“ energy access: feeding of isolated areas with no local energy resources ” a. clerici
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“ Energy access: feeding of isolated areas with no local energy resources ” A. Clerici Senior Advisor to The President of ABB Italy & WEC Chair of Study Group “Survey of Energy Resources and Technologies ”. Index. Introduction. Concepts for transport of electricity. - PowerPoint PPT PresentationTRANSCRIPT
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“Energy access: feeding of isolated areas with no local
energy resources”
A. ClericiSenior Advisor to The President of ABB Italy
&
WEC Chair of Study Group “Survey of Energy Resources and Technologies”
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Index
1. Introduction.
2. Concepts for transport of electricity.
3. Transmission system configurations and technical / economical hypotheses.
4. Analysis of the results.
5. Final considerations.
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1) Introduction
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• In the present socio-economical environment it is quite clear that energy assumes a fundamental role for both the life of industrialized countries and for the development of LDC’s.
• In particular, electricity is becoming the most important form of energy for final consumers with ever increasing penetration rate: today around 1/3 of total primary energy resources are converted into electricity, compared to the 27% in 1973 and to the 44% in 2030.
• The link between electricity consumption and GDP is well recognized and therefore the correlation between poverty and access to electricity.
• Around 1.6 billion people (one quarter of mankind) are not yet connected to commercial electricity supply, and 80% of them live in rural areas.
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• At world level, the electricity consumption per capita is around 2.5 MWh/year but great differences exist. 23 MWh/capita x year Norway 15 MWh/capita x year Finland, Sweden,
Canada, US 5.5 MWh/capita x year Italy 2.7 MWh/capita x year China 0.6 MWh/capita x year Africa and South Asia
• Africa with 14% of world population consumes about 3% of global electricity but the South Africa nation with 5% of Africa population consumes 41% of all Africa electricity energy.
• Excluding the countries located in the North of Africa and South Africa the main source of energy is wood.
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• Some African countries such as Angola, Benin, Congo, DR Congo, Ivory Coast, Kenya, Nigeria, Senegal, Sudan and Tanzania consumes between 200 and 100 kWh/capita per year and Eritrea and Ethiopia just 50!
• Apart from slums of large cities, the problem to supply electric energy to persons who do not have access to it depends in many cases from the low density of population in areas far from harbours and main transport infrastructures; electricity is usually produced by small local diesel generators fed by oil transported over distances exceeding even 1,000 km in some cases.
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• The alternatives usually analyzed to feed these areas, apart from local diesel are:
use of possible local energy resources if / when available (biomasses, mini hydro, etc.);
use of photovoltaic (PV).
• The last alternative, even if of interest for some initial small consumptions is still expensive, would require energy storage and / or conventional generation spare capacity. Wind is not convenient in many internal areas and the same considerations for PV apply.
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• In 1985 a first study (A. Clerici – L. Paris “Transmission planning in developing countries” – CIGRE Dakar 1985, Paper 120-05) has been performed to check the possible cost competitiveness to transport the electricity produced by “convenient sources” to isolated areas distant some hundreds of km. And this even considering areas with possible initial load of few MW but with a large load growth potential as soon as electricity is available to start both domestic / handy craft / small industry / commercial consumptions.
• The initial study has been updated and here are reported some results of a new study performed in 2010 when oil price was around 70 – 80 $/barrel.
• From end of 2010 the oil price is increased above 100 $/barrel but this does not modify the approach and conclusions. In effect high oil prices make the proposed solution more attractive.
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2) Concepts for transport of electricity.
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• Transport of electricity from a single generating plant feeding different load centers can be cost competitive due to the economy of scale on investment cost and O&M costs and due to the higher efficiency of larger units. In addition such power plant can be developed in steps larger than the single load center demand with economic advantage.
• Beside the economy of scale one has to carefully consider the leveling of the load diagram and reduction of the peak load, resulting from load diversity when the different demand areas are connected to the single source.
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• The comparison has been therefore performed between two alternatives for electricity supply namely: local diesel generation for each load center; concentrated generation with relatively long and initially
lightly loaded transmission systems each one feeding a different load center.
• Concentrated generation can be hydro, gas turbine plants in single or combined cycle (depending on gas cost) or oil/coal fired plants (where cheap oil/coal is available). However the comparison still holds if instead of a power plant one considers, as power source, an interconnected system, as sketched in figure 1, far from the load centers. This helps cheap back-up capacity for the development of local volatile RES.
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Load Centers fed by local plants (A) or from cheap plants / interconnected systems (B)
Figure 1
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• The extensive parametric analysis has been performed, considering: different initial loads in the range 5 – 15 MW with different
load – growth; different ambient conditions; different financial conditions; different levels of reliability and related costs; a wide range for each parameter affecting the system
design and the final energy cost; the application of different available AC transmission
technologies.
• Only some results of the general investigation are here reported with the relevant basic assumptions.
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3) Transmission System Configurations and technical and
economical hypotheses
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Transmission System arrangement – SC = Series Compensation, SR = Shunt Reactors, SVC = Static Var
Compensation
OHTL
Figure 2
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• The base scheme for the transmission system arrangement as from figure 2;
• transmission voltage 138 kV or 220 kV;
• only one transmission line is foreseen to supply the remote load, thus accepting a low reliability figure for the first stage of the rural area electrification;
• suitable reactive power compensation (RPC).
• The RPC consists in: Shunt Reactors (SR) connected to the line side of the
breakers; Static Var Compensators (SVC): Series Capacitors (SC).
