Polymers in Solar Energy Utilization - American Chemical Society

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Flexible Membrane Linings for Salt-Gradient Solar Ponds R A L P H M . WOODLEY Burke Rubber Company, 2250 South 10th Street, San Jose, CA 95112

Hypalon, chlorosulfonated polyethylene, exhibits very low weight gain in brine solutions, even at elevated temperature. Although Hypalon has excellent outdoor weatherability and is widely used as a pond liner, i t has not been recommended for continuous high-temperature (90 ºC and up) service. As a flexible membrane liner, Hypalon is used as an uncured compound, to give easy and reliable seams both in the factory and field. Maximum service temperature for continuous exposure is 50 ºC for potable water. However, Hypalon has been used successfully to line a salt gradient solar pond, withstanding heat on a continuous basis up to the boiling point (109 °C) without degradation. Laboratory testing confirms that the weight gain at 100 °C drops dramatically from distilled water through gradually increasing brine concentrations. A return to distilled water from brine resumes the weight pickup, indicating that the hot brine does not cure the sheet. A new low-swell industrial grade performs even better. This combination of easy seaming and repairs, outstanding weathering--fully exposed, and performance in high-temperature, high-concentration brine solutions makes Hypalon a prime candidate for lining salt-gradient solar ponds. Utilization of solar energy to meet a portion of the needs of today's high technology, energy-intensive society, has become a national priority. Most solar energy systems collect solar energy for immediate use, but do not have the capability of storing solar energy as well. This means that the solar energy is generated on an intermittent basis working while the sun is shining brightly, but not working at night, or as effectively on rainy or 0097-6156/8 3/0220-0195$06.00/0 © 1983 American Chemical Society Gebelein et al.; Polymers in Solar Energy Utilization ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


POLYMERS IN SOLAR ENERGY UTILIZATION

cloudy days. This u s u a l l y means t h a t t h e s o l a r energy source i s used w i t h a conventional backup - e s s e n t i a l l y duplicating the required capacity. Imagine, i f you w i l l , a s o l a r energy c o l l e c t o r t h a t simultaneously s t o r e s t h e c o l l e c t e d energy f o r use a t anytime - day or n i g h t , r a i n or s h i n e , summer or w i n t e r . This c o l l e c t o r / s t o r a g e system has no moving p a r t s , uses the cheapest m a t e r i a l s a v a i l a b l e , and r e q u i r e s very l i t t l e maintenance. W i s h f u l t h i n k i n g ? No - such a system does e x i s t , and i s being developed commercially. The most complicated t h i n g about the system i s i t s name - Non^convective S a l t Gradient S o l a r Pond, (Figure 1) I t i s simply a pond, three t o f i v e meters deep, o f almost any shape and volume. I t contains water p l u s a water s o l u b l e m a t e r i a l whose d e n s i t y increases w i t h c o n c e n t r a t i o n . There are three l a y e r s - the bottom being a uniform, dense s o l u t i o n t h a t s t o r e s the c o l l e c t e d heat. The center l a y e r i s a non^convecting composite of c o n s t a n t l y d i m i n i s h i n g c o n c e n t r a t i o n (and density) l a y e r s working up toward t h e s u r f a c e . The top l a y e r i s e s s e n t i a l l y f r e s h water, and i s kept as t h i n as p o s s i b l e . The sun's rays penetrate the upper and middle l a y e r s , warming the dense s o l u t i o n at the pond bottom. This bottom l a y e r expands and convects the warmer s o l u t i o n upward toward the s u r f a c e . This convection i s stopped by the gradient l a y e r , which remains l e s s dense than the heated s o l u t i o n below. The heat buildup continues at the pond bottom as long as the s o l a r i n s o l a t i o n continues, reaching temperatures as high as 100°C o r higher ( l i m i t e d only by the b o i l i n g p o i n t of the s o l u t i o n ) . Usable heat i s obtained by c i r c u l a t i n g t h e bottom storage l a y e r s o l u t i o n through some type of heat exchanger, then r e t u r n i n g i t to t h e storage l a y e r f o r reheating. (Figure 2) The s o l a r pond can be l o c a t e d anywhere, but e f f i c i e n c y d i c t a t e s an area of r e l a t i v e l y high s o l a r i n s o l a t i o n . Economics d i c t a t e s p r o x i m i t y to a cheap source o f s o l u t i o n m a t e r i a l ( u s u a l l y a s a l t ) . To minimize heat l o s s e s , t h e pond should be as c l o s e as p o s s i b l e to the p o i n t o f heat use. The Need f o r Pond L i n i n g s I n i t i a l p r o j e c t s of major s i z e have been proposed for t h e Great S a l t Lake, The S a l t o n Sea and Owens Lake i n the United States (as w e l l as at the Dead Sea i n I s r a e l ) . Cheap s a l t i s r e a d i l y a v a i l a b l e at these s i t e s , and there i s l i t t l e concern about s a l t contamina t i o n o f t h e l o c a l ground water. These p r o j e c t s w i l l

