A buffet of options.
Amateur radio has a low barrier to entry, but once in the door the learning curve is fairly steep. This may originate from the wide breadth and depth of the hobby. There are so many subspecialties, it’s impossible for any one person to truly know everything. If you’re interested in taking your radio station off grid but are lost as to where to start, this one’s for you! If you’re already experienced in this area, please forward this article to a friend or spread it around via social media and club newsletters.
It’s not as hard as it seems.
It’s easy to get frustrated by the tangled mix of equipment on the market. What are the must-haves? What can be left out? There are several power sources available, but for this round we will focus only on solar because that is the easiest and by far the most popular. There’s good news for for prospective solar power hams: It’s not that hard!
For simplicity, we’ll assume a 100 watt radio transmitting 20% of the time. There are three basic components to an off grid radio system: A solar panel, a battery, and a controller.
Solar panels.
Is your station portable, or in a fixed location? For portable operation, a 100 watt panel is about as big as you can get and still be portable. If you are operating from a fixed location, or are willing to transport more than a 100 watt panel in your portable setup, then bump it up to 150-200 watts. Any more than that is over-engineered for a 100 watt radio.
It’s important to know that your panel will rarely if ever produce its full rated power due to variations in sun intensity and inherent inefficiencies in your system. Having a slightly oversized panel is worthwhile to make up for the losses.
Mono crystalline panels.
These panels are characterized by individual, well defined cells. They are more efficient than the other types, although only marginally so. Mono panels used to be more expensive than poly crystal or amorphous versions, but with advancing production and economies of scale, this isn’t really an issue any more.
Poly crystalline panels.
These panels are are characterized by a random or “broken glass” pattern in their cells. They are not as efficient as monos, but unless you’re planning on installing hundreds of panels, the difference is not meaningful.
Amorphous or thin film panels.
These are characterized by a solid black or grey panel where there are no defined cells. They are not as efficient as the preceding types, but can be made to be very flexible. This makes them the go-to choice for incorporating solar into an uneven or flexible surfaces such as a backpack or a curved roof.
Which one should you get?
Honestly, you’re going to be ok with any of them. Many hams prefer amorphous panels because they can be folded or rolled up to save space. Don’t fuss too much over a specific type of panel. Choose the one that fits your budget and physical requirements.
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A bigger battery does not equal a better deal.
For our 100 watt radio example I’m recommending a 35-50 amp-hour battery. Larger is not necessarily better. If you go with a bigger battery, you’ll of course have more capacity and run time on your radio, but you’ll also have longer charge times from the same 100 watt panel. The only way to keep charge times down on a larger battery would be to upsize the solar panel.
If you are deploying a portable system, bigger batteries plus a bigger panel equals more weight and bulk to lug about. Be careful not to let your project get away from you. It’s easy to fall into thinking, “Well, I planned for a 35 amp hour battery. For a few dollars more why not bump it to 60 or 75?”. I think every ham gets caught in this slippery vortex at some point.
Sealed and lithium batteries.
Gel cell, SLA, and AGM are the most well known types of conventional or non-lithium batteries. For this article we’ll refer to all of them colloquially as “sealed” batteries. Some manufacturers use their own terminology. The design differences between these batteries is too detailed to get into here; suffice it to say that they are cousins of each other and have similar performance characteristics.
There are also different versions of lithium batteries. The types most commonly used by hams are lithium ion (Li-ion, most popular), lithium polymer (Li-Po), and lithium ion phosphate (LiFePO4 or LFP). There are other, more obscure classes of lithium batteries but the preceding three are the most well known.
You may have heard of lithium batteries spontaneously combusting and starting virulent fires. Advancing technology has greatly reduced the risk of lithium battery fires. While the risk is not zero, when used and charged as designed modern lithium batteries are very safe.
Lithium batteries are lighter than sealed batteries, have a greater power density, and can be discharged almost to zero without damage. They also have a better power curve. This means they will deliver full power longer during their discharge. Sealed batteries will start at full power and slowly degrade over time. For the ham, a sealed battery will stop delivering sufficient current when it is down to 40%-50% as opposed to lithium which can go as low as 10%.
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The hidden cost of sealed batteries.
Sealed batteries are not a terrible choice, but the only real reason to use them is price. They are much less expensive than lithiums. But are they really? While sealed batteries do have a lower up-front cost, they will need to be replaced more often. Sealed batteries have a lifecycle of 300-1200 cycles, depending on the type of battery (AGM, gel cell, etc.) and the depth of discharge. The farther you drain them on each cycle, the fewer cycles you’ll get. Lithium batteries, depending on type, can go over 2000 cycles and can be deeply discharged. The bottom line is that in average ham radio use, you’ll likely replace several sealed batteries for every one lithium. It’s a “pay now or pay later” proposition. Lithiums are a better value vs. sealed when the cost is amortized over the service life of the battery.
Charge controllers.
The last link in the off grid chain is the charge controller. There are two basic styles: pulse width modulation (PWM) and maximum power point tracking (MPPT).
PWM controllers are the most popular for small systems, and they’re relatively inexpensive. They are a great choice when the panel voltage and the battery voltage are not too far apart. The only real disadvantage is the efficiency, which is only 70%-80%. Right out of the box, a PWM controller is going to “waste” 20-30 watts of a 100 watt panel.
The other type of controller is the maximum power point tracking (MPPT). These controllers are much more expensive than PWM’s but are over 95% efficient. They are not recommended for small systems because the advantage of efficiency is not justified by the increased cost. Furthermore, MPPT controllers are usually designed for higher power systems, which makes them overkill for small applications.
Good PWM controllers for hams run in the $40-and up range. MPPT starts around $120 and goes up from there. You may have noticed that online retailers sell inexpensive PWM controllers for under $30.00, and a few are even under $10.00. While I don’t suggest using these for anything other than experimenting/backup, they are surprisingly good for their price. Here is an entire article that talks about the nuances of the cheapie controllers. Lastly, make sure your controller is compatible with your battery. Some controllers will not work with lithium batteries.
Does this help clear things up?
If you’ve been lost in all the off grid radio products, technologies, terminology, and hype, hopefully this article will clear the fog and get you started. Don’t get overwhelmed. Remember: All you need is a solar panel, a battery, and a charge controller. That’s it. Get those three basic ingredients figured out and you are well on your way to off grid ham radio.
Thank you. It’s always good to reread and rethink knowledge. My radio use is mostly rural deployments. Fact is I don’t know how to use my equipment in a building with heat and air conditioning. ; )