What Size Battery Would You Need to Power Your House?

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dgpcolorado

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Thought this was fun:

As most here know, the Tesla "Gigafactory" is intended to produce batteries for stationary applications in addition to those used in the cars. Wired Magazine decided to take a look at What Size Battery Would You Need to Power Your House? For those of us with grid-tied solar, a battery backup is something that many of us have thought about. With a reliable — and affordable — battery system we could go off-grid.

The thought exercise in the article postulates a household usage of 2000 watts; that works out to 48 kWh/day. Seems way high to me since my household usage, exclusive of LEAF, is about 1/10th that. But I'm on the extreme end of conservation when it comes to electricity usage.

Anyway, by going with the highest density Li-ion battery, they come up with a battery volume of 0.52 m³ to generate 2000 W for a week. I'd need considerably less. But I don't agree with the assumption that a battery for a stationary application would need to have high density, since size and weight are relatively unimportant — unlike with an EV — and cost and materials usage would be the main concern. Nevertheless, it does appear that a battery to power a house for a week wouldn't have to be all that big, at least in physical size. But that 48 kWh for a week works out to 336 kWh, which is a pretty expensive battery if it is Li-ion. (Not that you'd really need one to last a whole week IMO.)

But, you ask, will it have TMS? ;)
 
dgpcolorado said:
Thought this was fun:

As most here know, the Tesla "Gigafactory" is intended to produce batteries for stationary applications in addition to those used in the cars. Wired Magazine decided to take a look at What Size Battery Would You Need to Power Your House? For those of us with grid-tied solar, a battery backup is something that many of us have thought about. With a reliable — and affordable — battery system we could go off-grid.

The thought exercise in the article postulates a household usage of 2000 watts; that works out to 48 kWh/day. Seems way high to me since my household usage, exclusive of LEAF, is about 1/10th that. But I'm on the extreme end of conservation when it comes to electricity usage.

Anyway, by going with the highest density Li-ion battery, they come up with a battery volume of 0.52 m³ to generate 2000 W for a week. I'd need considerably less. But I don't agree with the assumption that a battery for a stationary application would need to have high density, since size and weight are relatively unimportant — unlike with an EV — and cost and materials usage would be the main concern. Nevertheless, it does appear that a battery to power a house for a week wouldn't have to be all that big, at least in physical size. But that 48 kWh for a week works out to 336 kWh, which is a pretty expensive battery if it is Li-ion. (Not that you'd really need one to last a whole week IMO.)

But, you ask, will it have TMS? ;)

The grid if available, is the best battery you can have. Let the utilities store energy in water dams or giant underground batteries. It is not economical or a good idea otherwise.

However, I use about 80KWh a day (not including EV charging), so about 1.68 times his numbers so my awesome Tesla battery would only be 0.876m^3.

Of course this all assumes 100% efficiency in energy conversions. If the charger is 90% efficient and the inverter is 90% you are already at 1.08m^3.

But of course you also don't want 100% charge on your battery and you don't want 0%, so adopt the 90/10 and now you can only use 80% of the pack. So size up accordingly, now at 1.35m^3.

And are we assuming the battery doesn't degrade? Because designing for use now means that over time it won't be enough. Since we can call 80% capacity dead, scale up so that 80% meets today's needs right? Now at 1.68m^3.

I can buy 1.2KWh cells of LiFePO4 for $130 a piece, so my 154KWh/day or 1078KWh/week pack would be 900 batteries and cost $117K today. I would get about maybe 3K cycles? So just about 8 years. A cost of $14.6K per year for batteries alone.

Alternatively, I pay the permit & inspection fees once to have grid tied solar and no batteries required.
 
2k1Toaster said:
The grid if available, is the best battery you can have. Let the utilities store energy in water dams or giant underground batteries. It is not economical or a good idea otherwise.
A counterpoint, if I may.

Your judgment that the "...grid...is the best battery..." could be right or wrong depending on what's important to you and/or your starting assumptions.

You seem to be looking at the economics of storage and deciding that the grid is less expensive. It might be worthwhile to look at exactly what factors "economics" includes and ignores. Thermodynamics is one really important factor that economics doesn't consider. Climate change, poor air quality, acid rain, loss of biodiversity, the down-stream effects of dams, and poisonous fish that kids and pregnant mothers can't eat are others.

