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RegGuheert
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Re: What Size Battery Would You Need to Power Your House?

Wed Mar 08, 2017 12:25 pm

GetOffYourGas wrote:Thanks for running these numbers, Reg. I enjoyed following you on your thought process.
You're welcome! To be honest, the short-term numbers are a bit more challenging than I had imagined. (I already knew I was carrying 3 MWh across seasons.)

IMO, storage is the next big hurdle in the move to a renewable, all-electric society. But there are no simple answers, partly because we are increasing our electricity consumption (by moving to BEVs) at the same time we are attempting to clean up the electricity grid.
GetOffYourGas wrote:Although I use significantly less electricity than you (I have natural gas heat), I would hate to do the calculation for my home. My panels produce very nearly zero from December-February. One of the benefits of living in snow country.
Simply put, photovoltaics get much more difficult to apply as you move away from the equator. Batteries are very likely to be a part of the long-term solution to smooth out those short-term variations. But I suspect hydrogen will eventually be the solution-of-choice for seasonal shifting of energy production. But that will take a massive reduction in cost and a significant increase in efficiency.

BTW, I do think that the Enphase AC Battery will be successful in Hawaii. Electricity is expensive there and they are very close to the equator. As such, they do not have the huge heating requirements that we have so far north.
GetOffYourGas wrote:If one is truly to go off-grid, I would imagine you would want some sort of smart-home power management. For example, I come home and plug in my car to recharge, meanwhile I also turn the heat up. 30 minutes later, I'm firing up the oven to cook dinner. I know that I don't need the car charged until the morning, and would rather have dinner cooking than full heat to the house. Sounds like a challenging but fun problem to solve.
Yes, load management is something I'm a big fan of. Hopefully in the future we will be able to net-meter the energy into and out of our BEVs, including time-of-use considerations. As batteries get larger and more durable, that would provide high value to the grid, particularly if they could be charged in the daytime and discharged at nighttime.
RegGuheert
2011 Leaf SL Demo vehicle
10K miles: Apr 14, 2013, 20K miles (55.7Ah): Aug 7, 2014, 30K miles (52.0Ah): Dec 30, 2015, 40K miles (49.8Ah): Feb 8, 2017, 50K miles (47.2Ah): Dec 7, 2017.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

GetOffYourGas
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Re: What Size Battery Would You Need to Power Your House?

Wed Mar 08, 2017 1:01 pm

RegGuheert wrote:Simply put, photovoltaics get much more difficult to apply as you move away from the equator. Batteries are very likely to be a part of the long-term solution to smooth out those short-term variations. But I suspect hydrogen will eventually be the solution-of-choice for seasonal shifting of energy production. But that will take a massive reduction in cost and a significant increase in efficiency.


Don't forget other sources of renewables. I live downwind of the Great Lakes. That gives us lots of clouds/snow (which practically kills solar in the winter). It also gives us a lot of wind (no mountains upwind of us to divert/slow it down). There are more projects going in all the time. A new one was proposed for Tug Hill, just north of me:

https://www.wind-watch.org/news/2017/03/08/wind-farm-with-up-to-125-turbines-proposed-for-tug-hill/

Large-scale wind projects are, IMO, an argument against going off-grid. I hope to see the grid itself become more of a community asset, through which we all share our production and consumption of electricity.

Of course, wind doesn't eliminate the need for storage. It just reduces it. So I'm excited to see what solutions become available in the not-so-distant future. It could be hydrogen. It could also be massively distributed batteries (e.g. if V2G-equipped BEVs started to take over). It could be something I haven't heard or thought of yet.
~Brian

EV Fleet:
2011 Torqeedo Travel 1003 electric outboard on a 22' sailboat
2012 Leaf SV (traded for Bolt)
2015 C-Max Energi (302A package)
2017 Bolt Premier

Zythryn
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Re: What Size Battery Would You Need to Power Your House?

