House Battery and Energy Management

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Crimp Daddy

Member
Joined
Feb 21, 2018
Messages
963
@completelycharged

Thanks for helping me see the connection between cost per kWh, and life cycle.

I guess its the same math that explains why lithium cells are a much better deal than lead acid even with the bigger up front cost as it has a much longer service life.
 
Joined
May 25, 2017
Messages
396
Thanks for the replies! :) See my first post to see what I have planned to help reduce energy consumption. I double checked my math, and I've definitely taken into account that the cells with less than 100% DoD will not yield their full capacity. I've listed each cell's usable energy in Wh and have done the rest of the calculations based on that value. I'm not sure how to use the $/kWh value yet. And the math I used for price per year is rather clumsy still, with lots of assumptions I'm not sure about. I'm not really satisfied with it yet.

The cost of installation seems the most concrete number I can grab hold of in my mind. The cost does seem high, but I've checked over and over again, and I just don't see how to build a battery any cheaper. Also, yes, all the labor and time to build and install any of these batteries would be from me, and therefore free. I'd be able to pick up lead/acid batteries locally, but all other chemistries I'd have to have shipped. I accounted for that in the cost per cell or battery.

Oh, I've also chosen not to take weight, size, or maintenance into account as those are not really factors that apply to my situation. For other folks, these might well be important factors.

I have 3 locations I can place solar panels, but I still need to measure the areas so I can figure out how many panels I could fit. Then I have to learn how to figure out how much power that would generate, how to wire, local laws, etc... I just haven't tackled all that yet. I'd like to have some wind turbines too. I know even less about how to do that than solar panels though. Around here, we get a fair amount of wind in the winter time. My guess is though, that I'll probably always need grid power in the winter. Just too dark and cold. That's a gut feeling though. I haven't done any research to find that out for sure yet.

I expect this project will take years as I try to scrape the money together for ductwork improvement and furnace replacement. The furnace I have now accounts for more than 3/4 of the power bill in the winter. Not to mention all the other stuff I've got to improve.But like I said, that's all been listed on the first post. So I've got plenty of time to learn and plan before I get started. Of course, I will continue to collect 18650s in the meantime. Even if I don't use them for a powerwall, there's still tons of smaller projects to use them on. :)

Anyway, thanks for the responses. I'll have to re-read Completelycharged's post a few more times and try to wrap my brain around it! :)
 
Joined
Mar 7, 2018
Messages
1,055
I like pictures....


image_zjktqz.jpg


In the chart if you had a solar install of at least 7kW this could be what a winters day looks like for you.

The charge into the battery only needs to be discharged slowly and with a smaller inverter rather than trying to scale the system to run the house as a whole for 3 hours. If you need to go off grid for 3 hours to cover power loss then I would have thought the furnace is not a priority item to power during this time. The best equivalent for a battery for the furnace is just to heat up around 400kg of steel and then you have a thermal energy store to draw on for 3 hours. Batteries are expensive store of energy and storing heat via a battery will not be economically viable for at least 5 years, even with the best technology, compared to a passive heat store.

In terms of bang for the buck I would suggest that, if you can, install a wind turbine I would put this as the priority ahead of any solar or battery project. Take a look at pvoutput.org and find a site near you and look at the live output data as this will show yuou how much W output you would get for a solar install on your roof (look at which way the solar is also facing as this has a big impact). If you can mount the panels on the ground this may be a better option because you can angle the panels best for the low sun in the winter and ensure they are facing south.

If you had only a 500W wind turbine, which during the winter could average around 200W output, over a day this would provide 4.8kWh and this is greater than the output you might get from over 2000W of solar in winter. Some days this winter on my solar (8kW) I had less than 2kWh.... March is less than 15kWh.

I know this may not be what you want to hear as you are all fired up looking at battery storage but for your position, if money is tight, a battery system is at least 3rd on the list.... maybe the worst advice for a battery forum but that is what I would do if I were in your shoes due to the high heating load you have.


