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The over and under voltage is based on individual cells for lithium and not based on the entire battery voltage.
So if you have a 12V battery made of 4 LiFePO4 cells in series each with about 3.2V nominal the SBMS will measure each individual cell and the decision to stop changing will be made based on the highest cell voltage. So when any of the 4 cells in series gets to 3.55V the SBMS will stop the charging. Same for under voltage is based on the lowest cell voltage and when that gets to 2.8V the discharge will be stopped.
On top of that there is no constant voltage charge stage (so no absorption or float) since this will damage / degrade lithium cells but with only constant current stage the Lead Acid will not get fully charge and so get damaged / degrade fast.
Lead Acid likes to be fully charged as often as possible and spend time in float while Lithium-ion of any type will hate this so charging is done differently.
The absorption charge stage is sometimes used on Lithium cells when energy density is more important than cycle life like on cell phones and laptops where the extra 10 to 15% capacity by using the absorption stage is more valuable than higher cycle life (that is not the case in offgrid energy storage).
Road you comment on Google+:
"+Chris Brandstrom The SBMS is specifically designed for Lithium battery only so it will not work with Lead Acid. The charging is completely different for Lead Acid."
Why wouldn't it work, when you simply don't attach the BMS cables and set the overcharge and lowcharge voltage ? I am in the same case as chris, I will buy LiFepo4 in future, right now I have 2 Lead Acid in Series to get 24V System. But I would love to use my ordered SMBS120 to get a little more data, than I get with my 10€ China charge controller.
Many thx for you answer and congratulation for the SMBS development, you are making great steps :)
Sorry I have not seen your comment before. 16A is excellent for a single 255W panel (manufacturers for those panels will recommend 15 or 20A fuse).
The breaker is useful for easy disconnect. The SBMS has build in electronic over-current and short circuit protection but a single PV panel shorted will only generate the nominal current and is normal operation for panel so with a single panel or max 2 parallel panels there is no need for any sort of over current protection. So in your case you can use just a simple disconnect switch but circuit breaker can be used in the same way and is probably less expensive.
Yes there is no standard as far as I know for connectors/outlets but of course wires can be calculated based on length and max current.
With #14 AWG you can use a max 15A and with #12 max 20A while you will want to maintain a voltage drop of less than 5% max 10% from battery to your outlets.
With 12V you can have outlets for small loads of 200 to 250W max and that should be good for almost any electronics (laptops, TV, peltier fridge ...)
I use #12 AWG for outlets in my house with a 16A breaker and since I have a 24V battery I can handle max 400W on each outlet (not that I need anything close to that).
And for LED lights #14 AWG with 10A breaker is normally more than enough that will allow you up to 100W LED light with 12V not that you will need anything close to that unless you like blinding amount of light :)
You can use normal AC switches for lights since they will have no problem with just 12V DC and the limited current while for outlets is realy your choice since I'm not aware of any standards. (I did not decided as of now what I will be using for outlets) When I get time for that I will probably build some sort of "smart" outlets that will communicate with the mating outlet before allowing current.
I will be building an off grid home using the solar BMS system. I'm wondering what suggestions you have for a 12v household wiring system? As far as I can tell, there are no North American standards for such. Wire? Switches? Connectors/Outlets?
Thanks for an excellent project.
what's the exact Typ of DC Circuit breaker needed for a 24VDC System? I would like to have 16A as my solar panel only has 255Wp.
Best would be if you could name the circuit breaker used in your installation.
Electronic circuit breaker would be nice as well, but afaik they are ridiculously expensive compared to the "normal" ones.
The SBMS and DMPPT are designed for 12V and 24V operation or something in between if you want some non standard configuration but nothing above 8 cells in series so about 24V standard.
While two SBMS can be connected in series for 48V a lot of functionally will be lost and it is not something that I recommend.
There is normally no reason to go from 24 to 48V other than some small saving on cable cost.
In 24V the SBMS40 and SBMS120 support up to 500A loads so 12kW.
A single SBMS120 with full configuration 3.5kW PV array with ideally a 400Ah (10kWh) LiFePO4 can provide 240 to 300kWh/month depending on location and season.
