While the islands of Mauritius are too geologically young for the formation of fossil fuels, trees have been converting sunlight into sugars by photosynthesis and storing this energy as wood. For the first few hundred years of human settlement, energy was obtained from burning wood for heat and steam engines (devastating our forests), and hydropower from water wheels to drive mills. In 1899, the first electricity was produced using hydropower and by independence in 1968, it had become Mauritius’ primary source of electricity. As demand for energy, particularly electricity and private transport, increased, it became necessary to import greater volumes of fossil fuels.
Today, approximately 80% of electricity is generated from fossil fuels, much of it coal, nearly all transport depends on petroleum products and industry utilises both coal and oil for heating water and producing steam. Bagasse, the woody waste from sugar production is used to replace coal during the four month milling season at some power plants, however, the reduction in efficiency necessary for this fuel flexibility means that the precious little coal saved compared to dedicated coal-fired power plants. Demand fluctuations during the day are accommodated by oil-fuelled generators because the coal/bagasse ones are too slow to respond. Emergency supply, for example when a large coal/bagasse plant unexpectedly shuts down, is provided by a kerosene-fuelled gas turbine. The lack of flexibility in the overall electricity system is quoted as the reason why only limited amounts of solar and wind power, which are naturally variable, can be incorporated in the supply mix. Most of what has been added so far has been significantly subsidised by public funds.
Hydropower is approaching its maximum exploitable potential, especially considering the slow reduction in annual rainfall and that domestic demand is competing for the use of water stored in reservoirs. However, there is one relatively untapped resource. The waste treatment plant at St Martin is the only one that generates electricity, albeit for its own use, from the anaerobic digestion of sewerage sludge which produces bio-methane. This process also occurs in the landfill sites at Mare Chicose and the methane is finally being used there to generate electricity. One advantage of bio-methane is that it can be easily stored, especially compared to bagasse, and used to generate electricity on demand with very high flexibility, however, this useful property is not currently utilised in Mauritius.
In the long term, it is unavoidable that all electricity will be generated by renewable resources, since fossil fuels will either be exhausted or, for fear of global warming, left in the ground. As the the cost of photovoltaic solar power continues to fall, it will soon be the most cost effective method of generating electricity. Obviously, it cannot be produced at night and output is significantly reduced on cloudy days. On windy days, wind power could fill the gap, but obviously this cannot be relied upon. The critical step will be the development of large-scale, cost-effective electricity storage which will balance out the difference between variable demand and supply over a 24 hour period. How do we meet demand during the interim, while avoiding the need to build more coal power stations and locking the nation into long term contracts based on the increasing costs of fossil fuels?
First of all, demand for electricity should be decreased wherever possible. This is most relevant for industrial consumers who have long benefited from subsidised electricity prices. Their cost of electricity should be increased to market levels with subsidies invested as grants to install more efficient equipment. Industries should also be compelled to at least preheat water using solar heaters, and preferably use concentrating solar collectors (or photovoltaics) to produce steam.
Air-conditioning in homes and commercial buildings should be reduced by installing insulation, shading – ideally by solar panels for roofs and windows, and encouraging natural ventilation. Energy use in transport would be significantly reduced if citizens shared their cars and used public services. Various incentives have proved effective in other countries.
A growing proportion of the population and responsible businesses are ready to contribute to Mauritius’ sustainability by installing solar panels and wind turbines on their buildings, without the incentive of subsidies. This should be encouraged and will only be limited by the flexibility of the overall system, which can be enhanced by generating electricity from bio-methane on demand. To achieve this, anaerobic digestion of solids at the St Martin sewerage plant should be replicated at the other sites.
Future sewerage treatment should also include anaerobic digestion of the liquid fraction of septic waste, thus replacing the energy intensive aerobic systems which are currently used to clean our waste water. With much of the necessary infrastructure already in place, it would be relatively simple to increase capacity and anaerobically digest green waste at the sewerage plants as well. Capacity should be further increased by growing suitable crops in the vicinity, such as rapidly growing energy grasses which organically store energy from sunlight. They could be fertilised using the composted residue of digested sewage, while the residue of the digested grasses and green waste could be used to restore soil fertility of over-farmed soils. This neatly closes the nutrient cycle and reduces the demand for landfill.
Electricity from flexible, on-demand, bio-methane-fuelled plants permits renewables to replace a much greater proportion of fossil fuels because it allows the incorporation of more solar and wind power by balancing their variability. This leverage makes it anaerobic digestion a far more attractive target for subsidies than other technologies. Indeed, subsidies for large scale solar plants, especially on agricultural or forested land, should not even be considered since solar power will soon become cost-competitive. Moreover, since there is sufficient area on the roofs of buildings to meet our electricity needs many times over, undeveloped land should be reserved for more suitable purposes.
Concerned citizens are also beginning to consider replacing their fossil-fuelled cars with electric ones. This can be encouraged by using a “free-bate” system, where increased taxes on petrol and diesel cars can be used to subsidise electric ones and build a network of fast charging stations around the country without recourse to public funds. Intelligent charging systems for cars that are parked for longer periods can help balance the electricity supply and demand by switching on and off as required. As the storage capacity of vehicles improves, we can also expect to see electric powered lorries and buses.
Not everyone in Mauritius needs a highly reliable supply. Additional solar generation can be added without the need to support it with flexible, on-demand generation. The installation of smart meters allowing supplies to homes and businesses to be remotely cut, introduces “negaWatts” into the system whereby demand can be instantaneously reduced. Naturally, those opting in to the system would benefit by having to pay a reduced rate per unit of electricity, balanced by a higher price for those who want a reliable supply. This is an ideal way of reducing electricity bills for the poor without having to introduce costly subsidies.
By implementing this strategy, the whole country – homes, offices, factories and even transport – will be progressively powered by electricity from free, non-polluting renewable sources balanced by bio-methane in the short term and, in the long term, by electricity storage.