Tidal power
Tidal power is a means of generating electrical energy achieved by capturing the energy contained in moving water mass during tides. There are two main methods of achieving this, the first being the use of kinetic energy of currents between ebbing and surging tides, and potential energy from the difference in height between high and low tides. The second method is to build ocean-based dams or barrages.
The second method involves building a barrage and creating a tidal lagoon. The head of water is created when the water levels inside and outside the lagoon are different and this head is used to drive turbines. Tidal power is reliably predictable (unlike wind energy) and in Europe tide mills have been used for centuries, mainly for the grinding of corn. In the barrage the basin is filled through sluices and freewheeling turbines until high tide, and the gates and turbines are closed off. When the sea water falls to a sufficient level to create a head, the turbines then generate electricity until the head is low again and the cycle is then repeated.
Power can also be directly generated where there are large current flows such as the Cook Straight in New Zealand. Norway is also exploiting strong periodic tidal currents in narrow fjords using sub-surface water turbines.
Tidal power is predictable but does not produce energy 24 hours a day. A conventional design will generate power for between six and 12 hours out of every 24. The first commercial tidal power station was the Rance (France) tidal power plant completed in 1966. It has 240 MW installed capacity. There are several smaller projects in the USA, Russia and China. Under consideration are a large number of plants located world wide with capacities ranging from less than 50 MW to 50 000 MW. A problem with tidal power schemes is that they have a very high capital cost and very low running cost. As a result a tidal power scheme may not produce returns for years and investors are reluctant to participate in such schemes.
Wave power
Ocean waves, generated by a combination of wind effects and the rotation of the earth represent an enormous reservoir of natural energy. The leading company in this field is Ocean Power Delivery (OPD) which has developed the Pelamis system, which uses wave energy converter technology. In May 2005 OPD signed an order with a Portuguese consortium to install the initial phase of the world's first commercial wave farm. In mid 2006 OPD delivered the first three production machines. The wave farm at this stage will be rated at 2,25 MW. The technology harnesses wave power via semi submerged modules (which look like Japan's bullet train) each of which can currently generate 750 kW. A typical 30 MW installation would occupy a square kilometre of ocean.
A recent article in the local press indicated that the developers of a proposed R7 billion wave power generation scheme expected the project to be started by the end of 2006 with the possible sites being Mossel Bay, Saldanha or Port Elizabeth. The project developers are Ocean Power Delivery which was responsible for the Portuguese project. The total investment is for a 700 to 800 MW system, being rolled out over five to six years. The pilot project will initially produce 5 MW, growing to 40 MW. It is intended that the wave conversion systems (Pelamis) will be manufactured locally creating permanent new jobs once economies of scale are reached.
Another company which is active in the wave energy field is Wavegen which has installed its Limpet units on a number of Scottish islands. Its technology uses the surge dominated wave field adjacent to the shore and the units are rated at 500 kW. The Limpet system is constructed on shore and its low profile ensures that it does not intrude on coastal views. The plant on the Isle of Islay was the world's first grid connected commercial scale wave energy plant and was commissioned in late 2000. The Limpet uses an oscillating water column (crest and trough) with Wells turbine power take off. In the Faroes, tunnels are driven into the cliffs.
Pumped storage reservoirs
Pumped storage reservoirs are not really a way of creating new electrical power, but a means of storing it. All countries have peak and off-peak demand and in the latter case, excess power can be used to pump water to a high reservoir which has turbines at the output tunnel. When there is a significant demand for power the headgates are opened and water rushes down tunnels to drive turbines which in turn power generators. In Britain the largest such system is in Dinorwig in North Wales. Completed in 1982 this plant produces 1320 MW in just 12 seconds. Eskom makes use of this technology and operates both the Palmiet pumped storage scheme (400 MW) and the Drakensberg scheme (1000 MW). Pumped storage systems in other countries often make use of dams where the generating capacity can be increased through the higher water head.
Geothermal energy
The geothermal energy from the core of the earth is closer to the surface in some areas, including Iceland, New Zealand, the USA, Philippines and Italy. Iceland has commercialised this latent power and has 8000 MW of operational capacity. This is not a viable way forward for South Africa which has only a few hot water springs (eg, at Bela Bela [formerly Warmbaths]).
Solid biomass
This refers to the use of combustible solids, being wood, the biogenic portion of municipal solid waste or combustible field crops. Field crops can be grown specifically for combustion or may be used for other purposes; with the processed waste being used for combustion (this includes sugar cane residue, wheat chaff, straw, corn cobs, or any other plant matter). The burning process here produces no net CO2.
The UK in particular has been focusing on biomass and a couple of examples from there will be used. In 2002 it opened the largest and most-efficient straw-fired power station of some 36 MW. At that time the country also had the world's largest power station fuelled by chicken litter (38,5 MW) supplemented by wood chips and other biomass residues. They also had plants burning meat and bone meal for power production.
Closer to home sugar cane would be a good example as when crushed to pulp (Bagasse) it can be burned to produce steam to drive turbines. There are some small experimental biomass power plants running in this country but to my knowledge none are connected to the national grid. Biomass power stations are expected to stay small (< 50 MW) as a result of the logistics of gathering the fuel. They could however be used to power small industrial plants which could be producing more fuel as a by-product.
