I am looking into building my own battery pack. I have variable prices for my energy and would love to be able to charge the battery when the price is low and use it or maybe even deliver back to the grid when the price is higher. I live in a 220v area and wanted to know some recommendations for this project. I was looking into LiFePO4 Batteries but I don't know if there are any ready products to buy for my other requirements. I wanted to start small (max 5kwh) and be able to upgrade in the future.
Battery for variable price energy
- Thread starter Dutchie
- Start date
sunshine_eggo
Happy Breffast!
If this is for cost savings, please calculate the payback period.
Ampster
Renewable Energy Hobbyist
If your average is $0.15 per kWh and your low cost is $0.10 then your peak is probably as high ast $0.20 of more per kWh. The economic benefic is the differential from the low to the high. The usual concept is to charge the battery at low rates and use low cost power to offset loads at the high rate. That can usually be done with just a building permit depending on your jurisdiction. Selling back power from a battery most likely may require permission from your utility and is much more complicated. Batteries provide the best economic return when paired with solar panels. Otherwise a differential of $0.10 to 0.15 per kWh is a slow payback. Scalability will depend on the system design so a thoughful plan is necessary to optimise growth. Incremental growth will be more efficient if you have a long term plan that is articulated in kWhs for battery capacity and consumption and in kWs for daily peaks. One of those unit of measures iis time based and the other is based on instaneous consumption.
No those are the low in savings and the avarage savings. I had a difference of 50 cents even on 1 day. This I calculated over the last year. My price differs per hour so that is why I have such high differences.
So my average earnback wIth 5 kWh would be around 3,- per day.
I am counting on a payback time of 3 to 4 years.
So my average earnback wIth 5 kWh would be around 3,- per day.
I am counting on a payback time of 3 to 4 years.
Ampster
Renewable Energy Hobbyist
Averages are useless for calculating any kind of financial return. With a difference of $0.50 cents per kWh there is a real opportunity for a decent return on the investment in as system. The math is complicated but with spreadsheet skills and consumption data a simple model can be developed that can assist your planning.
I know how to calculate the payback time and time things like that. I am really interested if there is any system that can force the battery to deliver back to the power grid. In my area I will get back the same price for energy that I would pay at that time. So if I time it correctly to deliver back to the grid at those times it will make the payback time not so long.
Ampster
Renewable Energy Hobbyist
Yes, most hybrid inverters can be programmed to do that but the issue is regulatory not functionality. There are National Electrical Code, local building code, Underwriters Laboratory standards and a host of issues surrounding that functionality. The physics is the easy part.
As far as your question goes: (and answered by someone) delivering power back to the grid is where the problem exists. In fact in my area the power companies are specifically putting meters in which have live data feeds- one possible reason: To know when your pushing power back to the grid with an unapproved device.
So how do they know whether your doing it or not? Simple. They know if you have solar. So they know that between the hours of 8am to like 6pm you can produce electricty. But if you start backfeeding the grid at 8pm with your batteries, they will know. My interconnect agreement specifically does not allow the use of generators or batteries to "sell back" to the grid. Also, their time of day plan is very specific. ; you can only use the credits in the time frame you produced it.
Realistically, you'd have to push more than you use- and with a 5kw reserve, you'd most likely consume that within the day anyhow.
If your in CA or another area with default peak rates, your ideal scenario is to store the 5kw from overnight charging ( say 10pm to 6am) and switch over to batteries from 6am to 10pm.
The time of use system here is pretty abysmal- almost a 8x factor in price! But if your overall consumption is very low, actual cumulative savings is also low.
IF you want it for a different reason (battery packup, etc) then there is some real added value. But simply arbitraging energy from the grid isnt one of them.
Dont break any laws in your area. (disclaimer).
You need a charge controller to charge up your battery bank. You then need some current limiting device (buck/boost converter) to send the power to a grid tie inverter input. If you dont have a current limiter, you will dump the max amps of your battery into the grid tie inverter, and blow it up.
Set the current limiting device to the optimized discharge curve of your batteries.
Any power your house or circuit needs will be taken first. Whatever is left will dump to the grid.
Your meter needs to be ready for this. Some will not give you credit. Some will roll backwards . Some only roll forward!!
So how do they know whether your doing it or not? Simple. They know if you have solar. So they know that between the hours of 8am to like 6pm you can produce electricty. But if you start backfeeding the grid at 8pm with your batteries, they will know. My interconnect agreement specifically does not allow the use of generators or batteries to "sell back" to the grid. Also, their time of day plan is very specific. ; you can only use the credits in the time frame you produced it.
Realistically, you'd have to push more than you use- and with a 5kw reserve, you'd most likely consume that within the day anyhow.
If your in CA or another area with default peak rates, your ideal scenario is to store the 5kw from overnight charging ( say 10pm to 6am) and switch over to batteries from 6am to 10pm.
The time of use system here is pretty abysmal- almost a 8x factor in price! But if your overall consumption is very low, actual cumulative savings is also low.
IF you want it for a different reason (battery packup, etc) then there is some real added value. But simply arbitraging energy from the grid isnt one of them.
Dont break any laws in your area. (disclaimer).
You need a charge controller to charge up your battery bank. You then need some current limiting device (buck/boost converter) to send the power to a grid tie inverter input. If you dont have a current limiter, you will dump the max amps of your battery into the grid tie inverter, and blow it up.
