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A typical silicon PV solar cell is composed of a thin wafer consisting of an ultra-thin layer of phosphorus-doped (N-type) silicon on top of a thicker layer of boron-doped (P-type) silicon. An electrical field is created near the top surface of the cell where these two materials are in contact, called the P-N junction. When sunlight strikes the surface of the PV solar cells, this electrical field provides momentum and direction to light-stimulated electrons, resulting in a flow of current when the solar cell is connected to an electrical load Regardless of size, a typical silicon PV solar cell produces about 0.5 – 0.6 volt DC under open-circuit, no-load conditions. The current (and power) output of a PV solar cell depends on it’s efficiency and size (surface area), and is proportional to the intensity of sunlight striking the surface of the cell. For example, under peak sunlight conditions, a typical commercial PV solar cell with a surface area of 160 cm^2 (~25 in^2) will produce about 2 watts peak solar power. If the sunlight intensity were 40 percent of peak, this cell would produce about 0.8 watts.
Photovoltaic solar cells are connected electrically in series and/or parallel circuits to produce higher power levels. Photovoltaic modules consist of PV solar cells circuits sealed in an environmentally protective laminate. Photovoltaic panels include one or more PV modules assembled as a pre-wired, field-installable unit. A photovoltaic array is the complete power-generating unit, consisting of any number of PV modules and panels. The performance of PV modules and arrays are generally rated according to their maximum DC power output (watts) under Standard Test Conditions (STC). Standard Test Conditions are defined by a module (cell) operating temperature, and incident solar irradiance level. Since these conditions are not always typical of how PV modules and arrays operate in the field, actual performance is usually 85 to 90 percent of the STC rating. Today’s photovoltaic modules are extremely safe and reliable products, with minimal failure rates and projected service lifetimes of 20 to 30 years. Most major manufacturers offer warranties of 20 or more years for maintaining a high percentage of initial rated power output. When selecting PV modules, look for the product listing (UL/cUL/CSA), qualification testing and warranty information in the module manufacturer’s specifications.
Solar batteries allow for the storage of solar photovoltaic energy, so we can use it to power our homes at night or when weather elements keep sunlight from reaching the solar panels. Using deep cycle (AGM/Silicon/Lead Acid/Lithium) batteries, keeps the solar energy available at all times. Galex is focusing on delivering the best energy efficient solution for your solar power system.
Not only can they be used in homes, but batteries are playing an increasingly important role for utilities. As customers feed solar energy back into the grid, batteries can store it so it can be returned to customers at a later time. The increased use of batteries will help modernize and stabilize our country’s electric grid.
Solar inverters are used to convert the direct current (DC) electricity generated by solar photovoltaic modules into alternating current (AC) electricity, which is used for local transmission of electricity, as well as most appliances in our homes. Solar PV systems either have one inverter that converts the electricity generated by all of the modules, or microinverters that are attached to each individual solar panel. A single inverter is generally less expensive and can be more easily cooled and serviced when needed. The microinverter allows for independent operation of each panel, which is useful if some modules might be shaded.
Advanced inverters, or “smart inverters,” allow for two-way communication between the inverter and the electrical utility grid. This can help balance supply and demand either automatically or via remote communication with utility operators. Allowing utilities to have this insight into (and possible control of) supply and demand allows them to reduce costs, ensure grid stability, and reduce the likelihood of power outages. Smart inverters also plays a crucial role into smart buildings. Manage the solar power you need and use with your mobile devices. Stay connected to your solar system wherever you are!
PV solar arrays must be mounted on a stable, durable structure that can support the array and withstand wind, rain, hail, and corrosion over decades. These structures can be tilted or fixed angle determined by the local latitude, orientation of the structure, and electrical load requirements. To obtain the highest annual solar energy output, modules in the northern hemisphere are pointed south and inclined at an angle equal to the local latitude (more or less). Rooftop mounting is currently the most common method because it is robust, versatile, and easy to construct and install. More sophisticated and less expensive methods continue to be developed.
For PV arrays mounted on the ground, tracking mechanisms automatically move panels to follow the sun across the sky, which provides more solar energy and higher returns on investment. One-axis trackers are typically designed to track the sun from east to west. Two-axis trackers allow for modules to remain pointed directly at the sun throughout the day. Naturally, tracking involves more up-front costs and sophisticated systems are more expensive and require more maintenance. As systems have improved, the cost-benefit analysis increasingly favors tracking for ground-mounted systems.
Photovoltaic solar systems have a number of merits and unique advantages over conventional power-generating technologies. PV solar systems can be designed for a variety of applications and operational requirements, and can be used for either centralized or distributed power generation. PV systems have no moving parts, are modular, easily to install and upgrade. Energy independence and environmental compatibility are two attractive features of PV solar systems. The fuel (sunlight) is free, no noise or pollution is created from operating solar systems. In general, alternative energy systems that are well designed and properly installed require minimal maintenance.
At present, the high upfront cost of PV solar modules and equipment (as compared to conventional energy sources) is the primary limiting factor for the technology. Consequently, the economic value of PV systems is realized over many years. In some cases, the surface area requirements for PV arrays may be a limiting factor as well. Due to the diffuse nature of sunlight and the electrical energy conversion efficiency of solar panels, surface area requirements for PV array installations are on the order of 6 to 8 m² (64 to 86 ft²) per kilowatt of installed peak capacity.
However battery storage must be used. This type of system is extremely popular for homeowners and small businesses where a critical backup power supply is required for critical loads such as refrigeration, water pumps, lighting and other necessities. Under normal circumstances, the system operates in grid-connected mode, serving the on-site loads or sending excess power back onto the grid while keeping the battery fully charged. In the event that grid becomes unavailable, control circuitry in the solar inverter opens the changeover switch with the utility and operates the inverter from the battery to supply power to the dedicated loads only. In this configuration, the critical loads must be supplied from a dedicated distribution panel.