Solar-Electric System Overview
Equipment, Components, Material, and Processes
Every morning begins with the arrival of increasing amounts of diffused light from the sun. As the earth turns, the sun rises higher in the morning sky, and the day brightens, as more and more of the sun’s photons (literally particles of sunlight) pass through the air around us, illuminating our world.
How Solar Modules work
When photons from the sun (not necessarily direct sunlight) hit a photovoltaic (PV) Solar Module (also known as a “solar panel”), they pass through the outer protective membrane(s) (usually glass or EPDM) and strike the underlying semiconductor material of an individual Solar Cell (usually a semiconductor wafer), where some of the photons are absorbed as a result of the interaction of individual photons with individual electrons of the semiconductor molecules. As these photons are absorbed, their energy is imparted to the electrons, knocking them out of their orbits. Once the electrons are out of their orbits, they begin to move, creating direct current, which is carried into and out of the solar cell through metallic contacts that are connected to the Solar Module bus bar. The bus bar combines the current of all of the Module’s individual Solar Cells and connects it to the Solar Module’s junction box, which is connected by two wires into a source circuit (“string”) of panels, which in turn is connected to a Combiner Box.
Solar Module economics
Because the combined cost of Solar Modules is typically 40% to 60% of overall PV solar-electric system cost, selecting the type of module (crystalline, thin-film, laminated) and power rating that will meet project-specific needs and that will provide the best return on investment is of paramount importance. All Solar Modules should be bankable, investment grade panels, carrying a 25-year warranty backed by a manufacturer with a solid reputation for quality products and service and strong financials.
The current produced by up to 24 strings of Solar Modules is brought together in a Combiner Box, which combines the current and routes it through larger-capacity copper wires to the DC disconnect (a safety switch) that is collocated with an Inverter. A Combiner Box works in a solar-electrical system much like a manifold does in an automobile, which combines the exhaust from up to six cylinders and routes it through a single exhaust pipe.
Although Combiner Boxes typically represent less than 1% of overall system cost, it is important that they are of the highest quality:
- Weather- tight, powder coated, gasket-sealed enclosures
- Tinned copper bussing to withstand effects of temperature changes and moisture
- Rated for 600v DC
As the sun gradually rises, more and more of the sun’s photons are absorbed by the Solar Modules, and the voltage produced by the Strings of Modules builds until it reaches about 400 volts, turning on the Inverter, which begins converting the direct current produced by the solar module into alternating current, typically 480VAC, which is fed through an AC disconnect into the building electrical system and the grid. In addition to converting DC to AC, Inverters provide safety functionality, such as an integral AC disconnect, which automatically removes the solar-electric system from the grid in the event of a grid power failure (keeping power from flowing back onto the grid where it would be a hazard to utility repairmen) and automatically reconnects the solar-electric when grid power is restored.
At 7% to 12% of the overall system cost, Inverters are among the most expensive and critical component in a solar-electric system. All Inverters should be investment grade, carrying a minimum 5-year warranty, with warranty extension options, backed by a manufacturer with a solid reputation for quality products and service and strong financials and should be reliable, efficient, and precise.
Unlike Modules and Combiner Boxes, which are very rugged, Inverters have many moving parts and sensitive components, including the switching devices that convert the incoming direct current into alternating current and the fans that cool the switching devices and other components. It is essential that the Inverters are designed to operate comfortably within the site-specific operating conditions; that they have a long mean time between failures (“MTBF”); that they have quality, fast, local service and support; and that they have a strong warranty.
High quality Inverters offer efficiency 97% and above; lower quality Inverters have efficiency ratings as low as 93%. Because each percentage point difference in efficiency equates to a percentage point difference in revenue, this component of the value of a high quality inverter is easily quantified.
Almost all electrical equipment is designed to operate on grid voltage, which is delivered by utility companies in perfect three-phase sine waves. Because imperfect sine waves will damage multiphase electric motors, which is the type of motor most commonly used for commercial applications, and some sensitive electronics, it is essential to have an Inverter that produces accurate three phase sine waves.
The entire solar-electric system is linked to a remotely located Performance Monitoring Reporting System (“PMRS”). Performance Monitoring and Reporting Systems are combined hardware/software web-based management systems that track system performance, track site weather, generate system reports, send alerts if the solar-electric system begins to perform abnormally, and perform system diagnostics.