If more is needed or worse solar is available at the location adding more PV can be done with the DMPPT450 and in that case using the same small 10kWh LiFePO4 battery 300 to 500kWh/month can be achieved again depending on location.
If even more is needed two separate 24V circuits can be used splinting the loads in the house this also increases the reliability of the system.
48V is already unsafe for most people since PV open circuit voltage will be around 80 to 100V DC.
With 24V is much safer and considered ultra low voltage with open circuit voltage below 40 to 50V DC.
Congratulations on reaching your goal. I just have a quick question I am getting two of the sbms120 I was just wondering is it possible to hook these up in series for a 48 volt system or are we stuck with just 24?
The PV array need to match the battery voltage so with 4s LiFePO4 12V you will need to use 32 or 36 cell panels. The one based on 5" cells are around 100W and the ones based on 6" cells around 150W
The 60 cell PV panels will work only with 8s LiFePO4 or 7s LiCoO2, NMC or any other high energy density cells 24V (LiFePO4 is the most cost effective and safer for energy storage so I recommend that normally).
Is not that 60 cells will not work at all with a 12V Battery is that it will be extremely inefficient.
You can see the manual for SBMS100 and SBMS60 for more details since the new SBMS120 and SBMS40 will be very similar http://electrodacus.com/SBMS100/manual/SBMSmanual.pdf
See page 17 and page 18 for more details about selecting PV panels and battery.
Happy to see you kickstarter succeed.
I would like to know if I can use one 12V 90Ah Battery and one 60Cell Panel with the SBMS. As voltage of Panel and Battery are very different.
Many thanks in advance.
Scott, that cable will work for DMPPT but is not necessary in most cases to have such a high temperature cable since the cable will have a much lower working temperature in normal operation. Price is good but for about the same cost you can get 200C rated silicone cable and you can get as much as you need since that PTFE is normally more expensive and sometimes you find a good deal like that but maybe there is not enough for your application.
I usually recommend Winston LiFePO4 cells if you can find them but the newer generation GBS should also be good if you can not find Winston.
But that 3rd generation 200Ah cell is fairly old same as mine and they have newer cells that look completely different now and up to 400Ah cells.
Price seems high also since I plaid around 400CAD (at that time was same as USD) for my battery and that was exactly 5 years ago.
I do not want to advertise any company and did not looked much in to battery since I got mine but you need to shop more since that price is way to high for an old generation GBS battery.
Here is a link to the newer generation GBS the 400Ah cell http://www.electriccarpartscompany.com/400Ah-GBS-Batteries
and is $466 for one cell so 3.2V x 400Ah = 1.28kWh so $364/kWh
I know I will not be able to edit this comment so if you read this latter the information may be outdated.
Always search more since battery is one of the most expensive parts and quality of the battery is important.
The large manufacturers are Winston, CALB and GBS and this is also the order I normally recommend them even if I only have experience with GBS.
- Check out eBay "THERMAX M22759/29-20-4" for possible DMPPT load alternative:
20 AWG Nickel-plated copper, extruded PTFE and a polyimide hard coat (260C.)
- Does anyone here have a good source for high capacity GBS LiFeMnPo4 cells? (Best I have been able to find for the Gen3 200Ah cells comes to $543US/kWh (+shipping.)
- Would love to get SBMS120 as soon as they are ready (vs shipping with DMPPT450... ;-)
Congratulations Dacian on getting funded !!
I usually do an update when I have something interesting to show and I try to keep the number of updates to a minimum as I did on the last two Kickstarter campaigns.
My first update will probably be done when I have the first SBMS120 prototype ready and the update will contain some photos and technical details related to improvements over the SBMS100.
I noticed other projects do quite a bit of updates on Kickstarter during the project and after but I think that dilutes the importance of an update.
People that want to see more updates and details about the project will be able to do so by checking my google+ page https://plus.google.com/+electrodacus/
Congratulations Dacian! It would be great to see you use the 'update' feature of Kickstarter instead of just commenting so backers get notified of important announcements. Good luck with delivery
As of this moment the project is successfully funded.
Thanks to all that made this possible.
