Homemade Powerwall

[dh1]

I thought I'd start a thread on home made DIY power wall using LEAD ACID batteries.
Charge up the batteries when hydro rates a low and use the batteries to power part of the house when rates are high.

How many and what type of Deep cycle batteries would be needed?
Best inverter to use?
Best charger to use?

I know a lot depends on how big or how much kw load you want to run.

I put together a small backup system using 4 golf cart batteries, 1500 watt modified sign wave inverter and an automotive 12 volt charger a few yrs ago.
Found that it would run my washing machine for 3 loads no problem.
It also gave me power to run the fan in my wood stove so I had heat if the power went out.

I'd like to hear what has been done, how much it cost to setup, and the results you got.

[oil pan 4]

I am not sure it would ever pay for its self.
You are talking thousands of dollars of batteries, that need to be replaced every 10 years or so.
What is the difference between the low rate and peak rate?

I have a feeling when rates are high, it might be in the middle of the day, so grid tied solar should be cheaper and more effective.

[SDMCF]

Originally Posted by oil pan 4

What is the difference between the low rate and peak rate?

Depends on your local tariffs I guess. For me the cost varies hour-by-hour with no pre-set low rate and peak rate. The highest peak I have seen is almost 100 times the lowest rate, but that is misleading. More typical would be 3 to 6 times.

Originally Posted by oil pan 4

I have a feeling when rates are high, it might be in the middle of the day, so grid tied solar should be cheaper and more effective.

Yes, for me the peak rates are during the day, but that doesn't mean solar would necessarily be effective. There are many days when solar would produce basically nothing so some kind of battery storage would be essential for avoiding peak rate usage.

[dh1]

My current hydro rates are
Off peak = $.087
Mid peak = $.132
On peak = $.18
+ Delivery, + Regulatory, + Tax

[NiHaoMike]

I'm building my own "mini Powerwall" and doing the research, if you're planning to actually use it (as opposed to just let it sit near full charge most of the time), the most cost effective are Nissan Leaf batteries. Limit charge to 4.0-4.1V/cell and discharge to 3.0-3.2V per cell to optimize for lifetime. Limit charge rate to 1C or less most of the time, which in practice is a lot.

Balancing circuits are commonly available on the RC market but high current chargers and inverters that can deal with the oddball voltages aren't. I'm hacking a server PSU into a charger and the inverter is also a modified unit. There'll also be a few DC/DC converters for powering electronic loads directly (including Quick Charge 3.0 support) and some sort of Wifi/Bluetooth interface for remote control.

[oil pan 4]

Any idea what the pay back time would be, if ever?

[AC_Hacker]

Do you live in a remote area?

-AC

[NiHaoMike]

Originally Posted by oil pan 4

Any idea what the pay back time would be, if ever?

That varies a whole lot depending on a lot of variables. You would have to be on a TOU plan and/or have some form of local generation for it to get any direct savings. (Or go off grid.) It's pretty hard to get enough direct savings to make it worth it, but there are other considerations.

For a start, if the supply of electricity is unreliable in your area, you get a large UPS that lasts a long time even if used a lot. Or if you build it portable/semi portable, you can take it to where there is no connection to the grid, such as when camping. Actually, a popular use case are R/C hobbyists who fly model planes in large fields. To them, Leaf battery modules are just very large Lipos and using a few to charge smaller batteries to actually use in the planes is cheaper and easier to manage than just carrying a lot of the smaller batteries.

Another good use is to reduce the use of energy that is considerably more expensive than the grid, such as onboard a vehicle. Or put it on a cart and use it to power garden tools/other power tools if an extension cord is not a workable solution.

And last but not least, you get yet another toy to play with.

[LarryBertsc]

For me the cost varies hour-by-hour with no pre-set low rate and peak rate. The highest peak I have seen is almost 100 times the lowest rate, but that is misleading. More typical would be 3 to 6 times.