600w of panels only producing 200w of power

[hitek79]

I have six 100 watt panels, but currently my Tristar is reading out that only about 200 watts of power is coming in. Is this typical this time of year? I'm located in South Carolina right now, and the sun is fairly low in the sky obviously.

 

[Fyreman]

33% doesn't sound outrageous.

 

[Haf-E]

If you PV panels are mounted flat - then it is no surprise that they are only putting out 200 watts during the winter. Its basically a matter of geometry - there is a smaller amount of sunlight hitting the panel due to the angles involved. If you can - tilting the panels will help.

Also be sure that there NO shading on the PV modules - I've seen them mounted under cross bars and even full racks - don't do it. Shading 20% of the PV module can reduce output by 80% usually.

Also be sure that the modules are correctly wired - unless the controller is a MPPT type which can step down the voltage from a higher voltage array to the lower voltage battery - the voltage of the PV array for a 12v battery should be around 20 volts when it is not connected to the controller / battery.

 

[dwh]

Shading on even one cell can reduce a PV module's output by 1/3 or 1/2.

Also, you won't see the array producing much if the battery is full.

 

[Martyn]

I'd start by checking the panel out put before the controller, get a voltage and amperage reading and take it from there.

 

[Jonathan Hanson]

There's a fundamental truth about PV panel ratings you must consider: The factory rating is figured under conditions you'll never approach in the real world. Panel perpendicular to the solar source at noon, in ideal temperatures of 45º F or so. And it's probably fudged a bit at that. Even if you religiously oriented your panel directly at the sun from dawn to dusk, the charge will be less when the sun is lower in the sky and its light is filtered through more atmosphere. PV production also drops significantly in hot weather. I tell people to buy at least twice the PV amperage their calculations call for. So, yes, it's quite possible your panels are operating correctly. Still, it wouldn't hurt to run a system check.

 

[dstock]

I used one of these to diagnose my issues, then you can test at different points as mentioned above to see what you are getting an where the loss happens.

http://www.amazon.com/Watts-Meter-Analyzer-WU100-Version/dp/B001B6N2WK/ref=sr_1_1?ie=UTF8&qid=1418078136&sr=8-1&keywords=watts+up+meter

 

[Martyn]

There's a fundamental truth about PV panel ratings you must consider: The factory rating is figured under conditions you'll never approach in the real world. Panel perpendicular to the solar source at noon, in ideal temperatures of 45º F or so. And it's probably fudged a bit at that. Even if you religiously oriented your panel directly at the sun from dawn to dusk, the charge will be less when the sun is lower in the sky and its light is filtered through more atmosphere. PV production also drops significantly in hot weather. I tell people to buy at least twice the PV amperage their calculations call for. So, yes, it's quite possible your panels are operating correctly. Still, it wouldn't hurt to run a system check.

While there is some truth in what you have said, the major factor is that not all panels are created equal. Some panels produce exceptional amperage even in indirect light while other produce less than is advertized in full sunlight. We have seen panels that produce more amps than they say they are rated for. The trick is to find the good panels.

 

[Howard70]

Controller in Absorption Mode?

In addition to all the good comments above, we've found that we never see our panels full capability because our batteries are rarely drawn down far enough for our MPPT controller to dump full Absorption Mode voltage & current into them. Depending on how your battery monitor is wired, you can get some big draws going (fridge, inverter powering a small heater from the house, etc.) and then see what the total power into the system is. We have a system rated at 420 watts, but we've only seen a maximum of 350 watts going in (the battery bank is 540 amp hours).

Howard

 

[schulz11]

First off, nice build. That is one sweet rig.

Looking at your build thread, you have 3 strings of batteries which is a bad a way to go as they will not charge and discharge equally due to resistance, You should have one string of batteries in series of the amp hour you need and at most two strings. If you can rewired to to higher voltage and run and inverter at 110 you probably will make those batteries last longer.

Also I can not tell if you are running a MPPT Charge controller or the PWM. If it is the PWM you will never see full panel watts.

