House Battery and Energy Management

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Joined
May 25, 2017
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396
Hi folks. I've put all my time and effort so far into understanding batteries. I've not even begun to discover how to make one work for a whole house yet. In fact, I had only ever intended to use old laptop cells to make small projects; the largest being an eBike.

Since I've been part of this community though, the idea of a power wall has grown on me. It just makes too much sense to have one. So I'm going to add this to my list of things to do to make my house more energy efficient. It's already a long list...

First, a little info about the building. It was made in 1941, and the outer walls are cinder-block rather than wood. This makes it very durable as well as resistant to carpenter ants, mold, and rot. I live in the Pacific Northwest area of the US, so these things are big issues here! Unfortunately, the R value of cinder-block is around 2-ish. So we spend a lot of energy heating and cooling. The attic space is also under insulated. And under ventilated. The good news though, is that there's lots of room for improvement.

So there's two ways to reduce the electric bill:
- Use less engergy
- Find cheaper energy
I intend to work at it from both sides.

On the energy efficiency side:
- The old single-pane windows have been replaced with modern ones.
- The old back door made from a single sheet of plywood has been replaced with a modern insulated door.
- The front door and basement door need to be replaced.
- The basement is in the process of getting additional insulation
- The main floor walls need insulation. I'm looking at a product called Fill-5000 (basically a truckload of expansion foam) to insulate without having to tear the place apart.
- The attic needs proper ventilation and insulation.
- Ye Olde furnace could be replaced with a modern heat pump.
- Air ducts could be improved for better air circulation.
- Electric hot water tank could be replaced with an on-demand water heater.

On the cheaper energy side:
- Solar would work great in the summer, and ok in the spring and fall. Winter is almost always overcast here.
-I don't know if a wind turbine would be effective in my area or not. I have to read up more about it.
- I'm also looking at upgrading my little 1500W gasoline generator with a gasoline/propane generator closer to 3500W. Still reading up on that, but during a power outage, I could conceivably run the house of the battery, and at least slow down the discharge rate with the generator.
- And if all else fails, I can use the grid to keep the battery charged in case of power outage. This is more common in the winter due to wind storms.

Do people charge their batteries with more than just solar? I need to read more of the DIY builds here to see what others might be doing. Based on what little I do know, here is how I think a house battery might be set up:

image_gtmbiz.jpg


I know there are solar charge controllers with MPPT to get the most from the panels. I don't know how power from a wind generator would be controlled. I've never heard of a wind charge controller. I'd expect the gasoline/propane generator as well as the grid input would run on a regular A/C charger. Just have to find one to fit the battery.

As far as the battery, I know I'd want 48V, but I don't know the other properties yet. I'm not even sure what chemistry I want. They all have their pros and cons. I also need to learn what the energy usage of my house is like. I can get overall consumption from my power bill, but what about peak usage? How much power am I using if all my stuff is running at once? So I've got some learning there to do.

Related to that is the inverter. 48V DC to 220V A/C @ 60Hz. That should be no problem, but what about the Amps? Again, gotta know how much power my house uses so I don't accidentally buy an inverter that can't handle the load.

After the inverter is where my knowledge gets really limited. The inverter has to feed the service panel in order to feed the house. But it has to be able to isolate the battery power from the grid power in case of an outage. Turns out, its both illegal and immoral to electrocute linemen. But the battery still needs to power the house during an outage. I really don't know how all that works.
 

floydR

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Aug 23, 2017
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An Automatic transfer switch would be needed I believe.
48v split phase 220v a/c @ 60 hz for the inverter

later floyd
 

daromer

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If you check my videos you have videos about ATS as Floyd talked about. Thats one way to do it but let your electrician deal with that is my suggestion.
 

not2bme

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Oct 16, 2017
Messages
493
Depending on how much your budget is will also determine how you would go about installing it. Using an ATS means you're either on-grid or off-grid. All the ATS does is it detects if there's grid voltage, then otherwise it flips over to the backup (generator/solar/etc.). But I guess you can configure an ATS just to have it cut the grid off.

Otherwise you can have the power from the grid go directly to the inverter and then the inverter to a subpanel. This subpanel will have all your circuits that are on the inverter/solar/battery. These inverters can be an grid interactive or a hybrid/grid-zero inverter like a Mppsolar or Outback Radian. So they can use battery until it runs out and switch back to mains, and in the hybrid versions send power back into the grid (grid-tie).
 

egam

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Mar 9, 2017
Messages
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Before you insulate your house, have a blower door test run to check for air leakage. Do it now in the winter time. Then borrow or buy a thermal camera and walk around the house while the blower door test is running and look for cold spots around windows doors, foundation rim joist, etc.

