Retrofitting grid-tie system to off-grid in case of emergency

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  • BB.BB. Super Moderators, Administrators Posts: 29,041 admin
    Re: Retrofitting grid-tie system to off-grid in case of emergency

    One way to size the battery bank is to use 1-3 days of storage and 50% maximum discharge, along with 80% inverter efficiency to give you a "balanced" system design. So, using 2 days of storage:
    • 5,000 WH * 1/48 volt battery bank * 1/0.85 inverter efficiency * 2 days of no-sun * 1/0.50 max discharge = 490 AH battery bank.

    With a 490 AH @ 48 volt battery bank (flooded cell) and 5kWH per day of AC usage (charge during the day, use power at night), you can:
    • 490 AH * 1/8 hour discharge rate * 48 volt battery * 0.85 inverter efficiency = 2,499 Watt recommended max continuous load
    • 490 AH * 1/2.5 hour discharge rate * 48 volt battery * 0.85 inverter efficiency = 7,997 Watt recommended max surge/starting load

    Recommended DC charging current range is 5%-13% and never exceed 25% (usually AC charger). For 13% to 25% rate of charge, you should have a remote battery bank temperature sensor to reduce the chances of thermal run-away (if deeply discharging and fast charging backup).

    The DC charging range would be (again, everything I am using here assumes flooded cell battery bank--But will work fine with AGM too--AGM can source/sink more current than flooded cell and are slightly more efficient--And the numbers are not that exact--just carrying out numbers so you can reproduce my math and reduce rounding errors):
    • 490 AH battery bank * 0.05 rate of charge = 24.5 amps minimum
    • 490 AH battery bank * 0.10 rate of charge = 49 amps healthy nominal
    • 490 AH battery bank * 0.13 rate of charge = 63.7 amps max recommended no thermal management (and max cost effective solar recommended)
    • 490 AH battery bank * 0.25 rate of charge = 122.5 amps never exceed using thermal management for deep cycling recharge

    The typical AC genset to run the above AC chargers (assuming worst case of 80% efficiency and 67% power factor (again, there are lots of AC charger options--the below should be worst case--largest minimum genset VA rating):
    • 24.5 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 2,697 VA rated generator minimum
    • 49 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 5,394 VA rated generator minimum
    • 63.7 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 7,012 VA rated generator minimum
    • 122.5 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 13,484 VA rated generator minimum

    Typical solar array sizing using 0.77 derating (not sure of GT back feeding AC inverter--might be a bit more losses):
    • 24.5 amps * 59 volts charging * 1/0.77 panel+charger eff = 1,877 Watt Array minimum 5% rate of charge
    • 49 amps * 59 volts charging * 1/0.77 panel+charger eff = 3,755 Watt Array nominal 10% RoC
    • 63.7 amps * 59 volts charging * 1/0.77 panel+charger eff = 4,881 Watt Array "cost effective" 13% RoC for solar

    Note--I would suggest there is a maximum solar array to battery bank ratio--that if exceeded, can cause the battery bank to over voltage with Solar MPPT charge controllers (solar array can "overwhelm" the battery charging when MPPT sweeps are performed). I would suggest that is our standard for 100 AH @ 48 volts for every 1kW of solar array capacity--Or roughly 4.9 kW solar array... If the solar array is much higher than that, it appears that you can run the risk of over voltaging the battery bank/inverter electronics (exceeding ~72 volts). MPPT controllers run "sweeps" every so often to figure out the Pmax=Vmp*Imp ... And it is possible for a nearly fully charged battery to refuse to accept the sweep current (it has to go somewhere for a few seconds)--My theory to explain a few "odd ball" events we have talked about here before.

    Again, the above are all starting rules of thumbs. Once you have the needs nailed down and start picking hardware, can recheck/adjust as needed.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SulfurSulfur Solar Expert Posts: 62 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    westbranch wrote: »
    here is a cheap Li battery http://cgi.ebay.com/ebaymotors/130826602917

    user 'Solar-Dave' has several threads on electric cars, as well as others, there is a house runoff a Prius mentioned too.

    re NiCd's, what brand do you have?

