I have installed a Fox 8Kwh hybrid inverter with a 20Kw battery cube tied to 8Kwh solar panels to generate and store power to my home. The system is set up on self use as off grid and working well.
I wish to add a generator backup for when the solar generation is insufficient to restore the battery charge sufficiently before nightfall. Inputting the generator feed into the grid line what menu settings are required to ensure there is no backflow from the inverter (feed in) once the batteries attain their designated charge level. Can I just set the feed in power to zero in the setting on-grid menu?
Off grid setup with Generator backup supply
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Dave Foster
- Posts: 1328
- Joined: Thu Oct 13, 2022 7:21 pm
I think the best way to do what you want is to connect the generator to your consumer unit/fuse box on the load side of the main CT meter - then add a second CT clamp from the CT2 input, and clamp it to the generator live feed.
The inverter will see everything the generator produces as external generation (as if it were another solar inverter) - any excess above the house load will be used to charge the batteries automatically no settings required - when the batteries are full the inverter won’t attempt to use the batteries as long as the generator output covers the house load.
Unless you are running totally off-grid i.e. no connection to the any grid - in which case you will be running in EPS mode - the problem then is that anything that you connect to the grid input will force the inverter to switch back from EPS cutting off your off-grid supplies.
In which case you would need to set the EPS circuit so that it is live when the grid is active i.e. you may need to change the setting on bypass relay and turn UPS on - then connect the generator to the grid input.
When the generator starts there will be a small break in EPS power (~50 milli seconds) and then the inverter will run on the generator supply - if you don't want the inverter to try and back feed set your export limit to 0.
The inverter will see everything the generator produces as external generation (as if it were another solar inverter) - any excess above the house load will be used to charge the batteries automatically no settings required - when the batteries are full the inverter won’t attempt to use the batteries as long as the generator output covers the house load.
Unless you are running totally off-grid i.e. no connection to the any grid - in which case you will be running in EPS mode - the problem then is that anything that you connect to the grid input will force the inverter to switch back from EPS cutting off your off-grid supplies.
In which case you would need to set the EPS circuit so that it is live when the grid is active i.e. you may need to change the setting on bypass relay and turn UPS on - then connect the generator to the grid input.
When the generator starts there will be a small break in EPS power (~50 milli seconds) and then the inverter will run on the generator supply - if you don't want the inverter to try and back feed set your export limit to 0.
Thanks Dave for your advice. I have wired up the generator input line on the opposite side to the battery shed consumer unit (which is there to feed mains AC to two the tracker controllers). The working set up today is in EPS off grid with no mains tie in at all and no ability (no cable feed) for mains tie in, so if I understand correctly:
Firing up the generator on the grid input for the inverter would override the solar input. This makes sense as the inverter has power limitations so I can see why that would be a safety feature of this input or that input. If I were to only use generator feed battery top off after dark then I wouldn't be wasting solar and the PV1 plus PV2 input would be zero. I assume once the generator power was switched off then things would revert back to seeking EPS, ready for when the new day dawns? Is that a correct assumption? I know if I can get the batteries to 80%+ charge status after dusk then there will be enough to see through the night, even those long cold Winter nights when there will be a good amount of added heating load.
I'll set the 'on grid' feed in power to zero to ensure there is no possibility of back feeding. Using an 8Kwh generator on 20Kw battery storage there should never be a need to run the generator at night for more than a hour and a half. It should all work, so long as the EPS does default back into action automatically as the system set 'self use' work mode come the next day.
I have retained a grid mains switch in the house which I could just flip during the daytime and allow all the solar output to then top off the batteries but I want to run a test to see if we can survive on solar with generator backup at a cost advantage over the easier, from the comfort of the home flip a switch, solar with grid mains as the backup. If we can, then considering going fully off-grid would be a viable option. It's a big decision in the UK to move from a grid supply to go fully off grid as there is a hefty disconnection charge to add into the cost benefit analysis of the figures.
Firing up the generator on the grid input for the inverter would override the solar input. This makes sense as the inverter has power limitations so I can see why that would be a safety feature of this input or that input. If I were to only use generator feed battery top off after dark then I wouldn't be wasting solar and the PV1 plus PV2 input would be zero. I assume once the generator power was switched off then things would revert back to seeking EPS, ready for when the new day dawns? Is that a correct assumption? I know if I can get the batteries to 80%+ charge status after dusk then there will be enough to see through the night, even those long cold Winter nights when there will be a good amount of added heating load.
I'll set the 'on grid' feed in power to zero to ensure there is no possibility of back feeding. Using an 8Kwh generator on 20Kw battery storage there should never be a need to run the generator at night for more than a hour and a half. It should all work, so long as the EPS does default back into action automatically as the system set 'self use' work mode come the next day.
I have retained a grid mains switch in the house which I could just flip during the daytime and allow all the solar output to then top off the batteries but I want to run a test to see if we can survive on solar with generator backup at a cost advantage over the easier, from the comfort of the home flip a switch, solar with grid mains as the backup. If we can, then considering going fully off-grid would be a viable option. It's a big decision in the UK to move from a grid supply to go fully off grid as there is a hefty disconnection charge to add into the cost benefit analysis of the figures.
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Dave Foster
- Posts: 1328
- Joined: Thu Oct 13, 2022 7:21 pm
That is reassuring to be told it'll revert automatically to seeking out the solar input when the mains voltage is zero.
I just need to build a somewhat secure generator enclosure as that is an expensive piece of kit to have sitting outside unsecured. I've looked online for suitable options and they are silly money compared to a DIY effort. Back to the drawing board I'll head.
I just need to build a somewhat secure generator enclosure as that is an expensive piece of kit to have sitting outside unsecured. I've looked online for suitable options and they are silly money compared to a DIY effort. Back to the drawing board I'll head.
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Andrew37423
- Posts: 1
- Joined: Tue Jul 25, 2023 12:01 am
Hi baz, did you have any success charging the batteries from your generator, thanks.