Solar Energy Generating Systems

Solar Energy Generating Systems (SEGS)
Industry	Solar energy, Renewable energy
Founded	1984
Headquarters	California, United States
Area served	California, United States
Products	Concentrated solar power electricity generation
Owner	Terra-Gen, LLC (for SEGS VIII–IX since 2018), NextEra Energy Resources (former partial owner)
Number of employees	Approximately 140 (95 at Kramer Junction and 45 at Harper Lake)

Adapted from the English Wikipedia article Solar Energy Generating Systems, available under CC BY-SA 4.0Updated 7 August 2025

Solar Energy Generating Systems (SEGS) represents a concentrated solar power installation located in California, United States. Comprising three sites with a total capacity of 354 megawatt (MW), it held the title of the largest solar thermal facility worldwide for three decades until the Ivanpah Solar Power Facility overtook it in 2014. Additionally, SEGS was the top solar power installation across all technologies until the photovoltaic Topaz Solar Farm commenced operation in 2014. The system included nine separate solar plants situated within California's Mojave Desert, an area renowned for some of the nation’s highest solar radiation levels.

The initial SEGS I–II units (44 MW) were positioned near Daggett but have since been replaced by a photovoltaic array.

SEGS III–VII (150 MW) were established at Kramer Junction; all five of these plants have now been dismantled. These facilities were operated and partially owned by NextEra Energy Resources.

The two remaining plants, SEGS VIII–IX (160 MW), are located at Harper Lake. On January 26, 2018, ownership of these units was transferred to Terra-Gen, LLC, a company specializing in renewable energy.

A tenth plant, SEGS X (80 MW), was under development, while SEGS XI and XII were proposed by Luz Industries. However, financing difficulties led to the developer’s bankruptcy in 1992. Subsequently, the SEGS X site received authorization for the Lockhart Solar PV II photovoltaic project.

By 2021, most of the thermal plants had been decommissioned and replaced with photovoltaic systems on their original locations.

Plants' scale and operations

Prior to the decommissioning and conversion of SEGS I through VII to photovoltaic technology, these facilities had an installed net capacity of 354 MW (394 MW gross). Operating continuously at nameplate capacity would yield approximately 75 MWe, equating to a 21% capacity factor. The turbines were capable of running during nighttime hours using supplemental natural gas fuel.

According to NextEra’s 2009 data, these solar installations could supply electricity to around 232,500 households during peak daylight hours and reduce pollution emissions by approximately 3,800 tons annually compared to fossil fuel alternatives.

The entire system incorporated 936,384 parabolic mirrors covering an area exceeding . Arranged end-to-end, these mirrors would stretch over .

For instance, in 2002, constructing the 30 MW Kramer Junction facility required an investment of $90 million, with annual operation and maintenance costs amounting to $3 million—equivalent to 4.6 cents per kilowatt-hour.

Principle of operation

This power generation system employs parabolic trough solar thermal technology augmented by natural gas combustion. Roughly 90% of the electricity output is derived directly from solar energy. When solar input falls short of demand from Southern California Edison, natural gas is used as a supplemental fuel source.

Mirrors

The parabolic mirrors are shaped like quarter-pipes and focus sunlight onto glass tubes boasting a reflectivity rate of 94%, which surpasses conventional mirror reflectivity around 70%. These mirrors track the sun automatically throughout the day. To mitigate wind damage—resulting in roughly 3,000 mirror replacements annually—operators can adjust mirror positions before storms. An automated cleaning system maintains the reflective surfaces regularly. The term "field area" denotes the actual collector surface covered by these mirrors.

Heat transfer

Sunlight concentrated by the mirrors heats a central receiver tube filled with synthetic oil to temperatures exceeding . This concentration amplifies sunlight intensity by factors between 71 and 80 compared to standard sunlight levels. The heated synthetic oil transfers its thermal energy to water, producing steam that powers a Rankine cycle turbine for electricity generation. Synthetic oil is preferred over water as a heat transfer medium due to its ability to operate at manageable pressure levels under high temperatures.

Individual facilities

The SEGS power stations were initially developed by Luz Industries and became operational between December 1984 and October 1990. After Luz Industries declared bankruptcy in 1991, ownership of the plants transferred to various investors as separate entities, which led to the cancellation of further developments, including three additional planned facilities.

The Kramer Junction site employs approximately 95 staff members, whereas Harper Lake has a workforce of around 45.

