LiFePO4 - The future for off-grid battery banks?

[choyak]

Good day all.....
I'm not very good at this forum stuff, but I guess it's correct to stay on topic.

I will use Headway 38120HP (Red Cells) for an off grid system.

I've seen people using this in type of system while on Grid safely with a
Generator style pony panel. So you could collect sun all day and store into batteries,
run the house clocks and low consumption items while no one is home. Continue to
use during the evening until more consumption is required, then switch over to Grid power.

This way you get the best of both worlds, a back up without fuel and using solar to supplement

Any thoughts?

Tommy L sends....

This is basically what I did, the solar charge controller is set so when the battery voltage decreases, the controller clicks a relay which switches the load from inverter to utility, not synchronized, however but I notice no abberations in about 8 months so far.

[inetdog]

This is basically what I did, the solar charge controller is set so hen the battery voltage decreases, the controller clicks a relay which seeitches the load from inverter to utility, not synchronized, hosever but I notice no abberations in about 8 months so far.

Please read post #112 and tell us what your estimate is of your relative costs for "free" solar power versus grid power.
Thanks.

[choyak]

It is not 'free' at all, it is an interesting hobby for me.

I also removed a ton of typos.

[akb]

Switching to mains

This is basically what I did, the solar charge controller is set so when the battery voltage decreases, the controller clicks a relay which switches the load from inverter to utility, not synchronized, however but I notice no abberations in about 8 months so far.

There is an alternative, that is to switch in a Mains to nominal DC power supply Diode OR'ed with the battery feed to the inverter. That way if the Power supply is enabled a little before the output of the battery falls below this point there is a smooth changeover. The only issue is the added conversion losses in the power supply/inverter. It also can be activated when the solar system misbehaves during the day.

[T1 Terry]

There is an alternative, that is to switch in a Mains to nominal DC power supply Diode OR'ed with the battery feed to the inverter. That way if the Power supply is enabled a little before the output of the battery falls below this point there is a smooth changeover. The only issue is the added conversion losses in the power supply/inverter. It also can be activated when the solar system misbehaves during the day.

There are many UPS type inverter battery chargers that can be used for this purpose. Either time triggered to switch to mains power to utilise the cheap off peak power in Aust, or switched by a low cell alarm on the batteries and switched back off after say an hr or so, allowing the battery to recover a bit and hoping the solar kicks in before another low voltage alarm kicks in.
I was planning to move to this type of set up, but now the ig gum tree out the front is gone, even in the middle of winter I have plenty of solar for battery charging.
As far as cost, roughly AU$4,000 for 720Ah of Li batteries, around AU$200 for 2 x 1000w PSW inverters from evilbay, around AU$5,000 worth of solar panel that I could buy now for $2,500, and I thought I was being clever getting them before the price went up but then I've had cheap power from them so.....
Cut a bill of around AU$500 x 4 times a yr 2 yrs ago down to around an average of $150, but that will come down more now the tree is gone. At AU$1,400 a yr saving on power it will take a while, but I have 100% reliable power now and my bills are going down while everyone else is screaming because they are going up, over 100% increase in the last 2 yrs.... so my $500 power bills may have been $1,000 now, my system has run 24/7 for over 2 yrs now. Looking at it that way, it's already paid for itself... think I like looking at it that way better

T1 Terry

[akb]

Solar value

There are many UPS type inverter battery chargers that can be used for this purpose.
T1 Terry

The difference is a UPS needs synchronizing the mains to the Inverter to switch cleanly.
The DC summing prior to the inverter does not require synchronization and maintains Grid isolation.

