWh system.
By checking PG&E's website, and establishing our use pattern, it looks like we would be able to overproduce for our daily needs during the summer by around 2,500 kWh. Daily, during the summer, we should be able to store around 35kWh during off peak, then dump it into the grid at peak prices. Pricing is currently $.28/.38. I plan on charging the batteries through solar only.
Here's where I'm hitting the rocky road. My selling point is $.38/kWh. Should I use $.28/kWh as my generation figure? Or should I use the $.12/kWh that the sales literature said will be my 25 year cost of power generation?
I'm attaching a couple of pics. One is from the sales dude of our yearly usage and production. The second is a typical summer's day hourly use pattern - you sure can tell when the a/c kicks on lol.
So, best case would be to daily produce 35kWh at $.12, then sell it at $.38, 5 days per week.
35 (kWh) x .26 (.38-.12) x 5 (days per week) x 26 (weeks in 6 months ) = $1183 net.
A FLA battery system, if you shop, and diy the ****e out of it ( which of course means not attractive and a low Wife Acceptance Factor ) can be installed for around $200/kWh. Wholesale Solar has a 60kWh system for around $10k plus $2k for install and cables, chiropractor visit, etc.
So. if I'm looking at this right, it looks like 10 years to pay it off?
Around 12k expense and 1.2k/yr net?
This being the case, why would anyone get batteries?