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Forum Index : Solar : Off Grid Solar at just $0.16/kWh LiFePO4
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electrodacus Newbie  Joined: 30/03/2014 Location: CanadaPosts: 39 |
Almost forgot about you guys sorry for that. I mostly have time when I do a Kickstarter campaign the one I have now with the new version of solar BMS is almost at the end. That 16 cent/kWh is a bit misleading because that is the amortisation cost for all the equipment but not for installation. I moved offgrid about two years ago as some of you know and I was searching for solutions to power my house. Solar PV was an easy choice but battery was extremely expensive (I'm not referring to initial cost but at amortisation cost). My house (also build that one) is small you can even call that a small cabin is 65sqm (700sqft). It is also energy efficient so I only need an average of 80kWh/month. So if I'm to take how much energy I will use over 25 years (the normal life of PV panels) then 80kWh x 12month x 5 years = 24000kWh Now le me give you the total cost of my installation. PV panels 3x 240W each is about $200 total $600 PV support made of 2x4 just $35 Wires and DC breakers about $100 *Solar BMS (SBMS4080) $179 (the new SBMS100 can support much larger array 3kW) 2400W inverter $500 (only use this about 1h/day most things work directly from 24V DC) Battery is a 8 cell LiFePO4 from GBS so 24V at 100Ah and the cost for this was $1200 about 3 years ago. I will make a capacity test for the battery soon but if my expectations are right and I only have 5% capacity loss or less after 2 years of full time Off Grid use then I will need just another battery after 12 years to have 25 years life. So total initial investment is ( $600 PV + $35 support + $100 wires + $179 Solar BMS + $500 inverter + $1200 LiFePO4 battery ) = $2614 But in order for this to last 25 years I need another battery and a PV support since is made of wood so another $1200+$35 in about 12 years. So total expense over 25 years $2614 + $1235 = $3849 Now $3849 / 24000kWh = $0.16/kWh Here is a 7 day energy production and consumption graph for my house at the beginning of February this year  http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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| davef Guru  Joined: 14/05/2006 Location: New ZealandPosts: 499 |
electrodaus, And you wouldn't be getting a lot of solar at this time of the year in Saskatoon. I followed your Quickstarter campaign. Also, I have been "wading through" this topic at Cruiser forums After a month of spare time I have got this far. One of the main issues discussed is the use of BMS on boat "house battery" systems. Seems most are at 12V and the need for a BMS is seen as not necessary. You need HVC and LVC and a logging system to warn you when cells start to get out of balance. All top and bottom balancing is done infrequently for these low charge and discharge systems. Maybe, it becomes a bit more important at 24Volts. Seeing as we pay over $.20/kWh it looks like I would break even in 25 years, when I am 95. The trick will be to still remember how the system works at that point in time! What are your current thoughts on BMS for 24Volt systems? Regards, Dave |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
Hi Dave, Actually beginning of February when those 7 days where logged is quite good in regards to solar energy. You can see about 19kWh over 7 days that is around 80kWh / month same as average. The worst months are November and December when I only get to use about 60kWh the rest of the months are around 80kWh or above usually not over 90kWh. PV panels are set for winter time so in spring I get more than in summer months. Yes there is still not much interest in LiFePO4 based on my current Kickstarter is about the same as last year when I had the first campaign I just had the advantage that most of the first bakers came back again to get the new version. Well in Solar OffGrid you have realy small charge discharge rates and you can get away with not using a BMS (I did not had one of better than one year before I designed and build the first Solar BMS). I was manually balancing cells about once every 3 months or so and the 100Ah 8 cell (24V) battery was about 1% at most out of balance with daily use of course so not that much but still needed top balancing else the high cell will have been out of the 3.6V limit. This setup is usually done for 25 years so you need to do quite a bit of cell balancing even if is once every 3 months and you are always stressed you may damage the battery. But I think the largest advantage of having the Solar BMS is the fact that I can know the battery capacity. It was quite annoying not knowing how much capacity I have left since based on voltage you can not have any idea it may be 30% SOC or 70% SOC and will look about the same based on voltage. Is not like you saving much by not getting a BMS. Another big advantage of the Solar BMS is that id dose constant current charging only and no floating or constant voltage as Lead Acid solar charger do and that will be detrimental to LiFePO4 they do not like to be floating they prefer to stay as little as possible above 3.4V for long life. So having a proper Solar BMS will save you from manual balancing every few months and constantly cheeking the cell voltage + you have SOC indication + it will do proper charging for long battery life. I know it sounds like advertising but the main reason I build the solar BMS was because I wanted to have all that and there was nothing on the market to do so. Yes even LiFePO4 can not compete with grid in most places around the world is mostly a good solution for those that want or need to be offgrid. I definitely not recommend anyone to go OffGrid if they already have grid. I will say a BMS is need as long as you have more than 1 cell in series being a human BMS is realy not worth the effort + all the additional benefits related to SOC and energy use and proper charging as I mentioned before. But you may think I'm biased since I designed a Solar BMS :) http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
