ECO-FRIENDLY PRODUCT – Small Scale Hydropower Turbines

1. RESERVOIR AND DAM SETUPS: KAPLAN TURBINE

Ideal for high pressure and high flow reservoirs: In terms of scale, the Kaplan turbine is versatile and hence standardised designs can suit the micro-scale. It is an axial flow turbine and the area swept by the blades can handle large flows of water. Adjusting the blade angles can improve efficiency.

2. PUMPED-STORAGE: FRANCIS TURBINE

They work well for high pressure and medium flow reservoirs: Pumped-storage is good for communities where demand varies during the day. At low peak times the turbine-pump array can help transport and store water for irrigation and household use. Francis turbines are good for high pressure water transfer as they can deflect large volumes over narrow tubes.
Francis turbines are the most common at the medium scale. They draw in water flow axially and but forces are transmitted to the shaft radially. They tend to have the highest efficiencies of all the turbine types at optimum operation but they do not maintain this for lower flows. The guide vanes are adjusted for lower flows to reduce output power at the expense of efficiency.

3. RUN-OF-RIVER: STANDARD PELTON TURBINE

They are good for mountainous terrains with high water potential and variable water flow through penstocks (narrow tunnelling) (ESHA, 2004, p3). The Pelton works radially with bucket-like fins transmitting the hydropower. As opposed to the first 2 proposed designs, which are reaction turbines, the Pelton is an impulse turbine. The splitting edge between the cup pairs receives water jets. The kinetic energy transmission occurs as the water flows round the curved bowls with energy transfer to the shaft.

4. RUN-OF-RIVER: CUSTOMISED PELTON

The customised variety, designed for fit, would be an improvement on efficiency, for small scale hydro, though maintenance and general capital costs would be similar to the standardised version. The idea behind customisation is to have spare buckets or fins of various sizes ready for whichever flow conditions are prevalent at a particular time of the year.

5. RUN-OF-RIVER SETUPS: GORLOV HELICAL TURBINE

This design, invented in the early 1990s, is useful for tidal currents in rivers and can be attached as a discharge from an industrial plant or a major hydro facility. It is also versatile for reverse flows.
As an operating medium, run-of-river is difficult as optimisation of the turbines depend on the average flows of the river. Therefore seasonal rivers and rivers prone to flood are major problems. However, run-of-river has the least impact on the environment and new power generation technologies help optimise against variable flow. Pumped-storage usually requires greater lengths of pipe from which additional frictional losses reduce the efficiency of the system.

BASIS

The basis of power generation is the conversion of flowrate (kinetic energy) and head (potential energy) into useful work. This useful work is part of the theoretical power:
Theoretical power (P) = Flow rate (Q) x Head (H) x Gravity (g) = 9.81 m/s2
When Q is in cubic metres per second, H in metres and g = 9.81 m/s2 then,
P = 9.81 x Q x H (kW)
This is true for all designs for micro-hydro. The useful work depends on the particular design of the turbine and configuration with the alternator, generator and remaining infrastructure of the system.

LOSSES

There are losses though. The best small water turbines, which tend to be axial flow turbines like Kaplan, have efficiencies better than 80% (ITDG, 2006, p2). Most of the losses are due to frictional losses. These can be reduced by improving the piping materials, reducing piping length or changing system setup. However it is only by a small percentage. Certainly for low power outputs frictional losses are a large percentage. Most realistic figures are as low as 50% potential power (ITDG, 2006, p2).
Further system losses occur from the point of conversion into electrical energy, which is the useful work, to pure kinetic energy for running mills, whichever the case may be. In the case of producing electrical energy there are losses in the alternator (electromagnetic and heat losses) and losses in the transmission power lines.

OPTIMISATION

The most important design related losses come from load characteristics rather than demand characteristics. It is easy to calculate maximum, rated and minimum loads, but partial loads or flows take the experience of river flow fluctuations to determine.
Returning to end use considerations, it would be desirable that the design is versatile for both mechanical and electrical useful power, for a remote location where grid power access is unreliable but has an active industry of electro-machinery and household electrical appliance use.
To generate power, a standard alternating current (ac) signal with 3-phase power is ideal for micro-hydro between 100kW and 20kW (below 20kW single-phase power is satisfactory). This ensures that transmission losses are minimal for supply at 50 or 60 Hz to the user (Boyle, 2004, p151).

LOCATION

The remote area would be on a geography location of undulating or hilly terrain with yearly flowing deep rivers at a minimum. There would be a wider range of design choices if the location is mountainous or at a foothill but in order to mitigate locality risks, the selected design must be flexible. For example, low-head turbines are great for small-scale projects at rivers as long as flow is adequate. In this sense, the Gorlov is suitable.
Site selection depends on the geotechnical and hydrological (e.g. rainfall and flow data) site surveys. For this exercise, it will be assumed that a suitable site has been selected and that it is adequately close to the community.

PRODUCT RELIABILITY

Technically, the moving or falling water becomes the shaft power and the turbine converts the kinetic and potential energy into the rotational energy of the shaft, the work done of which is expressed as shaft power (kW).
The table above describes the most established turbine types with the exception of the Gorlov helical turbine. The Gorlov is a reaction type working at medium to low head pressure, and is very reliable for across variable head pressures.
On load requirements, hydropower clearly trumps fossil fuel based sources on the account that at low demand (e.g. residential use only), the turbine can still run at full load to provide the demanded power and pump water for irrigation or utility supply at the same time (fossil fuel turbines and their use brings mitigation costs on the environment and are not as versatile for multiple demand requirements). With the Gorlov turbine, the plant load factor (average power generated over maximum rated power) thus remains high throughout the year even though pumped-storage is not feasible.
As previously mentioned, the pumped-storage setup would put to good use turbines as versatile pumps, i.e. as reverse turbines. This would provide additional capability but constrains operating conditions for the turbine to work. In some cases usage of reverse-generators i.e. versatile motors, can be useful to drive these versatile pumps, but once again the efficiency of the system depends on the operating conditions. This lack of multiple utility of the Gorlov turbine is its major disadvantage.