Gebelein et al.; Polymers in Solar Energy Utilization ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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Membrane Linings for Solar Ponds


Surface convecting layer Nonconvecting layer (increasing salt concentration with depth) Storage layer (constant salt concentration)

Figure 1. S a l t gradient s o l a r pond. (Reproduced w i t h permission from Réf. 1. Copyright 1980, S o l a r Energy Research I n s t i t u t e . )

Figure 2. S o l a r e l e c t r i c a l power. (Reproduced w i t h permission from Ref. 5 . Copyright 1 9 8 l , McGraw-Hill.)



POLYMERS IN

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probably not be l i n e d as there i s no economic j u s t i f i d e a t i o n or environmental n e c e s s i t y to mandate a l i n e r . Only i f those environmentally n o n ^ s e n s i t i v e s i t e s near n a t u r a l l y o c c u r r i n g s a l t y lakes develop methane or other gas bubbles, may a membrane l i n e r be needed r e g a r d l e s s . Test r e s u l t s i n d i c a t e that bubbles upset the gradient l a y e r . However, many s m a l l e r i n s t a l l a t i o n s of s a l t gradient s o l a r ponds w i l l be i n areas w i t h permeable s o i l s , or where the leakage of s a l t b r i n e i n t o the ground and water t a b l e would be an environmental d i s a s t e r . Impermeable l i n e r s w i l l be a "must" i n these areas. The Requirements f o r Impermeable L i n e r s S a l t gradient s o l a r ponds present s p e c i a l problems not f r e q u e n t l y encountered i n combination. They i n c l u d e : 1. Chemical r e s i s t a n c e to s a l t b r i n e ~ ranging from s a t u r a t e d s o l u t i o n s d i l u t i n g down to e s s e n t i a l l y f r e s h water. 2. Heat r e s i s t a n c e - s e r v i c e a b l e from f r e e z i n g or below, to over 100°C, 3. W e a t h e r a b i l i t y - r e s i s t a n t to UV and Ozone and capable of continuous outdoor exposure, 4. D u r a b i l i t y - cost e f f e c t i v e performance f o r twenty (20) years or more. 5. R e l i a b i l i t y - p i n - h o l e f r e e c o n s t r u c t i o n , r e s i s t a n c e to mechanical damage, delamination and b l i s t e r i n g , 6. R e p a i r a b i l i t y - easy to seam w i t h seams stronger than the parent sheet. Homogenous seams that do not r e q u i r e s p e c i a l equipment or s k i l l e d operators f o r f i e l d r e p a i r s . The l o c a t i o n of a s i z a b l e volume of s a l t b r i n e i n most areas presents a p o t e n t i a l f o r s e r i o u s contamination. Leakage of b r i n e from a damaged l i n e r can "poison" the s o i l and the ground water over a wide area, i f not promptly r e p a i r e d . Proper s e l e c t i o n of the impermeable l i n e r i s e s s e n t i a l t o wide-spread use of s a l t gradient s o l a r ponds. Candidate M a t e r i a l s f o r Impermeable Membranes Many of the l i n i n g m a t e r i a l s commonly used f o r l i q u i d storage cannot be used i n s a l t gradient s o l a r ponds. Compacted s o i l s , n a t i v e c l a y s , s o i l a d d i t i v e s or s o i l cement, s w e l l i n g c l a y s such as B e n t o n i t e , are not impermeable to high temperature s a t u r a t e d s a l t b r i n e s o l u t i o n s . Only the f l e x i b l e membrane l i n i n g m a t e r i a l s o f f e r the p o t e n t i a l f o r impermeability (zero leakage)



