Solar salt tower. Talk To A Human

Vast Solar’s fix for tank leaks that stymied the first Tower CSP

A thermal storage tank failure ended Concentrated Solar Power (CSP) development in the US. At the world’s first utility-scale Tower CSP project with storage, the molten salt thermal energy storage tank sprang a leak.

SolarReserve’s Crescent Dunes 110 MW project was the only Tower CSP with thermal energy storage among the first five commercial CSP projects deployed in the US.

[In Tower CSP, an array of heliostats is focused on a receiver atop a tower, generating much higher temperatures than the initial form of CSP; parabolic Trough. While Trough operates at a relatively low temperature of 400°C, Tower’s higher temperatures enable more efficient operation at closer to 600°C.]

Since its tank leak nearly ten years ago, SolarReserve, the developer of Crescent Dunes, could not land its global pipeline of permitted projects.

ACWA Power is now completing SolarReserve’s Redstone project in South Africa, Grupo Cerro is bidding SolarReserve tower projects in Chile; Likana and Copiapo and Vast Solar in Australia is currently building its own unique CSP plant at the Port Augusta site where SolarReserve was not able to complete financing on its Aurora Tower project.

And no new tower CSP with thermal energy storage was commercially bid in the US.

Sharing knowledge helps all CSP

Knowing what caused this tank failure is crucial, Vast Solar CTO Kurt Drewes told SolarPACES in a call from Australia. He believes that to advance CSP, the industry must share solutions in commercial plants.

“Few technical problems cannot be solved with simple communication. They’re social problems,” he commented. “If we all share our problems, ideas, and lessons learned, we can solve these. But it’s been very hard because everybody’s behind commercial curtains.”

In a call from Australia, he pointed out that sharing commercial knowledge on thermal energy storage is not just important for the future of Tower CSP but also impacts the development of other technologies. These include standalone electric-to-thermal grid storage, solar heat for industrial processes, and hot solar thermochemistry for producing hydrogen and hydrocarbons like jet fuel.

“This is because the core value proposition in CSP is the ability to store thermal energy,” he explained. “That’s fundamental, and that benefit is seen in all kinds of other system configurations. And so it’s in everybody’s interest that we get this right.”

The problem is not the higher temperatures of Tower CSP

After studying the issue, engineers at Vast Solar concluded that the problem was not so much the higher temperature of Tower CSP but rather a greater temperature differential and higher friction that occurs within the hot tank.

The firm shared its findings in a presentation at the SolarPACES conference, High-Temperature Salt Tank Buckling Failure, and Bruce Leslie – Abstract.

“It took a while for us to understand that the buckling failure is more of a function of temperature distribution than the actual temperature,” Drewes said.

“Because the primary data was that the thermal storage in parabolic trough plants is fine, but not in Tower at higher temperatures. And the first obvious answer is that the only thing that’s different is the temperature. But we have shown that it’s a temperature distribution that changes with respect to space and, importantly, time.”

“These are very large storage tanks; with very large diameters and, in proportion, very thin floors. The ratio between these two is extremely low with these very big tanks. Certain parts of the tanks are hotter and colder; process changes can cause that. So it’s really a temperature distribution problem. ”

From Vast Solar’s High-Temperature Salt Tank Buckling Failure, presented at the SolarPACES 2022 Conference

How It Operates

A Solar Power Tower consists of a large circular parabolic trough with a receiver at the focal point.

The mirrors FOCUS the Sun’s energy onto this receiver, heating heat-transfer fluid (molten salt) and generating high-temperature heat. The hot molten salt produces steam that immediately turns a turbine and produces electricity, just like how conventional power plants generate electricity.

The system requires no solid fuel, emits no air pollution, and uses virtually no water in its operations.

Solar Power Technology Pioneers

There are two pioneers in the use of solar power technology. These are Solar One and Solar Two.

Solar One

The first commercial solar power tower, which ran from 1982 to 1988, was Solar One. It was built in the Mojave Desert. Although it could store energy used for start-up in the morning, it was not efficient enough.

The system also stopped working when there were passing clouds or the fall of night.

Solar Two

Because of Solar One’s lack of efficiency, it was redesigned and modified to become Solar Two, completed in 1995. Solar One used oil as a heat-transfer material, but the redesigned Solar Two system used molten nitrate salt, which is more efficient in storing thermal energy and is non-toxic and non-flammable.

