Varda Energy reads two million meters without a mainframe

The challenge

The mainframe had served Varda well for forty years. But it was built to read each meter once a month and bill from that reading. When smart meters arrived, the volume of data grew more than a thousandfold. The overnight batch began to overrun into the morning, and on the worst days it did not finish at all.

Every late batch meant late readings, and every late reading risked an estimated bill. In 2022, Varda's billing team handled 41,000 exceptions by hand. Running the mainframe cost more each year, and the people who understood it were leaving.

The approach

The first step was not code. We spent three months with Varda's four mainframe specialists, writing down what the old system actually did. They found 300 rules for validating, estimating and correcting readings, many of them added after some past incident and documented nowhere else.

We then built a meter data platform in the cloud that treats readings as a stream rather than a batch. Each reading is validated, corrected or estimated by the same 300 rules within minutes of arriving, and passed on to billing, settlement and the customer app.

“The mainframe team were not in the way of the project. They were the project. Nobody else knew what the old code really did.”

Then came what Varda's team named the quiet migration. Meters moved to the new platform in 40 groups of 50,000. For six months, both systems processed every reading, and every bill was compared before it was sent. Any difference held the bill until a person had checked it. Customers were never told, because nothing about their bills was meant to change, and nothing did.

What the new platform does

• Takes in 96 million readings a day as they arrive, not in a nightly batch.
• Applies the same 300 validation and estimation rules the mainframe used, now written down and tested.
• Shows customers their usage in the app within 15 minutes.
• Supplies half-hourly data for settlement, as the regulator now requires.

The outcome

The last group of meters moved in August 2025, and the mainframe was switched off in November. Billing exceptions have fallen by 60%, and the team that handled them by hand now works on improving the estimation rules instead. The platform costs 34% less to run than the mainframe did in its final year.

96 millionMeter readings processed every day, each within minutes of arriving.

Two of the four mainframe specialists now lead Varda's platform team. Varda runs the platform itself, ships changes every week, and has started using the same data to plan where the grid needs strengthening.