    No, have not needed to change the electrolyte in the ones I use. They were part of a 75 cell lot I obtained and the ones I use were from the ones that passed muster. a week long charge regimen is needed...

    email me for more info re rehabilitating them

    The NiCd's I can get are Mcgraw-Edison Americad HED-46, they are 46Ah, 1.2VDC
    Is there any way to tell if they can be rehabilitated without just trying it? I am leaning more toward NiCd at this time since the SI can charge them and they store much longer without killing them selves. but these would not be enough, I probably only could get about 46Ah at 48VDC of these things, so where do you buy NiCd batteries for solar? have you made new electrolyte with KOH before? where do you get the stuff that is supposed to float on top of the electrolyte to stop foaming?

    what do you mean when you say a week long charge is needed? wouldn't the SI just charge them each day if needed? do you know if the SI uses voltage to determine SOC on these things? or maybe a combination of voltage and tracking amps in and out?
  • SulfurSulfur Solar Expert Posts: 62 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    BB. wrote: »
    One way to size the battery bank is to use 1-3 days of storage and 50% maximum discharge, along with 80% inverter efficiency to give you a "balanced" system design. So, using 2 days of storage:
    5,000 WH * 1/48 volt battery bank * 1/0.85 inverter efficiency * 2 days of no-sun * 1/0.50 max discharge = 490 AH battery bank.

    With a 490 AH @ 48 volt battery bank (flooded cell) and 5kWH per day of AC usage (charge during the day, use power at night), you can:
    • 490 AH * 1/8 hour discharge rate * 48 volt battery * 0.85 inverter efficiency = 2,499 Watt recommended max continuous load
    • 490 AH * 1/2.5 hour discharge rate * 48 volt battery * 0.85 inverter efficiency = 7,997 Watt recommended max surge/starting load

    Recommended DC charging current range is 5%-13% and never exceed 25% (usually AC charger). For 13% to 25% rate of charge, you should have a remote battery bank temperature sensor to reduce the chances of thermal run-away (if deeply discharging and fast charging backup).

    The DC charging range would be (again, everything I am using here assumes flooded cell battery bank--But will work fine with AGM too--AGM can source/sink more current than flooded cell and are slightly more efficient--And the numbers are not that exact--just carrying out numbers so you can reproduce my math and reduce rounding errors):
    • 490 AH battery bank * 0.05 rate of charge = 24.5 amps minimum
    • 490 AH battery bank * 0.10 rate of charge = 49 amps healthy nominal
    • 490 AH battery bank * 0.13 rate of charge = 63.7 amps max recommended no thermal management (and max cost effective solar recommended)
    • 490 AH battery bank * 0.25 rate of charge = 122.5 amps never exceed using thermal management for deep cycling recharge

    The typical AC genset to run the above AC chargers (assuming worst case of 80% efficiency and 67% power factor (again, there are lots of AC charger options--the below should be worst case--largest minimum genset VA rating):
    • 24.5 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 2,697 VA rated generator minimum
    • 49 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 5,394 VA rated generator minimum
    • 63.7 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 7,012 VA rated generator minimum
    • 122.5 amps * 59 volts charging * 1/0.80 charger eff * 1/0.67 power factor = 13,484 VA rated generator minimum

    Typical solar array sizing using 0.77 derating (not sure of GT back feeding AC inverter--might be a bit more losses):
    • 24.5 amps * 59 volts charging * 1/0.77 panel+charger eff = 1,877 Watt Array minimum 5% rate of charge
    • 49 amps * 59 volts charging * 1/0.77 panel+charger eff = 3,755 Watt Array nominal 10% RoC
    • 63.7 amps * 59 volts charging * 1/0.77 panel+charger eff = 4,881 Watt Array "cost effective" 13% RoC for solar

    Note--I would suggest there is a maximum solar array to battery bank ratio--that if exceeded, can cause the battery bank to over voltage with Solar MPPT charge controllers (solar array can "overwhelm" the battery charging when MPPT sweeps are performed). I would suggest that is our standard for 100 AH @ 48 volts for every 1kW of solar array capacity--Or roughly 4.9 kW solar array... If the solar array is much higher than that, it appears that you can run the risk of over voltaging the battery bank/inverter electronics (exceeding ~72 volts). MPPT controllers run "sweeps" every so often to figure out the Pmax=Vmp*Imp ... And it is possible for a nearly fully charged battery to refuse to accept the sweep current (it has to go somewhere for a few seconds)--My theory to explain a few "odd ball" events we have talked about here before.

