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Old 09-07-2015, 04:46 PM   #1
Skoolie
 
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Yes, I said that right. 56 30-watt solar panels.

I work for a company that uses 30-watt solar panels. I recently acquired 56 panels from decommissioned units. 3 rows cover 33ft. The entire roof in solar panels. On the Plate:

48 volts
8 Trojan T-105-RE
4 CAT 1000w inverters
1 MorningStar 48V 40A PWM controller
1 Krieger 2000w (attached to enigine for bedroom A/C)

Runs:
1 Food processor for Baby Food
1 Sundanzer DCR225 refrigerator
3 LED Strip lighting
Occasional A/C
2 laptops
2 Cell phones
1 Tablet
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Old 09-07-2015, 04:50 PM   #2
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Sweet, about time someone set up a good size solar array.

Why 4 inverters, VS one larger good one?

Nat
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Old 09-07-2015, 05:02 PM   #3
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Great question. The most affordable inverters per watt are 1000w x 12v. I'm running 48v and need 4 to balence the load across each 12v set. Also, when we get back to our business in Nicaragua we will break the system into 4 - 12v parts. In the bus I'll run two 15A A/C breakers in a distribution box. One for A/C and the other for the rest.
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Old 09-16-2015, 01:12 PM   #4
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Here is the first draft of the Solar Array Schematic. You will have to click the link for the higher resolution .pdf. https://eljardinometepe.files.wordpr...lar-system.pdf

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Old 09-16-2015, 02:57 PM   #5
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Wow, that's.. interesting. I have to admit, it's an unusual combination of 8 T-105 batteries and a Xantrex charge controller, which are relatively premium or at least solid upper- to high-end stuff, with low-wattage panels and cheapest-per-watt inverters. I'm not saying it can't work; just that more often a system is high-end all the way through or cheap all the way through so this is just unexpected.

Anyway, I see a few small problems in the schematic:

- the battery bank is shorted. The batteries are strung in series for charging, but the pairs are also in parallel for discharging. There's a short circuit where the right-most battery negative connects to the gray bus bar and the third-from-right connects to that same bar. This creates a short circuit around the two right-most batteries (and so on across the rest of the array). Basically what you're building here is a charge pump with batteries instead of capacitors. Charge pumping is a common voltage conversion technique, but you'll need to add switches to break up the series string into 12 volt pairs, and switches to connect the pairs to the bus bar. The switches have to alternate: close the switches to make the series loop for charging and open the switches going to the 12v bus bars, then open the series switches and close the bus switches so that you can discharge. Obviously that presents a problem if you need to draw power from the bank during the day because it reduces the time spent charging. There are work-arounds for this too, but anyway my point is just that the schematic doesn't show the synchronized switches that are needed to make the battery bank part work out the way I think you're wanting it to work. Maybe also consider adding charge equalization across the 12v pairs? I know they'll be switched into parallel mode and intuitively the charge would equalize as a result, but given that you have to raise the voltage to almost 14v to really drive charge into a 12v lead battery, I wonder whether simply wiring in parallel is enough in practice to truly equalize them. I have no idea.

- inverters in parallel: not all inverters advertise this capability. I don't know whether it usually works anyway even on those that don't advertise it, but I assume you already picked a model you're sure supports this mode.

- AirCon: can't quite tell what is the objective here.. maybe for the A/C to run off the solar or the bus battery? Needs more switches so that the inverters on the two sides don't end up in a fight or back-feeding a supposed-dead circuit. Also consult the bus battery and alternator to see how they feel about this (we've had other threads about driving an ac-powered aircon from an inverter off the alternator, and usually concluded the aircon was too big and power hungry for this to make sense).

- 24v fridge and misc 12v loads: what is this portion trying to do? One could put two 12v loads in series across a 24v supply and at least have a prayer of working (so long as power consumption in both loads was guaranteed equal). But this part is confusing. Both terminals of the 24v fridge are connected to the gray 12v bus bar..

Summary: it needs a little refinement, but the concepts are basically sound and it's a creative solution. Good work.
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Old 09-16-2015, 06:50 PM   #6
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Primary design restrictions:

Keep total installation cost down
56 - 30w (2A) panels were free from a demolition project at work
25 - 12v 4A Morningstar charge controllers also free but didn't work them in.
I'll break the system down into smaller zones when we arrive back at the farm

Insects in the tropics are almost impossible to keep out of vented electronics like inverters and therefore need to be replaced often. The fridge can run on 12v or 24v. Other 12v lines are LED Rope lighting, the heater fans, and USB charging ports.

The aircon happend when I said off hand that it was probably enough solar panels to run an aircon. The hope was that it would mostly run when the bus was running and not off the solar. In the end it won't run once back on the farm so it is of lowest priority.

All that being said, in other forums I may be considering running an outback power charge controller eliminating the step down issues. Maybe wire the panels at 96v and the batteries at 24v. Then using 24v inverters to simplify the system further.
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Old 09-16-2015, 10:34 PM   #7
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If running Ac from the bus alternator, make sure you have a med, or large frame alt. A small frame unit will have a really low duty cycle and will burn out in no time.

Large frame 250 amp should be the minimum when running AC from the alternator if you want it to last.

Same go's for people trying to charge their house batteries from the alternator.

Nat
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Old 09-17-2015, 07:32 AM   #8
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I'll check on the alternator and see what size it is. I'm assuming that the size or quantity of alternators is what allow for top mount A/C on Coaches, Motorhomes and box truck refrigeration?
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Old 09-17-2015, 08:25 AM   #9
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I looks like a standard size alternator. I couldn't find any real markings. There is an ideler pulley bellow that looks to have identical mounts as the top alternator presumably holding the spot for a second alternator. Now the question becomes, would all that money to tie it into the solar and bus be better spent on an isolated gen set that could run the aircon or other occasional high draw devises such as power tools.

Again, after it's 6000 mile journey south it will put up on blocks to retire as a house/hostel dormitory and never drive again.
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Old 09-17-2015, 12:31 PM   #10
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Vocational vehicles where the refrigeration is often needed but is only needed while the vehicle is driving (passenger A/C or refrigerated cargo box) generally have a compressor driven directly off an engine. Fans don't need much power compared to the compressor, and they're electric. Those that need full-time refrigeration are usually done this way too but with an auxiliary engine that can be left running when the propulsion engine is off (reefer trailers for example). The compressor needs energy in a mechanical motion form; if that energy can be taken directly from a moving engine then it's more efficient (as compared to energy from moving engine to electricity, then electricity back to motion).

Seems to me that motorhomes often have a little bit of engine-driven A/C in the dash but the rooftop units are driven by an aux generator while underway (if desired).

If it'll just be parked forever at the end of the drive then maybe you don't need to worry about the longevity of the alternator.. so long as it survives the trip. Or you could pack a generator for the A/C and sell it or remove it for other uses when the bus is finally parked and plugged into grid power somewhere.
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