Another Solar Panel Question

[oldjohnt]

 Mornin gents, okay, over the winter I had several occasions to dry camp and test out the capacity of my 29 Ft Class C (relative low energy user, approx. say 125 to 200 Amp Hours per day) equipped with 470 Watts of flat rooftop solar and four Trojan T-105's (450 Amp Hours) which performed quite well. HOWEVER when the temperatures were 80+ I faced the dilemma to park in the shade where it was cooler,,,,,,,,,,,,,,,, or out in the sun which harvested more solar energy HMMMMMMMMMMMMM. Soooooooooo not being one who likes to discharge my batteries over 30% and one who prefers to camp in the shade when its hot, I ADDED ANOTHER 245 WATT PANEL YESTERDAY (90 cents per Watt) TAKING ME UP TO 715 TOTAL WATTS yayyyyyyyyy  

  QUESTION 1) We know you still harvest energy (albeit significant less)  even in the shade, so if the sun was bright yet you're under total shade my best "guess" is I might harvest say 30% as much as if in the sun. WHAT IS YOUR EXPERIENCE AND GUESS AS TO HOW MUCH IS HARVERTED IN SHADE (all else equal) VERSUS UNDER THE SUN ????? Even when I am parked in my pole barn covered lean to close under the roof I still harvest "some" energy so I'm hoping under a shade tree on a bright day I can keep up.

 My typical dry camping energy use is two powered roof vent fans (maybe 12 hrs per day),,,,,,,,, A small Haier dorm sized fridge 24/7 (maybe 50AH per day) ,,,,,,,,,,,,,Occasional water pump and kitchen vent fan and all LED lights. The onboard Generator is run maybe 30 mins or more per day for hair dryer and coffee and microwave (I prefer that method versus batteries and my 2 KW PSW Inverter) during which time my 80 Amp PD 9280 Smart Charger pumps a good amount of  charge into my battery bank SO OVERALL IM IN GOOD SHAPE even if parked in shade is my best guess. If not so be it lol if 715 watts isn't enough I can run the genset (and 80 amp charger) a tad more morning and evening, I've spent and updated ENOUGH as it is.

  QUESTION 2) I normally, of course, have windows open and BOTH front and rear roof vent fans exhausting air OUT OF the RV top. However I read on some forum its best to have one roof fan blowing air in and the other exhausting air out ????????????? Does that make any sense to yall???????????

 I had to upgrade to a 50 Amp MPPT Charge Controller so I'm selling my old 30 Amp TrakMax Smart 3 Stage MPPT temperature compensated.

 

  Be safe and best wishes

 John T   Back home again in Indiana

 

 

[lenp]

When my panels are shades (even a single "cell") the output drops to less than 10% of full sun.

Lenp

[Yarome]

You know how to fix all those issues at once don't ya?

Ya got wheels.... MOVE outta the 80+ degree weather stoopid. LMAO. 

I don't really know about the fans. If your windows are open then I would just exhaust. It they were closed I might do one in and one out. You're basically looking for air exchange for the best cooling affect.

From my own experience... when it gets really hot out I tend to leave my windows closed and do an in and out fan to pass air. It might just be my imagination, but it seems more effective moving air through the house than it is letting all the hot air from outside in.

[oldjohnt]

 Thanks yall, while in Florida this past winter especially late March and early April  (warmest overall I've seen in 8 years there) even if it was a bit uncomfortable hot during the day, it cooled enough at night to sleep where in the rear bedroom I set the roof vent fan BLOWING IN to get a slight down breeze which seemed better then it exhausting. I will give Yarome's windows closed, one fan in other out a try, never thought of that....

 I guess as far as solar performance in the "shade" only time will tell, but based on how it still yields even under my pole barn roof and past experience Ima thinkin with 715 Watts I will be okay even in shade on a bright day. Surely I can keep up if I limit my energy use to maybe 100 to 125 Amp Hours per day. If I can harvest say 14 charging amps for 8+ hours YEAH RIGHT YOU SAY LOL but that 30 minutes of generator and 80 amp charger per day may well keep me over the top. Again TIME WILL TELL

 Its fun to watch some of the You Tube videos of RV's at "Burning Man" to see all the swamp coolers and other methods used to keep cool in the blazing hot sun where they don't allow generators.

 

 Thanks, keep safe yall

  John T

 

[oldjohnt]

UPDATE, Today it was raining and all clouds and not any sun in sight (took RV out under pole barn) but my batteries still remained at 100% SOC and floating at the 13.6 volts the solar charge controller is set at, so Ima thinkin on a sunny day even under shade my 715 watts is gonna do the job yayyyyyyyyyyyyyyy if not I can fire up the genny and 80 amp charger for some time.

 

 John T

[baphenatem]

Much of the effect of shading depends on how the modules are wired together, i.e. series or parallel. Parallel connected modules are less affected than series connected ones. The output of the modules themselves are fairly linear, down to about 20% of full sun, at which point the bottom essentially falls out and things quickly drop to zero. If you find that you are not able to keep up with your energy usage under shaded conditions you might want to consider a set of portable modules that you can put out in the full sun. A couple hundred watts of well positioned solar can go a long way and quite often outperforms larger flat-mounted arrays.

[oldjohnt]

Thanks baph, Yep my three panels are connected in parallel and all have similar footprints. From what I observed yesterday (my charge level despite rain, full cloud cover with no sun in sight) on a bright sunny day even if under total shade I will be able to harvest enough energy to meet my meager demands plus replenish my battery SOC. That's why I upgraded to 715 watts because I prefer NOT to park in full sun when its hot. Although I don't need or want to mess with portable panels, you are indeed correct, a well positioned 100 watt aimed portable can harvest about as much in a day as a flat rooftop 200 watt in my experience even if you have to move it a few times a day. Had I rigged a system to tilt my panels I could have got by with the 470 watts I had, but I didn't want all the mechanics and structural and fabrication issues and opted instead to spend $220 for a third panel.

Thanks again, best wishes. Gotta love solar if you're a dry camper such as myself

John T

[lenp]

John,

Do you have a way of actually measuring the current going to your batteries?  I invested in a battery monitor system by Bogart Engineering http://dev.bogartengineering.com/products/pentametric

Very helpful in determining EXACTLY how well your system is performing.  No more reading battery volts and trying to figure SOC.  The PentaMetric keeps track of every amp in and every amp out so you ALWAYS know SOC.

Lenp

[oldjohnt]

lenp, Thanks, yes indeed my solar charge controller has a digital display of charging current, battery volts, % of SOC, panel volts and watts. In addition, I have another digital voltmeter on my house batteries visible while driving. Never have too much info right and I (Engineer and Geek per my daughter lol) actually enjoy looking at that info throughout the day.

John T