I wasn't aware that there was a new kickstarter, as I hadn't checked for a month or two. Looks interesting. And sorry, about my conclusion ... at those figures it is cheaper than being on-grid. So, I need to compare the $20,000 to 30,000 it would cost to connect to the grid with the total cost of going off-grid. Your controller, the panels I have and a set of batteries would be under well $7,000 to 8,000. That means I have an extra BIG pile of money to buy my 2nd set of LiFePO4 batteries. Thanks, Dave |
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| davef Guru Joined: 14/05/2006 Location: New ZealandPosts: 499 |
Sent you a PM. Dave |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
I sent you a replay already to your PM. Noting to be sorry about. And is not realy cheaper that to be on-grid. That is an idealized number based just on equipment amortisation the installation cost can be quite substantial and increase to even double that rate. But yes if the house is not already connected to grid and cost of connection is expensive it may not be worth. Some have realy large power consumption and for those it may be worth to connect to grid if they are not that technical and do not want to mes with DIY. I try to use battery as little as possible since that is the most expensive part. Like for the 9kW PV array I use for heating is a big saving to not have a battery. In that case even if use half a year for heating and not used at all in summer it will still amortize to 8.8cent/kWh. If I will be able to use all that energy from PV panels it will only be 3 cent/kWh Dacian. http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Hi Dacian, it is interesting to see how far things have moved in the last 18 months with the adoption of LFP cells. Not having to lean on a battery bank for hours each day with a large bank of solar panels running through two or more big expensive controllers is a revelation. I was looking at some data the other day, it took around 30 watts to raise the voltage and activate the bypass shunts to balance the bank in one of the systems that I maintain, it took between 4 to 7 minutes so the maximum draw on the panels during this time was around 500W. This is only set to happen once a month. That is a huge difference from the lead acid daily absorption cycling. If this is going to be a normal balance then we are talking about 360Wh per year and 84 minutes of balancing. A trivial number on a system that can output 50+ Kwh of solar power every day. I have been switching the excess panels out of the systems (based on battery SOC)to drive heaters and dc brushless motors on water pumps and compressors for a couple of years now with very few problems. The only real owner maintenance is to cycle the big Gigavac latching contactors driven by the BMS every second month to check they are still operational and will catch a overvolt or undervolt failure. Having only one controller and a very simple charge setting has cut the cost and risk of a failure to a minimum. I know that your SBMS unit is a fully self contained system aimed at the huge cabin/boat/caravan market and there is really no point wasting time and effort catering to the large family home end of the off-grid market ATM, but I thought you might be interested to see where some of the larger solar systems are heading in Oz. regards Yahoo I'm confused, no wait... maybe I'm not... |
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| electrodacus Newbie Joined: 30/03/2014 Location: CanadaPosts: 39 |
Yes the Solar BMS is aimed for smaller energy efficiency OffGrid homes mostly. The high ends SBMS100 will be able to support around 300 to 350kWh/month power consumption. This are average household consumption in most of Europe but is just 1/3 of an average house in Canada or US. Most of the energy is wasted on inefficient appliances (less strict standards than in Europe in that regard) and also a lot in cooling and heating again mostly do to efficiency and standards for home thermal insulation. I will heat my home with electricity in the future and for that I need around 1000kWh/month that is 12x more than the average 80kWh/month I use now but for that array I will not be using electrochemical battery to store the energy and in stead I will use a much less expensive thermal mass. My 14 cubic meters concrete floor can store 10kWh for each degree Celsius delta so up to 100kWh possible with a 10C variation allowed 17C to 27C. For this heating part a different type of controller will be use what I call a Digital MPPT and I will need to design and build that next probably as soon as I'm done with the Solar BMS design. Dacian. http://electrodacus.com/ https://www.youtube.com/user/electrodacus |
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