Hawaii Solar Integration Study Reveals Grid Impacts of High Penetration Renewables

(U.S. Department of Energy)  Hawaii has the most aggressive clean energy goals in the United States—and while the state has already deployed significant amounts of wind and solar power, the utilities on its islands need to know how their grids will operate with increasing amounts of renewable energy.

To shed light on the subject, the U.S. Department of Energy (DOE) and its partners have collaborated with local Hawaiian companies to complete the Hawaii Solar Integration Study—a first-of-its-kind detailed technical examination of the effects of high penetrations of solar and wind energy on the electrical grids on the Hawaiian islands of Maui and Oahu.

The National Renewable Energy Laboratory’s (NREL)’s recently released Hawaii Solar Integration Study Executive Summary highlights the key findings of the multiyear effort, which was jointly sponsored by the Hawaii Natural Energy Institute, DOE, Hawaiian Electric Company, Inc., and Maui Electric Company, LLC, under the auspices of the Hawaii Clean Energy Initiative (HCEI). General Electric conducted computer modeling and analysis of the Maui and Oahu transmission-level grid components. DOE’s National Renewable Energy Laboratory (NREL) formed a technical review committee to help guide the effort and leverage grid integration expertise from U.S. and international organizations.

The study included detailed computer modeling and simulations of the generation and transmission systems on each island to examine how future scenarios of high penetrations of solar and wind power will affect generator operations under normal system configurations. The distribution-level impacts were not assessed in the study.

The results provide a deeper understanding of the differences between distributed solar photovoltaic (PV) systems, centralized PV power plants, and wind power in terms of variability, ability to curtail power output, grid support functions, and characteristics relative to the load. The study found that adding large amounts of new solar power to the electric grids on Maui and Oahu—enough to achieve roughly 20% renewable energy penetration—will create operational challenges that could affect grid reliability, but those challenges are manageable for the scenarios studied with the recommended mitigation approaches and assumed system upgrades. However, the costs associated with the recommended mitigation approaches must be assessed relative to the identified benefits.

Ultimately, the insights from the Hawaii Solar Integration Study form a large body of knowledge for future grid integration studies, and the results can be used to further our understanding of grid integration in other island systems as well as in mainland U.S. systems with high regional solar and wind penetrations.

Hawaii Solar Integration Study Executive Summary

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Fewer Rain Forests Mean Less Energy for Developing Nations, Study Finds

That is the conclusion of a group of experts whose findings, released Monday, run counter to the conventional understanding of deforestation’s impact on watersheds.

For years, scientists and engineers have noted an increase in river flows when the trees along streams are removed. The water in the soil, which would otherwise have been taken up by the tree roots and sent into the atmosphere, instead moves directly into streams and rivers.

At the same time, large areas of tropical forest actually create rain clouds as moisture from their leaves evaporates. So the elimination of swaths of these forests decreases rainfall. Cut down enough trees, the scientists argue, and the indirect impact of lost rainfall outweighs the direct impact of removing trees.

The study, published by The Proceedings of the National Academy of Sciences, predicts that extensive deforestation will leave less water in the rivers to generate hydropower from projects like Belo Monte, which is under construction on the Xingu River in Brazil and will be the world’s third largest hydropower complex.

The Belo Monte project, whose massive scope and impact on the landscape have led to opposition, is expected to generate at least 4,400 megawatts of electricity, the study said. The project’s overall capacity would be more than 11,000 megawatts; because of wide variations in seasonal flows of the Xingu River, the lower output is what developers guarantee.

But the study warns that by 2050 as much as 40 percent of this power could be lost because of the reduced rainfall caused by regional deforestation.

Loss of tropical rain forests in the Amazon basin, Central Africa, Indonesia and other parts of the world has been a pressing environmental issue for two decades, but the debate has been framed largely in two ways. First, that the loss of the forests accelerates worldwide climate change be removing a large carbon sink that absorbs carbon dioxide from the atmosphere. Second, that the deforestation destroys the livelihoods of indigenous communities.

The idea that deforestation could reduce rainfall and thus economically harm a country like Brazil, which gets more than 80 percent of its energy from hydropower, is less familiar news.

Noting the established connection between the loss of trees and an increase in river flow, Claudia M. Stickler, the paper’s lead author, said researchers in the Amazon basin “saw effects where the conventional wisdom did not hold true.”

“They removed so much forest that it reduced rainfall and reduced the stream flow,” she added.

A co-author, Daniel C. Nepstad, who like Dr. Stickler works at the Amazon Institute for Environmental Research in Brasília, said rain forests create rain because they “are in the equatorial sun, evaporating a huge amount of water that goes up through the stems and into the leaves and out into the atmosphere.” That moisture feeds rain clouds.

In some eastern and southern tributaries of the Amazon, he added, “the cycle has changed.” The Xingu River, he said, is already near a tipping point where the increased flows caused by the loss of tree roots will be nullified by the overall loss of rainfall.

The authors concluded that “as tropical rain forest nations turn increasingly to hydropower to meet growing demands for ‘green’ electricity, it is important” that planners take into account the links between forest cover and stream flows.

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