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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Power optimizer</span></span>

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<div id="mw-content-text" class="mw-body-content mw-content-ltr" lang="en" dir="ltr"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><p>A <b>power optimizer</b> is a <a href="DC_to_DC_converter" class="mw-redirect" title="DC to DC converter">DC to DC converter</a> technology developed to maximize the energy harvest from solar <a href="Photovoltaic" class="mw-redirect" title="Photovoltaic">photovoltaic</a> or <a href="Wind_turbine" title="Wind turbine">wind turbine</a> systems. They do this by individually tuning the performance of the panel or wind turbine through <a href="Maximum_power_point_tracking" title="Maximum power point tracking">maximum power point tracking</a>, and optionally tuning the output to match the performance of the <a href="String_inverter" class="mw-redirect" title="String inverter">string inverter</a> (DC to AC inverter). Power optimizers are especially useful when the performance of the power generating components in a distributed system will vary widely, such as due to differences in equipment, shading of light or wind, or being installed facing different directions or widely separated locations.

</p><p>Power optimizers for solar applications can be similar to <a href="Microinverter" class="mw-redirect" title="Microinverter">microinverters</a> in that both systems attempt to isolate individual panels in order to improve overall system performance. A <a href="Smart_module" class="mw-redirect" title="Smart module">smart module</a> 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.

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<div class="mw-heading mw-heading2"><h2 id="Description">Description</h2></div>

<div class="mw-heading mw-heading3"><h3 id="Maximum_power_point_tracking_(MPPT)">Maximum power point tracking (MPPT)</h3></div>

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</style><div role="note" class="hatnote navigation-not-searchable">For broader coverage of this topic, see <a href="Maximum_power_point_tracking" title="Maximum power point tracking">Maximum power point tracking</a>.</div>

<p>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 the power can be efficiently drawn from the cell.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> 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.

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<p>Solar panels have similar issues due to the speed at which the cell can convert solar <a href="Photon" title="Photon">photons</a> into <a href="Electron" title="Electron">electrons</a>, 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, the "I-V curve".<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> In order to optimize collection, modern solar arrays use a technique known as "<a href="Maximum_power_point_tracking" title="Maximum power point tracking">maximum power point tracking</a>" (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.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>

</p><p>Traditionally, solar panels produce voltages around 30 V.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> This is too low to be effectively converted into <a href="Alternating_current" title="Alternating current">AC</a> to feed to the <a href="Power_grid" class="mw-redirect" title="Power grid">power grid</a>. To address this, panels are strung together in series to increase the voltage to something more appropriate for the inverter being used, typically about 600 V.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup>

</p><p>The drawback to this approach is that <a href="Maximum_power_point_tracking" title="Maximum power point tracking">MPPT</a> 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 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.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup>

</p><p>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.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> 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%.<sup id="cite_ref-8" class="reference"><a href="#cite_note-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup> 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.

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<div class="mw-heading mw-heading3"><h3 id="Isolating_panels">Isolating panels</h3></div>

<p>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.

</p><p>One solution, the <a href="Microinverter" class="mw-redirect" title="Microinverter">microinverter</a>, 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 <a href="Price_per_watt" class="mw-redirect" title="Price per watt">price per watt</a>.

</p><p>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.

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<div class="mw-heading mw-heading3"><h3 id="Implementation">Implementation</h3></div>

<p>Power optimizers are essentially <a href="DC-DC_converter" class="mw-redirect" title="DC-DC converter">DC-DC converters</a>, taking the DC power from a solar panel at whatever voltage and current is optimal (via MPPT), then converting that to a different voltage and current that best suits the central / <a href="String_inverter" class="mw-redirect" title="String inverter">string inverter</a>.

</p><p>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.<sup id="cite_ref-9" class="reference"><a href="#cite_note-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> 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.

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<div class="mw-heading mw-heading2"><h2 id="Notes_and_references">Notes and references</h2></div>

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<li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">Venkat Srinivasan, <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110320042908/http://gigaom.com/cleantech/the-three-laws-of-batteries-and-a-bonus-zeroth-law/">"The Three Laws of Batteries"</a>, GigaOm, 18 March 2011</span>

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<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text">N. Shenck, <a rel="nofollow" class="external text" href="http://alumni.media.mit.edu/~nate/AES/PV_Theory_II.pdf">"PV Power Systems: PV Theory II"</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20100719205838/http://alumni.media.mit.edu/~nate/AES/PV_Theory_II.pdf">Archived</a> 2010-07-19 at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a>, MIT</span>

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<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.innovativesolar.com/images/File/BSE_What_is_MPPT.pdf">"What is Maximum Power Point Tracking and How Does it Work?"</a>, BlueSky Energy</span>

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<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.backwoodssolar.com/catalog/Spec_Sheets/SolarWorld_245_Spec.pdf">SolarWorld's SW 245</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20120813034046/http://www.backwoodssolar.com/catalog/Spec_Sheets/SolarWorld_245_Spec.pdf">Archived</a> 2012-08-13 at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a> is a typical modern panel, using 6" cells in a 6 by 10 arrangement and a <span class="mwe-math-element mwe-math-element-inline"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle V_{oc}}">

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<annotation encoding="application/x-tex">{\displaystyle V_{oc}}</annotation>

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</math></span><img src="./50372875d5b3cde21c879306c04348a3ac5e0e47.svg" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:3.097ex; height:2.509ex;" alt="{\displaystyle V_{oc}}" loading="lazy"></span> of 30.8 V</span>

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<li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.sma-america.com/en_US/products/grid-tied-inverters/sunny-boy/sunny-boy-3000-us-3800-us-4000-us.html">SMA's SunnyBoy</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110408045414/http://www.sma-america.com/en_US/products/grid-tied-inverters/sunny-boy/sunny-boy-3000-us-3800-us-4000-us.html">Archived</a> 2011-04-08 at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a> series comes in US and European versions, and generally suggest 500 to 600 VDC inputs.</span>

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<li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://eiqenergy.com/parallel_solar/increase_power.php">"Increase Power Production"</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110516132706/http://eiqenergy.com/parallel_solar/increase_power.php">Archived</a> 2011-05-16 at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a>, eIQ Energy</span>

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<li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text">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.</span>

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<li id="cite_note-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-8">^</a></b></span> <span class="reference-text">Muenster, R. [“Shade Happens”] Renewable Energy World.com <a rel="nofollow" class="external free" href="http://www.renewableenergyworld.com/rea/news/article/2009/02/shade-happens-54551">http://www.renewableenergyworld.com/rea/news/article/2009/02/shade-happens-54551</a> 2009-02-02. Retrieved on 2009-03-09.</span>

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<li id="cite_note-9"><span class="mw-cite-backlink"><b><a href="#cite_ref-9">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://www.solaredge.com/sites/default/files/se_application_fixed_string_voltage.pdf">SolarEdge Technical Note - Fixed String Voltage, Concept of Operation</a></span>

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