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Thread: Grid tie with Export Wind/Solar with Growth

  1. #1
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    Smile Grid tie with Export Wind/Solar with Growth

    Grid tie with export of excess, 240vac single phase: I am starting out with 1 each 500 watt rated wind turbine (24vac rectified to 24vdc). At 50 mph the wind turbine has been documented to produce 45 amps so we have to take care of this situation also. I am planning on adding 3 more of the wind turbines and Solar panels up to maximum of 4000 watts combined output of wind and solar as finances permit. I also have to take into consideration when the charge controller offloads the wind turbine what to do with the power generated to not overspeed the wind turbines if the utility grid fails (which would probably happen in high wind situations). What charge controller, 240vac single phase grid tie inverter, battery combination, monitor equipment, etc do you suggest as not to waste initial investment and use the same equipment later with the completed larger system. Would it be better to put a transformer after the wind turbines to boost the output from 24vdc to 48vdc so 48vdc solar panels can be used? Is 48vdc that much better than a 24vdc system? Can the system also serve dual purpose and be used to generate stand alone off grid if the grid fails for an extended period of time like after a Hurricane with the same inverter? Is it better to use 2 smaller inverters and tie inverter outputs together? Is there a way to limit the export if required to keep batteries charged? My day loads are normally 4800 watts (I have seen 12,000 watt peak) and night 1,700 watts. I have been monitoring utility power usage with a TED (The Energy Detective) unit. I also have a portable generator (120vac or 240vac outputs) that can be used to charge the batteries with the right charger if required during outages.

  2. #2
    Join Date
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    Default Re: Grid tie with Export Wind/Solar with Growth

    mnittler, welcome aboard!

    Working your questions backwards...

    How much power do you use? There is peak power:

    1,500 watt heater uses 1,500 watts peak

    There is how much power you use:

    1,500 watt heater * 8 hours per day = 12,000 Watt*Hours per day

    And there is how much you are billed for by the power company (and appears on your TED).

    12,000 Watt*Hours = 12 kWH (kilo-Watt*Hours)

    If you pay $0.10 per kWhr--then:

    12 kWH * $0.10 per kWH = $1.20 per day

    When you talk about your power (4,800 Watts, 12,000 Watts peak, etc.)--So, I don't know if you are using:

    4,800 watts * 10 hour = 48,000 Watt*Hours = 48 kWH per day

    Or if you really mean:

    4,800 Watt*Hours = 4.8 kWH per day... Big difference!

    Now, working on what you need your system to do... Just as an FYI--building small Grid Tied systems usually not very cost effective. Can be done, but the smaller hardware is not cheap (pricing based on a $$$/Watt basis); plus adding design, permitting, labor, inspection costs are about the same for a small or a large system (by the time you get the people to your home for the install).

    You are typing about a 500 watt wind turbine and (seemingly) typing about a 4,800 watt load (may be 4.8 kWH per day--not sure).

    To the details. SMA makes a 700 Watt "WindyBoy" GT inverter for wind turbines. May be difficult to get. You would have to compare the Wind Turbine specifications to those of the WindyBoy to make sure that everything works together.

    Now, Grid Tied Inverters do not work if the Grid fails. GT Systems are the cheapest, most power, least maintenance for the $$$ spent.

    If, however, you do have lots of power outages or need backup power for specific reasons--A hybrid Solar RE system is a good choice (hybrid can do GT when grid is up, and off-grid when the grid is down).

    A GT inverter can be sized to the energy capability of the source (there are solar PV GT inverters that are as small as 200 watts each). But for hybrid/off-grid application, your inverter needs to be sized to the load.

    In your case, you talked about a 4kW hybrid/GT/off-grid system... And asked about what battery bank voltage you should use... For systems that large, you need a 24 VDC, or even better, a 48 VDC system. Low battery bank voltage + large inverter makes for very large DC current required from the battery bank (lots of large diameter copper wire, large fuses, large switches/breakers, etc.).

    Remembering the equation Power=Voltage*Current. Use 4x the voltage, the current is only 1/4 the amount needed (48 volt vs 12 volt system).

    Now--with Wind Turbines, for many of them, their output falls dramatically as the battery bank voltage goes up. So--you have to check the turbine's specifications.

    Midnite Solar is making an MPPT Charge Controller (wind turbine to battery bank) that may do a much better job at matching WT to Battery bank than anything else out there --- should be available sometime "in the near future" (end of the year?).

