Battery back up without solar

[brownerd]

OK, I know this is going to sound weird, but stick with me
I would like to build a 48 volt 280 AH battery using the 3.2 volt cells. I would like to charge the battery during off peak hours from the grid, then during peak hours I'd like to run my home. In the event of a grid outtage, I'd like to power my home from battery. I do not have solar (yet), so that wouldn'y be an option at this time. Are there any products out there that would allow me to schedule when I run from battery and when I run from the power company? I'd like to automate it instead of manually flipping transfer switches. Am I whacked, wanting to build something like this?

 

[chrisski]

That is an option among many inverters. You can set times usually referred to as SBU (Solar, Backup, and Utility) are primary throughout the day At different times.

I’d look at the rates in your area. A system like this may run $12k for a 10 kWh battery pack installed and at a savings of $.10 to $20 per kWh, payback time would be immense if you used 7 to 8 kWh battery backup per day.

EDIT: If you plan on expanding to solar later, make sure you talk through with the installer the placement of these future products. 3’ Spacing for batteries surprised me. This means they can only be placed 1 high on a typical wall.

 

[brownerd]

That is an option among many inverters. You can set times usually referred to as SBU (Solar, Backup, and Utility) are primary throughout the day At different times.

I’d look at the rates in your area. A system like this may run $12k for a 10 kWh battery pack installed and at a savings of $.10 to $20 per kWh, payback time would be immense if you used 7 to 8 kWh battery backup per day.

EDIT: If you plan on expanding to solar later, make sure you talk through with the installer the placement of these future products. 3’ Spacing for batteries surprised me. This means they can only be placed 1 high on a typical wall.

Thank you - you make a great point on ROI - I was kinda just wanting a project to work on, but was hoping it would be cheaper . I was looking at these batteries https://www.18650batterystore.com/products/eve-lf304-grade-a-cells-3-2v-lifepo4-304ah-battery to get 16 of them would give 300 AH at 48 volts ($2,160) then all the other stuff BMS, inverter... was hoping to spend $6,000 +/-
I hadn't thought about the spacing of components - thank you for that tip!

 

[Kenny_]

Well, not the same but I just put together a system using a Sungold 10K (about $1500) + sungold 48v batteries at about $1400/100AH.
a starter system with a single battery would be about $3k and would provide the functionality you want. Other batteries could be substituted or expanded etc... (I do have solar as well), but the Sungold 10k can be used without panels (or batteries for that matter). Check out the manual. It also allows scheduled charging times etc. but I have not used it that way or even tested the functionality.

But also like @chrisski says the savings are not necessarily that great. Payback time would be enormous...but if it's just something for you to experiment with then go for it!

 

[chrisski]

Thank you - you make a great point on ROI - I was kinda just wanting a project to work on, but was hoping it would be cheaper . I was looking at these batteries https://www.18650batterystore.com/products/eve-lf304-grade-a-cells-3-2v-lifepo4-304ah-battery to get 16 of them would give 300 AH at 48 volts ($2,160) then all the other stuff BMS, inverter... was hoping to spend $6,000 +/-
I hadn't thought about the spacing of components - thank you for that tip!

You could spend about that, but it would need to be DIY. I can’t handle the permitting side of DIY grid tied.

Those EVE cells are not UL approved and I doubt they’d pass an inspection.

 

[42OhmsPA]

Thank you - you make a great point on ROI - I was kinda just wanting a project to work on, but was hoping it would be cheaper . I was looking at these batteries https://www.18650batterystore.com/products/eve-lf304-grade-a-cells-3-2v-lifepo4-304ah-battery to get 16 of them would give 300 AH at 48 volts ($2,160) then all the other stuff BMS, inverter... was hoping to spend $6,000 +/-
I hadn't thought about the spacing of components - thank you for that tip!

Welcome to the forum.

What you are trying to accomplish is definitely attainable at a low cost.

The biggest question is are you worried about inspections and are you capable of installing it yourself?

Your ROI won't be great if your only concerned with charging during off peak rates. It will be completely worth it the first time the grid goes down in your area...

