In the first Techie Top Tip of 2019, Jordan, Technical wizard explains the benefits of oversizing an array.
"Oversizing a PV array in relation to the inverter is an easy and cost effective solution to maximise the benefits offered by solar PV. Put simply, it involves connecting an amount of solar panels that is greater in terms of Wattage than the rated capacity of the inverter; which allows the inverter to operate closer to its maximum output for longer periods throughout each day."
To understand how to oversize your PV arrays you must first know how to calculate their size. This can be done by multiplying the Wattage of a single solar panel by the total number of panels in the array. For example; 16 x 250W solar panels creates a 4000W (4kW) rated PV system.
To find out the size of an inverter either check the physical label on the unit or the data sheet online. If it’s an inverter that Segen sells then this information can be found under the respective tab on the products page of our portal. You’re generally looking for Rated Power or P AC.
On a typical 4kW PV system you may be tempted to choose a 4000W rated inverter to match the potential output of your array, but there are actually a few reasons why you may want to reconsider.
Take a 250W rated panel as an example; this panel is only rated 250W based on STC (Standard Testing Conditions) and these conditions are rarely met in real environments. Panel output can be affected by temperature, weather, module defects, shading and even local wildlife. You may find due to a combination of these factors your PV system is generating considerably lower than its total panel rating in Watts (and if you don’t notice this, the homeowner usually does). Oversizing allows you to reduce the effects of these factors as the added modules should make up for everyday energy losses.
More importantly in the UK if you were to fit a 4000W rated inverter you would actually be exceeding the acceptable limit for installing under G83. The primary limitation of any PV system in the UK is what the DNO (District Network Operator) allows you to export back to the grid. Despite the upper limit of the UK domestic system climbing to 10kW’s recently - the rules regarding G83 and G59 have remained the same. As such you cannot exceed 3680W or 16A per phase without having to file under a G59 application.
The G83 limit of 3680W is based on the rated AC output of the solar inverter and not the potential Wattage of the total number of installed PV panels. This is why some installers choose to fit as many panels as possible within an inverter’s acceptable limits so that the system generates consistently higher than a typical system without there ever being any danger of the system exporting more than it should.