PWM or MPPT?

[Flybob]

Which ever way you go. I would get twice the controller capacity you think you need now. If you ever want to add more panels, you will not have to buy a new controller. The incremental cost of a larger controller is much less than the cost of a second or new controller.

[Paulie1138]

IF, and only IF, you are going to us an MPPT, consider commercial or higher end residential panels. You will get more amperage, less line loss from the higher voltage, and price is lower, due to the glut of these on the market. Since there is less line loss with the higher voltage, one could save a Bit by buying a smaller gauge interconnect wire. I feel this is not a place to cheap out, bigger conductors will rule!

I just saw on C.L. here in the PHX area, 315 watt 9.9 amp 44v panels for under 100. These are used with less than a year on them. Using MPPT, you theoretically could get as much as 30-35 amps after the MPPT converts it down to 12 volts. From just one panel! Also, the higher voltage panels, in a side by side test will out produce the lower voltage panels in cloudy and shaded conditions.

However, they are usually a bit larger by a few inches, and a bit heavier than the 12 volt panels. I did my comparison under my shade structure with 3x 100 watt renology 12v panels, borrowed from the neighbor who ground deploys his. His are 4 years old. Placed my one 250 watt 48v panel in the same spot as the center Renology. My panel was used, about 10 years old....but free. Hooked them in series or parallel, the one panel had almost double the current of the three renologies. Both tests were connected to the same Morningstar MPPT 60 controller connected to my inverter with full batteries, running a 1200 watt hair drier. I did not repeat this test in full sun, out from under the shade structure. So, results may approach the same there. However, the one panel was only a bit larger than one Renology, so took up a lot less real estate than the 3. The renologies claimed 5.29 amps per panel at 12 v. The panel I used, 1x at 250 watts, 48 v, 9.8 amp. Factor this in when the MPPT controller drops the voltage, your current will increase. Example, assuming perfect conversions, divide 48 by 4 to get 12v, the current will multiply by 4. Means you could get 30-35 amps after the MPPT does its thing.

Charging the batteries is voltage and current dependent. The Higher voltage panels will have a higher voltage to begin with to trigger the charging electronics. So, the current after conversions should typically be higher.

So, with the above information, you can see why I went the way I did. Maybe I am missing something, but I saw no downsides with going at this just a bit differently. I can see that, if you choose to solely ground-deploy, the extra weight and size of the conventional panels would have over the 12v panels. If you are not going to boondock for long or much, then 1-2 100 watt 12v panels and a PWM will be great to help keep you topped off. If space is not a problem, 3-6 100 watt 12v panels and an MPPT controller. Space being an issue, mount 2 or more high voltage panels on the roof, make provisions to wire in additional 12v ground panels in series with each other, then parallel with the rooftop array, and MPPT. Remember to use blocking diodes whenever you hook up multiples of panels. I went ahead and installed them in my array to future proof, or if one panel does get shaded from the other. They are really cheap, just a few $ each.

Hope this all makes sense, and I aPAUL-ogize for getting wordy! I hope this helps anyone out when designing their system.

[TitanMike]

Thanks to all that have offered opinions and advice. I've made my decision.

After looking at my actual power consumption over a 4 day trip, and determining my daily Amp Hour per day requirement, I decided to buy a 160 watt Suitcase unit:

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1

I wasn't familiar with the company but for that matter I am not familiar with any company in the Solar business. I did some research and their panels get good reviews. In YouTube video reviews they appear to be quality built, even standing up to shipping abuse due to the cheap packaging

The only unknown is their controller but in the video review I watched as the unit was plugged in and began to charge a single battery at a respectable rate.

The Suitcase panel is reasonably sized, has reasonable output (about 8.5 amp at max sun and OCV ~18v), and appears to have reasonable construction quality.

I already have a Victron Battery monitor (BMV-702 with BT Dongle) so I can monitor charging parameters. The portable panels can be aligned to the optimum angle for location and sun position so they're actually more efficient than flat, non adjustable, panels on top of an RV. I can handle the hassle of unfolding and aiming.

I've found several Smartphone Apps that will use the phone's GPS to determine location and calculate the optimum tilt angle and direction (if your phone has a compass in it). They even use the phone sensors to determine the angle. With one app you merely update your position then place it flat on the front of the panels. Move and tilt the panels until the compass arrow points due North and the angle causes the display to turn green. I suppose one could also connect a multimeter to the panel output (input to controller) and aim panels for highest voltage output. This could be even done several times per day if one needs the maximum power output. Supposedly "tracking" can raise the efficiency of a panel array by 30-40% if adjusting both Tilt and Direction as the sun moves. Maybe not as much if one only moves the panels 2-3 times per day but I'm sure the increase would be noticed over time.

Doing this would also be of more benefit if using an MPPT controller or so I've read.

As for my choice of this panel setup versus Renology, Zamp, or some panels off ebay or Craigs List, it was fairly simple. Company selling it is a REAL company with a presence in the solar power industry. The setup is using monocrystaline panels which are purported to be the most efficient. Even if their controller needs to be "junked" I can add a Victron MPPT and still not even reach the price of a Renology 100 amp setup with only a PWM controller.

Delivered to my door, including shipping (actually free with Prime) and Sales Tax is just over $300. 60% more power available, approaching that of the Renology Eclipse (200 watt) which would end up costing me we well over $700.

I can't argue with MORE, MORE, MORE but for my needs it would be like buying a 1 Ton truck to haul my walk behind law mower. I don't run my microwave from an inverter. Running my lights, furnace, water pump, and Entertainment (TV,DVD,Stereo) use about the same power as this suitcase is capable of providing on an average day. I figure it will negate my need to run my generator for battery charging, running it only for the A/C on sweltering days. Only adding 24# to the amount of gear I will be packing so that's a benefit as well.

What's interesting is that this company supplies their smaller "suitcase units" with MPPT controllers with the 160 Watt panel setup with a PWM. Apparently they feel they can make the smaller panels perform like larger panels by wasting less.

BTW, first modification will be to move the controller from the back of the PV panel to my "Electrical Compartment" where I have two bus bars closely connected to the battery. Want to minimize line loss and keep the controller out of the weather. Who knows, the supplied PWM controller may be just fine.

It will show up Wednesday and by Thursday afternoon I'll know if it was a good deal or a mistake. If a good deal I'll be at least $400 ahead of where I'd be if I'd purchased a Renology Eclipse. Zamp is so overpriced they weren't even part of my consideration.

[Paulie1138]

Glad to hear we were of assistance. Enjoy the benefits of solar!