There are four main types of hydropower projects:
Run-of-river hydropower projects have no, or very little, storage capacity behind the dam and generation is dependent on the timing and size of river flows. Such projects fall naturally into two categories:
a) Upland projects that use the natural fall of the river to create the necessary head, which is then commanded by tunnel, canal or surface conduit. These are typically high-head, low-flow schemes.
b) Lowland projects that are sited at barrages on the more mature, lower reaches of rivers, where they rely solely upon the head created by the barrage. These are typically low-head, high-flow schemes.
Reservoir (storage) hydropower schemes have the ability to store water behind the dam in a reservoir in order to de-couple generation from hydro inflows. Reservoir capacities can be small or very large, depending on the characteristics of the site and the economics of dam construction.
Pumped storage hydropower schemes use off-peak electricity to pump water from a reservoir located after the tailrace to the top of the reservoir, so that the pumped storage plant can generate at peak times and provide grid stability and flexibility services.
Typical cycle times are 4 to 8 hours but some have cycle times of more than one day
Marine/offshore technologies a less established, but growing group of technologies that use power of currents or waves to generate electricity from seawater. These include hydrokinetic (river, ocean and wave), tidal barrage and tidal stream, osmotic and ocean thermal technologies.
Generally, for high heads, Pelton turbines are used, whereas Francis turbines are used to exploit medium heads. For low heads, Kaplan and Bulb turbines are applied. The classification of what ‘high head’ and ‘low head are varies widely from country to country, and no generally accepted scales are found.
• are technically simple.
• contain some equipment and material which may need to be imported
• have a long construction period when the project is large and there is a large civil engineering component
• have a long project life, typically 40 to 100 years or more
• have no fuel cost and low operations and maintenance costs (2 to 4% of capital cost)
• experience seasonal fluctuations in water flow which affects the cash flows
• have a wide range of capacity factors typically in the range of 25 to 90% but some outside this range, depending on the design basis
• offer other benefits including flood protection, drought management, drinking water supply, irrigation, navigation and tourism, all which typically do not offer clear and direct revenue streams to reservoir developers.
• have potential impacts on the local environments and the possible displacement of communities from project sites
• need major maintenance every 10 years for runner replacement, every twenty years for SCADA, control systems etc, every thirty years for switchgear and utility equipment.
• allow more renewable power projects, especially wind and solar, to be added to the system by providing rapid-response power when intermittent sources are off-line, and pump water to energy storage when such sources are generating excess power
• may affect more than one country and may need international agreements. Typically the upstream parts of the river is exploited for hydropower and the downstream parts for irrigation. The planned developments by one country to dam parts of a river may have negative implications for countries further downstream of the river, such as flooding and irregular water availability.
• impact the rate of sediment transport in a river, in many cases leading to sediments becoming trapped behind the dam rather than flowing downstream. This can have a direct effect on the operating life and the electricity output of hydropower plants, and the distribution of sediments and nutrients downstream. Effects of sedimentation include reduced reservoir and flood management capacity due to the loss of storage, a shortened power generation cycle, and higher maintenance costs.
The civil costs of reservoir schemes are very site specific and difficult to estimate without a detailed design.
How Promoter handles Hydropower Projects
Promoter can handle run-of-river, reservoir and pumped storage (but not marine yet).
It calculates the mainly civil engineering (reservoir, dam, tunneling, canal, infrastructure) element of the capital and operating costs separately from the electromechanical element.
For Run-of-river projects, the user sets the head, the average annual river flow, the residual flow required for environmental reasons and the average monthly variations in river flow over the course of a year. During the early planning phase, the user can carry out a sensitivity analysis by trying different sizes of turbines to determine the IRR and NPV allowing the user to pick an optimum capacity. This choice will determine the average annual capacity factor. This capacity is good for early planning purposes but must be confirmed by third party specialist studies later in the feasibility phases.
Typical Cash Flows
The following diagram illustrates the cash flows on a hydro power project.
The project has a high capital cost but very low operating costs. The chart also illustrates the need for additional investment in runners at ten year intervals.
Promoter takes into account seasonal variations and these can be clearly seen when displaying charts and reports on a quarterly basis.