This is Panda’s second price increase this year. It last raised its prices in May.
Last year it increased electricity prices five times and gas prices four times.
After the new price rises the average customer will end up paying about €2,500 a year for their electricity and €2,000 for their gas.
Daragh Cassidy of price-comparison site Bonkers.ie described the price rises as “astronomical”.
At the very start of last year, Panda customers were paying around €1,200 for their electricity and €900 a year for their gas, Mr Cassidy said.
“That’s an increase of around €2,400 a year. If you’re a top-rate taxpayer you’d need to be earning almost €5,000 extra to pay for the increase,” he said.
“Price hikes of this frequency and this magnitude are clearly unsustainable.”
In a notice on its website, Panda said the August 25 increases will mean electricity customers will pay an extra €287 a year on average, while the latest gas price rise will cost an additional €412 a year for gas customers.
It said the increases will be lower for customers on discounted plans.
Panda Energy managing director Brendan Traynor said: “Due to global factors beyond our control wholesale gas and electricity costs have continued to rise substantially and unfortunately the expectation is that these costs will remain high for the foreseeable future.”
He said the company had done its best to absorb the costs, but was unable to prevent hiking prices again.
On Monday more than a million households with Electric Ireland accounts are to be hit by a fourth rise in electricity and gas prices in a year.
The ESB-owned energy supplier is pushing up electricity prices by 11pc and gas prices by 29pc.
It is the second Electric Ireland price hike this year, and the fourth since last year.