Tonopah NV solar plant generates power at night

Crescent Dunes CSP plant, Tonopah

The Crescent Dunes Concentrated Solar Power plant 200 miles northwest of Las Vegas in Tonopah is now coming online. Unlike photovoltaic, CSP solar plants can store energy and thus generate power at night. 10,347 tracking mirrors, each about the size of a billboard, reflect the sun’s heat to the Crescent Dunes central tower to heat molten salt which powers turbines. The molten salt can also be stored and used to power the turbines for ten hours at full load at night. Thus, so long as the sun has shone that day in the Nevada desert, which it usually has, Crescent Dunes can produce electricity at night.

The Tonopah plant is next-gen CSP. Dry cooling technology minimizes water use, since the water is in a closed system, converted to steam then back to water over and over. Other CSP plants can store power, however none can do it as for as long as Crescent Dunes. This could be a game changer.

The facility still isn’t fully operational, but Painter said it is now in the final stages of startup. By early next year, he expects it to be delivering full power to NV Energy, which has agreed to buy the plant’s entire load at 13.5 cents per kilowatt hour — roughly twice the cost of power from a natural-gas fueled plant — for 25 years.

“We’re stepping through territory that’s never been stepped through,” Painter said. “We’re just being very cautious of how we bring it online.”

Solar Reserve, based in Santa Monica, explains how their molten salt system works.

Molten salt is circulated through highly specialized piping in the receiver (heat exchanger) during the day, and held in storage tanks at night – requiring no fossil fuels.

The tanks store the salt at atmospheric pressure.

Use of molten salt for both heat transfer and thermal energy storage minimizes number of storage tanks and salt volumes needed.

Molten salt is stored at 1050F until electricity is needed – day or night, whether or not the sun is shining.

As electricity is needed, molten salt is dispatched from the hot tank through a heat exchanger to create super-heated steam which then powers a conventional steam turbine.

The molten salt never needs replacing or topping up for the entire 30+ year life of the plant.

Heat loss is only 1F per day.

The salt, an environmentally friendly mixture of sodium nitrate and potassium nitrate, is able to be utilized as high grade fertilizer when the plant is eventually decommissioned.


Ripasso solar power most efficient yet at 32% conversion

Ripasso Energy CSP

Ripasso Energy concentrated solar power focuses the heat of the sun to highly efficient, zero-emissions Stirling engines. A test site in the Kalahari desert has reliably produced energy for four years and achieved a world record solar-to-grid electricity conversion of 32% and, big added bonus, uses no water, a major concern in deserts. By contrast, traditional solar PV has achieved about 15% usable grid power, while other forms of concentrated solar use water to power steam turbines.

The technology works by using the mirrors as giant lenses that focus the sun’s energy to a tiny hot point, which in turn drives a zero-emission Stirling engine.

The Stirling engine was developed by Reverend Robert Stirling in Edinburgh in 1816 as an alternative to the steam engine. It uses alternate heating and cooling of an enclosed gas to drive pistons, which turn a flywheel.

Ripasso says competing with the ever-dropping costs of solar PV is crucial. Their biggest challenge was getting funding from skeptical banks, so they secured private funding instead. Solar power like this would be an ideal way to power desalination plants on the coasts in deserts, as well as homes.

Ripasso Energy

Concentrating solar needs molten salt energy storage to survive


Concentrating solar power creates electricity by using the heat of the sun. The heat generally is focused to a central tower or stored in tubes next to parabolic troughs, then used to power turbines, creating electricity. Solar PV is way cheaper than CSP. However CSP has a huge advantage that makes it competitive. Excess heat can be stored in molten salt, then used to generate power when the sun isn’t shining or at night. Specifically, CSP can be used as backup power for solar PV when the sun is setting and demand is generally at its highest.

A ginormous CSP plant in Tunisia will generate 2.5 GW, equal to that big coal and nuclear power plants, when built and send the power to Britain via high-voltage DC cable. The builders say the cost will be competitive although Bloomberg New Energy disagrees.

