THE BASICS

We'll begin your Journey to electrical enlightenment with a quick overview of what goes into a home solar power system and a look at the specific components of the three main types of systems. Then we'll take a brisk walk through the installation process from start to finish. And that's pretty much all there is for the basics lesson, because then it's time to get to work.

Your first task is to make sure that a do-it-yourself (DIY) installation is not only desirable but also legal in your area. (It's not allowed everywhere.) If you give yourself the green light, great. If not, you can use this book to learn the essentials of going solar and gain confidence for choosing a good local professional solar installer and getting what you want. The next task is for everyone: determining how much electricity you use and thinking about where your solar system is most likely to go.

Anatomy of a Solar-Electric System

The science of turning sunlight directly into electricity is known as photovoltaics (PV), referring to photons of light and volts of electricity. Here's your 10-second lesson on how PV works: Solar panels, properly called PV modules (see You Say "Panels"; We Say "Modules,"), contain solar cells, which are most commonly made of layers of silicon, a semiconductor material made from sand (also the namesake of Silicon Valley). When photons of light enter a solar cell, they get absorbed and excite electrons in the silicon layers, causing them to move and, ultimately, flow continuously through a circuit of wiring that feeds into the PV system. Harnessing this electron flow is what gives you electrical power.

The electricity produced by PV modules (and used by all batteries) is direct current(DC), in which all of the electrons move in one direction only. Your home's electrical system and most appliances use alternating current (AC) power, in which the electrons move back and forth, alternating direction about 60 times per second. Therefore, PV systems include one or more inverters that convert the DC solar-generated electricity to usable AC power for your home (and, with grid-tied systems, for selling back to the utility grid).

All home PV systems start with a collection of solar-electric modules, called the PV array. The array can be installed on a roof or on the ground. The modules in an array are usually wired together in groups, each called a series-string. The series-strings are joined near the array at a combiner box or other device, and wiring from the box brings the power to the rest of the system components at the ground level. The first component that these supply lines connect to depends on the type of system. The following pages give you a snapshot of the three main systems. We'll cover system types and hardware in greater detail in chapters 3 and 4.

Grid-Tied System

A grid-tied system is by far the most common type of residential PV system, as well as the simplest and least expensive. It connects to the electric utility grid and uses the grid for both "storage" and backup. When the array creates more power than the house uses, the excess power is fed back onto the grid — turning the utility meter backward — and you get credited for it. When the house needs more than the solar array provides, the house automatically pulls power from the grid.

Advantages of grid-tied systems include simplicity, low cost, and low maintenance, making them the obvious choice for homeowners who are already using utility power, which is most homeowners. But the grid is also the main disadvantage: when it goes down, so does the PV system. This automatic shutdown function, called self-islanding, is required by utilities for grid hookup for the safety of utility personnel working on the power lines.

Grid-tied systems can use one or more string inverters, which convert power from DC to AC for a group of modules at once, or microinverters, which convert power from DC to AC at each individual module or a pair of modules. A third option is to add DC optimizers to a string inverter system. DC optimizers (see here) add some performance optimization and monitoring features offered by microinverters, but they do not convert DC to AC at the module.

Off-Grid System

The ultimate in self-sufficiency, off-grid systems have no connection to the utility grid and are therefore the best choice for homes far from utility lines. They include a bank of batteries for storing solar-generated power during the day and feeding the house with power at night. These systems also may get additional backup power from a fuel-powered (usually gas, diesel, or propane) generator, which should be installed by an electrician. All solar electricity goes through the batteries; it does not power the house directly from the array. The batteries are charged by DC power from the array and are monitored and controlled by a device called a charge controller. Battery power is converted to AC (through a DC–AC inverter) before supplying the house.

Grid-Tied System with Battery Backup

A grid-tied setup can be combined with battery backup such that solar power charges the batteries and backfeeds the grid when there's an excess. When the house needs more power than the solar array produces, it can pull from the grid or the batteries. When the grid goes down, the batteries supply power to a critical loads subpanel, which serves a few household circuits. This enables you to keep important things like the fridge, lighting, computers, and perhaps a gas furnace running during power outages. The batteries typically do not power the entire house, as this would require a larger, more expensive battery bank.

Grid-tied systems with battery backup are relatively complex, technically sophisticated, and pricey, costing significantly more than a standard grid-tied system. There are two main types of battery backup systems: DC-coupled and AC-coupled. DC-coupled systems are the historical standard, while AC-coupled systems are becoming more common and are the only type allowed by some utility companies, because they make it easier to track solar production.

A couple of important notes about grid-tied systems with battery backup:

1. Given the complexity of these systems, it's best to hire a professional for the system design and installation. (Only the installation of the array hardware is the same as that for the grid-tied and off-grid systems shown in this book.)

2. You can add battery backup to an existing grid-tied system, depending on the system...