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• The RPC limits the voltage fluctuations caused by load variation, switching on/off components, etc. From the studies performed these problems can be mitigated by:a) transformers having low magnetic flux density values at
rated voltage;b) operational limitations, such as avoiding simultaneous
starting of large induction motors.
• This system configuration permits to operate the system with an appropriate quality of voltage supply and without dangerous over voltages following breaker operations or faults.
• The maximum transmissible power with and without SC's and SVC's is shown in the diagram of Figure 3. The diagrams indicates that a compensation of 60% is roughly doubling the maximum transmissible power for a given system length.
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Influence of Series Compensation (SC) and/or Static Var Compensation (SVC) on maximum Transmissible Power
at 138 kVC = Equivalent Compensation
Figure 3
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• The basic assumptions for the reported results are: the characteristics of the transmission lines have
been taken from the African countries practices. The cost is strongly affected by environmental conditions and specific cost equations have been adopted.
Discount rate (DR): 11%; Economic life of transmission system: 25 years; Load growth (LG) rate: 5 and 10% per year; Maximum load fed by the transmission system has
been considered equal to 4 times the initial value; this in the assumption that the load in excess will be fed by different future systems.
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• For the remote concentrated plant a long run marginal cost of 5 c€/kWh was considered for a plant size of around 100 MW.
• For local diesel plants, costs are based on these average assumptions: capital cost (including reserve, ancillaries, etc.): [900
+ D(km)/10] €/kW; (D = distance from next harbour of load areas).
type of fuel: heavy fuel oil; life of plant: 12 years.
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4) Analysis of the results
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• The results for the following transmission systems alternatives are reported in the figure 4: transmission system lengths L from 100 to 500 km; average road distance D from next harbour 700 km; annual operation/maintenance costs: 2% of the total
investment of transmission to allow for good availability of system components;
international oil price (OP) of 75 $/barrel valid for 2010 when the study was performed.
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Isolated areas with small initial load and load growth of 5% - 10% per year (case of Villages 700 km from next harbour)
Figure 4
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• With initial small loads of 5-15 MW an energy transmission from 350-500 km is more convenient than local diesel generation; this even with the minimum Load Growth (LG) considered and equal to 5%.
• Clearly higher values of oil price and of load growth rates increase the advantage of transmission versus local generation.
• The 230 kV voltage level becomes competitive versus the 138 kV one, for larger initial loads (above around 10 MW) and larger distances.
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• An example of possible utilization of cheap power that could be economically transferred to hundreds of km for some tens of MW is the Saida – Naama - Bechar 230 kV system in Algeria. A single overhead transmission line with appropriate RPC systems is feeding villages in the desert 500 km far from main grid [F. Soukeur - L. Valfré. Long distance transmission in Algeria: technical economical considerations, commissioning and operation experience. CIGRE 2004. Paris].
• When the reliability requirements can be assumed increasing in time with the load and therefore with the socio-economical development of the area, the alternative of one initial circuit followed by a second one at doubling of load is the only alternative which can provide an actual starting of electrification at affordable prices.
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5) Final considerations
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• Africa is the continent with the highest percentage of people with no access to electricity and however it is also the continent with the minimum utilization (7%) of huge hydro resources (DR of Congo, Ethiopia, Cameroun), solar energy and biomasses.
• Theoretically both: the development of cheap large hydro plants connected to
inter-countries transmission systems and local distribution systems;
medium size plants to feed radially different isolated areas;
should be implemented.
• The first option requires long times, large investments and financial problems connected to political risks; the second option seems more viable in subsequent steps if the adoption of apt technologies and reliability criteria are taken as correspondent to the low level of initial industrialization.
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• With respect to no electricity it is better to have that soon and affordable for 360 days per year (with clear emergency suppliers for critical essential loads as hospital) without waiting for decades to get electricity 365 days per year with quality of supply we are used in Europe.
• Sophisticated standards are killing initial projects; clearly with the socio-economical development of the areas the reliability must be improved with adequate system redundancies.
• Even each practical case requires detailed analyses, the studies performed provide data for preliminary evaluations.
• With international oil price of 110 $/ton and load areas located at a road distance D=1,000 km from nearest harbour, it is economically interesting to feed from concentrated plants systems initial loads of around 5 to 10 MW located even at a distance of 350 and 550 km respectively from the generating source.
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• High values of initial load Pi, high load growth rates and low values for the opportunity cost of capital, increase the competitive distance of transmission versus local diesel generation.
• The road distance D of the “isolated area” from the nearest harbour plays an important role in the limit of competitiveness between remote concentrated generation and local diesel generation.
• The reliability required by the supplied loads has a substantial importance on the optimum transmission system alternatives and on its limit of competitiveness. In case of values of curtailed energy lower than about 0.5 US$/kWh, the solution with one circuit is the most convenient while for higher values of 2 $/kWh, the two circuits or the double circuit solutions are the most attractive for the transmission system.
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• With reliability requirements increasing in time with the load, the alternative of one initial circuit followed by a second one at doubling of load, can be competitive.
• Series Capacitors and / or Static Var Compensators enhance the advantages of possible transmission at lower system voltages, and extend the maximum transmissible power for a given system length (or the maximum transmission length for a given power).
• These types of “feeding” from programmable plants are also the basis for local development of volatile renewables which necessitate adequate spare capacity waiting for the development of cheap / reliable “storage systems”.
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