Proving the avoided CO2 impact of pumped-hydro energy storage solution of Zero Terrain



Energiasalv is the developer of Zero Terrain, Estonia’s first geotechnical pumped-hydro energy storage (PHES) solution that captures energy from renewables during low-cost periods and releases it when wind and solar power are unavailable. They tasked us to conduct an attributional and consequential Life Cycle Assessment (LCA) for their 500 MW PHES facility. The aim was to calculate its carbon footprint and evaluate the project’s benefits and positive environmental impact.

The essence of the project:

The project was challenging due to its innovative approach to the PHES facility. Unlike conventional systems that rely on geographical features like mountains and rivers, Zero Terrain allows building a PHES facility in flat regions. The lower reservoir is 700 meters underground and operates by storing excess renewable energy when available and then pumping water to the upper reservoir to generate power when renewable sources are not producing it. 

We closely partnered with the client to define system boundaries, assess material inputs and flows, and address any uncertainties. Understanding how this innovative technology operates helped us prepare for the LCA.


Our goal was to conduct the LCA of PHES, measuring how much CO2 emissions it caused and avoided. First, we completed the attributional LCA and measured the direct environmental impact originating from the project. Second, we did the consequential LCA forecasts on how ecological impact changes with altered practices, such as avoiding emissions by substituting natural gas-based electricity production and utilising mined limestone in road construction. 

The study covered the entire life cycle of the PHES, including construction, excavation, raw material transportation, waste management, operation, maintenance, and eventual closure after 90 years of operation.



Services provided:

  • Assessing material inputs and flows
  • Addressing any uncertainties
  • Calculating the project’s probable CO2 emissions
  • Forecasting environmental impact changes with altered practices 


Energiasalv’s PHES showed a shallow carbon footprint at 0.035 tonnes CO2e/MWh because of the LCA, surpassing many renewable energy options. 

The project benefits the world by avoiding the production of 0.45 tonnes of CO2e/MWh electricity during the first 20 years due to the replacement of fossil electricity. The emissions avoided by PHES electricity production are about eight times greater than the emissions it causes. Energiasalv’s PHES should balance out its mining, construction, equipment, and end-of-life emissions within just one year of operation.