75% of Renewable Energy Uses Distribution Grid... "Spain Blackout Could Happen Here, Too"

Distribution grid operates at a fixed power factor of 1.0
Vulnerable to voltage fluctuations from renewable energy
"Inverter performance and other upgrades needed"

Kim Juyeong, a lawmaker from the Democratic Party of Korea

Renewable energy accounts for 75% of the capacity connected to South Korea's distribution grid. Concerns have been raised that, if solar inverters disconnect all at once due to voltage or frequency anomalies, an incident like last year's massive blackout in Spain and Portugal could also occur in South Korea. The power grid must be strengthened urgently, including by improving inverter performance, to prepare for grid instability as renewable energy expands.

Kim Juyoung, a lawmaker of the Democratic Party of Korea representing Gimpo Gap, said so on October 19, citing data from Korea Electric Power Corporation (KEPCO) during a parliamentary audit of the Ministry of Climate, Energy and Environment and its affiliated and subordinate agencies.

According to KEPCO data, distribution grids account for 30.7 gigawatts (GW), or about 75%, of the 41.1 GW of renewable energy connection capacity. By number of connections, 99% use distribution grids. KEPCO operates its distribution grid at a fixed power factor of 1.0.

A fixed power factor is an operating method in which electrical equipment is run to maintain a predetermined power factor. A fixed power factor of 1.0 means that 100% of the total electricity supplied is active power, which performs useful work. When power equipment operates at a fixed power factor of 1.0, there may be insufficient reactive power to regulate voltage, potentially placing strain on the grid when voltage suddenly rises or falls. This means a sudden increase in renewable energy generation could cause problems for the grid.

KEPCO said that around 55,000 overvoltage events occurred on the 345-kilovolt (kV) grid last year.

Kim said that an expert panel from the European Network of Transmission System Operators for Electricity (ENTSO-E) analyzed the Iberian Peninsula blackout last year in terms of 14 factors, but identified overvoltage as the direct cause. The panel said that renewable energy operating at a fixed power factor and successive overvoltage-related disconnections of small-scale solar systems exacerbated the voltage rise.

Kim said inverters should be equipped with functions that prevent them from disconnecting even when a fault occurs in the grid. These include LVRT (Low Voltage Ride-Through), which enables them to withstand voltage drops; LFRT (Low Frequency Ride-Through), which allows them to remain operational when frequency deviates from its normal range; and HVRT (High Voltage Ride-Through), which enables them to withstand overvoltage while absorbing reactive power.

Kim asked KEPCO whether distribution-grid inverters had these functions, but the corporation did not submit the relevant data. Kim expressed concern that many solar inverters connected to distribution grids may lack functions for responding to voltage and frequency fluctuations.

KEPCO President Kim Dong-cheol said, "We have ensured continuous-operation performance for facilities of 90 kilowatts (kW) or more, and plan to expand coverage to facilities of 20 kW or more." He also said the corporation was developing and implementing plans to address LVRT, FRT, and HVRT by 2029, and planned to install synchronous condensers by 2034 to secure inertia.

Meanwhile, according to data from the Korea Power Exchange, solar power generation was around 25.2 GW at noon on March 29, accounting for 44.5% of total generation. At the same time, coal-fired power generation had fallen to around 6.1 GW. With the share of synchronous generation, which provides inertia, lower, the frequency drop could be greater if inverters all disconnect at once.

In that case, the under-frequency load shedding (UFR) system, a last resort, would be activated. However, even when distribution lines connected to solar power are disconnected, the actual reduction in load may be less than the set amount. Kim therefore requested information on whether KEPCO had determined the scale of distribution lines subject to UFR that are connected to solar power, how much the actual amount of load shed during daytime falls short of the set amount, and the results of any reviews.

"Renewable energy must continue to expand, but if the grid is not ready to accommodate it reliably, the public could bear the consequences of a large-scale blackout like the one in Iberia," Kim said. "We must accurately assess and disclose the performance of distribution-grid inverters, and prepare plans and budgets as soon as possible to upgrade existing equipment that lacks the necessary functions."

This content was produced with the assistance of AI translation services.