Panel Placement - having your panels flat, you will also never see full wattage from those panels. They need to be tilted into the sun. Just a little tilt directly into the sun will make a difference, but I know, the way you installed your panels that is going to be hard, but that is ok because you have 600 watts.

My comments above are not to say your system is crap, as I think you have done a great job with it, but the way you wired it up and positioned your panels, you will just never get your full power. Also, to keep those batteries happy, take a look at the charge and discharge rates your batteries need. For FLA batteries you need at least C/20 and a max of C/8. If you have 600 amps in your battery bank you need at least a 30 amp chargers (600/20) for you c/20 and a 75 amp charger for c/8.

 

[dwh]

Looking at your build thread, you have 3 strings of batteries which is a bad a way to go as they will not charge and discharge equally due to resistance, You should have one string of batteries in series of the amp hour you need and at most two strings. If you can rewired to to higher voltage and run and inverter at 110 you probably will make those batteries last longer.

It's one of those unfortunate compromises one has to accept when designing PV systems. These are especially plentiful when designing for mobile applications.

He could have wired the batteries in series to get a 36v nominal string, which the Tristar could handle, but then he'd have to also wire his solar array to produce a high enough voltage, and also get a 36v charger, and also add a converter to get 12v out of it.

Plus, by wiring the battery bank for higher voltage, he won't be able to use the vehicle's charging system to put some amp*hours into the bank while he's out and about driving around, without adding a DC-DC charger (12v-36v boost converter).


And then there is redundancy. Vehicles shake, rattle and roll. Things come apart, things break. If he loses one battery in a long series string, his electrical system is dead in the water. The way he's got it now, if he loses a battery, all he has to do is disconnect that one string and he's back up and running - though with only 2/3 the amp*hours capacity available.

The same problem applies to the PV array.

Panel Placement - having your panels flat, you will also never see full wattage from those panels. They need to be tilted into the sun. Just a little tilt directly into the sun will make a difference, but I know, the way you installed your panels that is going to be hard, but that is ok because you have 600 watts.

That's another one of those compromises. Building a tilting array on a truck isn't all that difficult, but the difficulty becomes bigger faster as the size of the array ramps up. It also depends on how the vehicle is going to be used. If it's just going to sit in one place most of the time, then it might not be too much of a PITA to get up on the roof and tilt the array every time you stop, and again to lay it flat before moving.

But if the truck is going to be on the move to a different place every day or two, then going through all that hassle isn't really worth it. Better to just flat mount the array, let it help out the alternator as much as it can while driving down the road, and accept that the PV system just isn't going to be the 100% optimized ideal that one can shoot for when designing for fixed installations.

 

[schulz11]

But if the truck is going to be on the move to a different place every day or two, then going through all that hassle isn't really worth it. Better to just flat mount the array, let it help out the alternator as much as it can while driving down the road, and accept that the PV system just isn't going to be the 100% optimized ideal that one can shoot for when designing for fixed installations.

Agreed on all points, but this is why he may only be getting 1/3 of is PV to the battery. Still a fabulous build in my opinion.

 

[hitek79]

Thanks for all the great input. Work has been crazy busy this week so sotry for the delayed response.

Last week I got to check on the batteries once, and I had hit about 300 watts that day. Today it's in absorb mode, so it sounds like I won't get max power in today. At least I know it's all working though.

Schulz11, do you have a link to the setup you're speaking of? The way it's wired now I have the positive on battery 1, and negative on battery 6. My understanding is that would charge them more evenly than positive on battery 1 and negative on battery 2. That is also how I have my wiring coming in to the bus.

I head to Vegas next week for the winter, so I'm assuming out in the desert I'll see a jump in power as well. The power build out has certainly been the most challenging part of this whole project. Way too many options and variables.

 

[schulz11]

Schulz11, do you have a link to the setup you're speaking of? The way it's wired now I have the positive on battery 1, and negative on battery 6. My understanding is that would charge them more evenly than positive on battery 1 and negative on battery 2. That is also how I have my wiring coming in to the bus.

http://www.smartgauge.co.uk/batt_con.html

What Batteries are you using - are you still using six - 6 Volt to attain a 12 volt system? How many AMPs do you want vs need?