08 November, 2018
How CSP’s Thermal Energy Storage Works
The hot storage tank at the 110 MW Crescent Dunes CSP power tower plant in Nevada
Here’s what captured sunlight looks like. This gigantic solar
thermal energy storage tank holds enough stored sunlight to generate 10
hours of stored solar power daily
The cheapest way to store solar
energy over many hours, such as the five to seven hour evening peak
found in more places around the world as solar PV adoption has grown, is
in thermal energy storage. Energy storage is a key to a renewable
energy-powered world. As the thermal form of solar, concentrated solar
power (CSP) is ideally suited to storing solar thermally.
There are several ways the various CSP
technologies receive the heated fluid to store thermal energy from the
sun, but once ready to store, a huge metal tank – like the one pictured
above – stores the hot liquid, whether in molten salts (at about 565°C)
for power tower CSP or in a heat transfer fluid (at about 400°C) for
parabolic trough CSP.
Think of this energy storage tank of
potential solar power as akin to the pile of coal outside an old coal
plant, or to the underground cavern full of natural gas waiting to be
burned up above ground in the nearby power plant.
The big difference is that in CSP this
stored “fuel” from the sun is reusable. Unlike the pile of coal or
cavern-full of natural gas, the heat-storing salts used in solar thermal
storage can be recycled daily within a tank like this for thirty or
Harvesting the solar for thermal energy storage
In tower CSP, a molten salt mix, like sodium nitrate
and potassium nitrate, is heated by reflecting sunlight with mirrors
onto a receiver atop a central tower that is encircled by a solar field
of flat mirrors (heliostats). This molten salt is cycled up the tower
“cold” at 260°C and is then heated by the focused sunlight aimed at the
receiver from the encircling solar field. Once heated, this now 565°C
molten salt flows down the tower where it can either be used right away
in the power block to generate electricity or be stored thermally in the
hot tank for use later.
In a parabolic trough type of CSP plant, the heat transfer fluid (HTF) –
which is usually an oil – is heated in pipes throughout the solar field
by reflecting focused sunlight on a narrow pipe that runs the length of
its reflecting trough-shaped mirrors (heliostats). This hot oil then
transfers solar-heat along bigger pipes to the power block where it can
either be used straight away or held in the holding tank storing thermal
energy until it is needed.
How the energy storage is used:
In both CSP technologies – power tower
and parabolic trough – when the thermal energy in the molten salt or the
HTF is ready to be used, it is sent to a heat exchanger. There its heat
is extracted and used to boil water to make steam to run a steam
turbine in a power block, like the earlier power plants that use up a
fuel, like natural gas, coal, or nuclear. Like the older thermal plants,
CSP generates electricity by rotating giant machinery.
With its heat extracted, the now
“cooler” molten salt is stored in a second tank ready to be sent up the
tower to be heated again by the sunlight reflected onto the receiver.
Similarly, in trough CSP, the hot oil,
once its heat has been extracted, is sent back out into the solar field
to retrieve the next round of heat and to bring it back to the power
block to be used again.
Molten salts lose only about 1 degree of
heat a day, so it is possible to store – and top up – this thermal
energy for months. Practically speaking, it is more profitable to use
the stored energy daily; to get paid for the daily and nightly
deliveries of electricity. But it is possible to size thermal solar
energy storage capacity relative to the solar field that harvests the
sunlight, so that it can be stored for months.
Molten salt thermal energy storage can
be heated and cooled daily for at least 30 years. At that point, the
tanks might need corrosion repair, so the molten salt would be cooled
off – a process that takes months – then emptied and then returned to
the tanks to supply another 30 or more years.
06 June, 2016
08 May, 2014
16 August, 2012
Date of Release: Thu, 08/16/2012 - 6:28pm
Author: Todd Hanson, Honeywell Sensing and Control (S&C), http://sensing.honeywell.com
For many facilities, the answer is a wireless network that connects the various remote switches and sensors with a centralized control infrastructure.
Industrial wireless networks, based on the IEEE 802.15.4 wireless standard, are very robust and reliable. Snow, rain, and dust storms all have minimal impact on its transmission range and reliability.
With a range of over 1000 feet (304 meters), 802.15.4 wireless networks provide excellent results in large open buildings and outdoor installations with a relatively open line-of-sight between switch and monitor. A 35 dB link margin ensures that minor obstacles or even intense precipitation will not compromise communications. Depending on composition, the signal can even penetrate intervening walls in some installations.
To ensure reliable operation and provide for almost limitless options for installation, 802.15.4 draws so little power that the switches can be operated by industry standard batteries rather than depending on un-reliable and expensive energy scavenging. With the proper design, a wireless switch should be able to operate for several years without a battery replacement or re-charging.
802.15.4 supports a simple star configuration network configuration with each switch in the network communicating to a.....