Authors: Daniel A'Vard, Alicia Webb
Hydro power is an established technology which is scalable to suit any project size from a 1kW single residence system to the enormous 3,800 MW snowy mountain scheme. If your community is lucky enough to have enough water, then hydro power can be a very affordable and reliable technology option.
Large hydro systems usually involve storage by use of dams, which have various environmental impacts. Small hydro systems are typically 'run of river' systems where rather than storing water up they simply operate dependent on the natural flow. These systems are much cheaper to construct and have a lower impact on the ecology of the area.
Identifying a location
Like with all renewable energy projects, the first thing is to identify a location where there is a good, reliable energy resource. In the case of hydro power, you need a river or stream that preferably flows all year. The two features of the water resource that are important are flow rate and head. Flow rate refers to how much water is flowing in the water course, and head is the difference in elevation from the beginning to the end of your water course. The combination of available flow rate and head define how much power you can generate.
The strongest hydro power resources have lots of water dropping really long distances. However, feasible hydro power resources can have one or the other. For example, some communities in the UK have built mini-hydro plants on small weirs where there is relatively little head but plenty of flow. In mountain regions hydro stations can use waterfalls with relatively low flowrates but high head.
Once you have identified a stream or river with the potential to be harnessed for hydro power generation, you will need to measure the flow rate and the head. These two factors will go together in calculating how much energy can be extracted.
A low head, high flow mini-hydro system on a weir in the UK.
Source: Torrs Hydro Blog
Measuring the resource
Measuring the head is reasonably straight forward. You need to consider where you will extract or divert the water from the watercourse, and you need to define where you will site your hydro turbine. The difference in elevation between these two points is the head, measured in metres. This can be done using a GPS or by checking the contours on a topographical map.
Measuring flow rate is more difficult. Flow rate is defined as the volume of fluid which passes through a given point per unit time. It is usually measured in cubic metres per second m³/s or Litres per second L/s (where 1,000 L/s = 1 m³/s).
To calculate flow rate you need to know the cross sectional area of the watercourse, and how fast the water is travelling. This can be done in low-tech fashion using a bucket for low flow rate streams, or using some geometry and a timed float for larger streams. If you want to be high-tech, you can purchase flow rate monitoring equipment from a specialist supplier.
Flow rate changes seasonally and depends on weather patterns. It's important to measure it for a long period of time, preferably a year in order to fully understand your resource. It's best to ask an experienced person the best way to measure your flow rate.
A high head, low flow mini-hydro system.
Source: Micro Hydropower
Available flow rate
The available flow rate is the rate at which water can be sustainably extracted from the watercourse (even if it will return to the stream after generation). It is usually less than the water course flow rate, which allows some of the water to continue to flow uninterrupted. How much water needs to remain uninterrupted depends on the unique ecology of the watercourse as well as the seasonal changes in flow rate.
The available flow rate will usually be determined in conjunction with the manager of the watercourse, and probably environmental specialists in stream ecology and flow characteristics.
Project technology and scale
There are various types of hydro turbines that are suited to different conditions. A hydro expert will be able to assist you in selecting the right technology and capacity for your water course.
Small hydro has typically employed either impulse turbines, such as Pelton, Turgo and Crossflow, or reactive turbines, such as the Kaplan or Francis, but there are an increasing number of Archimedian screw turbines being used.
The Archimedian screw design is popular for low head applications in community projects in the UK. It is a variation on an ancient greek design, where water flowing down the 'screw' device causes it to turn and generate power.
More details about turbine designs can be found in the article Mini hydro.
Energy offtake considerations
Behind the meter
If your hydro project is relatively small (in the order of tens of kW), it may be easiest to connect to an energy user directly rather than negotiating a connection to the electrical grid.
The viability of this depends on three main variables:
- the distance between your generator and a potential energy customer
- the energy consumption of the customer
- the expected energy output of your generator
If the energy output of your generator is less than or approximately equal to the energy used by the customer, you might be able to connect up directly, like a rooftop solar panel connects to a house. If the energy customer needs more energy than your hydro plant is providing, they will import it from the grid as usual. If the hydro plant is providing more energy than the customer needs, some energy may flow out into the grid.
If your project will generate more energy than a nearby customer can use then you will need to connect to the electricity grid. Grid connection options need to be investigated and taken into account from the very beginning of your project development. Expert consultants can help you undertake a grid study, which involves modelling to determine the effect your hydro generator will have on the electrical network under different generating conditions.
The electrical grid is broken into two main parts — distribution networks and transmission networks. Community scale projects will almost always connect to the distribution network, which has a lower voltage. Before you begin investigations, you need to find out which distribution network service provider (DNSP) operates in your area. This should be straightforward to find online.
Once you know which company you're dealing with, you can begin discussions about the project, and your options for connecting up to the grid.
An important part of the planning process of any project is the prefeasibility study. This is essentially a process of considering and analysing the technical viability of the project in the context of all of the social and environmental costs and benefits, as well as the economics.
In your prefeasibility assessment you should consider:
- The reasons behind the project, and the goals you hope to attain.
- The power output requirements/goals (more than one scenario can be discussed here if necessary)
- The availability of the site(s) for the project, and any associated costs such as lease agreements.
- Any environmental concerns at the site(s) including endangered species, proximity to houses etc.
- Social factors that may impact on the project's development and affect the project costs.
Resource and technology
- Assessment of available flow rate and generation capacity
- The predicted hydro resource at the site(s)
- Description of suitable hydro generators
- Description of other equipment required including the turbine housing, and associated electrical equipment.
Energy offtake options
- Investigation into offtake options including grid connection or connection to a direct energy consumer (behind the meter)
- Energy sales, customers and pricing options
- Cost estimates of project capital expenditure
- The eligibility of the project for grants, tax concessions and other incentives.
- Who the likely financiers/projects investors are.
- The comparative costs of alternative energy sources.
As with all community-based projects, it's important to begin consultation with the community as early as possible. The more informed and included people feel from the very early planning stages, the more likely they are to become investors later on. Good consultation should aim to:
- Improve community and stakeholder understanding of the project's aims, benefits and likely impacts.
- Incorporate community ideas and feedback, as well as increase the community's support and sense of ownership for the project.
- Address any concerns early on, especially those that may impact on or even prohibit the project's development.
It is likely that you will need to consult with local government, state regulatory and planning authorities, and community interest and industry groups. Formal approvals are likely to be required from a number of authorities, and it is the developer's duty to determine their approval requirements.
Go to case studies to see examples.