Low Head and Ultra Low Head Hydro
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Technology Name And Capacity Range:
Low Head Hydro - 5 kW to 250 kW
Ultra Low Head Hydro - 1 kW to 5 kW
Introduced to the Market:
Example / application:
- At the very small end of this capacity (i.e. picohydro of 5 kW or less): off-grid hydro system, often charging batteries as back-up, that can run modest homesteads, power fencing, pumps, etc.
- At the larger scale end systems, can also work off-grid or, depending on the available programs with the utility, may be able to sell power into the local distribution grid as a long term source of additional income.
See Other Resources
Remote hydro can replace alternatives which in long run could prove to be more costly such as grid extension or diesel or gasoline generators. Hydro has the added benefit of being quiet and non-polluting.
Grid connected hydro has the opportunity (given utility cooperation and price contracts) of providing a sustained source of income on farms. It can sometimes provide, with the proper switching and controls, a secure source of power in case the grid fails.
Hydro electricity can, of course, be exploited at many scales depending on the volume of water flowing and the drop or "head" it falls before going through a turbine. Capacities relevant to on-farm use generally fall within two categories:
Low Head Hydro: 5 kW to 250 kW and head between 1 and 10 metres
Ultra Low Head Hydro: 1 kW to 5 kW and head between 1 and 5 metres
Head RangeBetween 1 and 10 metres
Energy Production per unit capacity:8000 to 4000 kWh / kW installed
Cost ranges - Installed and energy:
$2000 to $9000 / kW installed
$0.03 to $0.10 / kWh
The cost of a system depends on many factors such as the kind of equipment used, the quantity of equipment needed, the cost of civil works, and the quantity of work that you do yourself and that you contract out. Furthermore, each hydro site is unique because about 75 percent of the development cost is determined by the location and site conditions. Only about 25 percent of the cost is relatively fixed, which is the cost of the electro-mechanical equipment.
Skills / training for design and installation:
- Low Head hydro: will require, in most circumstances, the assistance of trained professionals to develop the site and to supervise the installation of civil works with electrical and mechanical equipment. For example work in rivers has demanding environmental constraints and connection to the grid is at high voltages with low tolerances.
- Ultra Low Head Hydro (system with a head of less than 5 metres and outputs of only several kW or less): prepackaged turbine / generator systems can be purchased from suppliers or in some cases do-it-yourself plans can be purchased from popular magazines. The supplier of these systems can generally provide all the assistance you'll need in installing an ultra-low head system.
Operation & Maintenance Requirements:
- Low O&M - daily cleaning at intake in flood season (ex: cleaning the trash rack used to filter debris and prevent it from being drawn into the turbine at the penstock pipe intake) or during winter to keep intake areas ice free. Periodic troubleshooting of mechanical valves and electrical controls. Periodic changing of oil in gear casings after a fixed number of hour's operation.
Run-of-River - Reservoir
Most micro-hydropower systems operate "run of river," which means that neither a large dam or water storage reservoir is built nor is land flooded. A small weir is often used to impound a small reservoir to maintain flow into the intake which directs water along a canal or pipeline. Generally, only a fraction of the available stream flow at a given time is used to generate power and this has little environmental impact.
A reservoir or dam add complexity and cost as well as environmental issues to the project. In low head hydro projects these options rarely can be justified from a cost stand point or from the delays and approvals required to dam a river.
Off-grid / On-grid interconnection
Off grid supply from hydro faces the same issues as all renewable energy sources:
On grid supply must face rigorous utility connection demands:
- Is the supply dependable? Do I have to back it up with storage batteries?
- Will I require a load controller to ensure a constant voltage and frequency?
- What kind of current do I need AC or DC? If AC then an invertor will be required to condition DC current.
- Is the flow intermittent? Will I require some generating source as back up such as a gasoline generator?
- Low head remote generators generally are controlled electronically which add additional expense. Available flow is used to generate all the power possible without mechanical restrictions. This means that electronic controllers will shunt power to different purposes; productive demands (say in the home or hot water), storage (batteries) or a waste heat sink.
