Pumped Hydro Energy Storage with Enhanced Weathering Carbon Removal

Ideal projects in sustainability are large enough to notably reduce emissions while also providing supplemental climate benefits. Such “green investments” remain underfunded due to high initial costs and uncertain monetary returns. Here, I will present a green infrastructure project that reduces emissions, removes atmospheric carbon, and provides reliable short- and long-term revenue streams.

The titular concepts address two underexplored yet crucial sustainability goals: grid-scale energy storage (pumped hydro) and carbon dioxide removal (enhanced weathering). The resulting projects would justify large investments by presenting multiple revenue streams, mitigating emissions, and actively removing carbon dioxide from the atmosphere.

Let’s first consider pumped-storage hydropower (or “pumped hydro") [1], which stores the extra electricity on a sunny day to supply clean energy when the wind stops blowing. Pumped hydro storage relies on electrically pumping water to a higher elevation, converting electricity to potential energy. Upon releasing the elevated water, gravity-driven flows spin turbines and regenerate clean power.

Pumped hydro is highly efficient (70-85% energy retention), can provide grid-scale electricity, and has a long infrastructure lifetime (30-60 years) [2]. These attributes make it an attractive alternative to batteries when considering large-scale energy storage applications. They also make it long-term profitable through the sale of electricity. Bolstered by the nation's largest pumped hydro facility, Virginia's annual hydroelectric generation revenue exceeds $400M [3].

There are many benefits to incorporating pumped hydro into our power grid. It would help us move to 100% renewable energy by addressing the generation intermittency of solar panels and wind turbines, while making renewable generation more profitable by providing cheap storage when energy demands are exceeded. Pumped hydro can even make fossil fuel use more efficient through "peak shaving," a practice that reduces operation of the dirtiest power plants

The drawbacks to pumped hydro are installation costs and water use. Pumped hydro facilities require digging large basins and water pathways, installing supporting equipment, and accumulating water. The novelty of this proposal is to mitigate these drawbacks by siting pumped hydro projects in areas where land extraction yields a valuable commodity and carbon dioxide removal is achieved during installation and operation.

Carbon dioxide removal prompts our return to enhanced weathering. “Weathering” is the natural breakdown of rocks [4]. When certain rocks weather, they absorb atmospheric carbon and convert it into solid decomposition byproducts. “Enhanced weathering” accelerates these natural processes [5], typically by dispersing sediments over land or into waterways.

Limestone and olivine are two widely abundant rocks that are commercially valuable and exhibit the desired weathering chemistries [6]. In both cases, extraction would yield a short-term revenue stream via sale of the commodity. A greener choice would be to spread these rocks over soil, a technique that was shown to absorb carbon dioxide and improve crop yields [7, 8]. Such a strategy achieves carbon dioxide removal without the large land-use requirements associated with similar carbon removal approaches [9].

These pumped hydro projects would generate revenue and actively remove atmospheric carbon for their lifetimes. During operation, water flows would erode the same basins to continue the enhanced weathering. If nearby waterways are accessible and ecological systems remain unharmed, “open-loop” projects could send the sediment-rich water into oceans and help reduce ocean acidification. Alternatively, “closed-loop” projects could separate out the sediments for continued dispersal. Finally, any future implementation of carbon fees or credits would enhance the profitability of these projects by explicitly compensating owners for their clean power and carbon removal.