2oldman
Indio CA
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Joined: 04/15/2001
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Yeah.. the scheme is probably not good. If I want these in series I should series all of them and get a controller to handle the voltage.
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Salvo
California
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Joined: 06/01/2008
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OK, let's do some science.
1. Measure the total solar current going into the batteries.
2. Cover 1/4 of a panel with a sheet and measure current.
3. Cover 1/2 of same panel and measure.
4. Cover the entire panel and measure.
5. Uncover panel and verify measurement in step 1.
That should do it.
Sal
pianotuna wrote:
How many cells would you prefer I cover? I have two sets in series/parallel.
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pianotuna
Regina, SK, Canada
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Joined: 12/18/2004
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Hi Salvo,
Weather and time permitting, I'll try that this weekend.
The batteries will be "right up" so I'll have to create a load--I know the Fridge draws 30 amps on the Inverter.
I'll be taking the readings from my 3024di Blue Sky controller and will list voltage and amperage. I'll take ten readings and throw out the high reading and the low reading and average the results.
Salvo wrote:OK, let's do some science.
1. Measure the total solar current going into the batteries.
2. Cover 1/4 of a panel with a sheet and measure current.
3. Cover 1/2 of same panel and measure.
4. Cover the entire panel and measure.
5. Uncover panel and verify measurement in step 1.
That should do it.
Sal
pianotuna wrote:
How many cells would you prefer I cover? I have two sets in series/parallel.
Regards, Don
Kustom Koach Class C 28'5" 256 watts solar, 875 amp hours in two battery banks 12 volt batteries 2500 watt inverter.
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TechWriter
Green Bay, WI USA
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Joined: 12/22/2002
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2oldman wrote:I have 3 panels, about 120w each. I want 24v from them, so I want to wire 2 in parallel, then series those to the third one. Whaddy think?
Run them in series for a 36V system. Then buy a controller that automatically adjusts PV input voltage (12, 24, 36, 48, or 60V) to battery voltage (12 or 24V).
I use a Xantrex XW-MPPT60-150. However, next time I'd probably use Outback's FLEXmax60 controller. Both controllers allow 60A input with a maximum OC voltage of 150 (check out Xantrex's Sizing Chart for details). While pricey, both controllers allow for maximum flexibility for connecting solar panels.
My six panels are in 3, 24V strings (instead of 1, 12V string) so that I didn't have to run 2-0 wire to handle the high current from my combiner to controller. Be CAREFUL of this when planning a system!
So, get controller that allows for expansion + add a FUSED combiner box between the solar panels & your controller.
Tom
2004 34' Sea Breeze LX 8341
Vortec 8.1L & W-22
w/Xantrex RS2000 inverter/charger +
Xantrex XW-MPPT60-150 60A Charge Controller with 760W (3/4 KW) of Kyocera solar
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liborko
Surrey, B.C.
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Nice installation techwriter. Since you have three sets of series connected panels I would be interested to see how the shade from the airconditioning units affect the output. Also I would connect each battery terminal from the series combos with a same size/length wire to the buss for equal charge/discharge currents.
To the OP: series connection of the panels is more suitable for permanent installations where all panels are equally exposed to the sun light. For RV I prefer running separate wires(appropriate size) from each panel to the circuit breakers and connect parallel at the controller.
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Salvo
California
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TechWriter can do the same test Don is going to do. Cover a portion of one panel and measure difference in total charging current.
I'm really surprised that some RVers chose series over parallel. Any shade will kill power from series panels. Current reduction will be an order of magnitude more than if panels were in parallel; - even with a larger voltage drop due to twice the current going through same size conductor.
The voltage drop between panels and controller isn't that big a deal. You're not going to lose much charging current. If you don't have a MPPT controller then it makes no sense at all.
Sal
liborko wrote:Since you have three sets of series connected panels I would be interested to see how the shade from the airconditioning units affect the output. Also I would connect each battery terminal from the series combos with a same size/length wire to the buss for equal charge/discharge currents.
To the OP: series connection of the panels is more suitable for permanent installations where all panels are equally exposed to the sun light. For RV I prefer running separate wires(appropriate size) from each panel to the circuit breakers and connect parallel at the controller.
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2oldman
Indio CA
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liborko wrote:To the OP: series connection of the panels is more suitable.. where all panels are equally exposed to the sun light..I prefer running separate wires(appropriate size) from each panel to the circuit breakers and connect parallel at the controller. Shading is almost never an issue, with the exception of a small shadow from the A/C dome early am. Running separate wire would be a difficult job on my rig, as it's pre-wired from the factory thru walls.
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pianotuna
Regina, SK, Canada
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Hi Salvo,
I decided to add couple data points.
Before test batteries at 13.2 volts on cigarette lighter tester, 14.1 volts, zero amps charging on Blue Sky 3024di. Fridge was run on inverter for ten minutes to take the first "bite" out of the battery banks.
cig blue
volts volts amps
12.8 12.8 5.8 all panels
12.5 12.7 3.4 full panel covered
12.5 12.7 3.9 1/2 panel covered
12.5 12.8 5.6 1 cell covered
12.5 12.9 5.7 all panels
12.7 13.6 5.9 all panels inverter off
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Salvo
California
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Thanks for the data Don. You have 4 panels, wired in a series/parallel configuration.
The 4 panels produce 5.8A, or 5.8/4 = 1.45A/panel.
When 1 panel is covered, output is 3.4A.
If all panels are connected in parallel, output would be 3 * 1.45W = 4.35W.
Calculating parallel advantage over series:
Advantage = 4.35W/3.4W = 28%
Don's panels can deal with shade better than your typical panel. It would be great if others (with series panels) make similar tests.
There is a huge disadvantage going series. Shade is the worst enemy of solar.
Sal
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MrWizard
Van Nuys, Ca
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Joined: 06/27/2004
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series panels carry the same current, it is the voltage that is increased ( just like batteries )
2 pairs in series
in his PP series is 5.8 amps thru each pair
each pair is splitting the 5.8 amps at 2.9 amps per panel
total wattage from the panels is 5.8 amps * the stacked voltage of the pairs, the voltage from ONE pair is the same as the voltage from (1) panel ( the amps are doubled ) (just like wiring up 4 6v trojans) (except the voltages are higher) and the final output voltage is determined by the controller ( a MPPT controller functions similar to a switching power supply ) ( but its chopping up DC instead of AC )
the advantage of series is higher wattage at lower amps creating less Vdrop across the resistance of the wire going to the controller,
after the controller you are dealing with 14+ volts to charge the batteries and need the shortest run of the biggest wire to avoid losses
if you stack the voltages to high and reduce it to 14+ you have losses in the controller
seems to me: paralleled panels using heavy gauge wiring from the junction box to the controller can give better efficeny and less loss in the controller and more power to the batteries, but you do need high output panels that will produce a charging voltage per panel without being stacked, this quality and the wire cost more money to install than purchasing lesser panels and stacking them.
Options, always have options, and the journey goes much smoother
....
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