Power optimizer
Overview
Power optimizers are a technology developed to maximize the energy harvest from solar photovoltaics systems. They do this by maximizing the output from each solar module in a string. Because solar modules are usually wired sequentially within an array, when one fails, the entire system can see electricity generation significantly reduced. By avoiding this problem, power optimizers can increase the performance of solar systems, improving an owner’s return on investment (ROI). They can also increase the available installation area for a PV system, particularly in sites prone to partial, temporary shading.
Disproportionate power loss
Because of their sequential wiring, power mismatch between PV modules within a string can lead to a drastic and disproportionate loss of power from the entire solar array, in some cases leading to complete system failure[1] Shading of as little as 9% of the entire surface array of a PV system can, in some circumstances, lead to a system-wide power loss of as much as 54%.[2]
To explain the mismatch problem, most panels are created with a centralized form of performance optimization carried out by the array solar inverter. Most solar arrays also comprise panels connected in a series of parallel strings. Each panel feeds a DC current into the inverter, which then converts it to AC using while also optimizing the PV array's power generation through maximum power point tracking (MPPT). In turn, each panel is comprised of cells also connected in series.
To prevent the whole string of cells failing when one cell underperforms — like Christmas tree lights, which are also strung together in series — the typical installation is equipped with "bypass diodes." These reroute the current around the underperforming cells. The catch is that rerouting the current loses not only the potential energy from these cells, but also lowers the entire string's voltage.
The inverter is left with bad options: optimize the voltage for the underperforming string or maximize the energy harvest from the unaffected strings. In most cases the inverter chooses the former, causing the energy harvest of the impaired string to drop to near zero.
Mismatch can be caused by a range of real-world phenomena including mis-performing solar cells, particularly in older systems where the cells have been in situ for a period of years. Another key cause of mis-matching panel performance is in some cases structural objects such as trees or handrails. Over time, this power loss can have significant impacts on a solar array owner’s return on investment (ROI), impacting the economic rationale for solar power, leading to installers and home-owners not utilizing roofspace because of the shading and mismatch problems.
Power optimizer solution
Power optimizers can recoup up to around 50% of this lost energy. They do so by harvesting the maximum potential power of each module individually. They can thus significantly enhance the ROI for the array owner. They can also increase the available surface area for the installation of a solar array, particularly in situations where there may be structural shading of the array at certain hours of the day or during certain seasons of the year. Manufactured by National Semiconductor, of California, under the proprietary name of SolarMagic power optimizers, they will be commercially available from May 2009.[3]
== Notes and references ==
- ^ Chaintreuil, N. et al. “Effects of Shadow on Grid Connected PV System” INES R.D.I. Laboratory for Solar Systems (L2S), Le Bourget-du-Lac, France. Bruendlinger, R. et al. “Maximum Power Point Tracking Performance Uner Partially-Shaded PV Array Conditions” Paper submitted to the 21st European Photovoltaic Solar Energy Conference, 4-8 September 2008, Dresden, Germany.
- ^ Muenster, R. [“Shade Happens”] Renewable Energy World.com http://www.renewableenergyworld.com/rea/news/article/2009/02/shade-happens-54551 2009-02-02. Retrieved on 2009-03-09.
- ^ Wilson, R. ["National Semiconductor protects solar panels from shadows"] http://www.electronicsweekly.com/Articles/2009/03/05/45608/national-semiconductor-protects-solar-panels-from-shadows.htm, EletronicsWeekly.com, 2009-03-05. Retrieved on 2009-03-10.