Control Gurus Advice needed.

[Garry]

What is needed to connect a wind generator to a

solar powered grid-tie inverter? SMA who

manufactures SunnyBoy inverters has modified

their inverters software to run more efficiently

with a given wind generator. If one limits the

open circuit voltage of the genny to a value

acceptable by the inverter and is not to

interested in the highest efficiency, what else

would be required. Please be gentle with your

explanations. I studied industrial control

electronics in the very early seventies and

never used the info since.

Thanks

Garry

[Opera House]

If you have a constant source of wind, all you need is a shunt regulator with a good size capacitor bank.  The problem I see is what kind of load doesn't care if the power is there or not?  If you are just heating water you don't need a regulator.  Other devices need to be protected from low voltage.  The shunt regulator would also need to be shunting the same current as the load would be prior to turning on the load.  You may be generating the desired voltage but once the load is applied the mill would stop.

You question really can't be answered till you specify what your load is.  This question doesn't come up because a battery is far cheaper than the regulator solution.

[Garry]

My load is the inverter dumping into the power grid. The grid tied solar inverter warns specifically against connecting to batteries.

Garry

[wdyasq]

http://www.homepower.com/files/GS_9.pdf

Personally, I'm not a fan of grid tie.

Ron

[Garry]

Thanks for the info. My utility supports grid-tie and I currently am dumping 24 63 watt panels into the grid daily. My problem is a .8kw genny that I need to tie into this system. I am finishing up a 10kw genny that will be grid tied also.

Garry

[Chiron]

Have you contacted the manufacturer?

Looks like these units can use anything from 139 to 400 VDC input and self regulates the load. Can your wind unit put out that kind of voltage? 150VDC minimum for grid tie. Probably rectify the output and feed the inverter with it maybe with a cap bank in paralel with the input.

I don't know about the SunnyBoy inverters but the large Trace/Xantrex units take the output from the generator, rectify it and dump it into a capacitor bank then the inverter takes power from the caps and puts it on the grid.

On an straight induction generator turbine the inverter keeps the voltage on the cap bank at a constant value. The inverter pulls just enough power from the cap bank to keep the voltage on the caps constant so they don't overcharge and the inverter operates at it's best efficiency.

From what I could find the SunnyBoy works pretty much the same but without schematics and a good service or instalation manual I can't tell for sure.

Ah ain't no GooRoo, Ah works fer a livin'

[Garry]

I just mentioned the SunnyBoy because they have already done this. They will not discuss this unless one is a genny manufacturer. The unit I am using for the solar cells currently is the Trace SunTie, see specs below.

Electrical Specifications

  AC Output Voltage (Nominal)   240 VAC

  AC Output Voltage Range   211-264 VAC

  Continuous Power (@ 45 °C)    STXR2500 2500 VA

  Efficiency (Peak)   91%

  AC Output Characteristics   Current Source

  Frequency (Nominal)   60 Hz

  DC Input Voltage (Nominal)   48 VDC, Typically 4 nominal 12 VDC PV modules, in series

  Sunsweep MPPT Voltage Range   44-85 VDC

  Sunsweep MPPT Full Power Output   STXR2500 52-75 VDC

  Absolute Max PV Open Circuit Voltage   120 VDC

  Waveform   Sine Wave, Voltage referenced - current source

  Total Harmonic Distortion   Less than 5% at rated power per IEEE929 and UL 1741 (all models)

  General Specifications

  Operating Temperature Range   -38° F to 113° F (-39° C to 45° C) (A full temperature versus performance curve is available in the manual)

  Enclosure Type   Outdoor, powder coated aluminum enclosure, fully screened, rainproof

      Optional rainshield required for outdoor installation

  Unit Weight   35 lb (16 kg)

  Shipping Weight   40 lb (18 kg)

  Inverter Dimensions (H x W x D)   33 x 13 x 5" (83 x 34 x 13 cm)

  Shipping Dimensions (H x W x D)   38 x 16 x 10" (94 x 39 x 24 cm)

  Mounting   Vertical wall mount only

  Altitude   15,000' (4,572 m)

  Warranty   Five years (applicable to products manufactured after Feb 03)

  Part Numbers   STXR2500 - Sun Tie XR Inverters

      STRS - Rainshield

      STRM - Remote Meter

  Features & Options

  Forced Air Cooling   Standard dual speed DC brushless fan

  Islanding Protection   Standard over/under AC voltage and frequency detection plus active islanding protection

      Meets IEEE 929 and UL 1741 requirements

  User Display   Standard backlit alphanumeric LCD display for system status and daily energy harvest (Wh)

