Feb 15, 1982 - remains open concenning the suitability of below-grade materials. The optical ... atures. As a result, air condjt'ion'ing'loads and electric energy demands are ...... the current stage of development although the concept 'is techn'ica11y ..... The estimate is preliminary because a conceptual rathen than a formal.
5107-4
Solar Ponds Project
Solar Pond Power Plant Feasibility Study for Davis, California Y.C. Wu M.J. Singer H.E. Marsh
J. Harris A.L. Walton
February 15, 1982
:.. Prepared for The City of Davis Through an Agreement with National Aeronautics and Space Adminlstration by Jet Propulsion Laboratory California lnstitute of Technology Pasadena, California (JPL PUBLTCATTON 82-1 6)
Reference to any Specifjc Comrnercial Product' Process, or Service by Trade Name or Manufacturer Does Not Necessarjly tonst'itute an Endorsement by the U. S. Government or Jet Propul s'ion Lahroratory ' Cal i
forni a Instj tute of Technol
ogy '
ABSTRACT
The c1ty of Davis, Califonnia, feas'ibility of constructing a solar
sponsored this study to determjne the pond power plant at Davis. The work was commissjoned by Davis under an agreement wjth the National Aeronaut'ics and Space Administratjon. Conducted by the Jet Propulsion Laboratory, Pasadena, Cal i forni a, the study 'i ncl uded site vj sits, weather data compi 1 at j on, so'il and water analyses, conceptual system des'ign and ana'lyses, a material and equipment market survey, conceptual site layout, and a pre'lim-
inary cost estimate.
Resul ts of the study i ndicate that a sol ar pond power pl ant at Dav'is 'is technically feasible but economica11y unattractive. The r"elatively small scale of the proposed plant and the high cost of importing salt resul ted i n a d'isproporti onately hi gh capital i nvestment w'ith respect to the annual energy production capacity of the plant.
In the future, source
if
is
low-cost hardware developed and an economical becomes available, a reassessment of the concept would be Cycl e optimi zati on and i ncreased p1 ant sj ze woul d al so i ncrease
of salt
warranted. the economical attractiveness of the proposed concept.
1't1
ACKNOWLEDGEME NTS
This study was conducted by the Jet Propulsion Laboratory through NASA Task RD-152, Amendment No. 313, and was sponsoned by the city of Davis, California, (P.0. N0.01276) and the Pacjfic Gas and Electric Company. The results pnesented in this report reflect the contr"ibutjon of members of the Jet Propulsion Laboratory staff. Dr. Y. C. Wu was the principa'l invest'igator and provided overall task coordination. Major contnjbutors to the
study jncluded Mn. M. J. Singer, System Analysis; Dr. H. E. Marsh, Soil and Water Chem'istry; Mr. J. Harri s, Construct'ion and Cost Est jrrrates; and Dr. A. L. Walton, Economic Analys'is. In addition, the Pacific Gas and Electric Company, the city of Davis, and the Un'iversity of Califonnia at Davis pantjcipated in the study by providing data, soil samples and 'independent analyses.
IV
CONTENTS
SUMMARY....................oo.......................
PART
ONE:
EXECUTIVE
PART
Tt.lO:
SOLAR POND POWER PLANT FEASIBILITY STUDY FOR THE CITY 0F DAVIS,
1.
2. 3.
4.
1
CALIF0RNIA........... .............1-1
5.
PLANT DESCRIPTIONS
5..l
........... ..,5-1 5.2 POWER CONVERSION SUBSYSTEM... ... .5.1 5.2.1 The Turbogenerator Unit................o......... ..5-1 5.2.2 Hgat Exchanggrs............ ........ ... ....... .5-5 5.2.3 Feed Pump.................................. 5.2.4 0rgan'i c Fl ui d............................. ........ .5-5 5.3 TRANSPORT AND AUXILIARY SUBSYSTEMS.O"""O' ........'5.5 5.3.1 Hot BF.ine L0op......................................... .5-5 5.3.2 Cool ing Water L00p.......................... ............5-5 S0LAR P0ND C0MPLEX.
5.3.3
Surface Flush'ing, Brine & Fresh Water Make-Up...........5-8
.............................5-8 5.3.5 Water Treatment Faci I ities..... i o ....... .. .5-8 5.3.6 Miscel'laneous Service Equipments ...o..........5-9 5.4 INSTRUMENTATION AND CONTROL. . . .. .5.9 . .. . . 5.4.1 Cl imatological Data........... ...........5-9 5.4.2 Solar Pond Characteristics..... .....5-10 5.4.3 Fl ow Stream Charactenist'ics.......... .........5-10 5.4.4 Equipment Status............................... o........5-10 5.3.4
Wave
Suppression Subsystem.
ooo
6.