You can use a smoke pen or a smoldering cigarette to identify where air is coming in.

Have the rim joist area (if your house has a rim joist) in the basement foam sealed with closed cell foam.

Go up into the attic and foam seal all of the perforations for plumbing and electrical that come up through walls into the attic space.
Put foam dog houses over the can lights and use expanding foam to lock them in.
Caulk around window trim and door trim to cut air flow.
remove baseboard trim and caulk the joint between the floor and the wall and then put the trim back.
The air sealing is the least expensive best bang for the buck in the entire house.
After air sealing the house, repeat the blower door test.
 
Joined
May 25, 2017
Messages
396
Thanks all for the responses.

It's extremely difficult to get professionals in to do work on just one house. At least around here. I also live from paycheck to paycheck, so my overall budget is just what little I have extra at the end of the month. So these larger jobs can be quite a challenge, but given time, I'll get them done. :)

I've been reading up on my local electrical provider, and they have a particular way they prefer on-site power to connect with the grid. They're not too keen on house batteries for some reason. But I'll leave the grid connection stuff up to them. Looks like there are going to be some kind of subsidization for folks installing solar panels in the near future.

I've also been searching for power usage monitors. I found one I think is promising:https://smile.amazon.com/dp/B075K6P...liid=I2FK0N9K0AXYIE&colid=2PNK8X8OP06KO&psc=0Not the most expencive one I've seen, but also not the cheapest. Seems to have fairly good reviews too.

Another thing I continue to consider is what battery chemistry to use. Now, I love 18650 cells. But they seem to be getting more and more difficult to find used at $1 per cell. I'm just not willing to pay more than that for a used cell that may or may not work. And so many are needed for a power wall, than I'm not sure it's the thing I want to do. I've expanded my research to include other formats and chemistries. So far, the top contenders are those big Headway cylindrical cells (LiFePO4), Lead-Acid, or maybe Nickel-Iron. I only recently heard of the Nickel-Iron ones, but the more I read about them the more fascinating they become. I won't be able to properly compare them though until I know how much power my house uses.
 

BlueSwordM

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Jul 5, 2017
Messages
423
First off, save some money before doing this. Being prepared financially is quite important.

Also, the reason they aren't keen on house energy storage is because if it isnt done well, there is some very high voltage which can go back to the grid if it isnt done well, and when there's a lack of a functioning electrical grid, that can be very dangerous not to know there is some voltage going through.
 
Joined
May 25, 2017
Messages
396
Well, some good news: It turns out my power company replaced my old meter with an electronic one a while back, and that has automatically connected me to their power monitoring data. So I don't need to spend money on my own monitor. I can read their data for free!

Some not so great news: It seems that between my old inefficient house, and my old inefficient electric furnace, I'm using somewhere between 50-150 kWh of power each day. Really depends on weather. December and January tend to be the coldest months here, and I can use up to 5,600 kWh in a month. Looking back on my records, it was way worse before I replaced all my single-pane wood frame windows with double pane vinyl. In the summer I use around 1,000 kwh in a month.

Is that a lot? It seems like a lot. I've been reading other folks' powerwall builds here. They are fantastic, but they focus on building the battery packs mostly. I'm still reading though, and the more I learn, the more I know what to pay attention to as I read. I'm still trying to figure out how to size my house battery based on my daily power usage. Websites and videos all tell me to add up individual devices and estimate how often I use them. Seems though, that knowing my daily consumption is what I'm after, and I already know that. But it fluctuates so wildly between winter and summer. Which extreme should I use? Should I average them?

Another factor I need to know, I think, is how many Amps would be drawn from the battery at a given time. This one seems a bit more straightforward to me. As far back as the records go, I've never peaked at more that 5,600 W at any given time. My power meter seems able to record power usage in 15min intervals. This data seems to only be kept for a couple months at a time, but lucky me, I'm looking at Dec. and Jan. My two most power hungry months. I figure if I round that up to 6,000 W, then the most I'd draw from the battery, at 48V, would be 125A. So as long as I design my battery, cables, and inverter to be able to handle that kind of load, I should be fine. Especially since the majority of the time, my power consumption is way lower than that. The 5,600 W peak only happened once during the two coldest months.

