配置储热系统的塔式光热电站顺应未来低碳发展的需要，并能实现24小时发电。粒子吸热器技术有可能降低塔式光热发电的成本，因为它可以将现有565°C的熔盐工质运行温度提高近一倍。
高温意味着高效。粒子吸热器能够与高效率的超临界二氧化碳和吸气式布雷顿动力循环相匹配，使太阳能在高温热化学过程中取代化石燃料，比如满足在800°C的温度下分解水以提取氢气或在1300℃下的喷气燃料中制造碳中性太阳能燃料。
Al-Ansary指出：“我们对沙子工质十分感兴趣，因为无论用量多大，你都无需考虑其成本问题。”一定程度上来说，一些材料，特别是工程粒子可能在初始投资中占据相当的比重。“当你需要数千吨工程粒子时，你可能需要投入较高的资金。”
一直以来，有很多清洁能源领域的创新性研究在实验室研究获得成功后，由于缺乏商业化试验而导致相关技术最终“流产”。然而粒子吸热器研究小组非常幸运，他们得到了沙特电力公司的支持，并可以积极开展相关工作。
与熔盐储热类似，沙子每天损失的能量不到其储存能量的1％，但是其温度几乎可以达到熔盐工质的两倍。Al-Ansary表示，这是其对粒子吸热器感兴趣的主要原因，同时他本人拥有15项专利，相关研究成果还在一些行业期刊上获得发布。
“熔盐工作温度限制在565°C左右。”他说，“但是，采用不同种类的粒子作为吸热介质，可以获得更高的温度，甚至高达1000°C。我们小组采用不同的围护结构设计，使用简单的砌筑材料和隔热性能良好的箱体，能够实现每天的热损失降低到1％以下。”
“事实上，沙特电力公司的部分工程师每天会和我们一起开展研究工作，并进行一定程度地调整。在我们的共同努力下，我们可以确保粒子吸热器的设计是成熟的。当我们进入第三阶段的工作时，其将完全实现商业化。”
另外，桑迪亚国家实验室建设的光热发电系统镜场面积更大，这对早期测试起着非常重要的作用。虽然位于利雅得的测试设备较小，但是其可以作为完整的发电系统（含换热器和燃气轮机系统）进行全流程演示。
与熔盐塔式光热发电系统不同，燃气电站利用热压缩空气进行发电，目前装机5MW的燃气电站已实现商业化应用。这种涡轮机已通过欧盟直接燃气加热接收器的测试。这种经过验证的设计与光热发电的粒子吸热器的设计概念相契合，只需在设计上进行些许更改。
正如Al-Ansary所述，这项研究从实验室规模到走向商业化是一个不寻常的过程，需要冷静与信心。尽管创新的清洁技术对于创造一个宜居的环境至关重要，但是要实现轻松的跨越绝非易事。“但是，幸运的是，我们获得了支持。”Al-Ansary补充道。
Particle Receivers to Get First Commercial Trial – in Saudi
Arabia
A new solar technology is twice as efficient, cutting the cost of
solar thermal energy, by raising operating temperatures to 1,000°C,
almost twice the 565°C molten salt temperature in current
concentrated solar power (CSP) tower plants.
For most innovative research in clean
energy, the dreaded “Valley of Death” after lab scale success is
the sad place where great innovations go to die for lack of
commercial trials.
But that will not be the case for
particle heating receiver (PHR) technology that was first
conceptualized at Sandia National Laboratories and is now being
researched worldwide.
PHR is cutting edge technology for
tower CSP, a form of solar that converts the sun’s heat to power.
CSP with thermal energy storage is an important key to powering a
carbon-constrained future, because its thermal storage enables
solar generation at any time of day or night.
There is an unobstructed path from
lab to commercialization for Hany Al-Ansary, Professor in
Mechanical Engineering at King Saud University (KSU) and
international collaborators investigating one alternative approach
using a red sand abundantly available near Riyadh in Saudi
Arabia.
The KSU approach relies on the sand
flowing through a cavity receiver in the tower, while other
promising approaches use different particles in free fall or in an
enclosed receiver.
Saudi Arabia will be first to commercialize particle receiver
technology
The Saudi Electricity Company is
funding and assisting with the research into using the red sand
approach for heat absorption in PHRs, and intends to enter the
planning phase of a commercial trial in 2018. This sort of
commercial support and trial is essential to developing
technologies.
Like molten salts, sand loses less
than 1% of its stored energy daily, but it can achieve a
temperature almost twice as high. This is the main reason for the
interest in particle receivers, according to Al-Ansary, who holds
15 patents and has published in peer-reviewed
journals.
“Molten salt is limited to around
565°C,” he said. “but depending on which type of particles, you can
get much higher temperatures, up to 1,000°C. Our group worked on
different containment structure designs, and with simple masonry
materials and a well-insulated tank, we reduced heat loss to under
1% per day, similar to molten salt.”
What is the advantage of particle receivers?
Tower CSP with thermal energy storage
is an important key to powering a carbon-constrained future,
because its thermal storage enables solar generation at any
time.
Particle receiver technology has the
potential to reduce the cost of tower CSP, because it can nearly
double today’s power tower temperatures, which top out in molten
salt technology at 565°C.
Researchers have investigated many
materials for the particles. The advantage of sand is cost. At 5
MW, this particle receiver design would cycle more than 2000 tons
of sand through its system.
“We’re excited about sand because it
doesn’t matter how much you need, the cost is almost nothing,” he
pointed out. At scale, some materials, particularly engineered
particles, could become a considerable fraction of initial costs.
“When you are talking about thousands of tons of an engineered
material, that can become prohibitive at some
point.”
Al-Ansary presented the paper on the
results of the red sand tests in particle receiver tower CSP at the
23rd SolarPACES Conference in Chile.
How the particle receiver works
At a 20 MW-electrical scale, the
receiver aperture would be about 10 meters wide by 10 meters tall
and sand would be fed from the hopper to fall in a curtain a few cm
thick through a 10 to 15 meter wide slot, exposing the sand
particles to the heat of 1000 suns of intensely focused sunlight
from a solar field of mirrors reflecting sunlight into the receiver
aperture.
Unlike the energy storage tanks in
molten salt CSP, the hot and cold storage tanks could be stacked
right inside the receiver tower along with the heat exchanger, so
there is much less pumping of storage material, reducing parasitic
costs.
For a 20 MW plant, the tower would be
about 150 meters tall and about 30 meters in diameter with the
storage tanks stacked vertically inside. The discharge point of the
cold tank would be about half way up the tower, “so we only need to
lift the particles from the middle to the top to heat
them.”
The sand particles never fall fast,
thanks to chevron-shaped obstacles that slow their descent, an
innovation previously tested at Sandia in the US by the
international research group. Without the obstacles, sand
accelerates to 5 or 6 meters per second, even in just a 1 meter
drop height.
The obstructed flow maintains a dense
curtain of particles everywhere in the receiver, so that all the
concentrated radiation is absorbed by the falling
particles.
With particles slowed by the
chevrons, Al-Ansary’s group got results of about 1,000°C in the lab
without the sand agglomerating, and even out in the field, attained
temperatures above 700°C.”