7.
START-UP AND OPERATION OF THE
6.I
START-UP.....
6.2
OPERATION AND MAINTENANCE
POND
........6-1
COST ESTIMATE
COSTS............... 7.2 OPERATION AND MAINTENANCE C0STS............... 7 .3 ENERGY C0STS 7
.1
CAPITAL
v'l
..........7-l ......,7.7 ... ...7 -1
Costs..........,............., ...7 -t 7 .3.2 Thgrmal Energy C0sts.................. o................ .7-3 7.3.1
8.
Busbar El ectrjc Energy
PROJECT MILESTONES AND CONSTRUCTION SCHEDULE
8.1 8.2 8.3 8.4 8.5 8.6 8,7
PROJECT
MANAGEMENT.........
SITE SIUDY AND
ENVIRONMENTAL
..............,......8-1
EVALUATION................... .. ..8-I. O
DESIGNS, SPECIFICATIONS AND GENERAL ENGINEERING. MATERIAL, EQUIPMENT AND SUppLy ORDERS....... POND
CONSTRUCTI0N.......
o..
.. ...
INSTALLATION OF POWER CONVERSION, TRANSPORT AND AUXILIARY
SUBSYSTEMS.... .................... FILLING OF THE SOLAR
POND AND THE ESTABLISHMENT OF THE
GRADIENT...... 8.8 POND WARM-UP.. ..... 8.9 PRELIMINARY OPERATIONS.....
....8-1
....8.2
....8-2 ......8.2
MISCELLANEOUS ISSUES
9.I 9.2 10.
.. . ... .8-1
o...... o...........8-1 ..... .8-1
NECESSARY SALT
9.
...
EVALUATION......... SUPPLYING THERMAL ENERGY FOR PROCESS USE..... CONTINUED
SITE SPECIFIC
.....9-1 ...9-1 ..10-1
CONCLUSIONS AND RECOMMENDATIONS
REFERENCES....
...11-1
APPEND I XES
A.
PRELIMINARY LABORATORY ANALYSIS OF SOIL AND WATER SAMPLES......A.1
B.
NOTES AND DISCUSSIONS OF POND CONSTRUCTION AND POND
c.
SOLAR POND POWER PLANT COST
BREAKDOWN
vii
LINING.....B.1
.......O""""....'C-1
F I GURES
1. Site Layout for a 300 kW. Solar Pond Power Plant at Davis......2 2-I.
The Solar Pond
3-1.
Compari
4-1.
The Proposed Davis Solar Pond Power
son
Electric
Power Generatjon
C0ncept.......o.....,.2-3
of the Spectnal Absorption........
4-2. Solar Pond Temperature and
Power
..
.3-1
Plant Flow Schematic ..4-z
0utput
Profiles.......
...4-4
4-3. Daily Operating Houns of Solar Pond at 300 kt,Je Gross 0utput....4-5
Schematic... Pond and Power Stat'ion Platform.
......5-2
5-1. Solar Pond Dike Reinforcement 5-2.
Maintenance
5-3.
Proposed Power Cycle and Essent'ial
5-4.
Wave
Suppressjon Network,
Schemat'ic.........
7-1. Solar
Pond Powen
Plant
Inlet
Economy
....5-3
Components.... .........5'4
and
0utlet Pipe
of Scale....
Arnangement
....
.5-7
.............,.7-4
8-1. Tentative Project Milestones for the Davis 300 kW. Summen
Construction....... 8-?. Solar Pond Construct'ion Schedule.... A-1. Apparatus for Test of Soi I Permeabi l'ity............... Peak'ing So'lar Pond Power Plant
...8-3 ..8-4
....A-2
A-2. Permeation of Water and Bnine in Davis Pond Soi'l Sampl€........A-3 A-3.
Comparj
son
of the Spectnal
Absorpti on. .. . .. . .. .. . .
...A-7
B-1. Site Layout for a 300 kW. Solar Pond Power Plant at Davjs...,..B-2 B-2. Solar Pond Di ke Reinforcement Schematic.. o.....................8-3 B-3.
Mai
ntenance Pond and Power Stati on
Pl
atform.
..
......... ... B-4
TABLES
1. 2.
Cost
Summary
of Davis Solar
Cost
Summary
of an Alternate
Pond Power
..............3
Dav'is Solar Pond Power
Plant......4
Davis............................3-2 of Heat ExchangerS................... .....5-6
3-1. Climat'ic Data fon the City of 5-1. Characteristics
Plant
v]'r
1
7-L.300 k}{e
Summer
Peaking Solar Pond Power Plant Cost Summary.....7-2
C-1. Preliminary Solar Pond Construction Cost Estimate (1) Without Liner. ...... ............ r......................
