Photovoltaic Tutorial

Table of Contents:


Note: To look up photovoltaic terms highlighted in yellow throughout this guide, we recommend that you bookmark this glossary provided by the National Renewable Energy Laboratory (NREL).

A home solar electric system is basically a power plant built to serve one customer -- you. Even better, the source of its energy doesn't need to be mined, drilled or hauled anywhere for processing. There's no trail of toxic pollutants and greenhouse gases. The sun just sits there in the sky, open for business most days of the year, giving away its joules for free. Who said fighting climate change had to be difficult? With photovoltaics, you can tap into that hydrogen gold mine above as easily as flipping on a light switch in your house.
Most home photovoltaic systems supplement power from the utility grid, providing the same high-quality AC current needed to power appliances, lights, tools and other loads. An inverter transforms the DC electricity from the solar array once it moves downstream to your main service panel. Whatever electricity is not needed immediately in your home gets deposited into the grid, available for use elsewhere in the neighborhood. Naturally, your meter will record that contribution.

While the cash outlay for a home PV system is on par with a new automobile, the investment should earn you big money over the long haul. For the average homeowner, the breakeven point is typically about seven years. After that, your earnings start to accrue on utility charges you no longer pay each month. And if financing the system purchase is a problem, an FHA energy efficient mortgage may be available to cover the cost of the installation. Tax credits and rebates are also available. Moreover, since utility rates are expected to spike in coming years, it means your decision to go solar now can amount to a huge cash bonanza down the road.

Now here's the very good news... Through the tax year of 2016, the IRS will reimburse a homeowner for 30 percent of the cost of a qualifying PV system in the form of an income tax credit. For example, if your system costs $24,000, your credit is $8,000. Add to that other incentive programs offered jointly by state governments and utility companies, and you can recoup up to 40 percent of your investment within a year (or less) of your system going online! See Tax Credits and Incentives for details.

There are other perks as well. Depending on the utility company, payment of your monthly kilowatt hour charges may be deferred for a year once your PV system goes online. That can add up to $1,200 or more. (You can use this money to make loan payments instead.) At the end of 12 months' time, the utility will true up your bill, subtracting your earnings in solar power from those kilowatts furnished by the grid. Either you'll pay the difference, or the utility will issue a credit for what it owes you.

If you can't get a loan or find the money to purchase a solar power system outright (which is usually the best approach), in some states you can lease the equipment or enter into what's called a Power Purchasing Agreement. A PPA lets another company finance the installation and own the equipment. Then that company acts as your solar utility.

Diagram showing the flow of energy through an off-grid PV system. In order to store generated power for later use, a bank of batteries is needed. A charge controller regulates the flow of PV electricity into the batteries so they won't get over or under charged. Although most grid-tied (i.e. grid-connected) systems don't use batteries, having back-up power for long-term outages is not a bad idea.

What's included in this tutorial

This online guide introduces you to the components of a residential grid-tied PV system. It also explores options like a backup battery bank and data monitoring equipment. While your local solar company can provide some of this information, it helps to be an informed shopper. Nowadays, many companies charge $200 for the initial home visit and site survey. While they may offer to cancel the fee if you agree to their purchase terms, should you decide not to accept the company's bid, you'll be out all the cash.

So read on. Once you learn about all the equipment and how it's fastened together to generate electricity, you'll be ready to tackle the next tutorial on this website, Steps to Going Solar. This guide walks you through the site assessment, system sizing, component selection, and installation details. You'll also find a complete set of sizing worksheets. (While you may not be interested in the nuts and bolts of planning an installation, be sure to take a peak at the cost/payback/profit analysis on the worksheet menu.)

Of course, recommends that you hire a licensed contractor to oversee or complete the tasks involved in any installation. No building inspector will approve the work if it doesn't meet the requirements of the National Electric Code and local ordinances. So if you do decide to take a chance and go it alone, you better do your homework first.

Whether your home's solar power will plug into a utility grid, or act as a standalone unit, your contractor will design a system to generate sufficient power to meet your needs for 20+ years. Standalone PV systems require detailed planningto cover 100% of your electrical needs, since there's no power grid to fall back on. On the other hand. most city/suburban homes use grid-tied systems that offset only a portion of what the power grid provides. That's because your utility's baseline rate is relatively cheap. So cheap, in fact, that it might require 20 years to reach a breakeven point if you were to produce 100% of the electricity you need annually. It's more practical to offset just the higher tiered or peak rates, since this is where utility customers generally get taken to the cleaners each month. Thus, the majority of grid-tied PV systems are designed to deliver a 30-65% offset, which means a system size of 2-6 kilowatts and a price tag (before tax credits) of $12,000 to $24,000.

Once the solar electric system is installed and commissioned, your role as homeowner consists mainly of watching your net meter pile up the energy credits, sort of like a stock that never goes down (except maybe in winter). Since most photovoltaic panels (aka modules) are guaranteed to produce power efficiently for 25 years, you'll probably never need to replace them. Only occasional cleaning and inspections are necessary after the system is up and running, since there are no moving parts or motors to worry about.

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Next: Anatomy of a PV Panel

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