Research with speakers of the world’s under-documented and under-described languages frequently requires that linguists work in places without a regular supply of electricity. Almost all the fieldwork that I have carried out, for example, has been in places where I have had to supply my own electricity to run laptops, recharge batteries for recorders and flashlights, and other electrical needs.
In many cases, a solar power system is the best option for generating and storing electrical power, and this post is intended to provide information about the components of basic solar power system that will supply electricity for typical linguistic fieldwork needs.
The basic solar system I describe here has five major components: 1) a solar panel and cable; 2) a switch; 3) a charge controller; 4) a battery; and 5) an inverter. Note that the recommendations that I make below are based on the assumption that you will be making your purchases in an a decent-sized, but not super-large, urban center relatively close to your field site. In the case of fieldwork in Peruvian Amazonia I have in mind cities like Pucallpa, Iquitos, and Yurimaguas. And let me add that if you’re buying your solar panel equipment in a place like this, there will be businesses dedicated to solar power systems. If you are new to setting up solar systems, I recommend explaining your needs (and experience) to the people you buy your equipment from, so that they can help you make good choices and help you learn the details of how to set your system up. My experience is that folks in solar power businesses like these are generally very helpful.
In this post I describe the basic component; in the next I describe how the set them up.
A solar panel generates a voltage when exposed to sufficiently strong light, and if hooked up to a battery correctly, will charge the battery. In the basic system I describe here I recommend and assume a rigid glass panel (a.k.a., a monocrystalline solar panel), which has the advantage of being more efficient, cheaper (per Watt of power), and more easily available in most parts of the world than flexible (a.k.a. polycrystalline) panels. (In the kind of places where I have bought panels in Peruvian Amazonia, only monocrystalline panels are sold, so it really might not be an issue at all.)
An important question is the size (i.e., maximum wattage = power) of the panel one should get. This depends on light conditions where you are, and what your electrical needs are, but my rule of thumb in the field sites I work in is 10 Watts per hour of laptop use per day. This covers both my laptop needs and the need to recharge other smaller pieces of equipment (tablet, rechargeable AA batteries, etc.). Note that I work a couple of degrees from the equator, so keep that in mind when calculating for your own needs. I generally aim for a 90 Watt panel per researcher, assuming about 9 hours of laptop use per researcher per day. This is more than enough during good sunny weather, but also builds up enough a reserve in the battery, and generates enough electricity to keep me going during long stretches of cloudy weather. If you are planning to use other electricity-intensive devices, you will need to adjust accordingly.
Note that the price of solar panels has come down a great deal in recent years. To give you a sense, a couple of months ago I bought a 190 Watt panel in Iquitos for about $200 dollars. This included a 10 meter insulated cable that runs from the panel to the rest of the power system, to which I turn next.
You will need a cable that runs from your solar panels, set up outside, to the rest of your solar power system, which should be located under a roof, near where you will be using your laptop. I find a 10 meter cable to be more than enough in my field sites, but if your panels will need to be located further away from the rest of your power system, get a longer cable accordingly.
Next, a switch. Although not 100% strictly necessary, I recommend installing a switch between the solar panel cable and the rest of the system. There are many options, but an adequate electrical switch will cost you only a couple of dollars and can be picked in a decent hardware store. You just need to make sure that it will be easy for you to attach the two wires from the solar panel cable in one end, and two wires leading to the rest of the system at the other end.
Next comes the charge controller, which adjusts the voltage coming out of the panel so that it charges your battery properly. Charge controllers can be very, very inexpensive, but I recommend getting one that will tell you the voltage of your battery (see why below). Even so, the charge controller will probably only cost you about $10-15. These too have become very inexpensive.
Next comes the battery. There are lots of options (about which I may say more in a later post), but here I will assume a non-sealed lead-acid car battery (i.e., a standard car battery), since these can be found in most urban locations of more than a couple of thousand people. Car batteries come in different “sizes”, where the size is measured in Amp-hours (Ah), which indicates the total electrical charge a battery can hold. The more Ah a battery can hold, the more expensive it is, and the heavier it is (that’s the lead part of lead-acid). The main reason to have more, rather than less, battery storage capacity is that this is what will allow you to continue drawing electricity when the solar panel is not generating much current, e.g., during cloudy days, or at night, when panels generate no current at all. My rule of thumb is about 5Ah of battery capacity per planned hour of laptop use. Since I normally do fieldwork with another person, and plan for 9 hours of laptop use per day per person, I normally aim to get a battery in the vicinity of 90Ah.
With the simple setup that I am recommending it is a little difficult to know exactly how much usable charge you have in your battery. When the battery is new and fully charged, the battery voltage should be 12.5V or a little more. As you use up the charge in the battery, the voltage will drop, but you should not let it drop below 12.0V. You can continue to draw current below 12.0V, but this will reduce the capacity of the battery and shorten its lifespan.
The final major component is the inverter. The inverter connects to the battery and turns the 12-ish DC volts of the battery into AC current (which is what standard wall current is). You can purchase inverters that output 110V AC or 220V AC; I get 220V AC inverters, since that is what is used in Peru. In any case, an inverter has electrical outlets into which you can plug your devices. Note that inverters have a maximum wattage rating, which indicates the maximum power they can draw, and inverters with lower wattage ratings are less expensive than those with higher ones. Laptops draw about 60W at most, and so I get pretty much to lowest wattage inverters: 300W. I get pure sine wave inverters (since this is better for electronics) and they cost me $30-$40.
There are also some minor components. You will need several meters of electrical wire to connect the switch to the charge controller, and the charge controller to the battery. You will also need connectors that will allow you to connect wires to the terminals of the battery (in Peru they are called bornes). I recommend inquiring about these with your local solar power expert: they will be able to tell you what is used locally.
In the next post I will discuss setting up the the solar panel system.