....C-2
C-2. Preliminary Solar Pond Construction Cost Estimate (1) With Liner........... o..... o...............................C-3 C-3. Cost Information for Various Subsystems, Miscellaneous Items, and Annual 0peration and Mai ntgnanc€...........................C-5 C-4.
Fi
nancial
ParametgrS......... ...... ....
r.
C-5. Typical Output of rlPL Solan Pond Power Plant Economic Analysi s Computer Program. . . . . . . . .. . . o. . . . . o.... . .. . . ..
ix
r.
. . .C-6
..r..
...C-7
..
PART EXECUTIVE
ONE SUMMARY
EXECUTIVE
SUMMARY
This neport presents the results of a solar pond power plant feasjbility study conducted for the city of Davis, California, and the Pacific Gas and Electric Company (PG&E). Dav'is has a land resource site that contains abandoned sewage evaporation ponds and experiences a daily summer electric demand peak. The concept of constructing salt grad'ient solar ponds in the abandoned sewage ponds and i nstal 1 i ng el ectri c power convers'ion equ'ipment to supp'ly peaki ng electric'ity offers benefits to both the city and to PG&E. Approximate'ly 170 acres of dry pond structures are available for conversion to solar ponds. For study purposes, the f ol I ow'ing power p'lant requi rements and conf i gu rati on desi gn gu'idel 'i nes were establ i shed:
(1) (2) (3) (4) (5) (6)
plant gross output - 300 kt,'l. 0perate plant 6 h/day from June thnough Powen
Septemben.
of existi ng di ke structunes. Develop a new water well for the waten supp'ly.
Maximum
use
Import sal t. Investigate the the pond linen.
sujtabjlity of using existing
gnound
clays fon
the Department of Enengy sponsorship, JPL'has been involved in othen s'imilar feasjb'if ity studjes; therefore, a s'ignificant data base and analytical capability were available to suppont this study. As a result, the Under
study included site visits, weather data comp'ilation, soil and water analyses, a materjal and equipment market survey, conceptual system design, generation of a conceptual site layout, and a preliminary cost estjmate. In addition to this contnacted effort, PG&E conducted sjte soil testings. Results will be available in a separate document. While conducting this study, a possible secondary appfication of supplying seasonal thenmal energy to a nearby HuntWesson tomato-pnocessing plant was suggested; howeven, time and funding I i m'i tatj ons prevented a detai 1 ed analysi s of thi s appl i cati on. The baseline power plan! configuration cons'ists of a 17,.l00 m2 U.22 acres) solar pond, d 4,050 mz (1 acr^e) evaporat'ion maintenance pond, a power statjon pad and water well (Figure 1-1). The solar pond'is 2.55 m (8.4 ft) deep, and the plant 'is entirely self-contained. The p'lant can operate at capacity from April to September (exceeding the design goa'l of June to Septemben). Gnoss output w'i1'l be 300 kW and net output will be 230 kW. 0ver a fu11 yean the plant w'ill deliver 0.3576 x l0o kWh of elec!rica1 energy to the grid. Altennat'ively, the solar-pond can supply 4.943 x lOb kwh of thermal energy at 85oC (.l85"F) or 7.34 x 10b kwh at 60'C (140'F) to a thermal load.
The estjmated total plant capital cost'is $2,.l42,000 (a summary breakdown 'is presented 'in Tabl e I ). Power pl ant equi pment i ncl udes the Ranki ne-cyc1e turbine generator, heat exchangers, and control subsystem. The transport and auxiliary subsystem includes the pipes and pumps to move hot brine and coo'l'ing water to the heat exchangers,'in-pond pipes and diffusers, pond ma'intenance equipment and control, and monitoring equipment.
I
N
.=
MAIItlTEIIIAiICE
POiln
:: .-= a=
i:
=:
=. aa
EX ,/'
a=/
POWER
STATIOil
REIITITORCED
DIKE
TRAK RAIIIGE
i
z?/idr'Il
ilrilrr rrr r llr\
I
i
I
=-122
Flgure 1. Site Layout for
a
TO DAVIS
m
300 kWe Solar pond Power Plant at Davis
2
the outset of the study, salt for the solar pond was recognjzed as be'ing a significant cost dniven. PG&E and JPL independently researched From
Table
l.
