Planning the Installation of Your Off-the-Grid Power System

Not enough can be said about the do’s and don’ts of safely and correctly installing an electrical power system. Here are just a few to give you a general idea.


1. Always follow the National Electrical Code (NEC). This sounds simple, but it requires a boatload of learning and research – to understand and then to apply it correctly. A note of history – the NEC was first established in 1896. It was developed because of the mass confusion of using 5 electrical installation codes in 1895 and the increasing number of electrical fires. It is constantly being reviewed and updated and there are specific sections for solar, wind, hydro, generators, etc.

2. Size your system correctly and error on the plus side. A little overkill won’t hurt and goes a long way if something fails or starts to over heat.

3. Always use the proper size fuses.

4. Always install with an electrical permit. Permits are not expensive and will give you the peace of mind that what you did is correct. It also allows you to get a Certificate of Occupancy (C.O.) from your county inspector, covers you with your home owners insurance and it is the law.

If you don’t and anything happens due to your installation, you have just given your insurance company a way out – and they will take it!

5. Remember that being remote, means no close fire protection; so pay close attention to all details.


1. Never undersize wire, fuses, disconnects, conduit, boxes, grounds, etc. Never oversize fuses or use a substitute.

2. Don’t use just any wire, check amp rating, check listing, locations and size.

3. Don’t install to ‘just get by’, you will end up living with it and it won’t be correct.

4. Don’t rely on the guy down the road who helped so and so set up his system. There are a lot of up and coming solar installers who are not insured, not trained and not certified.

5. Don’t do any electrical wiring/installations unless you fully understand what you are doing – mistakes and accidents can do serious damage, cause fires, cause explosions and loss of life.

As you can see, this is a very short list and only touches on a few items. Consult the NEC for all questions.

We should now talk about system sizing. Sizing your system is the most important task that you can help your installer with. That is because you know exactly how much power you use in everyday living. Sounds complicated!!!

Not really. Let’s look at a sample list of items you may use on a daily basis:

* coffee maker 900 watts 15 min.
* microwave 1400 watts 20 min.
* 20” television 50 watts 3 hours*
* stereo 25 watts 2 hours*
* vacuum cleaner 980 watts 20 min.
* iron 1200 watts 30 min.
* hair dryer 1500 watts 8 min.
* washer (front load) 145 watts 1 hr./load*
* computer90 watts 2 hours
* freezer, refrigerator, cook stove – we recommend propane instead of electric

So you see it’s easy – most appliances have the watts or amps printed on a fixed tag on the unit. You can convert amps to watts by using for following formula. Watts = Amps x Volts (120). We want to know watts because that is where we start with energy used and this amount is what we need to produce from our solar panels, wind generator and or gas generator. We take the total daily usage from the example list in watt\hours. Multiply the percent of the hour (i.e. 15 min. equal .25 of an hour) by the watts.

Our example shows 2,344 watt hours being used on a daily basis. Now that we have an idea of the power we need let’s look at solar panels. Framed solar panels are the most common vs. flexible panels and power film. Solar panels are also called modules, different name but same product. Solar modules come in a variety of sizes, usually determined by wattage.

An example is a solar panel made by Shell called SP150, its rated power is 150 watts, weighs about 33 lbs and is 64” long by 32” wide by 2” deep; a large rectangle. Different manufacturers do, of course, different things to enhance or build their panels. This can be ‘techy’ and the end result is usually the same – just compare that the wattage, voltage and warranty are the same when you check one product to another. Some modules already have a pre-wired positive and negative cable (short ones) others a simple junction box on the back side for wiring connections.

Another very important item to be aware of is UL listing. If you buy or your installer sells you any electrical product i.e. panels that are not UL Listed, the state electrical inspector will reject the installations. A few manufacturers and suppliers will sell you non UL listed equipment if you ask for it. You may know that UL are the initials for Underwriters Laboratory, a testing company that tests products for safety and performance.

Anyway back to module sizing – we also need to make a choice between 12 volt, 24 volt or 48 volt for our energy system. These are the standard flavors, but not the only ones. A modest system can do well on 12 volt, a system that needs lots of power may need 48 volt. However most homes have a 24 volt system and are adequately powered. Not all modules com in either 12 or 24 volts.

If you use 12 volt modules for a 12 volt system it’s pretty straightforward with regard to wiring. If you use 12 volt modules for a 24 volt system you have to use 2 panels wired in series to get 24 volts. We can talk a lot about different voltages and wiring at another time. For now let’s get back to sizing our system. Let’s use a standard 120 watt module that is 24 volts. This panel will produce 120 watts (rated) per hour of direct sun.

In Colorado at 39 degrees latitude north we can receive 5.7 hours of direct sun per day. Direct sun hours are call insolation hours. If we multiply 120 watt (module) by 5.7 hours we get 684 watts. Modules are not 100% efficient so we need to down rate their output by a factor of .7. This means our 120 watt module gives us 479 watts per day. Our daily use says we need 2,344 watts so we divide that 2,344 by 479 to get 4.89 or 5 panels.

Note, there are options to increase your output and factoring in autonomy; this means how long can you use your system without being charged, i.e. no sun. Please keep in mind that, sooner or later, you will have to get ‘techy’ if you plan to do it yourself. Sometimes it is better not to try to build your own power plant when there are professionals that can find out what your requirements are and deliver a product suited to your needs.

About the Author
Larry LeDue has been designing, installing, and servicing solar systems since 1990. He is an active/certified member/installer with COSEIA; and lives with his wife in an active and passive solar home they built in South Park, Colorado.

This article is the property of Sustainable Solutions, Inc.
You may use it for noncommercial purposes, provided this credit line is included in its entirety.

Return to Top