Battery less vs. battery based grid tie

Dave AngeliniDave Angelini Solar Expert Posts: 6,184 ✭✭✭✭✭
Is there a good link on the forum that I can send a friend who just has to have a battery based grid tie. I have been trying to show her the cost, complexity and loss of space are not woth it. I have been trying to get her to see Bill's method of gen back-up to batteryless.

Pulleeezzze help!
"we go where power lines don't" Sierra Nevada mountain area
 http://members.sti.net/offgridsolar/
E-mail [email protected]

Comments

  • AntronXAntronX Solar Expert Posts: 462 ✭✭
    Re: Battery less vs. battery based grid tie

    If she wants battery backup for grid failures and to have the independence to show the finger to the power company and cut the cord, then I would not try to persuade her away from battery based system.
  • mike95490mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Battery less vs. battery based grid tie

    If one is tech savy, and can manage battery maintenance & replacement, and has $ to throw at it, and doesn't mind loosing 40% efficiency, then a battery based system works.

    A 20lb propane tank and EU2000 will also work if the power goes off once in a while.

    I think the answer in this case, is EU2000 for occasional outages.
    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 ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Battery less vs. battery based grid tie

    In terms of cost difference it's about the same as grid-tie vs. off grid: $0.50 kW/hr for grid-tie vs. $1.00 kW/hr for off grid. Kinda nasty expensive for those few occasions when the utility is down. The generator is cheaper by far.
  • BB.BB. Super Moderators, Administrators Posts: 32,740 admin
    Re: Battery less vs. battery based grid tie

    Dave,

    Is not one of your systems (pictures, etc.) a good description of a Hybrid system...

    About the only difference is the AC utility line plugged into an XW Hybrid inverter/charger?

    I guess the question too is how much power does your friend use/expect to use during a power failure (10x what you off-grid guys use in a day?). And would they need a backup genset any way (at least on the coast here, power failures are pretty much a winter wind/rain storm and there is little sunlight during those times).

    If they want just a little power for UPS like function--perhaps a small Xantrex Inverter/charger + genset is the answer (and some solar panels--but that would be a waste most of the time unless an XW hybrid type inverter is used).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • sub3marathonmansub3marathonman Solar Expert Posts: 300 ✭✭✭
    Re: Battery less vs. battery based grid tie

    With a battery based system you can shift loads from peak to off-peak by using the battery based system, so that could be an additional financial incentive. Also, you don't have to worry about getting fuel for a generator if your batteries are good. And the batteries do take up a bit of space, but I built a table around them so I actually added usable space for me. Also, I don't see that it doubles the cost of electricity generated (from the often mentioned $0.50 to $1.00), but I haven't done the calculations for my system yet. In addition, there is a federal tax credit for PV systems, including the batteries, so you're able to essentially get the batteries for 30% discount. Also, I think the Xantrex XW series are high quality inverters, and they need a battery system.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,184 ✭✭✭✭✭
    Re: Battery less vs. battery based grid tie

    Thanks everyone! There was not anything that I missed in my initial cost package to my friend but since I never do grid-tie I wanted your views! She is #38 for me, solar wise...

    Anyway, what I ended up doing because she does not even go into the hgher rate tiers, and this really is a personal choice, is to present the option of charging an electric car with her home solar. Even then it really makes little financial sense but there is at least a strategy that I can "sleep with". She has a Prius and a second all electric car could get her to work.

    This whole process has made me realize that I need to figure a better way to present this in the future. The one thing I could not explain to her ( I used the common safety for utility workers) is why a battery less grid tie system can't make electricity during the day in an outage?

    So, Why? I know about AC coupling and all that but why can't a system do this? This is not 1979 it is 2010. My wife says I need to keep you guy's thinking! Keep you out of trouble on these hot days! Take care!
    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Battery less vs. battery based grid tie
    So, Why? I know about AC coupling and all that but why can't a system do this? This is not 1979 it is 2010. My wife says I need to keep you guy's thinking! Keep you out of trouble on these hot days! Take care!

    Nothing to synch to.
    SunnyBoy has a system - the "Island" I think it's called? - which does allow production without grid.

    But basically there's nothing to stabilize a GT inverter without an external power source (unlike the battery-based inverter wich functions independently).

    Not a very detailed or good explanation so Bill can make it better. Right Bill? :p
  • BB.BB. Super Moderators, Administrators Posts: 32,740 admin
    Re: Battery less vs. battery based grid tie

    Right Marc :p,

    Two major issues... One is that a GT inverter does not regulate grid voltage or frequency. The Utility is basically an "AC Battery" and the GT inverter is like the alternator on a car supplying energy to the battery and car electrical system.