  AC Disconnect   Standard double-pole 15 amp, 240 VAC branch rated circuit breaker

  DC Disconnect   Standard single-pole 100 amp, DC rated circuit breaker

  Remote Monitor   STRM - optional remote display unit for status, resettable Wh meter, tech menu, and daily energy harvest with 50' cable

  Rain Shield   STRS - optional protection rain shield for outdoor installation

  PV Ground Fault Protection System   Standard on STXR1500 and STXR2500

  PV Combiner Board  Standard  STXR2500 with 6 fused inputs, 20 amps maximum per input

  Lightning Arrestor AC/DC Protection   Standard on all models

  Regulatory Approvals

  UL Listed to UL 1741 - 1st Edition

  cUL Listed to CSA 22.2 No. 107.1-95

Thanks

Garry

[Chiron]

Ok Gary, if it's a Trace unit I'm pretty sure they're using the same inverter scheme they use on larger units. I went to the Xantrex site and got the manuals for your unit.

I'd suggest rectifying the output of the gen if it isn't already and putting about 100,000 uF (0.1F) rated at least 100V in paralell with one of the DC inputs. An inverter that was designed for solar probably doesn't like to see much ripple.

One problem I can see is at 800W a 48V gen is going to be pushing the 20A inputs close to thier limit and a gust could blow the fuse. You might get away with bridging 2 of the inputs to handle surge loads that got past the caps. Each input is diode protected so it should share the load pretty evenly.

Another alternative if you have 3 inputs open and a 3 phase gen is to rectify each phase and use one phase per input but you'd need more capacitance to smooth out the DC and 3 times as many of them.

Cheap-n-easy overvoltage protection for your inverter and no load overspeed protection for the gen.

Since your grid tie and the inverter shuts down if you loose the grid use a double throw relay with a 120VAC coil and heavy enough contacts to handle the gen output, hooked into the AC line or just plugged into the wall.

The normaly open contacts would go to the inverter, and the normaly closed contacts would go to a dump load. When you have grid power the gen is connected to the inverter until you loose grid power, then the relay de-energises and keeps your mill loaded so it doesn't go into overspeed.

Just some ideas while I'm finishing my coffee...

[Victor]

The MPPT algorithms for solar and wind are not the same. This is why the SMA Windy Boy has different software/firmware.

 "If one limits the open circuit voltage of the genny to a value acceptable by the inverter and is not to interested in the highest efficiency."

 If the wind turbine without the solar were to be connected to the inverter I would expect the turbine to be overloaded to a deep stall then either stay there with efficiency probibly< 1% or possibly unload up to the voltage limit and then repeat the overloading. In any case I would expect extreemly poor operation, ie it woudn't work.

 If the solar was also connected I would expect the wind turbine to confuse the MPPT of the inverter enough to addversly effect the power production of the solar. Effectivly lowering the efficiency to <0%.

 Then there is also the possibility of a glitch in your voltage limit smoking the whole works.

 I know this post sounds overly pessamistic (my wife accusses me of my pessamism to the point of it being an inside joke) My view is that if you address all of the possible failure modes of a design, then it works. I have a high success rate.

 I could be wrong but I am sure enough about this not working that I would not even try it.

 However it is your dime. I certainly have and do take risks "just to see" and if you are confident in you voltage limit, you would not be risking much more than your time. We would all bennifit from your findings.

 Can you tell us more about your 10 kw machine? Are you planning to grid tie it also?

Best of luck

Victor

[Garry]

Thanks for the ideas. This will give me a starting point. I will try this because I don't see an alternative. The .8kw will give me something to play with and learn from before I smoke a lot of electronics on the big genny.

Thanks again

Garry

[Garry]

Thanks for the warning. There are a couple of pictures taken awhile ago in my files. Just a 36 inch dia. double rotor mounted to a semi-truck wheel riding on a semi-truck axle. Thirty foot dia. three blade rotor on a 65' tower with a dedicated winch to raise and lower the tower. The final stage of the winch was built out of the semi rear axle differential.

Garry

[pyrocasto]

I'm looking into the possablities of grid tie myself. I know alot of people have grid tie gennys, I just havent seen any homebrew gennys, and no specs on them either.

[srnoth]

Just my 2 cents,

The power produced by wind turbines fluctuates a lot more than solar. That's why they make both SunnyBoy and WindyBoy inverters. Why not just go with a separate inverter for each of your systems. A SunnyBoy for your solar, and a WindyBoy for your turbines. Gives you redundance as well.

Stephen.