Generators and PV

[Dennis Alwon]

A local contractor called me, which was a mistake as I don't know PV, and asked what he should do with this job he has. The owner has a manual generator and when he turns it on the solar people told him he needed to cut off the solar breaker so as to not backfeed the inverter. Is this true? If so what is the basic setup if you have an automatic generator. Apparently the homeowner wants a permanent setup.

 

[winnie]

The problem is not back feeding the inverter, but rather the inverter trying to feed the generator.

The inverter thinks the generator is the grid, and the generator is not capable of absorbing PV production.

Generally you want some sort of automatic way for the transfer switch to trip the PV out, or you want a system with local energy storage which will automatically turn the generator on if the batteries get too depleted.

In theory an inverter could be designed to guarantee playing nice with a generator, or a generator could be designed with a 'dump load' to be able to absorb power as necessary. I don't think such systems are available in practice.

Jon

 

[Dennis Alwon]

So is there a way to have the ats control the solar by installing a contactor on the solar power. Normally the power company energy goes straight thru to the solar allowing it to function but when the power company power drops out can the ATS also shut down the contactor with some low voltage.

I really don't deal with generators or ATS so I am not familiar with what mechanisms are inside that box.

 

[Steve16]

The simplest way is to have the solar connected via a line side tap with a fusible disconnect. This way the utility and solar are both isolated when he turns off the main and pivots the interlock.

The complicated part is if the homeowner doesn't own the solar. The solar company will likely have something in their contract where they have to do the work to change the solar interconnection

 

[tortuga]

There are a ton of 'sunny boy' inverter systems around here they were popular over the last 15 years.
I am no expert but the coolist thing I have worked on is a 'sunny island' its a special inverter you add to the existing system along with a small battery bank that allows both systems to run at the same time. I was not on the sales end but it seemed like the cost was not that bad.

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[jaggedben]

While I'd prefer the solar be connected on the line side of the ats, a contactor is another way to do it. However I don't see the point of the contactor unless the solar is connected somewhere far away (e.g. subpanel).

 

[tortuga]

If I spent the $$$$$ on solar and then $$$$ on a generator, i'd spend a little more for a battery to have them play together.

 

[jaggedben]

If I spent the $$$$$ on solar and then $$$$ on a generator, i'd spend a little more for a battery to have them play together.

It doesn't really work like that, certainly not for everyone.
Most people expect to get payback on the solar and get -$$$ to -$$$$$ over its lifetime. Also the upfront solar cost to elimate a bill can vary from $$$ to $$$$$$, where as the generator cost (with ATS) doesn't vary as much, probably minimum $$$$. Batteries as also in the minimum of $$$$ range, but quickly go higher. Meanwhile a portable generator with manual interlock can cost only $$ so if the customer saves only $$$ over 25 years by going solar they still have a net negative cost. But if at best solar usually saves $$$$ over it's life then it can pay for a generator or batteries, but not both. Only people with $$$$$$$$$$ can really just pay for it all.

 

[electrofelon]

A local contractor called me, which was a mistake as I don't know PV, and asked what he should do with this job he has. The owner has a manual generator and when he turns it on the solar people told him he needed to cut off the solar breaker so as to not backfeed the inverter. Is this true? If so what is the basic setup if you have an automatic generator. Apparently the homeowner wants a permanent setup.

Dennis, so in the OP you said "manual generator" but then ATS got thrown around. Which is it?

In practice, I doubt an inverter would qualify one of those cheap portable generators as an acceptable power source, and even if it did for a time I suspect it would trip out if inverter output exceeded load before anything got damaged.....but I know, "it probably will be ok" isn't a very professional answer to give a client.

 

[PWDickerson]

If he is going to convert the MTS to an ATS, he should move the solar interconnection to a point that is on the line side of the generator switch. If that is very difficult/expensive to do, look into installing a contactor to open the solar circuit when the ATS flops.

 

[analog8484]

Is there any special requirements for such contactors? Would typical HVAC contactors be adequate?

 

[GoldDigger]

There are a ton of 'sunny boy' inverter systems around here they were popular over the last 15 years.
I am no expert but the coolist thing I have worked on is a 'sunny island' its a special inverter you add to the existing system along with a small battery bank that allows both systems to run at the same time. I was not on the sales end but it seemed like the cost was not that bad.

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www.sma-america.com

Yes, the Sunny Island, like some single box "hybrid" inverters popular at the same time, included a transfer switch and a current monitoring interface. The Sunny Island only interoperated with the Sunny Boy grid interactive inverters, which had two special features.
1. They could be configured to loosen up the qualifying criterea for the "grid" source and
2. They could controlably throttle back their output in response to a change in frequency from the Sunny Island.

 

[jaggedben]

Is there any special requirements for such contactors? Would typical HVAC contactors be adequate?

No, and yes. On the AC output of the solar of course.

 

[Dennis Alwon]

Dennis, so in the OP you said "manual generator" but then ATS got thrown around. Which is it?

In practice, I doubt an inverter would qualify one of those cheap portable generators as an acceptable power source, and even if it did for a time I suspect it would trip out if inverter output exceeded load before anything got damaged.....but I know, "it probably will be ok" isn't a very professional answer to give a client.

The man has a manual Transfer switch now and he manually has to turn off the solar but now he wants an ATS. Obviously there needs to be a way to shut down the solar.

If he is going to convert the MTS to an ATS, he should move the solar interconnection to a point that is on the line side of the generator switch. If that is very difficult/expensive to do, look into installing a contactor to open the solar circuit when the ATS flops.

I haven't seen the job but that was a thought another friend and I had thought about. The contactor may be the easiest but I am not sure what voltage coil is needed for the transfer switch.

 

[rainwater01]

The man has a manual Transfer switch now and he manually has to turn off the solar but now he wants an ATS. Obviously there needs to be a way to shut down the solar.



I haven't seen the job but that was a thought another friend and I had thought about. The contactor may be the easiest but I am not sure what voltage coil is needed for the transfer switch.

I installed a generator on a grid tied system once. The Generac ats comes with an unused micro switch. I used a 24 volt power supply near the main panel and mounted a box with a contactor in it to break the connection to the solar interconnect breaker. Then just ran a thermostat cable to the micro switch in the generator.

I would prefer to put the solar ahead of the generator too though.


Sent from my iPad using Tapatalk

 

[ggunn]

Yes, the Sunny Island, like some single box "hybrid" inverters popular at the same time, included a transfer switch and a current monitoring interface. The Sunny Island only interoperated with the Sunny Boy grid interactive inverters, which had two special features.
1. They could be configured to loosen up the qualifying criterea for the "grid" source and
2. They could controlably throttle back their output in response to a change in frequency from the Sunny Island.

With the caveat that I haven't worked with a Sunny Island in several years, another issue is that the Sunny Island is a 120V system, so for a 240/120V service you would need two of them.

 

[Dennis Alwon]

Thanks for the input. It was pretty much what I imagined except I didn't understand why you couldn't back feed the inverter with the generator. Winnie straightened that out in post #2.