Dennis Gilles May 31, 2013

1. Dennis Gilles May 31, 2013

2. Forward Looking Statements This presentation contains certain “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. All statements other than statements of historical fact are forward-looking statements, which reflect the company’s current expectations and beliefs regarding its future results of operations, performance and achievements. These statements are subject to risks and uncertainties and are based upon assumptions and beliefs that may or may not materialize. Forward-looking statements may be identified by words such as “will”, “could”, “prospects”, “potential”, “planned”, “expected”, “estimates”, "schedule", "anticipates" and similar terms. These forward-looking statements include, but are not limited to, statements concerning the company’s strategy; operating forecasts; capacity, financing and construction of new projects or expansions of existing projects; working capital requirements and availability; illustrative plant economics; and the use of share price value projections. Forward-looking statements are not guarantees of future performance and are subject to various risks and uncertainties that could cause the company’s actual results and outcomes to differ materially from those discussed or anticipated, including the factors set forth in the section entitled “Risk Factors” included in the company’s Annual Report on Form 10-K for the year ended December 31, 2012 and its other filings with the Securities and Exchange Commission. The company does not assume the obligation to update any forward-looking statement. All financial information presented in U.S. dollars unless otherwise indicated.

3. Geothermal Resources in the Western U.S. Data source: United States Geological Survey. Map Credit: Billy Roberts

4. Geothermal Power Background • Produced by utilizing heat that naturally exists within the Earth’s crust • National Renewable Energy Lab (NREL) estimates that heat within 10,000 meters of earth’s surface is 50,000 times greater than energy that is available from petroleum and natural gas • Geological anomalies create “shallow” reservoirs of geothermal fluids (steam and water) that can be economically exploited • Typically reservoirs are 1,000 – 12,000 feet deep • Geothermal fluids act as heat carriers. Those fluids are piped to the surface and used to drive turbine generators • Geothermal fluid is reinjected to sustain reservoir pressure • Geothermal power is renewable without significant output deterioration over time

5. Steam Power Plant • In dry steam or flash power plants, the hot steam (or flashed hot water) passes directly into a steam turbine. • The steam spins the turbine blades, which in turn spin the generator making the electricity. • Condensed steam is returned into the reservoir to be reheated.

6. Binary Cycle Power Generation • In a binary cycle plant, hot water from the ground is run through a heat exchanger to vaporize a working fluid (hydrocarbon or refrigerant) that powers the turbine generator. • The geothermal water is returned into the reservoir to be reheated.

7. Geothermal Overview • Large existing installed base in the United States • 3,386 MW(2) in production as of year end 2012 • Comparative production of geothermal, wind, and solar in the United States in 2012(1) : (thousand MWh) • Wind 140,089 • Geothermal 16,791 • Solar 4,342 • (Wind surpassed geothermal in 2005) • Globally, there is 11,224 MW(1)in production • United States is the largest producer in the world • The first geothermal power plants in the U.S. were built in 1962 at The Geysers dry steam field in Northern California • The Geysers are the largest producing geothermal field in the world • Geothermal power has incredible potential as an energy source US Electric Geothermal Resource Survey Source: US DOE NREL Estimated US Geothermal Potential Shallow – Identified…………………….30,000 MW Shallow – Unidentified………………..120,000 MW Co-production & Geo-pressure……>100,000 MW Enhanced Geothermal Systems.. 13,000,000 MW • GEA Data for 2012 • Source: EIA Data for 2012 7 Source: NREL

8. Geothermal Electricity Production in U.S. by State • California 2,732 Megawatts • Nevada 517 Megawatts • Utah 48 Megawatts • Hawaii 38 Megawatts (25% of Big Island’s total energy) • Oregon 33 Megawatts • Idaho 16 Megawatts • Alaska 0.7 Megawatt • Wyoming 0.3 Megawatt Dry Steam: 1,585 MW Flash: 997 MW Binary: 804 MW Total 3,386 MW Source: Geothermal Energy Association – 2013 Annual Generation Report

9. Total Projects in Development by State Total Planned Capacity Estimated State Projects Additions (MW) Resource (MW) Low High Low High AK 6 50 50 95 95 AZ 2 2 2 102 102 CA 33 995 1,061 1,736 1,827 CO 3 20 40 60 60 HI 3 - - - - ID 11 83 83 439 514 ND 2 0.60 0.82 - - NM 1 15 15 - - NV 75 1,056 1,061 2,150 2,275 OR 18 73 77 208 270 TX 1 1 1 - - UT 19 215 215 260 280 WA 1 - - 100 100 TOTAL 175 2,511 2,606 5,150 5,523 Source: Geothermal Energy Association – 2013 Annual Generation Report

10. World’s Largest Geothermal Fields (MW capacity)

11. Why Geothermal? • Versus Traditional Power Generation • Clean and renewable generating source • Cost competitive with traditional sources in many geographic areas • No commodity risk and/or price volatility from fuel inputs • No emissions = easier permitting process in power hungry Western US • High availability versus all technologies • Incentives enhance attractive project returns • Base load power • Not dependent on variables such as the time of day, cloud cover, etc. • 95% utilization versus 30-35% for wind and solar • Can constitute larger portion of a utility’s generating portfolio • Results in lower production costs per megawatt produced • More attractive project returns • Smaller footprint and reduced visual impact versus wind and solar • However longer development lead times and higher exploration risk/cost Wyoming Coal Plant • Versus Other Renewable Power Generation Natural Geyser 11