    If you have ever disconnected a car battery from a running car--you frequently find that the alternator (and generators on older vehicles) cannot actually maintain 14.2 volts--it goes all over the place (and frequently burns out all of the light bulbs in older cars without all the electronics, ask me how I know :roll:--I hate to think what happens in a modern car with a bunch of electronics/computers).

    Can you make an alternator/DC generator that will make stable power without a battery--Yes, but it is not done (probably more expensive and not really needed because the battery is already in the car).

    The second issue is that solar power is variable and the AC loads require exactly 120 VAC 60 Hz or they don't work correctly.

    To build an off-grid capable system, it could be done without a battery but the solar panel output would always have to be greater than the output power (sun, clouds, night, starting loads, etc.). While a solar panel + capacitor could take care of starting loads--for long term stable AC power, the solar panel would have to be way larger than the actual loads to supply useful AC power (microwave oven turns off, TV goes dark, computer/network goes down every time a bird flies over or a cloud passes by).

    Similar to an electric car powered only by solar panels (if it was possible/practical). Only drive in full sun, go through a tunnel and the car dies, cloudy weather--no drive, night--forget it, etc.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Battery less vs. battery based grid tie

    The SMA Sunny Island system will automatically take care of matching the variable PV output with the variable loads. You could get away with installing a really small battery bank and a small sunny island if you wanted to rely purely on the PV power.
    Although there might be a limit to the difference in output between GTI and sunny island.

    I've seen the setup working in the SMA lab, and the response between turning on a new load and the GTI putting out more power was quite fast, within a few seconds.
  • BB.BB. Super Moderators, Administrators Posts: 32,740 admin
    Re: Battery less vs. battery based grid tie

    Hmm... If the Sunny Island "GT system" responds within a few seconds... Then it really needs the Sunny Island Inverter+Battery system to carry through the starting loads... Which only makes sense as the "true" GT / Utility Interactive systems apparently have a "fairly long" time constant (per a Solar Guppy post in another thread, probably to prevent oscillations between the inverter and utility power).

    An Off-Grid inverter would need to respond within 1/2 cycle (1/120 Hz = 8.3 mSec) to be a "useful power source" for an off grid system.

    -Bll
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: Battery less vs. battery based grid tie

    Not sure if we're talking about the same response here, I meant the response to varying the GT output based on the loads when already operating in off-grid mode. And in this case the GT has to be a sunny boy.
    E.g.: Grid is down, batteries fully charged, GT and AC loads and SI are all on the same AC bus. Frequency is now controlled by the SI. If the loads are less than the GT then the time it takes for the SI to increase the frequency and the GT to reduce it's output correspondingly is only a few seconds.

    EDIT: Ah, I think I see what you mean now, yes the SI will have to carry the loads through until the GT can respond.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,184 ✭✭✭✭✭
    Re: Battery less vs. battery based grid tie

    If you have to have two inverters it really make little sense for my "hypothetical" customer. I am thinking that with the modern slow start refrigerators someone would devise a way to avoid spoiling food and batteries.

    I like the idea of no driving at night Bill, not sure about the tunnel part yet...
    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • RCinFLARCinFLA Solar Expert Posts: 1,460 ✭✭✭✭
    Re: Battery less vs. battery based grid tie

    One thing that came to mind....

    Solar Maxima is coming 2011-2012. Some predictions are it will be worse since 1958.

    Demand for power distribution transformers may go up. ;)
  • tallgirltallgirl Solar Expert Posts: 413 ✭✭
    Re: Battery less vs. battery based grid tie
    RCinFLA wrote: »
    One thing that came to mind....

    Solar Maxima is coming 2011-2012. Some predictions are it will be worse since 1958.

    Demand for power distribution transformers may go up. ;)

    Huh? Which predictions, and which way "worse"?

    Besides, the likelihood we reach Solar Max in 2011 or 2012 is close to nil. We still setting records for "boring". This cycle would have to get past the "Yawn" level of excitement first.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Battery less vs. battery based grid tie

    Actually, NASA and NOAA are predicting the peak of Cycle 24 in May 2013. It's not supposed to be a particularly high peak, but they think there is a good chance of a few pretty big flares.

    http://www.swpc.noaa.gov/SolarCycle/SC24/index.html
Sign In or Register to comment.