Considering batteries without solar

[BoronSandal]

Another thing I think would help with reducing utility bills is replacing our heating and cooling systems with a passive solar system using the sun to keep a mass of sand very hot like an oven (this is called a sand battery) then use this for heating, and also use it for cooling because an Einstein Refrigerator has no moving parts and only requires a heat source on one end to make cold on the other end

 

[BoronSandal]

I did the math on a recent $400 Bill. Over half of our use is already super off peak

Are you charging an electric car overnight?

 

[DIYrich]

I'm also in San Diego and I've also been considering the same thing. Maybe we could work together on this.

Here's what I've been thinking:
- 5 kWh of battery should be enough to offset peak 4-9pm usage (battery cost is around $200 per kWh) and will have the fastest payback
- the EV-TOU5 rate plan is needed https://www.sdge.com/total-electric-rates (currently summer high, mid, and low time of use rates are 0.81629, 0.48129, 0.15351 and winter are 0.51149, 0.44775, 0.14520 plus a $16/mo fee, and Summer is June 1 - October 31 (5 months) and Winter is November 1 - May 31 (7 months))
- an inverter with enough output to run any combination of house things
- something like a programmable automatic transfer switch to prevent backfeeding the grid and to enable battery charging on a schedule
- a 48 volt system is ideal to minimize losses
- if all 5 kWh are used to offset the highest rate, the savings will be about $100/mo during the 5 summer months and $50/mo during the 7 winter months or about $850/yr meaning the system should pay for itself in less than 2 years.
- Will Prowse has suggested making the system portable by mounting it to a dolly

For $9k you can get the eg4 18kpv and the 14kWh powerpro. Yes, it extends the payback to 11 years (before federal 30% tax credit). But, you now have grid down backup and easy way to add solar.