Contrary to Nur Energie’s estimations, Bloomberg New Energy Finance calculates that most solar thermal plants would need a power-purchase agreement in excess of $200 per megawatt-hour to be commercially viable.

This compares to just under $100 per megawatt-hour for PV “in a similar sunny location,” Chase said. “The only reason anyone would give you that premium is if you were supplying power that matched the demand of the grid you were feeding into better than PV does.”

And that is exactly what CSP does, it provides large amounts of power precisely at the time when solar PV can no longer do so. And this is the only reason it remains viable competition.

This is particularly the case in markets such as South Africa, where there is a need to meet evening demand peaks that PV cannot handle. South African regulators have approved at least half a dozen CSP plants with storage.

BLS explains how CSP works.

Although there are several different CSP technologies, they all involve reflecting sunlight onto a focal point that contains a heat-transfer material. The heat-transfer material, usually synthetic oil or molten salt, is collected in a heat storage unit and eventually used to create steam that powers conventional generators. One advantage of CSP is that at night or on extremely cloudy days, the conventional generators can be run on natural gas or petroleum, allowing the plant to continue to generate power when the sun is not shining.

That’s right. CSP is not completely renewable. The turbines can run off carbon fuel too. However, they are still way greener that say, a coal plant.

Philippines has 2,000 inhabited islands, struggles with power shortages


Electricity is expensive in Philippines, compounded by growing shortages. The government has responded by leasing more power, paying big customers to generate their own power (probably by diesel), yet these seem stopgap measures. With so many islands, distributed energy via rooftop solar could help substantially.

The power profile of the three major island groups is quite different. Visayas and Mindanao get half their power from renewable sources, geothermal and hydro respectively, while Luzon relies heavily on coal. Yet new growth for all three will mainly be coal. (Big hydro is controversial, some think big dams are so damaging they shouldn’t be classified as renewable. Yet, the power does indeed come from a non-carbon source.)

The three main island regions of Luzon, Visayas, and Mindanao each have distinct generation profiles. In the northern part of the country, Luzon’s capacity is mainly powered by fossil fuels, with anticipated capacity additions of more than 500 MW, most of which will be coal-fired. Visayas, in central Philippines, currently relies heavily on its geothermal resources, but has plans to add 300 MW of coal capacity by 2017. In the south, Mindanao relies heavily on its hydropower resources, with plans for both additional hydropower capacity and additional coal-fired generation to increase system reliability.

Their Secretary of Energy says rooftop solar actually cheaper than coal.

As a simple example, the cost of electricity from a coal plant can run up to P5.50 per kilowatt hour, plus P6.50 for distribution and transmission, which amounts to P12.00. If you install solar panels on your rooftop, you will only spend P9.00 per kilowatt hour for generation and no cost for distribution or transmission. This already saves you up to P3 per kilowatt hour.”

Let’s hope Philippines makes a big push towards rooftop solar.

Grid-scale solar growing fast, yet still quite small


Renewable energy, especially solar and wind, gets lots of attention, yet it still a tiny part of total power generation worldwide.

Large-scale solar PV grew a startling 40% in 2014, from 21.7 to 35.9 GW, an increase of 14.2 GW in just one year. The US has the most capacity at 9.3 GW, followed by China at 8.5. While this is certainly impressive growth, solar PV is still, globally speaking, a minor player.

In 2012, worldwide installed electricity was 5549 GW, the last year the US Energy Information Agency has data for. Thus, 35 GW is 0.06 of that total, less than 1%. The real percentage would be even smaller than that, since installed electrical has increased since 2012.

The World Coal Association, certainly not an unbiased source, says 41% of world power is generated from coal with the US at 45%.

California is a leader is renewable energy. This image, which is updated daily (PDF), shows how renewables in California are still a relatively small part of the mix. Renewable energy spikes during the day due to solar, then quickly drops off. ‘Imports’ is power coming in from other states. ‘Thermal’ is power from something being burned, specifically coal and natural gas. So, at the daylight peak, renewable energy in California is about 22% of total energy generated. This is impressive (and growing). However most other states (and  countries) lag way behind this. this.

California power production by type. 03/04/5
California power production by type. 03/04/5