California’s energy crisis, with its well-publicized rolling blackouts, effectively depleted the state’s 15 percent energy reserve. In efforts to restore it, Gov. Gray Davis is calling for a heavier reliance on green power—including solar—through the California Power Authority. The “Greening Public Buildings Program” aims for installations of 625 megawatts on state and local government buildings and schools by 2006. Thirty million dollars of tax-exempt industrial development bonds are available to provide below-market-rate loans to manufacturing companies producing or choosing to install clean energy solutions. Add that to a “Buydown Program” for homeowners. While that state is leading the way, it is not alone. Dozens of others also host rebate and tax incentive programs.
What does this mean for the electrical contractor? Opportunity. Yet many contractors are unfamiliar with the details of the technology. “It’s so close to our traditional work,” said Todd Stafford, director of instrumentation, solar photovoltaics curriculum development and training for the National Joint Apprenticeship Training Committee (NJATC), which is offering “Solar Training for Contractors” at sites across the country. “It takes very little additional knowledge from what they already know to be able to pick this industry up.”
And what would that knowledge be? Here’s a primer.
The basics—Learn the lingo
Solar photovoltaic cells, which convert sunlight to electricity without any moving parts, noise, pollution or radiation, are made of a semiconductor material treated chemically to create positive and negative charge layers. Cells laid side-by-side form a module. Several modules form an array. It produces a direct current (DC). Conversion from DC to alternating current (AC) is accomplished through an inverter.
Conduct a site survey
“Each system is different. Each application is different,” said Terry Colbert of Dynalectric, San Diego. Checking out the physical situation where an installation will be placed is the first order of business. For instance, are there trees that will grow and be a problem later? “Even shade from an antenna will cause the cells to stop functioning, turning them into a resistor and cutting down on output to system,” said Colbert. “If part of one set of modules is blocked, it will shut the whole panel down.”
Take advantage of pre-engineered systems
While there are companies that manufacture the components of photovoltaic systems, integrators create pre-engineered systems by buying components from a variety of companies and then assembling them as a kit with an inverter, charger, control, battery backup and all the disconnecting means already installed. “If electricians don’t understand how to mix and match pieces, the system may not work at optimum performance. Or at all,” said Stafford.
Learn installation methods to use with DC
Traditional wire splicing that is used with AC is not recommended with DC. Using the twist-on wire connections on DC power sources will generally cause a hot spot over a period of time, a fault condition that can start fires and depreciate performance. While most electricians know about overcurrent protection means, fuse holders and fuse sizes, wire conductor size and temperature de-rating, which is covered in the apprenticeship program, they need to learn how to apply that knowledge to the photovoltaic field.
Install disconnect means on every power source
“We’re used to disconnecting the switches and working on the load side which is no longer energized when it’s in the ‘off’ position. Now it’s going to be energized,” said Stafford. On the terminal block locations, where the hardware, terminating conductors from DC side to the inverter to AC is mounted, there has to be a disconnect means—a way to shut off the photovoltaic array and the battery sources as well as any emergency standby generators that may be available if there are any critical load backups.
Establish a single point of reference
With photovoltaics, electricians must combine grounding systems and bonding systems to create one single point of ground for the inverters. At that point, an installer bonds the neutral and the ground together that maintains a single point of reference for all the overcurrent protection devices.
Determine the airflow around the array
While the heat of the sun provides the fuel for photovoltaic modules, it can also create problems. How? Heat creates resistance. An air gap underneath panels helps cool them. While some systems are installed to sit directly on a roof, with edges that prevents the wind from getting underneath, that is not the installation recommended for the typical modules, which sit above the roof and have air flow on both sides.
Understand the value of single or string inverters
Here’s a scenario. An installer does a site survey, notes that the sun hits the roof in both the morning and the afternoon and installs modules on both sides of the roof. Does this sound logical? If that is set up as a single system with one inverter, the module that is in the sun in the morning will act as a resistor while the afternoon sun heats the other module. An alternative is to use two string inverters, like two separate arrays. When the one module is in the shade, that inverter automatically shuts it down. For the cost of another inverter, more energy is created with a better payback.
Understand the importance of the array angle
“Generally for one single installation, an array should be face due south, tilted at latitude, for all-year performance,” said Stafford. Then again, with an understanding of different parameters, the installation can sometimes be manipulated. Colbert and fellow teacher/electrician, Richard Case, are teaching a class at the San Diego JATC, in which the students are constructing a 32 kW system on the roof of the JATC facility. “Instead of pointing our array due south so that it would peak out at noon, we tilted our array so that it points west and peaks around 1:30 p.m.,” said Colbert. The change in direction results in the creation of more energy during peak hours. Since the utility pays more for energy created in that time slot, the JATC profits. “We moved our power curve into a more profitable direction of the sky,” said Case. “Calculations for time of use, and orientation are rather complex, and are affected greatly by season. However, we are forecasting about a 15 percent increase in the value of our annual production.”
That’s not a bad idea for any business. EC
CASEY is the author of Women Invent! Two Centuries of Discoveries That Have Shaped Our World (Chicago Review Press). She may be contacted at Scbooks@aol.com.