A Radio Amateur’s Guide To Solar Panels.

One of the perceived barriers to off grid amateur radio is the selection of solar panels. Most hams fall into one of two categories: Those who spend many hours researching the various options and end up more confused than when they started; and those who impulsively buy whatever is cheapest/easiest to find and end up with poorly chosen solar panels that do not meet their needs. This does not have to be hard. It’s time to cut the fluff and give radio amateurs the information they need to select solar panels that work for them and their wallet.

The Big Three.
There are three basic types of solar panels: Mono crystalline, poly (or multi-) crystalline, and thin film. The basic design of solar panels has been the same for decades. Advancements in the composition and purity of silicon, which is the main ingredient in solar panels, has made them more efficient. Improved manufacturing processes and economies of scale has made them cheaper. Solar panels that cost over $6.00 per watt a decade ago are now available for less than $2.00 per watt. Solar is on the cusp of becoming mainstream.

Monocrystalline Solar Panels.
Monocrystalline panels use the highest quality silicon cut into individual cells (thus the “mono” designation), which gives them their characteristic “cell” appearance. Because they use the highest grade silicon, they are also the most efficient and have the benefit of more watts per square foot. They are generally considered to be the “best” solar panels. As one might guess, they are also the most expensive.

Poly (or multi) crystalline solar panels.
Instead of cells being individually cut from a silicon ingot, the polycrystalline manufacturing process involves pouring melted silicon into a mold. They can have either a “broken glass” appearance, or look like one solid panel with thin wires to define the cells. The result is a less expensive but also less efficient panel. Polycrystalline solar panels are by far the most popular and account for a majority of the market.

solar panels


Mono vs. poly: “Better” is not what you think.
The technical differences between mono- and poly crystalline solar panels are very subtle to the radio amateur. Mono panels produce about 4% more wattage per square meter than polys, which makes them smaller for the same wattage output.

This sounds like it might matter, but with solar panels, better is not always better, especially when cost is factored in.

Example: A 100 watt Renogy polycrystal panel commonly sold on line costs $124.00 and takes up 1055 square inches of space. Renogy also makes a monocrystal version of this exact same panel, except that it is $150.00 and 873 square inches.

Therefore, radio amateurs have to ask themselves: Is having a mono crystal panel that saves only 182 square inches over its poly cousin worth an extra $26 (per panel) for the same amount of power? Mono crystal panels also have a longer service life and a greater tolerance for extreme temperatures, but don’t read too much into the benefits: These low single-digit percentage advantages would mean something if you were building a 100 acre commercial solar farm, but for the off grid ham, what you get for what you pay in a monocrystalline application is very hard to justify.

Thin Film Solar.
The third major category of solar panels is thin film solar. These come in a few different variations, but the common theme is a silicon photoreactive semiconductor applied to a substrate, usually thick plastic. The fancy wording is simple in principle: They take the solar silicon material and use adhesive to stick it to a flat plastic base, kind of like a bumper sticker.

The subcategories of thin film solar panels are: amorphous silicon, cadmium telluride, and copper indium gallium. Thin film solar panels are often collectively referred to as amorphous panels regardless of their actual composition. There is not much difference in performance between the three, and when buying thin film solar panels the package information may not necessarily specify which type it is. Don’t worry; it doesn’t really matter.

Most of the small panels sold in hardware and sporting good stores are from the thin film family. They can be identified by a flat black color in a lightweight (sometimes plastic) frame with wires forming lines across the panel.

Thin film solar panels have three big advantages: First, they are inexpensive when used at low power levels (more about that in a moment). Second, they are the easiest to find and can be bought almost anywhere. Lastly, they can be flexible and formed into many shapes. Portable fold up/roll up solar panels popular with campers & outdoorsmen are made with the thin film process. If you cannot lug around a hard, inflexible panel in an aluminum frame, then thin film is the solution.

The main disadvantage of thin film solar is low efficiency, usually below 10% as compared to 13%-19% for monos and polys. Thin film solar panels give diminishing returns as the power level goes up. At higher powers above 60 watts you could end up with thin film solar panels that are substantially larger and cost more than a poly or mono crystal; as the technology improves this dynamic is becoming less of an issue.

Although thin film is considered the lowest class of solar panels, do not take that as an automatic deal breaker. There are many applications where thin film is the only and best option.

So what should you buy?
What to buy is a personal decision because everyone’s needs are individual. If ultra-portability is not a major issue, then polycrystalline solar panels provide the best value for the dollar. I personally use only polycrystalline solar panels for my permanent home system. Because of their popularity, they come in many sizes and are very competitively priced. Their slightly lesser performance compared to monocrystalline panels is more than offset by the reduced cost.

If you must have the very best and don’t mind spending the money to get it, or your space is so limited that even a few square feet makes a difference, then monocrystal solar panels are for you. Keep in mind that “the best” is going to cost substantially more than second best and give you only very minor increases in performance.

If you need portability, want to fold or roll the panel, or if the panel will need to be formed into an unusual shape, then the only option is thin film. I use a 25 watt thin film panel to run my portable QRP radio and get great results. The panel folds neatly into a small package and fits in a backpack.

What you need to know–key points.

