Tidal energy harnesses the power of ocean tides to generate electricity. It has advantages of being a renewable source that produces no greenhouse gases or waste once constructed. However, suitable tidal sites are limited and tidal power is only available for around 10 hours per day. The closest tidal power plant is the Annapolis Tidal Power Station in Nova Scotia. Tidal energy does not contribute to global warming as it releases no pollutants, but constructing large tidal plants can cost up to $48 billion. Tidal power costs a comparable 5-8 cents per kilowatt hour to generate as oil.