    Again, the above are all starting rules of thumbs. Once you have the needs nailed down and start picking hardware, can recheck/adjust as needed.

    -Bill

    thanks, your information was very helpful, since I may never use the batteries and SI due to hopefully always having a utility grid, I think that NICd batteries may be a better choice for me since they last longer, what do you think? where can I get them?
  • BB.BB. Super Moderators, Administrators Posts: 29,041 admin
    Re: Retrofitting grid-tie system to off-grid in case of emergency

    NiCad are pretty rugged batteries--But as I recall, they are not near as efficient when charging as Lead Acid.

    Also--A bigger issue--Make sure you can "dispose" of the cells for a reasonable cost. Cadmium is one of those metals that can be a real bear to "recycle" (because of government regulations).

    There is (or claims to be) only one place in the US that recycles NiCad batteries and they charge ~$52 per 70 lb box of batteries (includes shipping)....

    http://www.inmetco.com/services_battery.htm
    Pre-paid Battery Recycling Order Form (PDF - 67Kb)

    I don't know how one would recycle the batteries locally (scrap yard, battery distributor, etc.)? It appears that in the US, NiCads include the recycling charge when purchased--So, it is possible that when recycled, if you can find a place to accept them, there may be either no charge or just a shipping charge.

    Regarding the use of NiCad batteries--They are "different". and at the relatively low charge rates used in solar for recharging, they appear to not be very efficient:
    NiCad and NiMH batteries are amongst the hardest batteries to charge. Whereas with lithium ion and lead acid batteries you can control overcharge by just setting a maximum charge voltage, the nickel based batteries don't have a "float charge" voltage. So the charging is based on forcing current through the battery. The voltage do do this is not fixed in stone like it is for the other batteries. This makes these cells and batteries difficult to charge in parallel. This is because you can't be sure that each cell or pack is the same impedance (or resistance), and so some will take more current than others even when they are full. This means that you need to use a separate charging circuit for each string in a parallel pack, or balance the current in some other way, for example by using resistors of such a resistance that it will dominate the current control.
    The coulometric charging efficiency of nickel cadmium is about 83% for a fast (C/1 to C/.24) charge, and 63% for a C/5 charge. This means that at C/1 you must put in 120 amp hours in for every 100 amp hours you get out. The slower you charge the worse this gets. At C/10 it is 55%, at C/20 it can get less than 50%. (These numbers are just to give you an idea, battery manufacturers differ).


    I have seen different numbers and statements about NiCads, so I am not clear which ones are accurate or not--If you have the brand/model number, perhaps you can find some more information on the web.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    So how many Ah of battery capaicity would be recommended for a 48VDC system that can comfortably pull 5kwh per night

    I get that at night from my 360 ah flooded lead acid bank (48v), which drops the bank to about 75% SoC. A 25% depth of discharge (75% SoC) is an economical "compromise" depth of discharge for long battery life versus cost.

    I probably missed something above, but I'm not understanding why you're looking at these exotic batteries. They are likely to be complicated, expensive, and easy to damage from a new user. What's wrong with a big, inexpensive and locally-sourced flooded lead acid bank? It's very likely to be the least expensive route, will give you many years of service, and if you make a mistake and damage them, as some new users do, you won't be out huge amounts of $$$.
  • SulfurSulfur Solar Expert Posts: 62 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    Eric L wrote: »
    I get that at night from my 360 ah flooded lead acid bank (48v), which drops the bank to about 75% SoC. A 25% depth of discharge (75% SoC) is an economical "compromise" depth of discharge for long battery life versus cost.

