STATUS OF THE SEGS PLANTS

D. Kearney, H. Price, I. Replogle, T. Manes, J. Costanzo, Y, Gilon, S. Walzer Luz International Limited, Los Angeles, California, U. S.A.

ABSTRACT

Nine Solar Electric Generating Systems (SEGS) are now supplying 354 MWe peak power to the utility grid in Southern California. The facilities all utilize LUZ parabolic trough collectors matched with Rankine cycle steam power plants. With design solar-to-electric efficiencies of almost 23% and productions up to 0.53 MWh/m2 of solar field, the plants are generally operating well by standards of reliability and performance. The mature plants all achieved capacity factors of 100% or higher during the critical on-peak utility production period in 1990, with annual electric generation performance being dependent on the maturity of an individual plant. Future plans call for advancements in both the solar field and overall power plant system design.

KEYWORDS

Solar electric; parabolic trough; SEGS; solar thermal; electricity; power block; LUZ

INTRODUCTION

With the addition of the 80-MW SEGS IX unit to the Southern California Edison utility grid in September, 1990, the SEGS plants now have a total operational generation capacity of 354 MWe net. These plants, located in the Mojave Desert of California and primarily serving utility peak demand needs, operate to provide full power during high demand summer afternoons and evenings using both solar and supplemental natural gas energy. The plants also generate solar electricity at all other times, given sufficient insolation. Additional natural gas is used selectively during winter days. The total contribution from solar energy is 70% of the annual electrical output (Solar energy provides 75% of the total thermal input, in accordance with federal regulations). Table 1 shows the current status of the SEGS facilities, all of which have generally been operating routinely and well.

The design, installation and operation of each series of plants gained from experience with the previous plants. There were improvements in many areas such as system configuration, solar field design, power block component selection, construction techniques and operating methods. Design improvements to the solar field allowed a steady rise in collector operating temperatures from about 316°C to 39ГС which, in turn, led to a higher turbine inlet steam pressure and a moderately higher superheat temperature supplied by solar energy alone. This gain plus an increased turbine capacity and the introduction of reheat to the steam cycle brought turbine efficiencies up to almost 38% in the solar mode of operation from an initial 29%. Solar field optical efficiencies increased from 71% to

TABLE 1 Characteristics of the SEGS Plants

Full

Turbine Cycle

ImB

Operating Turbine

Solar Reid

Efficiency

Annual

Plant

Year

Status Caoacitv Temo

Size

Solar

Nat. Gas

OutDut

(MWe net) (°F)

(M2)

(%)

(%)

(MWh)

I

1985

Operational

13.8

307

82960

*31.5

NA

30100

II

1986

Operational

30.0

316

188990

29.4

37.3

80500

III

1987

Operational

30.0

349

230300

30.6

37.4

92780

1 IV

1987

Operational

30.0

349

230300

30.6

37.4

92780

V

1988

Operational

30.0

349

233120

30.6

37.4

91820

VI

1989

Operational

30.0

391

188000

37.5

39.5

90850

VII

1989

Operational

30.0

391

194280

37.5

39.5

92646

VIII

1990

Operational

80.0

391

464340

37.6

37.6

252750

IX

1991

Operational

80.0

391

483960

37.6

37.6

256125

X

1992

Construction

80.0

391

483960

37.6

37.6

260841

‘Includes natural gas superheating

80% which, combined with the improved cycle efficiency, brought the annual design electrical production from about 0.42 MWh/m2 to 0.53 MWh/m2, an increase of 25%.

Design annual solar-to-electric efficiencies are 11.5% for SEGS lll-V and up to 13.6% for SEGS VI-VIII based on total insolation, with 13.2% to 15.6% solar-to-electric efficiency based on insolation in the plane of the collector. Peak solar-to-electric efficiencies reach 23% for the latest plants.

Costs of construction and operation of the SEGS plants saw reductions over this period. Total installed costs in 1990 dollars dropped from $5979/kW for SEGS I to $3011/kW for SEGS VIII. As a result of this progress plus the performance gains, 30-year levelized electricity costs (in 1990 dollars calculated on the basis of SEGS financing by private investor partnerships) went from 26.5 cents/kWh in SEGS I to 8.9 cents per kWh in SEGS VIII.

Updated: August 24, 2015 — 9:51 am