Now I can start working full time on the project.
I just added that pledge level for you.
I've just pledged for the two SBMS40 package. I'd like to double the pledge for a total of 4 SBMS40s. What is the best way to go about that? KS doesn't seem to let me pledge twice for the same thing.
Bidirectional current sensing on the shunt, and a digital signal to stop.
That's all you had to say.
Yes I use my location and my system as an example since is the one I know best.
Is also true that with solar PV you have all paid in advance.
While my circumstances look particular all people will have fairly different requirements access to sun and different prices for alternative energy sources the PV will still be less expensive in majority of those cases.
The amount of sun in most locations there (Australia) is as good or better than mine plus the climate is better (not as cold as here) so less energy is needed for a house.
If I where to move my house almost anywhere in NSW Australia I could get away with just about half the PV array I need here because of much lower space heating/cooling needs.
Having your own water stream while great is not that common and my system has nothing against that. You can use the output from a pelton wheel generator on both SBMS and DMPPT the only requirement is for the generator output not to exceed max allowed open circuit voltage and that can be done easily with that sort of predictable generator and a bit of extra automation.
I do not think an engine will be that happy ruining on that sort of recycled vegetable oil.
The "free" fuel idea is also not something you can seriously consider when trying to compare energy sources.
I heard this argument before with wood where people lived in a forest and where able to cut the wood for "free". When you get in to the details of what free means it turns out that is not as "free" as you initially imagined.
Numbers are necessary if you want to provide a good proof that a cheaper source of energy than PV is available.
Things to consider with this sources like wood or vegetable oil is cost in getting the raw material the process needed to make that usable (cutting for wood or cleaning/filter for used vegetable oil) transportation if the fuel needs to be transported to your location and not least labor (amount of time spend cutting wood or filter oil).
The other very important cost with this sources is the burner, engine cost amortization since in case of PV solar this is almost "free" and for sure free of maintenance since is just a simple heating cable (less than $500 value in my particular case with no maintenance and extremely long life >50 years).
Select one fuel you think is cheaper than PV and take all cost in to calculation as mentioned above then you will probably realize that it will be more expensive. If not let me know and I can look over those numbers.
This new SBMS will probably have bidirectional current sensing on the external current shunt but the reason I do not mention that is because I want to discourage people to use gasoline/oil generators or grid since most if not all of this sources will be more expensive than PV and is a bit hard for people to understand that.
Also the external generator will need to be able to stop when SBMS say so since SBMS can not do anything other than give a digital signal a 0 or 1 and if the generator fails to respond to this then you will damage the battery by overcharging.
I consider all suggestions but if they do not make sense to me then I will not implement them just because customers ask that.
There are many cases where uninformed customers create a demand for a product that makes no economic sense for them and there are of course business that supply this demand.
Both SBMS and DMPPT where designed for personal use since there was nothing on the market to offer this.
Yes you have rolled out those numbers on countless occasions that proves that at least in your location with plenty of space and being stationary that amortised cost of solar over 20 years or so is by far the cheapest source of energy- assuming you have that up front capital.
But your circumstances are so particular. There are many circumstances where other charging inputs are highly desirable and maybe necessary. Many people will already have them in place so cost is not an issue. For instance, friends of mine who have been off grid since the early 70s in subtropical rain forest in northern New South Wales in Australia. They have had a pelton wheel running during the very cloudy wet season for 40 years now. It was rebuilt a few years ago and will probably run now for many more decades. Why not make allowances for this kind of input/equipment?
In my case I have over 3000L of stockpiled used vegetable oil, clean and settled, and an ongoing supply that cost me nothing (about 40 minutes to pump 1000L every few months). In a cold location a co generation arrangement could utilise much of the waste heat from an engine running on this for DWH and space heating.
I also make quite a bit of biochar. Mostly out of waste wood that is lying around that would probably end up being burnt anyway. The waste heat from this process can be utilised in a range of heat engines (I have a fairly low efficiency ORC) and then cascaded further into space heating.
Look I dont want to get bogged down too much in the numbers, I just want to illustrate the plethora of other quite sensible and productive alternative energy sources that people may want to charge there SBMS equipped Lithium battery banks with. To Say that PV is the cheapest (over 25 years) and practical on its own in all locations and scenarios is unrealistic and limiting.