Not sure where in the state you are. This is a 4.8kW install in the west. Directly south facing with almost ideal angle for the solar panels. The ideal equivalent for you....
https://pvoutput.org/intraday.jsp?id=11202&sid=9215
Output is a bit higher than I thought for March.
My panels are laid almost flat so the worst situation for low sun in the winter.....

Another point to take into account - if you can get paid for exports from the solar then the rate at which you get paid could swing the desicion back to solar - same could be true for a wind turbine. You get paid for the excess in the summer to help offset winter.
 
Joined
May 25, 2017
Messages
396
Cool! I will definitely look into wind turbines. I've never heard of using hot metal to store heat. I'll have to look into that too. At least one of my 3 surfaces is already slanted South. The roof isn't, but the third location hasn't been built yet. It may have to be flat, but I'd rather put a Southern angle on it too if I can.

Just for fun, I did another sheet based on summer power usage. The same battery that would last 6 hours in the winter would last 20 hours in the summer. Also, the graph made me think... I don't remember if I mentioned that all these calculations I've done assume that no other energy source other than the battery is available to run the house at full power. This would be a worst case situation. Of course if it were a temporary situation, like a power outage with no wind or solar available, I could always turn the furnace off and limit use of the other appliances to stretch the battery out for several hours. But I could do that with any of the battery chemistries so none of that would matter until I know how much power I could produce onsite.

All these calcs so far are just to give me a rough idea of how much each battery chemistry might cost to do the same job. I still have to find out how much surface area I have for solar and how I might get some wind turbines. I'll probably tackle that next. :)

PVoutput.org is an interesting website. I live in Shelton, wich is a couple hours drive South of Seattle. We get a little more rain and clouds than the Seattle area, but usually not by much. Lots of sun in the summer though. :)
 
Joined
Mar 7, 2018
Messages
1,055
A long wile ago I installed over a thousand of these... they are electric storage heaters with an iron oxide brick that is heated to around 200-300C. The natural convection then allows the heat to escape through a vent in the top (no fan, etc.).

For a thermal store of energy from electric they are the equivalent of a 2-6kWh battery depending on size for the wall units.

Plus side is they will last for decades..... very few parts to go wrong or wear out...
[img=300x224]http://centralne-ogrzewanie.pl/wp-content/uploads/2010/10/elektryczny-piec-akumulacyjny-grzalki-300x224.jpg[/img]
 
Joined
May 25, 2017
Messages
396
Feels like it's been a while since I've posted, but I've been busy with lots of projects. Finally got my old car running. (Had to learn how to rebuild and adjust a 3bbl carburetor.) Extracted a 3ft root out of a drain pipe which caused leakage in my basement this last winter. Discovered my motorcycle has a bad final drive, so I'm waiting on parts to finish that, and my backup motorcycle has a bad carburetor. Just got finished taking that apart.

I did get a chance though, to finally take some measurements of the various flat areas around the house that might accommodate some solar panels. The existing places are the carport and roof. The carport has 24'x24', 576 sqft, and the roof has 21'x18', 378 sqft. Eventually I'd like to build a pergola (I think it's called) over my deck which would be 16'x15', 240 sqft, and a sort of lean-to over an additional parking area which would be 16'x8', 128 sqft.

That all adds up to 1,322 sqft, but I'm guessing that not all of it would be usable due to the shape of the panels, attaching hardware, and other things I haven't thought of, so I figure rounding down to 1,200 sqft would probably be more realistic.

I got some numbers off a panel available at Amazon just to have something to play with. I'm hoping there are better deals out there, but just to start, they've got a panel that is 100W and covers approximately 7 sqft. It would take around 170 of these panels to cover the 1,200-ish sqft I've got available. So that would give me about 17kW of advertised power.

Based on what I know about weather patterns in my area, as well as data from a couple of websites that you guys have shared (thanks!) I think I've got the expectation of the solar panels being about 3% efficient for around 3 hours per day in the winter, and something closer to 80% efficient for 8 hours per day during the summer. That works out to 1.5-110kWh per day depending on the time of year.

