Generator and Windy Boy

David and Laura

Due to several issues (detailed further down in this post), it is somewhat difficult for us to to directly connect a generator to the SMA-based system that we're building. However, we think we have found an good option, as described below.

Generator Use

We are designing our system so that the generator will only be used as a second-last resort to avoid low-SOC damage to the battery bank. (The last resort would be to ask a friend to bring over a portable generator)

Being pragmatic, we also suspect the generator will end up being used a few times during the fall and spring when we have weeks upon end of no sun, and thus will make a conscious choice that our need for electricity outweighs our ecological desire not to consume any fossil fuels. (We'll see how we do here)

We're installing a 1000 amp-hour battery bank. Our existing generator (an SDMO ALIZE 8000 SDE) is rated 8KW, but we've found that when run with a continuous load, it is best run it at 5KW (this works out to 20 amps of current at 240 volts).

Charging the battery bank from a 50% SOC to 100% SOC would take approximately 500 amps-hours * 48 volts, or 24000 watts-hours of power (assuming 100% efficiency). Derating it down to 30,000 watts-hours of power is more realistic, which means that we would have to run the generator for six hours. (assuming our calculations are correct)

AC Coupling

In an SMA system, a generator is typically connected to the AC inputs of the Sunny Island. However, the generator MUST match the phase configuration of the Sunny Islands, and SMA systems are very touchy with respect to which generators they work with. Other folks we know have not had much success in this area. Another problem is that dirty generator power is supplied directly to the loads, which is unacceptable to us.

(As an aside, we've lived in many places where there is extremely poor power quality, and we've observed very high mortality rates of electrical and electronic equipment when it is subject to frequent spikes, surges, dips and outages. Ever since 1995, we've run all of our electronic equipment through a double-conversion UPS — neighbouring businesses typically had to replace their equipment each year, and we've never had a major equipment failure yet. Power quality saves money!)

Ideally, we'd like to be able to connect the generator much like how another solar array or wind turbine is connected, via AC-Coupling. That way, all the regulation is done by the SMA equipment.

Doing some research, it appears that this is actually a supported configuration. Quoting from the Windy Boy manual, "Furthermore, the Windy Boy can be used as inverter for power conversion based on permanent magnet generators (hydro power systems, combined heat and power plants, diesel generator, etc.). The manufacturer of the wind turbine system or generator should have his system set up for operation with the Windy Boy (also see the Windy Boy planning guidelines in the download area of www.SMA.de/en)."

Here's a slide from SMA illustrating the concept:

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What appears to happen is that the AC from the generator is fed through a high-voltage rectifier to generate DC, which is fed into the Windy Boy. It's pretty straightforward from a theoretical standpoint, though you do need current limiting, like what is done with a EV charger. This can be accomplished by adjusting the load curve in the Windy Boy, or with an external AC -> DC converter.

Based on this, the most basic configuration would be:

AC Generator -> 30 amp Breaker -> DC Rectifier -> 30 amp DC Breaker -> Windy Boy -> AC Load Centre

Using the SMA Windy Boy protection box is an option, but it is designed for a three-phase AC input.

I've done some research on the web, and it appears that while uncommon, a number of people have set up this sort of configuration.

Has anyone on this board set up or heard of a similar configuration?

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westbranch

Re: Generator and Windy Boy

Hi David, first you do not want to gen charge to 100%, far better to go to ~80% each day over the rough patch of no sun.
You also want to try running at at least 50% load for best economy to power generated.

hth

NorthGuy

Re: Generator and Windy Boy

David & Laura wrote: »

Charging the battery bank from a 50% SOC to 100% SOC would take approximately 500 amps * 48 volts, or 24000 watts of power (assuming 100% efficiency). Derating it down to 30,000 watts of power is more realistic, which means that we would have to run the generator for six hours. (assuming our calculations are correct)

As it gets closer to 100% SOC batteries will take less and less current, so it would take much longer than 6 hours to put 30kW in, and also will be progressively unefficient towards the end. It is probably better to stop at 85-90%.

David & Laura wrote: »

Has anyone on this board set up or heard of a similar configuration?

