The project wants to put up four turbines on Mynydd y Gwrhyd

The Awel Aman Tawe energy project said it was being charged for the mail, sent by someone opposed to its scheme for the upper Swansea and Amman Valleys.

Manager Dan McCallum said: "We know it is the one person as the handwriting is the same."

The project has withdrawn its freepost address to block the letters.

Mr McCallum said sales of the scheme's fund-raising Christmas card would continue, but supporters would now have to put a stamp on their envelopes or order via its website.

The scheme, which employees nine full-time staff, had sold around 4,000 Christmas cards and, with donations, has raised around �7,000 towards the �10,000 it needs to appeal against the decision to turn down its windfarm plans.

The project wants to erect four wind turbines on Mynydd y Gwrhyd in Neath Port Talbot.

The plan was rejected due to its likely visual impact

Neath Port Talbot planners rejected the scheme in September on the grounds of its likely visual impact.

The project, which has a year to appeal, sees the windfarm as a way of securing jobs in the Upper Swansea and Amman Valleys.

It said profits from the sale of electricity generated by the turbines would be used to fund local regeneration initiatives.

Solar panels

Mr McCallum pointed to the consultation of 13,000 local residents in 14 villages surrounding the site, and the subsequent "clear majority in favour of the project" in the referendum on the scheme.

He said the hoaxer had sent in more than 100 envelopes stuffed with old newspaper: "This fraud just shows how petty and vindictive some individuals are who oppose us.

"It just makes us more determined to win our appeal as this windfarm will safeguard the jobs of our nine staff in an unemployment black spot and help create about 40 new jobs by ploughing all the profits from the wind farm into local regeneration projects."

In February 2005, the project helped Gwaun Cae Gurwen Primary School in Ammanford become the first in Wales to install solar panels.