If you plan to do this yourself on a budget I'd recommend the Envision 305ah cells from 18650 (they are restocking next month) and a budget AIO inverter so you can add solar later.
I'm running the same inverter that @Kenny_ mentioned, I got mine from the OEM SRNE. I have over 1Mwh of solar and AC through it with no issues.
You could easily do this for under $4000 including the cost of, BMS, tools, wire, fusing, enclosure, etc.
If you're looking for full compliance and inspections that cost could easily double.

 

[brownerd]

Thank you for all the replies! You have given me a lot to think about. Now my head hurts

 

[hwy17]

If you're on PG&E you can consider just installing one single cheap DIY heat pump or HPWH in order to get onto the E-ELEC rate.

If you're on SMUD you really probably can't save any money at all. They're already cheap.

 

[brownerd]

If you're on PG&E you can consider just installing one single cheap DIY heat pump or HPWH in order to get onto the E-ELEC rate.

If you're on SMUD you really probably can't save any money at all. They're already cheap.

I'm on SMUD - it's funny - I went to their web site and looked at the solar options... It shows how long until there is a return on the investment, but for me it said N/A. My wife works a goofy schedule, so she is sleeping at 5:00PM, in the summer i crank down the AC, so she can sleep, but my electric bill gets pretty high for doing that. I was thinking if I could run from battery during the peak I could save some $$$. Our AC is newer (21 seer), but living in a 2 story (and not having a split/zoned HVAC) makes it difficult.

 

[tmprof]

Originally, I was thinking about doing the same thing, but after I got my solar and battery backup, I realized there is loss when you convert from AC/DC, and in this case, you convert AC to DC to put it in the batteries, and then convert DC back to AC to use in your house so just know it's not 100% efficient.

 

[Vigo]

My Growatt inverters have a setting for that. You can also put the ac input to an inverter/charger on a simple timer switch as long as it can handle the current. So that part is cheap and easy.

But you really need to figure out how many Kwh you're trying to cover with batteries. That's going to determine how expensive this is going to get.

 

[JäseH]

I've been looking into doing something similar. I use about 38,000 kWh annually, including my vehicles. During peak months, around 40% of my consumption is outside the free night plan hours (smart meter). I estimated around 14k for 80 kWh of storage, which includes a buffer to limit degradation. These are with ots smart LFP packs. I would need a 10kW inverter to cover my consumption. I have a natural gas fired generator for emergency outages. Is there any reason this wouldn't work? It's basically arbitrage using a free night power plan.

 

[zanydroid]

I've been looking into doing something similar. I use about 38,000 kWh annually, including my vehicles. During peak months, around 40% of my consumption is outside the free night plan hours (smart meter). I estimated around 14k for 80 kWh of storage, which includes a buffer to limit degradation. These are with ots smart LFP packs. I would need a 10kW inverter to cover my consumption. I have a natural gas fired generator for emergency outages. Is there any reason this wouldn't work? It's basically arbitrage using a free night power plan.

Still need to calculate the levelized cost of storage. Also, there’s no guarantee free night power plan will always be there, so you have to bake in that risk into the financial model/risk tolerance

And how big is the spread anyway between regular rate plan and $0.00? I thought electricity tended to be super cheap anyway in a lot of places with free night power plan.

 

[JäseH]

Still need to calculate the levelized cost of storage. Also, there’s no guarantee free night power plan will always be there, so you have to bake in that risk into the financial model/risk tolerance

And how big is the spread anyway between regular rate plan and $0.00? I thought electricity tended to be super cheap anyway in a lot of places with free night power plan.

I'm at 12.6 cents currently. Free nights are around 23 cents during the day with no delivery charge. With a delivery charge days are around 18 cents. I would do a 36 month to mitigate the risk of the plan going away. Break even would be around 4 to 6 years I think, depending on the cost of other hardware like inverter, racks, cables, etc.

 

[SeaGal]

Originally, I was thinking about doing the same thing, but after I got my solar and battery backup, I realized there is loss when you convert from AC/DC, and in this case, you convert AC to DC to put it in the batteries, and then convert DC back to AC to use in your house so just know it's not 100% efficient.

... I've measured about 85% for the round trip over last winter (with Solis Hybrid inverter and 14.3kWh DIY battery pack).