Is there any technical reason why the SBMS can not monitor/count an external charging current?
It's not a deal breaker for me. I still look forward to receiving my multiple SBMSs. And I hope you continue to develop stuff.
I don't know if we would be considered 'customers', but if you do decide to develop this into a more widely marketed product, ie you intend to be a business or company. Then the standard practice would be to listen to customer suggestions and requests.
Perfect, thanks for the insight!
My intention is to continue to create the DMPPT450.
The demand seems low for the DMPPT450 right now but I'm sure it will get better.
There are just less than 20 DMPPT450 selected by backers but I will need to build at least 100 PCB's in order to keep the cost acceptable.
Many parts are common with SBMS so volume for parts is not that much of a problem becose of that.
If you do not need the DMPPT right now you can wait since my plans are to continue to build both the SBMS120 and the DMPPT450 as long as there is a demand for it.
DMPPT and SBMS are also open source so worst case you can build one or two even if it is more expensive (low volume) it will still be worth building.
Do you anticipate a future version of the DMPPT or at least holding some stock for a while of the 450? I'm a couple of years off the need for this but it's perfect for my application. I'm currently in for the SBMS120 so am considering if it's best to include the 450 or hold off.
Hi again Dacian
Thank you for your quick and thorough response.
I will setup a switchover circuit that will then be controlled by the SBMS to switch the server from my solar setup to the city's grid (I live in a german city, where 90% of the energy is being produced renewably). The server is already hooked up to a ups so a switchover using two relays won't be a problem.
Anyways thank you again. I'm really looking forward to get a new solar setup in order to replace my lead-acid mess :D
Yes it can handle 10 x 300W even 12 x 300W (72 cells) of solar PV panels.
The 60 cell panels are still more common and may have a smaller price per watt they are also slightly smaller and easier to work with and install.
The 72 cells have higher max power point voltage but the same max power point current so 12 x 250W panels will charge the battery at about the same rate (same charge current) as 12 x 300W panels that is the reason I recommend the 60 cell panels.
If long cables are needed to connect the PV panels then 72 cell panels can be an advantage since higher voltage drop can be allowed on the cables so there can be a bit of savings on cables.
Yes the SBMS only accepts rechargeable Lithium cells of any type and currently the Lithium cell with highest charge voltage is around 4.2 to 4.3V (absolute max is 4.5V on SBMS so future Lithium cells will also be supported).
There are no 8V cells of any type as far as I'm aware so you probably have a pack with multiple cells probably 2s Lithium cells or 4s Lead Acid (Lead acid cells are not supported by SBMS only Lithium).
Typical configurations for 24V battery will be 7s high energy density cells like LiCoO2, LiNiMnCo (NMC) ... each cell charged at max 4V so that it will have a higher cycle life 2000+ cycles instead of just around 500 cycles at 4.2V (100% DOD) that will make for a max pack voltage of 28V (4Vx7) and minimum 23.1V (3.3Vx7) ideal range for 24V nominal devices.
Or what I normally recommend and use 8s LiFePO4 with 28.4V (3.55V x8) max charge voltage and 22.4V (2.8V x 8) minimum again ideal for 24V nominal devices.
Max cell capacity is not limited 9999Ah can be used (that is limit set in software) but since battery is expensive you will want to minimize the capacity needed and what I recommend is 24V about 400Ah with 3000W of PV panels. Smaller battery capacity for 3000W panels will charge the battery to fast and degrade the battery and higher battery capacity will start to be less cost effective since battery will not be used much each day and the battery normal aging will become an important factor in degradation exceeding the cycle life degradation thus making less cost effective in therms of cost amortization.
I will assume that server will work 24h/day and in that case an average of 25W x 24h will require 600Wh in 24h and and that will require a 150 to 250W PV panel in good solar conditions (having the panel on the balcony railing may not provide optimum orientation to sun) and your location is also important.