    Anyway, if you are looking at a 120/240 VAC Hybrid Inverter system in the 4-6kW range--Take a look at the Xantrex XW system (hybrid inverter, solar charge controller, wiring box, generator controller, etc.).

    If you are "cash poor" and looking for emergency power, then start with the Inverter + battery bank, and a 240 VAC backup genset. Add solar panels and wind turbine(s) as finances allow.

    Just a warning--Wind Turbines are not my favorite form of energy generation (personal opinion)... Typically they produce much less power than promised, require more maintenance than claimed, and few people live in areas with sufficient wind for them to generate reliable power).

    Lastly, and what should be first, is to work on conservation at your home first... It is almost always a better investment for your to replace your old power hungry devices, add insulation, double pane windows, CFL lighting, turning off unneeded items first--before you spend your first dollar on Wind/Solar/RE power generation.

    But--you probably know this last part -- You already have TED. Good job.

    You have brought up a lot of issues/questions--And each deserves its own thread for full discussion.

    Let us know where you would like this discussion to head next.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  3. #3
    Join Date
    Sep 2009
    Location
    South Texas
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    Smile Re: Grid tie with Export Wind/Solar with Growth

    The 4.8kw/hr was a daytime afternoon average usage per hour. The grid tie will take care of the short term overages that go to 8 and 12kw/hr. Eventually I was planning on adding 4 wind turbines (4 each * 500) = 2000 watts, I figure realistically 2kw/hr rating divided by 2 = 1000 kw from wind turbines when the wind is blowing decent. I live on the edge of a lake with the wind coming off the lake. I have not been able to find the WindyBoy GT anywhere and unless I am reading it wrong the input voltage to WindyBoy is in the 100ís DC (I have 24vdc) Well actually, I have found the Windyboy listed a few places but the web sites have not let me put it in the cart so I just felt that something was up for it to be consistent across the board. Is it possible/practical to bump the 24vdc wind turbine output up to 48vdc with transformer? I have already changed lights to CFL, Insulated inside of attic roof rafters with Icynene, Changed sliding glass door to double insulated French door, installed high eff 16 and 19 seer air conditioners, and installed TED monitoring device. Do you know of a passive solar hot water heater and where to purchase for diy (it usually does not freeze where I am)? We do have a lot of sun so Solar as the primary might be the way to go, I was just thinking of a mix of both since the sun does not shine at night but sometimes the wind does blow at night. Do you know of any other grid tie inverters that do not require battery bank?

  4. #4
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    Default Re: Grid tie with Export Wind/Solar with Growth

    I will try and address your points--be aware, many of the answers are for "typical" installations/usage. They may or may not be what is best for you. But, but because of the complexity of the discussion--I am going to keep it simple for now:

    Quote Originally Posted by mnittler View Post
    The 4.8kw/hr was a daytime afternoon average usage per hour. The grid tie will take care of the short term overages that go to 8 and 12kw/hr.
    kWatts (and Watts) are already a "Rate" (like miles per hour). So, 4.8 kWatts for 10 hours would be 4.8kW*10Hours=48kWH usage (for 10 hours).

    You have not said what your monthly energy usage is--but it sounds like you are in the 2,000-4,000 kWhrs per month range (SWAG) with much of your power being A/C. If you have electric heat/hot water/cooking--there may be alternatives that are more cost effective.

    Just as a simple comparison--you may be paying $0.10 per kWhr for electricity. A 3kW or larger solar Grid Tied system may cost you around $0.15-$0.30 per kWhrs or so (assuming 20 year life). A full off-grid system may cost you $1-$2+ per kWhr (hybrid system somewhere around $0.30-$0.50 per kWhr (batteries and extra losses/hardware add quite a bit to the costs). State and Federal tax credits will affect the costs (numbers are very rough estimates to guide the discussion--actual numbers may be different).
    Eventually I was planning on adding 4 wind turbines (4 each * 500) = 2000 watts, I figure realistically 2kw/hr rating divided by 2 = 1000 kw from wind turbines when the wind is blowing decent. I live on the edge of a lake with the wind coming off the lake.
    I am not a fan of small wind--most wind installations do not generate anywhere near 50% of name plate rating... Many generate will under 10% or even down to 3% of nameplate rating.

