Question about DIY solar wiring off grid in Hawaii

[terracore]

3 Charge controllers.

2 Flooded batteries (parallel).

1 Inverter.

The knowledge I have found says, always connect the charge controllers and inverters to the same battery. Further search seems to be inconclusive.

Comments/Suggestions/Thread hijacks welcome.

[kander]

Your correct in your assumptions on how to hook them up.. Im not sure what the reasoning for 3 charge controllers for two batteries.

[randomq]

Ideally you have the same resistance along each string of batteries and connections to controller/inverter/etc. That way they charge and discharge evenly.

If your batteries are in parallel like this:

Code:

a (-)battery1(+) b
   |          |
c (-)battery2(+) d

Then I would connect controllers/inverters/loads to a & d, and then periodically (say whenever you clean your contacts every few months) switch to c & b.

[terracore]

"Im not sure what the reasoning for 3 charge controllers for two batteries"

Good question.

1) Two 40 amp and one 30 amp MPPT charge controllers WAY cheaper than one 90 amp charge controller, and higher capacity.

2) Three separate solar arrays. One wired in series, two in parallel, due to types of panels used and sun tracking orientation.

3) Scalability. I was able to start small, and grow as finances allowed.

4) Redundancy. When charge controller goes bad I lose ~33% of power instead 100%.

It's not perfect. Charge controller losses during night higher. I'm sure there are other negatives as well.

[kalakoa]

Difficult to answer without knowing the battery arrangement.

Interconnect size matters; it's best if these are larger than the feed wiring. The "cross-corner" connection described above is actually best practice (and described somewhere in the Outback documentation).

The other issues are "how many things can you fit on the battery terminal". Simple installations can use terminal risers (if you find these), but a terminal block is really the best solution. Example:

https://lugsdirect.com/7006-4-14AWG-2-0-...re-lug.htm

These exist in other configurations and in a "multi" with insulated base and separators. Otherwise use nylon hardware to bolt them into a plastic junction box. Mount it on the wall with all your charge controllers. Large barrel to a big battery cable, charge controllers and DC distribution on the small barrels. Connect inverter directly to batteries or daisy-chain the DC block off the inverter (or its class-T fuse and shunt if your system has these, which it should). This reduces the system to one or two battery connections, which will easily fit stock terminals.

Use a standard automotive pigtail fuseholder as the connection between charge controllers and the terminal block. ATC fuses are rated for 32V.

[kander]

@terracore
I guess you wont have to worry about the batteries getting charged with that much current to keep them topped up. Resistances in your setup are going to be negligible as long as your using big awg between inverter and batteries. Chargers not so much because of the overkill on solar.
Hope to hear you get more batteries to store all the solar energy you can but I suppose this is a budget issue with just two batteries.

[terracore]

Thanks everybody for your input.

It is a budget issue... sort of. I have a unique setup where I only use solar power when it's available. If no can solar, the system automatically switches to grid. Think of "grid tie" without any grid tie. I get all the advantages of a 30K solar system, but only spent a few K. So my payback period is measured in a few years instead of 3 decades where it finally "pays off" when the panels are at the end of their lifetime.

The batteries only really exist because inverters require them, and to deal with those times the draw exceeds what's available under cloud cover. It also allows me to run the entire house off a very tiny generator, used only occasionally, during extended power outages. If ever necessary. But if grid power suddenly became very expensive for long term, I could add batteries to my system and use little (or no) grid so long as it was the most economical solution.

[kander]

@terracore
that makes a lot of sense. Sounds like a pretty good system. Yea I know the Schneider grid ties require batteries and maybe more. Might as well use all you can when you can because the power company doesn't seem to want to pay for what you generate.

[ProjectDomecile]

I'd be very, very interested in seeing the breakdown/parts list for your whole setup.

[terracore]

Some day when I get everything permanently installed I plan to do a virtual tour of the system with pictures etc but for now it looks more like a fire hazard.

Currently I have the three arrays on the roof where one is oriented for morning/noon sun and the other two for afternoon/evening. This allows me to start using the solar from about 0800am to 0530pm though if it is clear I can start it sooner or end it later.

The grid power is hooked to a cheap digital "smart" wifi plug. "Smart" means that it is programmable through phone app and can be controlled anywhere my phone has a cell or wifi signal. So I can switch from grid to solar power using my phone even if I'm not home. It also tracks electricity usage. When the plug cuts off the grid power the following transfer switch switches to inverter power:

https://www.amazon.com/gp/product/B004S5...tl?ie=UTF8&psc=1&linkCode=ll1&tag=pw016-20&linkId=d25f751e8e2fa370169bbd6859b72822&language=en_US

I have a second transfer switch that monitors the battery voltage and if it gets too low it switches from inverter back to grid power. The unit is programmable, when the voltage rises back to whatever level I select it switches back to solar/battery power again:

https://www.amazon.com/gp/product/B07D41...tl?ie=UTF8&psc=1&linkCode=ll1&tag=pw016-20&linkId=0245c717f32d554d2f091e5ed915895f&language=en_US

The transfer switch is more variable than how it is marketed, for example you could use it to turn on a battery charger instead. Or to only operate some loads when your batteries are fully charged and at float, so as to not let excess power "go to waste". I currently use my "excess" power for an LED grow light so my extra power is effectively turned into salad greens, however I am currently just turning the light on manually until my system is further developed.

I am currently using the system to power a chest freezer (it only runs during solar hours so it is 100% solar powered, it only gets back up to about 12 degrees from being off all night), UV water sterilization unit, pump for solar hot water system, side-by-side kitchen refrigerator, and everything in my office (DVR for security system, modem/router, computer, monitor, etc). It shaves about 30% off my monthly electricity bill.

After Iselle I had my house wired to accept power from a generator with the grid lockout per code. I can use the same generator inlet to run the entire house off my hybrid solar system for power outages etc using the following adapter:

https://www.amazon.com/gp/product/B074PW...tl?ie=UTF8&psc=1&linkCode=ll1&tag=pw016-20&linkId=68f347b2d11b64aa033516490e5b082e&language=en_US (just make sure not to turn "on" any 220v circuits on the electrical panel or else they would be running on a "brownout" or more than likely would trigger inverter's overload shutoff). I put red markers on the panel switches that control the stove etc to remind me not to turn them on.

I have a 2,000 watt pure sine wave inverter with a 20 amp outlet. The normal draws on it are about 600 watts total and almost 700 watts with the LED grow light on. During punishing heat I turn the grow light off and run a 6000 BTU air conditioner if there is enough sun to power it, or about 1100 watts total. Anything more than that and my panels can't keep up.

The system is flexible in it's use and power storage is expandable. It is a backup power source at the same time it pays for itself by giving me sub $100 electricity bills.

During extended power outages I can run the whole house off the system as described above if I need to, keeping combined draws within the inverter's capability of course, and replenish battery draws at night using a 40 amp charger (~500ish watts) connected to either small generator or even a vehicle with a 1,000 watt inverter. The batteries supply the occasional power draws above that amount, and get topped off when it's below that amount. (Much quieter and fuel efficient than a big whole-house gas generator). Or I can just shut a lot of stuff off and go batteries only for as long as that lasts.