An off-grid install in the city

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jonescg   1 GW

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An off-grid install in the city

Post by jonescg » Mar 03 2018 7:06am

A friend has a workshop in Perth which hadn't had the power connected for over 3 years. At this point the energy retailer requests that an inspection be done on the wiring to make sure it's up to code before hooking you up (at your expense). I think it's also true that you pay rates based on the expected rent it would get - and unpowered units are effectively storage units, and attract less rent. So double win.

So, the job was obvious - install a solar array with a battery and inverter, and run the workshop off grid. So with a bit of searching on Gumtree you can find cheap used solar panels going for under 40 cents a watt, usually with all the racking gear too. He wanted a decent sort of a setup as he will be charging his electric car from the unit on occasion too. So we settled on a 5.5 kW system using a Victron MPPT 150/100 solar charge controller. It charges a 48 volt battery of 200 Ah capacity or greater. Not bad for $1100 - in fact we could have got it for $860 if I acted on a sale but didn't :x

The flat roof meant making up some trianglular frames from 40 mm aluminium and mounting all the PV racking gear on that. It's a bit of a windy spot so I made sure there were plenty of screws holding them down.
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9 x 200 W panels means a working voltage just short of 120 V DC. Three in series to get 120 V, and three of these in parallel at the junction box.
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We only have 1.8 kW of solar on the roof for now, but we should be pushing 100 amps into the battery when we do.
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Second hand solar is cheap cheap cheap! If you can source some batteries like this one (old UPS batteries) for next to nothing, you have a well powered site at your disposal!

Hillhater   100 GW

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Re: An off-grid install in the city

Post by Hillhater » Mar 03 2018 9:18pm

Nice one Chris !
Are you running 240v circuits off it via an inverter,? Or just 48v ?
Is there a simple way to check if a used panel is working normally and not defective ?
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craneplaneguy   10 kW

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Re: An off-grid install in the city

Post by craneplaneguy » Mar 03 2018 11:10pm

Check the open circuit voltage, for starters. If that's good odds are the panel is OK. In fact, odds are the panel is OK anyway, if not physically damaged. The only bad one I ever had was run over by a tractor. One with the glass shattered still put out power for a couple years.

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jonescg   1 GW

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Re: An off-grid install in the city

Post by jonescg » Mar 04 2018 6:36am

He'll be running an inverter from the main battery, and powering all manner of stuff from the AC circuits it affords. For lights and other predictable, DC loads he may well end up just going 48 V DC from it. You can buy four 12 V LED lights and put them in series. Likewise you can adapt a refrigerator to run on 48 V DC instead of 240 V AC. Then the essentials are covered - lights to see your way to the beer fridge :D

I know he's also got a couple of UPS units that run on 96 V and 72 V batteries (all picked up for free out of the skip bin) and he can just charge them up from the inverter. It's a bit of a mess around, but stored power on tap is a good thing.

As for the panels, I've been involved in the procurement and installation of over 50 panels now, and all of them are still delivering as much power as they did on the day they were installed. They are being pulled off roofs not because they don't work, but because it's cheaper to upgrade to a bigger (5 kW) system than to add to existing systems. In fact I reckon my mate will be struggling to use the power he's got just from one array, let alone three!

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Re: An off-grid install in the city

Post by titooon2014 » Mar 26 2018 8:52am

That's a nice and clean install, Bravo !

One thing, for lead acid batteries, you usually want to charge them @0.2C max or you'll decrease their lifespan quite drastically, especially above 0.5C. For a 200Ah battery, 0.2C would mean no more than 40A (200*0.2) usually.
Moreover, as your battery gets old its capacity goes down (it's likely not 200Ah anymore), you are even stressing them more...
If you can, hook at least 48V500Ah for durability.
If you can't, make sure to monitor the battery temperature when charging at full power for safety. If it gets too high you will have to limit the current. - If you have multiple batteries in series, make sure you check all batteries temperature every once in a while after some time @100A.

And keep up the great work ;)

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Re: An off-grid install in the city

Post by craneplaneguy » Mar 26 2018 10:20am

Indeed, a very cool installation and use. That's great you have a line on used panels, cheap, I'll chime in also to anyone who has a chance to buy used, go for it. NOT like buying a used car....if they look intact, no broken glass or twisted framing, and show voltage, you are good to go! Pretty much as simple as that.

I saw these new type of attach brackets the other day, specifically for metal roofs installs. I really like the way they attach above the water line, up on the ridge, with the attach screws in shear. I may be using just this type for an upcoming job, and all I would do is put in an extra conventional screw or two in the roofing near the new brackets. www. s-5.com

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Re: An off-grid install in the city

Post by billvon » Mar 26 2018 4:42pm

Hillhater wrote:
Mar 03 2018 9:18pm
Is there a simple way to check if a used panel is working normally and not defective ?
Bring a DMM with a current setting up to about 10A. Check open circuit voltage and short circuit current in the sun. Voltage should be very close to what the label on the back claims; as long as current is within about 50% of the Isc claim the panel is good.
--bill von

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Re: An off-grid install in the city

Post by billvon » Mar 26 2018 4:49pm

jonescg wrote:
Mar 03 2018 7:06am
Second hand solar is cheap cheap cheap!
Be careful with mounting. Solar arrays are usually rated to 100+ MPH winds, and I have a feeling that "lots of screws" and some 40mm aluminum may not necessarily give you such a rating. This is important both for the safety of the array and the safety of people around you; a panel that gets ripped off becomes a missile at those wind speeds, and a single such impact will cost your friend far more in legal fees than he saved by not using grid power.