    If you live in an area with very high average winds (10-12 MPH or greater) and mount on 60'+ tall towers--you may get useful amounts of energy.

    Turbines require large swept area (large diameter blades) to gather power. For example, one of the more efficient "home sized" wind systems has 3.7 meter diameter blades (12'+). It is rated around 1.8kW and will generate, very roughly, around 100-600 kWhrs per month (when it works).
    I have not been able to find the WindyBoy GT anywhere and unless I am reading it wrong the input voltage to WindyBoy is in the 100ís DC (I have 24vdc) Well actually, I have found the Windyboy listed a few places but the web sites have not let me put it in the cart so I just felt that something was up for it to be consistent across the board.
    Yes--I have heard that it is not easy to get one.
    Is it possible/practical to bump the 24vdc wind turbine output up to 48vdc with transformer?
    Typical alternator has three phases--so you would need several transformers to up the voltage... Probably not practical--but I would ask at www.otherpower.com and see what they suggest.

    GT Inverters for wind--you probably need to pick an inverter first, then find which turbines will work with it.
    I have already changed lights to CFL, Insulated inside of attic roof rafters with Icynene, Changed sliding glass door to double insulated French door, installed high eff 16 and 19 seer air conditioners, and installed TED monitoring device.
    Sounds like you have really been working at energy conservation.

    Anything you can do to further reduce the electric load (like shedding electric hot water, electric cook top, electric heat, using laptop computers instead of desktop machines, etc.) will help a lot in reducing your electric loads and having a cost effective grid tie / hybrid / off-grid system.
    Do you know of a passive solar hot water heater and where to purchase for diy (it usually does not freeze where I am)?
    www.solarroofs.com has been used by a poster here (Solar Guppy) in years past--and he was very happy with there product.
    We do have a lot of sun so Solar as the primary might be the way to go, I was just thinking of a mix of both since the sun does not shine at night but sometimes the wind does blow at night.
    For 99.9% of the people out there --- my personal recommendation (plus a $1.50 will buy you a cup of coffee):

    1. Conservation (and shifting optional electric loads to alternative heat sources--if practical).
    2. More of #1 (running joke here)
    3. Solar Thermal (hot water, hot air, etc.)--Solar hot water is cost effective--but can be a plumbing hobby for maintenance.
    4. Solar PV panels with Grid Tie Inverter (cheap, efficient, no backup power)
    5. Solar PV panels with Hybrid Inverter (not cheap, is efficient, backup power)
    6. Solar PV panels with off-grid power (expensive, not very efficient, 24 hour power)
    7. Wind Turbine plus battery bank (may be off-grid or hybrid inverter)
    8. Wind Turbine wth GT Inverter (no battery). Big questions if this is a good fit with most of the GT Inverters for wind system.

    Do you know of any other grid tie inverters that do not require battery bank?
    Not for Wind... Sorry (I am not in the solar industry--just reading around here and other places).

    I am working on a FAQ for the beginners forum... It is not formatted yet--but you may see some answers/help for many of your questions:

    Working Thread for Solar Beginner Post/FAQ

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  5. #5
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    Default Re: Grid tie with Export Wind/Solar with Growth

    Quote Originally Posted by mnittler View Post
    I am starting out with 1 each 500 watt rated wind turbine (24vac rectified to 24vdc). At 50 mph the wind turbine has been documented to produce 45 amps.
    So 500 watts at 50mph ... sounds like a airx type wind generator... figure about 50-75 watts in a stiff wind ( 20 mph ) or more like 5-10 watts as I have seen them in action on a sail boat that had a pair of them.

  6. #6

    Default Re: Grid tie with Export Wind/Solar with Growth

    Does anyone want to live anywhere the wind blows steadily enough at 50 mph to produce any significant amount of kilowatts?
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  7. #7
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    Default Re: Grid tie with Export Wind/Solar with Growth

    I was planning on starting with 1 each TLG-500 wind turbine, 5' blades, 50 lbs, (grow to 4 each turbines with solar added): TLG-500 is 12vac or 24vac 3 phase output to be able to use smaller wire with supplied rectifier to be installed in front of charge controller to 12vdc or 24vdc. Real world sustained test (not instantaneous) @13.1vdc 5mph=1 amp, 7mph=2amp, 9mph=3amp, 11mph=4amp, 12mph=5amp, 13mph=6amp, 15mph=7.5amp, 16mph=8amp, 25amp=23amp, 30mph=37amp. Shunt brake @ 50mph, self furling design above 50mph. If not self furling then puts out 100amp at 100mph but would burn up after 2 hours thus self furling blades designed in. Mfg said to add 1.5mph to each value for same amps at 24vdc. My normal wind speed is 11-16mph. August and September has been almost wind dead this year. Is it better to use large grid tie inverter or several smaller grid tie ones? Can export be limited and still be grid tied? At this point I would not have to worry about export because usage is above possible production so extra has to be made up by grid.

