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A Solar Energy System That Works At Night

by Ken Jorgustin

Solar energy is power from the sun. But what about power during the night?

Here’s how it’s done:


Batteries! Solar energy is radiant energy collected from the sun. Not only can it be harnessed and converted immediately to household electricity, but it can also be harnessed and stored in special batteries to be used later (when the sun goes down).

While the technicalities of a solar energy power system may be somewhat complicated and require a certain level of “know-how” in the field of electromechanical & electronics, these systems can be professionally installed or you might even consider a specially designed portable system.

The key to a 24-hour (around the clock) solar energy system is battery storage.

Even during the day you might encounter a period of sufficient cloudiness which will reduce the energy output from the solar panels. Energy output (the converted electrical power) will be reduced or greatly reduced, even to the extent that your connected devices might switch off. The batteries however will make up the difference when solar output is reduced.

The design of a battery storage system requires its own unique technical expertise while considering the specific battery type, size, charge/discharge parameters, load expectations, configuration and interconnection, and much more.

My own personal system at home currently consists of 24 AGM deep-cycle batteries which provide enough stored energy to run the house without issue overnight and beyond, until such time that the solar panels kick-in and start charging the batteries once again when the sun is shining.
Portable Solar Energy System
For those who may be interested in procuring a portable solar energy system with sufficient power to run your essential systems (or more), or to bring along camping, the cabin, or for emergency, etc.., there is a company who offers several portable solar energy systems which may be of interest.

Their portable solar generator kits include foldable solar panels, a “Humless power system” and the connecting cables.

The system is simple. Direct the solar panels towards the sun, the system will start charging and will continue until the batteries are full. The solar panels will also power your electronics while charging the batteries.

Speaking with the owner, their batteries are uniquely designed lithium to withstand the rigors of reliable charge/discharge with built-in safety mechanisms for protection against over-charging or excessive discharge.

Because of the lithium design the overall system weight is far less than others and therefore opens the door for other uses – which make it truly portable.

Currently they offer three systems:
.64 kWh solar kit
1.3 kWh solar kit
2.0 kWh solar kit
kWh?
You might be asking, “What’s a kWh”? A kWh is a kilowatt hour. Think of it as as powering something that consumes 1,000 watts for one hour.

For example: If using 800 lumen LED bulbs (equivalent to the old 60-watt incandescent bulbs), the energy consumption of a kWh would be equivalent to powering about 125 of these LED bulbs for one hour! Or, about 12 for ten hours!

Note: A 800 lumen LED bulb consumes just 8 watts compared to it’s 60-watt incandescent counterpart of old…

LED Light Bulb Cost Savings Over Incandescent

Another example: My most recent chest freezer consumes 450 watts in a 24 hour period. That’s just 19 watts per hour on average. So, this chest freezer consumes 0.19 kW in one hour, or 0.19 kWh.

When determining the capacity requirements of a solar energy system, one thing that you might do is add up the power requirements of the things that you might be connecting.
Alternative energy sources are a great way to further your self-sufficiency and decrease your dependency on other external systems. I plan to write more articles about this in the future ?

 

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6 Ways to Hack Outdoor Solar Lights for Survival

Solar Lights for Emergencies

It’s that startling moment when the lights go out in the middle of the night.

You haven’t had time to mount your flashlights next to your bed. And you can’t find your candles in the complete dark. As you stumble about, you notice a white glow coming from your vegetable garden.

It’s the solar lighting you put out there earlier this year.

Often overlooked as a preparedness tool, solar lighting is something we should all consider. You can use them in many other ways than just looking pretty: from increasing egg production, to charging batteries, to preparing your unprepared loved ones.

Here are six hacks to maximize the usefulness of this green gadget:

1. First, replace the batteries

Yep, manufacturers lower their costs in building solar lights by using low-quality batteries. It’s often why solar lighting gets mixed reviews – it’s not the light, but the battery that failed. Replacing the low-quality ones with higher quality batteries is the secret to both longevity and efficiency of using solar outdoor lights indoors.