For us in the UK, it's worth it because a) I have solar and only use grid top-up charging for about 4 months a year and b) our cheap night time rate (over 7 hours) is half the price of the peak rate for the remaining 17 hours AND the peak rate is around the equivalent of 0.45$ per kWh.

 

[Daddy Tanuki]

... I've measured about 85% for the round trip over last winter (with Solis Hybrid inverter and 14.3kWh DIY battery pack).

For us in the UK, it's worth it because a) I have solar and only use grid top-up charging for about 4 months a year and b) our cheap night time rate (over 7 hours) is half the price of the peak rate for the remaining 17 hours AND the peak rate is around the equivalent of 0.45$ per kWh.

Sounds like Tepco in Japan. evening night time savers plan is stupidly cheap, but only if you are running 200 volt split phase. (I do at the main house). so solar in the day night time savers plan at night just have not done the battery thing yet as my solar covers 130+% of my daytime on average. (i get monthly payback.)

in about 3 years my solar plan will switch, and at that time I will definitely be looking at batteries for the main house, but with no payback as the payback will become minimal, so use and charge batteries at night, and then if batteries deplete use night time savers plan to charge (a little) and run what not.

 

[OffGridForGood]

I got "into solar" exactly like this, without any PV at all. Just an inverter and a single 5kWh server rack got me started - effectively a really big UPS for lights and small outlets in my shop.
I live in an area with frequent power outages - generally during winter - and my business was being affected by the outages. I just wanted the lights to stay on, and be able to run small tools (and make coffee) anytime the utility was out, rather than paying staff to stand in the dark while I had to decide "will I send everyone home, or will the power be back on in 20-minutes?"
I can't count how many times we pulled out the honda generator, got it up and running, pluged in some lights just in time for the utility to come back online...ok time to put the generator away again - just as the power tripped again.

Most inverters can be set to Utility First, and then put the Utility input on a HWT 240v timer (available at Home Depot) to supply utility only during your off peak rate ToU. The timer will allow current only during the low cost time of day for recharging the battery, then when the timer cuts off the utility power, the Inverter will switch on. The electronic timers can be programed for week-days, week-ends etc if your ToU rates follow different schedules during the week, and they have an over-ride button - so you can switch on or off with the press of a button without changing any programing if you need utility.

OP mentions DIY battery build, so we can assume they are confident in their own skills. Thing to check, running A/C will mean: high in-rush starting load, be sure to pick an invert capable of starting your A/C system; A/C power consumption - check the battery you are planning will have the capacity needed to power this load for the duration you need.

 

[Brett V]

I started with a 1500 watt inverter and a big rack of AGM batteries to act as a ups for a few essential things in the house. Then moved up to a 6k Growatt and one battery with the same intended purpose. I just wanted things in the house to work without running the generator all night if the power was out. It worked perfectly and I would have probably never started putting in solar had the world not destabilized as it has over the past few years.

 

[k490]

When I first came here, I thought I wanted to build a DIY battery and inverter that would back feed to my panel during peak hours and charge during off-peak hours. I would add CT clamps keep it from back-feeding the grid. When I did a deep dive into my bill I figured out when you add all the fees and tax to off-peak not really saving as much as you think. This is why my bill got so high even when I run most things off-peak. The ROI wasn't there to do that. Now I'm working on an off-grid system that I can transfer in different circuits through a generator transfer switch. I will have 12 395-watt panels. Fully permitted system will cost over 25k even DIY utilities make you jump through lot of expensive hoops keep the cost high they don't want you to get solar.

 

[Kenny_]

When I first came here, I thought I wanted to build a DIY battery and inverter that would back feed to my panel during peak hours and charge during off-peak hours. I would add CT clamps keep it from back-feeding the grid. When I did a deep dive into my bill I figured out when you add all the fees and tax to off-peak not really saving as much as you think. This is why my bill got so high even when I run most things off-peak. The ROI wasn't there to do that. Now I'm working on an off-grid system that I can transfer in different circuits through a generator transfer switch. I will have 12 395-watt panels. Fully permitted system will cost over 25k even DIY utilities make you jump through lot of expensive hoops keep the cost high they don't want you to get solar.

This....