Click on below image to download the Digital MPPT presentation.
Solar BMS (Solar Battery Management System) is a solar charge controller designed to replace the Lead Acid solar charge controllers most people use today in Offgrid, RV, Boats and multiple other applications with 12V and 24V systems.
Solar BMS can be used with 3 up to 8 Lithium cells (any type) or supercapacitors.
The new SBMS100 will have multiple improvements over the first generation SBMS4080 see further for details.
Simplified circuit diagram for the SBMS100 with max configuration.
(Two PV arrays each with 6x 250W PV panels for a total of 3kW of PV panels).
Lithium and in particular LiFePO4 is a better long therm investment than Lead Acid batteries.
--LiFePO4 has 2000 to 8000 cycles (70% to 100% DOD) vs Lead Acid 250 to 1200 cycles (20% to 50% DOD).
(This means you can get LiFePO4 with half the Lead Acid capacity since LiFePO4 can be discharged deeper and does not have to be fully charged as Lead Acid). --LiFePO4 has a charge / discharge efficiency of 95 to 98% vs Lead Acid just 50 to 75%. --LiFePO4 will cost about the same as Lead Acid with 2x capacity.
(A half capacity LiFePO4 will perform the same or better do to ability to discharge deeper and stay discharged with no effect on life cycle and do to better charge / discharge efficiency) --LiFePO4 protected with Solar BMS can last 20 to 30 years where a typical Lead Acid will only last 4 to 6 years. --LiFePO4 can be 5 to 10x better value than Lead Acid over the life of the battery
--The cost benefit are not the only benefits.
- LiFePO4 can be installed indoors with no need for external venting since it does not produce flammable Hydrogen gas as Lead Acid. - LiFePO4 even at the same capacity as Lead Acid is much smaller and lighter (in some applications this can be important). - LiFePO4 is maintenance free (AGM also claims that but in solar applications you probably need an expensive (1 Liter/kWh) gasoline or diesel generator to recharge the battery if there are more than two consecutive cloudy days else the battery life will be drastically affected)
Some Links in support to my claims:
Here is a similar Solar BMS from Sony using LiFePO4 (Lithium Iron Phosphate) battery to store solar energy but designed for grid tied systems Link and a more detailed document here Link
Bosch has a similar grid tied solar storage system see Link using Lithium Iron Phosphate with a 7000cycles and 25years life claim.
For Batteries you can check the Winston specifications for their Lithium Iron Phosphate batteries Link. There are other manufacturers of Lithium Iron Phosphate personally I use GBS cells since they where available about 3 years ago locally and where the best option for me at that time. But Winston and others seems to have better specs. My battery has already two years of full time offgrid with daily deep discharge and there is no measurable degradation see my house power consumption graphs below for more details.
The photo above describe my solar setup and is made out of a 720W PV array (3x240W 60 PVcells/panel) a storage battery (made out of 8 cells from GBS each cell is 100Ah and 3.2V nominal all connected in series for a total of 24V ) and the SBMS4080 made a reality with the first kikstarter campaign.
The power/energy graph below was done using the data logging functionality of the SBMS4080 installed in my OffGrid house
Data acquisition was done every minute for 7 days so 1440 datasets /day x 7 days = 10080 data sets
Each dataset looks like the one below:
And the content is Date,Time, individual voltage on the 8 cells, battery current and solar PV current.
The format is this Y,M,D,H,M,S, ,Cell1[mV],,,,,,,Cell8[mV],BattCurrent[A/10],SollarCurrent[A/10]
Total battery voltage and current was used to calculate the power from the PV panels and power getting in or out of the battery.
The orange graph is the power generated by the 3x 240W PV panels and is always positive. Since this is done in winter here the outside temperature was low (-10C to -20C) allowing for good output from the solar PV panels as you can see in the graph getting around the nominal 720W in the afternoon.
The total energy from the Solar PV panels is the area in orange including the one not visible because of the blue graph overlap. The visible part of the orange area is actually the Load energy as the difference between the orange area PV energy and blue area above the zero line that represent Battery charging energy.
Click on the graph to download the raw .csv file generated by SBMS4080.