Also, any battery system typically costs more in battery replacements than the power is worth. Is there a reason you didn't go with a grid tied system?
He'll be running an inverter from the main battery, and powering all manner of stuff from the AC circuits it affords. For lights and other predictable, DC loads he may well end up just going 48 V DC from it. You can buy four 12 V LED lights and put them in series.
Not if they are CF or modern LED lights. The ballasts will "fight" and tend to not work well. For older LED+resistor lights or incandescent lights they work OK. (Of course if one burns out they all burn out.)
Likewise you can adapt a refrigerator to run on 48 V DC instead of 240 V AC.
No, you really can't. You need an inverter there.
--bill von

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jonescg   1 GW

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Re: An off-grid install in the city

Post by jonescg » Mar 26 2018 8:34pm

Perth never gets 100 mph (160 km/h) winds. I calculated the wind load on these arrays and it worked out to about 25 kg-force per screw for a 100 km/h wind. Plenty of strength in the fixings, but thanks for your concerns all the same.

"Is there a reason you didn't go with a grid tied system?"

Yes, we know batteries are consumables, but if you read the first post you will see that 1) he had acquired the batteries for free and 2) the workshop had not been connected to the grid for 3 years, meaning it was an expensive process to get it reconnected. 3) a workshop with no grid connection pays less rates to the local government than one with a grid connection.

He is running LED lights like this on 48 volts right now :? But if it can't be done I guess it can't be done hey ;)

And yes, you can install a brushless 48 volt motor (complete with it's own inverter) to run the fridge compressor.

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Re: An off-grid install in the city

Post by billvon » Mar 27 2018 12:08am

jonescg wrote:
Mar 26 2018 8:34pm
Yes, we know batteries are consumables, but if you read the first post you will see that 1) he had acquired the batteries for free and 2) the workshop had not been connected to the grid for 3 years, meaning it was an expensive process to get it reconnected. 3) a workshop with no grid connection pays less rates to the local government than one with a grid connection.
Well, I hope it keeps working for you. A lot of people have tried it and found out that they lose money in the long run.
He is running LED lights like this on 48 volts right now :? But if it can't be done I guess it can't be done hey ;)
Like I said, if they are simple "three LED's in series with a resistor" (like the sort of lights used as car light replacements) then they can work out just fine. Ballasted LED's (the really efficient sort) tend not to work so well.
And yes, you can install a brushless 48 volt motor (complete with it's own inverter) to run the fridge compressor.
Well, if you are going to do that, just get a (much cheaper) 120VAC inverter and run your original 120V compressor. "Re-motoring" compressors is not possible in most cases, since most refrigerators use sealed compressors.
Last edited by billvon on Mar 27 2018 4:11pm, edited 1 time in total.
--bill von

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jonescg   1 GW

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Re: An off-grid install in the city

Post by jonescg » Mar 27 2018 1:00am

Or just buy a 24 volt / 48 volt fridge. Only has to keep a carton of beer cold :)
https://www.energymatters.com.au/westin ... p-362.html

Yeah the LEDs are pretty basic - no ballasts or anything like that. So far so good. All up he's going to have a 5.5 kW solar system with 12 kWh of lead AGM batteries for about $5000. He wouldn't have done it unless the batteries were free.

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Re: An off-grid install in the city

Post by billvon » Mar 27 2018 4:11pm

jonescg wrote:
Mar 27 2018 1:00am
Or just buy a 24 volt / 48 volt fridge. Only has to keep a carton of beer cold :)
That is mission critical, agreed. Generally DC fridges tend to be pretty expensive (low demand.) Peltier junction (car) fridges are tempting but are horrendously inefficient.

If you are going to go the DC route, consider a vaccine fridge - they are designed to work with solar, and contain material that will keep the fridge cold all night without power. That becomes one more load you don't need to put on the battery. (You can also build one yourself with some cans full of eutectic salts, but you have to get the transition temp. just right.)
--bill von

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Re: An off-grid install in the city

Post by Hillhater » Mar 27 2018 7:47pm

jonescg wrote:
Mar 27 2018 1:00am
...... All up he's going to have a 5.5 kW solar system with 12 kWh of lead AGM batteries for about $5000. He wouldn't have done it unless the batteries were free.
?? If the batteries were free, and the panels were cheap , used,...how come the $5k ?
You can buy a new 5kW system fully installed and guaranteed for $3300 !
EG:- http://gdaysolar.com.au
(Maybe you cannot get that price for an off grid install ?)
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jonescg   1 GW

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Re: An off-grid install in the city

Post by jonescg » Mar 27 2018 8:14pm

Hillhater wrote:
Mar 27 2018 7:47pm
jonescg wrote:
Mar 27 2018 1:00am
...... All up he's going to have a 5.5 kW solar system with 12 kWh of lead AGM batteries for about $5000. He wouldn't have done it unless the batteries were free.
?? If the batteries were free, and the panels were cheap , used,...how come the $5k ?
You can buy a new 5kW system fully installed and guaranteed for $3300 !
EG:- http://gdaysolar.com.au
(Maybe you cannot get that price for an off grid install ?)
The panels are about $400/kW on Gumtree, so there's $2200.
The Victron MPPT 150/100 solar charge controller was $1200.
The 48 volt to 240 volt AC inverter (3 kW/6 kW) will be $1000.
All the cables, brackets, conduits, isolators and junk makes up the rest. Oh, and my time to install it.

