Wednesday, November 13, 2013

New Solar - Better Than The Old Solar - PART 4

Nope, Didn't Take Any Rain Photos!
    Rain. Rain. And more rain. Bleh. You know, it's REALLY difficult to test Solar panel output when it's dark, cloudy and raining! I had almost a whole day before it got nasty and cold. Oh, yes... wind too. While I did manage to get some testing done, I really wouldn't consider it final. It had its upsides though! Testing in bad weather can show the weaknesses in any system. Especially solar charging systems. If everything works in cloudy, rainy, overcast and miserable weather, than it's a fair bet that it will work better in beautiful, sunny and cloudless days in the summer!

Example Stats (Prototype)
Even with the horrible weather, I was getting a significant amount of current (Amps) from the panels. In bright sun, we theorized that I would get around 8.5 Amps per panel, so for all three I should have about 25.5 Amps flowing at around 20-24 Volts. This is about 20% (or more) better than the previous aluminum backed, China sourced panels. Since I am using an MPPT controller, I can get "extra" amps out of the system if the voltage is high enough. I've seen upwards of 32 amps into the batteries from the original prototypes in full sun. In, not so great, overcast weather (all I have to work with this week!) I have seen 22.7 amps into the batteries from the new prototypes.
The production panels should be a little bit better.

Temporarily Mounted Prototype
What does all this actually mean? Well, if you left the system alone to do it's thing, you'd have a system that would likely fill your batteries each day (from the previous night's use) before sundown. In a typical RV with 2 deep cycle "house" batteries you get around 100 amp/hours per battery. That gives you 200 amp/hours to play with each night. Of course, the recommendation for Lead-Acid wet cell batteries is to never discharge them beyond 50% capacity. So, we're back at that 100 Amp/hour rating for a typical two battery system. Now let's say you use all 100 amp/hours in a given night. You have to put that back in the next day. Due to inefficiencies in charging and how batteries are actually charged you'll need to put back around 120% or so of the capacity. Figure you need to generate 120 amp/hours of power to fully recharge the batteries. It's a little bit more complicated than that... with tapering charge and such, but we'll ignore that for now.

45 Minutes After Dusk With 1 Panel Connected
If your Solar charging system is generating 25 amps every hour (amp/hours) you will get 100 amp/hours in 4 hours and 125 in 5 hours. So, on a typical Summer day with 7 or more hours of sunlight you would be charged in a bit less than 5 hours. After that, you can have the rest of the day to use "free" power. I use the extra time to heat water** (slowly) for my hot water system, but you can use any 12V item without drawing your batteries down.

**Will outline the hot water system in a later article.

My 2 Battery System
What if you have 4 batteries? OK, same math applies. 4 batteries at about 100 amp/hours per battery equals 400 amp/hours total, with 200 amps usable. If you use all 200 amp/hours, you'll need a bit more than 8 hours to fully charge with the basic three panel system. Personally, with even basic conservation and LED lighting, I don't believe you'd need that much power, but to each his own! This is doable in the summer, but cloudy days, rain, etc., will prevent you from fully charging. In my case, I just run the generator or drive a few hours and let my alternator finish up the charge. Or... you could simply add another panel. Another 8.5 amps or so, would speed up the process. The system I have set up is designed to be modular.
What I use To Tally Remaining/Charging To The Batteries
As always, before you buy, do an energy audit. Figure out (REALISTICALLY!) what you will draw out of the batteries in a given night and match that with the solar charging system. This will result in a system that will work, essentially, transparently. With little or no user intervention. My old system worked flawlessly, until the panels died. The new panels, made in the US and with a warranty will be much better. So far, they have been!

I'll be doing additional testing over the next week. Hopefully the weather will cooperate. Since the sun is so "weak" now, I should be getting worst-case-scenario numbers. That will give me a good indication of true performance.

Once again, STAY TUNED!

Be Seeing You...Down The Road,

Rich "The Wanderman"

*See Part - 1
**See Part -2
***See Part - 3

See Original Article


  1. Please, Rich, battery capacity is rated in AMP-HOURS, not in amps. Amps is a flow rate into an appliance or from the panels. 25 amps into the batteries charges 100 amp-hours in 4 hours time. You can use 100 amp hours at a 5 amp consumption rate fpr 20 hours till it is used up. Of course you don't want to use more than 1/2 the battery capacity if you want long battery life.

    It is really hard to educate consumers on proper battery care when people are reading mis-use of terms.

    1. Anon,
      Wow, I had no idea a typo would generate such a response! All fixed now.

      Rich "The Wanderman"


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