11.7.1 Types of Scheme

opendate_range22 Dec, 2020, 9:00am - 12 Mar, 2021, 5:00pm
11.7.1 Types of scheme

The flow rate in the river is the volume of water passing per second.  The gross head is the maximum available vertical fall in the water from the upstream level to the downstream level.  Two hydro projects with the same power output could be very different; one using a relatively low volume of high-speed water from a mountain reservoir and the other using a high volume of water in a slow flowing river.  As such, hydro schemes are classified as low, medium or high head schemes.


​​​​​​​ Low head schemes

Low head systems typically have a gross head of less than 10m.  Reclaiming Lost Power identified the potential of low head hydro resources ​​​​​​​existing in disused mill sites, weirs and untapped areas around the county. These low head sites (< 10 m) have the potential to create employment, revenue and further enhance the green economy for County Kilkenny.

Low head systems are generally located in lowland areas, abstracting water from rivers through the use of weirs with diversion of a proportion of river flow to a leat (millrace) and from there to a turbine house. Water is returned to the river downstream of the turbine through a tailrace. Low head schemes are very dependent on flow, and may shut down during periods of low rainfall. 


​​​​​​​ Medium-high head schemes

While there is no explicit definition, medium head systems typically have a gross head of between 10 – 50m, and high head schemes typically have a gross head of >50m. Medium and high head schemes typically, but not always, are larger in terms of installed generation capacity. In any case, there is little scope for development of these types of schemes in County Kilkenny.  Only one site, on the River Blackwater is a high head scheme and the Greenville Mill hydroelectric scheme is already in place there.