What is Run-of-River?
Run-of-River hydroelectric (ROR hydro) projects generate electricity by channelling natural stream flows and utilizing natural elevation differences in mountainous regions like British Columbia.
A portion of the mountain stream is diverted by an intake structure into a buried pipe (called “penstock”) where it is channeled downstream into turbines. The flowing water causes the turbines to spin. A generator is directly attached to the turbines and creates electricity. The water from the turbines is released unaffected back into the stream.
Run-of-River is a readily available source of renewable electricity in carefully selected watersheds.
It plays a prominent role in sustainably meeting British Columbia’s growing energy needs and reaching greenhouse gas emissions reduction targets. ROR hydro projects directly distribute economic benefits to a larger number of communities and municipalities compared to Large Hydro projects. ROR projects are also situated closer to points of electricity demand thus reducing transmission losses. The scattered distribution of ROR Hydro projects lowers the overall power system risk versus large electricity sources in a single location.
Run-of-River vs Conventional Storage Hydro
In conventional storage hydro, a dam is placed across a river to create a reservoir with most of the water impounded behind the dam and the flow downstream regulated, which changes the natural variation of flow for the entire downstream river.
Run-of-River hydro projects have a much smaller environmental footprint compared to traditional reservoir storage hydro because they typically have very little water storage capacity thus less land is flooded, reducing potential footprint. With ROR hydro, only a portion of the stream flow is affected, and only a short length of the river experiences reduced flows. The volume of water a ROR project may divert through penstocks to run turbines depends significantly on stream morphology and environmental characteristics, but a typical plant utilizes less than two-thirds of a river’s annual flow. Immediately below ROR Hydro powerhouses, all flows diverted to produce power are returned to the stream and the natural downstream flow patterns are preserved.
Without storage, however, ROR hydro supplies electricity only as natural flow allows. Flow conditions conducive to ROR power generation do not always correspond to times when electricity demand is high. Accordingly, both technologies have advantages and disadvantages and should be viewed as complementary resources.