Cost Summary of Davis Solar Pond Powen Plant (4.2-Acre Pond, 300 kWe Installed Capacity)
Cost
Cost Items
(ie81$)
Management 100,000 Des'igns and Specifications 100,000 Power Plant Equ'ipment 536,000 Transport and Auxi f iary Subsystems 604,000 Pond Constructi on 236,000 Sal t 385,000 Li ner I Bl ,000 Total Capital Costs 2,142,000 Annual Operation and Maintenance Costs 73,000 Project
the market and found that forty dollars per deljvered ton was the best available price. This single element amounts to $385,000. The need for a syntheti c I'inelin the sol ar pond 'is uncertai n. PG&E conducted soil tests and found clay type sojls at the surface and below grade. JPL conducted laboratony tests on a sjng'le-sunface sample. The results of the tests showed that the surface clay was not sufficiently impermeable. Therefore, for purposes of this study, a Iiner has been'included. The question, however, remains open concenning the suitability of below-grade materials. The
optical quafity of the
underground water its use.
A high-perfonmance pond will result from
at
Davis
is
extremely good.
A 300-kW peaking plant and a 4.ZL-acne solar pond at Davis is clearly not cost effect'ive. The projected busbar electric enengy cost is 1,451 mills/kWh. If the pond is used to supply thermal energy for industrial pnocess use, the estimated thermal energy costs are $22.37 /ni I I ion Btu and $1 5.05/mi I l'ion Btu for temperatures of 85"C (185'F) and 60'C (140"F), respectively. System optim'ization to achjeve betten performance and clay substitution for the proposed syntheti c I'iner mi ght produce a 30% reducti on 'in busbar energy costs but cannot
make
the plant cost effect'ive. Several factors combine to produce these results:
(1)
The plant is small and achieves no economy of scale. The large cost elements related to the powen plant and transport equipment are strong'ly si ze-dependent. At the 300-kW I evel these costs nonmal 'i ze to $3800/kW 'instal I ed. From studi es rel ated to the Sal ton Sea exper'iment, power plant and transport system costs are $2240lkw installed for a 5-MW plant and $.l230/kW for a 600-MW p1ant.
(2)
The
plant has
been designed as a peaking unit, and the load facton is 181,. The same power conversjon unjt could run at a baseload level w'ith a 20- to Z5-acne solar pond and produce 5 times more
low:
energy per year.
(3)
The cost of salt and the synthetjc liner account for 26% of the total installed cost. This 'is an expense that a more favorable site,
e.9., the Salton
Sea
or south
San Francisco Bay, would
not incun.
electric energy cost could be realized by developing the potentia'l of the site w'ith a baseload power p1ant. To illustrate this potentia'l , an extrapolated est'imate of the costs for a 100 acre solar pond power plant at the site was made, and the results are summarized in Table 2. The nesults jndicate a busbar electric energy cost of 433 mi11s/kWh. In the futune, d lower-cost power conver"sion system might be developed that could also
full
Lower busbar
significantly Table
change
2.
the results of this study.
summary of an Alternate Davjs solar Pond power plant (100-acre Pond, 1.20 Ml,le Installed Capacity)
cost
Cost Items
Project
Cost (1981$) 500,000
Management
Design and Specificatjon
500,000
Power Conversjon, Transport and Aux'i 1 i any Subsystem
3,240,000
Pond Constructi on
I,337,000
Salt
7,485,000
Li ner
3
Total Capital
Costs
1
Annual Operation and Maintenance Costs Annual Power 0utput: Busbar Energy
Cost:
8.76 x 433
106
,793 ,000
6,855,000 400,000
kl^lh
mi I I s/kWh"
e
PART
TI.JO
SOLAR POND POWER PLANT FEASIBILITY STUDY FOR THE
CITY OF DAVIS, CALIFORNIA
1-1
SECTION
1
I NTRODUCT I ON
I.I
GENERAL BACKGROUND
The city of Davjs, California,'is a leader in energy conservation and energy management. Dav'is was the first c'ity in Cal'ifornja to inst'itute bu'il d'ing energy standards and conti nues to provi de j nnovati ve sol uti ons to energy consumption problems. The Pacjfjc Gas and Electric Company (PG&E) is very supportive of the efforts of Davis, and the ut'i1ity and the city at t'imes undertake cooperati ve projects. The climate of Davis is characterized by h'igh summer afternoon temperAs a result, air condjt'ion'ing'loads and electric energy demands are high from June to September. Electric power production using solan energy appears to have merit because solar energy avajlabil'ity will closely match
atures.
the load
demand.
One of the solar options that is be'ing examined for electric power production is the salt gradient solar pond (so1ar pond). Davjs owns appnox'imately .l70 acres of land along the city's nonthenn boundar"y. A hope exjsts f or devel opi ng a porti on of thi s area i nto an energy park . The s'ite cons'i sts which were formerly part of a sewage of predominantly dry evaporat'ion ponds,.l.52 treatment piant. The ponds are about m in depth and have a clay soil base.
The city of Dav'is, in pantnership with PG&E, commissioned the Jet Propulsion Laboratory (JPL) to conduct a small p'lant feasibility study. The study was constra'ined jn time and budget and therefore was l'imited in scope.
