electrodacus
New member
- Joined
- Dec 10, 2018
- Messages
- 14
I'm new here and this is my first post.
Over the last few year I designed an open source Solar BMS and had them funded successfully trough Kickstarter currently I'm on the third generation of Solar BMS and running my forth Kickstarter. While I read the rules of the forum not sure if is OK for me to link to my Kickstarter page so I will not do that.
Solar BMS is an all in one BMS + solar PV charger + advanced energy monitor.
The main reason I started designing this about 7 years ago was that I was moving offgrid and needed some energy storage solution for my house. I looked at Lead Acid that is even today used by most offgrid people and found that storing energy in those was more expensive than I will have liked so looked in to Lithium as a possibility and that was the time that A123 started advertising their LiFePO4 that just looked more than perfect for what I needed.
Since there was no BMS for LiFePO4 I decided to do designsomething myself and started looking for best solution. Just at the same time Intersil announced the ISL94203and that was exactly what I needed and started designing something based on that even if only the spec was available at that time and I was the first one to order sampled when they where available.
I was thinking it will be a relatively simple design and just build a unit for my own use but as I started working I realized it was way more work than estimated and as I shared the idea and prototype on my youtube channel other people become interested so I was going to build a few for them also so that was when I did the first Kickstarter.
From there it evolved to new more advanced levels and on last Kickstarter I added a completely new product the DMPPT450 again taking way more time than initially estimated but it was worth the trouble as now it fully heats my house (DMPPT may be completely different from what you imagine so read the user manual for more details).
I will be happy to answer any SBMS or battery related questions.
I think LiFePO4 is far superior for energy storage than LiCoO2 or NMC that are designed for high energy density to the detriment of cycle life and that is why I selected LiFePO4 for my own use.
Typical LiCoO2 and NMC are good for 500cyles at 100% DOD (of course a bit more if you limit the DOD) and while they are great for both portable electronics and EV's they are to expensive for typical stationary energy storage applications.
When I say expensive I refer to cost amortization overthe usable life of the battery and not the initial equitation price.
Typical LiFePO4 are good for 3000 to 6000 cycles at same 100% DOD so an order of magnitude better and more than adequate for energy storage applications.
There are two main mechanisms for battery degradation one is the known cycle life and the other less known but even more important is the calendar aging.
Typical calendar aging is in the region of 0.5% to 2% capacity loss per year dependent of the quality of the additives added to batteries and manufacturing quality but also very dependent on cell temperature. As a general rule a 10 degree Celsius increase in cell temperature will double the rate of calendar aging degradation.
I did a precise capacity test when I installed my 8s10p A123 battery about 4.8kWh usable and I repeated the same test after a year of full time use in my offgrid house.
So over 8544h (that is about 356 days) the house used a total of 1122.349kWh + 373.944kWh = 1496.293kWh that is an average of 4.2kWh/day or 126kWh/month
Out of all that 806.714kWh went trough battery so in average day 2.27kWh went out of the battery and that is about 47% of the battery capacity that is around 4.8kWh
The result in capacity loss was just 0.9% and large part of this is due to normal aging maybe 0.6% and just a smaller part maybe 0.3% is due to cycling. The reason that calendar aging was so low has to do with the quality of A123 cells but also low internal impedance and low charge/discharge rate in this application 0.25C max charge and 0.5C max discharge thus battery temperature was never more than 2 to 3C above ambient and ambient inside my house where battery are is +18C to +26C all year.
I have a lot to say about this subject but I will leave it at that for the first post
Over the last few year I designed an open source Solar BMS and had them funded successfully trough Kickstarter currently I'm on the third generation of Solar BMS and running my forth Kickstarter. While I read the rules of the forum not sure if is OK for me to link to my Kickstarter page so I will not do that.
Solar BMS is an all in one BMS + solar PV charger + advanced energy monitor.
The main reason I started designing this about 7 years ago was that I was moving offgrid and needed some energy storage solution for my house. I looked at Lead Acid that is even today used by most offgrid people and found that storing energy in those was more expensive than I will have liked so looked in to Lithium as a possibility and that was the time that A123 started advertising their LiFePO4 that just looked more than perfect for what I needed.
Since there was no BMS for LiFePO4 I decided to do designsomething myself and started looking for best solution. Just at the same time Intersil announced the ISL94203and that was exactly what I needed and started designing something based on that even if only the spec was available at that time and I was the first one to order sampled when they where available.
I was thinking it will be a relatively simple design and just build a unit for my own use but as I started working I realized it was way more work than estimated and as I shared the idea and prototype on my youtube channel other people become interested so I was going to build a few for them also so that was when I did the first Kickstarter.
From there it evolved to new more advanced levels and on last Kickstarter I added a completely new product the DMPPT450 again taking way more time than initially estimated but it was worth the trouble as now it fully heats my house (DMPPT may be completely different from what you imagine so read the user manual for more details).
I will be happy to answer any SBMS or battery related questions.
I think LiFePO4 is far superior for energy storage than LiCoO2 or NMC that are designed for high energy density to the detriment of cycle life and that is why I selected LiFePO4 for my own use.
Typical LiCoO2 and NMC are good for 500cyles at 100% DOD (of course a bit more if you limit the DOD) and while they are great for both portable electronics and EV's they are to expensive for typical stationary energy storage applications.
When I say expensive I refer to cost amortization overthe usable life of the battery and not the initial equitation price.
Typical LiFePO4 are good for 3000 to 6000 cycles at same 100% DOD so an order of magnitude better and more than adequate for energy storage applications.
There are two main mechanisms for battery degradation one is the known cycle life and the other less known but even more important is the calendar aging.
Typical calendar aging is in the region of 0.5% to 2% capacity loss per year dependent of the quality of the additives added to batteries and manufacturing quality but also very dependent on cell temperature. As a general rule a 10 degree Celsius increase in cell temperature will double the rate of calendar aging degradation.
I did a precise capacity test when I installed my 8s10p A123 battery about 4.8kWh usable and I repeated the same test after a year of full time use in my offgrid house.
So over 8544h (that is about 356 days) the house used a total of 1122.349kWh + 373.944kWh = 1496.293kWh that is an average of 4.2kWh/day or 126kWh/month
Out of all that 806.714kWh went trough battery so in average day 2.27kWh went out of the battery and that is about 47% of the battery capacity that is around 4.8kWh
The result in capacity loss was just 0.9% and large part of this is due to normal aging maybe 0.6% and just a smaller part maybe 0.3% is due to cycling. The reason that calendar aging was so low has to do with the quality of A123 cells but also low internal impedance and low charge/discharge rate in this application 0.25C max charge and 0.5C max discharge thus battery temperature was never more than 2 to 3C above ambient and ambient inside my house where battery are is +18C to +26C all year.
I have a lot to say about this subject but I will leave it at that for the first post