Grid-tie now battery backup later

What are the ramifications, if any, in building a grid-tie system and then adding battery backup later?

Thanks.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Grid-tie now battery backup later

    Depending on your emergency power needs, Grid Tied Power is around 77% efficient and Off Grid Power is ~52% efficient (plus, you can only store ~3 days of power for off grid, and the Utility Grid can "store" months to a full year of power)--You may need to install more solar panels to make up for the additional losses and limited amount of storage capacity--Plus a backup generator if you need 100% reliable emergency power (i.e., energy during bad weather).

    Next, most high end MPPT solar charge controllers can operate from ~72 to 150 VDC and most GT inverter operate at ~200-600 VDC (Xantrex does have a 600 VDC input MPPT charge controller--but it is not cheap). So, you would, probably, have to rewire your solar array to meet the different input voltage requirement.

    Next, take out the current GT inverter and install a Hybrid inverter (if you want GT+Off Grid backup power) or install a pure Off-Grid Inverter.

    And then you would have to install a large battery bank (roughly, a 6kW 48 volt input inverter should have a 600 AH @ 48 volt battery bank).

    Lastly, you would need to rewire your panels to have a "protected" sub panel that would operate with Grid or Off Grid power (if you are building a Hybrid system).

    There is an alternative... Keep the GT solar system, install a pure Off-Grid solar system with an inverter capable of connecting via "AC Coupled" to your GT inverter. When the power fails, the Off-Grid inverter takes over, and will work with the GT inverter to either supply AC power to your loads, or even accept energy from your GT inverter to recharge the battery bank ("back-drive" your off-grid inverter).

    It does work, but there is more research and ensuring proper component selection with your Off-Grid inverter (not all off grid inverters are capable of "AC Coupled" operation and controlling the state of charge of the battery bank).

    And, of course, you still need an off-grid inverter and a large AC battery bank for operation even with the GT inverter input to your system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sundownrsundownr Solar Expert Posts: 25
    Re: Grid-tie now battery backup later

    Thanks Bill... good information.
  • sundownrsundownr Solar Expert Posts: 25
    Re: Grid-tie now battery backup later

    "Next, most high end MPPT solar charge controllers can operate from ~72 to 150 VDC and most GT inverter operate at ~200-600 VDC (Xantrex does have a 600 VDC input MPPT charge controller--but it is not cheap). So, you would, probably, have to rewire your solar array to meet the different input voltage requirement."

    When referring to a 200-600 VDC operating range, what exactly does this mean?

    Thanks.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid-tie now battery backup later
    sundownr wrote: »

    When referring to a 200-600 VDC operating range, what exactly does this mean?

    Thanks.

    Central Grid-Tie inverters run directly from strings of panels that together form an array with a Vmp in that Voltage range. Battery-based inverter systems (including GT hybrids) usually run standard array Voltages of 12, 24, or 48 nominal. The Xantrex XW MPPT80-600 is the only charge controller capable of utilizing the high Voltage GT arrays to charge 24 or 48 Volt battery banks.

    For the most part, adding battery back-up later is usually a matter of putting in a separate system or doing a massive overhaul of the existing one as Bill said.
  • sundownrsundownr Solar Expert Posts: 25
    Re: Grid-tie now battery backup later

    "Central Grid-Tie inverters run directly from strings of panels that together form an array with a Vmp in that Voltage range. Battery-based inverter systems (including GT hybrids) usually run standard array Voltages of 12, 24, or 48 nominal. The Xantrex XW MPPT80-600 is the only charge controller capable of utilizing the high Voltage GT arrays to charge 24 or 48 Volt battery banks."

    48 volts is my maximum voltage and I am looking for a GT inverter which can do it all, namely have a built in 48 volt, charging regulator and whatever other goodies. If you know of such a good GT inverter, please let me know.

    Thanks.
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Grid-tie now battery backup later

    Xantrex, SMA, Outback (I think), and perhaps a couple others have "Hybrid" Inverters that can operate from a 48 volt (or 24 volt for some models) battery bank.

    Basically (the Xantrex XW family--simply the one I have read the most about), is like a whole house UPS system... And you just need to supply the 48 VDC battery bank (600 AH for a 6kW model) and you can connect your solar, wind, water charging sources directly the the battery bank.

    When the Grid is up, the XW will take any excess energy (above ~52 VDC battery float voltage) and push it out to AC wiring of your home (and to the grid if XW power is greater than power used by your home--which will "turn your power meter backwards"--Of course, depending on your utility requirements/billing plan).

    The XW has two AC inputs--One from Grid and a second from an AC backup generator. And the XW can charge upwards of 100 Amps of 48 VDC from your grid/genset into your battery bank (and it can even "load share" with your genset--It will cut back on charging current if generator loads are high, or even support generator AC output if the AC loads exceed the generator output--pretty cool).

    You can start by reading about the XW system and learn its basics... Then start with reading about the others systems to understand their pros and cons.

    It can be a fairly complex subject (building your own GT/Off Grid power system with generator backup).

    The XW (and possibly some other Hybrid type inverters) is/are also "cheap enough" that it can be cost competitive for a pure off grid system too (also nice, because it is easy to add AC Grid power later--If it every comes).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid-tie now battery backup later
    sundownr wrote: »
    "Central Grid-Tie inverters run directly from strings of panels that together form an array with a Vmp in that Voltage range. Battery-based inverter systems (including GT hybrids) usually run standard array Voltages of 12, 24, or 48 nominal. The Xantrex XW MPPT80-600 is the only charge controller capable of utilizing the high Voltage GT arrays to charge 24 or 48 Volt battery banks."