  • There are three main types of solar panels: monocrystalline, polycrystalline, and thin film.
  • Monocrystalline solar panels use the highest quality silicon, produce the most power per square foot, and are less sensitive to temperature extremes. They are also the most expensive.
  • Polycrystalline solar panels are the most popular and come in the most varieties. They do not perform as well as monos, but the differences are not meaningful to the off grid ham and are more than offset by their lower cost.
  • Thin film panels come in three different versions: amorphous silicon, cadmium telluride, and indium gallium. Thin film solar is much less efficient than the other types and is best suited for low power applications or where the panel needs to be folded or rolled.

Most of the data about solar panels that’s out on the internet is not inaccurate, it’s just hard to figure out what matters and what doesn’t. Today we’ve cut through the chatter and focused on the big picture from an amateur radio operator’s perspective. The service life of a solar panel can run over two decades, so the decisions you make now will be around for a long time. With the right knowledge, you can make confident choices that you won’t regret later.

To learn more about other off grid ham radio solar options, check out my previous article, Solar Panel Kit Systems: Unwrapping The Package

13 thoughts on “A Radio Amateur’s Guide To Solar Panels.

  1. greekpreparedness

    I got 2 questions:
    1. Is it true that one ma bet more power out of a thinfilm panel in the duration of the day? The theory being that it is not demanding on the angle of the light.
    2. what are the 3 types performance when partly shaded? (say a branch). I heard that one type looses output for the whole panel.

    much needed article Chris, thumbs up!

    1. Chris Warren Post author

      Hello Mr. Greek! 1) It is true that thin film panels are less particular about their angle to the sun, but the advantage is statistically insignificant, especially considering that they are barely half as efficient as mono- and -poly crystalline panels to begin with. 2) No solar panel works well in the shade; I think that’s kind of obvious. Some mono crystalline panels will shut down entirely if even part of it is shaded, but there are not many of those types out there. The charge controller will smooth out the voltage variations due to lack of light, but any way you look at this, shade means less power. Thanks for being a regular reader, Greek. I really appreciate it.

  2. spacecase0

    mono panels make lots more power on overcast days than poly will,
    also mono will make more power than poly ones with the off angle of the sun
    unless you have a sun tracking system on a clear day, the mono crystalline win by quite a bit for total energy collected.
    at least that is what my personal tests have shown with my solar setups and others I have checked out

    1. Chris Warren Post author

      Everything you say is correct, but as mentioned in my article, there is an issue of “bang for the buck.” While spending an additional 20% or more for a mono crystal panel just to get a few extra watts is a purely personal decision, it’s important for radio amateurs to understand that poly crystal panels by a very wide margin offer the most watts per dollar. Also, sun trackers are something of an anachronism and you hardly ever see them because it’s far less costly to add extra panels to make up for unfavorable angles of the sun than it is to install mechanical trackers. Thanks for stopping by Off Grid Ham, Mr. Space. I appreciate your input and hope you’ll come by again.

    1. Chris Warren Post author

      Almost all my stuff came from Northern Arizona Wind & Sun http://www.solar-electric.com Also, Amazon is starting to carry a lot of great panels, including the Renogy panel mentioned in this article. Thanks for stopping by Off Grid Ham, David. I hope you’ll come back and bring some friends!

  3. Tony

    Greetings from Ireland. I am just wondering if it is possible to run a QRP rig directly from a solar panel? I had considered simply putting a regulator ic such as an LM317 set at 11 Volts between the panel and the 5 Watt rig. The panel is rated 20 Watts and in good daylight yields 20 Volts. Would this work and if not why not? Thanks in advance. dear EI5EM, Tony.

    1. Chris Warren Post author

      Hi Tony, and greeting from the middle of the USA! A 20 watt panel should not need a controller, but if your panel is putting out 20 volts unloaded, then you may be the exception. As for using an LM317, what you basically would be doing is making your own controller. I think that’s a very clever and workable idea, but there is no way to tell how much power you are losing in the conversion. Right now I am putting the finishing touches on an article that addresses your concern. It will be posted this weekend. The article itself is about going off grid for little money, but it will include a test to determine if you need a controller or not. I hope you’ll stop by for that one. Thanks for your comments, and we hope to see you again soon.

  4. Tony

    Thanks for swift reply Chris. I look forward to your upcoming article. My QRP rig runs 5W at 12 Volts. Allowing for losses etc I figure it needs about 10 Watts DC. My panel is rated 20W but is a Chinese import so rating may not be accurate but I bought it as an experimental item. Thanks again de Tony EI5EM.

    1. Chris Warren Post author

      Sure thing, Tony. Your 10 watt estimate looks about right. Keep in mind too that due to varying sun you will not be getting 20 watts out of the panel all the time, or even most of the time. This is why I recommend to readers that they get a panel bigger than they think they will need.

  5. Tony

    Thanks for swift reply Chris. I look forward to your upcoming article. My QRP rig runs 5W at 12 Volts. Allowing for losses etc I figure it needs about 10 Watts DC. My panel is rated 20W but is a Chinese import so rating may not be accurate but I bought it as an experimental item. Thanks again de Tony EI5EM.


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