When people talk of solar power efficiency they are almost always referring to the conversion efficiency of the photovoltaic (PV) panel. The PV conversion efficiency is the ability to turn available sunlight into a DC voltage and current. For most mass produced panels the efficiency number is in the teens. Improving the PV efficiency without increasing the cost improves the cost efficiency of solar power. Cost efficiency is the important number ($/watt).
There is another very important efficiency in the chain – the electronics conversion efficiency. The inverter and associated electronics have several functions. For a grid tied system they must convert the DC power from the PV panel into AC power, then sense the electric grid waveform and synchronize the output. PV panels have differing electrical characteristics under different temperature and illumination conditions. The goal is to always get the highest power output, and that output is dependent on voltage and current. The optimum operating point is called the Maximum Power Point. This point will vary with solar intensity and panel temperature, so complex algorithms might be involved to monitor and optimize the system production. Once the DC output is optimized the next opportunity is the efficiency of the conversion to AC power. The efficiency for this is much higher than PV efficiency. Some inverters currently operate at over 95% efficiency, though the average is probably closer to 90%. These efficiency numbers can also vary depending on the amount of load on the system.
As you might conclude improving the efficiency anywhere in the system chain (PV panels, power tracking, or inverter electronics) will improve the overall system efficiency and lower the cost/watt. Texas Instruments supplies several electronic components for a variety of inverter manufacturers including the recently announced Delfino MCU. We are striving to improve the tracking and conversion efficiency across the operating range of the PV panels and the inverter system. Solar power has always been the power of the future – and the future gets a little closer with every small efficiency gain.
Paul Westbrook
Sustainable Development Manager, SMTS, LEED AP
Original publication date: 03/11/2009