Set the current limiting device to the optimized discharge curve of your batteries.
Any power your house or circuit needs will be taken first. Whatever is left will dump to the grid.
Your meter needs to be ready for this. Some will not give you credit. Some will roll backwards . Some only roll forward!!
Largest limiter on this is the battery capacity. And you still have to make sure you have the grid interconnect if you actually want credits from your utility company. I only get credits with mine in a 1:1 swap.
thanks for all the info. I looked into delivering back to the grid and that will have some problems with law and such. So I will switch to using the energy of my own at those times. I have a normal use of 0.6 kw when we are a sleep. The high is before that and in the winter and summer the airconditioning will run lots of time and tv computer it can add up easy fast so I will be able to use the battery at a high point most of the times. So it will maybe be a little less savings then 3 per day but I think it will be more than 1 per day and it will be more in the future.
So then I still have the question what system would you suggest for only using it myself and not delivering back to the grid.
So then I still have the question what system would you suggest for only using it myself and not delivering back to the grid.
Johan
Off-grid energy systems enthusiast.
@Dutchie - Zelf bouwen is het goedkoopst. En anders gewoon een server rack vol stouwen met deze:
https://signaturesolar.com/shop-all/batteries/
https://signaturesolar.com/shop-all/batteries/
joanna_lannie
Maybe sleepwalking now
- Joined
- Sep 14, 2021
- Messages
- 188
If you like to get your hands dirty and keep costs to a minimum, DIY batteries are the way to go. But if you want to pay and wait, then OTS batteries are the way to go. The difference between DIY and OTS batteries is the construction process and price, which mainly depends on your preference. In terms of brand, it is recommended to choose multi-person purchases (many people in the forum will share), and cheap batteries are not recommended, because the high probability is a trap.
Your doing it reverse. You want to change it to battery in the daytime, and charge while you sleep. As far as I'm aware for every implementation of time of day use, it is more expensive during the day, and cheaper at night. Thus you want to charge at night and use during the day.
There are even giant air conditioners that freeze water at night to provide cooling durning the day.
Oh that is something. It's like inverse solar production pricing. The issue would then be how much can you store in that short periods of time between 1230-1500
I'd consider some of the high charge rate batteries, which is generally opposite of what people use here which are slow charging all day from solar. Once you go outside that window the charges go right up to normal, making it kinda moot between equipment costs, battery wear, and efficiency.
I'd be trying to find ways to run the hot water heater during that time, doing laundry, dishes, etc..
I'd lean heavily toward either a massive bank that can take a massive charge rate... At least large enough rate to match your use rate over the other 17 hours.
I'd consider some of the high charge rate batteries, which is generally opposite of what people use here which are slow charging all day from solar. Once you go outside that window the charges go right up to normal, making it kinda moot between equipment costs, battery wear, and efficiency.
I'd be trying to find ways to run the hot water heater during that time, doing laundry, dishes, etc..
I'd lean heavily toward either a massive bank that can take a massive charge rate... At least large enough rate to match your use rate over the other 17 hours.
The low starts at 12:00 and will end at 16:00 the prices are per hour. But I don’t know how fast LiFePO4 can charge if I would be able to fully charge them in those hours. And if I don’t cover the whole other time I would at least cover some of it. And i already plan my using a lot when we use the dishwasher and do the laundry.
sunshine_eggo
Happy Breffast!
I kinda feel like this is being approached without any meaningful info.
On a typical daily basis:
Are you in Germany or dependent on their power systems? This pricing looks like the result of cutting out all nuke power in favor of PV.
On a typical daily basis:
- How many kWh do you use during peak hours?
- How many kWh do you use during off-peak hours?
- What is the highest wattage item you intend to power via batteries during peak power?
Are you in Germany or dependent on their power systems? This pricing looks like the result of cutting out all nuke power in favor of PV.
I live in the Netherlands. And your questions:
It depends if I have a work from home day or not but without using the airconditioning around 1 to 2 kwh. When the temp rises or lowers it will become more depending on the need for cooling and in the winter heating.
My off peak hour usage is around 0.5 kwh without using cooling or heating and here goes the same.
I think the airconditionings is going to use the most power. I have 2 units atm with both a usage of around 3kwh. I would rarely use them at the same time.
It depends if I have a work from home day or not but without using the airconditioning around 1 to 2 kwh. When the temp rises or lowers it will become more depending on the need for cooling and in the winter heating.
My off peak hour usage is around 0.5 kwh without using cooling or heating and here goes the same.
I think the airconditionings is going to use the most power. I have 2 units atm with both a usage of around 3kwh. I would rarely use them at the same time.
sunshine_eggo
Happy Breffast!
Concerning the A/C, you're giving energy units. I'm asking for power. Are they mini-splits?
So, just picking numbers for the purposes of calculation:
0.04/kWh average off-peak
0.25/kWh average on-peak
That's a 0.21/kwh difference. Assuming you can move all energy usage to off-peak, that's about 0.60/day savings.
You're probably looking at at least €1,000 in batteries/equipment. It's going to take you 4.5+ years to break even.
So, just picking numbers for the purposes of calculation:
0.04/kWh average off-peak
0.25/kWh average on-peak
That's a 0.21/kwh difference. Assuming you can move all energy usage to off-peak, that's about 0.60/day savings.
You're probably looking at at least €1,000 in batteries/equipment. It's going to take you 4.5+ years to break even.
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