There’s a lot of debate out there on whether to use NiCD or NiMH batteries (such as the amazingly awesome Eneloop, of which I find myself collecting). If you live in a climate with moderate temperatures and a good amount of sunlight, a NiMH battery is your best choice. If not, opt for quality NiCD batteries, as they will tolerate a broader range of conditions than a NiMH will.

2. Turn it into a battery charger

Solar lighting can be used as a battery charger. You can use solar lights to charge batteries during the day, and then remove the batteries and use in other devices. Solar outdoor lights then serve double-duty and give you extra flexibility.

When looking for outdoor solar lighting that might be used indoors or as a battery charger, be sure it has an on-off switch. You’ll save energy for other uses and you may not want your house lit all night. Plus, a switch will allow you to convert it into a dedicated solar battery charger.

Most lights house a single battery, but if you get solar lights with at least two batteries, the light output is quite a bit more, and your charging capacity has doubled.

3. Remove the shades

Because the decorative shades impede the light, removing them will expose more light and the difference can be drastic.

4. Duct Tape over the light sensor

Most outdoor solar lights have a small sensor that works to turn off the lights at dawn. When using them indoors,you may also have other light sources that would trigger the sensor, so use some of your massive stock of camo duct tape to tape over it, effectively disabling it temporarily and keeping the light on.

5. Light up your coop and increase egg production

Increase egg production by putting a solar lamp in a chicken coop in winter and get more “daylight” for egg production. The solar lights can be hacked to extend the solar chip outside of the coop, while keeping the light itself inside the coop.

6. Prepare the unprepared

As I’ve said before, one of the best ways to prepare the unprepared is by giving practical gifts that can be used in an emergency. And this is a sly one.

You can’t very well show up with a hostess/birthday/Christmas gift of a H20 1.0 Personal Waterstraw (well you can, but you’ll probably compromise your OPSEC in the process), but you can show up with a wonderful treat for their lovely garden or eating area. And the bonus is you won’t have to explain yourself to a chorus of“are you like one of those doomsday preppers on TV?”

Pair the lights with a pack of good rechargeable batteries, and baby, you’ve just set them up with a solar battery charging solution that also runs double-duty as emergency lighting – cleverly disguised as a gift.

Solar Lighting options

So where to get good solar lights? It’s tough: If you buy online, you’ll encounter a lot of mixed reviews. If you pick some up at a dollar store, there’s no reviews at all to rely upon. And buying a cheap light just because it’s cheap won’t get you anywhere, worse yet, it will give you a false sense of security.

I’m a firm believer in doing your research – and online shopping. When I shop online at a site like Amazon, I can review the reviews and do price-comparisons to make sure I’m getting the best option out there. I’ve reviewed about a dozen options and these are my top three picks for outdoor solar lighting for the purposes as discussed:

1. Inexpensive Power-Houses

At less than $2 a piece, these solar lights are an inexpensive solution. I don’t plan on using these lights as a replacement for regular bulbs; and at this price, as one reviewer pointed out, you couldn’t buy the solar cell, battery and LEDs. This is an ideal set to gift to an unprepared loved one as well – the price is low enough to pair with some smashing batteries without busting the budget — and you’ll be preparing a loved one with a sneaky solar battery charger as well.

2. A Spot-On Spotlight

A spotlight is also an excellent choice – they tend to have larger solar panels and charge faster. This one, while it has a few mixed reviews (mainly due to damage in shipment) is the one for me. I just bought a tiny house and plan to use it to light my flag at night until someone I love needs some batteries charged.

3. Hanging tree lights

What can I say? I’m a total girl when it comes to the “pretty” factor. These solar lights for trees have pretty good reviews and well, they’re just so flippin’ pretty. Plus, you can just flip them upside down for indoor use. Perfect for my sister-in-law and her lovely (and useless, non-fruit-producing) trees. She won’t even know that I just set her up with a solar battery charger like a total “prepper”.