1.2
STUDY GUIDELINES AND OBJECTIVES
The study focuses on the cost and technical feasibility of construct'ing a solar pond power p'lant on the Davis site. The conceptual design is based upon "off the shelf" handwane, imported salt and maximum utilization of an existing pond structune. For study purposes the plant 'is designed to:
(1) (2) (3) (4) The
Develop 300 kW gross power output. 0penate fon a minjmum of 6 h/day from June to September. Prevent saline contaminatjon of the undengnound water system. Include a water well for the fresh waten supply.
specific object'ives of the study are to: (1) (2) (3) (4) (5)
Size the solar pond. Devel op a conceptual pov./er p1 ant desi gn.
Predict system performance. Est'imate total pl ant cost. Estimate a construction schedule.
1-3
A secondary objective was added to_the study to evaluate the possibjljty seasonal solar pond thermal energy ior a nearby Hunt-Wesson tomato-processi ng p1 ant.
of^ providing
L-4
SECTION 2 THE SOLAR POND
CONCEPT
A solar pond is a body of water that converts solar energy into thermal energy. Currently, research is being conducted to develop several classifications of ponds typically labeled "salt gradient," "saturated," "shallow" and "membrane. " Among these cl assi fi catj ons the sal t gradi ent pond 'i s recei vi ng the most attention because of its jnhenently large thermal storage capacity, potent'ia11y lowest cost and capabifity of coupling with electric power generation equipment. Fon these reasons, a salt gradient pond (hereafter referred to simply as pond or solar pond) is proposed for the Davjs appljcation.
In a normal body of water a portion of the solar radiant energy penetrates 'into the sub-layers. As the radjant energy passes through successjve layers, jt is gradually absorbed and causes the water to wanm. The wanming decreases the density and the waten rises, canrying with it the absorbed solar energy. At the surface the energy is lost to the atmosphene by nadiation, evaporation, and convection. Thus, the body of water remains cool. In a salt gradient solar pond density is made to increase with depth. This condjt'ion is ach'ieved with a high salt concentrat'ion at the bottom and a low concentration at the surface. l.lith a sufficiently high salt concentration or density, lower zone waters can absorb solan energy and yet remain denser than the waters immediately above. Convective curnents ane elim'inated; theref ore, the I ower zone waters rema'in i n pl ace and cont'inue to absorb sol a n energy. Tempenatures approach'ing 100'C (2I2"F) have been observed'in the bottom zone of working solar ponds.
of salt watet,2.5 to 5-m Salt gradient ponds ane typically large bodies.l.2 gravity is or greater while the bottom layer the deep. The specific of .l.0. js ponds, depending on size and depth, are maintained near The surface ther"efore, can and, energy amounts of thenmal capable of storing tremendous generation power basis. In electric on a continuous 24-h/day supply energy power load power p'lants with pond base-load deliver can applications solar meet levels to h'igh at output be openated 0.9, or they can factors of 0.8 to peak demands.
pond will have three distinct layers or zones: an 1ayer, a middle non-convective 1ayer, and a bottom stonage upper convective 1ayer. The upper convective layer, which has a very low uniform salt concentration, 'is 0."l5- to 0.3-m thick; it exists because of wind-induced m'ixing and diurnal effects of heating and cooling. The energy absorbed by the uppen layer is lost; therefore, efforts must be taken to minimize 'its thickness.
In practice a solar
'layer^, al so known as the gradi ent zone, 'is 1 .0 to I .3-m deep with salt concentration increas'ing with the depth (from less than 41. at the top to as high as 251. al the bottom). This zone is the key to the successful operation of a solar pond. It allows radiant energy to penetrate to the lower zone and acts as an'insulator between the bottom and upper layers, The non-convecti ve
a function s'imilar to the glazing layer of a flat plate co1lector. 2-r
The bottom, or storage, zone i s convecti ve w'ith a un j f orm h'i gh sal t con centratjon. This zone may be l- to 4-m deep, depending on the storage needs of a specific app'lication. The types of salt that can be used jn a solar pond include sodium ch1or.'ide, magnesium chloride, sodium carbonate, sodium sulfate and others. The basic requirement js high solubility and transparency. The amoun! of salt required for initjal start-up is 1arge, r'anging from S5b to 900 kg/m2 of pond anea.
During the normal operation of the pond, salt will gradually diffuse the bottom to the surface 1ayer. This action tends to degrade the salt gradient. In order to mainta'in the necessary salt gradient, the surface layen must be flushed wjth fresh or low salinity water from time to tjme. Meanwhile, high salinity brjne must be injected into the bottom layer to make up the salt loss. fnom
Figure 2-1
js a schematic diagnam of a solar pond power p1ant.
