Householders who generate electricity via solar panels should be paid more by power firms, the Green Party has said.
Photo cells on the solar panels convert sunlight into electricity
Utility companies pay homeowners for energy generated by their panels but charge more when selling power back.
"You could be exporting more electricity than you actually use and yet you are still getting a bill," said senior Green politician Sian Berry.
She demanded greater transparency as a way to end "complex, contradictory" regulations on renewable energy.
"Some of the time, people will be exporting electricity," Ms Berry told the BBC News website following the publication of a report she wrote on the UK's energy policy.
"For example, in the daytime when it's sunny, they might be at work and not using any electricity, so it will go to the National Grid.
"They'll be paid for that, but a really derisory rate - whatever the electricity company feels like giving them."
'Speed up decisions'
She went on: "Then in the evening when they go home and they need to pull electricity from the grid, they're paying the full sum.
"You might get 5p per kilowatt hour to export it and 11p to buy it back in again."
A "very simple system" was needed instead of "eight complex, contradictory policies, none of which are working", she added.
Her report also called for low-cost, interest-free loans for households with lower incomes, so they had greater help in taking advantage of renewable energy.
It suggested communities should be able to set their own targets for making new buildings more energy-efficient, and asked for greater resources so council planners could "speed up" decisions on renewable energy schemes.
A spokesman for the Department for Business, Enterprise and Regulatory Reform said the difference in tariffs reflected "the expected difference between wholesale and retail price in any market".
"In many situations where traded volumes are small, it is uneconomic for suppliers to purchase this electricity," he added.
He said his department could intervene if it was unhappy with "rewards" offered by energy suppliers, as a result of the Climate Change and Sustainable Energy Act.
"We are prepared to use those powers if necessary but any decision will come after the Ofgem study into how the market is working, which is expected later this year."