Thursday, April 16, 2020

Fixes and Fails - Solar

Shortly after we got our 2019 Thor Palazzo 33.2, I started looking at options for installing Solar panels. After opening the Microwave once while on the Inverter and watching the light flash like a strobe light, I knew I also needed to upgrade the Inverter to Pure Sine Wave.

First, let me start with what I learned:

There are two types of Solar charge controllers, PWM and MPPT.  The PWM controllers require solar panels that run at the same voltage as your batteries and really just manage the charge cycle.  MPPT controllers allow you to run the solar panels at a higher voltage than the batteries and it converts the higher voltage into more amps into the batteries.

Solar panels have three important characteristics, Watts, Voltage, and Maximum amps they allow.  The Watts identify the maximum power you can get from your panel under optimum conditions, such as sun high in the sky and panel at 90𝇈 to the sun.  Most solar panels I have seen allow about 10 amps of current and are rated for 12 volts nominally (which actually could produce up to 20 volts).

Our coach came with a 30 amp PWM controller and one 100 watt solar panel, which could produce 20 volts and about 6 amps.  The panels were connected to the PWM charge controller over 10 gauge wire, which should be able to support 30 amps, so I could add two more solar panels to this configuration for 300 watts.  Now since it is a PWM controller, I would need to connect the panels in parallel, which would keep the voltage the same, but increase to amps to a possible 30 amps.  Any more panels would require that I have a larger gauge wire to support the additional amps in addition to needing a larger charge controller.

Since I was going to need a new charge controller anyway, I elected to go with a MPPT (Multi-Point Power Tracker) controller.  I choose the Victron MPPT 150/85, which would allow me up to 150 volts from the panels and 85 amps to the batteries.  Since I have only 10 gauge wire running from the roof down to the charge controller, I will need to limit my amps from the solar panel to 30.  I wanted to install six of the 160 watt Renogy monocrystalline panels (polycrystalline are less expensive, but also less efficient), which can produce 8 amps each, so if I just connected them all in parallel I would have 48 amps.  That would probably burn through those 10 gauge wires, so I elected to connect them in two runs of 3 panels (2x8 = 16 amps).  Now running 3 panels in series will keep the amps the same as one panel, but multiply the voltage by 3 (3x22.9 max volts = 68.7 volts), which is well within the 150 volt range of the Victron MPPT 150/85.  The downside is that if any one of those 3 panels gets shaded, it reduces the current of the entire string. 6 panels at 160 watts each would give me 960 watts of power and 960 watts / 12 volts = 80 amps, so I need wires from the charge controller to the batteries that can handle 80 amps DC.  I googled it and decided that I would need 2-0 gauge wire to connect to the batteries.

OK, have I lost you yet?
  • PWM vs MPPT
  • Increase Volts by connecting in series (Positive to Negative)
  • Increase Amps by connecting parallel (Positive to Positive & Negative to Negative)
  • Shade on any one panel will reduce the entire string in series
  • MPPT controller will take higher volts and produce more amps to the battery
  • 2-0 battery cables
OK, now that I have the Solar all planned out, add it to my Amazon cart along with cable, connectors, and mounting brackets.

The inverter that came with the coach is a modified square wave inverter, which means that it produces alternating current that basically just jumps from positive to negative (little more complicated, so google it for more info).  A pure sine wave inverter transitions from positive to negative gradually, which means it creates a curved wave that transitions from positive to negative.  This is the type of power you have in your house and exactly what most electrical equipment is designed to use. 
Old Magnum ME2012 Inverter
Since I wanted to upgrade to a Pure Sine wave inverter.  I discovered that Magnum makes a lot of their inverters in exactly the same form factor, which means I could replace the Magnum ME2012 2000 watt inverter with the Magnum MS2012 (Pure Sine Wave) 2000 watt inverter and it should fit in the same place with the same connectors.  Plus I found an Open Box one on Amazon for $200 off.  Into the cart. In retrospect, I wish I had also upgraded to a 3000 watt inverter, since I found that the Microwave uses close to 2000 watts all on its own.