Wed Mar 08, 2017 2:15 pm

RegGuheert wrote:
Zythryn wrote:I would suggest your estimates don't show how much it would cost to go off grid. They estimate how much it would cost to go off grid with those specific batteries.
Actually, this house has been nearly off-grid in the past. For nine months of the year the 2880 Wp array provided all of our electricity and about half during the other three months. The electric water heater remained on-grid. Heat was provided using a wood-pellet stove rather than a heat pump. The clothes dryer and oven ran off propane rather than electricity. That was until the house was hit by lightning and I lost an inverter. Also, we did not have an electric car consuming over 2 MWh of electricity each year back then.

No, this calculation is intended to see what is involved in eliminating the flow to the grid with our fully-electric house. (We still have the wood-pellet stove and can operate in the case of emergencies for long periods of time, so that is not my intention.)


I applaud your energy efficiency, but once again, you take the most expensive solution and state it as a general case.


RegGuheert wrote:
Zythryn wrote:Ironically enough, just as I was getting started in Excel, our power went out!
That is ironic! :)

Whew, back up again after a couple of hours, temp in the house only went up a couple degrees ;)

RegGuheert wrote:
Zythryn wrote:I am planning to go back to November 1st up through today.
Unfortunately I don't have data going back prior to October 1st.
For reference, here is Virginia, my meter reversed direction around November 20, 2016. In 2015, it was around November 1. Yours likely reverses prior to that.

Our meter "reverses" direction every night.
Our first measured daily net loss was in early October, although I am sure there are days every month.
Our first measured weekly loss looks like it was the last week in November.
Monthly loss would be December.
The first monthly gain would be February, weekly looks like the first week of January and daily, well those are scattered throughout the winter.
http://www.netzeromn.com/blog/the-envelope-please

RegGuheert wrote:
Zythryn wrote:My first thought was to plot hourly kW usage (basically kWh) to get the worst case scenario.
That's roughly what the 1-hour column provides for me.
Yep, thank you again, this is a much better way to look at it than daily. The line between hourly data and power requirements for either battery backup or going off grid is much more direct.

Zythryn wrote:I could track net power use, but with such a short timeframe I'm thinking worse case is better.
This would put disproportionate weight on our car charging. One of the cars is mostly charged during sunlight hours.
So, I am tempted to subtract the car charging out of the data.
Don't you have a Tesla Model S? If so, does it have a 20 kW charger in it? That could cause you to draw power from the grid no matter when it is charged.

The standard charger in a Tesla is 10kW. The car can be set to charge at less than the maximum. I typically charge at 18A or about 4.2kW.
If I were going off grid, I would likely set them to charge at 12A/3kW. For our driving habits, that is sufficient.
I also try to charge when the sun is shining, which means the car has little impact on the net power use of the house.

RegGuheert wrote:
Zythryn wrote:I also need to calculate the energy needed over a longer timeframe.
This is tricky, as the length of time varies depending upon the sunshine.
This is were net metering REALLY provides its magic: The last two years I have "stored" over 3 MWh each year in Spring, Summer and Fall. This year I am hopeful to store over 4 MWh before wintertime. If I do, the thermostat may go up a couple of degrees next winter! :)
Zythryn wrote:This should be fun, once the power comes back on.
Yes. We find electricity is very useful around here!


Here too!
And now that it is back...
So our highest hourly power use between November and today was 4.4kWh.
So this can be taken care of by a single PowerWall. The duration is going to be the killer.
December 5th looks like one of the higher use days. However, while the hourly high use for 4.4kWh (around dinner time), our daily use that day was 26.7kWh.
We would need two PowerWalls to supply power that whole day without any changes to our routine, if we had no solar panels.
With the solar panels, we are down to a deficit of 17kWh for that day.

Power outages, and going off grid are very different though.
Being on the grid, we can bake, cook, charge our cars, etc, whenever we like.
In the event of a day, or longer, power outage, we can easily limit the amount of cooking we do and many other activities that take power.
Going off grid though, requires a more regular focus on power use. For example, I would not have a small fridge downstairs.
We would bake during daylight hours with lots of sunshine and store the results.
I'd rely a lot more on the microwave during dark hours.

