A power optimizer is a DC to DC converter technology developed to maximize the energy harvest from solar photovoltaic or wind turbine systems. It is done by individually tuning the performance of the panel or wind turbine through maximum power point tracking, and optionally tuning the output to match the performance of the string inverter (DC to AC inverter). Power optimizers are especially useful when the performance of the power generating components in a distributed system vary widely, such as due to differences in equipment, shading of light or wind, or being installed facing different directions or widely separated locations.
Power optimizers for solar applications can be similar to microinverters in which both systems attempt to isolate individual panels in order to improve overall system performance. A smart module is a power optimizer integrated into a solar module. A microinverter essentially combines a power optimizer with a small inverter in a single enclosure that is used on every panel, while the power optimizer leaves the inverter in a separate box and uses only one inverter for the entire array. The claimed advantage to this "hybrid" approach is lower overall system costs, avoiding the distribution of electronics.
Most energy production or storage devices have a complex relationship between the power they produce, the load placed on them, and the efficiency of the delivery. A conventional battery, for instance, stores energy in chemical reactions in its electrolytes and plates. These reactions take time to occur, which limits the rate at which power can be efficiently drawn from the cell.[1] For this reason, large batteries used for power storage generally list two or more capacities, normally the "2 hour" and "20 hour" rates, with the 2 hour rate often being around 50% of the 20 hour rate.
Typical cell I-V curves showing the relationship between current, voltage and total output for differing amounts of incoming light.
Solar panels have similar issues due to the speed at which the cell can convert solar photons into electrons, ambient temperature, and a host of other issues. In this case there is a complex non-linear relationship between voltage, current and the total amount of power being produced as shown by the "I-V curve".[2] In order to optimize collection, modern solar arrays use a technique known as "maximum power point tracking" (MPPT) to monitor the total output of the array and continually adjust the presented load to keep the system operation at its peak efficiency point.[3]
Traditionally, solar panels produce voltages around 30V.[4] This is too low to be effectively converted into AC to feed to the power grid. To address this, panels are strung together in series to increase the voltage to something more appropriate for the inverter being used, typically about 600V.[5]
The drawback to this approach is that MPPT system can only be applied to the array as a whole. Because the I-V curve is non-linear, a panel that is even slightly shadowed can have a dramatically lower output, and greatly increase its internal resistance. As the panels are wired in series, this would cause the output of the entire string to be reduced due to the increased total resistance. This change in performance causes the MPPT system to change the operation point, moving the rest of the panels away from their best performance.[6]
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.[7] 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%.[8] Although this problem is most notable with "large" events like a passing shadow, even the tiniest differences in panel performance, due to dirt, differential aging or tiny differences during manufacturing, can result in the array as a whole operating away from its best MPPT point. "Panel matching" is an important part of solar array design.
Isolating panels
These problems have led to a number of different potential solutions that isolate panels individually or into much smaller groups (2 to 3 panels) in an effort to provide MPPT that avoids the problems of large strings.
One solution, the microinverter, places the entire power conversion system directly on the back of each panel. This allows the system to track the MPPT for each panel, and directly output AC power that matches the grid. The panels are then wired together in parallel, so even the failure of one of the panels or microinverters will not lead to a loss of power from the string. However, this approach has the disadvantage of distributing the power conversion circuitry, which, in theory, is the expensive part of the system. Microinverters, at least as late as early 2011, had significantly higher price per watt.
This leads, naturally, to the power optimizer concept, where only the MPPT system is distributed to the panels. In this case the conversion from DC to AC takes place in a single inverter, one that lacks the MPPT hardware or has it disabled. Advanced solutions are able to work correctly with all solar inverters, to make possible optimisation of already installed plants. According to its supporters, this "hybrid" approach produces the lowest-cost solution overall, while still maintaining the advantages of the microinverter approach.
Implementation
Power optimizers are essentially DC-DC converters, taking the DC power from a solar panel at an optimal voltage and current via MPPT, then converting that to a different voltage and current that best suits the central / string inverter.
Some power optimizers are designed to work in conjunction with a central inverter from the same manufacturer, which allows the inverter to communicate with the optimizers to ensure that the inverter always receives the same total voltage from the panel string.[9] In this situation, if there is a string of panels in series and a single panel's output drops due to shade, its voltage will drop so that it can deliver the same amount of current (amps). This would cause the string voltage to drop as well, except that the central inverter adjusts all the other optimizers so that their output voltage increases slightly, maintaining the fixed string voltage required at the inverter (just at reduced available amperage while the single panel is shaded). The down side of this type of optimizer is that it requires a central inverter from the same manufacturer as the optimizers, so it is not possible to gradually retrofit these in an existing installation unless the inverter is also replaced, as well as optimizers installed on all panels at the same time.
↑ 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 Under Partially-Shaded PV Array Conditions” Paper submitted to the 21st European Photovoltaic Solar Energy Conference, 4–8 September 2008, Dresden, Germany.
An uninterruptible power supply or uninterruptible power source (UPS) is an electrical apparatus that provides emergency power to a load when the input power source or mains power fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions, by supplying energy stored in batteries, supercapacitors, or flywheels. The on-battery run-time of most uninterruptible power sources is relatively short but sufficient to start a standby power source or properly shut down the protected equipment. It is a type of continual power system.
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially used for electricity generation and as photosensors.
A solar inverter or photovoltaic (PV) inverter is a type of power inverter which converts the variable direct current (DC) output of a photovoltaic solar panel into a utility frequency alternating current (AC) that can be fed into a commercial electrical grid or used by a local, off-grid electrical network. It is a critical balance of system (BOS)–component in a photovoltaic system, allowing the use of ordinary AC-powered equipment. Solar power inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protection.