The solar
solar energy jnto thermal energy, and a Rankjne-cyc1e heat the thermal energy into shaft power that in turn produces an electric output. Cold water for condensing the organic fluid may be taken from the uppen convective zone of the pond or from any other convenient sounce. pond transforms eng'ine converts
A solar pond in a high insolation zone can achieve a work'ing stonage zone tempenature of 80 to 85'C (176 to 185oF) and a thenmal enerly coll6ctjon efficiency of 15 to 20%. The convension of the ther"mal energy to electric energy will be.|.0 8 to 9% efficjent and pnoduce an overall solan to electric efficiency of to 1.5%. Although the efficiency appears to be 1ow, a salt grad'ient solar pond electric power system can be economically viable because jt can be built from low cost materials and components.
Salt gradient solar
ponds have been
built
and put
into serv'ice'in
various
countnies of the wonld since the .l960s. The most notable ponds are located at Ejn Bokek on the Dea Sea in Israel, at Mjamisburg,0hio, and at Albuquerque, New Mexico. A large solar pond powen plant experiment is also being planned at the Salton Sea in Southern Caljfornja. The technology is ready for applica-
ti
ons.
2-2
CONDENSER
@
ETECTRICITY
COLD WATER
\\,i\... \ \, \ l. a. t\)
(,I
TURBINE
t\t\\\\ \\ \\ \\
PU'NP
\ \
Figure 2-1.
GENERATOR
EVAPORATOR
The Solar Pond Electric Power Generation Concept
SECTION
3
DESIGN, ENVIRONMENTAL AND OTHER CONSTRAINTS
3.1
DESIGN PARAMETERS AND CONSTRAINTS
The fol l owi ng des'ign pararneters and constra j nts were establ j shed f or" thi i nvesti gati on:
(1)
The solar pond and the evaporation pond are abandonded sewage tneatment ponds.
the existing
to make maximum
s
use of
(2) If possible, locally available clay materials shall be used as the
pond 1 i ni ng materi al .
(3) (4)
Al
I
nequi
red salt 'is to be imported.
Local ground water
pond.
is to be developed for fjlling
and maintaining the
(5) The plant will be designed to pnoduce as a mjnimum,300 output for 6 h/day from June to September.
kl^l gnoss
(6) The mechanjcal components will be off-the-shelf wher"e they are availab1e, sim'ilar to those used by 0rmat Turbines, Ltd. of Israel (Reference l).
3.2
(7)
Mechanical subsystem cost estjmates
SITE
ENVIRONMENTAL CHARACTERISTICS
3.2.1
Cl
imati
w'ill
be based upon Ormat equipment.
c Characteri sti cs
Pert'inent cl'imat'ic j nf ormati on 'is compi I ed and summari zed i n Tabl e 3-l . The data are mostly compiled from the recorded data for" the city of Davjs. Sacnamento data is used to fill data gaps.
3.2.2
Soi
I
Pnoperties
of on-s'ite materi al s i s desi rabl e 'in the constructi on of the ponds. The material must have the qualit'ies of (1) forming an impermeable pond ljnen to prevent seepage of brine and (2) not reacting with the hot brjne to genenate H25 gas, which could advensely affect the sal'inity gradient. Use
Prel'imi nary soi 1 characteri st'ics were determi ned f rom a I aboratory analysi s sample taken from the bottom surface at one location of one of the abandoned ponds. The results are reported in Appendix A. The results indjcate that (l) the surface soil does not have adequate sealing properties; it is more silt-l'ike than clay-like; and (2) there is no evidence that potential heatst'imulated, gas-produc'ing bio'logical activity exists.
of a soil
3-1
Table EVAPORATIONA PRECIPITATIONA MONTH
(,
m/s
x l0-9 m/s x l0-9
JAN.
12.69
35.4
FEB.
22.12
27.9
MAR.
39.20
20.6
APR.
62.1 I
t5.t
MAY
88.35
JUN.
05.32
5.0 .|.0
JUL.
10.89
0.1
AUG.
98..l 9
SEPT.
8l .40
0.5 .|.9
0cr.
52.27
9.4
NOV.
25.08
20.9
DEC.
12.32
29.6
AVERAGE
59.1 0
I
I
l\)
3.9
3-.l. Climatic Data for the City of Davis
t^lI NDb
t^lI NDb
AVE.