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to high temperature concentrated s a l t b r i n e s o l u t i o n s over long periods of storage time. F l e x i b l e membrane l i n e r s f o r ponds, p i t s , lagoons, canals and r e s e r v o i r s were introduced f o l l o w i n g World War I I . Many p l a s t i c s and rubbers have been used. Thermoplastics are r e a d i l y and r e l i a b l y seamed, but a r e u s u a l l y b u r i e d f o r p r o t e c t i o n against UV. Vulcanized or cured rubbers have good weathering f o r exposed s e r v i c e , but are not r e a d i l y seamed once they are cured. Thermop l a s t i c rubbers o f f e r good weathering i n a d d i t i o n t o easy seaming. They are u s u a l l y supported or r e i n f o r c e d w i t h an open-weave s c r i m encapsulated between two o r more p l i e s of rubber to improve t h e i r "green" s t r e n g t h . Examples of each group would i n c l u d e : Thermoplastics Polyethylene P o l y v i n y l Chloride Vulcanized Rubbers Butyl EPDM Thermoplastic Rubbers C h l o r i n a t e d Polyethylene C h l o r o s u l f o n a t e d Polyethylene There a r e many a l l o y s , blends and m o d i f i c a t i o n s o f the b a s i c m a t e r i a l s , as w e l l as new polymers that a r e c o n s t a n t l y being introduced. Time and t e s t i n g of t h e v a r i o u s candidates w i l l i d e n t i f y those m a t e r i a l s t h a t w i l l perform best. In 1970, DuPont introduced Hypalon 45, a thermop l a s t i c grade of c h l o r o s u l f o n a t e d polyethylene s y n t h e t i c rubber, f o r a p p l i c a t i o n s as a pond l i n e r m a t e r i a l . I t was one of the f i r s t t h e r m o p l a s t i c elastomers r e t a i n i n g easy s e a m a b i l i t y both i n the f a b r i c a t i o n p l a n t and i n the f i e l d , and possessing outstanding r e s i s t a n c e to outdoor weathering. L i n e r f i e l d performance under the a c t u a l c o n d i t i o n s of use i s t h e most r e l i a b l e i n d i c a t o r of s u i t a b i l i t y . S a l t gradient s o l a r pond technology has l a r g e l y been developed w i t h i n the l a s t f i v e (5) y e a r s . Very few commercial i n s t a l l a t i o n s e x i s t even today, so that l i t t l e comprehensive i n f o r m a t i o n about f l e x i b l e membrane l i n e r s has been developed. However, there i s a c l o s e l y r e l a t e d end use that o f f e r s extensive commercial background and experience. The i n i t i a l use of hypalon as a l i n e r f o r a s a l t g r a d i e n t s o l a r pond came about s t r i c t l y as an a c c i d e n t . For many y e a r s , the manufacturers and d i s t r i b u t o r s of propane and butane l i q u i f i e d gas, have used huge underground s a l t deposits t o provide storage f o r l i q u i d gas buildup during the summer. The gas i s withdrawn d u r i n g



