Pseudo Grid-Tie

[valterra]

Don't shoot me for my hairbrained idea, if that's what it turns out to be.  Ghurd has been ever-so-patient with me via email, and I wanted to post this idea in my diary, so people can tell me what is wrong in my thinking.

I have 1 wind gen (approx 30-40 watts) and will be putting up another one just like it.  They are both Ameteks motors.  I also have harbor freight's 45 watt solar kit.

So total current system right now is 125 watts on a really good day.  I know that's not too much, but it's a start.  I plan to add much more later, and that brings me to my question.  I don't want to "waste" any of this electricity that I am making.  On windy days, I've been turning on a laptop and small television in my garage, which is a total waste, and then if I leave them on too long, I drain my battery dead.  That's not good either.

What I want to do is have my RE stuff contribute as much as possible to my energy budget.  I've already done the usual stuff - CF lights and all.  We don't use a terrible amount, but obviously more than 125 watts peak.  I want the system to be able to take larger and larger chunks out of my grid dependence as I add more and more pieces.  Make sense?

Basically the way grid-tie works.  The way I related it to Ghurd was on fat days when you are generating a ton of electricity but using little, you are fully living on your RE.  But when you fire up the microwave or vacuum cleaner, you are using the Grid.  

I don't really think I want to do grid-tie what with all the expense of equipment and the hassle of paperwork and fees, etc.  Plus I don't currently think I'll be selling back any time soon.

Is it possible have a "pseudo" grid-tie system, where you "tie into" your own house's power, but you are isolated from the real grid?  Make sense?  If the grid was DC, you could be "dioded off" from the grid.  Your generated power could be hooked up in parallel to your grid source power, and the diodes would prevent voltage from entering the grid (you know, shocking linemen during an outage and all that).

Is it a stupid idea?  Is there something maddingly simple that I am missing?

In conversations with Glenn, we've bounced around the idea of using his circuit to either switch on

[valterra]

oops, ignore that last partial sentence.  :-)

[zeusmorg]

  "If the grid was DC, you could be "dioded off" from the grid.  Your generated power could be hooked up in parallel to your grid source power, and the diodes would prevent voltage from entering the grid (you know, shocking linemen during an outage and all that)."

 Well, unfortunately the grid is not d/c so diodes won't work. The only way to use the electricity would be on dedicated(separate) a/c wiring, or have some sort of switching system to go from grid a/c over to your inverter supplied lines. Unless you truly do use certified grid tied equipment the two have to be isolated at all times and that means totally isolated.. grounds too.

 It would be possible to make the system switch over automatically via battery voltage sensors, and relays however I haven't seen anyone do that yet. Possibly even tap into the low voltage warning circuit in your inverter, if it has one.

[DamonHD]

You might remember what I have done which is switch over some loads from a/c to 12V (RE) automatically when the battery is full and back when the battery is starting to fade.

That removes the load from AC without getting a tie to the AC itself.

http://www.earth.org.uk/low-voltage-drop-out-circuit-design.html

Something like that might work for you too.

And I have added grid-tie PV also, and they play nicely together, ie when my laptop switches over to 12V DC then there's another 20W of my PV generation liberated for export to the grid!

Rgds

Damon

[valterra]

Damon, do you have a modification that would work for 110v (USA)?  And is the circuit itself limited by an amount of current, or is it simply a switch that doesn't care what the actual load is?

[DamonHD]

My circuit is for DC since I have DC loads.

I can't remember if I pointed out this before, by Solar John:

http://solarjohn.blogspot.com/2008/03/carpe-diem.html

So in his case he displaces grid use for 110V AC appliances without grid-tie.

Rgds

Damon

[Tom in NH]

Valterra, How would you feel about a sine wave inverter that runs off storage batteries. The batteries would be charged by a combination of your wind turbines and utility power if it is needed. The inverter would supply power to a number of isolated circuits, that is, they would not be connected to the utility power.

Such a system would be pseudo-grid because grid power would be available to keep your batteries charged during extended periods of no wind.

I have done this myself with my solar panels. You can build such a system yourself with a (powerful) battery charger and a switch to control it (see my blog page that describes such a system: http://altenergy.blog-city.com/gridcharger.htm

Commercial units are also available that do this. Email me off-line if you'd like some prices. -tom

[valterra]

That is interesting, and essentially what I'd like to do eventually.

I had a long conversation with the ever-so-patient GHurd, and he gave me a lot of pointers.  First was that I'm using way too little of a battery.  Before I worry about all this other stuff, I need to be sure to have enough capacity to not cycle the battery every 2 minutes when the wind's not blowing.

Eventually, yeah, I'd like to essentially replace entire circuits in my house with an RE-power, grid-backed-up system.  You know, a UPS but in reverse.  

And of course, I'll run as much stuff as I can directly on 12VDC also.

Thanks for all the information guys!  :-)