Blue Power Blog

In cooperation with the European Ocean Energy Association, a new Leonardo ENERGY eBook on current ocean energy projects.

Just as it seems like solar is about to turn the corner, wind power technology is out of its adolescence, and even Biodiesel has its own day (March 18th, Rudolf Diesel's Birthday), there isn't much left to do but twiddle our thumbs and wait around for these technologies to be refined and adopted. The people at Verdant power have other ideas. They have developed riverine, or tidal, 'kinetic' hydropower. It requires no damming or redirection of water, and uses relatively small slow spinning turbines which resemble wind turbines. They are currently testing it in New York City's East River, powering a parking garage and a supermarket on Roosevelt Island. The technology is clean, out of sight, and the New York State Energy and Research Authority (NYSERDA) has identified over a Gigawatt (1,000 Megawatts) of potential capacity in the state. California has identified over 1.5 Gigawatts of potential (put into perspective, 1 GW is enough power to run approximately 1 million homes).

Electricity from the difference in salt concentration

Blue energy is a special way of harnessing solar energy. The sun evaporates sea water, leaving the minerals behind in the sea. The evaporation creates clouds, which then fall back onto the earth as rain and snow, creating rivers of fresh water that flow back into the sea. The difference in the salt concentration between the river water and sea water can be used to generate electricity.

Potential contribution to the energy mix still unknown

There is a growing consensus as to the degree renewable energy sources will be able to contribute to the energy mix in the next 20 years. However there is one element that may be underestimated; the power of the oceans.

Due for commissioning in Póvoa de Varzim, Portugal

The world's largest wave powered electricity generation plant is almost ready to go into operation on the coast of Póvoa de Varzim in northern Portugal. It uses the same Pelamis system from Ocean Power Delivery Ltd that was successfully tested at the European Marine Energy Centre in Orkney. It consists of three 750 kW units, for a total of 2.25 MW. Two units have already been installed at the site. The third unit is currently being assembled at the Peniche shipyard.

Reference:

Review on the website of Ocean Power Delivery Ltd

Statkraft in Norway has, for some time, developed concepts for osmotic power, i.e. the power from the differences in pressure between salt seawater and sweet freshwater, the latter passing through a membrane (see figure below).

The potential is far from negligble. The Norwegians estimate their potential to be 12-25 TWh annually corresponding to 10-20% of their present generation capacity. For Europe, they estimate it to be 200-250 TWh, according to an article in the Swedish magazine ERA.

The same source says that they have managed to boost the membrane capacity from 0.1 W/sqm to 2 W/sqm, and that they aim for 5. The membranes are said to be produced in the Netherlands where there is also a similar idea developed within a project called Wetsus.

(Click image to enlarge)

One thing seems fairly sure about the future of sustainable energy systems, and that is that they will use a wider variety of resources and be less dependent on a few sources than at present. Still, we may have to take a step back and consider our options. Biofuels will be part of the solution, but may not be the only solution. So we are warned by Professor Peter Crane, Director of the Royal Botanic Gardens, Kew. His worries are about soil degradation, over-utilizing in monocultures and biodiversity.

Going direct from the sun would at least avoid these pitfalls. ECN in the Netherlands now reports that state-of-the-art PV systems have a payback time of less than two years. Such systems would not have the negative land impact, but rather would make use of the waste land we have on our rooftops. From the Dutch perspective, they would reduce the GHG-emissions by more than 85% at the least. At present, it is 570 kg per MWh to 80 and in future 30. See figure below.

Figure: PV-system under an irradiation of 1700 kWh/m²/yr (Southern-Europe) respectively 1000 kWh/m²/yr (Middle-Europe).

The birth of a new industry

2005 was a breakthrough year for ocean energy. The Annual Report of the Ocean Energy Systems Department (OES) of the International Energy Agency (IEA) even calls it ‘the birth of a new industry’. Indeed, the first order for a commercial wave farm took place in 2005 with Ocean Power Delivery signing a deal with a Portuguese consortium for the installation of three units capable of 750kW each.

In the meantime, development is continuing with new prototype installations being built in Australia, Canada, Ireland, Italy, and the U.S. Also in 2005, policy makers in several countries made announcements of incentives for ocean energy systems. In the UK, for instance, the Marine Renewebles Deployment Fund was created, and in the U.S., the 2005 Energy Policy Act recognizes ocean energy as an eligible renewable energy system.

Harnessing 20% of the US offshore wave energy potential at 50% efficiency could make a contribution to the US electricity supply equivalent to conventional hydro (around 200 TWh). In addition, there is potential from tidal currents, currently that is still under investigation (reference). According to a white paper from EPRI's Ocean Energy Programme, the world installed capacity for ocean wave power is 2.29 MW, as of September 1, 2005. Obviously the technology is still in development, but a 100 MW facility can be envisioned for 2010 with a production cost of 8-16 c/kWh, well below the cost of wind power when it started its growth curve. Capital costs for wave power plants are lower than for wind, but operating and maintenance costs are an attention area. As any flow energy source, ocean power is intermittent. Wave power has a strong seasonal variation, but the good news is that these energy flows are much more predictable than solar or wind energy:

• availability of wave power is predictable days ahead, compared to hours for wind and minutes for solar
• tidal currents even follow patterns that are fixed for centuries

Environmental performance, potential, cost and intermittency characteristics make ocean power an attractive option for the future diversified energy system, but it would be a very pleasant surprise if this technology were to make a sizeable contribution before 2020.