Archive for November, 2011

November 18, 2011

A New Momentum for Geothermal Energy in the UK?

When we talk about renewable energy in the UK we tend to think about on- and offshore wind energy, solar power or the recently emerging new tidal and wave developments. And while geothermal energy is often forgotten about it seems that they may receive more attention in the future thanks to renewed interest from developers.

When is geothermal energy efficient?

Geothermal energy is essentially using the heat of the Earth, ‘generated’ by the radioactive decay underneath us. The most ideal places for harnessing this heat depends on the geothermal gradient of the area, the temperature difference between the surface and the core of the Earth. This is on average 25-30C degrees per kilometer increasing with depth, but can be significantly higher in areas near tectonic plate boundaries or in places where the crust is thinner than usual.

Geothermal energy can be used in two ways: the hot water and the hot dry rock found below are used for heating (directly or indirectly) as well as for electricity generation.

In the UK

Despite the lack of popularity of geothermal energy projects there are already some successful developments in the UK.

One of the earliest developments exists in Southampton, where a Combined Heat and Power (CHP) station operates, providing district heating, not only used in houses but also in shopping malls and hotels in the city – since 1986.

Also, last year the Department of Energy and Climate Change (DECC) announced the ‘Deep Geothermal Challenge Fund’, which awarded significant funding to three projects in Newcastle and Southampton.

In the Gardens of Eden

The latest large-scale project is probably the planned geothermal power plant of 5MW at the Eden Project in Cornwall. This part of the UK is one of the most suitable places for geothermal energy development thanks to its geology, featuring granite bedrock.

The drilling to the hot dry rocks underneath is expected to start next year after all permissions have been granted, and should reach a depth of 4-5 kilometres. Besides the Eden development it is anticipated to also provide power for 3-4000 homes in the area.

The project seems to be rather promising, which could mean that the whole geothermal energy segment might gain momentum in the UK in the near future.

Reasons could include that geothermal energy is available 24 hours a day; it’s clean, sustainable, but not greatly supported by the government – yet.

 

Written for the Energy Saving Warehouse

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November 16, 2011

OTEC, Energy From the Sea

OTEC is an emerging technology that harvests energy from the ocean but does not involve waves or tides. OTEC stands for Ocean Thermal Energy Conversion.

This technology is actually not that new, as first attempts for developing an OTEC solution took place at the end of the 19th century and it has been more seriously researched since the 1970s, however the increasing focus on fossil fuels paused these developments.

Today, Japan is one of the most interested countries in the technology having started tests in 1970 with a 100 kW plant by the Tokyo Electric Power Company, while nowadays the Saga University runs a dedicated laboratory. India has also recently joined the group of key researchers, while the US has its main experimental site on the technology in Hawaii, at the National Energy Laboratory.

OTEC - Lockheed Martin.com

How does it work?

The system utilizes the temperature difference of the deep cold water and the warm surface waters, producing electricity through heat engine systems.

There are three types: open, closed and hybrid cycle technology.

In the open-cycle system the seawater is pumped into a low-pressure chamber so it boils, vaporises and powers the turbine, thus generates electricity. Later the cold seawater helps in condensation, and the seawater will become pure water, which can then be used for various purposes or re-cycled.

The closed-cycle system differs in that a low-boiling-point fluid is used, usually ammonia or freon, which is heated through a heat exchanger by the warm seawater. Another heat exchanger helps at the condensation phase.

Hybrid systems combine the two technologies.

Where can it be used?

As with all heat engines the greater the temperature difference the better the results. Thus the OTEC technology could be used best in the tropical waters with about 20 degrees difference between warm surface (typically about 25C) and cold deep water (about 5-10C at one kilometre depth). This means it could be promising for islands, especially those facing regular challenges with constant electricity supply.

Systems can set up on land, on continental shelves or they can float to provide easy access to deep cold water.

Two new facilities are planned now in the Bahamas as agreed between Ocean Thermal Energy and Bahamas Electricity. These are expected to be the first commercially operating ones, not only providing electricity but also fresh water and would support sustainable food production.

The Maldives is planning to also investigate the technology in the rush to improve renewable energy usage in the country.

Also, the DCNS Group focuses on various marine energy resources and plans to build OTEC systems on the La Reunion Island, in the Indian Ocean. They have also been working on a feasibility study for Tahiti, and a 10 MW-factory is planned for Martinique.

Pros and Cons

Advantages of OTEC include its continuous operation, as it is not prone to changing weather conditions like wind, waves or tides, and it can support desalination processes hence offering clean water. The system can also help in areas where cooling is needed, for instance for agriculture or air-conditioning.

One of the main disadvantages is the difficulty of finding the right location, efficiency and so feasibility.

As issues with fossil fuels grow it seems that research on OTEC technology may be gaining momentum again.

Written for the Energy Saving Warehouse

Image: Lockheed Martin

 

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