Georgia Power linemen install photovoltaic panels on poles as part of an 18-month research project.
Photovoltaic (PV) panels are soaking up the sun's energy at the top of 50 distribution poles in Georgia. Georgia Power's linemen installed the solar panels as part of an 18-month research project with the Electric Power Research Institute (EPRI). The organization is studying how PV can affect the utility's distribution system in various climates and weather conditions. The purpose is to determine the overall PV performance in Georgia and the potential issues of high penetration of solar PV panels on the distribution system.
In December 2010, Georgia Power linemen installed 50 solar panels across the state. They installed seven solar panels on distribution circuits in six different cities, including Augusta, Columbus, Jonesboro, Macon, Savannah and Valdosta. The crews installed eight solar panels in Rome, Georgia. EPRI and Georgia Power selected the sites based upon a variety of environmental parameters, such as the cities' temperature, cloud cover and solar intensity.
Selecting Panel Locations
Once Georgia Power identified the list of cities, the utility then had to select certain distribution circuits based on a few factors. Engineers working in the seven different cities chose both the distribution circuits and pole locations for the panels. In each city, they selected one distribution circuit based on geographical diversity. The circuit had to be large enough in order to gain an adequate sampling of the geographical area.
In each circuit, the engineers chose seven Georgia Power-owned pole locations to house the solar panels. They used a Solar Pathfinder to determine the pole locations that received the most sunlight intensity and the least amount of shading. The engineers spaced the pole locations at least 1,000 ft apart, but not more than 1 mile apart.
To avoid shading on the panel, they took care to avoid any permanent obstacles such as buildings, trees and overhead lines. Shading reduces the power output of the solar panel. They also had to ensure that there was adequate ground and pole clearance for working space in the future. The engineers selected pole locations to control these hazards, but in some situations, the linemen had to modify the pole before they could install the solar panel.
Installing the Pole-Top Solar Panels
Georgia Power's distribution automation engineering team and line crews worked together to install the panels. The distribution automation engineering team constructed the solar panel assembly and trained the line crews on installation procedures. The solar panel assembly included the PV panel, pole-mount frame, monitoring equipment and fused service disconnect. The Georgia Power line crews installed the pole-top solar panels and will be responsible for maintaining and troubleshooting the panels during the 18-month project.
The team used Canadian Solar Inc. PV panels, which measure 3 ft by 5 ft. These panels generate about 200 W of electricity at maximum sunlight. For optimal sun coverage, the panels were positioned to face south and were installed at a 30-degree angle from the horizon.
The solar panels use PV cells to convert sunlight into electricity. As the sunlight strikes the PV cell, electrons are dislodged, creating an electric current. Solar-produced energy from these panels is not being stored. The energy is being delivered directly to the distribution system after being converted from direct current (40 V DC) to alternating current (240 V AC) using an Enphase Energy microinverter.
The linemen connected the solar panel to a distribution transformer through the secondary wires and a fused service disconnect. With the introduction of the solar panel, the transformer's demand is decreased, thus reducing the power requirements for the utility.
Whenever a utility adds distributed generation, such as solar panels, to the system, the company must employ methods to prevent the backfeeding of power during outage situations. This was Georgia Power's main safety concern and the microinverter was the solution. If the utility's power is lost, the microinverter will automatically open to separate the solar panel from the utility. This eliminates the possibility of backfeeding. The utility's distribution circuit must be energized for 5 minutes before the microinverter will make the connection.
The microverter is supported on the pole by a pole-mount frame manufactured by DCS Electronics. In addition to securing the solar panel to the pole at the proper angle, the frame also secures the monitoring box and the fused service disconnect.
EPRI designed the equipment, which monitors electrical, solar and environmental data at 1-second intervals. The monitoring box contains the power meter, pyranometer, thermistor and data logger. This monitoring equipment requires 120-V AC power from the utility to operate. The linemen installed a 120-V AC fused service disconnect for protection.
The power meter is a two-way meter that monitors the current, voltage and power output from the solar panel and input from the utility. The pyranometer monitors the sun intensity. This data is compared to the output of the solar panel to determine if it is operating properly. The thermistor monitors the temperature of the solar panel's surface. The pyranometer and thermistor will help to determine the efficiency of the solar panel. The data logger collects, stores and sends all this data to EPRI using an AT&T cellular signal.
Once the solar panel assembly was completed, it weighed about 90 lbs and required two people to lift it. The first challenge was to get the assembly up the pole safely. The pole-mount frames included lifting bolts for the bucket trucks to use to lift the solar panel assembly to make installation easier and safer. The pole-mount frame was bolted to the pole and secured with side supports. This eliminated twisting of the panel assembly.
The most significant challenge was clearance. The solar panels were installed below power and communication lines. For safe working space, the panels were installed either 40 inches or 72 inches below the lowest communications attachment depending on the location of overhead wires. They required more clearance if wires were directly above the panels. The solar panels must have a ground clearance of 11 ft over walkways or 15 ft over roads.
All components of the solar panel assembly were grounded together with a continuous grounding electrode and bonded to the pole ground. Requiring two buckets trucks and at least three linemen, the installation of one solar panel took about three hours to complete.
The distribution automation engineering team visited the Georgia Power headquarters in each of the seven cities to train the region personnel and line crews. The classroom-based training included instruction on installation, use and troubleshooting procedures.
For better understanding, field-based training included a demonstrational solar panel training pole that was built on the back of a trailer. This training pole included a fully operational solar panel showing all connections and required clearances. The line crews particularly enjoyed this training pole because it provided a visual representation.
All region personnel were excited to be included in the project that was leading the company in the study of solar panel technology.
Conducting Ongoing Research
EPRI plans to monitor each of the panels for power output and sunlight input at 1-second intervals for 18 months. The researchers will determine how much electricity each panel generates and how well they perform under diverse weather conditions.
EPRI is determining the ranges of overall PV performance in Georgia and characteristics and comparing variable issues such as passing clouds. So far, the researchers have discovered that the panels tend to perform in areas that are cool and less humid. In comparison, they don't deliver as much power output in cities with extreme heat and humidity.
After the study is completed, the panels will stay in place, and Georgia Power will monitor the long-term results. By working together, the utility and EPRI hope to identify whether or not the panels have an effect on the operation of the distribution system. They can then better understand the feasibility for photovoltaics on a wide-scale basis.
Alabama Power, a sister company, also has begun to participate in the EPRI research project. The utility installed 49 solar panels during 2011 across its service territory.
Georgia Power has been partnering with EPRI on renewable research projects for years, and by participating in this study, the utility hopes to find a way to feed clean, green electricity into its distribution system.
M. Scott Gentry (firstname.lastname@example.org) is the distributed generation services project manager for Georgia Power Co. He has been with the company for the last 15 years and works out of the Atlanta office but travels statewide. He has worked in region distribution engineering and has also worked as a project manager in the unregulated distribution business. He is responsible for managing the contracts for the utility's solar customers through the buy-back program and ensuring that the customers get interconnected to the system properly.
James Dye (email@example.com) is a distribution automation test engineer for Georgia Power Co. who helped to coordinate the photovoltaic installations in the field. He has been with the company for 10 years and works out of the Austell office. He worked as a region distribution engineer for eight years in the Macon, Dublin and Smyrna areas. He has been in the distribution automation department for the last two years focusing on the smart grid for Georgia Power.
Canadian Solar Inc. www.canadiansolar.com
DCS Electronics www.dcsfabshop.com
Electric Power Research Institute www.epri.com
Enphase Energy www.enphase.com
Georgia Power Co. www.georgiapower.com
Solar Pathfinder www.solarpathfinder.com