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Hydro Resource Evaluation Tool
engineering options
Grid Connection
Small scale hydro plants can be connected to the national electricity grid or can be stand-alone systems.
If a hydro plant is connected to the national grid, a power producer can sell an excess of the electricity production to electricity companies. In the case of off-grid generation, the electricity is consumed directly by a user or can be stored in the batteries.
Privately-owned distributed generation including hydro electricity generation is a fast growing sector. Small scale hydro resources are often found in the less populated areas with lower load demand. Due to the capacities of small scale hydro plants it means that they will be connected to medium or low voltage networks.
Historically, electricity networks were designed to transfer electrical power from the high voltage transmission grid to customers distributed on lower voltage systems. The design is based on the assumption that power is transported in one direction and that load patterns are fairly predictable with well known daily and seasonal variations. These networks were operated passively to ensure that consumers were supplied with the quality of electricity within statutory limits.
However, in case where distribution generation is comparable to or higher than the local demand it is likely that it will affect the network power flows and the voltage could go beyond the statutory limits [Harrison et al]. The distributed generation is geographically disperse and delivers intermittent supplies of energy to the distribution network. The connection of distributed generation can result in power flows going in both directions. The presence of distributed small scale hydro generation can affect the operation of the distribution network in a number of ways [Harrison et al], including:
- Bi-directional power flow and the potential to exceed equipment thermal ratings;
- Reduced voltage regulation and violation of statutory limits on supply quality;
- Increased short circuit contribution and fault levels;
- Altered transient stability;
- Degraded protection operation and coordination.
To connect to the distribution network, the developer should submit an application form to a local Distributed Network Operator (DNO). DNOs will then assess the impacts an individual distributed generation scheme can have on the distribution network.
More information on how to connect to the distribution network is available on the National Grid website at
http://www.nationalgrid.com/uk/Electricity/GettingConnected/dnoConnected/
The website provides a Distribution Network Operator map which shows the relevant Distribution Network Operator for the area where a connection can be made. (http://www.nationalgrid.com/uk/Electricity/AboutElectricity/DistributionCompanies/DistributionCompanies.htm)
A FAQ section of the website provides the developer with useful information. This section can be accessed at http://www.nationalgrid.com/uk/Electricity/GettingConnected/faq/
The Technical Guide to the connection of generation to the distribution network (2003) is available from the BERR (now DECC) website at http://www.berr.gov.uk/files/file15194.pdf
The Grid Connection website (https://www.gridconnection.co.uk) offers a cost effective service for assessing the connection of a range of renewable energy generations sources to the electricity grid.
Due to the high costs of grid connection, the hydro plant should be located close to the existing grid infrastucture.
References
- G.P. Harrison, A.E. Kiprakis and A.R. Wallace, A New Era for ‘Mini-hydro’, International Water Power and Dam Construction, 2002, v54 (11), pp 20-24.
