A garden of flowers that produce- rather than consume- energy sounds unreal, but that is the concept behind AORA's innovative solar plant.

Located in the Arava desert in Israel, a solar "garden" comprised of tulip-shaped sunlight collectors towering to more than 35 meters generates power by using ultra-high temperature concentrating solar power (CPS) technology.

AORA, a pioneer of distributed solar thermal technology(DST) based in Israel, set up their first solar "garden" in Kibbutz Samar in the south of Israel in 2009 on a 2300sq metersplot of land. Since it was first switched on four years ago, the plant of yellow tulips has been generating 100kw of power per hour for the grid. But that was only the beginning.

Recently, AORA set up shop in Spain's coastal city of Alemria, where it opened Europe's first gas turbine solar thermal power station in Platforma Solar Almeria (PSA). The station produces 100kw of electric power to the grid and 170kw of thermal power as byproduct, enough to provide energy to nearly 50 average households. In addition to production of electricity, the heat can also be used for cooling and desalination processes.

Credit: AORA

Flower-power

Facing each tulip from the ground are 50 solar panels that focus the sun's rays into the "bulb" of the flower made of solar receivers, where the air is heated to nearly 1,000 degrees Celsius. Fitted inside the "bulb" are 100kw gas turbines that turn thermal energy into electric energy.

AORA's smart hybrid operation system enables to continue producing energy even when sunlight in itself is insufficient. More specifically, the system can "run" on natural gas, diesel, bio gas, bio diesel and LPG as well as sunlight to ensure that energy supply is uninterrupted in any weather condition.

Air instead of water

AORA's solar system can operate in various locations and conditions "as long as it's not too hot and humid", says CEO Zev Rosenzweig. Unlike other solar power plants that use steam or oil when transferring energy from solar radiation to the turbine, AORA's smart system uses pressurized hot air. A compressor pressurizes the air by volume (e.g. one cubic meter). The amount of energy that can be transferred by the reflected solar heat depends on the mass of the air that is compressed and sent to the solar receiver. When the air is hot, its density decreases and after compression, the volume contains less mass. As a result, the energy transfer to the turbine is lower than when the air is cool.

To overcome this weather condition, a very fine water mist (in amounts much smaller than other solar systems) is sprayed into the air ahead of intake. When the mist evaporates, it takes the energy out of the air and leaves it more dense. However, if the relative humidity of the ambient air is too high, like in Dubai, where it can reach 98%, the system simply doesn't have enough "material" to work with. But these conditions are rare and are, therefore, not a setback for AORA's expansion plans.

Credit: AORA

Tulips all over the world

The plant in Spain is just the beginning of AORA's venturing outside of Israel. "Spain has the most developed program to support solar energy development and we were offered a position in a prestigious research park in Almeria", says Rosenzweig. But 2012 is looking to be the year when AORA's tulips will blossom all over the world.

A significant order of demo units of the system is headed to the USA and plans are currently being devised to set up sites in Latin America and Eastern Europe by the end of 2012.

Potential uses

Because they are scalable, small and do not require speciphic geographical conditions for set up, AORA's plants can be built near or around nature reserves, zoos or parks without causing environmental damage. Several small plants connected together can produce enough energy to power entire cities. Thet can also be used in the private sector.

Some of the uses discussed by AORA with potential private buyers include a mine in Cyprus that needs electricity and hot water, an industrial park in India that needs 24/7 power for its industries and power supply for a housing development in California consisting of 60-70 housing units based on high electrical usage.

Rising above the competition

The idea behind AORA's system, which was first conceived in the Weizmann Institute of Technology in Israel by Prof. Jacob Karni over 30 years ago, is to utilize the maximum of solar power as it travels through the air. It is achieved by building smaller plants where mirrors are all close to the collecting station.

The tulip system, despite not being the first or only solar power plant in the market, still manages to stand apart from the competition, and not only due to its unique design. Although Photovoltaic systems (PV) are also modular and price-wise may be cheaper, they do not provide utility grade power. As opposed to AORA, PV are not hybrid systems, so they can't work 24/7.

AORA's plants use considerably smaller amounts of water compared to CSP steam plants, which are also not scalable and provide non solar time power from storage that is very expensive.

Despite the fact that capital cost per megawatt for large scale CSP (without storage costs) is the same as for AORA, the latter uses less land, which means a smaller carbon footprint. "[AORA] can be financed in stages, making it easier to finance a $500 million plant for 100MW", says Rosenzweig.

An additional advantage of the AORA system is its flexibility in installation and repair. The amount of units to be purchased and installed by potential buyers is tailored to the needs of each buyer, since different uses will require different amounts of electricity. When it comes to repairs, only one unit is shut off each time instead of the entire plant, which means that power supply is not hindered.

Forecast: bright and sunny

Along with requests and orders coming in from the business sector, according to Rosenzweig, AORA has been receiving requests for plants from towns in Spain that wish to acquire their own generating capacity and towns in Mexico that expressed interest in their own plants following them being "subjected to load-shedding by national utility when demand is too high in New Mexico".

With more and more countries and communities discovering the importance of sustainability and the advantages of solar energy, it looks like AORA's tulips will soon be a part of many countries' landscapes.