Pumped Hydroelectric Energy Storage (Central Molokai Circuits)

Project #8

Seven notable water tanks and reservoirs were part of a preliminary assessment for pumped hydro site suitability in 2007. The most promising opportunity for significant pumped hydro storage is based at the Kualapu’u reservoir, with possible links to a network of smaller upland reservoirs.

Pumped hydro uses excess renewable energy to pump water up to a higher reservoir, then when energy is needed it lets the water flow back down to create hydroelectric power. This could lessen the need for chemical batteries. In a high renewable scenario, there is likely a need for long-duration, multi-day energy storage currently not available from battery storage technologies. In order to retire the Pālāʻau diesel units, a long-duration resource will be required to operate during low solar events. A pumped storage plant may meet these needs. Pumped hydro requires an upper and a lower reservoir, separated by a significant change in elevation. Kualapuʻu Reservoir in central Molokai is the largest reservoir on island and has the greatest potential to connect with other existing reservoirs where pumped hydro feasibility and capacity could be explored further. Smaller reservoirs on Molokai could also be assessed for pumped hydro potential. The concept of pumped hydro is popular in the community; however, a deep dive analysis is required to assess the best options for Molokai using current technologies. See 2007 Molokai pumped hydro feasibility study in Appendix A for more information.

Project Description

  • Onsite generation decreases the risk of electric disruption for critical infrastructure and takes into account sea level rise/road flooding/etc. that could isolate certain areas for long periods of time.

Pumped hydro uses excess renewable energy to pump water up to a higher reservoir, then when energy is needed it lets the water flow back down to create hydroelectric power. This could lessen the need for chemical batteries. In a high renewable scenario, there is likely a need for long-duration, multi-day energy storage currently not available from battery storage technologies. In order to retire the Pālāʻau diesel units, a long-duration resource will be required to operate during low solar events. A pumped storage plant may meet these needs. Pumped hydro requires an upper and a lower reservoir, separated by a significant change in elevation. Kualapuʻu Reservoir in central Molokai is the largest reservoir on island and has the greatest potential to connect with other existing reservoirs where pumped hydro feasibility and capacity could be explored further. Smaller reservoirs on Molokai could also be assessed for pumped hydro potential. The concept of pumped hydro is popular in the community; however, a deep dive analysis is required to assess the best options for Molokai using current technologies. See 2007 Molokai pumped hydro feasibility study in Appendix A for more information.

Strengths

😊

  • Has a very long life cycle (40+ years) which means it will likely cost less over time than large-scale batteries.
  • No polluting chemicals.
  • Uses agricultural water only; does not involve drinking water.
  • Could potentially be co-located with floating solar on Kualapuu Reservoir

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Weaknesses

  • There are few suitable sites for pumped hydro that would be productive and wouldn’t require major additional development (such as building a new reservoir).
  • Engineering, permitting, and construction of this kind of project will take many years.
  • Upfront capital costs are very high.

Opportunities

😍

  • Projects could provide grid services for the larger Molokai grid and support future smart grid innovations.
  • Can design Molokai regional systems to support mobile emergency generators and additional cold storage units (for food and mass casualties) that strengthen emergency response and disaster preparedness facilities.
  • Smart meters provide detailed insight on how RE is performing and how much energy is being used/generated to help energy operators protect the grid and homes.
  • Hui Up style programs could be a solution for supporting privately-owned critical infrastructure in equipping their facilities with RE systems.
  • There are few suitable sites for pumped hydro that would be productive and wouldn’t require major additional development (such as building a new reservoir).
  • Engineering, permitting, and construction of this kind of project will take many years.
  • Upfront capital costs are very high.

😱

Threats

  • “Hosting capacity” for rooftop PV is very limited. Therefore, new onsite RE would likely need to be paired with batteries and energy exporting options may or may not be available.
  • Siting requires two water reservoirs (an upper and a lower reservoir).

Community Position

The Molokai community is in FULL SUPPORT of and committed to co-designing a site specific community-scale solar project for Maunaloa/West Molokai that provides the level
of energy quality, stability, resilience, and economic relief the Maunaloa community needs.

Project Specific Requirements

  • Community-based site specific project design that provides a detailed cost analysis and understanding of trade-offs between potential project sites and critical infrastructure location, tech options, community needs, potential grid services and configurations (e.g. islandable or hybrid microgrid), responsible end of life plans, environmental and cultural impacts and the other energy system requirements described earlier.
  • Maunaloa/West Molokai’s RE project must account for current community needs, future growth, grid hardening, and the potential diversification of energy generation for West Molokai.
  • The Molokai community, and especially those who live in Maunaloa/West Molokai, will have the final say on how RE projects like this can support them individually and as a community.
  • Disallow HECO self-build from competing in potential project RPF; thereby promoting competitive bidding.

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