Image caption One of the world's biggest tidal energy turbines being prepared for deployment in Scotland

The UK is underestimating the amount of electricity that could be generated from tidal sources, new research says.

The analysis says that estuary barrages and tidal streams could provide more than 20% of the nation's demand for electricity.

Despite high costs, experts say tidal power is more reliable than wind.

The predictable nature of tides makes them an ideal renewable energy source, the journal Philosophical Transactions of the Royal Society A reports.

But finding effective ways of utilising their latent power have proved elusive.

Start small, learn quick and build up Dr Nicholas Yates, National Oceanography Centre

Essentially, engineers try to tap tides in two ways: one involves building barrages across tidal estuaries that use the ebb and flow of the waters to turn turbines - a major project of this type had been proposed for the River Severn.

The other method involves planting turbines underwater in fast flowing tidal streams in areas such as in coastal waters around Cornwall and Scotland.

Smaller better

In the Royal Society report, researchers say they are "extremely optimistic" that both types of technology can be realised and relatively soon.

Image caption La Rance in Brittany, France, is the site of the world's first tidal power station

"From tidal barrages you can reasonably expect you can get 15% of UK electricity needs, that's a very solid number," co-author Dr Nicholas Yates from the National Oceanography Centre told BBC News.

"On top of that there is a 5% tidal stream figure, and with future technological development that is likely to be an underestimate in my view," he said.

The massive Severn estuary tidal barrage scheme had been rejected by the coalition government because of its environmental impact, but ministers have indicated they are open to review the idea.

Despite his faith in the idea of barrages, Dr Yates, who carried out the research with colleagues at the University of Liverpool, says he is against building one across the Severn.

"I think it's unfortunate that attention for tidal range has tended to focus on the Severn, it's the wrong place to start, it's too big," he said.

"Start small, it's what the Danes did with wind - start small, learn quick and build up.".

Developing power from offshore tidal streams is fraught with difficulty, as the BBC discovered when reporting on the emerging industry in Scotland last year.

Better than wind

But according to the authors of the latest research, 2013 could see a big breakthrough in tidal stream power. A company called MeyGen is planning to deploy tidal stream technology in the Pentland Firth that will initially generate up to 40MW of electricity, enough to power about 38,000 homes.

"This is a crucial milestone for us, it will be the first array of tidal stream turbines," observed report co-author Professor AbuBakr Bahaj from the University of Southampton.

"It will be a viable proposition for us in energetic areas of the sea - it will be give us another element in the energy mix that's more reliable than wind."

Another key element that researchers have looked at in this research is the quality of the power produced by tidal sources.

The SeaGen project in Northern Ireland is the largest grid connected tidal turbine in the world.

Analysts have been looking to see if the power produced suffered from flicker, caused by loads that vary. It's an established problem with older wind energy turbines and something that causes consumers great annoyance when it happens to their lights.

"In general, the results were very good, the flicker levels were quite low," said Joseph MacEnri from ESB International who assessed SeaGen.

"Overall this device behaves like a modern, well-behaved wind turbine."

While the report paints a positive future for tidal power, a critical element is money.

In the past month ,the EU has announced funding in the region of £30m for two UK tidal projects.

Investors in tidal technology are currently rewarded with a payment of £40 per megawatt hour for energy generated from renewables, but this scheme will end in 2017.

According to Prof Bahaj, this could have serious implications for the nascent industry.

"It depends on the subsidy. Without it, it wouldn't stack up financially."

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