It was composed of 2,000 heliostats and a better storage system. Additionally, it had a tracking system so that the heliostats could follow the Sun with their mirrors.

The University of California, Davis utilized the Solar Two as a telescope to measure gamma rays hitting the atmosphere after its decommissioning. Solar One and Solar Two’s central were torn down in 2009.

Environmental Concerns

The Solar Power Tower system is free of greenhouse gas emissions, air pollution, and noise.

Although the Solar Power Tower itself creates no waste, its production can emit certain gasses such as carbon dioxide (CO2). contributing to global warming. Its construction may also require energy for materials processing, fabrication, transportation, and installation.

Second, the demand for water for these solar towers may be seen as an issue because a large volume of water is required to operate. To address this concern, research on alternative cooling technologies is being explored.

Finally, the use of these towers has harmful effects on birds. Birds that fly in the way of the focused rays of the Sun can be incinerated. Some reports claim that one bird dies every two minutes at power plants.

Advantages and Disadvantages of Solar Power Tower

Solar power towers pose both advantages and disadvantages.

Advantages

• Although Solar Power Towers rely on the Sun and its ability to power up towers depends on daylight, these plants can continue producing energy even when the Sun goes down.
• They produce electricity 24-hours a day, unlike conventional energy sources such as coal and oil, which are limited by supply and production costs.
• It does not require any fuel, only abundant and free sunlight.
• Solar Power Towers do not produce any harmful emissions or waste.

Disadvantages

• The Solar Power Tower system is currently the most expensive form of solar power.
• Its construction requires a vast area of land.
• Compared to Stirling systems. its efficiency is lesser.
• As the number of large mirrors increases, more support is needed for a rigid structure.
• The efficiency of the solar power tower system can be affected by the wind causing problems with the mirrors.

Some of Our Commercial Solar Projects

The timing is right.With the cost of commercial solar at a historical low and the federal and state incentives still high, the timing is perfect.

Investing in Solar will beat any mutual fund, stock or other low to mid-risk investment. An investment in solar will return between 10–15% per year over the life of the system, while being extremely low-risk as an investment.

Every 450 spent on solar will return 450.50 to reinvest in your business. Solar frees up expenses for reinvestment rather than costing you additional expenses as other capital projects would. And the money it saves you increases each year as the cost of power rises.

Quality Plating Case Study – 127.3kW

Quality Plating will save 450.8 million over the next 30 years with their solar array, which will pay for itself in less than 4 years.

Research annual usage to analyze energy usage, implement efficiency measures, and reduce demand charges.

Implement a three-step process to evaluate the current equipment, upgrade fixtures, and install new solar array on roof.

Improved efficiency in usage and demand to achieve Net Zero for power usage, and spend less annually than previous monthly power bills.

Across the Intermountain West, commercial solar panel installation is becoming increasingly popular – and not just among big corporations. Businesses of all types are reaping the benefits of photovoltaic power, saving thousands on electricity costs, enjoying an increased cash flow and seeing a speedy return on investment. Commercial solar projects generate good press, too, and since many people prefer to support environmentally conscious enterprises, going green can help a business grow.

Simply put, harnessing the power of the sun helps create a brighter future for businesses. The Intermountain Wind Solar team has extensive experience completing commercial solar panel installations for a wide range of companies and organizations in Utah, Idaho, Wyoming, Nevada and Oregon. Here are some of the businesses that are investing in solar energy:

• Agricultural Operations – Farms and ranches need electricity to operate machinery, to heat and cool buildings and to light up the property. After adopting photovoltaic power, energy is no longer such a substantial overhead expense.
• Convenience Stores Gas Stations – For these businesses, electricity is a major expense. Solar panel installation is a Smart investment, as PV systems help offset the costs of running the lights, coolers, freezers and gas pumps at all hours.
• Data Storage Centers – In order to maintain security and provide around-the-clock access to information, the servers at data centers need to be kept cool. And, many tech companies are turning to commercial solar for a reliable source of power.
• Hospitality-Related Businesses – Hotels, restaurants, theme parks, event venues and other businesses focused on leisure, recreation and tourism often face high electricity bills. Going solar is an effective solution, as it greatly reduces energy costs.
• Manufacturing Facilities – A massive amount of power is required to keep factory equipment, industrial lighting and HVAC systems up and running. To meet their energy needs and bring down operating costs, many manufacturers are installing solar panels.