**Operational history and data for SEGS plants (1985–1990)**
Facility	Year commissioned	Location	Turbine capacity		Collector area	Operating temperature	Gross solar electricity generation (MWh)
Facility	Year commissioned	Location	Net (MW)	Gross (MW)	(m²)	(°C)	1985	1986	1987	1988	1989	1990
SEGS I	1984	Daggett	14	14	82,960	307	19,261	22,510	25,055	16,927	23,527	21,491
SEGS II	1985	Daggett	30	33	190,338	316		25,085	23,431	38,914	43,862	39,156
SEGS III	1986	Kramer Jct.	30	33	230,300	349			49,444	61,475	63,096	69,410
SEGS IV	1986	Kramer Jct.	30	33	230,300	349			52,181	64,762	70,552	74,661
SEGS V	1987	Kramer Jct.	30	33	250,500	349				62,858	65,280	72,449
SEGS VI	1988	Kramer Jct.	30	35	188,000	390					48,045	62,690
SEGS VII	1988	Kramer Jct.	30	35	194,280	390					38,868	57,661
SEGS VIII	1989	Harper Lake	80	89	464,340	390				114,996
SEGS IX	1990	Harper Lake	80	89	483,960	390				5,974
Aggregate			354	394	2,314,978	19,261	47,595	150,111	244,937	353,230	518,487

**SEGS plant operational data and history (1991–2002)**
Gross solar electricity generation (MWh)
Facility	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000	2001	2002	Avg. (1998–2002)	Total
SEGS I	20,252	17,938	20,368	20,194	19,800	19,879	19,228	18,686	11,250	17,235	17,947	17,402	16,500 !348,950
SEGS II	35,168	32,481	36,882	36,566	35,853	35,995	34,817	33,836	33,408	31,207	32,497	31,511	32,500 !571,696
SEGS III	60,134	48,702	58,248	56,892	56,663	64,170	64,677	70,598	70,689	65,994	69,369	66,125	68,555 !995.686
SEGS IV	64.600 51.007 58.935 57.795 54.929 61.970 64.503 71.635 71.142 63.457 64.842 70.313 68.278 !1.017M
SEGS V 59.009 55.383 67.685 66.255 63.757 71.439 75.936 75.229 70.293 73.810 71.826 73.235 72.879 !1.014M
SEGS VI 64.155 47.087 55.724 56.908 63.650 71.409 70.019 67.358 71.066 68.543 67.339 64.483 67.758 !878k
SEGS VII 58.373 46.940 54.110 53.251 61.220 70.138 69.186 67.651 66.258 64.195 64.210 62.196 65.048 !834k
SEGS VIII 102464 109361 130999 134578 133843 139174 136410 137905 135233 140079 137754 138977
Total !8.967M

**SEGS plant operational data and history (2003–2014)**
Net solar electricity generation (MWh)
Facility	2003	2004	2005	2006	2007	2008	2009	2010	2011	2012	2013	2014	Avg (2003–14)	Total
SEGS I !98k
SEGS II !204k
SEGS III !713k
SEGS IV !717k
SEGS V !726k
Total !7M

**SEGS plant operational data and history (2015–2021)**
Net solar electricity generation (MWh)
Facility	2015	2016	2017	2018	2019	2020	2021	Total	Total 1985–2021
Total	539k	501k	455k	468k	366k	237k	198k	2.75M	18.78M

Beginning in the year 2017 the original thermal plants SEGS I and II were substituted with photovoltaic installations named Sunray 2 and Sunray 3 respectively.

This collection of nine facilities stands as one of the most significant commercial solar thermal power investments of its time with cumulative net output surpassing eighteen million MWh by the early decades of the twenty-first century.

Harper Lake

Before the Ivanpah Solar Power Facility began operations in 2014, SEGS VIII and SEGS IX () held the distinction of being the largest solar thermal power plants worldwide, both individually and collectively. These two units represented the final, most sizable, and technologically advanced installations among the nine SEGS plants, all engineered to capitalize on economies of scale. Although plans existed for a tenth plant, they were abandoned following Luz Industries' bankruptcy, and construction never started on the authorized eleventh and twelfth plants, each designed to generate 80 MW. Subsequently, Abengoa Solar developed the neighboring 280 MW Mojave Solar Project (MSP), which employs comparable concentrating solar thermal trough technology.

Beginning in February 2020, SEGS VIII discontinued natural gas combustion, with its final output recorded in October 2021. SEGS IX ceased using natural gas in October 2020, except for a brief period in January 2021.

Kramer Junction

Situated at , this location benefits from approximately 340 sunny days per year, making it exceptionally suited for solar energy production. It experiences an average direct normal radiation (DNR) of 7.44 kWh/m²/day (310 W/m²), ranking among the highest levels across the United States. This site was home to SEGS II–VII, which were retired in 2019. By 2021, these units were being replaced by a new photovoltaic installation called Resurgence I.

Daggett

SEGS I and II, positioned at , were under the ownership of Cogentrix Energy (Carlyle Group). SEGS II was decommissioned in 2014 and succeeded by Sunray 3, a photovoltaic system with a capacity of 13.8 MW (EIA plant code 10438). SEGS I ceased operations in 2015 and was replaced by Sunray 2, a 20 MW PV installation (EIA plant code 10437). Both Sunray 2 and Sunray 3 commenced electricity generation in 2017 according to EIA records.

Accidents and incidents

In February 1999, a mineral oil storage tank holding 900,000 US gallons exploded at SEGS I (Daggett), producing flames and smoke visible over an area exceeding half a square mile. Emergency responders evacuated nearby areas to safeguard adjacent containers containing sulfuric acid and sodium hydroxide.