Including at least some of the externalities traditional economics ignores is enough to dramatically change the judgement on using the grid.

Not an attack or a judgement, just a quick view of what I've been trying to wrap my mind around as I've been trying to cut the cords.
 
AndyH said:
2k1Toaster said:
The grid if available, is the best battery you can have. Let the utilities store energy in water dams or giant underground batteries. It is not economical or a good idea otherwise.
A counterpoint, if I may.

Your judgment that the "...grid...is the best battery..." could be right or wrong depending on what's important to you and/or your starting assumptions.

You seem to be looking at the economics of storage and deciding that the grid is less expensive. It might be worthwhile to look at exactly what factors "economics" includes and ignores. Thermodynamics is one really important factor that economics doesn't consider. Climate change, poor air quality, acid rain, loss of biodiversity, the down-stream effects of dams, and poisonous fish that kids and pregnant mothers can't eat are others.

Including at least some of the externalities traditional economics ignores is enough to dramatically change the judgement on using the grid.

Not an attack or a judgement, just a quick view of what I've been trying to wrap my mind around as I've been trying to cut the cords.

Cost is not the only option. In fact I am generally the first to point out that money isn't everything and gladly pay more for something with less of an impact.

However, individual battery solutions don't seem like the way to go. Everyone storing their own inefficient batteries that degrade and wear out versus the government or utility companies storing power in a large industrial way. For instance it is not feasible for you or I to build a dam and pump water upstream with excess solar production, but a utility can.

My assumptions come from the point of view that the grid is not a bad idea and very stable. I have maybe an hour or less per year where the grid goes down. Last year it was down for a grand total of 2 hours because a dump truck ran into a ground-level neighbourhood distribution box after the guy who parked it didn't apply the parking brake. Whoops! 2 hours out of a year is 0.0228% downtime, or 99.9772% reliability. Why distribute all these inefficiencies to individual areas to cover a problem that doesn't exist.

In the Armageddon scenario, I already have a way of power the house without the grid (solar) and something tells me that will be the least of my worries. And who would want to draw out their existence longer in a world without the internet!!!!! (j/k) But seriously, in Armageddon where the grid goes down indefinitely, I will have better things to worry about, and I probably won't be running 80KWh a day. My 11KW of panels will be more than I could use, until the zombies rip them from my roof.

If you live in sub-Saharan Africa where you might be lucky to get 2 hours a day of grid power if it is on at all that day or where the "stable" parts still experience 4-5 power cuts of greater than 3 hours (PER WEEK!) then obviously personal storage looks a little better. But here in the western world, it is not something we have to worry about and should have the guts, brains, and money to throw money at the problem collectively.
 
The prospects of significant number of folks going off grid gives the utility companies nightmares. And the day may come when it's economically feasible even for non-eccentrics. When that day approaches don't be surprised to discover there are suddenly laws or punitive fees against self-sufficient electrical systems.
 
And are people buying these to get power for a week, or to buy power at off-peak rates and then consume the power during peak rates? You need drastically less capacity to power your home for 18 hours (of which you'll only be awake and active for 6) than powering the home 24/7 for a week.
 
I have maybe an hour or less per year where the grid goes down.

Now think about people who experiences dozens of outages a year, some of them in Winter, and the grid looks less like the ideal way to store power.

I'm considering two battery UPS systems for our house, as a short-term alternative to running the Honda-clone generator. I figure that since I'm the only one here who really needs constant heat in Winter, I'll make my room the center of the upstairs UPS Zone, and run an electric heater (these are what really run up the consumption, but if the power is Clean, then the heat is as well) as well as a light and the PC, from a 100-150AH AGM battery. There would be a second, similar or smaller-sized battery downstairs, to run the fridge in Summer or a smaller heater in one room in Winter. The sump pump is already on a UPS. Since our affordable choices for heating here are fuel oil or hydro-power (from a 100+ year old dam), we have an electric-intensive house. I'd love to have a ground-source heat pump system, but we can't afford one.
 
There's a guy on TMC who got a fully intact 85kw pack and he's using it for grid storage.. he's pulled it all apart, etc.. look it up there and his story..