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the w i n t e r season of peak demand to supplement production c a p a c i t y . These storage caverns are c a l l e d " s a l t domes" and are a l s o used f o r t h e s t r a t e g i c crude petroleum reserve storage program. (Figure 3) S a l t domes a r e formed by d r i l l i n g i n t o a s a l t d e p o s i t , then f l u s h i n g f r e s h water down the h o l e , which d i s s o l v e s the s a l t , c r e a t i n g a c a v i t y . When the proper s i z e and shape i s formed, t h e top i s sealed around the access pipe. The l i q u i f i e d gas ( o r crude o i l ) i s then pumped i n t o t h e cavern, d i s p l a c i n g the saturated b r i n e . The s a l t i t s e l f i s impermeable t o the gas o r o i l , and the underground storage cavern w i l l h o l d t h e l i q u i f i e d gas. Cheap storage i n an environmentally secure l o c a t i o n i s the end r e s u l t . (Figure 4) To r e t r i e v e the s t o r e d product, the process i s reversed. Saturated b r i n e i s pumped i n t o the cavern and the d i s p l a c e d l i q u i f i e d gas i s withdrawn. Saturated b r i n e must be used, as f r e s h water only makes the h o l e b i g g e r , r a t h e r than merely d i s p l a c i n g t h e product. Therefore, a working s a l t dome must provide ( g a l l o n f o r g a l l o n ) surface storage f o r saturated b r i n e . These b r i n e p i t s are slowly f i l l e d w i t h b r i n e as i t i s d i s p l a c e d by the l i q u i f i e d gas during the summer, and s l o w l y emptied during the winter t o r e t r i e v e the product. These b r i n e p i t s a r e u s u a l l y l i n e d w i t h a f l e x i b l e membrane l i n e r to prevent wide-spread s a l t contamination of the ground and ground-water, as w e l l as t o prevent l o s s of the s a t u r a t e d b r i n e , needed f o r recovery. Review of I n s t a l l a t i o n s Using F l e x i b l e Membrane L i n e r s Hypalon has been a m a t e r i a l of choice f o r years as a b r i n e p i t l i n e r - p r o v i d i n g e x c e l l e n t r e s i s t a n c e t o the concentrated b r i n e s and weathering w e l l , i n s p i t e of the wide l e v e l f l u c t u a t i o n s of b r i n e s t o r e d from Winter t o Summer. Normally t h e b r i n e i s r e c i r c u l a t e d to maintain a saturated s o l u t i o n a v a i l a b l e f o r displacement. O c c a s i o n a l l y , however, an unexpected r a i n f a l l can deposit a l a y e r of f r e s h water on top of the b r i n e . An example follows : In e a r l y 1976, we i n s t a l l e d a Hypalon membrane l i n e r f o r the storage o f saturated b r i n e at an A r i z o n a gas t e r m i n a l . The t e r m i n a l i s l o c a t e d above a s a l t dome used to store l i q u i f i e d butane and propane during the summer months, which i s withdrawn during the peak use of the w i n t e r months. The pond measures approximately 405 χ 580 χ 40 f e e t deep and holds s a t u r a t e d s a l t b r i n e to d i s p l a c e the l i q u i f i e d gas f o r withdrawal. During t h e f i r s t summer of o p e r a t i o n , the


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Figure 3.

S a l t dome storage.


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Figure k. Major s a l t deposits i n the U n i t e d States and Canada. (Reproduced from Ref. 1. Copyright 19Ô0, S o l a r Energy Research Institute.)



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c i r c u l a t i n g pump broke down and was out o f s e r v i c e f o r over 6 weeks. A r a r e summer r a i n deposited a l a y e r of f r e s h water on top of the b r i n e . Upon s t a r t - u p of the r e p a i r e d pump, the housing grew so hot that the operator dragged a thermometer across t h e bottom of the pond, measuring 190°F. I n a d v e r t e n t l y , they had formed a s a l t gradient l a y e r preventing convection and a l l o w i n g the bottom temperatures to b u i l d . While i t was not p o s s i b l e t o inspect the bottom a t the time, we i n s t a l l e d an i d e n t i c a l pond adjacent t o the f i r s t one the f o l l o w i n g s p r i n g . The f i r s t pond was drained t o i n s t a l l an e q u a l i z a t i o n pipe between the two ponds. The Hypalon, although s l i g h t l y puckered from the heat, was i n e x c e l l e n t p h y s i c a l shape, and we were a b l e to bond a shroud over t h e e q u a l i z e r p i p e without d i f f i c u l t y , using Hypalon adhesive. ( I f the m a t e r i a l had been completely cured by the hot b r i n e , t h i s would not have been p o s s i b l e ) . Both ponds are s t i l l i n a c t i v e s e r v i c e , and have performed w e l l f o r over 5 years. The t e r m i n a l i s l o c a t e d i n the middle of farming lands, where s a l t leakage would have had s e r i o u s e f f e c t s . No contamination problems have occurred i n v o l v i n g the Hypalon-lined b r i n e ponds. The Hypalon l i n e r had performed w e l l under the temperature c o n d i t i o n s a c c i d e n t a l l y imposed upon i t , which were f a r above the recommended operating range. At about the same time, one o f the f i r s t s a l t gradient s o l a r ponds was being constructed and put i n t o o p e r a t i o n a t the U n i v e r s i t y o f New Mexico i n Albuquerque. Constructed i n l a t e 1975, i t used a 5 p l y Hypalon l i n e r of 45 m i l thickness t o l i n e a s m a l l , c i r c u l a r pond of approximately 60,000 gallons c a p a c i t y . During the summer of 1977, i t exceeded 90°C f o r the f i r s t time. I t peaked above 90°C again i n 1978 and 1979, and reached 109°C i n J u l y , 1980. The pond i s s t i l l o p e r a t i o n a l and b e i n g monitored, so we have not been able t o i n s p e c t the Hypalon l i n e r - but i t i s s t i l l f u n c t i o n i n g without leakage a f t e r s i x years of s e r v i c e , and there are no apparent signs of any degradation. (Figure 5) Test Data on Hypalon Performance i n S a l t Brines In an e f f o r t t o confirm the performance of Hypalon l i n e r s i n concentrated b r i n e s o l u t i o n s at h i g h temperat u r e s , immersion t e s t s were s e t up. Potable grade Hypalon, which was used i n the b r i n e p i t s as w e l l as i n the New Mexico s a l t gradient pond was compared to a new grade of Hypalon - i n d u s t r i a l grade, which shows l e s s water s w e l l at e l e v a t e d temperatures. Both m a t e r i a l s were t e s t e d i n d i s t i l l e d water as a c o n t r o l and i n 20%



