| Application of biomass-energy technologies |
|VI. Conversion of biomass into electricity|
Mauritius is dominated by the production of sugar, which represents around 88 per cent of the cultivable area Sugarcane accounts for nearly 20 per cent of the country's gross domestic product (GDP) and over 40 per cent of its export earnings. The economy is thus quite sensitive to fluctuations in domestic sugar production and world sugar markets. Almost 60 per cent of total energy
Notes: $1 -17.2 Rupees (Rs.) (January 1990).
The economic analysis of the wood gas-based electricity system was carried out using a discounted cash flow (DCF) technique, namely, net present value (NPV) method as follows:
NPV - Present value of life cycle benefits Present value of total life cycle costs. Total lifecycle benefits were calculated from the sale of electricity. The unit cost of sale of energy (Rs/kWh) was computed by setting NPV-O and solving for the cost of energy. The unit cost of energy was calculated taking a discount rate of 12 per cent, for the wood and gasbased system and then compared with a diesel-based system of similar capacity.
2 Life of gasifier 50,000 hours; annual maintenance cost 5 per cent, and operational level 20 hours/day.
Cost per month is calculated considering the current energy consumption of 10.74 kWh per day. Labour is priced at Rs. I 5 for 8 hours, and wood is freely available from the energy forest Its market price is Rs.0.25/kg of twigs.
Source: Revindranath et al, 1990; Ravindranath And Makunda, 1990 requirements in Mauritius (excluding wood fuels primarily used for cooking) are met by bagasse-fired generation of power and steam in the sugarcane industry. Bagasse is playing an increasing role in power supply and currently provides around 10 per cent of Mauritius' electricity requirements. Woody biomass supplied approximately 63 per cent (3.5x106 GJ) of all the energy required for household cooking in the country in 1988. There is a potential for producing 10.2x106 GJ, using the by-products of the sugar industry and to a lesser extent solar energy.
According to Baguant (1990) the Flacq United Estate Limited (FUEL) is the largest sugar estate in Mauritius with an annual average production of 700,000 tons of fresh cane, and 79,000 tons of sugar. FUEL was among the first sugar estates to produce excess steam for production of electricity for sale to the national grid in the mid-1950s. In 1982, the FUEL sugar estate installed a dual-fuel, bagasse and coal furnace to produce electricity all year-around and substantially increase its output. Bagasse is used at the rate of about 3540 t/hour and coal at about 14 l/hour. A boiler with capacity of 110 t steam/in, 42 bars pressure, 440°C and a condensing turbine coupled with a generator of 21.7 MW led to an average production of 75x106 kWh of excess electricity (30x106 kWh produced solely from bagasse during the crop season and 45X106 kWh from coal). This represents about 12-15 per cent of the total electricity requirements of Mauritius.
In 1989, the electricity output by FUEL increased to 94X106 kWh (26x106 from bagasse and 68X106 from coal) representing about 16 per cent of the country's total requirements and resulting in over 80 per cent of the electricity being sold to the grid. Unfortunately detailed economic costs of production are not yet available fdor the updated plant following negotiation with the electricity boards, but some available information is set out in table 13.