Back-up Generator with Solar

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Matt N

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Alameda, CA USA
I'm trying to figure out if there's a way to ((automatically)) transfer a power to a generator when the utility goes down--on a house with solar panels?
 
I think they call that a hybrid system in the code book. I'm positive there is a type of ATS for your application.

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There are invertors for off grid systems. Do you have a battery bank? Do you install solar systems? Unless you do this as a specialty it may be difficult to find what you need.

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There are a few ways to do this. Assuming the existing solar is a standard grid tied system without batteries, then the easiest solution is to connect the solar on the utility side of the transfer switch.

That way the solar will disconnect when the power goes out and not try to reconnect when the generator starts.

If you want to run both the generator and pv during an outage, then it gets more complicated, but possible. Usually not worth it for residential projects, unless they are off-grid or lose power for extended periods. It can make sense for larger commercial projects and microgrids where the PV is less expensive than diesel fuel.

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I thought this is why solar systems have a battery bank? Because why would you need a generator?, unless your in a place without a lot of sun, then again why would you put in a solar system?

Your better off hooking the house up to a bike


“ shoot low boys their riding shetland ponies”
 
BBEE said:
There are a few ways to do this. Assuming the existing solar is a standard grid tied system without batteries, then the easiest solution is to connect the solar on the utility side of the transfer switch.

That way the solar will disconnect when the power goes out and not try to reconnect when the generator starts.

If you want to run both the generator and pv during an outage, then it gets more complicated, but possible. Usually not worth it for residential projects, unless they are off-grid or lose power for extended periods. It can make sense for larger commercial projects and microgrids where the PV is less expensive than diesel fuel.

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Thank you for your response.
Generators haven't been a thing here (Near San Francisco) in CA until the devastating wildfires of the past few years. So even 32-year electricians are having to learn a new tricks. The client is trying to decide between battery backup versus a generator.
What are we talking for the "more complicated" option?
 
Ohms law said:
There are invertors for off grid systems. Do you have a battery bank? Do you install solar systems? Unless you do this as a specialty it may be difficult to find what you need.

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Its a design/build project and many of us here in CA just don't have much experience with natural gas generators. I am not the solar installer...and just trying to serve the clients needs; which may likely be impossible.
 
Matt N said:
Its a design/build project and many of us here in CA just don't have much experience with natural gas generators. I am not the solar installer...and just trying to serve the clients needs; which may likely be impossible.
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I would recommend getting a solar company involved. Most of the time you wont be able to get solar components unless you are a authorized installer per the solar manufacturer i.e (enphase).

In South Dakota we have tons of generator setups all over due to ice storms. In your case a natural gas generator may not be the best if gas utility shuts gas supply off during a forest fire, maybe a portable generator for just essentials. It's hard to say and depending on what the customer is willing to spend.

Are you a authorized generator installer? You may have trouble installing or getting support for future issues if not.

It's really hard to give you a definitive answer. You may need to reach out to solar installer to get options. In South Dakota we have a installer that generally does a 4kw grid tie system for $15,000. They are the only in my area of South Dakota. If you go next door to Minnesota there are many more solar companies as they get more incentives.

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If the solar connects on the load side of the transfer switch then you would need to do a battery system with another inverter for the batteries. Then the solar could be AC coupled to that. The battery inverter would then tell the generator when to start and stop.

Another option to interconnect the solar on the load side of the transfer switch would be to install a contactor on the output of the PV inverter. The coil of the contactor would be powered through an aux contact in the transfer switch, so the contactor would open upon loss of utility power. This would allow the generator to power the backup loads, without the solar coming back online.

A third option is doing sophisticated generator and inverter controls that isn't practical in a residential setting.

You are probably aware of this already, but when the solar is operating it produces however much power is available from the PV panels regardless of the load. So if the generator is operating and the PV is operating the extra power has to go someplace. That could mean the pv inverter will just trip off, the generator will trip off, or more than likely it will damage the generator.

This is why the simplest and cheapest option is just to install the PV on the utility side of the transfer switch.



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Ohms law said:
I would recommend getting a solar company involved. Most of the time you wont be able to get solar components unless you are a authorized installer per the solar manufacturer i.e (enphase).

In South Dakota we have tons of generator setups all over due to ice storms. In your case a natural gas generator may not be the best if gas utility shuts gas supply off during a forest fire, maybe a portable generator for just essentials. It's hard to say and depending on what the customer is willing to spend.

Are you a authorized generator installer? You may have trouble installing or getting support for future issues if not.

It's really hard to give you a definitive answer. You may need to reach out to solar installer to get options. In South Dakota we have a installer that generally does a 4kw grid tie system for $15,000. They are the only in my area of South Dakota. If you go next door to Minnesota there are many more solar companies as they get more incentives.

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Thanks,
I may suggest solar with ample battery back up,only, because there is always plenty of sun during fire season.
 
BBEE said:
If the solar connects on the load side of the transfer switch then you would need to do a battery system with another inverter for the batteries. Then the solar could be AC coupled to that. The battery inverter would then tell the generator when to start and stop.

Another option to interconnect the solar on the load side of the transfer switch would be to install a contactor on the output of the PV inverter. The coil of the contactor would be powered through an aux contact in the transfer switch, so the contactor would open upon loss of utility power. This would allow the generator to power the backup loads, without the solar coming back online.

A third option is doing sophisticated generator and inverter controls that isn't practical in a residential setting.

You are probably aware of this already, but when the solar is operating it produces however much power is available from the PV panels regardless of the load. So if the generator is operating and the PV is operating the extra power has to go someplace. That could mean the pv inverter will just trip off, the generator will trip off, or more than likely it will damage the generator.

This is why the simplest and cheapest option is just to install the PV on the utility side of the transfer switch.



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Thanks for the detailed response. I'm going to suggest that the client do solar with battery backup. This generator part is giving me a headache ;)
 
Solar Power System with Generator Backup with the solar contractor will size your array in the same manner as a grid-tied solar PV system, since the generator has no relevance unless the utility power goes out.
 
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