Not the big numbers I'd hoped for, but then I've not had a chance to research wind power yet. Also, I'm by no means an expert at solar. I could have all of this wrong! 110 kWh would be enough to cover a lot of days in the summertime though. In fact, last year's bill could have been covered from April-October with that amount of power. Though we only get that kind of sun from about May to September.
 

thanar

Member
Joined
Feb 12, 2018
Messages
154
rebelrider.mike said:
Hi folks. I've put all my time and effort
...
On the energy efficiency side:
...
- The basement is in the process of getting additional insulation

You really do not need heat insulation for any basement; underground keeps warm in winter and cool in summer, always.
 

solar_18650

New member
Joined
Apr 4, 2018
Messages
19
Regarding the solar panels it would probably be better to look at using fewer higher powered panels (around 250-300W 36V) instead of the 100W ones from Amazon.

These will be better suited for a higher voltage mains connected install than the 100W panels and would probably work out cheaper in total compared to the 100W panels if you can find a reasonable supplier.

You would connect the panels in series into a string (to determine the voltage), which you can make several of, these strings are then connected in parallel to increase the current.

Monocrystalline panels are more efficient than polycrystalline but are more expensive.
 
Joined
May 25, 2017
Messages
396
Some of my basement walls are exposed to the outside above the ground. It's those areas I'm working on. Especially where the main floor joists meet the walls. That area is especially thin and lets a lot of heat out in the winter.

I found a couple of local solar companies. Smart Energy Today, and South Sound Solar. Both have facilities in Olympia, near where I live. I'm particularly interested in Smart Energy Today, as they offer several products and services besides solar, for making houses more efficient. Neither company has specific panels listed though. But I did find some 300W solar panels from a company in California. They are cheaper and seem to offer more energy per sqft than the 100W panels. So that's a step in the right direction. :)
 
Joined
May 25, 2017
Messages
396
Still struggling to wrap my brain around solar. I haven't been able to give as much time to it lately, but I have been watching the areas whereI want to put solar panels, and I think I have a better idea as to where panels will work and where they won't.

So the roof area gets lots of direct sunlight, so that whole area is good. The carport only gets direct sun on half of it, so I'm only counting the lighted square footage. Anyway, here is what I've come up with based on numbers I could find:


image_frqtxx.jpg


I hope most of it is straightforward. At least until the last few columns. The idea is that adding up all the panels I can fit would produce 13.8kW. But I've also got to take into account the hours of daylight I can expect, as well as how overcast it is going to be. I split my year into winter and summer. (7 months of crappy weather, 5 months of excellent weather) I also looked up some numbers from websites about what I can expect from each "season". Apparently, in the winter, I can get 3 hours of good daylight per day, but because of the overcast conditions, I can expect about 3% efficiency during those hours. So 13.8kW * 3% * 3 hours = 1.2kWh per day. Maybe this is expecting too little? I don't know. Those are the numbers I found.

Summer looks a lot better. Same solar panels but with 80% efficiency (in direct sunlight) for 8 hours per day are the numbers I found. So 13.8kW * 80% *8 hours = 88.3kWh per day. I only need 50kWh in the summer to power my house for a day, so I should have enough to power my house during those 8 hours as well as 1.6kW to charge the house battery with at the same time. I'm skipping a lot of math here, but I think that works out to 30A available to the battery over the 8 hours of sunlight.

The winter will of course, be terrible for solar, but I'm also looking into wind. Every website I've found has a different average wind speed for my area so I'm not sure how much wind I actually get. It seems to me there is more during winter, so I hope it can supplement the solar for those months. But 5 months a year without a power bill is still pretty good, right? :)

My understanding is that with a wind generator, I'll need some kind of automatic switch from battery to dummy load (I don't know what those are called yet) a charge controller (I've read that MPPT controllers are bad for wind generator applications) and some kind of regulator/rectifier to make sure the power is DC and the Voltage doesn't get too high. And I guess a diode somewhere. Not sure how this all fits together yet, but I'm still reading...
 

