U.S. Geothermal Confirms Reservoir at WPG Geysers Project

BOISE, IDAHO--(Marketwired - Sept. 21, 2015) - U.S. Geothermal Inc. (TSX:GTH)(NYSE MKT:HTM) (the "Company"), a leading renewable energy company focused on the development, production, and sale of electricity from geothermal energy, is pleased to announce it has received the reservoir engineering report for the WGP Geysers project from third party engineering firm GeothermEx Inc..

As previously announced, the Company successfully completed a flow test program in June on the three largest production wells at the WGP Geysers project in northern California confirming that the wells were still open and ready for production. GeothermEx Inc. (a Schlumberger company) designed the isochronal (step-rate) flow test program, and monitored the testing of the wells.

GeothermEx reports that the four production wells are capable of delivering an initial capacity of 28.1 MW (gross) or 25.4 MW (net) based on current power plant steam conversion rates from a detailed design for a 28.8 MW (net) power plant. These longer term tests show the wells would initially produce a combined total of 458,000 pounds per hour of steam compared to 462,000 pounds per hour of steam from short term tests performed when the wells were first drilled, demonstrating that the capacity of the wells is virtually unchanged. Using the average steam production rate from these wells and an assumed interference factor of 30%, GeothermEx estimates that an additional 2-3 production wells would be needed to support the long term operation of a 28.8 MW (net) plant.

Two methods were used by GeothermEx to estimate the long term capacity of the WGP project, and both support a high probability that a 28.8 MW (net) plant can be operated for 25 years, given the modern plant design and the available productive area. The first is the p/z method, an established natural gas reservoir engineering calculation that is routinely used at The Geysers. Based on the plant design and the increase in available injection that would result from WGP's planned hybrid cooling system, GeothermEx estimates that the reservoir could support the 28.8 MW (net) plant for up to 54 years. The second method, which is an empirical approach based on GeothermEx's extensive experience at The Geysers, is used to estimate the steam production capacity per acre within the productive area of a geothermal leasehold. On this basis, GeothermEx reports that the productive acreage within the WGP leasehold has steam reserves sufficient to supply up to 44 MW (net) with a conventional injection level of 25%, and potentially more at the higher injection levels associated with the planned hybrid cooling system.

"The results of this analysis from our test program clearly shows that the WGP Geysers project has approximately 30 megawatts of steam, drilled, tested and ready for production, and that, with the higher injection rates provided by hybrid cooling, it has the reservoir to support long term generation," said Dennis Gilles, CEO of US Geothermal. "We are pleased with last week's passage of SB-350 in California, which now raises the Renewable Portfolio Standard for the state to 50% renewable energy by 2030, the highest in the country, and we anticipate this will increase the interest in a power purchase agreement for our WGP Geysers project. We are also pleased to announce that the recent forest fires reported in The Geysers area did not impact our geothermal wells, project equipment, or project site."

About U.S. Geothermal Inc.:

U.S. Geothermal Inc. is a leading and profitable renewable energy company focused on the development, production and sale of electricity from geothermal energy. The company is currently operating geothermal power projects at: Neal Hot Springs, Oregon, San Emidio, Nevada and Raft River, Idaho for a total power generation of approximately 45 MWs. The company is also developing projects at: The Geysers, California; a second phase project at San Emidio, Nevada; the El Ceibillo project located near Guatemala City, Guatemala; and at Crescent Valley, Nevada. U.S. Geothermal's growth strategy is to reach 200 MWs of generation by 2020 through a combination of internal development and strategic acquisitions.

Please visit our Website at: http://www.usgeothermal.com

The information provided in this news release may contain forward-looking statements within the definition of the Safe Harbor provisions of the US Private Securities Litigation Reform Act of 1995. Readers are cautioned to review the risk factors identified by the company in its filings with US and Canadian securities agencies. All statements, other than statements of historical fact, included herein, without limitation, statements relating to the future operating or financial performance of U.S. Geothermal, are forward-looking statements. Forward-looking statements are frequently, but not always, identified by words such as "expects", "anticipates", "believes", "intends", "estimates", "potential", "possible", and similar expressions, or statements that events, conditions, or results "will", "may", "could", or "should" occur or be achieved. These forward-looking statements may include statements regarding perceived merit of properties; interpretation of the results of well tests; project development; resource megawatt capacity; capital expenditures; timelines; strategic plans; or other statements that are not statements of fact. Forward-looking statements involve various risks and uncertainties. There can be no assurance that such statements will prove to be accurate, and actual results and future events could differ materially from those anticipated in such statements. Important factors that could cause actual results to differ materially from U.S. Geothermal's expectations include the uncertainties involving the availability of financing in the debt and capital markets; uncertainties involved in the interpretation of results of well tests; the need for cooperation of government agencies in the development and operation of properties; the need to obtain permits and governmental approvals; risks of construction; unexpected cost increases, which could include significant increases in estimated capital and operating costs; and other risks and uncertainties disclosed in U.S. Geothermal's Annual Report on Form 10-K for the year ended December 31, 2014 filed with the United States Securities and Exchange Commission and Canadian securities regulatory authorities and in other U.S. Geothermal reports and documents filed with applicable securities regulatory authorities from time to time. Forward-looking statements are based on management's expectations, beliefs and opinions on the date the statements are made. U.S. Geothermal Inc. assumes no obligation to update forward-looking statements if management's expectations, beliefs, or opinions, or other factors, should change.

The NYSE MKT and the TSX do not accept responsibility for the adequacy of this release.