So there you have it, 3 options for solar lighting and 6 hacks you can do to them to make them moresurvival-y. Are you using solar outdoor lighting in a novel way in your preparedness plans? Do tell!

Happy prepping!

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Build A Solar Dehydrator For All Of Your Garden Bounty

Build a solar dehydrator for all of your garden bounty. This is a great diy project if you want or need to dehydrate a lot of food. It is perfect for folks that follow a raw diet or are mostly vegetarian. When preserving foods you have a few choices and a lot of folks like to can their foods for storage but canning does affect the nutrients because the food is cooked, where dehydrating only removes the moisture content of foods leaving all the nutrients behind. Another plus to dehydrating is storage space. Dehydrated foods take up much less space than either canned or frozen. While a lot of people have electric dehydrators, these can take hours to dry foods and they are using energy the entire time. This diy solar dehydrator tower by Peak Prosperity can dehydrate a great amount of foods while it costs nothing to use because it drys with the sun.He built it using some recycled materials to help keep costs down but says the family is mostly vegetarian so they dehydrate a lot of their garden produce. As long as you have a place to build this that can catch enough sun you could dry a lot of your garden produce, saving on energy and storage while retaining all of the nutrients in the foods.

This is a story of one of the steps my family has taken towards increased resiliency, including actions taken to build a more sustainable lifestyle and invest in our food security.  My family lives on mostly a vegetarian diet. We currently grow a large garden and plan to grow most of our food for the full year. Growing a year’s worth of food brings up many questions, but the most critical one is how do we preserve the bounty of our garden?  Of methods that I know of, one can dry, ferment, can, or use cold storage. Canning heats the food and takes away some of the nutrients. Not all foods can be stored in cold storage (but I am working on this, as well). We have an Excalibur dryer but find it takes forever to dry things and the electricity to match.

So I decided to build a solar dehydrator. After researching different design ideas, I went with a design that I could use some recycled materials and materials left over from other projects, plus some new. I also wanted a high-capacity design that could dry a lot of food at once. This design has a heat collector and a tower.

Construction

First, I built the foundation out of 4×4 pressure treated (PT) and some not PT. The wood that did not touch the ground did not need PT. The site was also at a slight slant, so I doubled the wood under the tower. The design has a 4′ square tower and an area for the metal that is used for the heat collector mass. I dug trenches in the dirt, drilled screws into the 4×4’s and filled the trenches with concrete. I set the 4×4’s (with the screws down) in the trenches, then leveled the 4×4’s and bolted the intersections together. Then I covered this with 1/2″ plywood that I painted black.

We have a shop in town that sells recycled construction materials (Habitat for Humanity Restore) that makes finding used materials easier for these types of projects. I was able to find three 5′ long, 6″ diameter, single-wall stove pipes and one 14″ diameter single-wall pipe. The three 6″ pipes fit nicely inside the larger pipe. I painted the pipes black with high temp paint (the same paint that you paint a woodstove with). I was going for as much mass as I could get to dry a lot of food at once.

Next, I built the tower. I used 5/8″ plywood siding, as I have this thing for making structures that not only function, but look nice as well. You could use 1/2″ CDX plywood instead, if you chose. Since the plywood is 4′ x 8′, it took 3 sheets (the door is on one side). The framing, including the rafters was made from 2×4 studs. I was able to get a recycled 3′ wide door with a full dual-pane window. This I framed in on the west side of the tower, so the food would not be in the direct sun, but you could see inside. (It could have also been in the rear.) The roof is slanted to allow for an exit vent in the rear. The exit vent opening should be approx. equal to the inlet opening. I covered this with galvanized welded mesh wire on the outside (for animals) and window screening on the inside (for insects). I covered the roof with 1/2″ plywood and scrap metal roofing.