The single large panes 200 to 300W are made with 60 or 72 cells and those are only good for a 24V nominal battery thus you will need to configure your battery as 8s
If for some reason you prefer a 12V battery then the panels will need to be 32 or 36 cell panels that are usually rated at around 100W if they are made with 5" cells or 150 to 180W if they are made with 6" cells.
With a 500Wh battery capacity and a 200 to 300W solar PV with good solar coverage you will be able to supply power to the 25W server in a sunny day but most likely will not be able to provide enough energy in a cloudy day (not for full 24h operation).
To get a better idea a single 250W PV panel at my location can produce 1200 to 1400Wh in a sunny day while minimum in a completely overcast day will be just 100Wh.
So in a sunny day the 250W panel will produce up to 2x as much as the server needs (600Wh) while in an overcast winter day there is only enough energy for 4h of server operation.
what kind of setup would you recommend for me:
I can hang a few solar panels on the railing of my balcony.
I want to power a server with an average power draw of 25w completely off solar as well as a few LED's with a total draw of 20w and some other devices with an average of 30w.
I don't earn much money because I'm still a student.
I thought about getting 8xGBS 20Ah LiFePO cells in a 4S2P config for around 500 Wh and a single 200-300Wp Solar Panel. Does that sound like an ok config for what I'm trying to accomplish?
Thanks in advance!
I have backed the SBMS120 and would like your advice on the following
Can it handle 10 X 300w PV (72 cells) panels to give 3KW rather than using 12 X 250w PV (60 cells) panels ?
If so, apart from cost is there other disadvantages in such a setup for charging a 24V battery?
Is there a maximum voltage limit per battery cell or the only restriction is the battery not exceeding 32V?
E.g. Can it handle a 24v battery made up of 3 X 8v cells ?
Also, is 400Ah the maximum Ah it can handle for a 24V battery?
Yes the SBMS40 has a single PV input in order to keep the price down but in your case with just a 100Ah 12V battery that should be good enough.
Since you already have that DC to DC charger you can continue to use it to limit the alternator current.
You can build your own linear current limiting circuit with just a power transistor and very few other parts if you are up to that or you can get one of those LTC3780 based DC-DC converters with CC and CV and use that to limit the current. Most of those are 10A but you can find some that are 20A rated or you can parallel a few of those 10A by adding a diode on the output of each.
Sorry this was not a clear answer it all depends on you but SBMS40 should be just fine the max charge current on that can be up to 48A (that is where the over current protection is set) and for the load there is no real limitation since you can use up to a 500A external current shunts if you want to connect a large inverter.
As mentioned in some of the earlier comments is best to use solar PV as much as possible and not need the car alternator since that energy is more expensive.
I would like to use your expertise to help me choose the correct SBMS. At the moment I am backing SBMS40 but I am considering upping it to SBMS120 as there are 2 PV inputs.
At the moment I am running 100Ah 12V lithium cells in my car. They are charged with ePower 30A DC to DC Charger - Enerdrive EN3DC30 (http://www.outbackmarine.com.au/epower-30a-dc-to-dc-charger-enerdrive-en3dc30) connected to car's alternator and solar panels - it can charge battery from both sources as needed.
Obviously SBMS40 should be more than enough to work in this system as a BMS but would it be possible to connect both solar panels and car alternator directly to SBMS120 and skip the DC-DC charger altogether? I guess I would need to limit the current it takes from the car battery not to fry the alternator. Are there any 20A-30A limiters able to do that or should I just stick with my system and add the SBMS40 only?
Sorry for the beginners questions and thanks for your help.
My main target in creating my offgrid house system was cost.
So the fact that there are no gasoline generators involved or propane backup heating has to do with cost amortization.
I think I mentioned in the other comment in a bit more details but to summarize the cost amortization for different energy sources is:
PV panels 2.4 cent/kWh
LiFePO4 25 cent/kWh
Thermal storage 0.5 cent/kWh
Propane 25 cent/kWh
gasoline generator >100 cent/kWh
car alternator >100 cent/kWh
Even if just 5 to 10% of the energy is produced by one of the last 3 options the cost will increase considerable so much so that having an oversize PV array 2x to 5x larger than needed in average will still be a better solution.