    I probably missed something above, but I'm not understanding why you're looking at these exotic batteries. They are likely to be complicated, expensive, and easy to damage from a new user. What's wrong with a big, inexpensive and locally-sourced flooded lead acid bank? It's very likely to be the least expensive route, will give you many years of service, and if you make a mistake and damage them, as some new users do, you won't be out huge amounts of $$$.

    I plan on always being connected to grid and these batteries are for emergency use only, so there is an advantage to have batteries that can sit unused for a long time without killing themselves. I have not decided but am trying to get other peoples opinions. replacing batteries every 5 years, when I am not even using them, seems like a waste. but I don't know what the NiCd's cost, so that might change my mind?
  • westbranchwestbranch Solar Expert Posts: 5,138 ✭✭✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency

    hope this works for the PDF


    here are a couple of links

    http://www.saftbatteries.com/Home/tabid/54/Language/en-US/Default.aspx#

    http://www.informups.com/ni_cd.html

    http://www.houseofbatteries.com/saft-batteries-m-27-l-en.html

    http://www.cecns.co.uk/alcad/

    re Recovering cells.
    I use a small 12v SB2000e charger on my NiCd's. 2parallel banks.
    My experience is that they are tough as hell and live very long lives is treated well. Mine overwinter in an unheated cabin @ -30 or colder and keep on running ( never mind that E-gizer bunny).
    to recover them from being stored you need to charge them for 15 hours at a constant current , then a 5 hour discharge at C/5, record cell V, recharge 15 hrs, test 5 hrs again, do 5 tests altogether looking for bad cells, particularly in the 4 1/2 and 5 hr time slots. Replace any cell that fails at hr3, my observation.

    see section 8.6 of this doc c:\email\attach\Block Battery Tech.pdf
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Eric LEric L Solar Expert Posts: 262 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    I plan on always being connected to grid and these batteries are for emergency use only, so there is an advantage to have batteries that can sit unused for a long time without killing themselves.

    Even if you find a battery (NiCad?) that can be treated that way, backup power systems need to be regularly run and tested if they're going to be reliable, whether it's a generator or UPS-type system like you're considering. You have to consider that things can wear out or malfunction over time, in some cases especially if they aren't used (capacitors in electronics, e.g.). If you never cycle the backup system, it will eventually fail without you noticing and then when the big day arrives and you need it, it's not working.

    Whatever battery you choose, I think you'll want to cycle it regularly; maybe one night a month go off grid with it. This will cost you only a tiny amount in lost productivity (say 5 KWH times whatever you get for selling to grid per KWH). But this way when the system is really needed you will be much more confident it works and you'll be more familiar with how everything functions.

    IMO, once you recognize the need for regular cycling anyway, you realize that there is less need for having batteries that can be left unused for very long periods (and also realize that you're going to have to commit to some regular maintenance time and effort to have a reliable back up). But that's my perspective.
  • SulfurSulfur Solar Expert Posts: 62 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency

    when I last posted my system was a SB7000 and 28 240 watt Sharp panels, I ended up buying a Sunny Island 6048 and eight 6VDC golf cart batteries from Sam Club. I plan to only use the system as grid tied and the SI and batteries are only to be able to utilize the solar system if the grid goes down. I wired it so I can power the whole house in an off grid scenario, so normally I leave the SI off and not connected at all. Using a 200amp transfer switch to eliminate possibility of backfeeding down grid. I have tested it and it easily powers the house including a hot water heater when the sun is shining, I only have 208 Ah of batteries at 48VDC so I would not be able to let the house use much power at night if the grid were to go down.

    When in off grid mode and a large load turns on, the SI will draw that load from the batteries until the SI changes the frequency of island grid which increases power production from the SB7000 or if it was charging the batteries then it just immediately slows or stops that charging and inverts power from batts if needed in conjunction with SB7000 feeding house. So the power from the SB7000 feeds the house directly at 240VAC and does not pass through the SI. I am using an Outback 120VAC to 240VAC transformer to step up and down between the SI and my house panel. I bought another SB7000 and 28 more panels and will have them installed within a month hopefully.

