Synergy is being accused of failing to adequately inform customers about a decision to slash the amount it pays under a renewable energy buyback scheme.

Some are accusing the electricity retailer of sneakiness and trying to hide the bad news.

Synergy customer David Humrich has been signed up to the Renewable Energy Buyback Scheme (REBS) for years, receiving rebates for the excess power he generates through the solar panels mounted on his roof.

He said he was shocked at the way he found out that the amount he earned from it had been cut.

Mr Humrich said the news was hidden in the fine print of a Synergy newspaper advertisement, which was plugging the fact power prices would drop as a result of the carbon tax being abolished.

While Synergy was entitled to cut the rate under the scheme, he said his main issue was its failure to adequately inform customers of the move.

"You'd think that they would give you some sort of indication, send a letter that they are going to take this away from me and nothing like that has happened at all," Mr Humrich said.

"As distinct from three years ago when they told me the rate was going up - I got a nice letter explaining it all in great detail.

"It's been super sneaky the way they've done it... without any indication up front to the people who contract to them to buy and pay back electricity.

"I don't think it's very fair."

Buyback rebate slashed 20 per cent

Under the scheme, customers are paid for any excess power their solar panels generate and pump back in the grid.

The rate has been cut by about 20 per cent - from 8.85 cents for each unit of electricity to 7.13 cents.

WA Sustainable Energy Association CEO Dermot Costello agreed that Synergy's notice of the rate cut was poor.

He said many of his members were unaware of the change.

"It's strange that it was kind of stuck in the bottom of an advertisement for Synergy.... it seemed a little bit underhand I guess," Mr Costello said.

"There was very little notice given... if there was a bit more openness about it, it probably would have just left a better taste in the mouth."

A Synergy spokesman said the rate decrease was only approved by the state's coordinator of energy on August 29.

He said information on the changes was currently being sent to all affected customers.

"The logistical aspect of communicating and calculating the impact of the repeal of the carbon tax on retail tariffs, along with the change to the REBS buyback rate, to our one million customers has been challenging," the spokesman said.

"We have tried to manage the process as efficiently as possible to ensure our customers are clearly informed."

The change to the rate took effect from Monday.