TasNetworks has revealed it has been underpaying up to 10,000 Tasmanian households with solar panels for the energy they pump back into the grid.

The business has promised to pay the amount owed to affected customers, which is expected to cost about $2.4 million.

A customer alerted TasNetworks to the issue earlier this year.

The business found a fault with meters installed since March 30, 2011, which failed to accurately record the amount of electricity being generated when heating or hot water is being used in the house.

TasNetworks spokesman Mike Paine said the payout would not push up power prices.

"The average for our customers on our testing is around $240 a customer," he said.

"There will be no impact on pricing as a result of this and we will incur all the costs internally as a business."

Jack Gilding, from solar panel owners' advocacy group Renewable Energy Alliance, said he believed it was not the only example of customers being short-changed by problems with TasNetworks' systems.

"They're not getting the benefit ... and what TasNetworks is about to do isn't going to fix that," he said.

Communications, Electrical and Plumbing Union spokesman Todd Lambert told 936 ABC Hobart that "people at the top" should take responsibility for the error.

"We're looking at accountability for the bureaucrats that are in charge of these decisions, as opposed to our guys on the front line that seem to be getting the abuse for decisions that are made that are out of their control," he said.

TasNetworks said it would write to affected customers this week and begin a program of replacing all faulty meters that could take months to complete.

Mr Paine said contractors would be hired to replace the faulty meters.

"There will be a number of extra contractors engaged, no doubt, but if we're going to do this in a timely manner we need to do that," he said.