One room solar

I live in the desert and wanted a be able to run a small one room portable AC at 900 watts continuously during a power outage. I pretty much used Will’s videos to guide me all the way. MppSolar 24v all-in-one, Daly BMS, 80 amp circuit breaker to the battery, lifepo4 100 ampHour Chinese sourced cells 8 in series, 30 amp Bussmann breaker to the panels with an on/off switch, 4-used 250 Watt panels in series from SanTan Solar ($50 each), Victron battery protect set to program 8. It works great on battery alone before I got the panels a get close to 3-hours of AC, with a solar assist to be determined.

Nice! It's goid to hear some real experience using an AC off of batteries as well. Keep us posted on how much longer you could run PV assisted.

I switched the cables to the solar breaker to 10 gauge since this photo. My question, do I need to earth ground the panels ( sinking an 8 foot ground in AZ cement like soil is no easy task). I have a long metal fence nearby that runs to a block wall is grounding to that a bad ideal?

Donald Siegel said:

I switched the cables to the solar breaker to 14 gauge since this photo. My question, do I need to earth ground the panels ( sinking an 8 foot ground in AZ cement like soil is no easy task). I have a long metal fence nearby that runs to a block wall is grounding to that a bad ideal?

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Well I think grounding to a metal fence is a bad idea. For personnel safety reasons. Develop a grounding electrode, ground rod, ufer ground, copper water pipe run in direct contact with earth for many feet. Ground rods are not always driven into the ground, sometimes a trench is dough and the rod is buried in the trench. you mentioned 900 amps in first post, was that ment to be 900 watts ?

Randy, Great catch on the orientation of the grounding rods. In the AZ hardpack a shallow ground rod trench wouldn't be useful even if it were 50' long as dry earth doesn't give provide good "earth" ground. The benefit of a driven-in ground is that once you get 4-5 feet down the substrate starts to have moisture. Though it's not necessarily wet, minor dampness helps to conduct electricity. A ground essentially conducts excess electricity to "earth" to be disbursed.

There are ways however to set a ground without having to simply "hammer" into the cement-like southwest ground:

The first is to wet the ground, wait a bit and hammer your grounding rod until it becomes difficult. Then remove the rod, fill the resulting hole with water, wait a bit and reinsert the rod. After a short wait hammer again. Repeat the steps until you've reached your target depth.

Secondly, try essentially the same process with a piece of galvanized pipe with "teeth" cut in the leading edge. When driving the pipe, keep it full of water and turn the pipe between strikes to let the "teeth" cut the wet earth. Repeat until you've reached the target depth.

Drive a short ground rod into the ground, attach your ground wire and waterproof the exposed assembly. When you need to use whatever is attached to the ground, drip water onto the grounding rod or drip water onto the soil where the rod enters the soil to allow the soil around or below the rod to become wet and conduct the excess electricity down to the "earth".

I've use all of these techniques in the SouthWest and the deserts of the middle-east and they work well. The "wet-earth" method should only be used when nothing else works as it's wasteful.

Donald, Good Luck!

RandyP said:

Well I think grounding to a metal fence is a bad idea. For personnel safety reasons. Develop a grounding electrode, ground rod, ufer ground, copper water pipe run in direct contact with earth for many feet. Ground rods are not always driven into the ground, sometimes a trench is dough and the rod is buried in the trench. you mentioned 900 amps in first post, was that meant to be 900 watts ?

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Thanks for the excellent description on earth ground rods set in the desert. In a way grounding a DIY solar setup on say a cabin with no other electrical on an empty lot seems easier than grounding an off grid home setup if any part of it is in your home. For an at home set up apparently I need to get the ground for my panels and my PIP inverter bonded to the existing homes electrical ground system and earth connection. If you have a separate 8-10 foot ground rod near the panels to ground them, and run the solar wires into your house where you mounted the inverter you now have two disconnected ground systems with a possible electrical potential between them. They may in a lightning strike or other high voltage or amp event arc from one to the other taking the path of least resistance burning your house down with it. I think I can clamp onto our nearby copper cold water pipe that is already earth grounded with a proper ground clamp. I’ll have our electrician consult on what I really need to do, so it’s done right. If I learn anything from that work I’ll be glad to share it.

NEC Grounding Electrodes.

Grounding vs. Bonding

RandyP said:

Well I think grounding to a metal fence is a bad idea. For personnel safety reasons. Develop a grounding electrode, ground rod, ufer ground, copper water pipe run in direct contact with earth for many feet. Ground rods are not always driven into the ground, sometimes a trench is dough and the rod is buried in the trench. you mentioned 900 amps in first post, was that ment to be 900 watts ?

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Having a fence as the only ground could be bad, but having it grounded as well as the rod, and water pipe is a good plan.
Basically everything that is metal should be grounded.
But the main ground system needs to be permanent and protected from damage.

Basically everything that is metal (fault current carrying item) should be bonded. There should be only one grounding electrode system and one grounding electrode conductor per electrical system.

RandyP said:

Basically everything that is metal (fault current carrying item) should be bonded. There should be only one grounding electrode and grounding electrode conductor per electrical system.

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Close.
but current code for me is two ground rods spread at minimum 6’ apart both connected to the panel with an unbroken #4 solid conductor.
Basically, the better the connection to earth the better. But it all MUST be tied together. There cannot be different ground potentials.

Donald Siegel said:

I live in the desert and wanted a be able to run a small one room portable AC at 900 amps continuously during a power outage. I pretty much used Will’s videos to guide me all the way. MppSolar 24v all-in-one, Daly BMS, 80 amp circuit breaker to the battery, lifepo4 100 amp Chinese sourced cells 8 in series, 30 amp Bussmann breaker to the panels with an on/off switch, 4-used 250 Amp panels in series from SanTan Solar ($50 each), Victron battery protect set to program 8. It works great on battery alone before I got the panels a get close to 3-hours of AC, with a solar assist to be determined.

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Donald, just to be clear, I believe you mean watts when you say amps

Donald Siegel said:

I live in the desert and wanted a be able to run a small one room portable AC at 900 amps continuously ............. 4-used 250 Amp panels in series from SanTan Solar ($50 each)............

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In both cases quoted above, should the Unit of measure be changed from 'amps (Amp)' to 'watts (watt)' ?

RandyP said:

In both cases quoted above, should the Unit of measure be changed from 'amps (Amp)' to 'watts (watt)' ?

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Either that or he runs a MASSIVE solar farm...

Yes watts, a typo.

Nice set up. One thing I would suggest is using a mini-split instead of a portable AC. They are a lot more efficient (probably close to cutting your power consumption in half), way quieter, and can heat if needed.