Either time triggered to switch to mains power to utilise the cheap off peak power in Aust, or switched by a low cell alarm on the batteries and switched back off after say an hr or so, allowing the battery to recover a bit and hoping the solar kicks in before another low voltage alarm kicks in.
I was planning to move to this type of set up, but now the ig gum tree out the front is gone, even in the middle of winter I have plenty of solar for battery charging.
As far as cost, roughly AU$4,000 for 720Ah of Li batteries, around AU$200 for 2 x 1000w PSW inverters from evilbay, around AU$5,000 worth of solar panel that I could buy now for $2,500, and I thought I was being clever getting them before the price went up but then I've had cheap power from them so.....
Cut a bill of around AU$500 x 4 times a yr 2 yrs ago down to around an average of $150, but that will come down more now the tree is gone. At AU$1,400 a yr saving on power it will take a while, but I have 100% reliable power now and my bills are going down while everyone else is screaming because they are going up, over 100% increase in the last 2 yrs.... so my $500 power bills may have been $1,000 now, my system has run 24/7 for over 2 yrs now. Looking at it that way, it's already paid for itself... think I like looking at it that way better

Commenting on your savings, there is now another issue for currently installed Grid connected systems. With the reduction of the feed-in tariff down to less then 20 percent of the original tariff, if you want to upgrade a solar system that has the high feed-in tariff any modification means the complete system reverts to the low rate. Not ideal economically. So how do you benefit if you cannot touch the original system.
If you have a pure low voltage DC system independent of the grid, no modification is done to a current system you can get additional value without modifying any mains system.

[Beanyboy57]

Commenting on your savings, there is now another issue for currently installed Grid connected systems. With the reduction of the feed-in tariff down to less then 20 percent of the original tariff, if you want to upgrade a solar system that has the high feed-in tariff any modification means the complete system reverts to the low rate. Not ideal economically. So how do you benefit if you cannot touch the original system.
If you have a pure low voltage DC system independent of the grid, no modification is done to a current system you can get additional value without modifying any mains system.

Not sure which state you live in but I haven't heard of a drop of less than 20 per cent of the original tariff. Here's a quote from Synergy in WA.
•A reduction in the rate paid for exported energy under the FiT from 40c/kWh to 30c/kWh effective on and from 1 October 2013 (this affects only those customers currently receiving 40c/kWh).
•A further reduction from 30c/kwh to 20c/kWh will come into effect on 1 July 2014 (this will affect only those customers receiving 30c/kWh at the time of the change).
•An extension to the scheme duration by two years, from 10 years to 12 years, calculated from the date of the commencement of the first contract, relating to the premises where an eligible customer was paid the Feed-in Tariff rate. This includes those customers receiving the 20c/kWh
So here in WA we are getting a reduction in the rate but also an extension in the time it will be paid.

Currently my system of 3kw completely pays for my electricity bill and has also paid back to me $492 in credit, so that means for the past 2 years I have removed a yearly bill of around $1500. So, in summary my system which cost me $7000 has paid back $3492 in just over 2 years. I am reasonably happy with that. I should mention that I educated my family to be aware of how much electricity they are using and we all travel a lot so the house only has one occupant for a few weeks here and there over the year, but other times there are 3 or 4 people at home.

[T1 Terry]

This was the reason for not going with the feed in to the grid idea when it first came out. If it looks too good to be true and the govt is offering something for nothing, you can be sure there will be catches and you will loose in the long run. A neighbour a few houses up fitted grid connect, tried to sell the house and get extra for the solar, it reduced the selling price of the house. Why, the new owners could only get 8 cent per kWh for all the power generated by the solar, but had to buy back any power used at 45c peak, ranging down to 18 cents off peak, but without the meter, a flat 22 cents at that stage. If you have solar fed to the grid you must have a smart meter and you must pay predatory pricing. So to get the price he wanted for the house he had to pay to have the solar removed, then copped a penalty from the people who fitted it because the rebates and green certificates were no longer valid, cost him heaps and he had panels no one wanted to buy because they were grid connect voltage and size, not suitable for caravans or motorhomes. The guy next door said he was going to buy the system off him so he had planned to move the rebates etc to him to keep everyone happy, till the neighbour found out his whole system would drop from 60 cents to 8 cents per kwh, he decided against it
I am very happy with my solar/battery/inverter system, the next stage is to fit up a UPS 3kW inverter/charger, I've already got it so I may as well use it, just link another section of the house wiring to the inverter rather than the grid, probably the circuit that supplies the lights/ceiling fans and bathroom exhaust fan and heat lamps. The tendency to turn every 2400w appliance on at the same time in the kitchen first thing in the morning would require a much bigger inverter for that 5 min load... re educate the wife to not do that, yeah right.

