Benefits of Distributed Power Generation
There are several benefits of combining small decentralised power plants - such as the 17 small 5 – 20 MW plants being implemented under GET FiT – within the power generation mix. These include reduced power losses as a result of having more generating plants with a greater geographical coverage, improved security of supply, and improvements in the power system stability, both locally and nationwide.
Improved power system stability
As mentioned above, a sudden load change that is larger than can be accommodated by the spinning reserves within a few seconds can cause serious grid instability. For example, consider that a major power line supplying towns in Western Uganda from Kampala disconnects due to a fault, and the spinning reserves of the distributed power plants in the West are limited. In this case, the Kampala area will suddenly have a power surplus and the generators in this area will quickly reduce power production to compensate for reduced consumption, as described above. On the other side of the faulty line, the loads of the Western grid will start to disconnect as local load shedding starts after the frequency goes below a certain limit. Load shedding will continue until the loads are low enough to be balanced out by the available local power production in the ‘islanded’ (isolated) part of the system. Hence, the distributed generation will continue to provide power to parts of the islanded grid until the faulty main line has been fixed and re-connected.
When, on the other hand, the distributed power plants produce power in excess of the load of the nearby towns, a different scenario ensues. Consider, for example, Western Uganda, where the GET FiT hydropower plants Sindila (5.25 MW), Ndugutu (5.9 MW), Rwimi (5.45 MW), Nyamwamba (9.2 MW), Lubilia (5.4 MW) and Kyambura (7.6 MW) and the Nyamagasani plants (20 MW total) are being developed. In many cases, this area will have a power surplus, due to lots of hydropower production located in a relatively lightly populated area. If the transmission line supplying this area were disconnected due to a fault, these power plants would have sufficient capacity to supply the local demand, and the inhabitants would not notice the fault.
In addition, local power production improves the local grid stability with regard to voltage levels. The distributed power plants in the GET FiT portfolio are all equipped with their own voltage controllers, which help to control the voltage levels in the local grids. This will contribute to improved local grid stability in many rural areas.
Reduced power loss
Another benefit of GET FiT distributed power is the reduced power loss in power lines. In 2018, the expected total power loss target is 18.1% in Uganda. Power loss increases with the length of the lines and varies with the line voltage level. Higher voltage levels result in lower losses and vice versa. Take for instance the GET FiT supported 6.5 MW Muvumbe hydro power plant in Kabale, South Western Uganda. Since its commissioning in Q2 2017, the plant supplies part of the demand in Kabale town. Therefore, it is no longer necessary to transmit the full power required for Kabale town all the way from Mbarara over the existing long 33 kV line. This directly reduces the line losses. Power plants with a greater geographical distribution generally contribute to a large reduction of the grid power losses.
Improved security of supply
GET FiT increases security of power supply in Uganda. Mixing decentralised run-of-river hydropower1 and solar power production with regulated hydropower makes it possible to improve the utilization of stored potential energy in the water reservoirs, like Lake Victoria. After commissioning of the additional large hydropower plants on the Nile, Karuma and Isimba (totalling some 780 MW), more than 75% of power production in Uganda will come from large Nile-fed hydropower plants. This means that the Ugandan power system will be increasingly exposed to hydrological variations, making the country more vulnerable to the potential effects of future dry periods.
The GET FiT power plants are spread across different parts of the country, and thereby contribute to reducing the pressure on Lake Victoria as Uganda’s main source of energy. As mentioned in the above sections, they contribute to this both through reducing losses and stabilizing the grid. However, they also contribute to increasing supply security by being able to displace power production from large hydropower plants on the Nile if needed.
For example, when solar energy is being produced and can supply the grid in preference to regulated hydropower, the water that would otherwise be used for hydropower generation can be stored and used later, either during periods when solar power cannot be harnessed or during drier periods. In this way, storing the water, and the potential energy, in a reservoir is analogous to the power stored in a battery. With respect to bagasse thermal power plants, such as Kakira in the Get FiT portfolio, this type of generation makes it possible to use cheap bio waste from sugar production to produce power. This additional source of power further contributes to balance of power sources and complements the supply of power to the grid from e.g. hydro and solar.
Uganda well on track with VRE approach
Solar power plants are categorized as Variable Renewable Energy (VRE). It is beneficial to have VRE’s located in different geographical areas, as has been done in Uganda so far, because different parts of the country are likely to experience different weather conditions at a given time. For example, it may be cloudy in Tororo but sunny in Kabulasoke on the same day. The total solar power production will then have a smoother overall output, which makes VRE plants easier to manage. In Uganda, the GET FiT solar projects, Soroti (10 MW) and Tororo (10 MW) Solar in the East, as well as the planned Xsabo solar plant (20 MW) in Kabulasoke, Central Uganda, are good examples of this geographical spread.
1 The GET FiT hydropower projects are «run-of-river», meaning that they do not have significant reservoir/storage capacity, and thus cannot be used for energy storage.