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The surge of Renewable Energy (RE) and particularly Solar PV in the journey to replace fossil fuels, is producing excess energy that is way more than the demand on sunny days. The visible network demand too is getting reduced by behind the meter installed residential PV. This is leading to energy prices approaching close to zero and even negative in sunny parts of the day.The lack of demand is leading to widespread curtailment of RE. This near free energy is creating opportunities for lower round trip efficiency storage options. Pumped hydro energy storage(PHES) operates between two reservoirs by pumping from lower to the higher reservoir when energy is cheap, to store gravitational energy and allows water to flow down from higher to lower through a turbine to dispatch the stored energy during peak demand. Freshwater PHES traditionally offered 80 to 90% efficiency, though seawater PHES can be as low as 72% if the sea is 3 to 4 km away from the dam. Market share of PHES is still around 95% of energy storage in 2019. However there are not enough sites available to scale PHES by 10 times to meet the projected demand to 2040. Building new dams or boring long tunnels is expensive and the low cost sites are already developed and water is scarce globally especially inland. All of which makes it very difficult to use conventional PHES to meet the urgent new large (over 1000GW) global energy storage requirements necessary to firm Renewable Energy sources.
This paper examines the existing river channel downstream of existing dams, as the potential free lower reservoir. Water from the dam is allowed to dispatch energy by installing hydro turbines or using existing hydro turbines. The water flows down stream at rates around 0.5 to 1m/s causing it to take several hours to flow down 10km to 30km. A suitable point is found where the river meanders back towards the dam and the straight-line distance is shorter. Water is pumped back from such downstream location(s) back into the dam using close to zero or negative cost( a revenue opportunity) RE. The low cost of the energy used for pumping up say between -1000 and 10$/MWH makes it viable to operate such river channel based pumped hydro even if the round trip percentage efficiency is only in the high 50s. We modelled the Burrinjuck Dam and the Murrumbidgee river down stream of the dam, to find a 1210MWH daily storage opportunity offering a round trip efficiency of 58% using only 7GL (7%) of the 1026GL capacity of the dam. This means the PHES operation can continue even, if in the dry years the dam is only 30% full(300GL). We believe such a river channel based PHES is possible in most existing dams all over the world unlocking a new massive potential for PHES, to ease the transition to renewables at an affordable cost. This could be the missing piece of the puzzle.