RENEWABLE ENERGY RESOURCES

The percentage of renewable energy generated in Hawai‘i has doubled since 2014.

BATTERY ENERGY STORAGE SYSTEMS (BESS)

Often included or integrated with renewable energy systems, battery energy storage systems store excess energy for use later. Batteries that store excess renewable energy and discharge when that energy is not available extends the usefulness and improves the predictable availability of renewable sources. Batteries come in various sizes ranging from home-use to utility-scale and can be made from a variety of rechargeable mineral elements. Currently, the most commonly known system is lithium-ion, but the industry is going through a significant transformative phase as scientists are innovating solutions to increase battery performance and diversify production options to lessen reliance on specific minerals.

BIOENERGY

Bioenergy comes from organic materials (anything that used to be alive or parts of a living thing, such as leaves, branches, wood chips, paper, algae, or manure). Biomass can be used to produce electricity, can be converted into liquid fuels (called “biofuels”), or can be burned to produce heat for cooking or other uses (such as wood in a barbecue grill).

Click below to view a map of bioenergy projects in Hawai‘i. Disclaimer applies.

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Biomass

Biomass is plant and animal matter and includes energy crops, wood, grasses, algae, vegetable oils, and agricultural and municipal wastes.

Biofuels

Biofuels are liquid fuels made from biomass. As defined in Section 486J-1 of the Hawai‘i Revised Statutes, “Biofuels means liquid or gaseous fuels produced from organic sources such as biomass crops, agricultural residues, and oil crops such as palm oil, canola oil, soybean oil, waste cooking oil, grease, and food wastes, animal residues and wastes, and sewage and landfill wastes.” They include:

  • Ethanol
  • Biodiesel
  • Bio-based diesel fuel (also known as green diesel)
  • Bio-based gasoline (also known as green gasoline)
  • Bio-based jet fuel (including sustainable aviation fuel)
  • Bio-based pyrolysis oils
  • Hydrogen (from biomass sources)

Photo courtesy of Pacific Biodiesel (www.biodiesel.com). The founders of Pacific Biodiesel, Bob and Kelly King, are farming sunflowers and other crops at their farm on Maui, showcasing a community-based model of sustainable agriculture, renewable fuel and food that is helping Hawaii achieve a clean energy future.

GEOTHERMAL

Geothermal energy comes from heat inside the Earth. Geothermal energy can be harnessed to produce electricity and can also be used for heating and cooling purposes. It is particularly prevalent in Hawai‘i’s young islands, most notably on the volcanically active Hawai‘i Island. However, the resource is not limited to areas with volcanic activity. Geothermal energy can be generated anywhere there is adequate subsurface heat with underlying geology that allows for “optimum geothermal play” or a geological setting that includes a heat source, a migration pathway, a heat reservoir, and potential for economic recovery. Geothermal sources may be accessed through wells that tap into steam, hot water, or geothermal fluid that when brought to the surface can be used to turn turbines, which in turn drive generators to create electricity.

The Kilauea East Rift Zone, thus far the only region developed for geothermal energy in Hawai‘i, has all the attributes necessary for energy generation. Hawai‘i’s only currently operating geothermal facility, the 38-megawatt Puna Geothermal Venture (PGV) power plant, is located in this region. Geothermal is a low carbon energy resource as it does not produce any greenhouse gas emissions and, as a steam-based resource, generally provides the same amount of output at all times of the day. In 2021, geothermal energy from PGV provided Hawai‘i Island with 17.6% of its electricity needs. Prior to the Kīlauea eruption in 2018, geothermal energy from PGV provided an estimated 31% of the island’s energy.
Other areas in Hawai‘i have been studied and show suitable attributes for geothermal energy generation. In general, the probability of accessible geothermal heat decreases as you move up the island chain to the older islands; however, certain areas on these islands, including Oʻahu, where energy demand is high, exhibit geothermal resource probabilities that may make it plausible for electricity generation. Probabilities are believed to be higher in areas of rejuvenated volcanism, such as areas on the south flank of the Koʻolau mountain range (Ito, et al., 2017).

Click below to view a map of geothermal projects in Hawaii. Disclaimer applies.

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Geothermal energy Resource Studies

Used with permission. Image sources: Lautze, N., Thomas, D., Waller, D., Frazer, N., Hinz, N., & Apuzen-Ito, G. (2017). Play fairway analysis of geothermal resources across the state of Hawai‘i: 3. Use of development viability criterion to prioritize future exploration targets. Geothermics, 70, 406-413. Final probability map anticipated for publication in 2022. Probabilities of a geothermal resource are colored. Areas with restricted land access are shown in striped and crosshatch patterns (e.g., National Park lands, protective conservation districts, and urban areas). Red boxes outline areas proposed for Phase 2 study. White triangles indicate the calderas of the main shield volcanoes. White stars mark the locations of the Saddle Road well and Puna Geothermal Venture (PGV).