And of course, this winter wasn't the coldest we have ever had. Non-the-less, I would estimate one PowerWall would be sufficient to get us through two days of no power at reduced capacity (no car charging, no oven, etc). A day and a half of the absolute worse case scenario of zero solar power (which is unusual).

Going off grid though, with no changes, would have required about 1200 kWh of storage (peak to trough of our production graph).
This would be about 95 PowerWalls! Or about $500,000. Very expensive indeed.
Pulling the cars out of the formula, it would be about 40 PowerWalls (the garage just might be able to fit that;)).


The above is all without the cars.
Previous owner of Prius, Volt & Leaf
Current owner of Model S
http://www.netzeromn.com

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RegGuheert
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Re: What Size Battery Would You Need to Power Your House?

Wed Mar 08, 2017 3:24 pm

Zythryn wrote:Our meter "reverses" direction every night.
Our first measured daily net loss was in early October, although I am sure there are days every month.
Our first measured weekly loss looks like it was the last week in November.
Monthly loss would be December.
O.K. That matches us so far...
Zythryn wrote:The first monthly gain would be February, weekly looks like the first week of January and daily, well those are scattered throughout the winter.
http://www.netzeromn.com/blog/the-envelope-please
O.K. That's different. February is always a significant loss for us. March is the first month with gains.
Zythryn wrote:The standard charger in a Tesla is 10kW. The car can be set to charge at less than the maximum. I typically charge at 18A or about 4.2kW.
If I were going off grid, I would likely set them to charge at 12A/3kW. For our driving habits, that is sufficient.
I also try to charge when the sun is shining, which means the car has little impact on the net power use of the house.
Thanks. I had forgotten that the Tesla is programmable. I agree that charging at the lowest power level necessary makes a lot of sense.
Zythryn wrote:So our highest hourly power use between November and today was 4.4kWh.
That's very good! I suppose that is the beauty of a ground-source heat pump versus a air-source heat pump like we have. Your house is WAY better insulated than ours, though your outdoor temperatures are also lower. Below about 10F, the resistive heaters come on in our air handler. I don't know their exact power rating, but I expect the entire system likely draws about 15 kW when they are on.

OTOH, it appears you have an 18.6 kW PV array on your home. Certainly in the springtime your production must approach that level. The inverter needs to be sized for the maximum power flow in either direction if you intend to keep all electricity in-house. I would think that your house may have as much as 14 kWh flowing out during some hours of the year. Peak is probably sometime in April, but you must also have fairly-high production hours in the middle of the wintertime.
Zythryn wrote:So this can be taken care of by a single PowerWall. The duration is going to be the killer.
December 5th looks like one of the higher use days. However, while the hourly high use for 4.4kWh (around dinner time), our daily use that day was 26.7kWh.
We would need two PowerWalls to supply power that whole day without any changes to our routine, if we had no solar panels.
With the solar panels, we are down to a deficit of 17kWh for that day.
That's extremely good! If only more homes were built the way yours is...

I will note that I see single-day consumption numbers in the middle of December of about 3X what occurred on your graph December 5. (That would match my worst day, which was December 16, 2016.) I also see three-day drops in both the middle of December and around the 10th of January that appear to be 200 kWh total drops. The middle day in each of those drops appears to be a drop of over 80 kWh. Of course that data includes your cars, but all my data includes my LEAF, as well.

It seems to me that you will come in WAY below the 22 MWh/year that you mention on your website, even while fueling two EVs. Let's say the EVs use about 5 MWh/year total. That would mean the rest of the house consumes 17 MWh. Do you have an updated estimate where you will come in for the year?
Zythryn wrote:And of course, this winter wasn't the coldest we have ever had.
No, in fact it was one of the warmest here. But it followed a warm summer in which we used much more electricity for air conditioning than normal. The result was that are total electricity usage was very close to normal.
Zythryn wrote:Non-the-less, I would estimate one PowerWall would be sufficient to get us through two days of no power at reduced capacity (no car charging, no oven, etc). A day and a half of the absolute worse case scenario of zero solar power (which is unusual).
I think we'd need 25 Powerwalls to cover the same two worst-case days here. (In reality, we would just turn off the heat pump and burn wood pellets. The pellet stove only draws about 120W of electricity.)
RegGuheert
2011 Leaf SL Demo vehicle
10K miles: Apr 14, 2013, 20K miles (55.7Ah): Aug 7, 2014, 30K miles (52.0Ah): Dec 30, 2015, 40K miles (49.8Ah): Feb 8, 2017, 50K miles (47.2Ah): Dec 7, 2017.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

VitaminJ
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Re: What Size Battery Would You Need to Power Your House?

