Energy Storage Options

Pumped Hydropower Storage

Review the viability of pumped hydro projects, specifically the Kauai proposal, for energy storage.

A configuration of two water reservoirs at different elevations that can generate power as water moves down from one to the other (discharge), passing through a turbine. Power is also required to pump water back into the upper reservoir.

Pros: pumped storage can provide an efficient way to store energy and quickly generate power during high demand periods. Provides a renewable source of energy.

Cons: unclear if Maui has suitable sites. Can be controversial due to alternative uses of the water and potential environmental concerns. The proposed project in Kaua‘i was canceled following litigation.

Hydrogen Energy

Can it be cost-effective when we have a surplus of solar power during the day for electrolysis?

The storage of energy in the form of elemental hydrogen, which can be used to generate electricity in power plants, power motor vehicles either directly or thru fuel cells, among other applications. Production from renewable energy sources is typically called “green hydrogen”.

Pros: can be produced via electrolysis with solar, wind or geothermal power, and is much less expensive when there is surplus energy generated. The only “emission” is water.

Cons: hydrogen energy is only as clean as its feedstock. Most hydrogen energy produced today is made from steam reforming of natural gas. Production from electrolysis is very expensive. Hydrogen has a round trip efficiency of 65% and if using fuel cells, only 31%. This results in high production costs using electricity from the grid, and in some cases renewable projects.

Battery Storage Options

Battery energy storage systems (BESS) that use various chemicals in groups of batteries for storing electrical energy. These include lead-acid, lithium-ion, lithium iron phosphate, iron oxide, and seawater. Most recent and near-term planned utilization of BESS is largely based on lithium-ion batteries.

Pros:

While trade offs exist for cost, safety, efficiency, and power delivery characteristics, deployment of a large BESS can alleviate some of the concerns of lack of firm power with solar and wind energy production. Long duration batteries could provide “firm” energy. Iron oxide batteries have long duration storage capacity, over 12 hours.

Cons:

BESS typically last no longer than 15 years, and are susceptible to overheating or overcharging; and they require regular maintenance, including monitoring the battery charge levels and ensuring that the system is functioning properly. The most common Li-Ion battery can provide 4 hour peak energy, which is not long duration. Long term management of energy storage, namely recycling or decommissioning, has not been resolved and presents challenges.

Gravity Storage Options

Gravity storage for energy is a way to store and use energy by using the force of gravity. It works by lifting a heavy object, like a large block or a container of water, to a higher position when there is extra energy available, like from wind or solar power. Later, when energy is needed, the object is lowered, and its weight turns a generator to create electricity.

Pros: This method is good because it doesn’t produce pollution, can store energy for a long time, and works well with renewable energy sources. ,

Cons: It requires a lot of space, is expensive to build, and only works in places with the right conditions, like hills or tall buildings.

FLYWHEELS

Mechanical devices that store energy as kinetic energy by rotating a heavy mass rotor, cylinder or wheel at high speeds. When energy is needed, the flywheel slows down, and the kinetic energy is converted by a motor back to electricity). Can be used in homes to store excess energy from rooftop solar panels.

Pros: offer rapid charging and discharging, high life cycle and minimal environmental impact; costs are comparable to battery energy storage.

Cons: can be noisy; can only provide a relatively low energy storage capacity compared to batteries and can be expensive for large-scale applications; potentially hazardous failure modes.