    It would be nice if the SB and SI could provide better real time trending options, the sunny portal data update is usually delayed by several hours, the Sunny Webbox does allow nice real time snap shot data but not real time trending, that needs to be improved by SMA.

    My current panels are mounted facing South at 17 degrees from horizontal, the max power they could produce at winter solstice was 4300 watts, now they are producing about 5400 watts max, I did not have them installed during summer solstice, so not sure what the system max will be. The next 28 panels will go in yard at 30 degree angle, which SMA software says is ideal for my area. 6700 watts is supposed system max. I bought SB7000's on ebay, 1 used and 1 new old stock, $2200 each. The panels also bought from ebay for $0.80/watt, now you can get them for $0.75/watt. Panels are wired in 2 strings of 14 into the one SB7000 that is in service right now.

    I had to cut down a tree that was giving me shade once we got into winter time, so I recommend measuring winter time sun angle so folks know what shade problems they will run into.

    My area has a good net metering program. So far I am happy with the system, it has been a fun little science project.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    Sulfur wrote: »
    Panels are wired in 2 strings of 14 into the one SB7000 that is in service right now.
    What's the Voc of those modules and how cold does it get where you are? If they are Sharp NU-Q240F2, then Voc is 37.4V. A string of 14 gives you a string Voc of 524V at STC, and the upper limit of the SMA7000 is 600V. You should be safe down to about +3 degrees F.
  • tmarchtmarch Solar Expert Posts: 143 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    Sulfur wrote: »
    when I last posted my system was a SB7000 and 28 240 watt Sharp panels, I ended up buying a Sunny Island 6048 and eight 6VDC golf cart batteries from Sam Club. I plan to only use the system as grid tied and the SI and batteries are only to be able to utilize the solar system if the grid goes down. I wired it so I can power the whole house in an off grid scenario, so normally I leave the SI off and not connected at all. Using a 200amp transfer switch to eliminate possibility of backfeeding down grid. I have tested it and it easily powers the house including a hot water heater when the sun is shining, I only have 208 Ah of batteries at 48VDC so I would not be able to let the house use much power at night if the grid were to go down.

    When in off grid mode and a large load turns on, the SI will draw that load from the batteries until the SI changes the frequency of island grid which increases power production from the SB7000 or if it was charging the batteries then it just immediately slows or stops that charging and inverts power from batts if needed in conjunction with SB7000 feeding house. So the power from the SB7000 feeds the house directly at 240VAC and does not pass through the SI. I am using an Outback 120VAC to 240VAC transformer to step up and down between the SI and my house panel. I bought another SB7000 and 28 more panels and will have them installed within a month hopefully.

    It would be nice if the SB and SI could provide better real time trending options, the sunny portal data update is usually delayed by several hours, the Sunny Webbox does allow nice real time snap shot data but not real time trending, that needs to be improved by SMA.

    My current panels are mounted facing South at 17 degrees from horizontal, the max power they could produce at winter solstice was 4300 watts, now they are producing about 5400 watts max, I did not have them installed during summer solstice, so not sure what the system max will be. The next 28 panels will go in yard at 30 degree angle, which SMA software says is ideal for my area. 6700 watts is supposed system max. I bought SB7000's on ebay, 1 used and 1 new old stock, $2200 each. The panels also bought from ebay for $0.80/watt, now you can get them for $0.75/watt. Panels are wired in 2 strings of 14 into the one SB7000 that is in service right now.

    I had to cut down a tree that was giving me shade once we got into winter time, so I recommend measuring winter time sun angle so folks know what shade problems they will run into.

    My area has a good net metering program. So far I am happy with the system, it has been a fun little science project.

