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Israel Science & Technology:
Solar Energy Sector

by Professor David Faiman
Ben-Gurion National Solar Energy Center,
Jacob Blaustein Institute for Desert Research,
Ben-Gurion University of the Negev


Science & Technology: Table of Contents | Space Research | Biotechnology


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BACKGROUND

Israel is located at the geographic latitude of approximately 30 o N, where the annual incident solar irradiance is about 2000 kWh per sq.m. It has, however, no natural energy resources; all of the country's electric power and fuel are derived from imported coal and oil. At present, the electrical generating capacity of the country stands at about 6.5 GW, representing approximately 1 kW per capita; but this value has increased in recent years as the need for electricity, in all walks of life, has risen. In such a situation it is, therefore, not surprising that Israel has pioneered the use of solar energy. Furthermore, with large areas of desert (approximately 60% of the country), it is natural that extensive R&D should be underway in order to enable the Negev desert to provide substantial amounts of solar-derived power in the future.

CURRENT USAGE OF SOLAR ENERGY

Domestic Hot Water

Perhaps the most common manifestation of putting the sun to work in Israel are the solar water heaters that cover roof-tops all over the country. Typical domestic units consist of a 150 liter insulated storage tank and a 2 sq.m. flat panel. The latter collects solar radiation, heats the water and passes it to storage in a pumpless, gravity-driven loop. These systems operate at an annual average efficiency of approximately 50%. It is therefore easy to calculate that such a unit saves its owner some 2,000 kWh per year in electricity costs, raising the temperature of a tankful of water by approximately 30oC above its starting point on an average day - i.e. heating water to a temperature of about 50oC. This means that most days of the year there is no need to employ the electrical backup heating coil (which all storage tanks contain) in order to ensure that the water is warm enough for washing. Larger systems, usually pump- driven, are to be found on high-rise housing projects, on several kibbutzim and at a number of industrial plants around the country.

Passive Solar Space Heating

Although Israel is commonly perceived as being a "hot" country winters can be cold, particularly in Jerusalem and other highlands - including those in the Negev desert. However, the climate is ideal for employing so-called passive solar heating. Basically this means designing a house so that it can heat itself with winter sunshine but remain cool in summer. The alternative active form of solar space heating, which employs solar collectors, electric circulation pumps and heat storage, although much researched elsewhere in the world, is not cost-effective in Israel because of the relative brevity of the winter season. The basic ingredients for a passive solar house in Israel are: (1) A well-insulated building envelope; (2) sufficient thermal mass to smooth out large temperature swings and provide night storage; (3) an appropriate area of south-facing windows. Typical solar houses in the colder parts of the country might involve a wall structure comprising a 1 cm. thickness of plaster on the inner surface, followed by 10 cm. of solid concrete for thermal storage, then 5 cm. of polyurethane foam insulation and, finally, some finish, depending upon local building codes, to protect the insulation. The roof would include 10 cm. of polyurethane insulation and the total area of south-facing windows would amount to about 15% of the floor area. In warmer parts of the country proportionately smaller window areas are needed. All windows would be provided with exterior blinds for reducing the penetration of unwanted summer sunshine. The first passive solar house in Israel was constructed from sun-dried adobe bricks and is located on the Sde Boker campus of Ben-Gurion University. Since its completion in the late 1970s the basic principles of passive solar design have been widely adopted by architects all over the country.

Photovoltaic Rural Lighting

At the time of writing (1997) there is no manufacturing industry for photovoltaic (PV) cells in Israel. This fact, coupled with the still relatively high cost of PV cells, has resulted in a relative dearth of PV demonstration projects despite the ideal climatic conditions the country offers for this technology. One sector does exist, however, in which there has been a relatively high penetration of PV into the public perception and this is at rural bus stops. A number of private entrepreneurs import the relevant components and market (usually to local authorities) lighting units which comprise a PV panel, a storage battery, a low-power lamp and control electronics for protecting the battery. In this manner, solar power is used for lighting these bus stops during night hours.

INNOVATIVE SOLAR DEMONSTRATION PROJECTS

With the onset of the energy crisis of 1974 a number of innovative solar demonstration projects were undertaken by Israeli industry and the government. The two most prominent in the private sector were an electricity- generating solar pond at the Dead Sea and a solar industrial process heat system in the north-west Negev. In addition, the government established a large solar test- demonstration facility in the Negev.

Electric Power from Saline Solar Ponds

The basic idea involves a pond of saline water, about 2 m. in depth, which is artificially maintained so that the degree of its salinity (and consequent density) is higher at the bottom than at the surface. Absorption of solar radiation by the floor of the pond heats the lower depths of water which are prevented from rising by their high density relative to the upper layers. In such a situation the temperature of water at the bottom of the pond continues to rise and is found to attain temperatures close to 100oC. Furthermore, since the ponds are very large - one demonstration pond, at Beit Ha'aravah, is 250,000 sq.m. in area - this represents a huge amount of stored energy. The Ormat Corporation who pioneered such ponds developed a special low-temperature turbine which enables the hot pond water to convert an organic fluid to vapor and thus produce electricity. For the Beit Ha'aravah pond, a 5 MW turbine was built.