    48 volts is my maximum voltage and I am looking for a GT inverter which can do it all, namely have a built in 48 volt, charging regulator and whatever other goodies. If you know of such a good GT inverter, please let me know.

    Thanks.

    There are at least two that fit that bill: The Xantrex XW 6048 http://www.solar-electric.com/xaxwhyin1.html and the Outback Radian GS8048 http://www.solar-electric.com/ourags8wain.html

    Both use batteries (48 VDC) and can sell 'excess' solar power to the grid and provide back-up when the grid goes down. The Xantrex is 6kW and the Outback is 8kW; both can be "stacked" to provide additional power.
  • sundownrsundownr Solar Expert Posts: 25
    Re: Grid-tie now battery backup later

    Problem is my maximum array is 12 each, 300W panels, set up in a 4 x 3 array, outputting 48 volts on each of the 3 series arrays. I should easily get by with a 3300W inverter.

    The Xantrex XW 6048 and Outback Radian GS8048 are really too big for my application... although they do meet the 48 volt requirement.

    Perhaps I do need to go to a 24 volt or 36 volt setup and thus is why I am asking.

    Note , my maximum target power requirement is to run 2 small 5000 window air conditioners, in case of a power outage in high summer heat.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid-tie now battery backup later

    Grid-Tie tends to be more efficient the larger it is.

    However, Xantrex has a 4.5 kW XW: http://www.solar-electric.com/xaxw12hyin.html and a 4 kW one that's 24 Volts: http://www.solar-electric.com/xaxwhyin.html

    Outback also has a 3.6 kW GT unit: http://www.solar-electric.com/gvfx3648.html and a 3 kW one: http://www.solar-electric.com/gvfx3648.html

    The Xantrex inverters put out 240 VAC. The Outbacks are 120 VAC but can be used with an autotransformer http://www.solar-electric.com/psx-240.html for 240 VAC
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Grid-tie now battery backup later

    Be advised that window A/C units use huge amounts of power. It is possible that your 3600 Watt array will be unable to meet the demand. Figure about 7 kW hours AC from that array per day, with good sun conditions. If you have the units, run one through a Kill-A-Watt meter and have a look at just how much power it will demand.
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Grid-tie now battery backup later

    Xantrex does sell a 4.5 kW 48 volt version (it is really not that much less money)...

    Another item to look at are Mini-Split A/C (and heat pump) systems... There is a 120 VAC Sanyo and several other 240 VAC versions (the Sanyo, can apparently, be programmed to take not more than 300 watts on low--and virtually no surge current).

    Sanyo Mini-Split AC
    Mitsubishi mini-split 26 SEER

    They are very solar PV power friendly. (you can search for more threads here by typing into Google "mini split site:wind-sun.com" -- The "site:" tag will limit searches to this forum).

    We are also a practical bunch here... If these are rare outages and don't last too long (week or two) and you have enough space to store fuel (propane, diesel, gasoline, etc.)--Many times gensets are a better "investment" over solar...

    Solar works great if the place is occupied 9 months of the year or more, and/or GT connected.

    For shorter term needs (week end summer cabin, occasional power outages, etc.), heavy conservation + a fuel efficient genset may be the better solution (and a small solar + battery , or battery+gen recharging for "quiet power" over night, etc.).

    One of things that many people do is get a 10+ kW genset to power everything--then find out that they literally drink more fuel that you can store on site through a planned outage (maybe upwards of 1-2 gallons an hour even with very light loads).

    So, we get back to conservation and knowing your loads... And possibly several solutions... A Honda eu2000i genset (1,600 watt) to run 90% of the time, and your 10kW unit for hot summer days/emergency backup for the eu2000i. The eu2000i will keep most people happy on ~2 gallons or so of gasoline per day (there are propane conversion kits available too).

    Diesels can use much less fuel (more efficient engine, more BTU/Gallon fuel)--But you do have to watch their minimum loading--Typically, you want around 40-60% of rated output minimum as a load to reduce "wet stacking", coking, glazing cylinder walls, etc...

    If you want an automated start genset--there are very few under 5-6kW that I have seen.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sundownrsundownr Solar Expert Posts: 25
    Re: Grid-tie now battery backup later

    "Another item to look at are Mini-Split A/C (and heat pump) systems... There is a 120 VAC Sanyo and several other 240 VAC versions (the Sanyo, can apparently, be programmed to take not more than 300 watts on low--and virtually no surge current)."

    Great idea for low power AC... thanks.
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Grid-tie now battery backup later

    Of course, the low power setting is also low cooling... The idea is you can run the unit on low during the day and pre-cool or keep an already cool room, cool.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,361 ✭✭✭✭✭
    Re: Grid-tie now battery backup later

    Xantrex XW inverter series (and outback and others) do NOT have a PV charger in them. They have a AC only charger. You will need a Solar PV charge controller, if you are wanting to harvest from PV panels.

    Most controllers take up to about 150VDC.
    Midnight makes some higher voltage versions
    Xantrex has one 600 V DC string controller.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

Sign In or Register to comment.