T1 Terry

[Beanyboy57]

I am very happy with my solar/battery/inverter system, the next stage is to fit up a UPS 3kW inverter/charger, I've already got it so I may as well use it, just link another section of the house wiring to the inverter rather than the grid, probably the circuit that supplies the lights/ceiling fans and bathroom exhaust fan and heat lamps. The tendency to turn every 2400w appliance on at the same time in the kitchen first thing in the morning would require a much bigger inverter for that 5 min load... re educate the wife to not do that, yeah right.

T1 Terry

I have a large shed at the back of my block, so I decided to fit it out with and off-grid system. I have 9 x 120watt 12 volt panels connected in series/parallel, a 24volt battery set, 2kw(3.5kw surge) inverter/charger which I power the shed with, but for most of the week it is not used. So I ran a cable to the house and put in an alternative electrical circuit to the kitchen. So I have a choice of mains power or battery back up to the kitchen. For the last 12 months this has been working fine and I never run the battery bank lower than 30% DOD so they are always 70% full (approximately). Plus it is increasing my rebate from the power company without them knowing that have increased the output of my system.
Just as an update, the Western Australian Government has done a back flip. They are going to leave the feed in tariff as it is..yahoo!!!!!

[reed cundiff]

Similar systems

Hi!

I have an off-grid home with LiFePO4 cells and did this for the *exact* reasoning above - I use it for cooking and all power for my home. I designed the system around the cells, and used a Morningstar MPPT regulator in 'custom' mode.

My pack was US$7000 and came with BMS it is 300Ah 51.2V (nominal 48V)

Any questions?

Steveg - We have 180AH (51.2 V (nominal 48V) of LiFePO4 cells in our 5th wheel (caravan to Brits and Aussies). The battery pack is from Manazanita and it came with BMS. Older son has been in solar design/fabricating/contracting in solar/wind for 25 years and he fabricated the system (Morningstar controllers and Magnum inverter etc). We use solar/batteries for microwave, refrigerator during the day etc. On bright days we use solar to heat water for shower. The 5th wheel has 1.4 kW of solar. We have been traveling with this setup for a year and have only tied into line power once and never into small generator except to run the 1 kW Honda once a month to make sure it still runs. We boondock on BLM and Forest Service lands. It is secluded, quiet, with lots of wildlife and cheap. Our son feels the future of off-grid will be LiFePO4 as their price decreases and folks learn to trust them more.
Reed and Elaine

[TroyDog]

Taking Home Office Off Grid

First post here, I have been following discussions with some interest.

I am in the process of taking my home office off grid, as being an electronics tech, thought it might be an interesting project.
Have installed 6 x 140 watt panels above our porch, wired as 3 sets of 2 series units cabled to the combiner breaker box, each set produces 44 max volts and a 35 volt tracking point.
Battery bank is 4 x 400 AH CA400 Calib Lifepo4 cells in series. Charge controller is an IPanda MPPT 60 amp device, inverter is an IPanda 1500 watt sine wave. BMS is the GamberBMS designed by an electronics tech in Canada. A Google search on these names will give you any the detailed info.

Charge controller has a user type battery selection mode, plug a laptop into it and you can set the bulk\float voltages. As there are no readily available Lifepo4 solar chargers off the shelf, this one seems ok and with bulk voltage set to 13.8, float set to 13.2 it charges the 12 volt battery quite well, the BMS is very configurable from its front panel display and is set for low cell = 3.0, max cell = 3.6 and balance voltage = 3.50. With these settings in this setup taking into account circuit breaker\fuses\cables voltage drops, the solar charger switches to float mode at cell voltages approx 3.55 in the region where the balance boards across each cell start to activate.

As the house is still on grid, I'm building a basic 60 volt 10 amp DC charger that connects to the solar charger input via ORed shottky diodes, if there hasn't been enough solar input during the day, the charger will switch on using night rate power to charge the battery. My office has several computers, server, stereo, lights and will run for over 2 working days (20 hrs) on a single charge. The idea being that the battery is not fully discharged on each daily cycle so hopefully will last 5000 cycles.

