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Old 09-22-2014, 01:21 PM   #1
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Solar Efficiency

I have 2-120 watt & 1-85 watt solar panel on my roof. This should provide 325 watt of charging. I checked each today and am getting ~4.6 amp on the two larger ones & 3.5 amp on the smaller on. This gives me +13 amp charging. I had the inverter on pulling a ~12 amp load running a small toaster oven to make sure the batteries were slightly discharged, down between 85% charged based on the panel. It was a sunny day, no clouds, the panels are flat on the roof, at noon the sun was about 60-70 degrees on the horizon.

I didn't have the voltage charging but if you assume 14.5 volts then the panels are providing me ~195 watts or ~60% of max. I've researched this in the past and believe my panels are charging about right.

Is this pretty much normal?
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Old 09-22-2014, 09:37 PM   #2
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I have two 120 watt 12 Volt panels and I don't believe I've ever seen over 12 amps. One of my problems though is we just don't seem to use the batteries enough to get them down below 95%.

Your situation is pretty normal IMO.
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Old 09-22-2014, 09:40 PM   #3
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Solar insolation goes as the cosine from the normal. 60 degrees from horizon is 40 degrees from normal or 0.76. So the most you could get with a possible 325 W is 247 W.

You will get losses from the panels to controller (the lower the voltage from the panels to controller, the greater the loss), a loss through the controller etc. Even apparently bright days may have atmospheric transmission losses through high clouds.

We have 1420 W of solar and the most we have gotten on a very clear day in mid-summer at zenith was 1320 W to battery. This goes down as the sun gets lower in the sky and we get 1000 W at best this time of year.

You could tilt them to be normal to sun's rays but this is a hassle.

Solar panels are cheap these days ($.50/watt). Would suggest that you just put on more flat panels. If you have a Monaco, you could easily put on 700 W or more. 700 is probably quite sufficient for most purposes.

You probably have room for as much as we have or more. We figure we could put on another 700 W on our fifth wheel but we figure we already have quite enough.

However, more panels could require more and heavier cabling and possibly a better controller. Since our system has the voltage coming from panels at 90 V, the Tri-Star MPPT-45 (Maximum power point tracking with 45 amps capability), is only handling 14 amps with 1300 amps), we do not need heavy cabling or a larger MPPT. You already have a system in place and additions are not that difficult to fabricate.
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Old 09-25-2014, 12:45 PM   #4
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I have 3 240 watt panels which are tilted toward the sun, and I regularly see 80 to 85% of rated output during the winter in southern Arizona. I run the panels in series, so I have around 90 volts at about 8 amps. (max) I'm using a Tri-Star MPPT 60. I run about 40 to 50 amps charging. I have seen full rated output, and even more than 720 watts under cloud-edge effect, but not very often... I also have two 100 watt panels that are flat mounted, and I rarely see more than 50% of rated output.
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Old 09-30-2014, 02:03 PM   #5
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REED,

WOW - I'm confused - you say you have a TS-45amp MPPT controller with 1,420 watts of solar panel array.... is that indeed true????????

You are asking it to do over 100amps at a nominal 12Vdc (14.8vdc) battery voltage.

My 550 watt array easily gives me 40 plus amps (TS-MPPT-60) at the "nominal" 12 Volt DC battery voltage. IMHO - A property designed system should very easily approach or even exceed the rated array wattage if using good panels and properly wired.

Jeep TJ5

That TS - MPPT - 60 as far as I am concerned is the top of the line controller. Hope you have the temp probe and the voltage sense lines connected as well as proper configuration via a PC not just the dip switches set and called good.
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Old 09-30-2014, 02:08 PM   #6
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I see now that there seams to be a lot of confusion

"However, more panels could require more and heavier cabling and possibly a better controller. Since our system has the voltage coming from panels at 90 V, the Tri-Star MPPT-45 (Maximum power point tracking with 45 amps capability), is only handling 14 amps with 1300 amps), we do not need heavy cabling or a larger MPPT. You already have a system in place and additions are not that difficult to fabricate."