The thermodynamic efficiency of such a comparatively low-temperature power-producing system is of needs small, approximately 1% at best. Accordingly, one would expect such a pond to produce, on average, only about 570 kW of electrical power. A 5 MW turbine would therefore, at first glance, appear to be hopelessly optimistic. However, the unique feature of solar ponds, compared with all other solar technologies, is their built-in storage capacity. It takes several weeks until the pond temperature achieves a steady state at its lower depths, after which, provided one does not withdraw energy at an average rate that exceeds the nominal 570 kW on an annual basis, one can in fact achieve vastly greater power outputs for a few hours each day - typically during the morning and evening peak load periods. In effect one allows the pond to absorb solar energy during the day but only operates the turbine in the early morning and late afternoon hours. Ormat's organic fluid turbine has turned out to have such a long life-time, partly because it is a totally sealed unit, that such devices are to be found all over the world in situations where low-temperature heat sources are available and electric power is required.

Industrial Process Steam from Parabolic- Trough Solar Collectors

The second large, innovative, solar demonstration project was one involving the use of parabolic-trough reflectors for producing industrial process heat. This was a proof-of-concept project that Luz Corp. carried out at a potato-chip factory in Sha'ar Ha'negev. For this purpose, sun-tracking glass mirrors, curved so as to form long lines of reflecting troughs, concentrated the sun's light onto a central tube through which oil was pumped. The solar-heated oil, at temperatures in excess of 200o C, was then used to produce steam in order to provide for the process-heat needs of the plant. Similar solar collectors were subsequently employed by Luz in their much-celebrated, record-breaking, 12.5 MW electricity-generating power station at Dagget, California. With this inroad into electric power production successfully accomplished, Luz went on to construct six 30 MW power plants, employing a larger size solar collector unit and even two 80 MW power stations which involved a third generation of yet larger solar collector units. All of these electricity-generating power plants were built in California. Although the US plants are still fully operative, Luz went bankrupt before they were able to complete negotiations for a similar solar power station in their country of origin.

The Ben-Gurion National Solar Energy Center (BGNSEC)

In addition to investment in the two private-enterprise projects referred to above, the government of Israel established, in 1985, a national solar technologies test center at Sde Boker in the Negev desert. The original purpose of the center was to demonstrate, in a comparative manner, the various alternative solar technologies that appeared promising for large-scale power production. These included a then-current Luz solar oil-heating loop and a system of very large parabolic mirror troughs, which were designed to heat water directly to steam rather than via an intermediate oil-heating stage. Unfortunately, this system was never completed by Luz and stands at Sde Boker, today, as a monument to a commercial enterprise that came within a hair's-breadth of being able to generate large-scale solar power in a truly cost-competitive manner. In addition to the solar-thermal demonstration systems at Sde Boker a number of photovoltaic systems were installed in a manner that would enable them to feed into the electrical grid. In 1991 the government charged Ben-Gurion University with the task of converting the BGNSEC into a solar research facility. Today, under its new operators, research at the center covers a wide spectrum of topics. In addition to electric power production, photovoltaics are investigated both at the systems and the device (new materials) level, solar radiation is studied both from the energy and the environmental (UVB/ozone layer) viewpoints and a number of large-scale projects, both at Sde Boker (giant parabolic dish) and in other parts of the Negev (200 kW PV system at Kibbutz Samar), are at various stages of planning and execution.

SOLAR R&D IN ISRAEL

Solar research and development is being carried out at a number of universities and research institutes throughout the country.

The Negev Solar Radiation Survey was established by the Ministry of National Infrastructure in the 1980s in cooperation with Ben-Gurion University's BGNSEC and the Meteorological Service. The Survey documents solar radiation (and other pertinent meteorological parameters) from approximately 10 sites in the Negev, in order to identify appropriate locations for solar power stations of the future and provide a data base for their efficient design.

Photovoltaics, although having little if any industrial backing in Israel at present, does enjoy a modest degree of government support because this technology may form the basis of some of the power stations of the future. Innovative methods for producing silicon solar cells are being investigated at the Jerusalem College of Technology (high-efficiency, single crystal cells) and at Tel Aviv University (amorphous silicon thin layers). New thin-film materials are being investigated for potential PV use at Ben-Gurion University of the Negev (C60), at the Technion Israel Institute of Technology (CdTe) and at the Weizmann Institute of Science (WSe2).

Solar-thermal power, another candidate technology for future power stations, is under investigation at Ben-Gurion University (parabolic troughs and a parabolic dish) and at the Weizmann Institute (solar furnace and central receiver tower), the latter with the active participation of industry. The Ben-Gurion University dish, to be located at the BGNSEC, will be 400 sq.m. in area and capable of concentrating the sun's rays up to 10,000 times. This is orders of magnitude higher than the concentration available from linear reflectors such as parabolic troughs and will accordingly permit a wide range of new research avenues to be investigated. The Weizmann Institute Central Receiver Tower, on the other hand, consists of a field of 64 so-called "heliostat" mirrors, each of approximate area 50 sq.m. that re-direct the sun's rays to a boiler, or some other suitable receiver, mounted on a tower some 50 m. in height. The combined effect of so many mirror surfaces, when focused onto a relatively small central receiver, can obviously produce extremely high solar concentrations.

The Weizmann Institute tower should not, however, be confused with yet another tower concept that is under active development at the Technion. This idea involves pumping water to the top of a very high tower (1 km. or more) which would be located in a dry desert area. The water would evaporate and the down-draft created by falling, cooled, moist, air would then drive a special wind-turbine located within the tower. This, of course, is a secondary use of solar energy but one which, nevertheless, has intriguing possibilities.


Sources: Israeli Ministry of Foreign Affairs

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