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Topic ClosedNew Solar Power System for Rpod
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Rustler View Drop Down
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Joined: 07 May 2016
Location: S. Oregon Coast
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Posts: 100 		Direct Link To This Post Topic: New Solar Power System for Rpod
    Posted: 30 Aug 2016 at 12:44am
I've finished installing the solar charging system on my Rpod. An extra 185-watt, 36-volt solar panel was employed along with a Morningstar SS-MPPT-15L charge controller. The solar panel will be deployed on the ground to enable placing it away from any shade on the Rpod. 

While the panel produces 36 volts at maximum power point, it is what's called a 24-volt panel, since it can charge a 24-volt (or less) battery. The maximum power point tracking charge controller down-converts the 36 volts to a level appropriate for charging a 12-volt battery. Since power in (nearly equals power out (at 95% efficiency) when voltage is reduced, the current increases.

The panel produces around 5 amps at 36 volts. In runs of 10 gauge cable up to 75 feet, it has less than 3% voltage loss due to wire resistance. Also since power dissipated in a wire varies with the square of current (power= current2 X resistance), the loss is considerably less. If I had used a 12-volt panel (which operates at 18-volts) the current would be at least double (185 watts รท 18 volts = 10 amps). With double the current, power loss with a 12-volt panel is quadrupled (22 = 4).

While medium power 24-volt solar panels can be a bit difficult to find, the advantages are worth the search:
  • Less percent voltage drop for a cable run of a given length
  • Less lower loss due to cable resistance
I have located a nice 24-volt, 120-watt panel (SLP120-24U) from Sunshineworks.com for $274, delivered. I will be ordering this panel soon. Its reduced weight compared with the 185-watt panel will be appreciated - 24 lbs. versus 37 lbs. And 120 watts should be sufficient for most usage.

But for now I've been testing the 185-watt panel. Even on a cloudy day it puts out 4-5 amps. In full sun it can deliver around 14 amps at 12.5 volts. 

I have quite a few photos of my solar charging system that I'd like to share, but I've struggled to post them. Even when I downsize them to less than 1024K, they are still enormous, requiring scrolling left/right and up/down to see the entire photo. Here's an example of a photo that's only 897 KB:



So how do I post a photo that can easily be viewed?
Russ
2009 Toyota RAV4
V6 w/ tow package
2016 Rpod 171 HRE
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johnmaci View Drop Down
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Posts: 202 		Direct Link To This Post Posted: 30 Aug 2016 at 7:45am
If you open your photos in MSPaint, then go to resize, pixels, and choose something like 800x600 or 640x480 you should be good to go. 
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Podster View Drop Down
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Posts: 1108 		Direct Link To This Post Posted: 30 Aug 2016 at 10:31am
A super easy way to share photos on line anywhere is to store them on a google account or flicker or some other photo share and then just post a link.  
Cliff & Raelynn
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furpod View Drop Down
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Posts: 6128 		Direct Link To This Post Posted: 30 Aug 2016 at 12:16pm
Originally posted by Podster

A super easy way to share photos on line anywhere is to store them on a google account or flicker or some other photo share and then just post a link.  


I like photobucket.. free, easy. upload there, open, select the link, copy and paste here..

Random photo from my bucket:
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Rustler View Drop Down
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Posts: 100 		Direct Link To This Post Posted: 30 Aug 2016 at 9:13pm
Thanks johnmaci, Podster & furpod for the tips. I'll use the Mac's Preview App to resize my photos. 
Russ
2009 Toyota RAV4
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2016 Rpod 171 HRE
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Rustler View Drop Down
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Posts: 100 		Direct Link To This Post Posted: 30 Aug 2016 at 11:19pm
Originally posted by Rustler



While medium power 24-volt solar panels can be a bit difficult to find, the advantages are worth the effort:
  • Less percent voltage drop for long cable runs of a given length
  • Less lower loss due to cable resistance
I have located a nice 24-volt, Solarland 120-watt panel (SLP120-24U) from Sunshineworks.com for $274, delivered. Today I ordered this panel for arrival in 3-4 days. Its reduced weight compared with the 185-watt panel will be appreciated - 24 lbs. versus 37 lbs. And 120 watts should be sufficient for most usage. Also the smaller size (versus the 185-watt panel) will allow stowing the solar panel in the shower while traveling. The 185 watt panel had to be carried on the dinette bed, since it was too large to fit on the queen bed or in the shower. My wife will be making a canvas carrying bag for the new panel to protect it and the Rpod's woodwork. 

But for now I've been testing with the 185-watt panel. Even on a cloudy day it puts out 4-5 amps. In full sun it can deliver around 14 amps at 12.5 volts. 

While waiting for my new 120-watt, 24-volt panel to show up I began wondering if I could hook up my two 24-volt panels in parallel:
  • Schuco MPE 185 MS 05 - 185-watt, 36.1 volts at maximum power point
  • Solarland SLP120-24U - 120-watt, 34.4 volts at maximum power point
My charge controller is a Morningstar Sunsaver MPPT-15L. So I sent a quick question to Morningstar Tech support, and got a prompt reply:

 As long as the max. power point voltages are within 10%, things should work OK. The controller will find the common voltage point to maximize the combined output. While the combined output of the two panels (305 watts) exceeds the capability of the controller (200 watts) it would not cause any harm. The output would always be limited to 15 amps into the battery, no matter what the combined output might be. But there are some advantages to hooking up both panels (or using a single panel with greater than 200 watt output):
  • When the sun is not at full height in the sky (early and late in the day), the 305-watt combination would put out more charge current than either of the two panels could do separately. But when the sun is closer full height, and the combined power output exceeds 200 watts, the charge current would be clipped at 15 amps.
  • With cloudy or hazy sky conditions the two panel array would produce more power subject to the same limitations as above.
  • During circumstances where there is a higher DC load the higher array production could speed up recharge or reduce how much the battery is discharged. I can envision emergency situations where the use of Ham radio for communication could put a significantly higher load on the DC system.
The following text and graph from a Morningstar white-paper shows the benefit.


I've also been thinking about a better way to tilt the new panel up toward optimum angle. This will involve some aluminum L-channels attached to a hinge point near the top edge of the panel. These could be swung out from the panel bottom to contact the ground. A short length of stainless steel cable will prevent the brace from spreading back too far. This should be both lighter and more easily adjustable than the metal conduit I've used on the 185-watt panel. I'll post some photos when this is completed. 
Russ
2009 Toyota RAV4
V6 w/ tow package
2016 Rpod 171 HRE
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Rustler View Drop Down
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Posts: 100 		Direct Link To This Post Posted: 31 Aug 2016 at 5:20pm
Originally posted by Rustler

[QUOTE=Rustler]
Below the circuit breaker is a meter which displays solar system parameters - charge current, battery voltage, charging watts and a fourth display (lower left quad) which cycles through max. volts, amp-hrs of charge, peak amps, watt-hours & watts peak. I'll likely add a high current capacity DC toggle switch to disconnect the meter from the battery. This will allow resetting the meter's parameters (particularly amp-hours and watt-hours) back to zero at the start of each charging session.

I've decided not to install a switch to reset the meter. It's just easier to briefly disconnect the Powerpole connection as shown below.


When the Powerpole is reconnected the meter is reset to begin determining charge amp-hours, watt-hours, amps-peak, etc. for the next charging session. 

This should work as well as an inline switch with a lot less hassle.
Russ
2009 Toyota RAV4
V6 w/ tow package
2016 Rpod 171 HRE
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