Are Photovoltaics Right for Me

An Economics Approach to Solar Power by Richard Perez

See why and howphotovoltaics can save you money in yoursystem. All swell details such as initial cost, payback time, & operating cost are revealed. Come see what PVs can do for you.

In the coming months we will be talking about a wide variety of topics relating to solar generated electricity: the PVs themselves, trackers, mounting racks, controllers, instrumentation, and how the PVs fit into the entire alternative energy system. This first solar article is about one of the most commonly asked questions about PVs. "Are PVs right for me? Will they work in my system. Will PVs save me money?" This is an economic examination of the use of photovoltaics in a small alternative energy system.

It's A System!

An alternative energy system is just that-- a system. It is composed of several parts, and each of these parts must be properly proportioned in order to economically function together as a system. A high degree of harmony and proportion between these individual parts is just as necessary in an alternative energy system as it is for say, an orchestra or a football team. So in order to discuss the economics of solar, we must examine the economics of the entire system.

In this example system the question we are asking is, "Is it economical to add photovoltaics to this system?" Well, first we need to know more about the people using the system, how much and what type energy they are planning on using.

Meet the Smiths

For this example, let's discuss a family of four members,

Mom, Pop and two children. Assume that this family, let's call them the Smiths, are considering moving to the country on their dream property. The only problem is that their dream property is located some 1 mile or more from the nearest electrical utility line. The power company gives Mr. Smith a quote of say $30,000. to

run the power lines to his property.

The actual rates for running in commercial electrical service vary with locality. In the Western US, the rate is about $5.50 per foot. In some US locales, the rate may be over $10.00 per foot. The Smiths are considering using a gasoline powered mechanical generator because as Mr. Smith puts it, "You can burn up a lot of generators and gas for $30,000."

Well, Mr. Smith is just about right. If the power company wants this much just to run in the power lines, then he can definitely generate his own electricity cheaper than he can buy it from the utility. Once Mr. Smith has firmly decided this, he then needs to consider what type of hardware and how much hardware he needs to roll his own power. Mr. Smith is hesitant; he is unsure if he knows enough about alternative energy to put the system together himself, have it work, and meet his needs.

The Smiths are also not pleased with the idea of a noisy generator running all the time. Noise is one thing they are moving to the country to get away from. The Smiths' property has neither wind or water power potential. Mr. Smith asks a company that specializes in alternative energy systems what his options are.

Planning Ahead is the Key

The first step in any alternative energy system is a realistic estimation of how much power and what type of power is needed. This estimate assures that the completed system will, in fact, meet the Smith's electrical needs.

Mr. Smith talks with his family and they decide that they are willing to limit their power consumption to essential uses only. The family needs electricity for such essential uses as pumping water from their deep well, lighting, refrigeration, a washing machine, a vacuum cleaner, sewing machine, kitchen appliances, and entertainment electronics. The company helping Mr. Smith suggests that since the deep well pump and the washing machine are such large and intermittent loads, they be powered only by a mechanical generator. This reduces the size of the batteries and inverter required for the system, and reduces the overall cost. Mr. and Mrs. Smith decide that they are willing to start their generator for water pumping and clothes washing periods.

This still leaves many appliances which will be operating on the battery/inverter portion of the system. Appliances like lighting, TVs, and Stereos are relatively small consumers but operate for hours at a time. The refrigerator turns itself on whenever necessary, and must have a continuous source of power. Small appliances such as the vacuum cleaner, sewing machine, food processor, VCR, and kitchen mixer are used intermittently, and it's not worth starting the generator just for them. Items such as these are prime candidates for battery/inverter supplied power. It is convenient, silent, and available 24 hours a day without the generator running at the time. The batteries are periodically recharged by the generator through the battery charger built into the inverter.

The Smiths draw up a list of each and every appliance they are planning on powering from the battery and inverter. On this list each appliance has its wattage noted, and an estimate of how many hours per day it will be operating. The sum of the wattages determines the size of the inverter, and the operating times determine the capacity of the battery pack. The company helping the Smiths suggests that their lighting and refrigeration be powered by 12 VDC directly from the battery. This reduces the size of the inverter, and once again saves the Smiths money.

The Smith's Electrical Consumption

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