Week 4 - Hydropower Flashcards
What are the different type of hydropower generators?
Dam (or storage) hydro: - Storage: days - months - Tends to be larger schemes Run-of-river hydro: - Storage: virtually none - Range of sizes Pumped storage: - Storage typically 8 hours - Tends to be larger
What sizes are hydropower divided into?
Pico/micro: <10kW
Mini/small: 100kW - 20MW
Large: >30MW
What are the hydropower components?
- Catchment area, defined by weir locatikn and the topology of the land.
- Weir or Dam
- Penstock, high pressure pipeline, open channel sometimes included.
- Power house, Low pressure tailrace to river
What is ‘Head’?
‘Head’ is the vertical distance between water levels behind the weir and the river below the power house.
What is the ‘static’ or ‘gross’ head?
The static or gross head (H_G) applies when water is not flowing between the intake and the turbine generator.
What is ‘net’ head?
As water flows, the turbine experiences a reduced or ‘net’ head (H_N) due to fiction losses in the penstock ‘head losses’ (H_L)
H_N = H_G - H_L
What are the major factors for calculating head loss?
Flow rate and diameter.
What does the friction factor depend on?
The friction factor depends on material and whether flow is laminar or turbulent, governed by the Reynolds number.
How is friction factor determined?
Usually determined using ‘Moody charts’.
Using Roughness ratio and Reynolds number.
When designing pipeline, what is the aim for the head loss?
The head loss is usually below 10% of the gross head.
This is ensured by optimizing the diameter of the pipe. However, there is a trade off in increasing cost as diameter increases for reduced lifetime energy losses.
How is River Flow approximated?
River flow is the difference of precipitation (rain and/or snow) and Evapotranspiration (evaporation from soil and plant transpiration).
Q = P - ET
What is a Flow Duration Curve?
A Flow Duration Curve is a form of cumulative probability distribution. Each point on curve shows proportion of time that flow rate is exceeded. It is created by ranking flows and determining exceedance percentiles.
How is exceedance percentile calculated?
E_P = rank / (n+1)
What is the design or rated flow (Q_Tmax)?
Q_Tmax is the design or rated flow at which max power is produced. No more flow can pass through penstock. Design flow typically mean or median annual flow. 30% exceedance common.
What is compensation or reserve flow (Q_COMP)?
It is the flow which must remain in river and not go through turbine to preserve life in river.
What is the turbine minimum flow (Q_Tmin)
If below this flow, the turbine shuts down. Determined by Q_Tmax and turbine type.
Area of a flow duration curve can be estimated by dividing area into columns of defined width centred on known flow rates. How is the available flow in any column calculated?
Q - Q_comp
What is the biggest issue when constructing a hydro power generator?
Biggest issue is obtaining credible data, which is very important for ‘bankability’ (i.e. funding) as well as desgin.
30 years of data at the site are required to get a good idea of local climatological norms.
Unlikely to be available so need to measure site for at least a year and benchmark against:
- ‘Analogue’ data from a nearby station.
- Standard flow duration curves based on national estimates.
- Hydrological models to generate flow data fron rainfall and evapotranspiration data.
Name some historical uses of hydropower.
- Water wheels for grinding corn.
- Heavy use during the industrial evolution to drive machinery as steam initially treated as backup during drought.
- The need for compact, faster and efficient equipment led to evolution of water turbine (Francis turbine in 1849 and Pelton wheel in 1870).
Name some hydropower stations.
- Hoover dam
- Kariba dam
- Itaipu dam
- Three Gorges dam
What is an Arch dam?
A dam shaped liked an arch. This gives strength to the construction and uses less material (Cheaper). Used at narrow sites and need strong abutments (substructure at end of dam).
What is a Concrete Gravity Dam?
Weight holds dam in place. Uses lots of concrete (expensive).
What is a Buttress Dam?
Face is held up by a series of supports. Significantly reduces cost. Flat or curved face.
What is an Embankment Dam?
Made of earth or rock. The weight of the st