Monitoring System economics
The cost associated with PMRSs is typically less than 1% of the overall system cost. Revenue grade metering (higher guaranteed accuracy) is required for all production-based incentives, including feed-in tariffs, renewable energy credits, and solar renewable energy credits. A quality PMRS will allow for outsourcing of service and maintenance, including management, monitoring, service, maintenance, and reporting, and will make system ownership easy.
Racking and Support Systems
The Racking and Support System must keep the Solar Arrays and associated wiring safe, sound, and secure for 25 years or more. There are four basic types of Racking and Supports Systems: Rooftop, Ground-Mount, Carport, and Multi-Purpose Raised Racking. The selected Racking and Support System must meet size and weight restrictions, severe weather parameters, geotechnical requirements, and other site-specific needs. Solar-Electric System plans must be reviewed and stamped by a structural and/or civil engineer(s) to ensure the systems do not compromise the buildings or ground upon which the systems will be deployed and to ensure code compliance. Ground-Mount, Carport, and Multi-Purpose Raised Racking systems may require zoning approvals.
Racking and Support System Economics
Racking and Support Systems can cost as much as 6% to 25% of the overall system cost and should be constructed of materials with an expected life of 25 years or more with a minimum material warranty of 25 years and minimum workmanship warranty of 5 years. The type of Racking and Support System and the design of the system will have a significant effect of the cost of installing the associated Solar-Electric System. And the orientation and tilt of a Racking and Support System will have a significant effect on the efficiency of a Solar-Electric System.
Self-adhesive laminated Solar Modules can be mounted on some membrane roofs without using a Racking and Support System, but their efficiency per unit area is lower than conventional crystalline panels.
Roof Mount Racking and Support Systems should be mounted on roofs that have suitable life expectancies.
Balance of System Materials
The Material used in the remainder of the Solar-Electric System (“Balance of System") is comprised of hundreds of different kinds of materials, much of which can be procured at varying levels of quality. Although electrical inspectors will typically ensure that the installed System is safe, their inspection criteria is based upon minimum standards and not based upon the 25-year minimum life expectancy of the System.
Balance of System Materials Economics
The Balance of System Materials typically cost between 4% and 7% of the overall System cost. All Material should conform to the 25-year minimum life expectancy of the System. All hardware should be made from the highest quality stainless steel, hot dipped galvanized steel, or other materials that will withstand the weathering, corrosion, perforation, stress fractures, and other antecedents to failure. Wire from Strings to Combiner Boxes and from Combiner Boxes to the Inverter should be UV resistant and rated for full weather exposure. Tie wraps should be used extensively for wire management, about 25,000 tie wraps for a 1MW roof mount installation, to gather and control wire so that the installation is clean and safe, while protecting the wire. Specialized wire management systems should be used for Ground Arrays and for Systems using Self Adhesive Laminated Solar Modules.
The importance of the efficiency, the quality, and the standards of excellence associate with the Installation of a Solar-electric System cannot be overstated. The best Equipment, Components, and Materials will be of little value unless they are part of a System that is designed, engineered, and installed properly. Moreover, once a System is installed, the System Owner is going to live with that System and ideally the people who designed, engineered, and installed it, for 25 years or more.
System Installation Economics
System Installation Costs, including design and engineering, are typically between 13% and 23% of the overall System cost, depending on the efficiency of the Installer.
Solar-Electric System Design should be accomplished by a team of engineers and installers who are assigned to the project and who visit the site to determine the best possible System configuration. Engineering should be done by an organization that specializes in Solar-Electric Systems, and whom has all of the engineering disciplines necessary for the preparation of complete plan sets, and that works closely with and is responsive to the installers. The installers should be solar specialists, who have a proven track record of high quality installations and who are fully accustomed to working with Solar-Electric System plans, equipment, components, and materials, as well as with the agencies, including local jurisdictions and utilities that are involved in permitting and commissioning.
Installers should be able to clearly address the following topics:
- Project safety
- Staging, including controls to limits the effects of the construction on facility business/operations
- Roof protection plans, methods, and procedures to insure the integrity of the roof is maintained, including the use of protective layers under all rooftop loading and staging areas
- Quality assurance and accountability, including aesthetics, wire management, conduit installation, wire termination and system testing
- Installation efficiency, including how teams are organized to do high quality work, efficiently with accountability
- How the relations with local utility, plan review, and the inspection authorities will be established and maintained
- Site cleanliness
- Tagging and labeling
- Interconnection commissioning protocols.
- Service and maintenance
- System documentation, including Operations Manuals and As-Built Drawings