He said David Cameron could not guarantee cheaper bills and tackling climate change would cost now in order to have cheaper renewable energy for future generations.
Speaking on a visit to Whitelee Wind Farm, in Eaglesham, just outside Glasgow, Mr Miliband also cast doubt on the SNP target of 100% of energy from renewables by 2020.
Last Month Mr Cameron said he would ensure energy firms offer their customers the lowest tariff.
Mr Miliband had a tour of the visitor centre then took questions from a small audience on energy policy.
Afterwards he cast doubts on the Prime Minister's pledge to lower energy bills for homes and on Alex Salmond's commitment to 100% of domestic electricity from renewables.
He said: "Over the next decade or more the trend will be upwards. That is the trend to tackle climate change.
"We need to make it as fair as possible and not an excuse to rip off consumers.
"David Cameron is not taking on the energy market, which is still gripped by the 'Big Six' companies.
"David Cameron cannot guarantee cheaper bills."
He was sceptical of the SNP's target of the equivalent of 100% renewables in eight years' time, after it increased the target from 80% after exceeding the interim target of 31% last year.
Mr Miliband said: "Seeing is believing. Let's see if they can deliver.
"Alex Salmond's record on straightness isn't what it might be.
"The bigger picture is the referendum, and it's important to energy.
"We are better off tackling climate change together.
"Scotland gets 20% of investment from the UK because of the natural resources and the rest of the UK benefits from cheaper energy.
"If Scotland was separate we would both lose out. Scotland wouldn't get investment and support and the rest would have to pay more. That is the reality."
Mr Miliband, a former Energy Minister in the last Labour Government, said the country needed a mix of energy sources and could not put all its 'energy eggs in one basket'.
He said we need on-shore and off-shore wind, nuclear and clean coal to ensure sufficient supply and not be left dependent on foreign imports.
Mr Cameron, he said, was guilty of promising great things on the environment before he became Prime Minister but not following though, which was creating uncertainty and was deterring business from investing in green energy projects.
He added: "If I am elected as the next Prime Minister We will put the environment at the centre of our priorities."