,3%

According to the International Energy Agency (IEO 2017), consumption of energy from renewable energy sources (including CSP) will grow at 2.3% annually between 2015 and 2040. Today, there are currently more than 40 solar thermal power plants operating around the world, with another 20 either in the planning stage or under construction. They tend to be located in areas with high solar irradiance such as Spain, India, South Africa, China, Chile, Australia, Middle East North Africa region (MENA) and the southern United States.

Demonstration of Concentrated Solar Power (CSP) plants began operating as early as the 1980s. Since then, advances have been made in both collection and energy storage. The solar tower is one concentration technique that has been developed.

How does it work?

Solar Tower Concentration Technique 1. Sunlight is concentrated and directed from a large field of heliostats to a receiver on a 195 m (640 ft) tower2. Liquid salt from the cold salt tank is pumped through the receiver where it is heated to 566 °C (1050 °F)3. The heated salt from the receiver is stored in the hot salt tank4. Hot salt is pumped from the hot salt tank through a steam generator to create steam, which drives a steam turbine, generating electricity5. Cold salt at 288 °C (550 °F) flows back to the cold salt tank6. Condensed steam from the steam turbine is recirculated for reuse

The design utilises molten-salt as a heat transfer fluid. Mixtures of nitrate salts typically melt at or above 130 °C (268 °F). They are maintained as liquids at temperatures of 288 °C (550 °F) in an insulated storage tank. The liquid salts are then pumped through tubes in a solar receiver where the concentrated radiation heats them to temperatures up to 566 °C (1,050 °F). The hot liquid is then sent to a high-temperature storage tank. The hot tanks are also insulated and can store thermal energy for extended periods. Thermal Energy Storage (TES) is used to compensate for varying demand and ambient conditions. When required, molten-salt is pumped to a steam-generator to produce steam for driving conventional turbines and generators. TES represents a distinctive advantage over other large utility-scale, renewable energy sources and can in some circumstances eliminate the need for backup fuel for power generation.

During the summer of 2013, a molten-salt tower system in Spain continuously produced electricity 24 hours per day for 36 days – a first-time achievement.

Crescent Dunes

One operating plant of this type is Crescent Dunes. Located at Tonopah, Nevada in the desert north of Las Vegas, it has a net electrical generating capacity of 110 MW and ten hours of TES. This means that the plant is able to generate power under full load for up to ten hours during peak demand. The sun is reflected from over 10,000 heliostats that FOCUS energy to the receiver located at the top of a 200 m (640 ft) tower.

Each heliostat is made up of mirrored facets which add up to an area of 115.7 m 2 (1,245 ft 2 ). The total collection area is over 1.2 million m 2 (12 million ft 2 ). Commercial start-up began in 2015.

Since that time Crescent Dunes has produced over 173 GWh of electricity, and it is estimated to provide peak power for 75,000 homes. CSP with solar tower(s) and molten-salt is the design basis for new planned projects in South Africa, Australia and Nevada.

The 100 MW South African Redstone project will provide peak power to approximately 200,000 homes, and have a TES of 12 hours. A new, larger scale Nevada project will have a capacity of 2 GW (2,000 MW) with 10 solar towers.

Crescent Dunes, is located at Tonopah, Nevada in the desert north of Las Vegas. It has a net electrical generating capacity of 110 MW and ten hours of TES. This means that the plant is able to generate power under full load for up to ten hours during peak demand.

What about nickel?

The use of stainless steel and nickel alloys has made higher temperature systems viable, where handling molten-salts was previously a challenge. Designers and engineers have turned to nickel-based alloys such as UNS N06617, N06625 and N06230 for receiver tube applications due to their high-temperature strength sustained over long periods – known as creep resistance. These alloys remain stable at the operating temperatures primarily due to their high nickel content, and have high oxidation resistance as well.

Stainless steel Type 347H (S34709) is used for the high-temperature storage tanks.

This article was published originally in Nickel Magazine VOL 33, NO2., August 2018. Nickel and sustainability:Towards a circular economy

ABOUT THE AUTHOR

Consultant to the Nickel Institute

Bruce knows a little about many things. He worked formally for 13 years at the Nickel Institute on product stewardship and life cycle issues and another ten years as an occasional consultant and writer. Prior to the Institute he spent 23 years with Global Affairs Canada (foreign affairs) and Natural Resources Canada on the mining side. He is a social impact investor and serves on various boards. He has a thing about space exploration.