MAX
m/s
m/s
3.44 3.4 9 4.02 4.02 4.20 4.47 4. il 3.89 3.49 3.00 2.82 3.1 3
sRcnRurNTo ( 1959-->1978)
c
DAVIS (l
/57-12/76)
-
OC
AVE . TEMPA
"c
TEMP "C
AVE. REL. HUMIDITYA
ffiN
I NSOLC W/nZ
2.8
I I .7
7.3
85
70
84
22.90
4.7
I 5..I
9.9
79
6l
lt8
29.50
5.4
I I .7
68
51
187
20.12
7.4
2l .g
14.6
58
43
2s4
I 5.65
9.9
26.0
I
8.0
5t
36
305
21.01
12.6
30.2
21.4
47
31
332
6.09
14.2
33.8
24.0
47
28
333
I
6.99
t3.B
32.9
23.3
49
29
298
I
g.78
12.9
30.9
21
.9
5t
31
243
30.40
9.7
25.1
17
.4
57
39
3I.29
5.8
17
.6
1r .7
75
59
.29
3.5
il.8
7.6
84
70
75
22.9
I 5.7
63
46
209
.l
31
3.67
averaged over
TEMP
26.92
8.6
a DAVrS (5/26-11/7e)
b
AVE.MIN.b RVr.MAX.b
entire
day
.l7.8
.l68 ,l07
The Dav'is so'i1 sample failed, in the permeat'ion tests, to form an expanded with water, which'is characterist'ic of good sealing c'lays. Both water and brine permeated the mater'ial at a rate approximately 200 times as fast as the acceptable seepage rate recommended by Ormat, Ltd. (Reference 1). Not one of three tests of the Davi s so'i l sampl e f or pond-degrad'ing m j crobi al acti vi ty showed any signs of gassing. This is promising, and some optimism can be attached to the results since one of the tests was des'igned as worst case with maximum potential for hydrogen sulfide generation. ge1
the Davjs soil sample was obtained from the surface 1ayer, the test results cannot be consjdered conclusive. The clay from lowen l ayers shoul d be further tested to pnov'ide mone compl ete i nformat'ion on the applicability of the soil as lin'ing materjal. Because
permeation
3.2.3 Water Quality The transmission of fight through the upper convective and gnadient zone direct'ly affects the performance of a solan pond; therefore, concerns over the quality of waten jn solar pond application are majnly related to the quafity of optical transmiss'ivity. For this reason, a water sample from a water well at the proposed site was studied. The results are reported and discussed in Appendix A. In summary, (1), because the well water is excel'lent, no decolorization is cons'idered necessary although usual settling and filtration may be desirable; and (2) because the study does not conta'in the effects of salt, study of candjdate salt effects on light transm'iss'ion should be conducted jn
the future.
Figure 3-1 shows the water light absorptivity of Davis water, distilled water, and Salton sea water within the light wavelength of interest to solar pond application. In general, clear water absorbs very little Iight in the 400 to 700 nm nange. If the water is turbid, s'ignificant absorption will show up in this range. Whether or not dissolved absorbers are present, water absorbs consjderable light jn the range above 700 nm. Effects of dissolved substances are in the blue end,500-nm or lower, of the spectrum. These effects are clearly shown jn Figure 3-1 between Salton Sea waten and distilled water. The optical quality of the Davis waten, as can be seen,'is better than the treated Sal ton sea water and 'i s al most as good as the di st'i I I ed water.
3-3
5 cm PATH IEII|GTH
s
SATTOII SEA WATER, SETTTED
i60 (f (,
s I
-F
ce ct q, E
TREATED SAITON SEA WATER
DAVIS
40
WE[l, ilOT SETTIED
(al DAUIS WELL, SETTIED; (b} SYTUTHETIC SAITOIiI SEA WATER DISTIILED WATEB \.
\.r-
--.-_
500
WAVEIEJIIGTH, nm
Figure 3-1. Comparison of the Spectral Absorption
SECTION 4 SYSTEM CHARACTERISTICS
4.I THE BASELINE SYSTEM The selected baseline power plant
will deliver 300 kl,le gross output
for at least 6 h/day to meet the peak demands experienced by the city of Dav'is during the summer months. The system has no nedundent components because non-operating time is sufficient for repair ,and regular maintenance. of the basel i ne system. Its main subsystems are briefly described below. The physical plant and jts essential components will be described 'in mone detals jn Sectjon 5. Fi gur"e
4.i.1
4-1 shows a
f I ow di agram
The Solar Pond Complex
The
solar pond complex consists of a solar
pond 17,.l00 m2 G.22 acres)
in anea and 2.55 m deep, an evaporation pond of 4,050 mz (l acre) in size, and a power plant site. Pond area is measured at the gradient zone-stonage zone interface.
4.L.2 The Power"
Conversi on Subsystem
The power convers'ion subsystem i s a 300-kl^l organi c Ranki ne turbi ne system that contains the following essential components: an organ'ic Rankine turbine, a generator, a vaporizer (or boiler)'including a sepanator, a preheater, a
regenerator, a feed pump, a condenser and the connect'ing pipe 1jnes.