HYDROELECTRIC (HYDROPOWER)

Flowing water — in Hawai‘i’s streams, rivers, reservoirs, pipes, and irrigation ditches — can be used to generate electricity. Hydroelectric facilities were among the first power plants in the islands, dating back to the late 1800s. Some of Hawai‘i’s existing hydroelectric plants date back to the early 1900s and have been maintained and upgraded to continue producing power. Currently, only the islands of Kauaʻi, Hawai‘i, and Maui have operating hydroelectric plants. Collectively, hydroelectric projects provided 1.2% of all electricity sold by Hawai‘i’s electric utilities to their customers in 2021.

Hawai‘i has “run-of-the-river” hydro plants, which means free-flowing water is used to spin a turbine and generate electricity. For these projects, a regulated volume of water is diverted from its natural waterway into the pumphouse and then rerouted back to its original waterway. The amount of energy generated by a run-of-the-river hydro plant depends on the volume of water in a waterway and the speed at which is flows. Electrical output from Hawai‘i’s hydro plants is heavily impacted by annual rainfall due to reliance on surface waters.

Another hydroelectric resource being explored in Hawai‘i is “pumped storage.” When extra electricity is available, pumped storage hydroelectric facilities pump water from a lower reservoir to an upper reservoir, where the water is stored (similar in concept to charging a battery). When power is needed, the water is released back down through a turbine to the lower reservoir. Pumped storage is more of a “closed loop” system — meaning it does not rely on external inputs of water to normally operate — which reduces reliance on rainfall. The exception is that water loss due to evaporation and natural seepage can occur, in which case the reservoir can be replenished with water from nearby waterways and rainfall. Unlike run-of-the-river plants, pumped storage hydro projects allow operators to control when a hydroelectric facility discharges electricity. In many cases, including the West Kauaʻi Energy Project now being pursued on Kauaʻi, solar energy is used to pump the water “upstream” from the lower reservoir to the upper reservoir, making these facilities 100% renewable. 

Click below to view a map of hydroelectric projects in Hawaii. Disclaimer applies.

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Courtesy Kauai Island Electric Utility

Hawaii Ocean

HYDROGEN

Hydrogen has several uses and applications. It is used as a transportation fuel. It can also be produced from renewable sources, stored, and then used in vehicles or to produce electricity. The production of hydrogen can be timed to make use of excess renewable energy that would otherwise be wasted (curtailed); likewise, the use of hydrogen to produce electricity can be timed to meet peak electricity demands. Like other energy storage systems, in theory hydrogen can be dispatchable: supporting the grid by absorbing excess electricity supply, and providing electricity to meet demand when needed. Finally, it can be blended and distributed through pipelines for use in homes and businesses as a component of utility gas.

OCEAN

The ocean holds a great deal of the Earth’s energy — the Sun heats the surface, wind creates waves, and tidal forces exerted by the Sun and the Moon create tidal fluxes. Hawai‘i has significant wave and ocean thermal resources but minimal potential for tidal energy due to its relatively mild tidal changes. Most potential technologies that would harness ocean energy resources are in early pilot stages and have not yet been commercialized.

Thermal Energy (heat)

Two major ocean thermal technologies are of interest in Hawai‘i: seawater air conditioning (SWAC) and ocean thermal energy conversion (OTEC). Both rely on the fact that the deep ocean is significantly colder than the tropical surface. Thanks to the volcanic nature of Hawai‘i’s islands rising from the seafloor, this deep cold water is close to shore in many locations.

The Hawai‘i Ocean Science & Technology Park at the Natural Energy Laboratory of Hawai‘i Authority (NELHA) on the Kona coast of Hawai‘i Island hosts Hawai‘i’s only active OTEC project — a pilot project developed by Makai Ocean Engineering called the Ocean Energy Research Center. NELHA also uses sea water air conditioning for its visitor center and other buildings on site.

SWAC projects have also been proposed off Honolulu; however, none have yet come to fruition.

Marine Hydrokinetic Energy (motion – wave or tidal)

Marine hydrokinetic (MHK) technologies tap the kinetic energy of the ocean — the energy carried by moving water. Most typically, the ocean’s motion is converted to useable electricity by a device that either spins as the water flows past it or bobs up and down in the water. This means MHK facilities can generate more electricity from the oscillating (short period) rough seas created by trade winds than the slow and spread out (long period) swells that generate the famously large waves in Hawai‘i. Therefore, Hawai‘i’s relatively consistent trade winds are attractive for MHK developers. 