12. Specific Barriers to Geothermal Development Drilling, Drilling, Drilling….. • High risk - resource discovery (3 to 5 years) • Cost per well $2 to $8 million • Lack of drilling and development price incentives • Need to reward investors with higher returns • Need to create new era of geothermal drilling based on feed-in tariff Other Factors….. • Long development lead times for plant equipment • Capital-intensive • Regulatory patchwork

13. This is what it is all about!

14. Direct use applications displace about 1.6 Million barrels of oil annually in the U.S. District Heating Process heat Agriculture Aquaculture Balneology (Hot spring and water bathing) Direct Use Applications

15. District Heating Applications

16. … a look at our company

17. _____________________________ • Vision: Building a sustainable, long-term clean renewable energy company • Management: Proven geothermal energy development and operating experience • Assets: Three operating geothermal power plants • 22 MW plant near Vale, Oregon • 9 MW plant near Reno, Nevada • 13 MW plant near Pocatello, Idaho • Advanced development properties • El Ceibillo near Guatemala City, Guatemala • San Emidio II near Reno, Nevada 17

18. U.S. Geothermal’s Producing Power Plants Operating Projects Development Projects Oregon Neal Hot Springs Boise Idaho Raft River Granite Creek Gerlach San Emidio Reno Nevada Neal Hot Springs, Oregon 60 to 70% Owned* 22 net MW San Emidio, Nevada 100% Owned 9 net MW Raft River, Idaho 50% Owned ** 10 net MW * EP=Enbridge, % subject to final calculations ** EP= Goldman Sachs 18

19. Neal Hot SpringsOregon’s First Commercial Geothermal Power PlantOnline November 2012

20. 22 net MW power plant Commercial Operation: November 2012 $130 million total cost $33 million ITC Treasury cash grant Possible additional $3.1 million after sequestration resolution $7.3 million BETC Oregon tax credit – payment pending $72 million (approx.) 22 year project term loan from DOE Fixed APR ~2.6% PPA with Idaho Power long term buyer with attractive pricing and terms Enbridge is equity partner Neal Hot Springs:

21. San Emidio Power Plant Online May 2012 21

22. NV Energy 19.9 MW PPA Reservoir with 20 year operating history New 9 net MW power plant (Phase I) $44 million total project cost Received $11.75 million ITC US Treasury cash grant $29 million construction loan - SAIC 20+ year project loan – pending Option for second 11 MW plant San Emidio Power Plant

23. Raft RiverPacific Northwest and Idaho’s First Geothermal Power PlantOnline - 2007

24. Raft River Operations 13 MW net capacity 10 MW current production 25 year Idaho Power PPA Allows separate REC sales Goldman Sachs tax equity partner since 2008 Excellent operating history $11 million DOE grant studying fracturing for increased production Resource expansion potential 24

25. El Ceibillo Project – GuatemalaDevelopment Drilling Started April 2013 25

26. El Ceibillo Project PPA MOU signed for 50 MW Current retail market $140 per megawatt hour Phase I: Planned 25 net MW power plant Estimated total project cost - $135 million Existing well field – 5 production wells Plan to re-enter 2 wells to deepen and drill new wells Confirmation reservoir drilling underway Adjacent to Guatemala City and main shipping port Transmission interconnect 2 km south Development decision tied to PPA, project financing, and equity partner Option for Second 25 MW Plant (Phase II) 26

27. U.S. Geothermal Growth Plan 4 Options Under Evaluation for Renewable Growth • Invest incrementally within existing Plant footprint for more MW • Add to Plant footprint by building new power plants on undeveloped acreage • Pursue development at currently held undeveloped sites • Evaluate other potential renewable growth opportunities • M&A • Greenfield Higher Focus Utilize stimulus package incentives: • Investment Tax Credit of 30% • Must be in continuous construction by 12/31/13 • DOE Cost Share Drilling Lower Focus

28. Quarterly Financial Results • All 3 projects online as of the middle of Q4 2012 • First two quarters with positive EBITDA, net income, and cash flow

29. Planned 2013 Performance Selected Metrics Total HTM Share Gross Project Capacity 65 MW Net Project Capacity 44 MW 29 MW Potential Annual Generation 340,000 MWh Gross Revenue $26.3 million EBITDA $12.9 million Net Free Cash Flow $ 4.0 million

30. … a new beginning Summary • Traded on NYSE MKT – HTM and TSX GTH • Recent transition from early development company to operating IPP • Proven management team • 10 years of successful project development and growth • 3 modern geothermal power plants, plus two advanced development projects • 65 MW gross generating capacity online during 2012 • Valuable, non depleting earth energy sources • Achieved positive net income, cash flow, and EBITDA • 2013 first year of sustainable earnings & cash flows • Under valued stock in oversold market 30