As you can see from the animated graph above the daily PV array production was between 4.285kWh in a full sunny day (Day 5) and 1.082kWh in a cloudy day with no sun breaks (Day 7). As I mentioned in the above tables in December I can get an even worse day with heavy snow clouds and short day that will only generate as low as 0.3kWh for the entire day with the same PV array.
The energy consumption for the 7 days has big variations from as little as 1.132kWh to as much as 4.822kWh with an daily average of around 2.7kWh and around 80kWh/month energy use if I where to extrapolate this 7 days. This is normal for February since days are already longer and less cloudy than December in my geographic area (Canada, Saskatchewan closest large city is Regina). In November and December my power consumption can drop to 60kWh/month and in spring summer it can get as high as 90 to even 100kWh/month it will depend on how much cooking we do.
Before getting in to details about my loads I will do a short explanations to the power graph by day. Day 1 (at about 10:00 there is a sharp increase in power that is do to the fact that I cleaned the panels of snow, at about 12:40 or so there is a short 2.5 minute increase in power consumption that was form the microwave reheating some food and you see that pulse at about -900W but the total power consumption is that + the solar PV power at that moment about 500W so the total load was 1400W from the DC side. Then later that day 15:30 we made a bread with the small convection oven and since that has a thermostat you see many on / off cycles to keep the set temperature. Then even later after the sunset around 20:30 I used the propane heater that has 3 pumps that work at different stages and all combined get to about 130W + the base load that was around 50W you see a peak of around 180W). Day 2 (About the same as first day some cooking with the convection oven and the water pumps from the heater during the day and a bit after sunset). Day 3 (No cooking so just DC loads mostly the water pumps for heating and you notice around 14:30 the battery was full but you will see this better in day 6) Day 4 (There was again a bit of snow on the panels in the morning and again the battery was full at around 14:30 even if we done some cooking). Day 5 (This was a full sunny day and I done quite a bit off cooking and the water pumps where running all day plus I used my larger computer not the laptop that is why you see higher power consumption after sunset). Day 6 (There where some clouds in the morning then I run the water pumps from the heater. The battery was fully charged by about 12:00 and the water pumps where running for another hour you see more often PV connected and disconnected do to larger load then when went shopping all day so only the small base load was on the refrigerator and one of the pumps at low setting. So all that is a good example of unused solar energy because it was not needed and this is normal in OffGrid situations since you can not sell the excess power. Once I will do my electric house heating with solar PV panels all that extra energy will be used to heat the house in winter but I will still need to find a use for extra energy in summer). Day 7 (This is the lowest solar PV production but it could have been even lower there where portion of the day where you where able to see where the sun is. If it was one of those days the power will have been always below 100W mark and the production will have been as low as 0.3kWh).
Even if this is Canada and you may expect low solar output it is not. As a comparison I get about the same amount of solar energy average over a year as in Sydney Australia. If you want to know how that compares to your location check out this great on-line calculator PVWatts for direct comparison with my location select Canada (SA Regina).
Pledge with PayPal
If you missed the Kickstarter you can use one of the buttons bellow to pledge for SBMS40, SBMS120 and DMPPT450.
After you make a pledge I will contact you on your paypal email address usually in 24h to 48h or you can write me with any questions to firstname.lastname@example.org
* Shipping is not included and I will ask you to pay for that at a later date (a few days before I'm **ready to ship).
Shipping costs are based on Canada Post and you can go to their website select "Tools" / "Find a rate" and on sending from Canada S0G1P0, weight will depend on what you get but SBMS40 should be under 500g including packing, SBMS120 will probably be under 700g and DMPPT450 should be around 1kg (I will only have exact weight when the final prototypes are done).
Shipping to Canada and US with tracking are typically between 15 to 25 CAD while international destinations as Europe and Australia are quite a bit more expensive depending on weight and type of shipping. As an example a 0.5kg or less parcel 25x18x4cm sent to Australia will cost 22.55CAD as small air shipping no tracking and 57.96CAD with tracking.
** I estimate the SBMS40 and SBMS120 will be ready to ship around July 2017 and DMPPT450 in October 2017.