Want to get it right

[Bart Loefer]

So before I start talking about watts and volts and the like I want to make sure that I have the concept right. I'm wanting to have either a HAWT or a VAWT. I know that either have some inherent advantage and disadvantages on the aesthetic side.

I know that a VAWT is more likely to perform better in a "dirty" air area. Beyond that my knowledge of them is limited at best.

So I'm wanting to put a turbine on a pole and most likely will be a PMA and from that turbine run thru a rectifier and then to a couple of batteries and from the batteries to a GTI. And the reason I'm thinking this is because the MPPT tries to keep up the best it can with the fluctuations from the turbine and feeding it into a bank of batteries and then pulling it out of the bank thru a GTI is a little more "forgiving". Am I correct in assuming this?

Also one other thing that I'm concerned with is over spinning the turbine in stormy weather. What type of braking system do I need in place. From what I've seen on youtube there are 2 approaches: 1. You flip a switch and it connects the wires together and "locks" the turbine in place, is this correct? 2. Run your wires thru a switch which in turn runs them thru resistors which places a load on the turbine and thus slowing it down that way.

Thanks in advance and please feel free to suggest any alternative approach.

[Rob Beckers]

Hi Bart,

Welcome to the forum!

There is no inherent advantage of VAWTs over HAWTs when it comes to turbulent air. Neither one works well with it. Have a look at https://www.solacity.com/small-wind-turbine-truth/ for a general discussion.

When battery-charging from a small wind turbine it's rare to use an MPPT charge controller. In fact the only one I know that can be used that way is the MidNite Solar Classic line of charge controllers. Generally small turbines are simply rectified and from there straight to batteries (with something to keep those batteries from overcharging).

Grid-tie inverters (GTI) are, as a concept, generally used without batteries. They have solar or wind on one side, the grid on the other side. There are off-grid inverters that turn battery power into grid AC, and that can synchronize to the grid and feed back excess energy to the grid, but it's a round-about way that's lossy and expensive if your purpose is to simply feed back to the grid.

That said, there is a severe shortage of GTI for wind turbines. The three manufacturers that used to make those (SMA/ABB/Ginlong) all have stopped production and largely support as well.

Shorting out a PMA to stop a turbine is brutal. It's much like throwing a piece of wood through the spokes of a bicycle wheel while traveling. Not recommended to stop a rotating turbine. It is used to keep a stopped turbine from spinning up. There are a bunch of ways of protect a turbine from high winds: furling (up or sideways), blade pitch control, dump load etc.

Hope this helps!

-RoB-

[Bart Loefer]

Rob,
Appreciate the reply, so a PMA wind turbine would just plug straight into GTI? I would think that you would need something between the turbine and the GTI to somewhat stabilize the amount of energy going thru the GTI. Am I correct in assuming that, or would you just wire it directly into your panel? I feel we may not be on the same train of thought. I appreciate the tutelage though.

[Rob Beckers]

Hi Bart,

The PMA produces (usually) 3-phase AC with varying frequency and Voltage. This goes through a 3-phase bridge rectifier to make DC out of it. Depending on the grid-tie inverter you may need to add some electrolytic capacitors on the DC side to smooth out the DC, but many have enough build-in that make that superfluous. Rectifying 3-phase produces pretty decent DC on its own, and SMA or Power-One/ABB inverters were perfectly happy with that. The GTI then takes care of exporting power to the grid. That's it!

To load up the wind turbine correctly so it spins at the right RPM for maximum power output for each wind speed the GTI has an "MPPT table", that is something you have to load, it will be different for each turbine. It has otuput power vs. Voltage pairs in it, telling the inverter how much output power to produce (Watt) for a given input DC Voltage. When you work your way backward through the equations that works out such that if the table is correct it will make the turbine spin at its optimal TSR for each wind speed.

-RoB-

[Bart Loefer]

Rob,
Once again thank you for the insight, I believe we are thinking along the same lines. However you are the expert here and any and all thoughts on this is greatly appreciated. I guess one last hurdle to get over here would be what do I put in line to prevent overspin on the turbine, or would the load that the GTI introduces be enough to keep the turbine acting as it should?

Thanks and as always have a good one.

[Rob Beckers]

Bart, it is up to you (or the turbine manufacturer) to make sure the turbine doesn't self-destruct when the load falls away. The grid can go down, it take 5 minutes for a grid-tie inverter to start up (a UL1741 requirement), etc. It is entirely possible that there is no load. Relying on the grid to keep a turbine under control would be a very bad idea.

-RoB-

[Bart Loefer]

Rob,
Thanks for the reply, I may have to look into other avenues to keep the turbine "in check" during high winds. If there happens to be anything that i may be overlooking please do feel free to let me know. Thanks once again.