    I'm going to do the same thing only on a smaller scale, I currently have a 6K system with a Sunny Boy 6000 and want to add another 4-5K with a Sunny Boy 5000 and a 5K Sunny Island with a Outback auto transformer.
    I have a question, will the other Sunny Boy see the output oF the 4-5K system as the grid and therefore come on when the grid is down?
    THANKS
  • SulfurSulfur Solar Expert Posts: 62 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency

    You will have to have the sunny island imposing an island grid and at least 100 Ah of batteries @48VDC to run the either one or both sunny boys without a utility grid.
  • SulfurSulfur Solar Expert Posts: 62 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency

    I used the SMA configuration software to determine that 14 panels was ok for my min temp, 15 panels however was supposedly too many. I should measure the max voltage on a cold sunny afternoon with the DC disconnect from the inverter, I don't think I have ever seen it over 500 volts once the inverter is on.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    Sulfur wrote: »
    I used the SMA configuration software to determine that 14 panels was ok for my min temp, 15 panels however was supposedly too many. I should measure the max voltage on a cold sunny afternoon with the DC disconnect from the inverter, I don't think I have ever seen it over 500 volts once the inverter is on.
    It's not the cold sunny afternoon you should be concerned with, it's dawn at the end of the coldest night. At that point, the inverter is drawing no current from the array so when the first light hits the modules the string voltage jumps up to Voc and the cell temp is whatever was the low temperature that night.
  • SulfurSulfur Solar Expert Posts: 62 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency

    that's funny because I first wrote that I should check first thing in the morning but then changed it to unconnected in the afternoon. Thanks for the tip.

    I will check that some cold morning and see how high the voltage is before the inverter kicks on.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    Sulfur wrote: »
    Hello, I have a grid tied solar system in Montana that I installed last year and have a question on retrofitting the system to off-grid in case of emergency.

    SB7000 with 28 Sharp 240watt panels (ND-240QCJ) self installed

    I am about to install another
    SB7000 with 28 more Sharp 240 watt panels and a SB3000HFUS with 14 Sharp 240 watt panels
    So a total of 70 panels and 3 inverters.

    I have a net metering power meter and this inverter I am about to install also came with a Sunny Webox for improved data logging vs my current Sunny Explorer via blue tooth which is weak.

    I only plan to use the system as grid tied but want to buy the hardware to be able to use solar power in case the utility power would go down for a long period of time. I have a generator that can power my house and enough gas for a few months, but want to be able to retrofit the system and have the hardware on hand to do so in case of longer power outage.

    There is a growing market for AC-coupled battery backup retrofits to existing grid-tie-only systems. The incompetent foreign and fiscal policies of America and just the growing tendency toward tyranny, and the out of control money printing could be having a role in this. Many solar vendor websites are showcasing AC-coupled battery backup retrofit kits now. Northern Arizona Wind & Solar should start also.

    Check out for wiring diagram - this one has implementation of a diversion load which allows absorption charging the batteries without backfeeding the grid during an outage:
    http://www.wholesalesolar.com/images/newsletter/MAGNUM-AC-COUPLED-LINE-DIAGRAM_large.jpg

    Magnum energy is the driver of this market. Most AC-coupled battery backup retrofits are on magnum inverters. Xantrex is late in the game but they do have a nice slideshow:
    http://products.schneider-electric.us/support/technical-library/?event=detail&oid=090089268089ab18&cat=0b008926807eae3f

    Many outback inverters support AC-coupling also. Not sure about the Radian.

    AC-coupling is more designed for infrequent storm outages or utility mishaps (open breaker creates outage for 2 hours, or blown substation transformer creates rolling blackouts for two weeks while they order and replace it) and can, with less efficiency, step up for long-term outages or california or 3rd-world-nation style rolling blackouts. AC-coupled battery based systems are a lot more efficient than DC-coupled when things are routine and working and just selling to the grid because you don't have the loss of charge controllers (step-down voltage, only to step it back up).

