Off-grid Power System

While it is possible to live without electricity, and even enjoyable to do so for brief periods of time, few things will improve your off-grid life style more than a reliable electrical power system. There are a lot of different ways to create electrical power. They all have advantages and disadvantages. This page will give you a general outline of what a power system will look like and summarize the pros and cons of the different ways of producing power including solar power, wind power, water power, and diesel generators.

Sources of Power

Power can be produced from sun, wind, water, or fire. Electricity is created when the heat or motion of these natural forces is converted by a device like an alternator or solar cell.

An alternator is an electro-mechanical device that converts mechanical energy into an alternating electric current. The mechanical energy is the rotation of the shaft of the alternator which is generally rotated using some sort of motor.

By contrast, a solar cell performs "direct conversion" of the energy in light into electricity using a unique physical property called the "photoelectric effect." Incidentally, the discovery of this property earned Albert Einstein the Nobel Prize in 1921.

But no matter which power source you use, none of them is "on" all the time, so when they are "on" we will want to generate extra power to store in batteries for when our power source is "off."

Full Time Power

Our off-grid power system will use an inverter, a device to convert the electricity stored in batteries to the house current that our appliances use. Many off-grid systems previously used 12 volt wiring for lights and appliances, but with the availability of modern inverters, standard 110 volt house wiring is the preferred approach.

With an inverter, you are not restricted to buying the RV-sized appliances that run on battery voltage. Since the inverter creates the same voltage supplied by utility companies, you can use the equipment you are accustomed to from "city life."

The inverter is on full time, converting the electricity stored in batteries to 110 volt house current whenever needed, and the batteries are recharged by our source of power, be it sun, wind, water, or fire.

Although inverters are not cheap, using one might actually be cheaper than wiring your house for 12 volt appliances. The cost of 12 volt lighting, refrigeration, washing, and other appliances is much higher than the cost of normal household models. These appliances are also smaller and of generally lesser quality. A 12 volt system will also use much heavier, more costly wire than the 110 volt system. Overall, the difference in wiring and appliance cost might just pay for the inverter. And once you have experienced the advantages of having standard household current available all the time, you would not change to 12 volt for any price!

Fire

Arguably man's first step toward civilization, fire remains possibly our greatest tool when it comes to generating power.  The heat of fire can be converted to electricity in many different ways. A steam engine converts the heat of the boiler fire into rotation of a shaft that can drive an alternator. The burning of fuel in a gasoline or diesel motor may likewise power an alternator.

A motor generator is generally the cheapest way to produce electricity. It works by converting a fuel, supplied from a fuel tank, into mechanical energy by a motor which in turn drives an electric alternator. The chief disadvantage of a motor generator is the continuing purchase of fuel, although renewable fuels do exist, petroleum is still the most popular and economically viable choice for most people.

Diesel generators are very reliable, plentiful, can be inexpensive if you know where to look, and are likely to be the most economical home power generation scheme available.  To find out how to locate cheap diesel generators checkout http://www.cheap-diesel-generators.com.  At http://www.homepower.htmlplanet.com you will find a detailed engineering economics comparison of solar power vs. diesel generator power.

Sun

Energy of the sun is solar energy. The usual way to make electricity from sunlight is the Photo-voltaic array (PV), or simply "solar cell." PV is what many folks think of first when they consider an off-grid power system. The advantage of PV is that it does not ware out, does not grow old, has no moving parts, and requires zero maintenance. This comes at a cost.

A PV array will cost $5 or more per watt of capacity. This means that a 1000 watt solar array will cost approximately $5000. This is by far the most expensive form of electricity generation. Depending on the part of the world you live in, an array of 3000 or more watts will be required to supply modest electrical needs. Such a system would cost more than $15,000 at current prices.

PV does have a place as part of a total system, but for most people the expense will rule out its use as the primary power source.

Wind

A wind generator uses a propeller or some other type of spinner placed where the wind will force it to turn an alternator. These are conceptually very simple and reliable and many thousands have been home-built by handy owners. There are also numerous commercial systems and kits available that can be installed with varying degrees of difficulty.

Wind power works best when a site can be found that is free of obstructions, where a tall tower can be placed, and where the wind is strong. The amount of power in a 20 mph wind is eight times the power in a 10 mph breeze, so the periodic storm that brings high winds will likely produce more power than many week's worth of gentle breezes. Do the math and decide for yourself if wind power will work for you.

Water

As water flows downhill, it converts gravity to speed. When this water runs into a turbine driven generator we convert the speed of the flowing water into electricity. Electric energy produced from flowing water is called Hydro-electric power.

Almost any stream that makes noise will produce noticeable power, but how much is another matter. Do the math to find out just how much.

Charge Controller

Of our four types of power sources three of them, sun, wind, and water, will often produce low voltage direct current electricity similar to a battery. To charge our batteries with this electricity we will use a charge controller. A charge controller, ironically, controls the charging of the batteries (duh!). It will regulate the rate of charge so the batteries are not charged too fast, and will keep the batteries from being overcharged.

A motor driven power source generally drives an alternator to produce alternating current (AC). This AC electricity is identical to what the electric utilities supply and can be used directly by household appliances, but it can not directly charge a battery.

To recharge our batteries from a generator we will use the battery charger that is built-in to every modern inverter. When the inverter is wired to our house, to the batteries, and to our generator. When the generator is off, the inverter converts battery voltage to household voltage. When the inverter senses voltage from the generator it automatically sets internal switches so that the house is being supplied directly by the generator and the inverter circuitry converts generator power to battery charging voltage.

A complete system might have both a generator and more renewable power sources simultaneously charging our battery bank. The inverter and charge controller are fully compatible and can be connected to the same set of batteries.

Batteries

The batteries are a special type known as "deep cycle" that are built to withstand the charging and discharging that happens in this system. The type and number of batteries are selected to provide enough power that the generator is run once a day or less.

You will find some folks using automotive batteries. You might also find some stores that carry "marine deep cycle" batteries. Neither of these items is what we want. The true "deep cycle battery has thicker gauge plates to withstand the repeated deep discharge that we will require for our off-grid power system. Other sorts of batteries will only cost us money in the long run.

To find deep cycle batteries look for battery wholesalers under "B" in your local phone book. A popular model is the Trojan T-105 battery used in golf carts.

Putting It All Together

Selecting what parts to use in your off-grid power system will depend on how much power you need. These are referred to as "loads" and one of your first chores will be to estimate how much load you have. Then you'll need to size the components of the complete system and hook it all together with cables and wiring of the proper size.

Got Questions?

If you haven't yet found the answer to that "electrifying" question about off-grid power, email us at geek@offgridknowhow.com. We'll be happy to get an answer for you.

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