{"id":15269,"date":"2015-10-05T09:09:20","date_gmt":"2015-10-05T08:09:20","guid":{"rendered":"http:\/\/en.sma-sunny.com\/?p=15269"},"modified":"2017-12-13T16:09:45","modified_gmt":"2017-12-13T15:09:45","slug":"string-versus-micro-which-is-the-right-choice","status":"publish","type":"post","link":"https:\/\/www.sma-sunny.com\/en\/string-versus-micro-which-is-the-right-choice\/","title":{"rendered":"String versus Micro \u2013 Which is the Right Choice?"},"content":{"rendered":"

When it comes to making decisions about a PV system, one of the most common decisions a system owner has to make is whether to choose a micro inverter or a string\u00a0inverter. As one of the only inverter manufacturers globally to offer a full range of micro, string and central inverters, SMA is best placed to understand the difference between each of these products and technologies, and provide the product best suited to each specific application. Below we discuss a number of factors related to PV systems and the relative advantages of both micro and string inverters to help make the right technology choice for each individual application.<\/strong><\/p>\n

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\"Roof<\/a>

Roof installations which might require the flexibility of a micro inverter<\/p><\/div>\n

Grid Support Functions & Install Flexibility<\/h5>\n

Where local grid operators require the PV system to have grid support functions such as reactive power, specific power factor correction set points, low voltage fault ride through or export control, string\u00a0inverters are the best option. SMA\u2019s current model string inverters all have the ability to provide varying levels of grid support dependent upon the individual requirements of the system and grid operator. Micro inverters are not able to provide the same level of grid support, yet.<\/p>\n

For system installs on tricky roof structures, or where sub-sections of a PV array need to be separated or installed on different orientations, a micro inverter can represent the simplest and lowest cost system. Since micro inverters are AC coupled and individually track their PV module\u2019s maximum power point, they are more flexible in how and where they can be installed compared to DC coupled PV panels and a string\u00a0inverter.<\/p>\n

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PV Array Oversizing<\/h5>\n

Oversizing the PV array is a tool used by system designers and installers to improve the performance of a PV system while reducing the specific cost in $\/W. It involves installing a DC rated capacity greater than the inverter\u2019s AC rating. It is possible to do this because under normal operating conditions, a PV array rarely achieves its rated output (mostly due to voltage dependant temperature de-rating<\/em>). Oversizing the PV array makes better use of the inverter\u2019s rated capacity and increases the energy output from a PV system. String inverters are the simplest, most suitable and lowest cost option for oversizing, because all that is required is to either increase the length of the PV module strings, or increase the number of parallel strings.<\/p>\n

It is also possible to take advantage of oversizing when using a micro inverter system, however, it will typically result in a much higher specific $\/W investment. To oversize a PV array using micro inverters requires the use of higher power PV modules. Since these modules typically attract a premium price compared to standard power PV modules, the overall system cost will be higher for a similar performance benefit compared to an oversized array with a string inverter.<\/p>\n

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Performance &\u00a0Shading<\/h5>\n

Under normal unshaded conditions, a string inverter will typically offer the lowest cost and greatest energy yield. For varying degrees of partial shading of the PV array, a micro inverter can offer slightly higher performance (~1 – 4%).<\/p>\n

Under normal un-shaded conditions<\/em><\/strong>, a correctly sized string\u00a0inverter system will typically outperform a correctly sized micro\u00a0inverter system by ~0.5%. Micro inverters are able to reduce some very small losses such as DC cabling and any module mismatch, but they have a lower operating efficiency. Put together, this means string\u00a0inverter systems will typically outperform micro inverter systems in normal un-shaded conditions.<\/p>\n

Under permanent or partial shade conditions<\/em><\/strong>, the answer is more complicated. To help understand these complicated factors, SMA commissioned a US based independent PV research laboratory (PV Evolution Labs) to investigate the effect of shade on system performance. The study compared a variety of shading conditions on the performance of a:<\/p>\n