Even if you drive your car because you need to drive if you use the alternator to charge the battery that energy will require extra gasoline same as if you use your car air conditioning unit and the fuel consumption will increase.
You will be using about 1 liter of fuel extra for each 1kWh you will be taking from the alternator thus the cost of that 1kWh of energy will be the cost of the 1 liter of fuel.
Ideally you will want to use most of the energy during the day (with an offgrid solar setup) but you can also do TIG welding during the night if battery is capable of providing that current.
A 24V 200 to 400Ah LifePO4 will have no trouble providing the power and energy for TIG welding.
My small efficient house needs just a 10kW of PV panels to provide both heating and electricity.
January will be the month where I will take the cost advantage of the 10kW PV array that is capable of producing an average of around 1165kWh in that months and from that about 100kWh will be used as electricity for appliances and about 900kWh extra will be needed for heating (the 100kWh used for appliances also contributes fully to heating).
This way the 10kW PV array can supply all the energy needed for electricity even in the worst overcast day and fully charge the battery so that battery capacity needed will be for just 24h instead of a few days as in traditional systems.
The thermal mass storage will be the larger one since is so much cheaper up to 50x less than LiFePO4 and that will need to be able to store a few days worth of energy for heating (the number of days will depend on the type of climate and amount of sun available there).
Adding backup for either electricity or heating is not needed and doing so will increase the cost not only because the alternative fuel is much more expensive but also because additional equipment will be needed that will also have a high amortization cost especially since it will be used as backup so not much.
I applaud your efforts to demonstrate extreme energy efficiency in your house and offer a vision of a 'solid state' off grid energy system largely free from moving parts and flammable fuels. Most people aren't nearly as averse to at least one mechanical heat pump (fridge) and usually some kind of back up charger/generator.
I realise that once you have your 14kW of PV you will effectively have instantaneous power every day- at least during the day. However many people may not have the need or ability to have that much PV, for instance if you are using the SBMS/lithium batteries in a mobile home. Or maybe have the occasional but real need to do some TIG welding or machining late at night ;)
I have found that direct DC charging of battery banks using vehicle alternators or permanent magnet generators, to be a very useful and relatively efficient method of supplementing PV energy when I have higher loads to run or when there is a serious lack of sun. Sometimes this has been on the road where as a byproduct of going for a short drive, I have recharged enough to run my fridge for a day.
Whether it is incidental charging from a vehicle or infrequent or emergency use from a small engine such as http://www.altendc.com/g3-gasoline-battery-charging-dc-generator - it seems like having the capability to integrate this into the SBMS/Lithium battery would add greater flexibility.
I was wondering if you could utilise a external shunt and few of the SBMS's extra pins to monitor a direct charging current and possibly control a contactor or engine shutdown to cease charging at set point. It would be similar (and for similar reasons) as the capability you have built in to the SBMS for using and monitoring an external shunt for larger inverters.
A number of people I know use other charging sources like wind, micro hydro, or co-generation, and it would be good to be able to have the SBMS recognise the charging contributions of these inputs to reflect the true State Of Charge of the battery bank and preferably have some control over limiting these inputs also.
The SBMS would not have so much control in regards to cell balancing but that would resume the next time there was sufficient PV energy.
Sorry to be such a demanding bastard;) but this could just be a software thing eh?
Thank you for the information Dacian. Your information has helped me decide the direction I want to go in with this project.
Thanks for supporting this project and glad you enjoined my youtube videos.
There is a lot I want to say in response to your comment and not sure where to start :)
SBMS and DMPPT are designed for full offgrid operation.
I think as of now battery storage of any type is not cost competitive with grid prices so having a grid connected battery will not be an economical solution in most places around the world.
Lead Acid will of course be the worse in therms of cost amortization even with very new Lead Acid batteries and grid connection and they can in real life exceed even $1/kWh stored over the life time so very high.
Net it will be using high energy density type lithium cells like those used in most EV's and the Tesla Powerwall 2.0 that best case scenario will have a cost amortization of at least 30 to 40 cent/kWh if battery is used quite heavy at least equivalent of once cycle per day and assuming Tesla will honor the warranty and replace the battery when it gets below 70% of initial capacity.