An example of growing fuel for use in a power plant again comes from the UK where a 44 MW biomass power plant is to make use of fast-growing willow trees. Planned to come on-line in 2007 this will be the largest biomass power station in the UK. Forty people will be employed at the plant itself while some 300 people will be indirectly employed through forestry and farming (which shows the potential for job creation). It will initially use burnt forest residue of sawdust, branches and off-cuts from a nearby saw mill, but farmers are being encouraged to plant willow trees whose wood will be the prime source of power.
Liquid fuels
While not directly for electricity generation, a lot of interest has been created for production of renewable liquid fuels such as ethanol and biodiesel. The latter could of course be used directly to power a conventional liquid fuel-fired power station.
Once associated with South America the production of ethanol has become a worldwide business and countries like Canada offer financial assistance in the construction of ethanol plants under the Ethanol Expansion Programme (EEP). With 15 existing plants that vary considerably in terms of output, with Round Two of the EEP Canada has allocated a further $46 million for the construction of a further five plants, the largest of which will produce 199 million litres of fuel per year. Canada under the EEP programme and private ventures expects to be producing 1,4 billion litres per year by the end of 2007. The target is to have 35% of all gasoline in Canada contain a blend of 10% ethanol by 2010. Despite worldwide production Brazil is still the largest ethanol market and maker. Last year the global production of ethanol displaced about 3% of natural gasoline with 40% of that coming from Brazil. In South Africa the fuel firm Ethanol Africa plans to build a string of maize to ethanol plants (the first at Bothaville has a completion date of late 2007) at a total cost of about $1 billion. They believe that government may make the use of a 10% ethanol blend mandatory and want to jump on that band wagon. Even if there is no regulatory blending here the company will export primarily to Europe, which already has mandatory use requirements for ethanol. At full capacity and if ethanol legislation is introduced here, Ethanol Africa's eight plants would provide only 10% of pump fuel requirements. At current prices, ethanol would be cheaper than oil blends and farmers hope to reap benefits by converting their surplus maize into ethanol. Ethanol is produced from grains such as corn and wheat. Canada is working on cellulosic technology that would allow ethanol to be produced from agricultural residues such as straw and corn stalks. Another South African connection with ethanol was highlighted in a recent newspaper article which indicated that Global Ethanol Holdings (80% owned by Investec) planned to issue more shares to pay for five ethanol plants (using grain and sugar) in the US. When fully operational in 2008 these plants will produce 2,8 billion litres of fuel.
The other renewable fuel is biodiesel, which can be produced on a small scale by a farmer himself and Argentina is building a prototype larger scale plant that will produce about 360 gallons of biodiesel and 10 tons of animal feed a day from 12 tons of soy beans. South Americans are already looking at mandatory mixing of biodiesel with the real thing, Argentina looking at a 5% mix while Brazil already has a mandated 2% mix by 2008 and 5% mix by 2013. Brazil opened its first commercial biodiesel refinery in March last year. Here in South Africa it is mainly farmers who are producing biodiesel on a small scale, sufficient for their own use and that of their neighbours. There is even a local company that has developed and sells production equipment for farmers. Recent news is that Sasol and the Central Energy Fund are considering the feasibility of constructing a 100 kilotonnes per annum soya bean-based biodiesel plant. Other possible sources of biodiesel that have been looked at include sunflower and the seeds of the Jatropha curcas tree. In all the proposed methods the primary output is biodiesel with cattle feed as a by-product. As regards soybean this used to be produced in considerable volume in this country but the lack of demand for soy oil killed this off. It could easily be resurrected and would create more job opportunities on farms. During July the SARS licensed the first commercial biodiesel producer. This is De Beers Fuel, whose pilot production plant in Naboomspruit (Limpopo) has a capacity to produce 3,6 million litres of diesel a month, using sunflower seed oil. Biodiesel Refinery Holdings has the sole mandate to market, sell and franchise plants on behalf of De Beers Fuel throughout Africa, Argentina and Brazil.
The production of biofuels is not cheap but the current high cost of crude oil and dwindling supplies of the latter are strong incentives for a local industry in both biodiesel and ethanol. The economic viability of producing biofuels will be threatened only if the crude oil price falls below $40 bbl. Compared with the use of crude oil bioethanol reduces CO2 emissions by 60% and compared to the use of oil from coal it produces five times less CO2 emissions.
Outlook for the local I&C industry
Within South Africa, the I&C industry is set to win no matter from where new electrical energy is produced. There is a real requirement for a new large base load capacity and in the interim that is likely to be provided through new coal-fired stations and nuclear plants (conventional and PBMR). Parallel development of green energy sources will also require sophisticated instrumentation and control systems and here one can look at increased solar capacity and the biofuels industry where the needs of both small and commercial scale plants must be satisfied. South Africa has a critical shortage of projected energy capacity and it will take at least a decade before the country catches up with demand. Look out also for the life extension of many of the existing coal-fired plants, with massive renovation including new instrumentation and control systems. I personally see the biofuels industry taking off in a big way with underutilised farmland producing a variety of raw materials, with widespread research to find the most cost-effective feedstuff.
Dr Maurice McDowell has many years’ experience as a technical journalist, editor, business manager and research scientist. His third party analyses of world-class companies and processes, as well as his insight into industry and technology trends are well respected.
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