Wed Mar 08, 2017 4:05 pm

While PowerWalls are totally cool, they are expensive. Adding batteries to your house can cost a lot less if you go with good old fashioned lead-acid. The house is not a vehicle and the batteries sit in the garage or shed and never move, so the biggest benefit of lithium, being lightweight, is wasted. A PowerWall 2 is 14kwh and 7kw continuous discharge which can be matched by 6x 100Ah 12v marine deep cycle batteries that cost about $100 for 100Ah new. 14kwh would cost $600 instead of $5,500, nearly 10 times less. Now the PowerWall probably actually can deliver a bit more of that 14kwh than the equivalent lead-acid bank, and of course it takes up far less space. I am years away from venturing into solar for my house, but you two who are clearly way deep into it; why are you speccing PowerWalls instead of cheaper lead-acid batteries? Especially when it seems like the economic factor is the biggest decider to go/no go.
2013 Ocean Blue SV w/ QC and LED
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RegGuheert
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Re: What Size Battery Would You Need to Power Your House?

Wed Mar 08, 2017 5:28 pm

VitaminJ wrote:While PowerWalls are totally cool, they are expensive. Adding batteries to your house can cost a lot less if you go with good old fashioned lead-acid. The house is not a vehicle and the batteries sit in the garage or shed and never move, so the biggest benefit of lithium, being lightweight, is wasted. A PowerWall 2 is 14kwh and 7kw continuous discharge which can be matched by 6x 100Ah 12v marine deep cycle batteries that cost about $100 for 100Ah new. 14kwh would cost $600 instead of $5,500, nearly 10 times less.
Actually, you need twice as many lead-acid batteries to get a similar capacity. And if you want a reliable system, you likely want to purchase 12 4-V L16 size batteries, each costing about $250 each, or about $3000 total, not including the expensive wires you will need to connect them. That gets you a 48-V battery with energy efficiency about 60% of the Powerwall 2, no capacity warranty and lots of operational limitations. You can expect to get about five years out of such batteries if you take very good care of them. If you want lead-acid batteries that will outlast the Powerwall, you will pay as much or more than you pay for the Powerwall, but they will still have the low efficiency.

If you want something that you can put in place an not have to fiddle with (until they are worn out in 10 years), then the Tesla Powerwall or the Enphase AC Battery are the way to go.
RegGuheert
2011 Leaf SL Demo vehicle
10K miles: Apr 14, 2013, 20K miles (55.7Ah): Aug 7, 2014, 30K miles (52.0Ah): Dec 30, 2015, 40K miles (49.8Ah): Feb 8, 2017, 50K miles (47.2Ah): Dec 7, 2017.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

LeftieBiker
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Re: What Size Battery Would You Need to Power Your House?

Wed Mar 08, 2017 6:25 pm

The house is not a vehicle and the batteries sit in the garage or shed and never move, so the biggest benefit of lithium, being lightweight, is wasted.


The biggest advantage is being able to discharge to 20% or even less, recharge, and repeated for hundreds to thousands of cycles without severe capacity loss.
2013 "Brilliant Silver" SV with Premium Package and no QC, and 2009 Vectrix VX-1 with 18 Leaf cells.

The most offensive, tasteless phrase in use here is "Pulled the trigger." I no longer respond to posts that use it.

VitaminJ
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Re: What Size Battery Would You Need to Power Your House?

Wed Mar 08, 2017 6:36 pm

Clear, succinct answers. Thank you, guys. I can't help but think that a smashed up Leaf with a good battery might be a good cost effective donor for a household system.
2013 Ocean Blue SV w/ QC and LED
- +0.2 mi/kwh Aeromods
- 2lb 5Ah LiFe 12v battery

GRA
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Re: What Size Battery Would You Need to Power Your House?

