The drive towards energy security and cleaner power sources has led to robust renewable energy capacity additions in India. Among renewables, solar and wind energy  – both intermittent sources have been added at a larger scale and must ensure reactive power (grid inertia) compensation and voltage stability for grid safety.

The solar and wind capacity in the total installed power capacity has risen from less than 10% at the end of 2013 to about 25.5% as of December 2022, according to Mercom India Research.

When renewable energy penetration in the power grid was much lower, it could be connected or disconnected without impacting grid stability significantly. However, with the increased renewable integration, any deviation seriously affects the stability and reliability of the grid.

Reactive power services are used to make sure voltage levels remain within a mandated range. The voltage support physically moves power from generation sources to the load. Reactive power significantly affects grid security as it impacts voltages in the system.

The government during the year has implemented measures after various energy loss incidents put the national grid at risk.

The Central Electricity Authority (CEA) recently reported 28 incidents where grid frequency deviated outside the prescribed limits, involving the loss of over 1,000 MW of renewable energy since January 2022. This has added to worries about more frequent power outages.

Most of the reported incidents were categorized under overvoltage during the switching operation, low-frequency oscillations of renewable energy, and faults near the renewable energy complex.

An analysis of these incidents revealed that inadequate reactive power support from variable renewable energy was one of the contributing factors both in static and dynamic conditions.

Solar and wind energy projects, which account for almost 63% of the country’s installed renewable capacity, defy CEA’s requirement of reactive power capability of 33% of the project’s generation capacity, particularly in the northern region. India generated 30 billion units of solar energy alone during the second quarter of 2023.

Following this, the CEA has directed all renewable energy developers applying for connectivity until April 30, 2023, to comply with CEA Connectivity Regulations by September 30 or face disconnection.

According to the regulations, it is necessary to have dynamically varying reactive power support during low voltage ride through (LVRT) and high voltage ride through (HVRT).

This is because fixed capacitor banks can only provide reactive support during steady-state conditions and deliver support in steps after a time delay. Therefore, providing dynamically varying reactive power support is crucial to ensure grid stability and security.

Dynamic support allows injection or drawal of reactive power within milliseconds to prevent outage during current/voltage overloads.

Speaking to Mercom, a system operator at GRID Controller of India, said, “A reason for the occurrence of low voltage, even 85% or below the nominal value, is the inability of the solar or wind generators to provide dynamic reactive support. In the case of solar projects connected to a pooling station, as the power injection to the grid increases with solar irradiation, the load on the outgoing high-capacity transmission lines also increases. This, in turn, causes the voltage at the pooling substation/connection point of the renewable generators to fall and even go below 85% of the nominal voltage.”

“Solar and wind projects that fail to comply with the CEA standards may then trip, leading to significant generation loss. Again, the unloading on outgoing lines may, in turn, trigger high voltage conditions. In this case, the wind and solar generator’s inability to provide adequate dynamic reactive power support is responsible for the voltage dip,” he said.

The higher the renewable energy generation, the greater the requirement for reactive power support.

According to a renewable energy project developer Mercom spoke to, the fluctuations and the tripping issues happen when there is no grid inertia or reactive power, which is created in most regions by the thermal or hydropower projects that have the capability of supplying the reactive power support as well as drawing it from the grid as and when required.

He said, “The issue particularly stems from regions like Rajasthan, where there is 66 GW of renewable capacity in the pipeline, and Gujarat, where 25-30 GW capacity is planned in Khavda region alone, and there are not many thermal or hydropower plants available to maintain the reactive power supply to avoid the grid from failing. Most renewable power projects built in the past never factored it in, which is why the Rajasthan grid collapses now and then, particularly in the renewable energy areas.”

In the absence of grid inertia from thermal or hydropower projects, it becomes necessary to install a variable compensator that can supply reactive power to the grid and draw it whenever required.

The System Operator explained, “For renewable projects, 0.95 power factor is fairly reasonable; generators located far from the load centers should have the capability to operate from 0.90 power factor lagging to 0.95 power factor leading, while those close to the load centers should be capable to operate from +0.85 lagging to -0.95 leading. For renewable generators, the 0.95 power factor translates to 33% of the active power, which is the reactive power capability that should be available up to the rated active power.”

To solve this pressing issue, developers have been advised to install a FACTS (flexible alternating current transmission system) device, like a static var compensator or a static synchronous compensator (STATCOM). These devices can vary their reactive power output at a faster rate, depending on their controller action. They use an Insulated Gate Bipolar Transistor (IGBT) and other thyristor control, supporting faster conversion capability.

Without clear instructions under CEA Connectivity Regulations to install these devices, many project developers have failed to factor in this obligation of providing reactive power support and hence consider its cost while bidding through the years.

Existing renewable projects without such devices are required to have a reserve capacity of inverter installed within the system. This ensures that even if they generate at full load, they still have the margin to provide some lagging or leading reactive power support to prevent that point of interconnection voltage from going outside the acceptable limits. The only other way is to go for external compensation at the plant terminal, a type of dynamic compensation device.

However, even with just capability, inverters go into sleep mode whenever the grid goes off, thus making a static or variable dynamic reactive power compensator necessary.

Another renewable energy project developer said, “The developers never had to worry about these factors previously because it was mostly taken care of at the substation level or by Grid India. With the rising renewable energy injection into the grid, it has become mandatory for developers to install such devices. For a 100 MW project on average, we would need to install 10 MVAr STATCOMs, which could easily cost around ₹3 to ₹4 billion (~$36.15 million to $48.2 million) and is a heavy price to factor into project costs.”

He added, “These additional requirements for existing projects were expected to be dealt with under the change in law clause in the PPAs. When the Grid Code came into existence in 2017, there were deliberations on what had to be installed – static capacitor banks, or a dynamic reactor, and then the STATCOM. All these equipments are capable of compensating the reactive power requirement of the grid. Developers are not saying no to installing this equipment, but the cost is a concern. This cost has not been factored into the tariffs bid earlier and hence has to come under the law change; otherwise, it will make the project unviable.”

A senior official at a government implementing agency agreed that installing devices for dynamic reactive power support would definitely impact the project costs and ultimately reflect in the tariffs in the future.

He said, “Previously, STATCOM devices were installed under the CTU scope. However, the CEA has recently enforced its connectivity regulations, insisting project developers install these devices at the power generating stations. For projects with finalized tariffs, the developers can approach the Central Electricity Regulatory Commission with requests to consider a ‘Change in Law’ condition for such cases and claim compensation. It will ultimately be up to the CERC to decide whether they want to grant it or not. As far as the government implementing agencies are concerned, we hold grid safety as the utmost priority and will ensure such devices are in place to avoid any grid failures.”

With grid security being a significant factor in managing the increasing renewable energy capacity, there seems to be no other alternative but to install the required STATCOM devices for projects in operation, ultimately leading to increased project costs, which may or may not be compensated under the change in law clause.

In the future, project developers will have to factor in these costs when bidding. Clean energy is bound to get more expensive, but the upside is that India can expect more disciplined and stable grid management, enabling effective injection of renewables into the system.