Solar Inverter and Specification Terms You Need to Know
Clipping/Scalping – This is the term used to describe the energy output that is lost due to undersizing an inverter. Any given inverter has a maximum power rating (at the residential level, measured in W or kW). When solar supplies DC power in excess of that inverter’s maximum power rating (what the inverter can handle), the resulting power is “clipped.” It’s important to consider the solar panel arrays’ maximum power output and select an inverter with the correct size, model, and type in order to avoid excessive clipping. It’s normal for the DC system size to be about 1.2x greater than the inverter system’s max AC power rating. For example, a 12 kW solar PV array paired with a 10 kW inverter is said to have a DC:AC, or “Inverter Load Ratio,” of 1.2. When one takes into account real-world, site-specific conditions that affect power output, it may make sense to size the solar array a bit larger than the inverter’s max power rating, as there may be very few “power-limiting days,” or instances of clipping for that system.
Inverter Efficiency – A percentage that tells us how much DC power input to an inverter comes out as usable AC power. No inverter is 100% efficient, although some come close in favorable conditions. In the conversion from DC to AC, power is lost in the form of heat. While inverter efficiency is an important factor to consider in the selection process, there are other factors to consider that also affect a project’s economics, such as warranty, price, expected life, serviceability, and monitoring functions.
Maximum Power – This is the highest amount of power allowed to feed into an inverter, which is a function of the inverter’s specifications or the maximum power a solar panel can produce. This will occur at the optimal trade-off between voltage and current along a given panel’s I-V (current and voltage) curve.
Maximum Power Point (MPP) – A solar system’s power output will vary with conditions, such as how much sunlight it receives, temperature, and other factors. A fixed-tilt, stationary, roof or ground-mounted solar PV system might only produce its maximum rated power during a limited period of the day. Every specific solar cell has its own unique I-V curve, which relates its maximum power output to variations in current (I) and voltage (V).
Maximum Power Point Tracker (MPPT) – A device that periodically tracks characteristics of a given panel, string of panels, or system, and optimizes and varies voltage and amperage accordingly in order to produce maximum power.
Micro-Inverter – A device that converts direct current (DC) produced by a single solar panel into alternating current (AC). Micro-inverters are commonly connected to and installed at the site of, or behind, each individual solar panel in an array. Most micro-inverter makes are installed in the field, while some come panel-integrated by the manufacturer. Popular brands of micro-inverters include: Enphase, Chilicon, APS, ABB, SMA, and SunPower.
Optimizer – A DC-DC converter, optimizer, or “panel optimizer,” is a module-level power electronic device that increases the solar system’s energy output by constantly measuring the MPPT of each individual panel. The panel optimizers relay performance characteristics via a monitoring system to facilitate operations and any necessary maintenance. In essence, optimizers support flexible system designs and arrangements – with multiple panel orientations, tilts, azimuths, and module types in a given string. Because optimizers are a DC-DC, or DC-coupled, technology, systems using this technology will generally be compatible with DC-coupled energy storage or battery backup solutions, like the Tesla Powerwall. Perhaps the most advantageous benefit of using a DC optimizer is panel-level MPPT, or max-power point tracking. The result is increased energy harvest from a panel system, especially when subject to periodic or sweeping shade.
Peak Power Point – Another term for Maximum Power Point (MPP).
String Inverter – The device that converts direct current (DC) electricity produced by groups of solar panels (called strings), into usable alternating current (AC) electricity. String inverters are considered a “mature” solar technology that has proved effective, safe, and reliable. Residential, 240V AC string inverters usually carry manufacturer’s warranties of about 10 years. When installed to a manufacturer’s specifications, code, and best practices, a string inverter may require service or ultimately replacement during a photovoltaic system’s lifespan. Check with Pick My Solar to understand what is covered by your solar system’s workmanship warranty, as well as the inverter manufacturer’s warranty. Depending on what one’s goals, budget, and preferences are, string inverters can be a great option for your solar PV system.