CEB renews call to pause rooftop solar systems, but energy experts question decision

The Ceylon Electricity Board (CEB) today renewed its call on owners of rooftop solar systems to temporarily switch off their systems, but energy experts have questioned the decision.

The CEB released its third successive statement calling for ‘supportive action’ from rooftop solar system owners to voluntarily switch off their solar PV systems during day time from 9.00 a.m. to 3.00 p.m. until April 21.

Asoka Nalanda Abeygunawardana, an electrical engineer, environmentalist and social activist reacting to the move said it was a questionable decision as the CEB was trying to stop the cheapest mode of power while operating the expensive systems.

He pointed out that was a clear case of failure of the CEB to manage the situation.

Several other associations including the Electricity users association have reacted strongly questioning the CEB’s decision.

 However, the CEB today said their request was made ‘with the utmost concern for the safety and stability of the national power grid during the Sinhala and Tamil New Year holiday period’.

‘Sunny conditions have led to a high production from rooftop solar at a time when customer demand is at its lowest, creating serious grid stability risks’, the CEB added.

The CEB further explained the decision as follows:

Why Is This Needed: The Technical Challenge in Simple Terms

When electricity demand drops significantly—like it does during the long April holidays—and sunlight is abundant, Sri Lanka's power system, for that matter in any other country, faces this challenge.

Here’s what happens:

• Too much solar power floods the grid during the daytime.

• Demand (usage) is very low, especially with most factories and offices closed.

• To balance this, CEB shuts down large power plants such as hydro, coal, and all other thermal plants.

However, CEB cannot control the production from rooftop solar PV systems, unless customers shut them down

• The larger power plants provide a critical service to the grid called "inertia", which helps keep the electricity frequency stable. Solar PV systems cannot provide such an assurance to the grid.

What is inertia?

Inertia is primarily provided by the spinning mass of large generators. It helps the grid to resist sudden changes in power. Without adequate inertia, even a small glitch can cause voltage or frequency problems, leading to partial or total blackouts.

This table compares the estimated customer demand and electricity generation at 12.30pm on April 11 and 12, and compares with a typical weekday, and highlights how stable or unstable the grid would be under different conditions. The table also shows how CEB managed on April 12 and what would have been the system inertia if it was not managed.