How to keep solar generators running at night

* Promises more effective thermal heat storage than current methods

* Company expects quick market penetration

* Says can match fossil fuel-fired power plants on price

NEGEV DESERT, Israel, Sept 22 (Reuters) – An Israeli solar power company, Brenmiller Energy, says it has developed a new, more efficient way to store heat from the sun that could give a boost to the thermal solar power industry by enabling plants to run at full capacity night and day.

By next year company founder Avi Brenmiller said he will have a 1.5 megawatt (MW), 15-acre (6-hectare) site in the Negev desert connected to Israel’s national grid, and a number of 10 to 20-MW pilots abroad are expected to follow, which will produce electricity at a price which competes with power from fossil-fuelled plants.

“A couple of years from now, not later than that, we will be putting full-size commercial plants to work. Because the basic technology we use here is a bankable technology … I’m sure that banks will not hesitate to finance such projects,” he said.

Many have tried to find ways to keep solar thermal power generators running after dark, but current solutions have shortcomings and have not always proven cost-effective.

The direct generation of electricity by photovoltaic (PV) solar panels is a far more common way to convert solar energy than by using solar heat to fuel thermal power plants, which take up more space and are not suitable for small-scale applications such as residential homes.

But a row of parabolic mirrors now tracks the sun at Brenmiller’s research site in the searing Negev desert, concentrating the rays to generate the steam needed to drive a turbine for producing electricity.

It is a technique that has been used for years but in addition to immediately generating steam some of the solar heat is also conducted by a fluid into a novel storage system buried beneath the mirrors which operates at 550 degrees Celsius.

This store can then be tapped at night or on cloudy days to keep the steam supply to the turbines flowing night and day, said Brenmiller, chief executive of Brenmiller Energy.

The innovation is in the cement-like medium that stores the heat, a technology that Brenmiller says is more efficient than other systems on the market, such as those using molten salt, which has severe price and operational drawbacks.

“We will have this technology at conventional fuel prices with the same availability around the clock. I think that’s the major breakthrough here,” he said from the control room of the project, which he called a working proof of concept.

Brenmiller was a co-founder and chief executive of Solel Solar, a producer of concentrated solar power fields which was bought by Siemens in 2009 for $418 million but subsequently closed by the German group last year.

He has already poured $20 million of his own money into the latest venture over the past two years.


Energy storage can be a key to bridging the gap between energy supply and demand across the globe, the International Energy Agency said in a report earlier this year.

The primary hurdle is reaching “grid parity”, or the point at which electricity generated from renewable energy sources costs the same as electricity produced by fossil-fuelled power plants. That is when, experts believe, environmentally friendly energy conversion can take off.

Grid parity has been achieved in some places with PV panels but while direct electrical energy storage is possible with batteries, they are still relatively expensive, use potentially toxic materials and cannot be applied on a large scale.

Meanwhile some thermal concentrated solar power (CSP) plants have introduced molten salt storage facilities that store excess heat for use in the night, like Torresol Energy’s Gemasolar plant in Spain, but while it works it cannot match the cost of burning fossil fuels and depends on subsidies.

There are also technical drawbacks to using molten salt. The salt stores the high temperatures in liquid form, but if the heat drops below about 220 degrees Celsius, it will freeze, potentially ruining parts of the system.

This is not an issue for Brenmiller, he said, as he uses a solid cement-like storage medium in a structure which is buried about two metres below the mirrors.

He would not give any details on the storage medium’s composition but said the system was similar to storage facilities under development called thermocline systems, which enable the heat to be conducted in, stored and conducted out again in a single tank, which is less costly than having to use two tanks to separate the hot and cold conducting fluids.

“In my understanding, there is no other technology like it in the world,” said Amit Mor, chief executive of Israel-based consulting and investment firm Eco Energy and a former energy adviser to the World Bank. “It can be very useful to developing countries and developed countries alike.”

An hour of sun produces enough energy to sustain three hours of equivalent electricity generation, Brenmiller said, and with every 24 hours of storage, 5 percent of the heat is lost.

It costs three times more to build than a conventional PV plant which can achieve grid parity during sunlight hours, but because it produces three times as much energy, the price of electricity is also at grid parity, he said.

In the United States and Israel, he expects electricity produced by the system to cost 12 cents per kilowatt hour, on a par with the average cost of grid electricity.

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