not2bme

Member
Joined
Oct 16, 2017
Messages
493
If you have a lot of tree cover then you might want to map out those elevations into a solar site survey chart. During winters the elevation changes so much that what I thought was great during winters was just horrible during summers once the leaves came back during spring. Vice versa that the sun will be low during winters and you might not even get sun on the roof. Sun will be overhead during summers won't be in the same spot during winter. Still you should expect at least 50% of summer output on a similar sunny day during winter. Some of the maps I've seen doesn't seem so bad in Washington state as long aso you don't live on the coastal area. Far inland seems better, probably just less cloud cover. Since you're thinking about buying new panels you might want to take the extra time surveying each spot for the best output.

http://solardat.uoregon.edu/SunChartProgram.html
I used the above chart along with an app called Dioptra to map out all the tree lines and it showed me the best spot for my panels to be at.
 
Joined
Mar 7, 2018
Messages
1,055
Wind uses a dump load (electric heater) to prevent the battery from over charging, in you case your existing demand could be used and just turn the electric furnace or AC on. The dump load is just another load switched on usually before the charge controller or after depending on how you set it up. Some use the dump load for braking for excess speed. Basically you can't take the load off a wind turbine otherwise it would spin up and destroy itself, hence if you can't charge the battery or use the power it has to be "dumped" usually in the form of heat.

The charge controller for wind with 48V the choice is limited as there are relatively few controllers that are actually designed properly in relation as to how the efficiency of the wind turbine and output works. Will do another post detailing this (chart and pictures...) as I am resorting to a different approach as the only good controllers I found are all grid tied and I will be off grid. Each wind turbine is different and has it's own dynamics.

MPPT for solar can search / hunt for the best output, with wind you can't allow the load to dissapear searching for optimum output as the wind turbine would spin up and destroy itself. The tracking is different as well in relation to the voltage vs current, with wind the current increases and the voltage does as well, MPPT for solar assumes a relatively flat voltage level and varying current.

All wind turbines (ones worth considering) give 3 phase AC output.

For wind, install as big as you can...

Alternative : Use any excess solar in the summer to freeze water... cheapest energy store for AC. 1m3 of water takes around 100kWh to freeze and a chest freezer or two full of water bottles can provide a large cold store. Not the normal way to approach things but I always look at "if it works, why not ?" Use second hand chest freezers.

Used (<3 years) 260W panels should be around $100... Use new in the good locations and used for the lesser areas..
 
Joined
Mar 7, 2018
Messages
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For a wind turbine the characteristics of it are something like this with the way that the voltage increases as the current increases up until the frequency and high current then start to dissipate energy in the form of hysterisis losses in the wind turbine core, which is why the current then starts to drop.


image_cciebq.jpg


The rpm would continue to rise if not restrained and destroy the turbine, which needs a way to either turn the turbine out of the wind, alter the pitch of the blades or for the blades to "stall" like an aeroplane and they then lose lift and lose energy to turn the turbine around. Braking the turbine effectively stalls the blades and reduces the captured energy, while turning out of the wind is the most simple option.


image_xtvmbb.jpg


Ignoring the rpm (only interested in volts at this point) simple PWM type wind controllers that try to hold a fixed voltage level and will stall the wind turbine in low wind speeds (lots of people complaining on the internet about low output but do not realise why...) and therefore the wind turbine will never return much energy until it is blowing a lot and then it will over speed and either burn out or destroy itself (another set of complaints).

What a good controller should do is PWM regulate as a function of the turbine rpm or MPPT track the profile for the specific wind turbine (not all turbines have the same characteristics, unlike solar. The other option is what some other controllers do is allow set voltage levels and power output to be defined, which can then be set and matched to a turbine.

The alternative DIY approach is to use a number of boost converters and set each boost converter to a higher starting voltage level and the output current to a given level.

In the diagram I show the first startup boost converter would have an input voltage minimum of around 48.5V and an output current of say 5 Amps. What would happen is that as the turbine starts up it would reach 48.5V and then start delivering power and the voltage would be held at 48.5V until more than 5A was output and then it would rise up.

The next boost controller would have a minimum input voltage of 50V and an output current of around 5A.

The next boost controller would have a minimum input of 52V and an output current of around 5A.

