Offgrid Solar/Battery Bank - Standby Generator Questions

mjp24coho

All - I wanted to get some input on a proposed backup generator setup for my off-grid solar set up. I'm planning my system to run half off solar/battery (120V small loads - lights, small refrigerator, etc), and half off a generator (240 V large loads - washer/dryer, vacuum, etc). The solar will be able to run 22 hrs of the day, but the generator will be needed to run for a few hours a day for the large loads. While the generator is running for the large loads, it will also be able to charge the battery bank through the inverter (and also run the small loads if the solar system is down). To do this, I'm going to have a main electrical panel (240V) and a separate sub-panel (120V). Attached is my proposed wiring diagram, showing both scenarios - when the generator is running and when it is not running. I wanted to get everyone's input to make sure this proposed wiring diagram will work. I'm looking at using a 13KW cummins-onan standby generator with a transfer switch. I like the features of this generator because it will allow me to monitor it, start it, etc. online when I'm not at the cabin. I'll set the generator to not automatically switch on when no inverter power is present; rather, I'll only want to turn the generator on manually (versus automatically). I understand the concepts behind the transfer switch, but not all the inner-workings. If I do it this way, whenever I start the generator, will it automatically cut off the power from the inverter to the subpanel (via the transfer switch - see attached diagram), and only allow power from the generator to go to the subpanel (via the transfer switch)?

Hopefully my questions make sense. I'd appreciate any insight, as well as feedback on the proposed wiring. I'll eventually have an electrician wire it for me, but I first want to make sure conceptually that this proposed layout will work.

Thanks!

vtmaps

Re: Offgrid Solar/Battery Bank - Standby Generator Questions

What is your inverter? How do you charge your batteries? If you have an inverter/charger I think you do not need a transfer switch. The inverter/chargers that I know about have the transfer switch built in. --vtMaps

mjp24coho

Re: Offgrid Solar/Battery Bank - Standby Generator Questions

The inverter will be an Outback VFX2812. I'll be charging the battery bank with an array of solar panels. I have a small system now, but these plans are for a proposed expansion. Part of my question is because the generator comes prewired with a transfer switch.

Volvo Farmer

Re: Offgrid Solar/Battery Bank - Standby Generator Questions

The way these inverters work is that you wire the generator directly to the inverter. When the generator is running, the inverter senses it, charges batteries with some of the generator power, and the rest of the generator power is available for AC loads. No inverting is taking place while you are charging batteries with a generator. The only reason you would need a transfer switch is if you should need to remove the inverter for service or something.

solarvic

Re: Offgrid Solar/Battery Bank - Standby Generator Questions

Sounds like you need to get rid of the large 220 vac loads and get a bigger inverter that outputs 220 ac. Change dryer, stove and waterheater to propane. I have all energystar rated appliances, gas dryer, gas heat, and gas cooking. stayed with electric waterheating by getting a GE Geospring waterheater. Also have a freezer and 21 cu ft fridge. Have grid pass thru the magnum 4000 watt 24 volt and can power my house preety well for a day without a generator if the grid goes down. I am not that knowledgeble to comment on your proposed drawing but some here are. Unless you have lots of power requirement for outbuildings ect. you could probably save money in the long run if you changed those 220 loads to propane or natural gas and get a big enough inverter and smaller generator that can provide your power needs. How small of a cummins can you get that still has the monitoring you want? i never had a cummins generator but have faith in cummins. Have an old dodge truck with a cummins. :Dsolarvic;)

mjp24coho

Re: Offgrid Solar/Battery Bank - Standby Generator Questions

Thanks. Maybe I can redesign the system to do 120V only. The generator I'm looking at is a Cumins-Onan 13KW home standby generator. It comes prewired with a transfer switch - can it be configured to not run with the transfer switch? Also, the generator has a wired remote operating screen/panel. I wonder how it is powered when the generator is not running? I assume that when normally wired with the transfer switch, then it would get its power from the grid. But that wouldn't be the case with it being used in an off grid solar/battery setup. Anyone have experience with this?

icarus

Re: Offgrid Solar/Battery Bank - Standby Generator Questions

For all you Onan questions,,: http://www.smokstak.com/forum/forumdisplay.php?f=1

Tony

dagr51

Re: Offgrid Solar/Battery Bank - Standby Generator Questions

Wouldn't the Onan be equipped with it's own starting battery that charges off from the generator when it runs?

mjp24coho

Re: Offgrid Solar/Battery Bank - Standby Generator Questions

Yes - I believe it is. I'm just not sure if it uses that battery to power the remote wired control panel (and if so, how long it would run off that battery), or if it requires AC power from the "grid" to run it when the generator is off.

dagr51

Re: Offgrid Solar/Battery Bank - Standby Generator Questions

Try checking the manual for the genny which should be available online. Either check to see if it directly states what powers the control panel or check the wiring diagram (12 vdc or 120 vac).

mjp24coho

Re: Offgrid Solar/Battery Bank - Standby Generator Questions

Thanks - I've also sent an email to Cumins-Onan to get their thoughts.