If the BMS detects a cell low, the office supply feed switches from the inverter to mains and the inverter is turned off. A cell high will turn the solar charger off, it should already be off, so acts to protect the expensive batteries.

This system is really a trial for doing the same for the whole house (the four cells are really spares for the larger bank), with 16 x 400AH cells (48V) and a 6kw low frequency sine wave inverter and 20 x 180 watt panels just waiting to go.

So far I'm very impressed with these cells, they are very efficient, sealed and hopefully will last for many years. Originally I intended to grid-tie, but the returns from that here in NZ will soon be approaching wholesale rates, so isn't worth while long term. Its an expensive project, but not when considered as part of the general house upgrade eg getting windows retro-fitted with double glazing, new carpets, kitchen, bathroom etc. I manufactured DIY solar hot water panels for the house HWC about 6 years ago, so 90% of our hot water is free, I want the power to be as well.

Cheers
Mike

[reed cundiff]

Mike

I found your write-up quite instructive. I guess your system will be approximately 32 kW-hours of LFP and 3.6 kW of solar. Is this 10 to 1 of LFP to solar pretty much the accepted ratio. We have a 5th wheel (caravan to you in New Zealand and Australia) with 9.5 kW-hours of LFP and 1.4 kW of solar so our ratio is fairly much the same. We have the LFP in series for 48 V nominal the same as you.

Our older son has been is in solar business (just finished sub-contract on a 1.8 megawatt system for power company) for 23 years. He is convinced that the future of off-grid solar systems is with LFP batteries as they become more accepted and the price decreases. He will probably be interested in learrninghow your system works out.

Reed

[TroyDog]

Mike

I guess your system will be approximately 32 kW-hours of LFP and 3.6 kW of solar. Is this 10 to 1 of LFP to solar pretty much the accepted ratio.

Reed

Hi Reed

Capacity is around the 21 KW hrs (52 volt bank), 5 KW hrs (13 volt bank) assuming 100% usage, our total daily draw off varies between 8.5 - 11 KW hrs per day.
3.6 KW PV array will generate approx 14 KW hrs per day in summer, probably half that in winter months, so I hope to recover 1 days usage from solar input, the balance if any via night rate power. Not sure about any accepted ratio, every site would be different depending on expected solar gain and draw down.

If there is much excess in summer, not sure what to do with it, some dump DC power direct into a low voltage HWC element, this wont work for me as I already have solar hot water panels. Could switch to grid tie mode, but the miserable 10c per KW Hr return isn't worth the hassle.

Right now my Chinese mppt solar charger (IPanda) seems to have a software design issue, when it wakes it-self up each morning it decides the panel array has zero capacity as of course at 7am in winter here its day light but no power as there is no sun on the panels, thus it switches itself to some sort of sleep mode, when sun finally hits the panels it remains in this mode producing zero power. The only way to make it go is to disconnect the panels with breaker switch, then reconnect, this wakes it up and away it goes. Think I will just put a time switch relay on its input and enable the PV array after sun up, dammit.

Cheers
Mike

[reed cundiff]

Mike

Thanks for the reply. The solar/LFP battery combination on our 10 m caravan are such that we have not tied into line power or generator since it was fabricated last June. We are at an RV (caravan) park at 7600' near Gunnison, Colorado. We hae a 30 amp outlet at our site and had no reason to hook up. Do not like RV parks in general so we are heading up to a great National Park campsite (this entire area is a National Recreation Site) for a bit more seclusion. There is a nesting pair of Bald Eagles about 600 m across the lake.

Am curious as to how the different battery banks work at different voltages.

Reed

[hbelanger]

Promissing opensource BMS

Hi All

New to this forum, but not new to renewable energy, so I thought I'd start off with sharing something promising to all of
the geek kind (like me) that are not affraid of a soldering iron and etching boards.

Opensource BMS --> Mod note - get permission from user name Jason before trying to hustle money here - kick start campaigns are often no more than solicitations for money from suckers.
Enjoy the freedom

Regards to all
Hugues