Maximum power point tracking (MPPT) or sometimes just power point tracking (PPT), is a technique used with variable power sources to maximize energy extraction as conditions vary. The technique is most commonly used with photovoltaic (PV) solar systems, but can also be used with wind turbines, optical power transmission and thermophotovoltaics.
A solar panel is a device that turns sunlight into electricity by using photovoltaic (PV) cells. PV cells are made of materials that generate electrons when exposed to light. The electrons flow through a circuit and produce direct current (DC) electricity, which can be used to power various devices or stored in batteries. Solar panels are also known as solar cell panels, solar electric panels, or PV modules.
Solar-powered pumps run on electricity generated by photovoltaic (PV) panels or the radiated thermal energy available from collected sunlight as opposed to grid electricity- or diesel-run water pumps. Generally, solar-powered pumps consist of a solar panel array, solar charge controller, DC water pump, fuse box/breakers, electrical wiring, and a water storage tank. The operation of solar-powered pumps is more economical mainly due to the lower operation and maintenance costs and has less environmental impact than pumps powered by an internal combustion engine. Solar pumps are useful where grid electricity is unavailable or impractical, and alternative sources do not provide sufficient energy.
A solar tracker is a device that orients a payload toward the Sun. Payloads are usually solar panels, parabolic troughs, fresnel reflectors, lenses or the mirrors of a heliostat.
A grid-tie inverter converts direct current (DC) into an alternating current (AC) suitable for injecting into an electrical power grid, normally 120 V RMS at 60 Hz or 240 V RMS at 50 Hz. Grid-tie inverters are used between local electrical power generators: solar panel, wind turbine, hydro-electric, and the grid.
A photovoltaic system, also PV system or solar power system, is an electric power system designed to supply usable solar power by means of photovoltaics. It consists of an arrangement of several components, including solar panels to absorb and convert sunlight into electricity, a solar inverter to convert the output from direct to alternating current, as well as mounting, cabling, and other electrical accessories to set up a working system. It may also use a solar tracking system to improve the system's overall performance and include an integrated battery.
The nominal power is the nameplate capacity of photovoltaic (PV) devices, such as solar cells, modules and systems, and is determined by measuring the electric current and voltage in a circuit, while varying the resistance under precisely defined conditions. The nominal power is important for designing an installation in order to correctly dimension its cabling and converters.
SolarEdge is an Israeli company that develops and sells solar inverters for photovoltaic arrays, energy generation monitoring software, battery energy storage products, as well as other related products and services to residential, commercial and industrial customers. Established in 2006, the company also has offices in Germany, Italy, Japan, and United States. It is incorporated in Delaware. The company was the first to successfully commercialize power optimizers, a device that offers module-level maximum power point tracking (MPPT), before feeding back the electricity generated into a central inverter.
eIQ Energy, Inc. is a venture-backed Silicon Valley startup that designs and manufactures power electronics for solar photovoltaic systems. The company's Parallel Solar technology, built around the vBoost DC converter module, is intended to reduce overall system costs and enable a true parallel architecture, benefiting system designers, installers and operators. eIQ Energy was founded in 2007 and is headquartered in Santa Clara, California.
tenKsolar designs, manufactures and markets an integrated photovoltaic system that leverages integrated electronics and a low-voltage, parallel architecture. Compared to conventional solar systems, the architecture provides 45% better energy density, higher reliability, and is the only PV system that is both shock and arch flash safe.
A rooftop solar power system, or rooftop PV system, is a photovoltaic (PV) system that has its electricity-generating solar panels mounted on the rooftop of a residential or commercial building or structure. The various components of such a system include photovoltaic modules, mounting systems, cables, solar inverters and other electrical accessories.
A nanoinverter, also referred to as a nano inverter or solar nano inverter, converts direct current (DC) from a single solar cell or small solar panel to alternating current (AC).
A photovoltaic power station, also known as a solar park, solar farm, or solar power plant, is a large-scale grid-connected photovoltaic power system designed for the supply of merchant power. They are different from most building-mounted and other decentralized solar power because they supply power at the utility level, rather than to a local user or users. Utility-scale solar is sometimes used to describe this type of project.
SolarBridge Technologies (SolarBridge) is a provider of solar micro-inverter, solar inverter for photovoltaic arrays. These types of products aim to increase energy harvest and reliability while reducing the cost of solar installations and maintenance for residential and commercial markets. The company was acquired by solar panel manufacturer SunPower in autumn of 2014. In 2018 SunPower sold the former SolarBridge microinverter business to Enphase Energy.
Tigo Energy is an American private corporation, headquartered in Campbell, California, United States. It provides products, technologies, software, and services to installers, distributors, and original equipment manufacturers within the photovoltaic industry. It specializes in module-level power optimizers and smart module power electronics.
Enphase Energy, Inc. is an American energy technology company headquartered in Fremont, California, that develops and manufactures solar micro-inverters, battery energy storage, and EV charging stations primarily for residential customers. Enphase was established in 2006 and is the first company to successfully commercialize the solar micro-inverter, which converts the direct current (DC) power generated by a solar panel into grid-compatible alternating current (AC) for use or export. The company has shipped more than 48 million microinverters to 2.5 million solar systems in more than 140 countries.
Photovoltaic system performance is a function of the climatic conditions, the equipment used and the system configuration. PV performance can be measured as the ratio of actual solar PV system output vs expected values, the measurement being essential for proper solar PV facility's operation and maintenance. The primary energy input is the global light irradiance in the plane of the solar arrays, and this in turn is a combination of the direct and the diffuse radiation.
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