If you want the guts of the goodies... page 6 here...
http://www.teslamotorsclub.com/show...ith-a-Model-S-battery-pack-at-the-heart/page6

If you want this guy's history, what he's doing (very complicated solar/off-grid setup) then goto the first page here...
http://www.teslamotorsclub.com/show...olar-with-a-Model-S-battery-pack-at-the-heart

Page 11,12 and up is also neat
 
LeftieBiker said:
I have maybe an hour or less per year where the grid goes down.

Now think about people who experiences dozens of outages a year, some of them in Winter, and the grid looks less like the ideal way to store power.

I'm considering two battery UPS systems for our house, as a short-term alternative to running the Honda-clone generator. I figure that since I'm the only one here who really needs constant heat in Winter, I'll make my room the center of the upstairs UPS Zone, and run an electric heater (these are what really run up the consumption, but if the power is Clean, then the heat is as well) as well as a light and the PC, from a 100-150AH AGM battery. There would be a second, similar or smaller-sized battery downstairs, to run the fridge in Summer or a smaller heater in one room in Winter. The sump pump is already on a UPS. Since our affordable choices for heating here are fuel oil or hydro-power (from a 100+ year old dam), we have an electric-intensive house. I'd love to have a ground-source heat pump system, but we can't afford one.

Ok, "dozens", so lets say 24 times where it goes out for 2 hours at a time? That's still 99.5% reliability, batteries are still useless. Use the grid. Your house doesn't instantly use heat. Your food doesn't instantly spoil. You have a generator for the times it is out for multiple days.

I have about 500 pounds of batteries that run my server rack. They are expensive and only last about 2-3 years before I have over 70 batteries to replace. Why? Because on the internet, 0.0228% is too high of a failure rate. If your website drops out for a couple hours, that could be thousands in lost revenue, and much more in bad PR, bad customer experiences, etc. But your average home, it doesn't make a lick of difference.
 
Ok, "dozens", so lets say 24 times where it goes out for 2 hours at a time? That's still 99.5% reliability, batteries are still useless. Use the grid. Your house doesn't instantly use heat. Your food doesn't instantly spoil. You have a generator for the times it is out for multiple days.

I never wrote or implied that I want to go off the grid - especially using batteries. I was just talking first about the grid not being so reliable for everyone, and, second, about my desire to avoid using the generator.
 
I plan to be able to go off grid, but normal use would be grid tied.

If I have the lowest off peak electric rate, my grid connection would only be midnight to 5am to charge my cars.

The sun will run the air conditioning during the day (off-grid), and batteries will handle the low sun angles and night time. In San Diego, provided my house doesn't get hot in the day time, we can get by with a very small A/C unit running, or no air conditioning at all.
 
2k1Toaster said:
...My assumptions come from the point of view that the grid is not a bad idea and very stable. I have maybe an hour or less per year where the grid goes down...
The same is true in my area, so I haven't seriously pursued the idea of battery backup.
...In the Armageddon scenario, I already have a way of power the house without the grid (solar) and something tells me that will be the least of my worries. And who would want to draw out their existence longer in a world without the internet!!!!! (j/k) But seriously, in Armageddon where the grid goes down indefinitely, I will have better things to worry about, and I probably won't be running 80KWh a day. My 11KW of panels will be more than I could use, until the zombies rip them from my roof...
How will you use your panels for this scenario? With my grid-tied setup once the grid is down my panels are offline. And I haven't the expertise to rewire them and cobble together some sort of inverter that can supply my house, at least while the sun is shining. I realize that there are some devices intended for this purpose but they are expensive and, since the grid is so reliable here, it is hard to justify the cost unless one is a committed survivalist or some such thing. (And if that were the case I'd have to move to lower altitude where subsistence farming is possible.)
 
TonyWilliams said:
I plan to be able to go off grid, but normal use would be grid tied.

If I have the lowest off peak electric rate, my grid connection would only be midnight to 5am to charge my cars.

The sun will run the air conditioning during the day (off-grid), and batteries will handle the low sun angles and night time. In San Diego, provided my house doesn't get hot in the day time, we can get by with a very small A/C unit running, or no air conditioning at all.
Why would you do this? Just because you can? Or would it actually be cost-effective due to your tiered electricity rates?

Just curious.
 
