The Skystream made by Southwest Windpower is a grid tie wind turbine that is designed to produce 240 volts AC at 60HZ (or 50HZ) no matter what speed the wind is blowing.
It does this by taking the wild AC from the alternator, rectifying it to DC and inverting back to AC.
It is quite unique as it is one of the few turbines that is truly plug and play. Simply connect the output of the turbine to a circuit breaker (like you would if you were adding a circuit to your breaker panel) and the turbine will do the rest.
The Skystream synchronizes with the power grid and starts pushing power into it, assuming the wind is blowing.
But what if you are off the grid and would rather charge batteries with your Skystream?
The good news is that it is possible. The better news it that it is easy assuming you have a sine wave inverter or inverters that make 240 volts at 60HZ (or 50HZ) and the inverter(s) output is at least high enough to handle the maximum output of the Skystream (about 2.5kW).
The Skystream needs to have a grid to push power into. Fortunately you have your own mini grid.
All you need to do is back-feed an AC breaker in your power system’s breaker panel, the same as you would in an on grid system. It is called AC coupling and is not very well known. The reason it works, is all the high end inverters (such as Magnum Energy, Outback Power, Xantrex/Schneider) are bidirectional. Normally, the power flows from the batteries through the inverter to the AC breaker panel. It will also flow from the AC breaker panel through the inverter to the batteries. In fact, charging your batteries by sending AC back through the inverter is very efficient.
When the Skystream turbine begins to push power into “your grid” the power will flow:
- To any loads you might be running like a fridge, freezer, lighting or whatever.
- Through your inverters (backwards) and charge the batteries.
The inverters will operate in reverse at the same rating as they operate normally. If you have a 4000 watt inverter, you can send up to 4000 watts back thru the inverter.
Although this method for battery charging works very well, there is one issue.
The batteries can be damaged if they are allowed to overcharge, as when the wind is blowing after the batteries reach a full state of charge.
But won’t the inverter(s) limit the current and act as a charge controller as the batteries reach a full state of charge?
No they will not. Although they have a charge controller built into their battery charging system it has nothing to do with AC coupling.
If you decide to AC couple a Skystream you must protect your batteries from overcharging!
You can protect your batteries by one of the following methods:
- Add a dump load to your system (preferred method)
- Add a circuit to disconnect the turbine when the batteries are full
Using a Dump Load with Skystream Wind Turbine
The best option to protect your batteries is to add a diversion load. If the batteries are full and the Skystream is still generating power, the power will go into the diversion load instead of overcharging the batteries.
Disconnecting the Skystream When the Batteries are Full
The Skystream in a very unique piece of equipment. As we have mentioned it has a built in inverter that connects to the grid automatically. If the turbine is not connected to the grid, a brake is applied. When the Skystream comes out of the box you will notice it is almost impossible to spin the rotor. That is because of the brake.
When grid power is applied, the Skystream will synchronize with the grid and release the brake. This takes about 5 minutes from the time gird power is applied. If the grid goes down for any reason (such as a wind storm, broken power lines)) the brake will be applied immediately to protect the turbine from over-speed. This is what sets the Skystream apart from all other AC wind turbines. The other wind turbines would over speed and be damaged if removed from the grid.
The second method of protecting your batteries from overcharge is by simply opening the circuit between the Skystream and the inverter(s).
This can be as easy as turning off the breaker, however that would not be automated.