MADRID, July 4 (Reuters) - Spain's main opposition People's Party (PP), which is leading in the polls ahead of the July 23 national election, would introduce a fee on renewable energy projects to pay for the administrative costs tied to them, it said on Tuesday.

Energy has become a hot topic in a nation facing a sweltering summer ahead of the snap election, with the centre right PP and ruling Socialist Party having different views about how to decarbonise the economy.

The PP, led by Alberto Nunez Feijoo, said in a manifesto unveiled on Tuesday that it would introduce "a milestone fee" to be paid by the company behind a renewable project and aimed at funding administrative costs.

The fee will cover "the cost of the service, similar to what happens for renewing a driving licence," a PP spokesperson said.

"This revenue will strengthen the administrative structure in charge of handling the procedures, speeding them up and addressing the problem caused by the high volume of applications," the spokesperson said, adding that the measure had the approval of the sector.

The PP also favours extending the use of the country's nuclear power plant, as well as supporting biofuels and green hydrogen, according to the document.

Outgoing Energy Minister Teresa Ribera criticised the plan for lacking details on key proposals, including on nuclear and water. "What they clearly say is that the (green agenda) has to be slowed down," she said. (Reporting by Pietro Lombardi Editing by Mark Potter)