Not sure for Tony but that is exactly what we do. We have 18 kWh of lead acid with 3 kw of solar with a xantrex xw 6048 inverter and an Outback FM80 charge controller. Most of our home with the exception of the geothermal, electric dryer and EVSE are on the inverter panel and when we hit on peak we get a signal from the meter that disconnects us from the grid so everything switches over to battery / solar. The biggest reason was I wanted to avoid a generator and I wanted it all to be fully automatic if the power were to go out. Many times the power in our neighborhood went out and we honestly didn't notice. Where we used to live we lost power regularly and for sometimes days at a time. Here we have lost power 4 times this year with the longest for about 12 hours.

As far as cost savings there isn't a whole lot of on peak power consumed, but it is more than offset by solar, I actually have the charge controller setup that when the batteries are full it closes a contact and turns on a resistant heater element in a pre-water heater to use up the excess power. If I am home I have used the 120 vac evse to use up some of that excess power, I would really like to upgrade my stock EVSE so I could charge from the inverter at 10 amps at 240 vac.

I toyed with the idea of grid tie but our utility requires a second meter with a second monthly base charge of $19 and would credit us at the $.06 cent / kwh rate, which could be offset by generated electricity, but I just stuck with what we have and added to it. I can go up to 4 kw of solar and might add that last 1k this summer. It will easily run our 1 or 2 ton (selectable) air source heat pump for AC in summer and heat in the spring and fall.
 
I should add we only charge the leaf or run the geothermal off peak as well. On peak we pay about $.22 a kWh and off peak we pay $.06. If we were to grid tie they would credit us $.06 for each kWh generated no matter when it was generated. Since we primarily use our solar during on peak time we are offsetting that $.22 rate.

In my calculations right about the time the system pays for itself we will have to buy new batteries again. So it basically pays for itself to exist. A genset on the other hand never has a break even and continues to cost money over time for fuel and maintenance, where the panels are continuously generating electricity. If I add another 1 kw of solar it will get closer to making $ in the long run. My last 1000 w of panels were just under $1000. My first 400 w of panels were $2,000 20 years ago...

Even with no sun, like during a snow storm we use about 5 kWh on peak so the batteries have no problem with that cycling. I also have a Honda 2000i with a 48 v battery charger so I can run that and charge about 1 kw if I really had no power or sun for a long time.

Today it is 2F outside with 20 mph winds and a -20F wind chill. In conditions like this being without power for a day would be very difficult. Although our 16,000 gallon indoor pool retains a LOT of heat to tide us over. If nessessary we can use the pool to run radiant heat, consuming about 100 w for a circ pump.

Again since the system is use use daily I know it works great as a backup.
 
Our situation is a little like BrockWI. We have about 36kW of lead acid storage at 24 volts, 24 volt inverter system, and about 1.8kW of battery charging PVs along with 2.46kW of grid tied PVs using microinverters (which are currently putting out 2.7kW due to bright sun and low temps). Also a 2.5kW wind turbine also charging the batteries. Our battery is sized to run our house etc. (not charging the Leaf) for 3 days minimum without discharging below 50%. We are fairly frugal with energy use and have a forced air woodburning furnace.
Our system has evolved from a totally off-grid system that we started building and using back in 1977 and brought with us when we moved in 1989 and have been adding to regularly.

My big concern today is that many utilities, at least in Wisconsin, are trying to add exorbitant fees that would make any kind of renewable energy grid tied system impractical from a financial point of view, and I am getting to the point where it won't take much to make me go back to a 100% off grid system again, especially if we are able to build the new house that we would like.
 
BrockWI, I'm surprised that such a complex system is cost-effective, to the point that it pays for periodic battery replacement. Your on-peak rate isn't that high compared to the horror stories from California. I agree that being without power in Wisconsin in winter is not an option!

Here I pay just the $16 a month minimum service charge to my rural power co-op. My solar covers all my usage and they let me accumulate solar credit over the summer to use in the winter; the flat rate for electricity is ~13.8¢/kWh IIRC. Electricity service here is extremely reliable and outages more than a few seconds or minutes are uncommon and those over a couple of hours almost unheard of. In my neighborhood lines are underground so trees falling on lines doesn't happen, although avalanches and rock slides have been known to take out the big high voltage lines. But the co-op has redundant lines in place for just such cases.