I went to my local glass shop and they had recycled (like brand new) 3/16″ thick, tempered glass shower doors. I framed in a triangular box to hold the shower doors. This area became the heat collector area. Again I covered the inlet with welded mesh wire on the outside (for animals) and window screening on the inside (for insects). This could be flat, as well, with corrugated metal sheets as the heat mass. I made covers for the inlet and outlet for winter.

Cool air comes in the heat collector area, is heated by the metal, and flows up thru the tower and out the top rear of the tower. It works like a woodstove or greenhouse. Heat rises.

Now for the food trays: I made 10 frames out of 2″ x 2″ wood, painted with mineral oil. They are 3′ square. The mesh covers an area of 2′ x 3′ (the mesh comes in 4′ width, so I cut it in half). This leaves an area of 1′ x 3′ opening. I covered 3/4 of this opening with plywood. The opening is on the outside of the frame, away from the mesh. These are installed in a staggered pattern, with the opening opposite on each. This makes the air flow on both sides of the food and slows it down, as it makes its way up to the exit vent. The food is sliced thin and placed with maybe 1/4 to 1/2″ between the pieces. This makes the hot air stay more on the bottom of the trays and move to the opening. The trays rest on angles mounted the inside walls of the tower.

Material for food trays: I used 1/4″ mesh welded wire, type 316 stainless steel, to hold the food. This type of stainless is best for acid foods. It’s expensive, but there are only two types of mesh that you should use for this: food-grade plastic mesh (which I could only find commercial grade) or type 316 stainless steel. (Window screen is fiberglass and can put fibers in the food; aluminum window screen adds aluminum to the food. So these should not be used.) The stainless mesh needs to be welded, not woven, as food can be caught in the weave. The stainless comes in 4′ wide and sells by the foot. I needed 6 square feet (2′ x 3′) per tray x 10 trays = 60 square feet x $6 per square foot = $360.

Final Thoughts

The overall project came out nicely and the ability to use a lot of leftover and used building materials makes this type of project creatively adaptable regarding the design and size of the final dehydrator. The size of our system gives us the capacity to dry and preserve large quantities of garden produce with limited light exposure (we live in a mountain home) and maximize our harvest yields. Some of the other things we will be exploring with our system are:

  • Creating an adjustable cover to regulate heat levels
  • Adding a wireless thermometer to monitor temps from the house
  • Evaluating temperature ranges and zones of differing heat levels within the tower.

I’m happy with how this project turned out, and I hope you will be inspired by my efforts. Do-it-yourself plans for capturing and utilizing solar energy are a solid step on the journey toward resiliency. I’m looking forward to increasing our year-round preserved food supply with homegrown dehydrated produce and dried fruit, and I look forward to sharing our experiences after we’ve used our solar dehydrator through another growing season.

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Emergency Power: The Top Portable Solar Panel Chargers for Disasters

From seasonal storms and natural disasters to hacking attacks and terrorism, we face more threats on our power grid than ever before. With much of our electrical infrastructure still relying on antiquated equipment and technologies, our power grid has become extremely vulnerable to disruption.

Luckily advances in solar technology has made it possible for everyone to at least have a small emergency solar backup, even if it’s just something that can keep your small electronic devices up and running. These small portable devices are not only great for camping and hiking adventures, but when disaster strikes they can help keep devices like cell phones, small tablets, flashlights, emergency radios, ham radios, and GPS devices up and running.

As these technologies continue to improve and be adopted by the public, prices on emergency solar chargers have continued to drop, making them an affordable addition to anyone’s supply list. Here are some of our favorites.

The SunJack Portable Solar Charger

emergency-power

The SunJack is something that I keep in all of my Bug Out Bags. It’s lightweight, provides enough power to keep my iPhone, handheld radios and backup batteries running indefinitely, and can provide power to anything that accepts a USB charger.

The SunJack 14W Solar Charger Panel can be picked up for about $80. Sunjack’s battery backup devices can be found for $40. Each battery backup takes about 5 hours to fully charge and holds enough power to charge an iPhone about 4 times.