Also, a completely off-grid install probably doesn't attract any/many lurks like an on-grid install.

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Re: An off-grid install in the city

Post by craneplaneguy » Mar 28 2018 9:43am

These are a super efficient way to keep the beer cold, once you get past the non traditional regular fridge style door. https://sundanzer.com/

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Warning on Used Solar Panels

Post by Alan B » Mar 28 2018 10:03am

Some of my Ham Radio friends did a group buy on used Solar panels. We measured open circuit voltage and shorted panel current and all was fine.

When the panels were put into service they were not able to make rated output. These measurements are NOT sufficient to detect all problem panels. These panels had some corrosion on the internal wiring which added a few ohms of resistance. This resistance was not sufficient to have any effect on either open circuit voltage or shorted circuit current. But it had a major impact on power output at rated voltage.

Measurements need to be taken of rated power output to detect this condition. Visual inspection turned up hints of the issue, but only a max power output measurement told the whole story.

We were able to return the panels.

Buyer Beware!

And Good Luck with your project. I have considered doing this at home for emergency power and electric car charging. Make zero permanent connections to house wiring to avoid the legal costs of licenses and inspections, other than perhaps a plug and cord backup charging connection for extended solar outages. Spend the funds on more panels, of course. In a power outage emergency use temporary cords to plug critical loads into the "solar generator" system, the main daily use of which would be to charge electric vehicles. It would require a 240V inverter at 3-6kw to get level II charging, and a battery with usable capacity equal to the car to fully charge it, or at least equal to a full day's sun output from the panels.

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Re: An off-grid install in the city

Post by craneplaneguy » Apr 02 2018 12:17pm

In 30 years of messing with solar, as in being off grid, selling a lot of them etc., I have yet to find a single module that has "gone bad." BUT, as you state, that doesn't mean it can't happen! So, though the odds are great that a simple open circuit check would suffice, more elaborate testing may be in order to CYA. On the other hand, cheap as solar is, new, buying new makes sense also. I just sold 12 280 watt REC modules to a guy for $165.00 each, including freight, 58 cents a watt and a factory warranty, being brand new.

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Re: An off-grid install in the city

Post by Alan B » Apr 02 2018 9:03pm

We purchased about a half dozen panels, most of them had problems. Perhaps these were ones that had been returned due to issues, and then passed basic tests for open circuit voltage and shorted current, so they "thought" they were OK. You could see some corrosion inside on some of the connections. So it was probably a manufacturing problem, maybe someone used the wrong flux, or sealed some moisture in, or the seals allowed some moisture in. It only takes a couple of ohms to cause these issues.

There used to be lots of panels left over from some big solar test. These were common in the used panel market about 20 or 30 years ago. They were a little discolored from the testing, some years of operation in a desert somewhere. They exhibited reduced output. I never bought one, they were quite inexpensive compared to new product at the time, of course panels then were quite expensive.

Panels undergo various forms of degradation. Some is slow, as in a small percentage of performance loss per year. Others are not as slow, like corrosion. I don't think anyone claims they will be 100% in 20 years use.

They have a lifetime.

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Re: An off-grid install in the city

Post by marcexec » Apr 19 2018 5:47am

billvon wrote:
Mar 27 2018 12:08am
jonescg wrote:
Mar 26 2018 8:34pm
Yes, we know batteries are consumables, but if you read the first post you will see that 1) he had acquired the batteries for free and 2) the workshop had not been connected to the grid for 3 years, meaning it was an expensive process to get it reconnected. 3) a workshop with no grid connection pays less rates to the local government than one with a grid connection.
Well, I hope it keeps working for you. A lot of people have tried it and found out that they lose money in the long run.
He is running LED lights like this on 48 volts right now :? But if it can't be done I guess it can't be done hey ;)
Like I said, if they are simple "three LED's in series with a resistor" (like the sort of lights used as car light replacements) then they can work out just fine. Ballasted LED's (the really efficient sort) tend not to work so well.
And yes, you can install a brushless 48 volt motor (complete with it's own inverter) to run the fridge compressor.
Well, if you are going to do that, just get a (much cheaper) 120VAC inverter and run your original 120V compressor. "Re-motoring" compressors is not possible in most cases, since most refrigerators use sealed compressors.
Make sure you feed you LEDs with 12.0V - there's a good article here: https://mkmakerspace.co.uk/testing-led-strip/
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