Off-Grid Power Basics, by "James Dernier"

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Electricity 101:
Electricity is fundamental to our first world every day life. We know electricity mostly in one of two forms in the home, from the wall, and in a battery. The electricity that comes out of the wall is high voltage (~110-120 volts [JWR adds: alternating current (AC), in North America--except Mexico, which uses a more macho 127  volts] AC), relatively low amperage, and alternating current. The electricity that is stored in batteries comes in a variety of voltages and amperages but is always direct current (DC). Size AA batteries are 1.5 volts, along with most other battery types, with the notable exceptions of 9 volt and your car’s 12 volt. Batteries can be split into two categories and many subcategories, but all will either be single use, or rechargeable, with the difference being the chemistry of the battery. Since the topic of my essay is alternate power, I am going to concentrate on rechargeable battery banks, and the generation of electricity.

Batteries 101:
Rechargeable battery banks or “house” banks are collections of batteries that can be charged and discharged as a group to lengthen battery life. Most modern battery banks are lead acid batteries, although there are various types. Deep cycle batteries are different from the lead acid battery in your car. The difference is the thickness of the lead plates in the battery. As a battery discharges, the lead plates become dissolved in the acid solution, and when it is recharged the lead plates reabsorb the lead in solution (not quite but close enough). If there the battery becomes too discharged, or is discharged too deeply too often, the lead plates become worn enough that they can’t reabsorb the lead onto the much depleted plate, and the battery needs to be replaced. This is why your car battery dies eventually, especially after a long period of disuse where it is slowly self-discharging, or after it becomes too deeply drained. Deep cycle batteries are less affected by those abuses because of their thicker plates, but they will eventually be destroyed by the same process as their chemistry is the same. Although the advantage that car batteries has is by having a greater number of thinner plates their cranking amps, or amps available all at once, is much higher. By linking many batteries together, the same amount of power drawn total is split more ways and is less per battery, which translates to a longer life for all of the batteries. Since all batteries are DC, you need a device called an inverter to change DC into AC, which is what most plug-in [household current] devices use.

Advantages of off-grid power:
Off grid power is power generated off of the electrical grid. The electrical grid is the power we get through the walls, and the power that is lost for a few days, weeks or months following a natural disaster. Off-grid power is power you generate so that if following a natural disaster or black out, or just if you are in the boonies, you still have power. There can be a mix of the two, so in case of emergency, or just for small amounts of power generation, you can have an inter-tied system in which you can have most of your power or regular use power from a utility company. Off-grid power’s primary advantage is if the grid goes down permanently or electricity becomes very expensive you can still generate your own. Charge Controllers let you put the optimal charging voltage into your battery bank. For optimal battery life, varying voltages should be used during the different phases in the recharge cycle. For all parts of the cycle you need more than 12 volts in the case of a 12 volt batter to recharge your battery, and the amount more will vary based on the type of battery you use.


PV Panels:
Photovoltaic ("PV") panels generate power from the sun. They generate DC voltage at small amperage, but they are very low maintenance; they are mounted on racks, and these racks can be connected to [passive or clock drive] trackers. This system lets you control the wiring, and trackers let the panel’s track the sun, as the sun travels across the sky, the angle at which the panel would optimally face changes. So to let the panels track the sun, you need a rack on a tracker. This increases the amount of sun hitting the panels, and thus the amount of electricity generated. [JWR adds: Unless you live in a equatorial region, you will also want to seasonally adjust the angle of your PV panel rack, to roughly match the sun's path above the horizon.]

Living with an Alternate Power System:
This can be a tricky thing, since we waste a lot of power every day. Phantom loads, or power used by devices that are not in use is a big contributor. TVs, VCRs and many other devices draw a substantial amount of power even when off, because they are in a state where they can be turned on right away, and draw power. Similar to when a car is idle, it might not be moving but the engine is on, and the car is using gas, just so it can move right away. Other things to avoid are incandescent lights, which draw several times what their fluorescent equivalents draw. Cooking and heating with electricity is also a big draw, microwaves, toasters, ovens, and space heaters are big electricity hogs with easy alternatives. Refrigeration is also a big draw, but there isn’t really an easy equivalent. There are other forms of preservation, but there is no substitute for refrigeration. [JWR adds:  Propane refrigerators are still made. Odds are that you can "size" your PV system much smaller if you use a propane refrigerator.] Most forms of electronic recreation can also be big draws, most notably the computer, followed by the television, and on to stereos.

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This page contains a single entry by Jim Rawles published on December 19, 2005 6:08 PM.

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