I have a ways to go yet, but I certainly know more now than I used to, and I'm definitely going to know more in the future before I start building anything. And at the same time, my house has a lot of potential for reducing overall power consumption, so I'll be working on that side of things too.
 

Korishan

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rebelrider.mike said:
Websites and videos all tell me to add up individual devices and estimate how often I use them. Seems though, that knowing my daily consumption is what I'm after, and I already know that. But it fluctuates so wildly between winter and summer. Which extreme should I use? Should I average them?
Yep, that's exactly what you needed was the daily consumption. Now that you know that, you can move on to the next step.
That next step really depends, though. You can either build a power storage for your max consumption (ie, winter consumption), or you can start doing some more power efficiency renovations to the house first. I think you will find that you are loosing a lot of heat somewhere and that is why you are using so much more power in the winter. So you may wanna look into your ceiling/attic areas and try to improve heat retention.
My uncle spent $200+ for Dec due to enormous heat loss. I don't think they really knew how bad it was before. You could sit in the chair next to the window and it felt like you had a fan blowing across your feet cuz the window was so badly sealed.

rebelrider.mike said:
Another factor I need to know, I think, is how many Amps would be drawn from the battery at a given time. This one seems a bit more straightforward to me. .... I figure if I round that up to 6,000 W, then the most I'd draw from the battery, at 48V, would be 125A. So as long as I design my battery, cables, and inverter to be able to handle that kind of load, I should be fine. Especially since the majority of the time, my power consumption is way lower than that. The 5,600 W peak only happened once during the two coldest months.
Right on track. And 125A draw isn't that bad, over all. You just need to size the individual packs to handle that draw.
If you design 14sXp where each pack is paralleled cells, then 125A draw / 1 per cell max = 125 cells per pack. You could also have two strings to handle the load, so you'd have each pack of about 80p (75 x 2 = 125, so rounded up to next size). This would be in line with what Pete and daromer and others hav others have done with multiple strings.

Now, if you figure out your leakages, then you can lower the needed amps quite a bit.

Always good to work things out before you build anything. Makes the work a lot easier ;)
 

not2bme

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Oct 16, 2017
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rebelrider.mike said:
Some not so great news: It seems that between my old inefficient house, and my old inefficient electric furnace, I'm using somewhere between 50-150 kWh of power each day. Really depends on weather. December and January tend to be the coldest months here, and I can use up to 5,600 kWh in a month. Looking back on my records, it was way worse before I replaced all my single-pane wood frame windows with double pane vinyl. In the summer I use around 1,000 kwh in a month.

Have you looked into heat pumps? It's far more efficient than any electric furnace. I am looking into a split unit myself and looking into something like a Fujitsu RLS3.
 

Oderus420

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Oct 1, 2017
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not2bme said:
rebelrider.mike said:
Some not so great news: It seems that between my old inefficient house, and my old inefficient electric furnace, I'm using somewhere between 50-150 kWh of power each day. Really depends on weather. December and January tend to be the coldest months here, and I can use up to 5,600 kWh in a month. Looking back on my records, it was way worse before I replaced all my single-pane wood frame windows with double pane vinyl. In the summer I use around 1,000 kwh in a month.

Have you looked into heat pumps? It's far more efficient than any electric furnace. I am looking into a split unit myself and looking into something like a Fujitsu RLS3.

I looked into Heat Pumps and was advised to not bother. Heat pumps don't work very well below -20C and depending on where you are, the Heat Pump won't perform as well as other areas. I think high humidity works better because there's more 'heat' in the air compared to here where we're almost considered desert it's so dry. Plus, natural gas is very cheap and excellent for heating a house.

My parents had a Heat Pump when we lived in Quebec where's the lots of humidity. In Calgary, it's just not worth it. So I'm told.
 

daromer

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Look at ground or deep drilled heat pumps. They arent as much affected by air temperature ;)

Though Im running heat pump here and its bloody efficient down to -18C. At -15 its still coop of 3x and thats rather good!
 

Oderus420

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daromer said:
Look at ground or deep drilled heat pumps. They arent as much affected by air temperature ;)

Though Im running heat pump here and its bloody efficient down to -18C. At -15 its still coop of 3x and thats rather good!

