Is Solar Power a Bright Idea?

(See diagram below article)

BEC receives numerous calls each month asking how to make power using the sun. In an effort to gain more knowledge about solar power, the Co-op joined the Texas Renewable Energy Industry Association and through that connection discovered a good solar class. In August BEC sent three employees to a North American Board of Certified Energy Practitioners (NABCEP) approved course on solar electric systems.

Bill Holmes, engineering supervisor, and David Baker, training coordinator, all spent a week in the Dallas area taking the forty-hour class. The course covered all aspects of small solar setups and included a hands-on lab where students actually built a small roof-top system.

BEC wants to share some of the information learned. Obviously, there is not enough space here to cover the many technical aspects and considerations. We’ll just look at some highlights.

Solar Panel Types

The small solar power systems that are used today on homes are based on photovoltaic (PV) panels that convert sunlight into electricity. There are three types of PV commonly used: Single Crystal Solar Modules; Polycrystalline Solar Modules; and Amorphous Thin-Film Solar Modules.

Single Crystal is the most efficient and is the type most often used as panels on homes to make electricity. They have proven to last 20 to 30 years after being installed. Polycrystalline Solar Modules are less expensive and less efficient. They are used in applications requiring small amounts of power. Amorphous Thin-Film Solar is the least efficient, but is very versatile. They are made of pliable material and have been incorporated into roofing material and windows.

Grid-Tie Most Popular

The four solar power production configurations are: day use without power storage; day and night use with battery storage; grid tied systems that work in concert with utility power and hybrid systems that use a combination of storage, generators and/or grid-ties. The most commonly used PV installation on homes today is the grid-tie system.

Grid-tie systems supplement the power you receive from the utility and can reduce your electric bill by supplying some or all of your power usage needs during daylight hours. The new meters BEC is installing will measure power movement in either direction. Under this configuration you would only receive a bill from BEC for the power you use above what your panels can produce.

These PV systems make electricity using panels installed at your home. When there is a power outage the systems will also turn off.

Inverter and Safety Switches

The power inverter is a key component in PV systems. The unit converts the DC power coming from the PV array to AC power that we use in our homes. It also integrates the power produced by the solar panel with the power from BEC’s grid. The inverter has special safety features that turn off power flow from the PV system in the event of a power outage. This prevents electricity from flowing to BEC lines while linemen are working on the wires.

A safety switch is required on either side of the inverter. The voltage is often as high as 400 on the DC side of the circuit and the switch should be clearly marked. The safety switch on the AC side must be a type that can be locked open by BEC.

Types of Installation

The roof mounted PV solar system is the most prevalent style of installation. It involves mounting a specially designed rack to a homeowner’s roof support trusses. The racks are required to hold the PV modules in place in winds up to 90 MPH (130 MPH on the coast). They are attached at the same pitch as the roof and set about four inches above the roof surface. In order to get good production the roof needs to be south facing.

A critical consideration is the possibility that an object might shade any part of the PV array. There cannot be any shade that strikes the panels during the day or during any season of the year. A small amount of shade hitting only one section will not only reduce electricity production, but it will reduce the life of the panel.

Pole mounted systems are gaining popularity in rural areas where home owners have more land. These systems are installed on a single pole and can be equipped with an adjustment to manually change the array’s orientation to harvest more sun during various times of the year. They can be installed tall enough so they are out of the way.

Solar System Cost

The cost of these systems has come down in recent years and there is currently a federal tax credit covering 30 percent of the cost. Costs can vary according to one’s specific circumstances and the type of installation (ground, pole or rooftop mounted).

Sources in the PV industry tell us these systems generally run $7.50-$8.00 per watt installed. A typical Grid-tie 3,000 watt (3 kW) system should cost in the neighborhood of $22,000 to $24,000. A typical 3kW solar system in the San Antonio area can expect to produce 4,139 kilowatt-hours over the course of an average year, according to the PV Watts website (from National Renewable Energy Laboratory).

Conclusion

Solar PV systems have come a long ways in improving efficiency, lowering cost and using sensible installation methods. But, it is still new to most folks and some installers may not be trained as well as in other more established industries. If you are considering a solar installation be sure you are confident the installers know their business.



Other internet resources:
 Texas Renewable Energy Industries Association (TREIA)
American Solar Energy Society (ASES)
National Renewable Energy Laboratory (NREL)