Off grid solar with grid as back up power

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CharlieNeedsHelp

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I am building an off grid system that should be enough for our use. I want to use the solar as primary power and then switch to the grid should the batteries get too low and power goes down. I am having trouble finding an automatic transfer switch that will work in this situation. Thank you in advance for sharing your knowledge.
 
We are allowing this for information on where to find an ATS for the OP's situation, please stay away from
"how to" information.
 
If you are not planning to ever export power back to the grid, you might be better off just turning on a battery charger connected to the grid at a certain battery voltage
 
You do not want a transfer switch for this application.

In asking for an automatic transfer switch, you are saying that you want a system which seamlessly starts using utility power when your 'off grid' system isn't up to the task. So you don't really want to be off grid, you want to maximize self consumption, and possibly avoid utility requirements for a full grid tie system.

In this case you want a hybrid inverter (PV and energy storage inverter/ charge controller) which can consume power from the grid, but cannot export to the grid.

Ask your PV supplier for that and I think you will achieve your design intent.

Jon
 
CharlieNeedsHelp said:
I am building an off grid system that should be enough for our use. I want to use the solar as primary power and then switch to the grid should the batteries get too low and power goes down. I am having trouble finding an automatic transfer switch that will work in this situation. Thank you in advance for sharing your knowledge.
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Most inverters for off grid are "inverter/chargers" and will do this automatically. Give it power and it will charge the batteries and transfer loads to the generator or grid supply.
 
CharlieNeedsHelp said:
I am building an off grid system that should be enough for our use. I want to use the solar as primary power and then switch to the grid should the batteries get too low and power goes down. I am having trouble finding an automatic transfer switch that will work in this situation. Thank you in advance for sharing your knowledge.
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You know that this isn't by a long shot the most economical way to provide power to the building, right? Just checking.
 
CharlieNeedsHelp said:
I am building an off grid system that should be enough for our use. I want to use the solar as primary power and then switch to the grid should the batteries get too low and power goes down. I am having trouble finding an automatic transfer switch that will work in this situation. Thank you in advance for sharing your knowledge.
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There are a whole lot of considerations to properly do what you are suggesting. The choice of a transfer switch is far down the list of more important things. You should get with a solar design and installation company that is experienced in battery backup and off-grid solar design
 
winnie said:
You do not want a transfer switch for this application.

In asking for an automatic transfer switch, you are saying that you want a system which seamlessly starts using utility power when your 'off grid' system isn't up to the task. So you don't really want to be off grid, you want to maximize self consumption, and possibly avoid utility requirements for a full grid tie system.

In this case you want a hybrid inverter (PV and energy storage inverter/ charge controller) which can consume power from the grid, but cannot export to the grid.

Ask your PV supplier for that and I think you will achieve your design intent.

Jon
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Thank you Jon for your thoughts. I should have been clearer in my request. I have solar and batteries on an out building (garage). Originally it was just going to supply the garage. Now I have enough to supply the house as well.
I have a 2/0 copper 4 wire feed cable between the garage and the house. All the batteries, inverters, and panels are in/on the garage.
I have not energized the feed to the garage because I am having trouble finding an automatic way of supplying power from the garage, or the grid. I can put an interlock switch, but I want it automatic.

I want to power the house by solar and batteries with the grid as a backup. I can live with the garage being without power should the batteries get too low. I do want to make sure I have grid power to the house should the batteries get low. Thank you to those with the helpful responses.
 
roger said:
We are allowing this for information on where to find an ATS for the OP's situation, please stay away from
"how to" information.
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Thank you. That is what I am looking for. An ATS that is UL approved and switch power without the need to start a generator.
 
They make inverters and equipment with these exact specs without having to reinvent the wheel by using an ATS. It will only use power from the grid as a last resort. Lots of people (think they) want to do this so it is a common feature.

A regular ATS such as common Kohler RDT may also be suitable. Feed utility in the generator side and inverter in the utility side. If the "utility" (inverter) goes away, it will seek the secondary source (utility). When inverter comes back it will return.
 
Birken Vogt said:
They make inverters and equipment with these exact specs without having to reinvent the wheel by using an ATS. It will only use power from the grid as a last resort. Lots of people (think they) want to do this so it is a common feature.
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It is definitely a common inquiry, but I can't say that I completely understand it. When you figure the "all in" cost of electrical energy from a PV system with batteries, it is nearly always much more more than buying kWh from the grid if the grid is already available. I guess I can see the romantic allure of living "off the grid", but if you have a grid connection, even if you are only using it as a safety net, you aren't off grid. If the grid is available and dependable, your economic interests are better served by spending your money on grid tied PV to offset your electricity bill. If you have outages that you want to be able to bridge, you are better served by buying the smallest battery system you would need to accomplish that purpose and only using it when you need it; battery systems are expensive, and they degrade proportionally with the number of discharge/recharge cycles you put them through.

That's my opinion, anyway.
 
ggunn said:
It is definitely a common inquiry, but I can't say that I completely understand it. When you figure the "all in" cost of electrical energy from a PV system with batteries, it is nearly always much more more than buying kWh from the grid if the grid is already available. I guess I can see the romantic allure of living "off the grid", but if you have a grid connection, even if you are only using it as a safety net, you aren't off grid. If the grid is available and dependable, your economic interests are better served by spending your money on grid tied PV to offset your electricity bill. If you have outages that you want to be able to bridge, you are better served by buying the smallest battery system you would need to accomplish that purpose and only using it when you need it; battery systems are expensive, and they degrade proportionally with the number of discharge/recharge cycles you put them through.

That's my opinion, anyway.
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I completely agree, not sure why people want to do this. Perhaps they actually like it as a hobby sort of thing? I might live off grid if I was independently wealthy and didn't have To work
 
The OP has an existing setup with solar and energy storage, at a detached structure.

They want to use their self generated power at the main house.

1) could someone with general and ATS experience suggest an ATS which would work as the OP suggested? EG expanding on what @Birken Vogt suggested in post 10.

2) I still believe that the best choice is some sort of hybrid inverter which can automatically use grid power in addition to self generated power. This has the huge benefit of doing things like adjusting loads to better match self production, and never having a 'transfer' interruption.

Is there any way the OP can use the existing feeder for DC and place a hybrid inverter at the main house, rather than a transfer switch?

Jon
 
electrofelon said:
I Believe on the large scale renewables are the lowest cost, at least up to the point below where storage be ones necessary. On the small scale off grid, which of course requires storage, no.
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This.

Solar power is currently the cheapest available source of electricity, if and only if you use the electricity when the sun is shining.

If you want to use electricity on your own schedule then solar power requires storage, and storage is very expensive.

IMHO the ideal system if you wish to maximize use of PV but still want the grid is to have PV without any energy storage at all, combined with some sort of home energy controller which time shifts loads to use power when the sun is shining. Eg over cooling your home when the sun is shining so you don't need AC after dark, heating the hot water tank, etc.
 
winnie said:
This.

Solar power is currently the cheapest available source of electricity, if and only if you use the electricity when the sun is shining.

If you want to use electricity on your own schedule then solar power requires storage, and storage is very expensive.

IMHO the ideal system if you wish to maximize use of PV but still want the grid is to have PV without any energy storage at all, combined with some sort of home energy controller which time shifts loads to use power when the sun is shining. Eg over cooling your home when the sun is shining so you don't need AC after dark, heating the hot water tank, etc.
Click to expand...

The energy controls (especially labor to design and install, if you are paying someone) are also expensive. A small to medium battery system without backup probably has better payback, at least where kWh costs are higher.
 
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