Hawai‘i hosts one of the world’s most unique MHK test facilities: Wave Energy Test Site (WETS) off the Kāneʻohe Marine Corps Base Hawai‘i (KMCBH) on Oʻahu. The WETS is a grid-connected hub on the bottom of the seafloor a few miles of KMCBH that enables MHK or wave buoys of various designs and manufacturers to connect to a grid-connected undersea hub. In partnership with the Hawai‘i National Marine Renewable Energy Center connected to the Hawai‘i Natural Energy Institute and the University of Hawai‘i, wave buoy manufacturers can test the performance of their wave buoy designs. KMCBH is located on the east coast of Oʻahu, which gets the brunt of the trade winds. 

SOLAR

Solar energy is energy in the form of light and heat from the Sun. Solar energy is harnessed for use and electricity generation primarily with two categories of solar energy system technologies: solar thermal and solar photovoltaics. Solar photovoltaics are most common for electricity production, while solar thermal systems offer significant energy savings through solar water heaters.

Click below to view a map of solar energy projects in Hawaii. Disclaimer applies.

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Photovoltaics

Photovoltaic (PV) systems do not have the moving parts (such as turbines) or steam production found in most other electricity generation systems. Instead, the sunlight shines on the solar cell and causes a voltage differential (photo voltaic) which generates direct electric current to be generated. Thousands of photovoltaic systems are in use in Hawai‘i. Some generate power for use on-site (such as on residential, commercial, and other buildings) in systems that are known as distributed energy resources, while other (larger) systems generate power that is provided directly to electric utilities to power the grid.

Solar Thermal 

Solar Thermal
NELHA CSP Pilot Plant, Used with permission, Photo courtesy of NELHA

Solar thermal systems (including solar water heaters) use the Sun’s energy to heat water for residential use (up to 160°F); industrial use, including air conditioning, plastic forming, and desalination (170°-750°F); or electricity generation (750°-2,000°F).
Tens of thousands of solar water heaters are used in residences throughout Hawai‘i, reducing utility costs for users by eliminating the need for traditional grid-powered water heaters.
Facilities that use solar thermal energy to generate electricity most commonly do so by concentrating solar thermal energy into a small area to heat working fluids (commonly water) to generate steam and drive a heat engine turbine to produce power; this is called concentrated solar power (CSP). The technology is not currently in use in Hawai‘i.

Photo courtesy of Hawai‘i Gas, Waihonu Solar Farm

WIND

Onshore Wind

Onshore Wind, or wind that is sited on land, has been developed on Oʻahu, Maui, and Hawai‘i Island. In total, nine utility-scale wind projects accounted for 8.1% of the total energy sales in the state in 2021. Onshore wind has not been a desirable technology in areas where there are large populations of endangered bird species. For example, on Kauaʻi, where there are large populations of seabirds, onshore wind has not been developed.

Click below to view a map of wind projects in Hawaii. Disclaimer applies.

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Wind turbines used for electrical generation primarily come in two design variants (horizontal axis and vertical axis) and three size classifications (utility, community, and distributed).

Most of the wind capacity installed in Hawai‘i is utility-scale horizontal axis turbines.

Offshore wind, or wind energy that is sited in the ocean, has not yet been developed in Hawai‘i and there is currently no timeline or specific plan to develop offshore wind in Hawai‘i’s waters. The discussion on the development of offshore wind has focused on projects connected to Oʻahu, as Oʻahu has the highest population, greatest electric use, and limited land space for the development of renewable energy. With the advancement of floating turbines, offshore wind has become more feasible for use in Hawaiʻi. Due to the volcanic formation of the islands, the ocean depth drops steeply off the coastline, making fixed-structure turbines (or structures that are mounted on the seafloor) infeasible. If developed, offshore wind facilities would be a floating turbine design with transmission by undersea cables

Offshore Wind

In 2021, the National Renewable Energy Laboratory (NREL) published the study titled The Cost and Feasibility of Floating Offshore Wind Energy in the Oahu Region. HSEO collaborated with Bureau of Ocean Energy Management and local stakeholders to develop the scope of the cost and feasibility study, which served to provide estimates of the cost of energy in regions of interest around Oʻahu while considering the technologies, ports, and grid connections that may impact the cost. Click here for a Fact Sheet on this study.

Photo courtesy of Hawaiian Electric, Wind Farm on Maui

RENEWABLE NATURAL GAS (RNG)

Renewable Natural Gas (RNG) also know as biogas, is a form of gaseous energy created from the decomposition of organic matter, such as wastewater biosolids, food wastes or animal manure under anaerobic conditions, or conditions without oxygen. Gas produced in this manner for production and use is pipeline quality and interchangeable with conventional natural gas, including synthetic natural gas (SNG) and liquefied natural gas (LNG), both currently used in Hawaiʻi.

There is currently one RNG plant located on O‘ahu, which utilizes the methane from the Honouliuli Wastewater Treatment Plant. The facility produces enough gas for more than 6,000 homes.

More information on the Honouliuli Natural Gas Plant operated by Hawai‘i Gas is available at: https://www.hawaiigas.com/clean-energy/decarbonization

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