What’s Your Angle?

I got a text from my friend Courtney, a few days ago. A while back he bought a bunch of Mobile Solar Generator stations at bankruptcy auctions. If you look back to my TURBOBEAST post you can read about the adventure of moving those things back to his house in North Carolina.

These contraptions are handy, but outdated.  He has removed the 250 watt panels and hung bigger panels, boosting the nameplate power from 2500 to 3800.  Only, he wasn’t getting 3800.

“So at 35 amps/54v, I’m getting 1900 watts out of my 3800 watt system (50%).  That sucks.  Is it because of the winter sun angle?  Panels are flat to the sky.”  

Yup.  Mostly.

A Suncalc screen shot
Suncalc screen shot.  Use the angle of elevation to determine how much effective sun is on your panels.

The new panels are huge compared to the old 60 cell panels.  Wider and taller.  Only 8 will fit.  He’s working on a modification to the articulated mount, but with the old mount they are not articulating very far without banging against the monstrous battery pack.  The panels on Sun King are flat, too, and winter is not my best season for charging.  Let’s look at a little math—I hate math, but it has its uses–and see if his stuff is working right.

I’m at latitude 30-ish and he is around 35, I think.  He thinks 33.  I’m going to just use the Raleigh, NC, airport to search in SUNCALC.  Suncalc is a free phone app you can download or you can use your computer, going to suncalc.org.  With this program, you can find the arc that the sun travels at any time of year, which you will find handy in case you can take down trees to catch a few more rays.  In THIS use, though, we will use it to determine the elevation of the sun, or the angle to the panels.

In this case, his panels are at 0 degrees elevation.  On your roof, you may have more of an advantage.

I searched the app on my phone for the airport, slid the timeline to high noon and it indicates the altitude is 40.12 degrees.  Now, if he had his panels angled at 40 degrees, facing south, he’d be dead-on to the sun.  Subtract your panel angle from the sun angle and whip out the calculator.  We have some trigonometry to do.  Easy trig, so don’t panic.

Turns out, you turn my phone sideways in the calculator app you have trig buttons.  Punch SIN (Uh, that’s short for SINE.  It isn’t naughty.) and then punch in the 40 degrees and the answer is…..  .64, meaning 64 percent.

Now that we’ve touched on the basics, let’s see if Courtney has anything to worry about.  .64 x 3800 = 2432 watts.  That’s the best he could hope for.  There could be a bit of high level haze (we almost always have that in NW FL), the trailer might not be level or the panels might have a bit of dust.  Additionally, the charge controller uses a little and he could have a little resistance in the system somewhere.  I wasn’t there, but time of day is critical in such a calculation.  At 10 am or 3pm, he’d certainly be missing half the power.  Anyway, if everything is as he says, panels are truly clean and level and sky clear, missing 632 watts seems a bit much.

I’d say, check the connections.  It is easy to not seat the contacts all the way when assembling MP4 connectors.  Checking with fingers or an infrared thermometer might find a warm connection.   Ask Walmart what can happen if you have the wrong or loose connections to the panels.  They have been known to have rooftop fires, losing more than just a few hundred watts of power.

Just for grins, I thought I would check my sun angle, too.  With a high noon angle of 45 degrees, best my boat’s flat panels could hope for is 70%.  Between the gloomy weather and the low angle, the boat has sometimes struggled to keep up with charging my vehicles this winter.  Lately, the days are starting to get longer and cold fronts have brought some crystal skies, so everything is caught up.

solar powered launch Sun King is a mobile power station
Yes, it is a boat, but it has a 16.6 kwh battery and a 5kw inverter. Useful during a power outage.

Yes, you need to check all the angles to make sure your system is performing well.


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