Do Solar Inverters Make Noise?
Electrical Noise Emissions from a Solar PV Inverter / Charger
Electrical interference is a problem that could be experienced with electronics of the solar power system. At least some noise is created by any new electronic equipment and almost all of the equipment now used in PV systems is new. Charging controllers and many inverters (particularly modified sine wave inverters) pose the most common problems. Nearly all charging controllers send pulsed power to batteries and high-speed electrical pulses are among the worst sources of interference.
Electrical interference may be in the form of radio waves emitted from a system (termed RFI interference–radio frequency interference) or may not be radiated, such as line noise from power or control lines (termed EMI–electromagnetic interference). Nearly all consumer appliances and electronic equipment sold today must comply with FCC Part B-which limits the maximum amount of EMI that can be radiated by devices. Yet almost all DC and solar equipment is excluded from Part B, meaning they can put out a lot of EMI and still be legal. In the case of grid-tied PV inverters, the specifications IEEE 1547, UL 1741 and FCC Part 15B provide guidelines for regulating the harmonic contents of the inverter output current and EMI generation. Such guidelines ensure inverters do not produce unnecessary noise and harmonics, which can contaminate the voltage of the AC grid.
Inverters can be categorized as square wave inverters (basic and least effective), modified sine wave (an approximation to sine wave output), and true sine wave by their output waveform. Any deviation from a true sine wave means that harmonics of high frequency are produced and can be radiated or conducted into the atmosphere. A simple square wave inverter simply switches every half cycle between positive and negative outputs. These inverters also have trouble starting motors, are less powerful and generate a lot of distortion that can be heard as a buzzing sound sometimes. The sine wave inverters are the most expensive inverters but they generate the purest AC current that matches the grid’s current, has the highest output and the least distortion. Modified sine wave inverters are in between and are used in PV systems where sensitive equipment is not in use. Modified square wave inverters are ideal for the service of a wide variety of loads including motors, lights and standard electronic equipment such as TVs and stereos.
Due to lower performance, engines such as refrigerator motor, pumps, and fans may use more power from the inverter, some fluorescent lights do not run as brightly, and some can bumble or make irritating bumbling noises. Appliances with electronic timers and/or digital clocks frequently struggle to operate properly.
Normally, noise emissions from inverters are minimized by a combination of shielding, noise cancelation, filtering, and noise reduction. For inverters and some other equipment, metal enclosures are popular. The use of twisted, shielded pairs for cabling is a common and efficient method. Filtering is a common feature of almost all electronics. The most common approach is to use condensers to get rid of the noise through a signal line or wire to ground. More recently, the use of ferrite chokes, cores, and beads to block the noise has become more widespread in PV installations. Noise emissions from PV systems are no big issue with correct equipment options, noise management strategies and sound construction practices.
What about actual sound from the inverter?
An inverter’s electronic noise can also have an audible component. Some electrical noise can’t be detected, but it’s a good idea to check the inverter’s decibel level before choosing the installation position in larger commercial inverters and some residential grid-connected or off-grid versions.
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