Best is LiFePO4 with a real world cost amortization of around 25 cent/kWh still to high to be competitive with grid prices but best solution for offgrid since then you need a battery anyway.
On the other side PV panels amortization cost is around 2.4 cent/kWh (based on 80 cent/Watt PV panel acquisition, 25 years amortization period and amount of sun at my location).
Average grid price is around 20 cent/kWh but it will depend on your location.
Other equipment as chargers, BMS and inverters also have a cost amortization associated with them so they need to be considered.
With this out of the way you can see how adding storage to a grid connected system is not an economical solution even if the grid will not pay anything for what you sent back to the grid.
If for some reason you prefer to have a battery backup and cost is less important then at least use just low cost PV energy to charge the battery and not grid. If battery is low then just supply the loads from the grid directly but do not charge the battery until the next day when cheap PV energy is available.
Each time you get 1kWh out of the battery you need to consider the cost amortization of that battery say 25 cent/kWh + cost of the energy you used to charge the battery say 2.4 cent/kWh from PV + the inverter cost amortization maybe another 3 cent/kWh or so just as an approximation (there are other small factors that add to this cost).
So you see as a fairly optimistic case each kWh going trough battery will cost you a bit over 30 cent/kWh
In an offgrid situation when you try to optimize the use by using most of the energy during the day directly from PV with less battery involvement the average energy cost can be lower than 30 cent/kWh even lower than 20 cent/kWh if you use over 60% of the energy during the day when is sunny since battery amortization cost will have less of an impact.
You will want to keep the battery size as small as possible so that it has a good amount of usage that way amortization cost will drop.
Batteries have two type of degradation one is related to cycling and the other with aging and in order to minimize the effect of aging you will want to cycle the battery as much as possible so that it will need a replacement in 7 to 10 years and not 20 years since then the aging will be the largest part of the degradation compared to cycling degradation.
In classic offgrid you normally want a 3 to 5 day backup battery (to deal with cloudy days) but having such a large battery is not cost effective so my solution was to combine house heating and electricity thus having a huge PV array that can fully charge a small capacity Lithium battery even in an overcast day thus battery capacity can be for just 24h much smaller and the rest of the energy will be stored in a much less expensive energy storage solution called thermal storage.
Thermal storage will of course be only used for heating or cooling and since is extremely inexpensive about 0.5 cent/kWh in therms of cost amortization you can have this as large as needed to cover 5 to 7 days.
The small Lithium battery will be charged at a normal 0.2 to 0.3C rate from that huge PV array by the DMPPT450 plus SBMS120 combination.
So in a sunny day just maybe 10% of the PV panels will be redirected to Lithium battery charging the rest of them will charge the thermal battery and in a cloudy day up to 100% of the PV array will be redirected to Lithium battery charging thus battery will still be fully charged and the large thermal battery will have enough energy stored to keep the house warm in that period.
SBMS120 can not be used with an inverter/charge hybrid the charge needs to be connected to one of the two PV inputs.
So the inverter will be connected to battery trough an external current shunt of up to 500A so up to 12kW inverter possible with 24V battery and the grid charger will need to be a separate device connected to one of the PV inputs.
Yes any inverter can be used including that Sunraiden 1000W if you want.
I have looked for the spec on Kickstarter but only seen the 12V version with 1000W peak output and I do not see a 24V version there.
This answer is quite long and not well organised but I hope it answers your questions.
I have been following you since the 4080 and sbms 100 projects. Watched every one of your YouTube video's. Very impressed with your engineering and quality of projects ability.
I wanted to back your sbms 100 but I just couldn't figure out how to get it to work with my system. In 2010 I installed a 6kw Xantrex XW system with 6kw of solar panels and battery backup. After I worked out a few bugs it works ok, but I never liked the lead-acid batteries. After seeing your sbms project I tried to figure out how I could use it to work with my system and li-ion batteries. With my limited knowledge I just couldn't figure out how to get it to work with my 48v battery system even with two sbms 100's. so I didn't support you on KickStarter at that time.
