A rural electrification project in Gabon will provide around 100 villages with electricity based on a solar power ‘microgrid’. The system will serve as a foundation for a future expanded energy system in the region.
Albin Schneider, Siemens Power Transmission and Distribution, Erlangen, Germany
The Siemens Power Transmission and Distribution rural electrification project in Gabon, Africa was drawn up over the period from 1999 to 2000 in cooperation with the Ministry for Mines, Energy and Petroleum. Its purpose is to improve the infrastructure in those areas which, for reasons of distance, cannot in the foreseeable future be linked up to the public supply network.
Furthermore, the Summit on Sustainable Development held in Johannesburg during August 2002 was a milestone for Africa and the world and has succeeded in making everyone aware of the finite nature of natural resources. One of the main resources addressed was energy, which is still largely produced from non-renewable sources today.
Figure 1. Installing a cubicle on concrete strip foundations. To simplify preparation of the foundations, a prefabricated frame is provided that has only to be aligned and cast into the foundations
Complying with the demands of the summit, Siemens has for decades been supporting customers in the selection and utilization of effective and economic power generation and distribution systems for the electrical infrastructure. Quite recently the demand for renewable energy generation plant has increased dramatically.
At the Johannesburg summit, Siemens presented its plans for the Gabon solar energy project, which will provide 100 villages in the country with the means to generate electrical energy for streetlights, household lighting, refrigerators, and telecommunications equipment. The project represents a tremendous step forward in providing the population with future-oriented technology. Now the previously used petroleum lamps are no longer needed, nor is the petroleum supply infrastructure, which also consumes considerable amounts of energy. Non-renewable energy resources are saved and the environmental impact of energy supplies in the region is reduced.
It is vital, however, that the correct components and ratings are selected, and that the optimum technical installation of those components is carried out in order to guarantee that the solar energy system can be operated in an environmentally compatible and cost-effective manner for many years to come. If just one component fails to function properly, then the service life of the entire system can be reduced drastically, thus thwarting the originally intended objective of eco-friendly and low-cost power generation.
With its large hydroelectric power plants, the south of Africa, in particular, is a pioneer in power generation based on renewable sources. However, the use of pure solar energy systems is not suitable for high power loads on economical and ecological grounds.
In remote rural areas, hydropower and solar power can both be used effectively to develop small independent micro-networks to bring a cost-effective solution to the customer. But only with sufficient long-term experience can these concepts be developed jointly with the operators and put into operation successfully.
Decentralized electrification of villages is usually, for reasons of time and cost, a matter of solar supplies. These “germinating cells” for a future electrical infrastructure are ideal for the frequently sunny climatic conditions encountered in African countries. Such cells satisfy basic requirements such as lighting, communications, water conditioning and field irrigation. If energy supplies are subsequently expanded, these systems can be integrated into the new network, or simply dismantled and reinstalled at another location.
The power rating for such systems should not exceed 1000 kWp, since above this level other generation forms are more efficient.
Figure 2. The cubicle contains all of the components required for a 220 V AC power supply
For the project in Gabon, the individual villages will be provided with prefabricated units, the exact number and size of which will be dependent on the population size. Four various sizes have proven most practical, however.
For supplies to public facilities such as schools and medical stations, power ratings of 660 Wp or 550 Wp have been selected. The difference between these unit types is solely in terms of the number of solar cells. The school system works with a 230 V alternating current, and will supply the school lighting. Special bulbs of 11 W/230 V which provide the same luminosity as standard bulbs of 60 W will be used. Plugs have also been installed for small electrical consumers.
The hospital system works also with a 230 V alternating current. The same 11 W/220 V bulbs used for the school will be used in hospitals to keep the number of spare bulbs small. A refrigerator of 200 l capacity allows the storage of medicine and a ceiling fan to ensure a pleasant ambient temperature in the consulting room. Plugs have also been installed for small charges.
To be able to cover substantial distances, all units are equipped with an inverter that converts the voltage of the solar cells into 220 V AC. This inverter is intrinsically safe, i.e. in the event of overload or short circuit, automatic disconnection is initiated and the inverter is automatically switched back in when the fault has been put right. This ensures years of maintenance-free operation. The individual components such as the cubicle, frame, batteries, etc. can be transported and installed without the need for any lifting gear.
The hospital, school and decentralized cubicles are of the same unique design. Outside the building, the cubicles are built on a concrete strip foundation. The inverter, with an integrated solar regulator, is installed inside the cubicle.
Between the casket and the distribution box installed inside the first room of the building, the current is carried by two electric cables, enveloped inside a plastic covered flexible pipe in. The accumulator station is located in the low part of the cubicle. It is made of solar type batteries placed on two shelves shaped like stairs. The voltage is 24 V DC.
The wire mesh cover opening, near the cable’s entrance, allows evacuation in case of a gas formation on the batteries. A battery’s fuse is installed at one pole to insure the appliances protection between the regulator and the battery.
Private households were connected up to a decentralized 12 V DC supply. The advantage of this individualized solution is that distances are of no consequence and the specification for 12 V DC energy-saving lamps practically rules out use of higher-power lamps, thereby preventing overloading of the system. Each house is equipped with an interior box cupboard IP54 type. The lid in front of the box is locked.
Figure 3. The compartment for supplying a private household weighs about 80 kg and is fitted with all the equipment necessary for a 12 V DC supply
Such an interior box contains:
- One solar regulator in 12 V DC
- One distribution box with: one terminal block for the regulator; one terminal block to connect the plug installed on the right side of the box; one terminal block for the lighting; one battery solar-type.
For connection of small-scale loads such as transistor radios, charging stations for radio communication and so on, a socket with plug will be provided, safeguarded against polarity reversal. The restrictions on connected load and on power rating of lamps contribute to a long service life for the controller and the battery. As each household is responsible for its own system, careful use of the equipment is ensured. Five to ten households were connected up to the power supply each day.
Installation of the solar system in Gabon took place in accordance with applicable IEC specifications for standard 240/400 V designs. This means that in a public network only the lamp need be replaced; the installation does not have to be modified. The battery compartment and relevant solar cells (2 x 55 Wp) can then be relocated.
Erection of the 18 W solar street-lights, which function wholly autonomously and can be set up however the sun shines without hindrance, proved that each time was cause for celebration throughout the village and is designed as follows:
A solar generator with a 110 W peak made of two solar modules SM55 is installed on a steel tube pole with a fixation stand. The box cupboard type is fixed directly on top of the pole.
Centralized rural energy supplies should aim at an interconnected energy grid involving generation sources such as wind, sun, small-scale hydropower plants and biomass. Renewable energy sources available locally can, despite fluctuations in the physical availability, frequently contribute to enhance supply reliability, to improve efficiency and to avoid environmental damage. A mix of power generation systems can balance out peak loads and depending on the time of day and year, efficiently cover energy demand.