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NaCl s o l u t i o n f o r 30 days @ 212°F. Results confirm that Hypalon shows much lower weight gains i n b r i n e than i n d i s t i l l e d water even a t e l e v a t e d temperatures (212°F). (Figure 6) Performance of i n d u s t r i a l grade Hypalon i s s u p e r i o r ( l e s s weight gain) t o that of potable grade, and i n d u s t r i a l grade i s recommended f o r s a l t gradient ponds, as p o t a b i l i t y i s not a c o n s i d e r a t i o n . (Figure 7) A d d i t i o n a l t e s t i n g a t v a r y i n g s a l t b r i n e concentrat i o n s i n d i c a t e s that any s a l t c o n c e n t r a t i o n above 1-1/2% e x h i b i t s the low s w e l l e f f e c t s on Hypalon. Only the surface l a y e r s of a s a l t gradient pond, which remain c o o l , do not i n h i b i t absorption. A low b r i n e concentrat i o n at h i g h temperature cannot occur i n a s a l t gradient pond. (Figure 8) The " p i c k l i n g " e f f e c t s of h i g h temperature b r i n e on Hypalon are not permanent or i r r e v e r s i b l e . Samples showing low weight gain a f t e r 30 days @ 212°F i n 20% NaCl s o l u t i o n s , showed t y p i c a l increases when t r a n s f e r r e d to d i s t i l l e d water a t 212°F. A l s o , the f a c t that the Hypalon exposed to hot b r i n e over long periods can s t i l l be seamed o r patched, i n d i c a t e s that c u r i n g of the Hypalon does not take p l a c e . (Figure 9) The Future f o r F l e x i b l e Membrane L i n e r s i n S a l t Gradient Solar Ponds The non-convective s a l t gradient s o l a r pond w i l l not v a p o r i z e metals, f l a s h steam or power your c a r or watch. I t s advantages are s i g n i f i c a n t , however: 1. S i m p l i c i t y - no moving p a r t s , except f o r heat exchanger. 2. C o l l e c t i o n plus storage - constant output possible. 3. Inexpensive m a t e r i a l s - s a l t , water, l i n e d hole-in-the-ground. 4. Provides heat f o r hot a i r , hot water, power. Its 1. 2. 3. 4.

drawbacks must be considered, as w e l l : Not p o r t a b l e . Large dedicated area r e q u i r e d - r u r a l . L o c a t i o n - near raw m a t e r i a l s . P o l l u t i o n p o t e n t i a l - i n many areas.

The use of an impermeable f l e x i b l e membrane l i n e r w i l l allow s a l t gradient s o l a r ponds t o be l o c a t e d near the energy user, by p r e v e n t i n g s a l t contamination o f the s o i l and ground water. The lessons learned i n the pond, p i t , lagoon and r e s e r v o i r f i e l d over the past 10-25 years must be understood and a p p l i e d . Design and c o n s t r u c t i o n


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F i g u r e 6.

Percent b r i n e i n i n d u s t r i a l Hypalon.




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Figure 7·

EXPOSURE

Percent b r i n e i n potable Hypalon.