The last boost controller would have a minimum input of 54V and an output current of 20A (brake, fail safe)

An additional boost could be added as a backup.

This way a few $15 boost controllers could do a far better job than a cheap PWM unit and allow them to be tuned / aldtered for any turbine.

For grid tie have a look at the settings for these units where they allow the current levels to be changed (hepefully the voltage as well)
https://www.aliexpress.com/item/100...ler-Resistor-for-3-Phase-24v/32771267646.html


image_bcmhsf.jpg



This unit seems to have no fan and an "integrated" dump load
https://www.aliexpress.com/item/48V...ybrid-charge-controller-500w/32813929689.html

I wonder what would happen if this unit needed to dump 500W for an hour and was attached to a bit of wood....

No indication if it actually tracks the rpm, volts, amps or just tries to stall the trubine delivering the maximum amps at the charge voltage.

So many of these type seem to be advertised so poorly, no wonder there are many people complaining about poor wind turbine output..... square peg, round hole.


With reference to my charts, notice that this item has a brake voltage option of 56V, note this is the 3 phase AC voltage....

https://www.aliexpress.com/item/Bra...wind-turbine-grid-tie-system/32298858960.html
 
Joined
May 25, 2017
Messages
396
This all got put on hold for 3 years, as I haven't had the time or money to deal with it. But it's given me time to think and consider many of the alternatives that folks here have suggested. Also gave me time to renovate my kitchen, and while I had the walls torn up, I ran a big ol' cable up to the second floor, and installed a sub-panel there. Now I can upgrade stuff upstairs without having to worry about how I'm going to get power all the way from the main panel in the basement up to the attic.

I have an attic fan and some soffit vents to install to increase the attic airflow. I also now have access to all parts of my attic space which I didn't have before. Which means I can now upgrade the wiring and install some good insulation. Turns out the section I couldn't get to has no insulation at all! Nothing! Great news for me, as installing proper insulation should make a big difference in energy usage.

My attic is actually split into 3 distinct sections because of the way the second floor was built. So I will need two more attic fans to finish the airflow improvement. But I already have a ridge vent, and 4 regular roof vents. So things are looking good there. Another section of the attic can get better insulation. The third area is already as insulated as would be useful. I've read that too much insulation can cause heat retention in the summer. The second floor gets HOT in the summer. 90F with 2 A/C units running. About 11,000 BTU total.

The overall plan has changed too. My house turned 80 years old this year! There are still places that need more electrical upgrades. So many things require their own circuit breakers though, that my standard 200A panel is filling up. I don't need more power, just more spaces for breakers. As many here have suggested, I'm thinking of adding a sub-panel next to the main one. I'm thinking I can leave the 240V breakers on the main, and put several 120V breakers on the sub. That being the case, I could put an isolation switch between the panels, and set up the sub panel to run on alternative power if there is an outage. In that case, I can select the circuits I want to power, and only run them during outages.

I think the alternative power will be a generator and house battery. I keep coming back to the fact that solar really only works well in the summer when I don't need it. Winter is when I need the most power, and I'm only going to be able to count on a bout 3% of the rated output on most winter days. Wind isn't a good solution in my area either. It's just not windy enough most days to make installing one worth it.

I'll have to decide which appliances and circuits I want to power during outages. All the 240V stuff is right out. I can live without those things for a while. I'm thinking the refrigerator, freezer, microwave, and a few lights and outlets should be fine. I just have to go back to the beginning and count up the energy and current for each thing like I did a while back for the whole house.

Blah blah blah, who wants to read all this anyway? But if you made it this far, thanks for your time. :) I just had some thoughts I wanted to write down and maybe see what y'all think.
 

OffGridInTheCity

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Joined
Dec 15, 2018
Messages
1,788
.....
Cycle life expectations are key to the whole economics..... work the cost to put 1kWh into your battery and get it back out again...
Yes sir. So far, I've spent $225/kwh (installed/hooked-up), to build an 81kwh 18650 second hand cell battery bank - average 90%+ capacity cells.
The 13kw PV array off-grid system has required an average of 36.3% DOD on this battery to enable 100% consumption of the power produced for my situation.

