Solar technology has gone through multiple stages of revolutionary development in the last few years. Tariffs have dropped; competition has increased; revenue maximisation has become more crucial than ever. This, of course, is achieved by boosting the plant’s reliability and efficiency through BoS (Balance of System) optimisation. So, inverter selection can make or break the success of a solar plant.
An inverter is the brain of a solar PV plant. Its main job is converting variable DC (direct current) to steady AC (alternating current). In addition to power conversion, solar inverters bring smartness to solar PV plants with the help of built-in SCADA (Supervisory Control and Data Acquisition) functionality.
The inverter has undergone various technological advancements over the past few years such as 1500V compatibility, optimised DC/AC ratios, better thermal management, outdoor technology, high power ratings and more to boost overall efficiency. Some of the current and future trends of Solar Inverter are explained in the following sections below:
Engineering and Analytics
At present, the primary function of an inverter is power conversion. But manufacturers are steadily improving BoS, as the focus is now on helping end consumers save more. Here’s what the future holds in store:
- String Inverters or central inverters with boosters will replace the string monitoring box
- Dc-field testing can be avoided by using the I-V curve scanning feature in string inverters
- String inverter will replace booster and central inverters system for more reliable and maintenance-friendly operation
- Solar inverters can replace capacitor banks and SVG for dynamic reactive power compensation in conjunction with PPC
- Solar inverters can be used as active power filters, frequency and voltage regulation devices in conjunction with PPC
In order to increase reliability and generation, inverter data analytics will play a prominent role for fault prediction. The uptime and reliability of the plant can be increased by performing preventive maintenance using fault prediction. Future inverters will be able to estimate the RUL (Remaining Useful Life) of major components like DC link capacitors, IGBTS, fans etc to help maintain spares inventory accordingly.
With recent improvements in semiconductor power devices, Si-based power switches can be replaced with GaN (Gallium Nitride) based switches. The advantages of GaN switches are listed below:
- Lower on-resistance giving lower conductance losses
- Faster devices yielding lower switching losses
- Less capacitance resulting in fewer losses when charging and discharging devices
- Less power needed to drive the circuit
- Smaller devices taking up less space on the printed circuit board
- Lower cost
With the advent of these GaN-based switches, inverters will be reliable, efficient, cheaper and smaller compared to present-day inverters.
In the early 2010s, solar inverters were developed based on two-level topology. But two-level topologies have disadvantages such as low power density, higher switching losses, high filter requirement, poor power quality etc., Later multi-level inverters based on NPC and TC-HB topologies were developed to address the issues found in two-level topologies.
In recent times, most central and string inverters have been based on three-level topologies. A few string inverter manufacturers have developed inverters based on 5+ level topologies. Multilevel topologies are more efficient due to the reduction in switching losses, more reliable due to reduced voltage stress on the IGBTs and have a high power density due to reduction in magnetics requirement.
Central inverters have evolved rapidly in the past ten years. In earlier stages, indoor central inverters up to 1 MW were developed which were either placed in RCC or Container for achieving IP54 rating. So later for better BOS savings indoor inverters ratings were increased upto 3.125 MW – but they were still placed in containers. Outdoor inverters have been developed to minimise the auxiliary power requirements and for efficient cooling techniques. In the near future, 5 MW IP65 rated outdoor central inverters suitable for sandy and dusty environments will be more widespread. In addition to that, central inverters with MPPT boosters will be developed to address mismatch losses due to soiling and ageing of PV panels. These losses alone account to 3%. Modular Inverters will be developed to increase the reliability and generation of the PV system.
String inverters up to 250KW with multiple MPPTs are developed for better BOS savings, low mismatched losses, reduced DC losses and early start-up of the plant. String inverter with I-V curve scanning feature will help the solar plant to predict and detect defective PV panels without additional testing requirement. Reactive power support at night function will be a standard offering in all central and string inverter offerings to meet the local grid requirements.
In BESS, inverters (or PCS) in conjunction with energy management system (EMS) will be used to support grid ancillary services like frequency control, peak shaving, energy shifting, voltage control etc., Battery PCS are similar in construction to solar inverters but can both export and import power from the grid to support grid and charge batteries as well due to which these are called bi-directional converters. They can operate in both on-grid and off-grid conditions.
Hybrid inverters are developed with the ability to extract power from multiple sources to supply multiple loads. These sources can be solar, battery pack, DG set and the grid. The loads can be a grid, micro-grid, EV chargers etc. Hybrid inverters come with a proprietary load management software that caters to different needs as per consumer requirement.
All in all, we’re looking at a near future where rapid technological developments will make solar PV inverters more reliable, productive and efficient, benefiting manufacturers, service providers and consumers alike.