That's a good alternative. Where I am, it can hit -30C easily and natural gas is almost as cheap as electricity yet more efficient for heat.
 
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I would love to have a heat pump! In my area, the climate is excellent for one to function. It rarely gets much below freezing in the winder. Snow is rare. In fact, we really only have two seasons: rainy and sunny. In the summer, it usually only gets up to about 95F (35C). So it should keep up in the summer too. I don't know if this is true everywhere, but around here, heat pumps have a build in backup furnace. Usually electric, but sometimes gas. The furnace kicks on when it gets too cold for the pump to keep up. Or for when it's defrosting.

But there's plenty to do to this old house to make it more efficient. The insulation is inadequate everywhere, and can be greatly improved in most places without a major renovation. The air ducts are a hodge-podge of different eras bolted together. They could most likely be moving air easier and with less power if they got modernized. So much stuff to do!

At some point, I'll post my math for battery design, but I'm still working on it. Still finding errors and omissions. :)
 

daromer

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In many cases insulation makes more out of it but its also alot more work. Installing just going from direct electric heating to a pump makes a difference. If its not that cold a normal air pump will do but for colder climates soil based one could work fine but for colder then deep drilled is better. Of course more expensive :)
 

floydR

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rebelrider.mike said:
I would love to have a heat pump! In my area, the climate is excellent for one to function. It rarely gets much below freezing in the winder. Snow is rare. In fact, we really only have two seasons: rainy and sunny. In the summer, it usually only gets up to about 95F (35C). So it should keep up in the summer too. I don't know if this is true everywhere, but around here, heat pumps have a build in backup furnace. Usually electric, but sometimes gas. The furnace kicks on when it gets too cold for the pump to keep up. Or for when it's defrosting.

But there's plenty to do to this old house to make it more efficient. The insulation is inadequate everywhere, and can be greatly improved in most places without a major renovation. The air ducts are a hodge-podge of different eras bolted together. They could most likely be moving air easier and with less power if they got modernized. So much stuff to do!

At some point, I'll post my math for battery design, but I'm still working on it. Still finding errors and omissions. :)

You might consider getting a mini split system, there are multi zone mini split systems some with backup heat.

later floyd
 

Korishan

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rebelrider.mike said:
I don't know if this is true everywhere, but around here, heat pumps have a build in backup furnace. Usually electric, but sometimes gas. The furnace kicks on when it gets too cold for the pump to keep up. Or for when it's defrosting.

Yes, that is correct. And depending on the unit, you can have anywhere between 1 element and 5 elements. Not sure when they kick in, though. But they are referred to as "Emergency Strips" on the thermostats. They run really hot when they come on. In fact, they won't engage until the blower fan has been running for a few minutes, then they turn on 1 element at a time with at least 1-2 minute intervals. Then when shutting down, they all go off and the blower fan will stay on for at least 5 minutes to make sure everything is cooled down. Of course, it is shorting out 240V through a resistor :p
 
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I've been reading on the different types of home power systems out there. I want to try and get my terminology right so as to make as little confusion as possible.

  • On Grid: Traditional use of power exclusively from the grid.
  • Battery Backup: System runs exclusively on grid power. A battery is kept charged and is used in the event of grid power loss to power the home.
  • Off Grid: Home generated power, for home use only. The grid is not even connected.
  • Grid Tie: System can be switched to use either home generated power, or grid power. The two sources are isolated.
  • Direct to Grid: System runs on home generated power, with excess power sent back to the grid. If the grid power goes out, the whole system is shut down for safety.
  • Grid Tie UPS: System runs on home generated power, with grid power as a backup. Excess power is stored in a battery, or sent to the grid if the battery is full.If home generated power is insufficient, grid power is added to compensate. If grid power is lost, home generated power can still be used, but is isolated from the grid.
That's how I understand it anyway. I don't think there is a universally accepted set of terms, but someone set me straight if I'm wrong! :)
That last one seems the most complicated and difficult for me to summarize. So of course, it's the one I'm going for. Here's a picture of how I imagine it might work:

image_iqskje.jpg


Is there even such a magic box that does all that? And what happens to my service panel? So much stuff I still don't know!
Well, at least I've figured out that 125A will give me a 10% safety margin. That right there took some math to figure out. But whatever inverter I use will need to be able to handle at least that much current. That safety margin will only get better as I make improvements to my house.