I love what Rohan commented about you. Everything he said is totally true! I'm not going to let this opportunity pass me by this time. I have ordered a new Powerwall 2.0 from Tesla. To replace my Xantrex inverter. My solar panels generate about 36kwh on a good day. That's not quite enough power to go off grid. So I'm still grid-tied. One Powerwall with it's 14kwh battery is good enough to power the house overnight, but that's about all. So I want some more back up power. That's where the sbms 120 will come into play. But I have a couple of questions to ask you:
I would like to use a inverter/charger with my sbms 120. Is it possible to hook-up the sbms 120 to an inverter/charger and have the charger part of the inverter run through the sbms 120 and charge the batteries? I know it's not very efficient to do this, but I will only run it when the sun is powering the house. Better than giving it back to the grid for half of what they charge me). I also have a Sunraiden 1000w solar inverter (another KickStarter project I backed). Would it be possible to hook-up the sbms 120 to it (you can look up the 1000w 24v on KickStarter for the specs). If not I will just use a regular inverter. Thanks for all you do, John.
Thanks for your support on my projects and the flattering comment :-) (that makes me a bit uncomfortable).
I love interacting with people like you that understand my technology and have a use for it but for anyone reading this please do not back my project if you do not have a need for my devices.
Your great insights into, and personal experience with, Solar PV, Lithium batteries, and Home energy requirements have led you to create some very impressive products. The 4080 from your first Kickstarter is still working great in my portable 60Ah Lithium system. The SBMS100 from your second Kickstarter now completely powers my house!
The way you think outside the box to maximize the performance, and minimize the size/cost, has enabled you to create products which are more powerful but yet cheaper than anything else I've seen on the market.
Your support has been way above the other 18 Kickstarter project which I've backed.
Your ideas can make a real difference to the world!
I strongly recommend anyone reading this to back this Kickstarter, and thus back Dacian in his projects, in any way you can. His products can make a real difference to the world (and the world needs all the help it can get!).
If you current situation doesn't need his device (e.g. you live in cloudy Seattle ;-), then just a donation would help, or, even better, back a device, and then donate it to someone whom can use it. If you need help finding a good home for it, let me know via Dacian, as there an many people in need of such things who can't afford them.
With the help of the good people of this world, this Kickstarter looks destined to be Dacian's third great Kickstarter Success!!!
All the best to all of you in your quests to save this planet!
The SBMS120 will be as efficient as SBMS40 when used with smaller battery and smaller PV array.
When battery is full the panels will be left open circuit. You can not normally charge directly from alternator since the alternator is constant voltage only and will push as much current as needed to get to around 14.4V and since LiFePO4 batteries have low internal resistance they will require huge currents to get to that 14.4V or close to (a few hundred to a few thousand of Amp) potentially damaging the alternator unless voltage drop on cable will limit that current or SBMS will actually disconnect because of the electronic overcurrent protection.
So in order to connect to alternator you will need a constant current supply between SBMS and alternator. There are low cost around $20 for just a 10A constant current supply and that can even be connected to a cigarette connector since is current limited and will not damage that connector or fuse.
In therms of cost energy from alternator costs above $1/kWh while PV panels can have cost amortization as low as 2.4 cent/kWh so is preferable to use solar as much as possible if cost is important (probably not so much if you just want a small system for something like a ham radio).
What is great about SBMS is that it has no electrical noise (there is no PWM) so there will be no interference with ham radio or any other audio or video device.
So yes there is no aspect of SBMS120 worse than SBMS40 in any use case other than the higher price.
I've been thinking of upgrading my pledge from the BMS 40 to the BMS 120. With my current battery bank, the BMS 40 is a perfect fit. Within a year or so, I plan on moving to more capacity. (I bought the small battery bank to learn about LiFePO4 before spending big bucks.)
Will the BMS 120 be significantly less efficient at 1/3 capacity than the BMS 40?
When the batteries are full, how do you shutdown the solar panels. Opening the circuit, or short-circuiting it? If by opening the circuit, could the BMS 40 be used to charge LiFePO4 from an automobile alternator & battery. I have a ham radio friend who would like to charge LiFePO4 from solar when home, but at least partialy charge them from his car when operating remotely.