    If you want to retrofit to DC-coupled, Xantrex does have a MPPT-80-600 charge controller that can work with grid-tie voltage levels. These are 2.5 times more expensive than 150 volt charge controllers and only hand 30% more charge current (80 amps vs 60)
  • SulfurSulfur Solar Expert Posts: 62 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency

    Since I had posted that a while back...I bought a Sunny Island and some batteries to accomplish what I was talking about, it worked well when I tested it off grid. I normally leave it turned off since my system is grid tied. I am flying to Mesa tonight, small world.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    There is a growing market for AC-coupled battery backup retrofits to existing grid-tie-only systems. The incompetent foreign and fiscal policies of America and just the growing tendency toward tyranny, and the out of control money printing could be having a role in this.
    Not to get (too) political, but it's not America but the entire world that is moving in this direction. Most other places, it is worse.
  • BB.BB. Super Moderators, Administrators Posts: 29,041 admin
    Re: Retrofitting grid-tie system to off-grid in case of emergency

    Yea:

    Jim Rogers: We’re Wiping Out The Savings Class Globally, To Terrible Consequence.
    For the first time in recorded history, we have nearly every central bank printing money and trying to debase their currency. This has never happened before. How it’s going to work out, I don't know. It just depends on which one goes down the most and first, and they take turns. When one says a currency is going down, the question is against what? because they are all trying to debase themselves. It’s a peculiar time in world history.

    I own the dollar, not because I have any confidence in the dollar and not because it’s sound – it’s a terribly flawed currency – but I expect more currency turmoil, more financial turmoil. During periods like that, people, for whatever reason, flee to the U.S. dollar as a safe haven. It is not a safe haven, but it is perceived that way by some people. That’s why the dollar is going up. That’s why I own it. Will I own it in five years, ten years? I don't know.

    I don't know what the answer is... (other than vote the current folks out of power--for what, a different set of folks that will be corrupted by money and power?)

    -Bill :cry:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    ggunn wrote: »
    The SI is a pretty versatile machine. It can throttle back the production of a SB if the power from it has nowhere to go. It can control relays for load shedding when resources are low. It can fire up a generator. It has in integrated transfer switch. I'm pretty sure you could get it to make coffee for you. :D
    But if you rely on SB's to deliver the majority of your load power and this includes some individual large loads, there could be some uncomfortable problems when a cloud goes by and the SI itself does not have enough capacity to make up for the lost power from the SBs. You could end up with your large load finding itself shed unpredictably.
    You should also make sure to size the battery bank for you SI sufficiently large to provide surge power, as for motor starting, since the SBs simply cannot provide any power beyond the limit of the instantaneous DC input from the panels. Also make it large enough to supply any critical loads during the night.
    SMA SB 3000, old BP panels.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    inetdog wrote: »
    But if you rely on SB's to deliver the majority of your load power and this includes some individual large loads, there could be some uncomfortable problems when a cloud goes by and the SI itself does not have enough capacity to make up for the lost power from the SBs. You could end up with your large load finding itself shed unpredictably.
    You should also make sure to size the battery bank for you SI sufficiently large to provide surge power, as for motor starting, since the SBs simply cannot provide any power beyond the limit of the instantaneous DC input from the panels. Also make it large enough to supply any critical loads during the night.
    Yeah? I still bet you could get it to make coffee. :D
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    ggunn wrote: »
    Yeah? I still bet you could get it to make coffee. :D
    I think that is a given.
    And a rather significant benefit. If it would toast bagels too, it might be enough for comfortable survival.
    However, a modern hyper-coffee-pot with solid state timer might not be as happy as a simple single burner hotplate. :-)
    SMA SB 3000, old BP panels.
  • SulfurSulfur Solar Expert Posts: 62 ✭✭
    Re: Retrofitting grid-tie system to off-grid in case of emergency
    inetdog wrote: »
    I think that is a given.
    And a rather significant benefit. If it would toast bagels too, it might be enough for comfortable survival.
    However, a modern hyper-coffee-pot with solid state timer might not be as happy as a simple single burner hotplate. :-)


    Your description of "comfortable survival" is exactly what I was shooting for when designing the off grid portion of the system, it is not ideal only having 208Ah at 48vdc but I may never really use other it than testing, so it is a compromise. System is normally grid tied.

    In a previous post I had discussed with someone what the max voltage open circuit would be with my system and later noticed that the Sunny Webbox tracks that and claims the 537 VDC has been my max voltage so far.
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