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2nd House
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# Posted: 26 Aug 2021 10:13pm
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I'm absolutely positive most have heard the question I'm about to pose...
For January 2021, we had a very bad winter. During that time, I was living full time in my cabin working remote, because the roads were too bad to get to civilization. Quite frankly, I was actually better off than those requiring electric...but that is another story.
So, during this month, when I did have grid power, I used 895 kw's.
Now, there are 31 days in January, so that is a very rough average of 28.9 kw's per day.
If a Tesla Power Wall new generation puts out 14kw, then I would need about two PowerWalls (and then some) to support that 28.9 kw's per day. This is assuming i have no electric recharging...just using battery power alone.
Is this logic correct?
Thanks for the help
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Brettny
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# Posted: 27 Aug 2021 05:51am
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Your wanting to basicly use a Tesla power wall in place of a backup generator?
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Nobadays
Member
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# Posted: 27 Aug 2021 10:28am
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A Tesla Power Wall is generally used in conjunction with solar charging... yes it can be used as a backup power source but as Brett says.."...in place of a backup generator? " yeah not a very efficient plan. In addition there are other lithium battery options that are far less costly.
Firstly though... 28.9kw/day is a huge number! I just looked back and our highest usage day in 3 years was 3.8kw/day we generally average around 3.3kw/day and we don't really conserve power.... freezer, electric fridge, sat internet, a few hours a day tv, microwave, basically we live like we were on grid.
Your first step might be to figure out where all that power is going! Are you using electric heat?
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Steve_S
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# Posted: 27 Aug 2021 11:04am
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I'm 100% off grid in North Eastern Ontario Canada near Algonquin Park. Run a 24V LiFePO4 battery banked system with 4Kw Inverter/Charger, 2Kw of Solar Panel, 30kWh of LFP energy storage. I also still have my original 24V/428AH/22kWh Lead Acid Bank as secondary. I do so because Winter sun hours can suck up here, especially when snowed on.
With all that said, I use on average of 3.5 to 4 kWh per day.
My cookstove, On-Demand Hot Water & Radiant Floor heating is LPG fuelled. No power hogs in general, microwave, coffee maker (thermal carafe no warmer). Very efficient self-build cabin though. All appliances & devices down to the GrundFos SQ Soft-Start water pump are as efficient as I can get on the market and no crazy out there stuff either.
Steve
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snobdds
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# Posted: 27 Aug 2021 11:23am
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28.9 KW / day is crazy.
Do you have electric heat? Even with that, that is a lot of power.
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NorthRick
Member
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# Posted: 28 Aug 2021 08:50pm - Edited by: NorthRick
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You should first look at why you are using so much electric power. Cutting that down, and I suspect you could cut it way down, would be more cost effective then PowerWalls. A lot more cost effective.
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ICC
Member
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# Posted: 28 Aug 2021 09:32pm - Edited by: ICC
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We solar generated and used about 18kWh a day so far this month and that is with some mini-split A/C and machine use in the shop. Even in winter with the split-mini used for some heat we seldom exceed that. What are you doing to use almost 29 kWh a day? Growing greenhouse pot?
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2nd House
Member
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# Posted: 29 Aug 2021 08:58pm
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test
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2nd House
Member
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# Posted: 29 Aug 2021 08:59pm
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Sorry, I made a mistake...
For January, 2021, I used 895 kWh...not 895 kilowatts!
For backup on my camper, I have two Battle Born batteries. These two batteries will run my refrigerator (3,000 watt inverter) and run all 12 volt systems, including the heater, which runs off a 12volt fan and propane...as most know.
The two batteries will also power my internet router so I still have internet, and it will power my TV.
All this is on one of the 2 legs on the camper. It is a 50 amp camper. Basically, I'm using the inverter as if the camper was a 30 amp system, not split phase.
With this setup, I've been able to achieve 4 days with full batteries, which is an enormous leap from the two deep cycle marine batteries I had. It's very rare that grid is not turned on in that time, to recharge the batteries. If so, I use a propane generator to recharge.
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ICC
Member
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# Posted: 29 Aug 2021 09:55pm - Edited by: ICC
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Kwh is the proper term for the amount of power consumed over a time period.
895 over a 31 day month is 28.77 kWh a day on average. I have on-grid family members who use 400 to 450 kWh a month in winter. 450 a month = about 15 kWh a day, average. Neither have electric heating but they have electric cooking ranges. In July/August they use about 700 kWh a month. They have refrigerated A/C. 700 kWh a month = about 23 kWh a day average.
895 kWh a month in January seems very high unless you use electric heating. Electric heating, with resistance-type heaters, is impractical with most off grid systems or battery backups.
How big a house? Electric space heat? Electric cooking range? Electric clothes dryer? Electric water heater? Electric heat that comes from use of heat pumps, like split-minis, is more efficient than resistance heaters and is practical. Heating with standard baseboard heaters or plugin portable heaters is a bad mix with power from storage batteries. It can be done but does require more battery, more cash outlay.
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Steve_S
Member
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# Posted: 30 Aug 2021 08:06am
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I'm going to Toss a couple of Battery Rocks in the calm waters, just for Kicks & Giggles.
Typically, the unwritten rule about Inverter Systems, is simply do not exceed pulling 250A from a battery Bank, if you need more, step up in Voltage and/or use Parallel Inverters.
KISS Numbers:
12V@250A=3000W (25A-AC), 24V@250A=6000W(50A-AC), 48V@250A=12,000W(100A-AC).
That's for 120V, divide x2 for 240V amperage.
