Should You Over-size Your PV Array?
Posted: 15 May 2019
Before tackling the question whether or not you should over-size your PV array lets first explain what we mean by over-sizing.
Over-sizing your PV array is when the total capacity of your PV array (solar panels) exceeds the size of your inverter. The way to check your PV array size is by multiplying the capacity (wattage) of a solar panel by the number of panels you have or plan to install. You can then compare this to the size of the inverter to distinguish whether you have over-sized your PV array (most inverters will have their size labelled on the component itself if you don’t already know).
So, if you have 20 x 250w panels, your full panel capacity would be 5kW. In many cases this is when households would typically opt for a 5kW inverter, so not to overload the inverter or waste energy.
However, what most people don’t know is by exceeding your inverters size with a few additional panels you can increase your inverters efficiency, increase your potential savings and reduce your bills further without breaking the rules on grid connection restrictions or damaging the inverter.
In fact, a 5kW inverter could take an additional 4 panels (totalling 24) equalling the panel’s capacity of 6kW.
Increase Inverters Efficiency
It’s rare that solar panels will generate energy at their maximum capacity due to so many external factors that can cause a drop. These factors can include weather, temperature, dust, shade etc. When power going to the inverter is under 30% of its capacity the efficiency* of the inverter drops. By having extra panels your system will generate more energy meaning the inverter will be converting energy at a higher percent with less chance of an interrupted drop.
*The efficiency of an inverter indicates how much DC power is converted to AC power.
In the case that your panels exceed the capacity of your inverter, any good quality inverter should be able to handle the excess (although it will essentially be wasted energy).
Increase Your Potential Savings & Reduce Bills Further
More panels equals more energy generated and more generated energy means less reliance on the grid, which in turn will reduce your power bills, giving you more savings. Annually you’d expect a 5kW inverter with a 6kW PV array to generate approximately the same amount of electricity that a 6kW inverter with a 6kW PV array would. This comes in handy when the grid you are connected to has restriction on what size you are allowed for your property.
Over-sizing Without Breaking Grid Connection Restrictions
In Australia there are restrictions on what size solar system you can have if you are grid connected. This is a restriction that energy retailers and the Clean Energy Council have put in place to avoid any disruption to the grid. Depending on which grid you are connected to the size restriction may vary, however for a single-phase home the maximum size is typically a 5kW inverter per property. If these restrictions are breached you are unable to claim any of the Solar Government incentives that are available in Australia. However a loophole around this restriction, which is stated in the Clean Energy Solar PV Design Guidelines is you can over-size your inverter by 33% meaning you can have a 5kW inverter with a PV array of 6.6kW. This will give you the benefits of a 6.6kW system without breaching any grid restrictions.
What Are The Disadvantages to Over-sizing?
Wasted Energy (clipped)
Whilst over-sizing your system by 33% won’t harm a quality inverter that is installed properly, there is potential for excess energy to be wasted. In perfect weather conditions (clear sky, 25-degree day) if your panels are generating energy in excess to the capacity of your inverter this excess power will be lost. When energy is lost from an over-sized PV array is is known as “clipped off” in the industry. While this is not ideal the occurrence of perfect conditions with no external factors hindering your PV array energy output is rare.
Lifespan of Inverter
By sticking within the regulations of over-sizing no more than 33% of your inverters capacity you will prevent any significant change to the inverter’s lifespan.
Benefits Outweigh the Disadvantages
Overall over-sizing your solar system can be hugely beneficial when staying within the Clean Energy Council guidelines. Not only is it a way to combat the grid restriction of a 5kW system, but it will maximise your inverters efficiency and generate more energy for your household with no to minimal risk.
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