History of Hydropower
Energy exists within any flowing water course, natural or man-made, and this energy can be extracted using hydropower technology. This concept of transferring this energy or 'power, from flowing water has been a longstanding tradition dating back to the earliest water wheels (used for milling, mining, water supply and irrigation) over 2,000 years, to the Roman, Greek and Han dynasties. With significant technological advancements in the 20th century, the evolution of hydropower escalated as a source of electricity led to a new scale of utilisation for this valuable energy resource. Today, hydropower remains one of the most efficient forms of energy production, with in excess of 90% efficiency typical of most well designed turbine installations.
Fig 1. Example of Traditional Water Wheel
Energy in Water
The energy extracted from hydropower facilities is derived from the potential energy, which is transformed into kinetic energy and is a function of two parameters; head and flow. The head is the energy per unit weight (or unit mass) of water. This static head is proportional to the difference in height through which the water falls. The volumetric flow of the water is also proportional to the amount of energy that can be extracted from a water source.
There are two main types of turbines; Reaction and Impulse turbines. The selection of a turbine to match head and flow conditions is an important factor when installing a turbine at a hydropower site. The following sections give a summary of the two main turbine types;
Reaction turbines are the most common type of turbines. They generate power from exploiting oncoming flows, as the turbine propeller blades absorb the energy from the moving water. The main types of reaction turbines include; the Francis turbine, the Propeller/Kaplan turbine, the Tyson, Gorlov and China turbines. Also, the development of reverse pumps or pump as turbines (PaT's) are used as reaction turbines. Low flow and high head conditions are the most suitable for reaction turbines and the typical turbine is used for enclosed water flows.
Fig 2. Selection of Reaction Turbines
Impulse turbines are typically more suitable for micro-hydropower installations e.g. run-off-river applications. This type of turbine has several benefits in comparison to the reaction turbine; it tolerates particles in flow, better access to parts, easier to fabricate and a better part-flow efficiency. The disadvantage of the impulse turbine is its unsuitability for low head sites. The Pelton, Turgo, Crossflow and Archimedes are the most well known types of impulse turbines and work under the principle of a jet of water acting upon buckets or runners on a wheel, which is rotated due to the force of the moving water.
Fig 3. A range of Impulse Turbines
Calculating the Power Potential
The potential power available at a hydroelectric facility can be estimated based on the hydraulic head and flow rate in the water course. The power available from falling water can be calculated from the flow rate and density of water, the height of fall, and the local acceleration due to gravity. In SI units, the power is:
P = ηρQgh
- P - power (kW)
- η - turbine efficiency
- ρ - density of water (kg/m^3)
- Q - flow (m^3/s)
- g- acceleration due to gravity (m/s^2)
- h - head of water (m)
e.g. Power is calculated for a turbine that is 85% efficient, e.g. water density of 1000 kg/m^3; a flow rate of 80 m^3/s; gravity of 9.81 m/s^2; and a net head of 70 m. In SI units: Power (MW) = (0.85 x 1000 x 80 x 9.81 x 70)/10^6 => which gives 46.7 MW
As previously stated, the selection of a suitable turbine is based on flow and head characteristics for a water course. The following plot is used as a guideline to decide on the most suitable turbine type for a specific site.
The classification of hydropower plants according to the power output is a matter of size, as shown in this table.
Pressure Reducing Valve (PRV)
Reduces pressure to a pre-set level downstream of the valve with the goal to keep pressure levels within a determined range throughout the network. Dŵr-Uisce project points PRV locations in water networks as potential sites for energy recovery.
Smart Network Controls
Sensing, actuation, and control functions are considered in order to describe and analyse a situation, and make decisions based on the available data in a predictive or adaptive manner, thereby performing smart actions. The deployment of smart network controls in Dŵr-Uisce aims at identifying energy recovery locations and optimise energy performance through the installation of turbines with a dual pressure reducing and energy production function.
Hydropower energy recovery in water supply networks is one of the targets of DŵDr-Uisce project. In this context a key element is the demonstration of the micro-hydropower potential in real networks. For this purpose, the feasibility of implementing this technology is assessed in water supply schemes.
Pump as Turbines (PAT)
Pumps as Turbines (PATs) are an unconventional solution for hydro power generation adapt to fit in many scenarios when a conventional turbine unit would not be suitable. Physical behaviour of PATs is similar to that of Francis turbines, but without possibility for flow regulation. Within last decades large numbers of PATs have been studied and implemented as power generators in many contexts like small hydropower schemes with low-head properties, water supply systems (WSS) and industrial applications as replacements of throttling valves. In particular, they proved to be very effective if used for micro hydro off-grid plants and in-pipe energy recovery.
Drain Water Heat Recovery (DWHR)
Currently, hot water from showers, dish washers, washing machines and other hot water consuming appliances is most often flushed through the drain, leaving a significant part of the energy unused. In modern building it is the most important source of energy loss. Drain Water Heat Recovery (DWHR) is the collective name of technologies attempting to utilize this untapped potential. These technologies help in both reducing the fuel and energy consumption related to heating, and allow for the application of wastewater source heat pumps, considered a renewable source of heat.
The Dŵr Uisce project aims at quantifying the potential impact of DWHR technologies in Ireland and Wales with respect to the environmental impact of heating and with respect to heating costs. A prototype of a DWHR system is a project deliverable as well.
Life Cylce Assessment (LCA)
LCA is a method of quantifying the environmental burdens for a product or service, such as a HP installation, through its life cycle. It provides a simple platform to evaluate any product or systems based on its associated environmental burdens. A detailed database of raw materials and energy processes is required to accurately report the environmental burdens for these projects. The outputs from LCA require the definition of system boundaries, i.e. the start and end points in which the LCA considers. The results can be used to compare different products, in the case of this project comparing energy recovery technologies and efficiency measures.
In 2009, the EU directive (2009/125/EC) was implemented for the eco-design of energy-related products, which aimed to promote the environmental performance of the product throughout its whole life cycle. Considering that the manufacture of a product requires energy and raw materials, both valuable resources that need to be managed effectively.
The technology platforms in the Dŵr Uisce project are adopting eco-design in their development to deliver low-carbon and resource-efficient systems in line with the circular economy agenda. Our previous work has examined the potential for eco-design post construction of several micro-hydropower projects, and from this, an eco-design approach was made in the delivery of project demonstration sites.