First RE System is Planned

Posted by Eric F on July 07, 2008, 03:15:43 PM

First RE System is Planned
Well, I'm ready to begin working toward my first system.  My plan calls for a 900W windturbine(already available to me, so that's a small savings) and about 1kw of PV. I want to make this joined together into a hybrid system that will be used off-grid. 

First, the wind turbine will be located 375 feet from the battery room.  I anticipate using 48 volt to keep the buried wiring size reasonable from the turbine back to the battery room.

Second, the PV will be located above the battery room on a roof area that is approximately 20 x 20 feet.

Batterys will be 6volt 200ah.  Bank will be 8 in series set up in two parallel banks.

I'm seeking advice about components I will be needing. And, how to set all this up to run power to a distribution panel that will be in my basement about 30 feet horizontally and 8 feet vertically from the inverters.

That's about as far as the plan goes at this point.

I look forward to helpful comments from the forum.   Thanks for putting up with a new member.

Eric

 

Posted by Thomas Allen Schmidt on July 08, 2008, 08:39:56 PM

Re: First RE System is Planned (Reply #1)
Wow! 375 foot, thats a long ways even for 48 volts nominal at only 900 watts. the Alt-E Stores wire sizing calculations would call for nothing less than 3/0 (pronounced three aught) at 3%. 750 foot of 3/0 even at $3.78 per foot would come to $1,475.50 good thing that wind genny is free!
http://wesbellwireandcable.com/THHN/THHN3_0.html
http://howto.altenergystore.com/How-to-Size-Wiring-and-Cabling-for-Your-System/a62/
Check my math though.
900 watts at 48 volts is 18.75 amps
18.75 x 375 = 7031.25
3 x 48 = 144
7031.25 / 144 =  a VDI of 49

Somebody please prove me wrong. Thats just too much!
 

Posted by Eric F on July 09, 2008, 10:02:37 AM

Re: First RE System is Planned (Reply #2)
I have no problem with your math.  However, I'm planning on using #2 AWG wiring for the long run.  I am calculating using about 5% to 10% voltage drop, which isn't uncommon for wind turbines.  Yes, the wiring is expensive.  But to get to the clean air this is where the turbine must go.

If I build my power base (battery room, inverters, etc.) at the tower base, I still need #4AWG to run the 115/120v to the house.  And, I then have to go 125 yards just to check and maintain the equipment.  I am planning on an annex to my garage which will be firewalled and vented.  It will use passive solar and a heat sink to keep the room above 10F here in northern Wisconsin winters.

I am actually more curious to hear what others are using for a charge controller to handle a hybrid system.  And I am still stumped on what PV panels I should be looking at.  I have many other questions that I'm sure will arise as I get further along.

Has anyone had any problems with zoning ordinances in their locale?  How have your worked through those concerns?

I appreciate comments, they really help me think through all this.
 

Posted by Thomas Allen Schmidt on July 13, 2008, 12:03:39 PM

Re: First RE System is Planned (Reply #3)
Sorry Eric if that came across as being facetious. I wanting to have a wind genny but my site is just not suitable enough to make it cost effective.  Among other things, a free standing tower over 100' would have to be constructed. I guess cynicism, prompted by jealousy, came through in my writting.
As for ordinances, the best place to find that out would be your local planning and zoning office. Those type of things can be way different from; state to state, county to county, city to city, town to town, well you get the idea.

If your in a rural agricultural area, you might see silo's. This could give you idea of how high a structure is allowed to be in your vicinity. Geology plays a role. It might be that the ground where you want to plant a tower cannot support or may require additional concrete to support it.
Heights, ground stability, proximity's, restrictions, petitions, permits, etc., etc., these are all the things that your local planning and zoning office will want to address and chances are they may have allready.
Here is an example of something that has been done by the Massachusetts Division of Energy Resources.
http://www.mass.gov/Eoca/docs/doer/renew/model-allow-wind-small.pdf
I can't help but feel that I am telling you a lot of stuff you may already know or have searched and found on the internet... But here it goes anyway. Just in case.
http://www.newfarm.org/features/0604/wind3/index.shtml
http://www.greengold.org/wind/documents/84.htm
http://www.wind-watch.org/news/category/locations/americas/us/wisconsin/

While searching I found several other sites from different states and read through them. My overall impression, for Wisconsin, is that the power companies what to desperately hang on to their monopoly of energy. If this is true, I wouldn't be at all surprised if they (the power companies the want to build megawatt wind farms) are influencing decisions made by law makers concerning small scale privately owned wind genny's in the residential arenas.

As for the PV, take your pick. Apples are Apples. Its of little matter wether its a Delicious Red or a Granny Smith, they are all good to eat. Personally, I perfer the Poly crystalline type. Hot climates may necessitate a higher voltage PV module. The trend would seem to be high voltage and high wattage PV modules and MPPT charge controllers. There seems to be very little information about singular charge controllers that can handle both wind and PV simultaneously unless it comes with a particular wind genny.
 

Posted by Mike Harrison on July 14, 2008, 10:36:23 AM

Re: First RE System is Planned (Reply #4)
Hi Eric,
In checking the NEC 2008 book, Table 8 Conductor Properties. Your suggested #2 wire in copper is .201 ohms/kFT and in Aluminum is .313 ohms/kFT.
The issue here is what is my wattage loss through this long cable run and what is the final voltage drop at the end of the cable run?  Ohms law and basic power formulas will give you these answers.
 
I squared * R = Power loss
and
E = I * R ,  for the voltage drop

Given: max amperage (I = 18.75 A)
    Max voltage (E = 48 vDC)
    Cable Ohms  #2 Copper@ .201 ohms per 1000 feet * 375 FT
                #2 Alu@ .313 ohms per 1000 FT * 375 FT
      Note: This being a closed loop DC circuit I must consider the cable run in both directions thus doubling my ohms total for the cable.
#2 copper ohms  (R = .15075 ohms total)
#2 aluminum ohms (R = .23475 ohms total)

Power Loss
I sq * R = 18.75sq * .15075 = 53 watts on copper
I sq * R = 18.75sq * .23475 = 82 watts on aluminum

Voltage Drop
E = I * R = 18.75 amps * .15075 ohms = 2.8 volts on Copper
E = I * R = 18.75 amps * .23475 ohms = 4.4 volts on Alu

Are these numbers tollerable??? Maybe!
Will your cable run be melting the snow between your wind tower and the garage with 53 watts? NO.
Will your wind mill be usually be outputting its maximum 900 watts and therefore 18.75 amps? No, so these numbers are based on a theoretical maximum which may not be achieved.
Will your batteries fail to fully charge? Yes, Your batteries really want 2.1v per cell ( 12.6 volts for a 6 cell battery). So hopefully the wind mill outputs just over 48 volts and the ocassions when your voltage drop over the wire is above 1 volt it will have little overall effect on your final delivered wattage to the garage.

Now increasing your cable size to 3/0 will give you a maximum voltage drop of 1.12 volts and only 21 watts of power loss.  Better? YES, but at what cost??? Price of #2 copper vs 3/0 copper.
MikeH.


« Last Edit: July 14, 2008, 01:14:21 PM by Mike Harrison »
 
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