4.1.3 Tnansport and
Auxi 1 i ary Subsystems
Elements in th'is category include a hot brine 1oop, cooling water 1oop, fnesh water make-up line, brine make-up fine, solan pond blow down fine, water treatment facilities, and wave suppression system.
4.2
GENERAL SYSTEM OPERATION
The general operation of the power system is best exp'lained by following the flows shown in Figure 4-1. In steady state openation, hot bnine from the solar pond is pumped through the vaporizer and the preheater to transfer the thermal energy to the organ'ic work'ing f1u'id; it is then returned to the
storage 1 ayer.
In the vaporizer, the wonking f'luid of the powen cycle is vapon'ized at a modest pressune and directed to the turb'ine. Expansion through the tunbine produces shaft rotation to drive the genenaton. After expansion to a lower pressure, the vapor passes through the regenerator, rejects pant of its thermal energy, and then condenses into liquid'in the condenser. The feed pump sends the liqu'id to the regenerator for preheating before returning it to the vaporizer to complete the cyc1e.
4-1
TRAITSPORT
SUBSYSTEM
(THoSE tIoT E|ICL0SED ttrt DASHED UitEl
HOT BBIiIE IOOP
cotIvERstoit
+ AUXIIIARY
BBIiIE MAKE.UP
I suBsysTEM \y
sotAR
pot[D
PREHEATER
sI
N)
soLAB P0trtD
FEEDPUMP
GEilERAT(lRI
WATER TBEATMET{T FACTU.
TIES
L
MAKE.UP
cooumc WATEB t00P
Figure 4-1. The Proposed Davis Solar Pond Power Plant Flow Schematic
WATER
Under normal operating conditions, the cooling water loop c'irculates waten from the surface'layer of the solan pond through the condenser and back to the sunface layer. Intermittently, when the salt concentrat'ion of the surface layer reaches a critical level, the returned cool'ing water is flushed into tie evaporation pond through the flushing ljne. In order to make up the waten loss by flushing and evaporation, fresh make-up water is supplied from time to time through the cooling water 1oop. The fresh waten is'normally treated jn a water treatment fac'ility before it enters the systemWhen neceslary, the cooljng water fnom the surface layer can also be pumped through the waten tneatment facility before it goes to the condenser.
brine make-up 1ine nuns from the evaporat'ion pond to the hot brine l'ine for r"egular^ brine make-up to the storage layer of the solar pond. The
4.3
SYSTEM PERFORMANCE
Solar pond performance varies as a function of both design and openating spec'if i cati ons. In genera'l , a pond wi th a shal I ow thermal storage l ayer (iower convecting zone) will provide peak output during summer and,no output Ouring winter roiths. A pond with a langer thermal storage layer ()2 m) can provide a more constant level of power generation thnoughout the year. A performance analysis was made fon the baseline system. The pond supplies thermal energy to the power converison subsystem at a constant temperature of 85"C (185'F) fr"om April to September. The annual-average pond thermal and power planfi net electricaI outputs during the fourth_I9ar, of operation are 33.00 Wt/mz and 2.39 W./nt, respective'ly. For_a 17,.l00-ma (4.Zl-acre) solar pond, this represenls-an annual-average net plectrical output rate of 40.82 kwe (0.357b x lOb/kWh"/!r, or 4.9433 x l0o fwhl/Vr). The electnical output ahd storage zone temperature profiles are shown in F'igune 4-2, while the number of hours the plant operates per day is shown in Figure 4-3. Analysis of these profiles jndicates that the solar pond powen 6 h/day plint will producL a nominal 300 kwe (gross) .l0. output for at least f rom approxi mate'ly Apri 1 21 to September
thermal energy is extracted at 6Q'C (140'F), the annual averaged thermal energy outpgt will be 48.77 Wr/nt which amounts to an annual total output of 7.34 x 10o kWht.
If
pond at Davis will be from 105 to .l20 Wanm-up times for a 2.55-m deep solar days if heating begins at the spring equinox (March 21).
4-3
TIME FROM MARCH 21, days 500
100.0 CJ o
5. I 5.
A-
87.5
EI = F
75.0
CE
o
62.5
C\I s
50.0
a-
l+1sr YEAR ->l+
2nd YEAR
1
+l+
000
3rd YEAR
+l+
1
500
-----l 4th YEAR-->I
STORAGE TEMPERATURE
EIECTBICAI 0UTPUT
x
10
37.5
= F--
25.0
rr
12.5
rF
c- ,
0
MAB.
MAR.
MAR.
21
21
21
Figure 4-2.
MAR. 21
Solar Pond TemperaLure and Power Output Profiles
MAR. 21
TIME FROM MAB. 21, days
rl
(g
E L
ut s. I l.tl
l