Switching back to batteries: I've been researching four chemistries; lead/acid, Li-Ion, LiFePO4, and Ni-Fe. There are other chemistries out there, but they are either too undeveloped, or just not feasible to use in a house battery. Some of the ones I immediately rejected were NiCd, NiMH, and saltwater.

Here's why the four chemistries first interested me:
  • Lead/acid: cheap, easy to get, easy to recycle. Weight and maintenance don't bother me. The best form factor for my use would be FLA
  • Li-Ion: potentially cheap, energy dense, long lasting, big coolness factor. The best form factor for me would be 18650s.
  • LiPO4: super safe, energy dense, long long lasting. Best form factor for me would be prismatic. Space is also not an issue for me.
  • Ni-FE: super rugged (electrically), will last longer than I will, coolness factor, can be repaired. Seems there is only the one form factor.
I'm still not quite ready to publish my math, because I think it still has flaws. At least I hope it does, because it keeps telling me I'll never be able to afford any of this, LOL. But I can at least make comparisons between the chemistries as far as cost to buy and maybe cost to own. After reading the datasheets on the batteries I would buy if I picked my favorite of each type, the order of cheapest to most expensive as far as purchasing would be:
  1. Li-Ion
  2. Lead/acid
  3. LiFePO4
  4. Ni-Fe
Here is cheapest to most expensive looking at price/kWh:
  1. Li-Ion
  2. Lead/acid
  3. LiFePO4
  4. Ni-Fe
Butthere is the cost of each over time. Again cheapest to most expensive life:
  1. Ni-Fe
  2. LiFePO4
  3. Lead/acid
  4. Li-Ion
Cost across the life of the battery is tricky though. It assumes you can accurately predict individual cell death. But of course, we Second Lifers know that some cells can last years beyond their predicted expectancy. The lithium based cells are certainly the least known as they're relatively new technology. Lead/acid is fairly accurate from what I've read. And Ni-Fe blows them all away with its ability to last 30 years between refurbishment, and the fact that with refurbishing, a cell can potentially last 100 years or more!

Longevity isn't everything though. One must also consider efficiency. Lead/acid and Ni-Fe have relatively high internal resistance, so they'll take more power to charge than a comparable lithium based battery. They also have a high discharge rate compared to lithium. They are so much more electrically robust than lithium cells though. So many factors to deal with!

Finally, here is why I may ultimately choose NOT to use each chemistry:
  • Lead/acid: Lifespan is too short. It's going to be a pain to swap them out every few years.
  • Li-Ion: I will need too many. Thousands! And they are getting more expensive due to increased demand.
  • LiFePO4: Low Voltage and energy density compared to Li-Ion. Very expensive to buy.
  • Ni-Fe: High discharge rate, low efficiency, uber expensive to buy.
Interestingly, the LiFePO4 is the one I have most difficulty dismissing for a house battery. Perhaps that means something...
 

not2bme

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Oct 16, 2017
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Some info in the FAQ
https://secondlifestorage.com/t-Frequently-Asked-Questions-FAQ?pid=20066#pid20066

I wrote this when I was bored.
https://secondlifestorage.com/t-Off-grid-solar-for-house?pid=23221#pid23221


As far as battery chemistries goes it falls into three categories:

1. Upfront Cost - How much it cost to get going
2. Life - How long the batteries last (also part of total cost of ownership/tcos)
3. Time/Effort - How much effort and time to build pack


1. Li-Ion - Upfront cost is low if good source and patience to find it. Otherwise mid to high. Life is good, hbpowerwall's been running strong for 2 years+ on recycled batts. You get 3000-5000 cycles so 10 years is possible lowering total cost of ownership. Time and effort is high to build.

2. Lifepo4 - Same as Li-Ion. The only thing is twice the space of Li-ion. Time and effort depends because if you get large prismatic packs ready made it's easy. if you get small cells then as hard as li-ion

3. NiFe - Upfront cost is high, very high. Life is good, but tcos is pretty bad because of the inefficiencies requiring larger panels. Can't pay for itself for a long time. For doomsday I'd recommend. Time and effort is low since cells are fairly large.

4. Lead-cell - Upfront cost is low to mid depending on how good deep cycle you get. Life is bad, even with the best of the best you can only 50% duty cycle to get any good life out of them so you have to double the amount or buy twice as often lasting 3-5 years max. Time and effort is relatively easy because of large cells.
 
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