  8. #8
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    Default Re: Grid tie with Export Wind/Solar with Growth

    I don't know much about the TLG--You should call/talk directly with NAWS (or the retailer/installer where you will be purchasing them from). The little customer feedback I have read -- seems to show that they really love these turbines.

    Regarding furling--yep, very good to be self furling. Some Mfg. try for just using the "electronic" braking and end up with lots of differing failures (burned up stators, blades flying off, etc.).

    My guess is that you will be most happy using your TLG on 12 volt battery bank if collecting the maximum amount of power into a battery is very important.

    Large or small GT inverters... For solar panels, generally the good pricing is for units starting around 3kW or larger. Smaller GT inverters cost more $$$/Watt (retail price/watt rating).

    The only truly small inverter (200 watt) are the Enphase units. It is an alternative to mount one GT inverter behind each 200 watt solar panel (connected to 240 VAC)--but I would look at the full system costs (Enphase requires extra monitoring hardware for logging and debugging--plus possibly a website subscription).

    My 2 cents--I would be looking a a solar PV array with a rough minimum 3.5 kWatts of solar panels on a 3kWatt GT inverter as a good starting point for pricing/quoting.

    For a true GT Inverter--there is no method of limiting the output other than the amount of sun and solar panels. And there should be no reason for further limitations (assuming your electrical panel and wiring is correctly sized and you are "legal with the utility"). The power company looks like a giant AC battery to your home. You can pump as much or as little as your solar+GT inverter has energy available. And your home's loads will take as much or as little power as they will need. You cannot tell that any of this is happening--except by looking at your power meter(s) as to which way the "power is flowing".

    If you are intent on connecting your wind turbines to export power to the grid--then, as far as I know, your options are pretty limited.

    From NAWS, you can get a Xantrex XW 4024 Hybrid Inverter. 4kWatt inverter + a 24 volt battery bank. You pump power into the 24 volt battery bank using anything you have available (solar panels, wind turbines, etc.). The XW Inverter basically measures the voltage of the battery bank. When the voltage exceeds 26 volts, the GT Inverter starts to draw power from the battery bank and export it to the utility grid. When the battery bank voltage falls back to 26 volts or less, the XW inverter stops sending power to the grid.

    The XW Inverter also has a lot more functions and options (generator control, generator 240 VAC input, off-grid support for utility failure, internal AC battery charger, etc.)....

    There is also a 6kW XW inverter--but it requires a 48 volt battery bank--too much for your TLG wind turbines.

    I still question about how much power you will be expecting from your wind turbines... Even at 16 mph and 12 volts, you are looking at 8 amps:

    P=15 volts * 8 amps = 120 watts

    Assuming your average load you want to offset is 4,800 watts:

    120w/4,800w = 1/400

    You would need 400 TLG's in a 16 MPH wind to "break even" on a 12 volt system... Even 4 of them would equal ~1% of your total load.

    What is your monthly kWH bill? I am not understanding your power generation philosophy. You seem to be asking about pretty small systems but have a very large energy consumption.

    For example, assuming you are near Brownsville Texas, using the PV Watts website (all defaults) and 10 kWatts of solar panels, it will generate about 1,200 kWhrs per month (during the summer).

    A 10kW system professionally installed solar GT Inverter might cost around $70-$80,000, with 30% knocked off by a federal tax credit (just a rough guess--I am not in the solar RE business and I do not know anything about your particular installation).

    If you want a "hybrid" system to handle power from your wind turbines and emergency power (grid fail)--you might add another $30-$40,000 to the above price (batteries, charge controllers, hybrid inverter, etc.... Just a really rough guess).

    Solar RE power is not cheap.

    -Bill

    PS: Don't let my guesses at your system cost drive you towards any decision.. They are just really rough guesses to get you an order of magnitude price of the systems you are looking at and help you understand how costs and functions are related.
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

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