The power co-op has been very supportive of renewable energy, primarily solar and microhydro, because that's what we, the member/owners, want around here.
 
Really the cost of the system is not much more than grid tie if you exclude the batteries, basically a more expensive inverter. The batteries are the real cost difference, and then you have to replace them. My first set went 12 years. I learned a lot on that set and hopefully this set will last even longer.
 
FWIW, I find myself nodding in agreement with most of what y2k ;-) says...

The grid, with its massive batteries, is the most efficient and potentially very clean way to distribute electricity to millions and billions of people, even if it is centralized and does entail externalities (and "cords"). Decentralized/home batteries come with (plenty of) their own, with the cord being a bit more metaphorical (to Tesla, electricians, the hardware store and/or your memory, wallet & time clock), but no less real. I wouldn't mind seeing the transmission lines going under ground (especially tied with a long-range Solar Freakin' Roadways infrastructure project), but overall I think the grid is indispensable and only going to get 'greener' from here on out.

I think the home batteries will still have a use for many (homes and businesses) with solar though, for the aforementioned purpose of reducing or eliminating grid use during peak hours. Also, if V2G/V2H ever takes hold (let alone takes off), millions of small 'home' batteries will be required and very useful, but huge batteries disconnected from the grid will be of no use at all.


I think (just maybe? :)) that MNLers do not represent a good "average" sample of the population as a whole. More here own single-dwelling houses, are quite familiar and "conversant" with electricity, understand the implications and consequences of "it all", and are proactive do-it-your-selfers (for lack of a better phrase) than the general population. I'd guess that most Americans live in multi-unit dwellings and/OR do know or want to put much effort into learning or doing anything about how pushing a button makes the TV or microwave go on. :-\


2k1Toaster said:
AndyH said:
2k1Toaster said:
The grid if available, is the best battery you can have. Let the utilities store energy in water dams or giant underground batteries. It is not economical or a good idea otherwise.
A counterpoint, if I may.

Your judgment that the "...grid...is the best battery..." could be right or wrong depending on what's important to you and/or your starting assumptions.

You seem to be looking at the economics of storage and deciding that the grid is less expensive. It might be worthwhile to look at exactly what factors "economics" includes and ignores. Thermodynamics is one really important factor that economics doesn't consider. Climate change, poor air quality, acid rain, loss of biodiversity, the down-stream effects of dams, and poisonous fish that kids and pregnant mothers can't eat are others.

Including at least some of the externalities traditional economics ignores is enough to dramatically change the judgement on using the grid.

Not an attack or a judgement, just a quick view of what I've been trying to wrap my mind around as I've been trying to cut the cords.

Cost is not the only option. In fact I am generally the first to point out that money isn't everything and gladly pay more for something with less of an impact.

However, individual battery solutions don't seem like the way to go. Everyone storing their own inefficient batteries that degrade and wear out versus the government or utility companies storing power in a large industrial way. For instance it is not feasible for you or I to build a dam and pump water upstream with excess solar production, but a utility can.

My assumptions come from the point of view that the grid is not a bad idea and very stable. I have maybe an hour or less per year where the grid goes down. Last year it was down for a grand total of 2 hours because a dump truck ran into a ground-level neighbourhood distribution box after the guy who parked it didn't apply the parking brake. Whoops! 2 hours out of a year is 0.0228% downtime, or 99.9772% reliability. Why distribute all these inefficiencies to individual areas to cover a problem that doesn't exist.

In the Armageddon scenario, I already have a way of power the house without the grid (solar) and something tells me that will be the least of my worries. And who would want to draw out their existence longer in a world without the internet!!!!! (j/k) But seriously, in Armageddon where the grid goes down indefinitely, I will have better things to worry about, and I probably won't be running 80KWh a day. My 11KW of panels will be more than I could use, until the zombies rip them from my roof.

If you live in sub-Saharan Africa where you might be lucky to get 2 hours a day of grid power if it is on at all that day or where the "stable" parts still experience 4-5 power cuts of greater than 3 hours (PER WEEK!) then obviously personal storage looks a little better. But here in the western world, it is not something we have to worry about and should have the guts, brains, and money to throw money at the problem collectively.
 
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