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by Chandani Jayatilleke

Foreign exchange requirements to import fossil fuel (coal, oil or natural gas) based energy generation will absorb Sri Lanka's net foreign exchange earnings from its major agricultural exports tea, rubber and coconut in about ten years, senior energy sector experts said.

Sapugaskanda plant

Therefore, the country should develop its own sources of energy to meet the projected increases in demand. While alternatives such as wind and solar-photo-voltaic are certainly important, that alone will not be sufficient in the context of the overall electricity needs of the country. This was revealed at an interview the Daily News had with two experts in the sector - Dr. Ray Wijewardene, a senior agronomist and engineer and P.G. Joseph, Director, Alternative Energy, Ministry for Economic Reform, Science and Technology.

Following are excerpts from the interview:

The capital cost of a wind power plant in Sri Lanka is comparable to that of a hydro power plant. However, the plant factor of a wind power plant in Sri Lanka is only 17% whereas a hydro power plant is 50%. Therefore the cost of electricity from a wind power plant in Sri Lanka is three times as expensive as the cost of electricity from hydro power. Similarly the cost of electricity from solar photo-voltaic (PV) is 12 times the cost of electricity from hydropower.

Therefore, the proposal to generate electricity from wind and PV to feed the national grid is not economically acceptable.

Fuel-wood farming

Fuel-wood farming, a new form of agriculture, of quick-growing and coppicing trees grown by farmers especially for fuel has shown up as the fastest developing and most environmentally-friendly source of energy in the US, Scandinavia, Europe and India.

Two-year old Accacia at Polonnaruwa

It is taking over from disbanded coal, oil and nuclear fuelled thermal electricity generating plants in many parts of the world not only as a more viable and economic way to generate power but also to preserve the environment. It is proving even better suited to the humid tropical regions of the world such as Sri Lanka.

This form of growing trees is called Short Rotation Coppice (SRC) farming. By this method, the side branches of the trees are periodically harvested while allowing the main stem of the trees to grow and mature.

After every harvest, new shoots appear near the cut area and they grow into branches to reach maturity and are harvested as fuel-wood. This process of repeated harvest from a single tree could go on for many years in some variety of trees such as Gliricidia or Leucena. While fossil-fuelled (coal, oil and gas) generators always and continually spew out tremendous volumes of carbon dioxide into the air, contributing to global warming, the carbon dioxide exhaust from wood-fuelled generators has been totally absorbed while the trees were growing. Thus it is well proven to be totally carbon dioxide neutral - the most environmentally benign of all forms of thermal power generation.

The establishment of SRC plantations with nitrogen fixing trees such as Gliricidia or Leucena in degraded land previously used by shifting cultivators upgrades such land to its initial stages. Thus preventing erosion.

Land

Fuel-wood farming is particularly well suited to humid-tropical regions in which Sri Lanka is located, as the growing of trees is well proven in the country. The growing on uplands, of the tree crops tea, rubber and coconut has sustained the nation's economy for well over a century. Further, erosion from plantation lands is a tiny fraction of that from the short-term arable (cultivated) crops, often also grown on the hill-sides.

Forests still cover two million hectares or 27% of the land, while plantation crops (tea, rubber and coconut) occupy one million hectares or 15% of the land. Paddy lands occupy a further 0.5 million hectares or 8% of the country. But a further 1.7 million hectares of hitherto sparsely-utilised scrub lands have been identified all over the country by the Land Use Policy Planning Unit.

Bio-mass energy for Lanka

After 15 months of planting, the first harvest of branches could begin. Within about six months or so (in the tropics) after harvest, fresh branches (coppices) would have grown radially and upwards from below the initial 'lopping' of the tree and are ready for harvesting once again. By contrast, in the temperate countries harvesting takes place annually and then only in the winter months. The 'coppicing' cycle of re-growth, lopping and re-growth again is continuous and is known to extend at least 25 years, by when replanting may sometimes be necessary. The need for added fertilizer is minimal and usually limited only to phosphate and potassium, the main nutrients removed from the soil with the fuel-wood. The practice of returning the ashes after combustion of wood would reduce the need for such fertilizer applications. A mix of species is usually encouraged for environmental reasons as well as for the very much better growth which usually occurs.

