Sierra Geothermal Makes Discovery at Alum and Reports Q1 2010 Financials

Sierra Geothermal Power Corp. ("Sierra") (TSX VENTURE:SRA) is pleased to
announce that it has made a geothermal discovery at its 100% owned Alum project
in Esmeralda County, Nevada. In addition, Sierra reports its Q1 2010 financial
results and provides an operational update.


Alum Project

The geothermal discovery comes from Sierra's slim well 26-19, which is
considered to be a geothermal discovery well due to the levels of permeability
and temperature encountered. The drilling of the slim well 26-19 concluded on
May 14, 2010. The well was drilled to a maximum depth of 1,484 meters or 4,868
feet. The preliminary bottom hole temperature of 146 degrees Celsius or 295
degrees Fahrenheit was recorded immediately after drilling stopped. Several
zones of high permeability were encountered between 1,116 and 1,325 meters
(3,663 and 4,349 feet, respectively). After coring through the 209 meter
permeable zone, a geothermal water sample was air lifted and flowed for three
days and samples were collected for analysis. Temperature measurements in the
completed well will continue until thermal equilibrium is achieved.


A temperature profile on the previously drilled well 25-29 was recorded April
30, 2010, five months after drilling was completed. The temperature log returned
a maximum of 130 degrees Celsius or 266 degrees Fahrenheit at 630 meters or
2,067 feet.


The cost for these wells is shared on a 50/50 basis with the US Department of
Energy (DOE) under the 2009 Geothermal Technologies Program grant award. The
total grant amount from the DOE for the Alum project was $5,000,000. The Alum
project was acquired from Geo-Energy Partners 1983 Ltd in 2006.


"We are grateful for the financial support that we are receiving from the DOE in
advancing our Alum project, as it has helped us make a discovery at Alum with
less capital than we would have otherwise employed. Numerous people were
employed during the drilling of these wells, showing that the DOE grant program
is working. We look forward to advancing the Alum project to the next level
which is drilling full sized production assessment wells," said Gary R.
Thompson, President and CEO of Sierra.


Q1 2010 Financial Results

For the first quarter ended March 31, 2010, Sierra reported a net loss of
$1,436,583 or ($0.01) per share compared to a net loss of $428,231 or ($0.01)
per share for the first quarter ended March 31, 2009. As of March 31, 2010,
Sierra had cash of $4,459,286 and working capital of $3,053,202, compared to
cash of $8,260,320 and working capital of $6,664,549 on December 31, 2009. The
full text of Sierra's unaudited financial statements and management's discussion
and analysis is available on the SEDAR website at www.sedar.com or at
www.sierrageopower.com.


Reese River Project

Sierra recently completed a review and analysis of new geological, structural,
and geophysical data at its Reese River project in Lander County, Nevada. The
integration of these new data sets into the Reese River conceptual model is the
result of successful collaborations with the University of Nevada, Reno and the
University of British Columbia. New data from detailed geologic mapping and
joint 3D inversion modeling of magnetotelluric and Z-TEM data highlight an area
of complex faulting coinciding with the change in trend of a major geologic
structure in the area. This structurally complex area (the accommodation zone)
may be a zone of enhanced permeability at depth and is of high geologic
interest. Also, the recent temperature hole 23-03, which was drilled to a depth
of 30 meters, returned a temperature gradient of 1,100 degrees Celsius per
kilometer or 61 degrees Fahrenheit per 100 feet. This hole also lies within the
inferred accommodation zone. Recent internally-derived resource estimates for
Reese River, using a Monte Carlo model, indicates 70 MW of power potential. The
increase is based on the recent step out drilling which Sierra believes has
identified a thermal anomaly larger than previously delineated.


Silver Peak Project

During February/March 2010, core well 38-11 was drilled at Silver Peak to 1,649
meters or 5,409 feet. This well was the first deep well at Silver Peak. A recent
stable temperature measurement recorded a bottom hole temperature of 103 degrees
Celsius or 217 degrees Fahrenheit.


The costs for these wells are shared on a 50/50 basis with the US Department of
Energy (DOE) under the 2009 Geothermal Technologies Program grant award. The
total grant amount from the DOE for the Silver Peak project was $5,000,000.


Imperial Valley Properties and Nevada Land Sale Results

Sierra has been notified that the Imperial Valley (Salton Sea) lands in
California, which comprise 3,442 acres, have been leased by the Bureau of Land
Management (BLM) to Western Geothermal Partners, LLC. The Salton Sea lands are
the last parcel of land to be acquired and paid for under the Cayley Geothermal
and Western Geothermal 2006 agreement. Cayley Geothermal Corp. is a wholly owned
subsidiary of Sierra. At the May 11, 2010 BLM geothermal land sale Sierra made
the winning bids on 4,541 acres adjacent to its Reese River project, 1,880 acres
at Sierra's existing Howard Project and 2,877 acres in close proximity to its
Alum project.


About Sierra Geothermal Power Corp.

Sierra is a Vancouver-based geothermal energy company focused on the exploration
and development of clean, sustainable power in Western North America. Sierra has
100% control over its 120,000 acre portfolio of geothermal properties in Nevada,
California and British Columbia. Sierra's projects have a combined total
estimated capacity of almost 400MW. One megawatt (MW) is enough to power 800
homes. www.sierrageopower.com


On behalf of the Board of Directors

Gary Thompson, P.Geo, President, Chief Executive Officer and Director

CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING INFORMATION

This news release may contain forward-looking statements. All statements, other
than statements of historical fact, included or incorporated by reference in
this news release are forward-looking statements, including, without limitation,
statements regarding activities, events or developments that Sierra expects or
anticipates may occur in the future. Forward-looking statements can be
identified by the use of forward-looking words such as "may", "would", "could",
"expect", "intend", "plan", "estimate", "anticipate", "believe" or "continue" or
similar words or the negative thereof. Forward-looking statements in this news
release include statements that Sierra is looking forward to advancing Alum to
drilling full sized production wells, that thermal equilibrium can be achieved
at its Alum slim well 26-19, that the structurally complex accommodation zone at
Reese River may be a zone of enhanced permeability at depth, that the size of
the thermal anomaly at its Reese River project has increased to 70MW, as
indicated by recent internally-derived resource estimates using a Monte Carlo
model, and that Sierra's projects have a total estimated capacity of almost
400MW. There can be no assurance that the plans, intentions or expectations upon
which these forward-looking statements are based will occur. Readers are
cautioned not to place undue reliance on these forward-looking statements, which
are not a guarantee of performance and are subject to a number of uncertainties
and other factors that could cause actual results to differ materially from
those expressed or implied by such forward-looking statements. These factors
include general economic and market conditions, availability of working capital,
changes in the law, actions of competitors, drill results, changes in
circumstance and Sierra's ability to implement business strategies and pursue
its business plan. In addition, all forward-looking statements involve risks and
uncertainties, including the risks and uncertainties detailed in Sierra's
filings with the applicable Canadian securities commissions, copies of which are
available at www.sedar.com. We urge you to carefully consider these factors. All
of the forward-looking statements contained in this news release are expressly
qualified in their entirety by this cautionary statement. The forward-looking
statements included in this news release are made as of the date of this news
release and Sierra undertakes no obligation to publicly update such
forward-looking statements to reflect new information, subsequent events or
otherwise, except as required by law.