The oldest battery now has 1,160 cycles (3.18yrs) with no detectable loss of capacity so far.....

One of the huge elephants in the room is 'number of cycles' you can get out of the battery. Early on, I hoped that the Battery University chart was more correct than less correct so I went for a large enough battery to shoot for low DOD / 7,000+ cycles. Maybe I'll live long enough to see how it turns out :)
1637683546050.png


P.S. While I understand the current popular focus is LifePo4 cells - the big hold-up for me is that many seem to be class B? / suspect history? and of course the price is higher than 18650 second hand cells. So can an 18650 battery at low DOD outlast 'abused' LifePo4 cells? - the answer isn't that clear to me. Maybe I'm just 18650 biased since it's too late for me :)
 
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Oberfail

Member
Joined
Jun 22, 2021
Messages
103
At which voltage span do you use your 18650's @OffGridInTheCity ?
My reason why i will go with 18650's, is because i found a source for 1€ per laptop pack with 6 cells on average. Factoring dead & not so good cells in, i'm probably going to land at 25 cents per cell.
 

OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
1,788
At which voltage span do you use your 18650's @OffGridInTheCity ?
My reason why i will go with 18650's, is because i found a source for 1€ per laptop pack with 6 cells on average. Factoring dead & not so good cells in, i'm probably going to land at 25 cents per cell.
Operate with 3.54v/cell low (inverter cut-off) and 4.0v/cell max. At 4.0v/cell (56v) the house will run thru the night till next day PV production - e.g 24hrs/day.

The overall yearly average hi is 3.83v/cell.
 
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Wolf

Active member
Joined
Sep 25, 2018
Messages
1,613
While I understand the current popular focus is LifePo4 cells - the big hold-up for me is that many seem to be class B? / suspect history? and of course the price is higher than 18650 second hand cells. So can an 18650 battery at low DOD outlast 'abused' LifePo4 cells? - the answer isn't that clear to me. Maybe I'm just 18650 biased since it's too late for me :)
Well I know I am 18650 biased and will go to great lengths to defend them or any cylindrical Li-Ion cells. The more I learn of them the more I like them. There is no other battery package that has as much energy density in such a small form factor as the Li-Ion cell. Which understandably makes handling them somewhat picarious. Nevertheless if you follow some simple rules Li-Ion is no more dangerous than a can of gasoline, aerosol spray can or a propane bottle for your grill.
If any of these items are treated with the respect they deserve you can consider yourself safe. I don't see everyone getting rid of hoverboards, laptop computers, external battery packs, smart phones, cameras, flashlights, lanterns, powered furniture, heated clothing, car jump starters, etc because they are Li-Ion powered and welcome them into our homes without a second thought about safety.
I like the relatively predictable charge/discharge curve. I like the the ability to build my own battery with as many or as few cells as I want to achieve the desired voltage and Ah output. I like recycling them in an effort to keep as many good cells out of the wastestream.
Once you understand the mechanics of a Li-Ion cell you learn which ones are good and which ones you want to stay away from.
Also the great amount of advancements that have been made to address the safety concerns.

It has been stated that LiFePo4 are safer and a "better alternative" to Li-Ion and I find that true if you are running around like a madman sticking an ice pick in every battery you can find. If you go by that criteria, yes the LiFePo4's are a better solution.
I on the other hand do not plan on putting the ice pick test to my batteries.
Additionally you are buying new cells which is not a "Second Life Storage" project you are contributing to the wastestream in the long run.
I do know one thing, LiFePo4 batteries are extremely sensitive to low voltages, <2.0v per cell. It seems if the cell is allowed to go <2.0V for even a short period of time the cell is no good and becomes a SD cell. I cannot say the same for a Li-Ion cell which with caution can be recovered as long as you are aware of the potential issues. The discharge curve is also relatively flat which is fine for voltage sensitive equipment but makes it a bit more difficult to judge the SoC.

So yea I am a 'Second Life Storage " advocate for 18650 Li-Ion cells.
Wolf
 
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