Wed Mar 08, 2017 7:12 pm

Since I used to design off-grid systems, I'll chime in.

1. If you've got the grid and it's reasonably reliable, especially if you've got net metering and PV, there's simply no financial justification for going off-grid unless your grid rates are in the stratosphere.

2. Using electricity for space heat/ranges/drying in an off-grid home simply isn't cost-effective unless you've got year-round hydro, and probably not even then. Occasional microwave use is okay.

3. Demand reduction is the name of the game - it's far cheaper to control your max. load by load-shifting than it is to try and run everything at once. As it's an individual home, you have complete control over how much you're willing to do this. Shave your peaks!

4. Before even thinking about going off-grid, first spend your money on getting the most efficient appliances, improving insulation, making use of passive solar, closing room doors, using task rather than area lighting (and shutting lights off as soon as you leave a room), putting always-on loads on switchable load strips etc. This ties in with number 3. It's still far cheaper, even with the huge price drop in PV and wind since I was doing this, to spend thousands on efficient loads rather than tens of thousands on extra generation and storage plus inverters. As a general rule, forget air conditioning - plan on evaporative cooling if your humidity allows, plus passive cooling (a heat pump's a good step, but better to limit its use by use of insulation and passive solar design instead).

5. Designing for year round off-grid, all you need is your worst case data in whichever season's critical for you (usually winter) , the number of days you want to have backup, and decide how much you're willing to practice demand reduction/load shifting. In other words, are you willing to hold off on doing the laundry until it's sunny/windy, use a clothesline, and make sure you're not operating your shop tools, the microwave and blender at the same time, while you've got the TV on.

6. If you want, it may make more sense to only provide enough back-up storage for whichever circuits that you consider critical in emergencies, typically enough to run the refrigerator and a few lights, plus a radio (and maybe charge a cell phone or two if you don't have a land line). Beyond a few days storage, a small genset is probably cheaper for rare outages.

The typical full size off-grid home around the Bay Area might use 2-5kWh/day (no car charging), some much less, versus the 18kWh/day average for PG&E. My usage in my current small apartment usually runs well under 2kWh, as I have a small single gas wall heater and a small gas range. Largest single electrical draw is the non-efficient apartment-sized (14 cu. ft.?) refrigerator, which is a max. of about 1.4kWh/day on the hottest days, maybe 400 Wh/day in winter. Going to a Sunfrost RF-16 running 12 or 24V DC would drop that to around 700 Wh/day, max. All other electric loads are either true/on/off or on switched power strips, to eliminate vampire loads, and I normally have just a single CF task light on. No security lights are used or wanted. All this is typical of off-grid practice (even though I'm on-grid now).

In summary, unless the average person living on-grid is willing to make major changes in their lifestyle, going off-grid is rarely a good idea financially or practically. My customers had already made that decision and mostly decided what parts of their behavior they were and were not willing to alter, so there was no problem.
Last edited by GRA on Wed Mar 08, 2017 7:19 pm, edited 1 time in total.
Guy [I have lots of experience designing/selling off-grid AE systems, some using EVs but don't own one. Local trips are by foot, bike and/or rapid transit].

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RegGuheert
Posts: 5617
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Re: What Size Battery Would You Need to Power Your House?

Wed Mar 08, 2017 7:19 pm

VitaminJ wrote:I can't help but think that a smashed up Leaf with a good battery might be a good cost effective donor for a household system.
Member 'offpist' did just that. It looks awesome! The difference is that one is an off-the-shelf product and the other requires quite a bit of engineering and fabrication.
RegGuheert
2011 Leaf SL Demo vehicle
10K miles: Apr 14, 2013, 20K miles (55.7Ah): Aug 7, 2014, 30K miles (52.0Ah): Dec 30, 2015, 40K miles (49.8Ah): Feb 8, 2017, 50K miles (47.2Ah): Dec 7, 2017.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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