GoalZero Nomad 7, Guide 10 Adventure Kit

emergency-power-2

Goal Zero is known for making high-quality solar chargers. For the last couple of years I’ve been using the Goal Zero Guide 10 Adventure Kit as an emergency EDC. The kit includes a Nomad 7 Solar Panel and a Guide 10 Power Pack that can charge AA and AAA batteries.

It’s small enough to slip inside your vehicles glove box, and has an added pocket that allows you to pack it full of extra Every Day Carry (EDC) gear.

The unit retails for around $130.

The Solio Bolt

emergency-power3

If you’re looking for something that you can literally slip in your pocket, then you need to check out the Solio Bolt or the Solio Classic2 Solar Charger. Both of these chargers are small, can hold their charge for up to a year, and their battery packs can hold enough juice to power the average smart phone about 4 times.

The Solio Bolt sells for $70 and the Classic2, which has an extra panel, sells for $100.

The iLand Trek Solar Kit

emergency-power4

While this is the priciest unit on the list, it also packs the largest punch. The iLand Trek Solar Kit comes with a 10W panel and a heavy-duty battery with an operating voltage of 5V-12V. That means this unit can power things like Ham, Marine, and CB Radios; camp lighting and computers; and even things like water pumps and tools. Check it out in action, powering my Emergency Ham radio Setup.

The unit retails for around $700.

The WakaWaka Power+

emergency-power5

The WakaWaka Power+ is another small, easy-to-carry solar kit that can slip inside just about any bug out bag or EDC kit. It does take a bit longer to charge, which is to be expected with these smaller panel units, but once fully charged it holds enough power to charge a smartphone in about 2 hours. It also comes with built in LED lights (5 to 75 lumens) that provide up to 150 hours of emergency lighting on a single charge.

The WakaWake retails for around $75.

The Powermonkey Extreme

emergency-power6

The best thing about the Powermonkey Extreme is the massive amount of power the battery holds. It comes with a 9000mAh lithium polymer battery, and can power virtually any 5V or 12V devices including handheld radios, DSLR cameras and tablet computers. It’s great for camping, and something I like to take with on all long-distance road trips.

It retails fora little over $100.

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Building Your Energy Stockpile: Make The Sun Work For You

sun

Solar chargers collect and store the sun’s energy so it can be used later on to charge small electronics that are often tremendously useful aids to survival.

As we have already demonstrated, you can recharge many small devices using solar energy for as little as $30. Unfortunately, the smaller models also have significant limitations that preppers need to be aware of.

For example, most chargers use small solar panel(s) that cannot fully charge the unit’s battery in a single day of sunshine. This makes them fine for topping of the charger’s battery or using them to recharge your phone while you are away from AC power for the day, but a poor choice for constant use such as charging multiple pieces of equipment simultaneously in an emergency.

Second, most small solar chargers do not have variable power output. There are a few models that do, but they are considerably more expensive. Maximum output varies by model and is pretty low. So while they may be able to charge a headlamp or a cell phone, they cannot charge large banks of small batteries or larger electronics such as most notebook computers and radio gear.

Portable Solar Solution

A good portable solar setup can do things that a pocket-sized device cannot, such as charging a car battery, running powerful portable ham radio equipment, drive fans, drive pumps, power electric hand warmers, charge banks of small batteries or charge several smaller devices all at once.

It can be a single “black box” that has the necessary components integrated into one product or you can buy the individual components separately. They are most often something in between, so you can mix and match solar arrays and batteries according to your needs and maintain a degree of modularity to prolong the life of the equipment in light of the fact that technology will change.

Whichever you choose, a portable power solution provides an enormous amount of flexibility over smaller integrated USB solar devices.

Whether manufactured or built from components, most are modular in design so you can use larger or smaller solar panels or batteries in order to meet your needs.

