How to maximise solar installation value with inverter clipping
As a solar installer, it is vital to know how to ensure a PV system is operating optimally and maximum value is being obtained for the home or business owner.
One of the lesser known ways to maximise value is with inverter clipping — but what is it and why should it matter to you?
What is inverter clipping?
Inverter clipping, or “inverter saturation,” occurs when the DC power from a PV system exceeds an inverter’s maximum input rating. The inverter may adjust the DC voltage to reduce input power, increasing voltage and reducing the DC. Alternatively, the inverter may restrict or throttle the inverter’s AC output.
Why is it important?
Contractors — more specifically, system designers — across the solar industry will evaluate the impact of inverter clipping on a system’s generation capacity and performance. Changing the DC/AC ratio is a powerful tool for optimising the system’s levelised cost of energy (LCOE) for long-term owners or increasing internal rates of return (IRR) for investors or developers.
In addition, it can make the power generation curve smoother to reduce the peak shaving pressure of the grid and increase the share of PV power.
Warning: not all inverters can accept higher DC/AC ratios!
If the inverter clips output power on the AC side, the internal AC components will wear out faster. Installers must be wary of overloading the DC side of the inverter as this may void the warranty, so it is crucial to check for a maximum DC/AC ratio on the manufacturer’s datasheet or consult SegenSolar directly.
Presently, some inverters reduce the DC input power and, therefore, the AC output power, without stressing internal components. Advanced string and central inverters will self-limit to protect the internal components, but any designer must keep the panels’ input voltage below the inverter’s maximum limit. Additionally, the maximum short circuit current of the system must not exceed the inverter’s rating or the maximum power rating of its DC components such as terminals, busbars and maximum power point trackers (MPPTs).
When is a PV system designed to clip?
An installer can determine what project size a new site can accommodate, but residential systems may be limited to a 40-amp breaker by the home’s main service panel. A larger, more expensive breaker panel would be needed to accommodate more solar. While a designer may be able to fit a more extensive PV system on site, a homeowner may decide to limit the inverter size to reduce costs or to match the site’s loads better.
Commercial building owners may find themselves in a similar situation if, for instance, their warehouse roof could accommodate 2MW of PV. However, if the local utility only accepts 1MW of power injection in the grid, commercial property owners should consider matching the panel output to this figure.
So, why would a homeowner or a commercial building owner encourage their solar designer to create a system that would clip the PV array power from 3% to more than 10%? In short, it is usually because the system owner wants to generate a higher IRR and increase the net present value (NPV) of cash flows.
Investors burdened by fixed costs — including permits, insurance, wire, racking and set O&M costs — want to get money back as quickly as possible. A high DC/AC ratio to maximise AC kilowatt-hour output helps to meet that goal.
Commercial asset owners will also design their systems to optimise IRR and NPV of cash flows accordingly. Large industrial-scale systems manage clipping loss to maximise profits during the first five years when both the Investment Tax Credit and the five-year depreciation revenues are realised.
Installers should take advantage of inverter clipping to accomplish the different goals of solar installations from residential rooftops to utility-scale solar farms.
Fine-tuning cash flows
Pushing the limits of DC loading on an inverter could be detrimental to its long-term service life. However, new inverters are designed to handle high-power systems. The total energy generation from the site is becoming more critical than clipping loss percentages, particularly for commercial owners. It is important to note that installing more modules does not increase the installation cost per panel. As more panels are added, the DC/AC ratio increases until the costs balance against any expected added revenue.
Midday sunshine on days of high irradiance will ‘max out’ the inverter’s AC output rating. What’s more, a PV system with a higher DC/AC ratio will produce more power in the early mornings and late evenings than a system with a standard ratio. The graph below demonstrates this:
Solis’ top of the range of solar products
DC/AC ratio limits are meant to ensure the AC components remain within their tolerances if the designer overloads the inverter on the DC side. Luckily, many new inverters (such as those in the Solis Residential Single-Phase portfolio) automatically reduce the AC output by adjusting the DC voltage and current.
Solis’ products have inbuilt protection features to guarantee the long-term safety and performance of the internal components. The inverters also have one of the broadest voltage ranges on the market (90 to 520V) and dynamic, independent MPPTs for higher generation during low irradiance conditions. Solis’ inverters also have a 1.1 * Pn (rated output) output capability allowing for more power when operating at full load.
For powerful, reliable inverters, explore Solis’ products with SegenSolar now for both residential and commercial PV projects.