Next, I started looking at batteries.  Our coach came with four 6 volt golf cart batteries.  They created 2 strings of 2 batteries each and then connected them in parallel.  So the two in series up the voltage to 12 volts and connecting those 2 strings in parallel doubled the Amp Hours.  Amp Hours (Ah) is basically how many hours the batteries can provide a certain number of amps.  As near as I can determine the golf cart batteries were rated for 170 Ah, so double for the 2 strings and we have 340 Ah.  That should let me run 340 amps for 1 hour or 34 amps for 10 hours.  But hold on, these are Lead Acid golf cart batteries, which means that using more that 50% of the capacity can permanently damage the batteries.  So realistically, I have 170 Ah before I would need to charge.  I can tell you from personal experience that the Residential fridge and the furnace (with over-night temps in the 40s) will use all of that over night!  I will post about that later.

Lithium Iron Phosphate (LiFePO4) batteries do not have a 50% usage limitation, so I started looking for the best option that would fit in my space and price range. I looked at purchasing cells directly from China and wiring up my own batteries, but Lithium batteries have precise parameters that need to be maintained and I did not feel comfortable buying a Battery Management System from China, where a failure could destroy my considerable investment in these batteries, so I finally decided that I wanted the Battleborn LiFePO4 batteries that have a 10 year warranty and built in BMS, but at $1050/each (I wanted 6), they were outside my budget.  So, I decided to wait, look for another post on batteries.

Our youngest son, helped us install the Solar and Inverter.  Truth be told, we helped him.

Un-packaged and inspected and installed brackets
I was short enough brackets for one panel and also needed cables that would connect to the MC4 connectors on the roof.  Amazon Prime 2 day delivery to the rescue!
We left the original 100 Watt panel connected
We bought about 10 tubes of the self leveling Dicor sealant and for every bracket, we wiped the area with alcohol, created a puddle of Dicor, set the bracket in the puddle, secured with self-tapping screws, and then covered with another puddle of Dicor.  Of course we were doing 6 brackets at once on each panel, so a lot of holding the panel in place with the other person cleaned and put down the first puddle.  We also bought a package a UV resistant screw down zip ties for holding cables and attached in the same manner.  You can see in the lower right of the picture, where we used a pair of splitters to combine our two strings into the connector that feeds down to the charge controller.  Rather than remove the old 100 Watt panel and risk having extra holes in the roof, we decided to just un-plug it and leave it there.

Blue thing is Victron charge controller, White is MS2012 inverter.
The charge controller was bigger than we expected, but we were able to mount it in front of the inverter that we replaced.
I mounted it upside down
Connected the charge controller to battery

We manufactured a stand-off by bolting together a couple of aluminum angle pieces and we installed an 80 amp fuse between the charge controller and the batteries

Voltages all checked out, but we were parked under a big tree, so not able to get a feel for how much power it would actually produce until a few days later.  I fired up the microwave while on batteries and quickly saw it pulling over 500 amps from solar.  I have since seen over 800, but you have to be in just the right position and it won't keep that level up for long.  Good news is that we can get over 200 watts even on a cloudy day.  The Victron charge controller has Bluetooth and there is an App to configure and monitor it.

Early morning on cloudy day
Noon after sun came out

I know someone is going to call me out because the Watts / Volts is not equal to the Amps.  The solar charge controller uses some of the power, so it will not be 100% efficient.  My system could support another 3 panels, but at that point I would have no room to walk around on the roof and would also have the possibility that it could produce more power than the 80 amp fuse we installed.

Lot to cover and already a long post, so comment if you have any questions.



  1. Probably not cost effective when you have ready access to power.

  2. I think I will continue just paying my electric bill every!roofers say solar panels can damage your roof

    1. I needed it for when I don't have power and no damage to my roof, which is no a shingle roof, occurred