Portable solar systems have the same principal components:

  • Battery (Stores electricity)
  • Power Output (USB Port, Auto Cigarette Lighter Receptacle, PowerPole Connector)
  • Charge Controller (Interrupts flow of power from the solar panel to the battery when full or too hot to avoid damaging the battery)
  • Solar Panel (Turns solar energy into electricity)

By choosing larger and smaller components, we can generate more power or store more power. The battery or battery bank stores the energy generated by the solar panels or array of them. The solar charge controller ensures that we do not damage the battery as the solar panels charge it.

Buy or Build?

If you prefer to purchase a solution there are many to choose from. You can buy a production model or even have a small business build to meet your needs. Buying is more convenient, but also usually costs more. It is OK to be a driver and not a mechanic, but most self-reliant people like to be able to maintain and repair critical equipment.

Greater than cost savings, for many, is the fact that doing often teaches us things that we cannot learn in any other way. Survival reigns supreme amongst DIY pursuits, and the process of building is educational.

Even if you value convenience over thrift, you should still understand your alternative energy system well enough to maintain it. You will not likely be able to send equipment back to the factory for repair if the grid goes down. If your concern is convenience, building your own alternative energy solution does not actually involve building anything. In many cases, all you need to do is read a little and plug in a few wires.

Whether you buy or build, you will still need to evaluate features. So I will go over the most critical points for each component. I will address solar charge controller and power outputs under battery as they are sometimes integrated.

sun1

Key Components

1. Battery

The battery capacity must exceed the draw your equipment demands from it. Select a battery with at least 50-100% greater capacity than you think you will need. You solar power generator will not be 100% efficient and the sun will not always cooperate with you. So keep in mind these about the battery:

  • Battery technology & portability: For this application, you will want a Li-ion battery. They are lighter, smaller, and typically last more charge cycles when deeply discharged. If weight does not matter, you can use larger, heavier, less expensive battery technologies.
    If you discharge a typical li-ion smartphone battery completely (100%) each time before you charge it, after doing this about 250 times, the battery will last about 75% as long as it did when it was brand new. Manufacturers very conservatively consider this the end of the battery’s useful life. It will still work, but it will not last as long. How do you make it last longer? Don’t discharge it completely or buy much larger battery bank than you will need so you do not have to discharge it deeply.
    If you only discharge a Li-ion battery to 50% of capacity instead of 100% (complete discharge), it will last 1200-1500 charge cycles. Discharge it only 25% and it will last 2000-2500 cycles. Recharge it after 10% and it will last 3750-4700 and you could use it every day for 10-12 years and it will last 75% as long as when brand new. Heat also shortens battery life so keep batteries cool and trickle charge them as opposed to rapid charging them.
  • Battery size: Calculate how much current your equipment will draw. This is not difficult and much has already been written on the subject, so I will not repeat it here.
  • Solar charge controller: This is needed to protect the battery against overcharging. Some batteries have one built in and some do not. Either is fine, but you need to be aware of whether or not the battery has one built in since you do not want more than one. If a charge controller is not integrated into the battery you buy, you will need to get one that matches the output of your solar panel since they come in different sizes. They are installed between the solar panel’s output and the battery’s input. If the adapters do not match, you can crimp on adapters that do.

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  • Charge state indicator: This is essentially a “fuel gauge” for the battery. It can be an LCD, series of LEDs, single LED or gauge that tells how capacity is remaining in the battery.
  • Variable power inputs: As supplied by the factory, many battery packs can be charged from a wall outlet, cigarette adapter or USB port in addition to a solar panel. These are power inputs. Consider how you plan to charge and maintain the battery before an emergency. It is convenient to be able to charge the battery from your home and vehicle without having to use the solar panel when you maintain it in between usage. Even if multiple inputs are not built in, you can still use a converter or adapter, but they add a little bulk.
  • Power outputs: This refers to the type of plug and how much current your devices will need and is typically expressed in voltage milliamp hours. They are often built into batteries along with a charge controller. Consider how power is input to the devices you use. Then consider other capabilities you might need in an extended emergency. If all your gear has 5v USB inputs, it’s best to get a battery with 5v outputs. Otherwise you will have carry an adapter to make the output usable for each device and it will decrease efficiency.