- Distribution, metering and control costs required to implement the project whether on private or utility property are costs that have to be borne by the proponent;
- Generally costly connection studies by professionals are required before connecting to the public grid;
- Contracts may be for the power you produce - but beware, there may be penalty charges for non-production. Seek professional assistance on contract issues;
- Controls must prevent islanding of your generator. That is, in the event the grid shuts down, your plant has to be instantaneously disconnected from it. If you wish to remain connected to a small micro grid (say your property) you will have to be prepared to function as a remote off-grid system with the extra costs involved (see above).
Resource assessment - sources/ accuracy:
The output of a hydro system is determined by two main factors: the head and flow of water. These need to be determined concurrently to estimate what your potential power output will be. As a preliminary step you can estimate both head (H) and flow (Q) at a low cost (see text for more details) before calling in professionals. With respect to estimating the design flow don't forget that:
- The flow in a river varies over the year; and that
- only some portion of the available flow will be used by the run-of-river system and that you will be restricted in the amount of water you can use by environmental regulation.
After your initial rough estimate enlisting the assistance of a hydrologist or a hydro engineer to quantify available flow is an important step. You should also make it a priority to determine how much water is available to you from a local provincial or conservation authority. These authorities may have helpful stream flow data from your stream or an adjacent water course. (see text and links for more information on estimating head and flow).
Estimating the energy output of the site and the economic of the project
Knowing the head and the flow, you may estimate the power output and then the energy output (see text for more details). Dividing the annual cost of the system by the energy produced by the site in a year will give an approximation of the unit cost of your hydro energy. This you can compare with the income you expect or the energy cost of alternatives to see if the project makes economic sense and how long it will take to reach payback.
If low head hydro passes this first "sniff test" there are more sophisticated analytic approaches you or a professional will make in subsequent analyses such as with RETScreen (see Additional Resources web links).
Issues and limitations:
- Matching cost effective technology with sufficient head and flow;
- Innovative design and proponent labour can decrease costs;
- Environmental and riparian approvals time consuming and costly;
- Grid interconnection encouraged in only a few provinces;
- Head & Flow.There is a head and a flow rate below which there is likely no economic advantage. These minimum heads and flow rates are difficult to specify because a combination of high values of one with low values of the other can give some useful power. For practical purposes, however, any head less than 1 m (3 ft.) is probably going to be uneconomic to develop. Similarly, 0.60 litres/sec (lps or 10 gal/min) can be considered the lower limit for the flow rate.
25 years +
RETScreen (see Other Resources)
Synchronizing a hydro generator with a fossil fuel generator for a remote application is costly but possible. It would rarely be economically justified for a low head hydro site.
Link to more detailed info (hyperlinks)
See text for links
Sources of supply
See text for links
Comments - Recommendations
Take your time to investigate and plan your system. There are many technical and non-technical questions that need to be addressed before investing too much money in equipment and professionals.
- Get rough estimates of the hydro resource available and the cost of development.
- Ownership of land and stream rights. (including access roads and transmission lines). Will provincial regulations allow me to develop my stream for a hydro application? Do I have access and rights to the water?
- How will my system pay for itself? If it is grid connection, will my local utility pay for the power I produce? How much? What are the steps required to connect? Is it worth it?
- Approvals (what federal, provincial and municipal approvals do I need?)
- Public/Neighbour's acceptance (Are my neighbours going to object during construction or once the system is installed?)
Head is the measurement of vertical drop from the intake to the outlet at the proposed hydro site.
Flow is the volume of water passing the proposed site in a given time.
Low Head Hydro - 5 kW to 250 kW and Head between 1 and 10 metres
Ultra Low Head Hydro - 1 kW to 5 kW and head between 1 and 5 metres
Picohydro: Very small hydro developments up to 5 kW.
Micro Hydro: Definitions vary for the capacity range of a micro hydro system. Although micro hydro is generally accepted as generating less than 100 kW some definitions can include systems up to 2000 kW.