PV Over Generation

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Tank11

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Hello,

I'm working on the preliminary design of a PV system for a small micro-grid application. The solar array will be in the neighborhood of 400 kW. There are plans for future growth but for now there are existing generators that provide the main power to the micro-grid. Thee client wants to supplement the power generation for now with the PV at a baseline of 50 kW.

Question: How best do we maintain a constant power input of 50 kW without over generating from the PV? If there is no load over 50kW, will the solar array stop producing power?

We're discussing relay protection to open the breaker feeding the system but this would then need to be reset each time it were opened.

Any input is welcomed.

Thank you.
 
A device called a network protection relay will detect reverse power flow in a feeder. What you do with that information is another question. You could use it to selectively shut down inverters or shut down panel strings to reduce their output.
A simpler solution might be to turn on opportunity loads such as water heating to keep the load above your solar output plus generator baseline.
To keep the generators running at a minimum base load, you would have to do the same logic with a wattmeter instantaneous analog or digital output as the control input to your logic.
 
The solar is somewhat secondary to your issue here. What you need is fairly large scale storage, which is an emerging industry. You also need some extremely sophisticated controls.

You probably ought to contract directly with a company that has expertise in the subject and not attempt to engineer this system yourself. JLM Energy would be one such company. I'm sure there are others, but probably not many who have a bona fide product. I have no association with JLM other than having listened to one of their webinars. They market their products as helping with demand management, but I think they could probably help with your client's wishes as well.

It may be possible to cobble together a system on your own with SMA's Sunny Islands or similar products, but that could be a real longshot in terms of feasibility.

If you were not thinking along these lines, then you shouldn't be specifying a 400kW array for 50kW max output.
 
depending on what type of inverters you have you could reduce the output of the inverter via a program/ software change.
 
Tank11 said:
Hello,

I'm working on the preliminary design of a PV system for a small micro-grid application. The solar array will be in the neighborhood of 400 kW. There are plans for future growth but for now there are existing generators that provide the main power to the micro-grid. Thee client wants to supplement the power generation for now with the PV at a baseline of 50 kW.

Question: How best do we maintain a constant power input of 50 kW without over generating from the PV? If there is no load over 50kW, will the solar array stop producing power?

We're discussing relay protection to open the breaker feeding the system but this would then need to be reset each time it were opened.

Any input is welcomed.

Thank you.
Click to expand...
Tank -
Is this connected to Utility power as well, or is it islanded (generators and PV - no utility)?

If there is a utility connection, is the intent to be able to operate both PV and gen with the utility out? This is about the same as being islanded.

ice
 
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Tank11 said:
Hello,

I'm working on the preliminary design of a PV system for a small micro-grid application. The solar array will be in the neighborhood of 400 kW. There are plans for future growth but for now there are existing generators that provide the main power to the micro-grid. Thee client wants to supplement the power generation for now with the PV at a baseline of 50 kW.

Question: How best do we maintain a constant power input of 50 kW without over generating from the PV? If there is no load over 50kW, will the solar array stop producing power?

We're discussing relay protection to open the breaker feeding the system but this would then need to be reset each time it were opened.

Any input is welcomed.

Thank you.
Click to expand...
You can do it with SMA Sunny Island (battery inverters) and Sunny Boy (PV inverters). You can configure them so that as the batteries approach a 100% state of charge the SI tell the SB to dial back their output until at 100% SOC the SB are shut down completely. The generator resides on the same AC bus as the SI and its battery charger so the production/load balance is monitored by the direction of current in or out of the batteries. It's pretty slick.
 
This idea doesn't sound like a good idea, a generator is less efficient when run at low loads so using PV to lower the load on a generator will not save as much on fuel cost as many think, but then it is kind of free energy so it will save some, just don't expect a big ROI as you might be thinking.

If we ever see DC generators or higher kva inverter out generators that the generator is not dependent to the frequency/RPM that makes most larger generators not very efficient, we will then see more viable systems that can include a generator, when a generators RPM are a function of the load instead of trying to maintain the frequency it will have the ability to throttle down as the load lessens.
 
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Right. That's why you have to have solar plus storage. With energy storage in the system the generator doesn't have to run all of the time.
 
ggunn said:
You can do it with SMA Sunny Island (battery inverters) and Sunny Boy (PV inverters). You can configure them so that as the batteries approach a 100% state of charge the SI tell the SB to dial back their output until at 100% SOC the SB are shut down completely. The generator resides on the same AC bus as the SI and its battery charger so the production/load balance is monitored by the direction of current in or out of the batteries. It's pretty slick.
Click to expand...

Wouldn't a 400kW array be a little beyond the Sunny Island's capabilities? I read that the Multi-cluster box maxes out at 12 inverters.

hurk27 said:
This idea doesn't sound like a good idea, a generator is less efficient when run at low loads so using PV to lower the load on a generator will not save as much on fuel cost as many think ....
Click to expand...

SMA's system allows the generator to be turned off if it's not needed.

I also don't think the OP really told us enough about the micro-grid configuration to know how significant a percentage of the load would be handled by PV.
 
jaggedben said:
Wouldn't a 400kW array be a little beyond the Sunny Island's capabilities? I read that the Multi-cluster box maxes out at 12 inverters.
Click to expand...

I am not an expert on such matters, but I am pretty sure that one can interconnect more than one multi-cluster on the same microgrid.
 
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