![]() They work with ungrounded PV array and require over-current protection of both positive and negative conductors as well as a special safety warning per NEC® 2014 Article 690.35.Simply put, series wiring will add the voltage of your panels together and parallel wiring will keep them the same. There are transformerless models as well. Note that many systems provide isolation between DC input and AC output in high-frequency boost converter stage, and do not use a bulky low-frequency output transformer. In this case, their inputs are paralleled, and outputs are connected in series. However, many of them can be synchronized and stacked in a so-called master-slave mode for 120/240 VAC output. In practice, inverter models usually provide only single 120VAC. The solar wiring diagram above shows a configuration with an inverter that provides 3-wire split phase 120/240 VAC which is typical for US household systems. That is why a special peak power tracker that charges the batteries while forcing the PV array to operate at an MPP is an important part of any solar system design.Ī DC voltage from the battery bank is then converted to AC by a DC-AC inverter. This requires different loading depending on the illumination and ambient temperature. To extract the maximum power out of the array, the PV panels should operate near maximum power point (MPP) of their I-V curve. To protect them from overcharging or from discharging by reverse currents, normally they are connected to the PV array via a battery charger. The current from the PV array is charging the batteries. It is a device that is designed to open the circuit when a certain leakage current to ground from an ungrounded bus is detected. The main DC disconnect switch is followed by a DC ground fault interrupter. A metal oxide varistor (MOV) is commonly used in such applications. To reduce the possibility of a fire and to protect the system from a damage caused by lightings, it is recommended to have a voltage-clamping device across the DC buss. Since PV arrays are mounted outside, they can act like lightning rods. A DC disconnect switch should be installed near the place where the cables from the combiner enter the house. The combiner's frame or the PV arrays grounding conductor should be wired to a ground rod located as close as possible to the arrays. However, most battery chargers and inverters come factory configured for negative ground systems. In theory, you can ground either plus or minus. In all solar wiring configurations, if the DC voltage is over 50 volts, one of two DC busses should be grounded, unless the system has additional protections per NEC® 690.35. However, I understand, with a proper conductor size, up to three strings are allowed to go to the same fuse. If you parallel several strings of solar panels, it is desirable to use a combiner with a fuse or a circuit breaker for each string to prevent the panels' damage from possible reverse currents. PV panels can be connected in series and parallel- see various solar panel wiring methods. In a single-phase 3-wire setup it has to be the neutral bus. Particularly, one AC output conductor is supposed to be grounded. However, it still may be a good idea to do the installations and grounding in accordance with the National Electrical Code (NEC®) NFPA 70 and UL 1741 as well as local electrical codes. Of course, you should check if your local authorities have any permit and safety requirements. As far as I know, there are no regulations that specifically pertain to the off-grid PV systems because they may be outside the jurisdiction of electric utilities. PRINCIPLES OF THE DESIGN AND PV ELECTRICAL WIRINGīelow is a simplified solar panel system wiring diagram for an off-grid home. By the way, another reason batteries should be used off-grid is to operate the PV cells near their maximum power point. ![]() Fuel-powered electric gensets are also often used as an another auxiliary energy source that simplifies the isolated system's sizing. To reduce the size of the panels and the battery bank, solar systems for off-grid homes are often supplemented with wind turbines that can produce electricity at night and during cloudy periods. ![]() If the off grid home has no other power source, both the PV array and the battery bank have to be significantly oversized by design to account for possibly several days of inclement weather. ![]()
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