With high voltage DC current, it is difficult for typical circuit protection devices to interrupt the circuit reliably under the range of operating conditions likely to occur in a solar energy system. Given that solar PV panels generate DC power, the current and voltage are constant for a given level of irradiance on the PV panels. This is driven by the fundamental principle that AC circuit voltage reaches zero volts twice during each voltage cycle, which is a key factor affecting circuit protection devices’ ability to interrupt the voltage safely and isolate the troubled circuit. It is much more difficult for a circuit protection device to interrupt DC voltage than the equivalent RMS AC voltage. The designer must carefully determine that the circuit protection device being used on the DC side of a solar energy system has been designed, tested and certified to a PV standard by an outside agency such as Underwriters Laboratories (UL) or VDE to be confident that the device will operate properly in the event of a fault. Although the circuit breaker method is convenient, as a general rule, it is not always the best approach. ![]() Wherever they are used, it is necessary to analyze the circuit to determine the available fault current (that is, the short-circuit current) of the system in comparison to the over-current capabilities of the components and then install appropriate circuit protection devices to prevent damage to PV modules, disconnects, wiring, and wiring devices.Ĭircuit breakers are often the preferred method of protection on the AC side of a solar energy system, and it may be tempting to try using the same circuit breakers on the DC side. These common connection points help simplify assembly and maintenance of the system. In most cases, multiple strings and arrays are connected using combiner boxes in accessible locations. Designing circuits and specifying components for these high voltage solar energy applications is very different from the same tasks when applied to other DC power systems or even high power AC applications.įigure 2: Typical solar energy electrical system In their new positions, these new PV system designers may be called on to design solar energy circuits on a scale of 1MW DC for connection to the electrical grid. For example, a company that is now producing small solar inverters may have previously focused on building power conversion or UPS systems. Solar energy systems involve relatively new technology, so PV system designers often have greater experience in working on different types of electrical and electronic systems. These engineers are typically involved with the design of electrical circuits for solar arrays, DC combiner boxes, or inverters. ![]() Many of these designers are charged with creating electronics that optimize the performance and cost of PV installations. Responsibility for practical PV electrical system development eventually falls on of the shoulders of electrical circuit designers, including those who work for companies that create complete solar energy systems, system integrators who provide turnkey systems to end customers, and designers of various solar energy subsystems. This need has been recently highlighted by an announcement from the US Department of Energy (DOE) regarding its “SunShot” initiative, which is aimed at reducing the total costs of utility-scale PV energy systems by about 75 percent, and designed to make them cost competitive with other methods of electrical power generation. Although a great deal of development work is still focused on making photovoltaic (PV) energy conversion more efficient, there is also an acute need to make the delivery of solar power more efficient, reliable and cost-effective. The global demand for green energy sources is driving strong market growth for solar power systems.
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