Some Li-Ion battery packs come with variable output which enables you to vary the output voltage and amperage. This is a great feature because it eliminates having to carry a different power adapter for every piece of equipment. You may still need adapters.

I swap my 12v DC equipment over to the same type of genderless connector called the Anderson PowerPole connector. This simple modification is performed by stripping and crimping power cables. If you can do that, you can drastically reduce the number of cables and connectors needed to run your gear off the same type of connectors.

  • Consumer Ratings: Even if you buy locally, it is still worth the trouble to checkout product ratings online before you buy. 

2. Solar Array

Years and years ago, (well over a decade) I shelled out around $375 for a Brunton Solaris 26 portable solar array that I still use today.

Unfortunately, inflation has practically kept pace the price drop in flexible (thin film) solar arrays so they aren’t a whole lot cheaper now than they were a decade ago and you can probably find the exact same product still available for sale for about $300. They are very durable and don’t have moving parts so they are pretty rugged.

The Solaris 26 folds up to the about the size of a notebook computer and unfolds to about 2 feet x 4 feet and has grommets in the corners to hang it from a pack, tree, tent or vehicle. I chose this model because it outputs 26 watts at 12v DC and I wanted it to be able to charge car batteries, gel cells or the considerable more expensive, larger and heavier Li-Ion battery packs of the day in order to run amateur radio equipment, small electronics, cell phones and notebook computers at that time.

sun3

Today, lighter Li-Ion battery packs with variable output are available. This is a boon to anyone planning to pack in this type of gear on foot, bicycle pack animals or using carts or other small transport.

What to look for in a solar array:

  • Technology and Portability, 1st Gen vs 2nd Gen: What are your size and weight constraints? If it needs to fit in a pack, you will probably want Gen 2 Solar panels. If it will be mounted to a vehicle, Gen 1 would be better. Gen 1 panels are the heavier glass ones, Gen II are the light, flexible thin-film ones. Gen 1 is a little more efficient in bright sun at lower latitudes and with optimal orientation, especially on a mount that tracks the sun, and are cheaper, and they are heavy. Gen II is more efficient in Northern latitudes, on cloudy days, with imperfect orientation and are more portable.
  • Output Current: For solar panels, this is normally expressed in voltage and wattage. To determine how much output you need you need for a particular application, you will need to calculate your electrical load and how long you will run it, but in practical terms, for a portable solution, you may have to start with what you are willing to tote around and work back to how much you can use your gear from there because how often you use your equipment is negotiable, how much weight you can carry before you start making soft compromises is less so.
    A 100W, 19v array is the largest you would want to pack, 50 watts or 25 watts at 12v still gives you plenty of power for what most people would normally carry in a pack. If you just bring a cell phone and maybe a headlamp, you can get by with an integrated device that produces a few watts and can fit in your pocket like the ones discussed in Part 1 of this series.

How do you determine the wattage and voltage your panel should be rated for? You need to be able to charge the battery. So for voltage, if you determined a 5v pack is best because your devices are USB, 5v will be most efficient. If you chose 12v or 13.8v for radio equipment or 19v for a notebook computer, the same thing goes. It is most efficient and less confusing at this stage to choose a panel with output that matches the voltage of the battery.

In determining the wattage, you will need to be able to bring the battery back up to full charge with the usable sun you have per day which averages about 6-7 hours on a sunny day, typically from 9:30am to 3:30 pm, but this differs somewhat by latitude and generation of solar panel.

  • Ruggedness and water resistance: What environment will you be using it in? Best case, equatorial desert and you shelter in when it rains, which is infrequently. Worst case? Torrential rains, high latitudes, 100% humidity, perpetual cloud cover, on a small boat constantly exposed to salt air. You also need to consider if you will constantly moving and how much of that movement will be in a straight line. Best case is you can use it in a secure camp where no one will try to steal it.
  • Consumer Ratings: Don’t forget to see how products performed for others before you buy.