207

208


Surface convecting layer Nonconvecting layer (increasing salt concentration with depth) Storage layer (constant salt concentration)


F i g u r e 8 . Temperature g r a d i e n t . (Reproduced w i t h permission from Réf. 1. Copyright 1980, S o l a r Energy Research I n s t i t u t e . )

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DISTILLED WATER SAMPLES: 30 DAYS / BRINE SAMPLES: 30 DAYS / FOLLOWED BY : 30 DAYS / DISTILLED

212 F 212 F 212 F WATER

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DISTILLED 15% NaCl BRINE WATER BRINE SAMPLE IN DISTILLED WATER

DISTILLED WATER

POTABLE GRADE HYPALON

Figure 9.

Brine/water

15% NaCl BRINE

BRINE SAMPLE IN DISTILLED WATER

INDUSTRIAL QRADE HYPALON

effects.



WOODLEY


of the pond, i n c l u d i n g s o i l s compaction, slope s t a b i l i t y , s o i l t e s t i n g and other p r e - i n s t a l l a t i o n c o n s i d e r a t i o n s are mandatory. I t must be remembered that the membrane l i n i n g i s not designed as a s t r u c t t u r a l member. I t s impermeability i s only e f f e c t i v e i f the t h i n sheet i s seamed c o r r e c t l y , i n s t a l l e d c o r r e c t l y and i s not r i p p e d , punctured or otherwise overstressed during i n s t a l l a t i o n or o p e r a t i o n . L i n i n g m a t e r i a l s , such as Hypalon, have the c h a r a c t e r i s t i c s needed f o r long s e r v i c e l i f e i n the proper s e t t i n g . The environmental r i s k s may be reduced i f current research on the use of f e r t i l i z e r s o l u t i o n s i n p l a c e of s a l t s o l u t i o n s f o r non-convective gradient type s o l a r ponds i s s u c c e s s f u l . Even though the raw m a t e r i a l costs are h i g h e r , reduced environmental e f f e c t s of a major leak i n a farming area o f f e r a great i n c e n t i v e f o r f u r t h e r development. T e s t i n g i s c u r r e n t l y underway at The U n i v e r s i t y of New Mexico u t i l i z i n g a s o l u t i o n of potassium n i t r a t e as the b r i n e . Although more expensive than sodium c h l o r i d e , the s o l u t i o n s of potassium n i t r a t e tend to be s e l f - s t r a t i f y i n g , making i t e a s i e r to develop and maintain the gradient l a y e r . A l s o , i f the s o l u t i o n was r e l e a s e d i n t o the ground through an a c c i d e n t a l rupture of the l i n e r , no s e r i o u s con*tamination of surrounding farm lands would occur. Without r e l i a b l e membrane l i n e r s , only the areas of b r a c k i s h water or b r i n e w i l l be acceptable f o r s a l t gradient ponds. In summary, s a l t gradient s o l a r ponds o f f e r great promise as a means of c o l l e c t i n g and s t o r i n g the s u n s energy. Although not a high-temperature c o l l e c t o r , the s a l t gradient pond can f u r n i s h heat and/or power, u t i l i z i n g a Rankine Cycle engine w i t h a s u i t a b l e l o w - b o i l i n g organic l i q u i d . The s o l a r pond provides both the hot b r i n e f o r the evaporation and the c o o l surface water f o r the condenser. The s e l e c t i o n of a l i n i n g m a t e r i a l i s most important. Leaks cause l o s s of b r i n e , l o s s of heat, loss of i n s u l a t i o n , and are p o t e n t i a l environmental p o l l u t a n t s . The w e l l documented h i s t o r y of the use of c h l o r o s u l f o n a t e d polyethylene f o r long term outdoor storage of s a t u r a t e d b r i n e s o l u t i o n s makes i t an e x c e l l e n t candidate. 1



210


Literature Cited 1.

Jayadev, T.S.; Edesess, Μ., "Solar Ponds", Solar Energy Research Institute SERI/TR-731-587, April, 1980.

2.

Weeks, D.D.; Long, S.M., Emery, R.E. and Bryant, H.C., "What Happens When a Solar Pond Boils?" Southwest Regional Conference for Astonomy and Astrophysics.

3.

Zangandro, F . , "Observation and Analysis of a Full-Scale Experimental Salt Gradient Solar Pond", Doctorate Thesis, University of New Mexico, May, 1979.

4.

Bryant, H. C., personal communication.

5.

Power, Vol. 125, No. 6, McGraw-Hill, 198l.

RECEIVED

November 22,

1982


Polymers in Solar Energy Utilization - American Chemical Society

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