NB: Above 50VDC is the Danger Zone for DC and other rules & tech come into play.
So let us say you want 30kWh of storage, there are PowerWalls (by Tesla) and similar from other Large Commercial Producers (several out there and all $$$) but those are also not just "Batteries" they are more complex than that... Inverters, Solar Controllers etc - depending on Product Line chosen and that chucks pricing into the air a bit.
Simple LFP (LiFePO4) Batteries which is the Safest of the Lithium Chemistries and also the least expensive and perfectly suited for ESS use (Energy Storage Systems). Currently the Best Bang per Buck is the 280AH Cells.
24V LFP requires 8 Cells, 1 BMS (Battery Management System), 1 Fuse (per battery pack) and a casing/frame. 48V requires 16 Cells.
8x EVE-280AH (K Series) Matched Cells: $128ea, $1024 USD.
https://szluyuan.en.alibaba.com/product/1600191395276-818604541/4pcs_EVE_280AH_LiFePO 4_LFP_3_2V_Cells_Battery_New_Version_LF280K_with_6000cycles_Fully_Matched_Genuine_Gra de_A.html?
1 pc JBD Smart BMS Common-Port with BlueTooth module, Cold Temperature cutoff. PART NUMBER: JBD-SP08S004 $79.00 USD
https://dgjbd.en.alibaba.com/search/product?SearchText=SP08S004
1 pc HelTec Active Capacitance Balancer Model Number: 0877A $25 USD
https://www.alibaba.com/product-detail/6S-7S-8S-5A-Lifepo4-Lithium_62357181825.html
1pc 200A BlueSea (Eaton) MRBF Fuse $25 USD assorted vendors
https://www.bluesea.com/products/category/16/72/Terminal_Fuse_Blocks
PLUS Shipping & Handling !
For a PROPER Quote on batteries, you must open a Chat/Messenger session and provide your address. The shipping Guesstimator is Whacked. Everything can be sourced via the one vendor (batteries) and can save some on shipping
24V/280AH/7168Wh/7.16kWh = $1153 USD
S&H < $500 USD. so total $1653 USD
4x 24V/280AH = 1120AH/28,672Wh/28.6kWh for $6,612 USD. + Inverter & Solar Controller.
NOTES:
Battery cells listed are Matched & Batched, these are more costly. There are Bulk Cells which are unmatched for less but can be problematic.
The BMS is a standard Known Good FET Based BMS. Above 150A a different grade of BMS is warranted.
The Active Balancer helps balance these large capacity cells to keep them in synch with each other.
LFP Battery Packs in Parallel share the Charge & Discharge amperage quite evenly. LFP Banks can be added to over time without concerns unlike Lead which has issues on aging.
Hope it helps, Good Luck.
Steve
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2nd House
Member
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# Posted: 30 Aug 2021 08:39pm - Edited by: 2nd House
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This past January, was probably the coldest January and february I have ever seen in my life in South Texas, as a matter of fact, there were several days that it was colder than Alaska.
Usually in South Texas, when it does freeze, it is a light freeze, and goes above freezing the next day...no big deal.
This past January and February, we had sub zero freezing for weeks. When I did have electricity, I was using a combination of propane heat, and two electric heaters to stay warm. Most winters here, the propane heater is more than enough.
So the 895 kWh's is the result of the coldest winter I've ever seen in my 62 years of living. I, and a lot of other people are hoping we dont see that again. It was a very expensive repair for months. I'm still finding broken water valves and poly line.
For backup, I'm using two Lithium batteries on my camper. These are countlessly superior than the two
wet cell deep cycle batteries I did have. With the two lithium batteries, I can run my refrigerator, TV, all 12 volt appliances, and keep the internet up and running for 3 days! By then Grid power is usually restored, and I simply recharge by grid power.
So enough of all that...
The reason I'm looking into this, is I would like to build a cabin in the back of the property, and there is no way grid power will ever be back there. So If I can have enough solar cells, to work for 4 day straights, and still power a mini split AC, that would be what I would be looking for. Heating, including hot water, and cooking range would be provided by propane.
I would think I would need twice the solar, so I could basically run off the solar panels during the day, and still have the batteries charged for the night. I do believe it would be a major investment in solar as the AC units would be running throughout the day, and most of the night, as it gets very hot out here during the summer.
Thanks for the help
Thank you Steve S...that's good stuff!
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2nd House
Member
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# Posted: 2 Sep 2021 08:46pm
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So I'm looking at Steve_S comment.
Question, is that 250 ah for all 8 batteries if set up as 12 volt? Which I assume would be running 4 batteries in series on both legs (as I call them), then the two legs in parallel.
Thanks for the help
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Steve_S
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# Posted: 3 Sep 2021 05:43am - Edited by: Steve_S
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4x 3.2V LFP Cells makes 12V, 8 Cells makes 24V and 16 Cells makes 48V. The cells are 3.2 Volts and those I showed carry 280AH Capacity.
I'm 100% Offgrid Rural & Remote - haven't had to pay Power Hostage Fees for a few years now. Love it when I have power when there is a blackout, since people saw "The lights up the Ridge" and more lights are ON now when there is a Blackout... hehehe....
With LFP we build / buy batteries of the correct voltage for the system being setup. WHY LFP, for Energy Storage Bang per Buck can't be beaten and it is the safest of Lithium Chemistries, no fires/explosions or other nasties. It's also the lowest cost as there is no Cobalt and other exotics.
Here is my Solar System (Last revision picture, out of date now) with 5 LFP(LiFePO4) Battery Packs in Parallel (CANNOT LINK IMAGE, So posted as Attachment.)
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