I thought about similar setup because I wasn't satisfied with the way my Inverter (Xantrex) shares charging with house loads. For myself, I concluded that buying a separate AC based battery charger designated to generator would be a better solution.

David and Laura

Re: Generator and Windy Boy

Re #2 - That's good to know. Given our generator size, that would entail adjusting the design charging load from 5 KW down to 4 KW for our 8 KW generator.

Does daily charging to 80% over an extended period of time (weeks) result in additional wear on the batteries?

Re #3 - It sounds like it would be a good idea to monitor the current from the generator. The Windy Boy will report this via RS485, which would provide an easy way to let us know when it's time to turn off the generator.

In a Sunny Island system, the current from the generator (through the Windy Boy) would first be used to supply loads, and only what remained would be used to charge the batteries.

A direct Generator -> Charger -> Battery bank is another option, but we would need to isolate the batteries during charging, since it looks like another charger would confuse the Sunny Islands.

stephendv

Re: Generator and Windy Boy

There could be some complications and quite a lot of additional expense going that route with a windy boy. Firstly, you'd need to spend thousands of $ on a 5kW windy boy and it seems that those models have an input voltage range from 246V to 600V, so you'd first need to transform your gen output and then rectify it. If it's a single phase gen, a simple rectifier might not be enough because the DC output might not be smooth enough.

That seems like quite a beefy generator, have you checked its output in terms of frequency and voltage? I'd be surprised if it's as dirty as you think it is. A lot of large off-grid systems run directly off generator power without any issues. My small honda (non-inverter type) with AVR handles 90% load with only a 2Hz drop in frequency and is 5V below the nominal 230V it's supposed to be. More than good enough for all electronics on the house.

BB.

Re: Generator and Windy Boy

David and Laura,

I updated your post from Amp to Amp*Hours and Watt*Hours (I think I understood what you where asking). Amps and Watts are a "rate" (like miles per hour). Amp*Hours and Watt*Hours are "amounts" (like total miles driven = Miles per hour * Hours of driving time).

And I don't think you really want to use a Rectifier on a single phase 120/240 VAC alternator (regulated output) into a Windyboy (or similar) hardware.

However, you can do a three phase alternator+rectifier or pure DC generator into (possibly) a Windyboy or other MPPT type hardware designed for the task.

I believe that is exactly what Chris Olson is doing. He makes his own alternators for his wind turbines--In this case, a 3 phase alternator + rectifier feeding a Midnite Classic MPPT charge controller (probably configured for a "wind type" power source).

This allows him to "optimize" the I*V curve for the Alternator+rectifier to the battery bank's voltage. Note that his design is a standard PMA (permanent magnet) alternator and is not "regulated" for output (other than RPM).

At the moment, I cannot find the thread where Chris is doing this.

-Bill

David and Laura

Re: Generator and Windy Boy

Bill: Thank you for your corrections.

A couple of updates:

We were able to get more detailed information on our generator. It's actually rated at 6 KW for sustained operation, so sizing everything for a 3 - 4 kW DC load sounds about right.

We also received confirmation from SMA that this is indeed a supported configuration.

Now, the trick seems to be finding a DC rectifier/power supply that is cUL or CSA approved... There's a number of them out there, but most of them are either being used for EV charging and are not listed, or are extremely expensive. I guess there isn't much of a market for this sort of power supply —*quite annoying given that almost every VFD has one inside it...

gww1

Re: Generator and Windy Boy

Not the thread that bill was mentioning but does exsplain the controller part.

http://www.fieldlines.com/index.php/topic,147227.0.html

gww

David and Laura

Re: Generator and Windy Boy

So, it turns out that the SMA Windy Boy Protection Box is _not_ UL rated, so that's out.

There's a couple of DC regulator devices that we've identified that are CSA/cUL rated, including one from Alpha:

http://www.alpha.com/products/industrial-power/item/spectra-single-phase?category_id=137

No word back from them on pricing yet.

Alternatively, we've found a few CSA/cUL rated 600 volt 1500 watt DC power supplies on eBay, so that's always an option too.