INCOME GENERATION AND COST EFFECTIVENESS

Immediate economic benefits are income-generating industries that make use of the power. The greater these benefits are the quicker returns on investment are realised. Major costs for investment are site preparation and capital cost of equipment. Small-scale hydro might not seem to be bankable per unit cost, with larger scale technology enjoying the economy of scale (ITDG, 2000, p9).
Due to the standardisation of design approaches, micro-hydro is becoming increasingly cost effective. Design selection is critical to improving cost effectiveness, as the selected design shall show. Also material choices are important. Maintenance costs, which are usually low with respect to total costs, should be considered in the design selection criteria as an economic factor.

RESOURCE USE

Remote areas tend to have a more sensitive relationship with the natural surroundings. Thus, minimal site development brings minimal environmental impact. In that sense the usage of existing infrastructure, where possible, should be encouraged to implement the micro-hydro project.
For the province or country to benefit environmentally, it would be suggested to use local materials, such as timber, aggregate and sand. This would not just reduce transport costs; it would increase accountability and responsibility towards the environment at the community level in the manufacturing and construction stages.
Innovation also comes into play here. Rivers also distribute sediment and dead matter down valleys, and reservoirs and canals tend to obstruct this natural process. Self-cleaning intake screens, just before the turbine blades, would ensure that natural flows continue and at the same time prevents obstruction in the power generation.

SOCIAL BENEFITS

Underpinning social benefits are the usage of a community’s full potential. The very process of design selection provides a lesson learnt to transfer as technology and knowledge. This in turn enhances the capacity for the community to run the programme of generating electricity and plan for future similar plans with near autonomy.
The key to increased autonomy is increased ownership at the local level. Ownership is not just at the operations phase. The project management team should include some potential expert users, with well aligned planning across from the development authorities to the financiers to the labourers. The use of local labour at all stages is good for early learning of the operations of the micro-hydro scheme. This would be a key linkage to successful operation whereby a smooth grid installation and operation is envisaged.
Where communities are run in a fragmented or distributive manner, a stakeholder engagement forum should be set up at the earliest stage of the project with fair representation to determine needs, expectations and collaborative opportunities. Technical problems can be solved at the community level in order to obtain a reasonable amount of understanding between the key leaders, especially key financiers.

1. DEVELOPMENT, MANUFACTURING AND TESTING

Gorlov concept, invented at Northeastern University in Texas, USA, has twisted airfoil blade design. It has reduced vibration and extracts energy across a wide area of the water flow profile.
It forms part of a Gorlov hydro electrical farm concept. See below how the concept arranges the units in a single axis, with a generator fixed to one end on the water surface:
Depending on the width of the river, multiple single axis arrays can be arranged to form a farm.
Initial tests of this relatively new design have been done before. Whilst it is reliable, turbine efficiency has been shown to be 35%(Guittet, 2008).
Hydrodynamic tunnels are typically used for testing prototypes. For the Gorlov turbine, the rotation speed of the machine and its torque are given special attention. This gives a performance indication under various conditions.
Its design ratings are determined by measuring forces on the turbine using force sensors (See Figure 10). The sensors are arranged to measure:

The testing rig allows for the dynamic reaction of the single axis system in real conditions. The test rails give sensitivity to the sensors for this aspect.
Finally pressure, flow intake and discharge are measured to complete the simulation of operating conditions for a prototype. This completes the data set to rig other prototypes and determine characteristic curves. The building of the first unit begins once tests are successful.
The blades are typically made of steel alloys but depending sometimes on material availability and cost, aluminium and fibre glass are feasible options. Metallic turbine blades are moulded, treated and bent at a manufacturing plant alongside the frame, which would be of a similar material. All parts can be assembled on site, including the generator and connecting cables.

2. BUSINESS PLAN & IMPLEMENTATION

The project should actually be an ongoing activity upto one year after installation, because the implementation phase allows good feedback* to perform future projects better. This also gives prospective investors the necessary confidence to fund the project (ITDG, 2000, p-iv). Micro-hydro has been neglected as a profitable venture for poor or remote areas because it has been impossible, at project conception, to project load and demand and thus mitigate risks.
The team bringing the technology into the community would be expected to be an appropriate technology organisation within government, private enterprise or an NGO outfit. This technology transfer team, that has demonstrated micro-hydro as successful in previous projects, will have project management expertise to oversee critical installation and implementation tasks.
* Items in italics are key attributes for Business Plan and Implementation
The business plan can be viewed as part of building the social infrastructure of health, school, industry and housing. A community team would be set up to work organically within the technology transfer team. A co-ordinating engineering manager, ideally from the same community with the same vision of developing the social infrastructure, can liaise the work of the 2 teams and will be in charge of ensuring that there is adequate manpower, trouble shooting know-how and managing materials for the site work and operations.
Implementation is the most critical part of the whole project. Whilst the new technology has been perfected on the test rig, the real time usage will determine its benefits as a truly eco-friendly product. Beyond the project scope, the users will also have to be ready to be connected to the micro-hydro output. So, the linkages with the power distribution authority that is setup parallel to the generation are important.