Protest organiser Richard Bonfield said he was "delighted" with Powys County Council's decision, and welcomed a public inquiry that would look at windfarm proposals in great detail.
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There will be a fresher feel with temperatures falling lower than on recent nights.
The accident between junction 24, Coldra, and 23A, Magor, has closed the eastbound carriageway.
Eloise Parry, 21, died after taking diet pills containing the poisonous Dinitrophenol (DNP).