As disturbance is minimal, wildlife - birds and small animals, quickly find an ideal home in such coppice plantations. While under moderately favourable conditions one hectare of SRC-farming could yield well over 25 tonnes of dry matter per year, a more conservative yield figure may be taken as 20 tonnes/ha/yr. Now, considering just 500,000 hectares, (one-third of the total scrub terrain) this land could conservatively produce 10 million tonnes of fuel-wood annually and on a continuing basis. This quantity of wood, when used to generate electricity could generate 10,000 GWh of electricity annually and equivalent to nearly twice the country's known hydropower potential and the equivalent of over 1,700 Mw of power-station capacity while operating for only 67% of the available time (plant factor).

Pricing

As regards pricing; energy-efficiency-wise, four tonnes of fuel-wood is approximately equivalent of two tonnes of coal or one tonne of oil. At current prices for oil of around Rs. 16,000 per tonne, the energy-equivalent price of fuel-wood would be about Rs. 4,000 per tonne. Surprisingly, the current (delivered) price paid for fuel-wood is only Rs. 1,500 per tonne.

Wood based electricity generating stations (between 1 to 20 Mw) are usually located throughout the country and in proximity to the energy-plantations as well as to the consumers. Transmission and distribution losses are thereby minimised. However, large fossil-fuel-based power stations necessarily have to be located around the coast. This involves costly transmission lines and extensive losses in distribution of the energy inland. Inevitably, the delivered cost of fossil-fuel-based energy will proportionately increase, thus off setting any initial cost advantage.

The table below gives a cost comparison of a large (1,000 Mw) coal based power station if constructed in the West Coast of Sri Lanka and that of a 500 kW wood based power station located in the Dry Zone.

Cost

From this analysis, it is clear that the construction of large numbers of small-sized wood-based power plants near the load centres is a better option than constructing large centralised coal-based power plants.

Employment

To reverse the current drift of rural youth to towns, fuel-wood farming provides a very viable and local source of highly profitable income. Just three hectares of land conveyed to a family for growing fuel-wood would conservatively produce 60 tonnes of fuel-wood annually, and even at the present delivered price of Rs. 1,500 per tonne represent in annual income of nearly Rs. 90,000 a year for what would really be part-time work. It would not interfere with the seasonal time needed for paddy cultivation or for remunerative work in local industry. 'Thus the 500,000 hectares (a third of the total scrub land available) would provide continuing productivity - and very remunerative 'base' employment - for 1,500,000 rural families or about one-twentieth of the present population in the country. This employment would become available to them in a healthy rural environment throughout the country rather than crowded into factories as in the 'western' pattern of industrialisation.

Conversion technologies

Wood could be used as fuel for two major applications: Heat applications, such as industrial process heat and electricity generation. As far as our local industries are concerned at present wood fuel is the primary thermal energy source. However, nearly 25% of petroleum imported to our country is used in industries to produce steam or hot air for drying applications. Wood fuel could easily replace imported petroleum in these applications. For this purpose we need a device known as thermal gasifier.

To produce electricity from wood fuel, there are primarily two technological options available. In one option, wood fuel is combusted in a boiler to raise steam at high temperature and pressure, very similar to traditional oil or coal fired systems. A high-pressure system is used to drive turbo alternators to produce electrical power.

This technology of using bio-fuels for electricity production has been extensively used all over the world, including Sri Lanka for many years. In Sri Lanka, all sugar industries use this technology to produce all the electrical and motive power needs of all the sugar factories. A second method of converting wood into electricity is through a process known as gasification. In this method, wood is partially combusted to produce a combustible gas.

This gas is first cleaned and used as fuel to drive IC engines, very similar to driving motor vehicles on LPG. This method of electricity generation is more suitable for smaller scale of operation.

A private sector institution has initiated action to install a 500 kW wood based electricity-generating facility in Sri Lanka.

Electricity generated from this facility would be connected to the national grid.

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