MPPT controllers are rated with watts in and amps out - so 1,420 watts down converted to 12 volts "nominal" is far more than the 45amp rated controller was EVER designed to handle. P=IE 1420/12=118amps - please help me understand
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Old 09-30-2014, 02:43 PM   #7
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Originally Posted by jacwjames View Post
I've researched this in the past and believe my panels are charging about right.



Is this pretty much normal?

I agree. Panels are rated in "perfect" conditions which they can create in a lab but we never see in the real world.....so I think you are doing pretty good.
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Old 09-30-2014, 02:54 PM   #8
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JACW... I get the same effect from my panels.... it is not out of the norm to view such seemingly poor performance when the angle between the panel and sun is so low but they will still offer you decent recovery time on a battery charge event as do mine. I have 500w of panel at the theoretical 5.5amps per panel (5 ea 100w panels) and I get about 7 amps of measured charge at the meter point...and it does a fine job of recovery when I discharge the battery to 70%.
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Old 09-30-2014, 02:55 PM   #9
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I guess it depends on the manufacturer of the panels and the installation

"I have 2-120 watt & 1-85 watt solar panel on my roof. This should provide 325 watt of charging. I checked each today and am getting ~4.6 amp on the two larger ones & 3.5 amp on the smaller on. This gives me +13 amp charging. I had the inverter on pulling a ~12 amp load running a small toaster oven to make sure the batteries were slightly discharged, down between 85% charged based on the panel. It was a sunny day, no clouds, the panels are flat on the roof, at noon the sun was about 60-70 degrees on the horizon.

I didn't have the voltage charging but if you assume 14.5 volts then the panels are providing me ~195 watts or ~60% of max. I've researched this in the past and believe my panels are charging about right."

From my experience (after installing 15 to 20 systems over the past several years) something is wrong with your installation (but we don't have enough data to really determine the issue one way or the other) - however if you are happy with it - enjoy and do not worry about it. I would have to assume your install is all parallel array and a nominal 12vdc (17 t0 20voc array). Hope your wire is properly sized.

I see way less than perfect conditions with my flat mounted 4 each parallel / serial K140 panel array but expect and do easily see the full rated power under good conditions.

I would expect to see (in your install) 25 amps to the LOADS - as I said "loads" not necessarily the battery bank.

Again if happy with it call it good and enjoy camping
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Old 10-01-2014, 08:41 AM   #10
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KJINTF:
Yes, I have the temp sensor and the voltage sense connection to the MPPT-60. Works much better that way. I see the max charge voltage vary considerably with temp swings of the batteries. (From about 14.4 when warm to about 15 when cold)
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Old 10-01-2014, 08:49 AM   #11
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Jeep guy

( Side not I have had 10 or 12 Jeeps over the years, love them, currently 1942 Willys MB, 2002 GC Overland, 2003 Wrangler Rubicon, plus the DRBIII tool - fun toys )

Yes the temp compensation will swing the charging voltage (again it is 100% configurable, might want to set a few limits) Suggest you set the High Voltage disconnect at 15.2 or thereabouts thus cold weather will not possibly cause the battery voltage to get too high, which could hurt the frig or other electronics
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Old 10-01-2014, 10:54 AM   #12
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Is this pretty much normal?
Yes JimJ, pretty usual in the imperfect world you and I admit to living in.

Apparently it must be possible to buy magic panels that do put out theoretical rated output and of course there are similar magic batteries that you need to make up a magic system that is always 100% full by 9am. Never seen one, but am always hearing about them.
Live in hope.
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Old 10-01-2014, 10:56 AM   #13
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some interesting side reading I found a while a back HandyBob's Blog « Making off grid RV electrical systems work
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Old 10-02-2014, 10:03 AM   #14
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Tony:

I have 240 watt grid-tie (37 volt) panels. I normally get about 80 to 85% of rated output on a sunny day, during the winter. These panels are not "premium-brand name" panels, rather they are inexpensive no-name ones. The wiring is properly sized and the panels are angled toward the sun. No magic. As I stated in another post, I have flat mounted panels on my coach roof and I rarely see more than 50% rated power. So there are lots of things that have to be right to get highest efficiency.
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