Molten Salt As Solar Heat Battery
by John Laumer, Philadelphia on 01. 3.08
United Technologies Corp.'s Hamilton Sundstrand unit, is teaming with US Renewables Group to commercialize a solar-power plant that will use molten salt to store the sun's heat and release it in a controlled manner for steady steam turbine power generation.
Hamilton Sundstrand officials say the solar-power business will be managed through a new entity called SolarReserve, which will hold the exclusive license to market and operate utility-scale solar-power plants world-wide. Under the agreement with US Renewables Group, Hamilton Sundstrand's Rocketdyne segment will provide heat-resistant pumps and other equipment, as well as the expertise in handling and storing salt that has been heated to more than 1,050 degrees Fahrenheit. The company says plants using this method will be able to generate as much as 500 megawatts of peak power or run continuously at 50 megawatts. One megawatt is enough power to supply about 1,000 U.S. households.
The salt system looks to be very efficient at heat storage. Potential issues are: 1,) the genius' at US Dept. of Homeland Security might regard the salt repositories as needing to be guarded from potential terrorists (potassium nitrate is a component of black powder); and 2.) concern trolls will point out that the commercially supplied nitrates are made from syngas produced either with natural gas or coal as feedstock.
...According to the company, molten salt loses only about 1% of its heat during a day, making it possible to store energy for long periods of time. The salt is a mixture of sodium and potassium nitrate.
Via::WSJ, Solar Venture Will Draw on Molten Salt; United Technologies, US Renewables Link Up For Clean-Fuel Project
Yep, it works great. We have the status quo who live for personal profit as our enemy.
Most of the molten salt research was done as a corollary to the nuclear program in the '60s and '70s. See the Molten Salt Handbook (1967) for probably the most comprehensive information on molten salts.
This method of heat storage is actually pretty old and works because molten salts have a very high heat capacity. Sodium and potassium nitrates work well because they have a much lower melting temperature than other salts. Salt peter is typically the optimal combination of potassium and sodium nitrates and I think you're overstating the risk of terrorism and the reactions of Homeland Security.
There are two or three main problems with molten salt heat storage. The first is freezing of the pipes which all require heat tape or another secondary heating method. The second is the development of very high temperature valves. Molten salt is also very corrosive so stainless steel is used for the tank and piping and it is prone to joint leakage. Like any chemical plant there would have to be some security and a constant staff.
This is the principle which the National Solar Thermal Test Facility operates at Sandia.
http://www.sandia.gov/Renewable_Energy/solarthermal/NSTTF/index2.htm
You can see it clearly on the right side of your plane when you fly into Albuquerque.
It would be interesting to try molten salt as an in house heat sink. This would work great with smart metering systems in cold countries. In the winter, you could heat your block of salt using cheap renewable energy when it's windy or sunny outside (and renewable energy is available) then use the molten salt to heat your house when electricity is more expensive.
I wonder if it would be possible to run the system in reverse in the summer, freeze the block of salt and cool the house with it when wind and solar isn't available.
This could work as a storage medium to even out energy flows from wind generators and solar photovoltaic.
BenE: I think this particular concept will only work at high temperatures for large scale installations. If the salt cools enough to solidify, then the entire system must be shut down until the solid blockage can be reheated and liquified.
A great deal of research was done in the '70s on phase changing or eutectic salts. Salt, like water becoming ice, has enormous energy capacities as it changes from a liquid to a solid. Some of these salts change phase near room temperatures, allowing them to act like batteries. So concepts and prototypes were installed in homes to test it out and they performed pretty well.
Problem was that the salts were expensive and had a number of associated hazards. So it wound up being more cost effective to use water or rocks and masonry as the storage medium and trade off the modest costs of more storage volume being needed.
But higher temperature salts are much less expensive, so when used on an industrial scale this could be a pretty exciting innovation.
@ BenE
This isn't really a very viable thermal battery for small scale applications . If you are using solar thermal, the point of contact of the beam has to be greater than 1000 deg F, which requires quite a few reflectors depending on the contact area. Otherwise you need a very high temperature heating coil (expensive) and are converting between 2 or more modes of energy transfer.
As soon as the salt freezes it is a very good insulator, so unless the salt can be maintained above it's fairly high melting temperature, it's not very useful since it will freeze on the heat exchanger. Since it is stored at such high temperatures you need really really good insulation, and even then the losses due to thermal gradient will be quite large. The molten salt thermal battery only really works efficiently at a large scale.
For small scale, using a heated water tank as a thermal battery is much more efficient and much less expensive since buying a whole bunch of salt peter is a fairly large investment and water is more or less free by comparison. There was a series of books published by MIT in the late 80s which details these methods, but I can't remember the titles right now.
Abe - and this is why all home-based solar thermal systems use a water tank for thermal storage. For direct use as domestic hot water, and also for indirect use in radiant floor heating.
I guess you'd call me a "concern troll," but molten salt is definitely a step in the right direction, if it is a step away from the toxins currently in many solar panels.
This is an example of Concentrated Solar Power (CSP) with Thermal Energy Storage (TES). The combination has the capability to turn solar energy into "baseload" generation. For example, startup Ausra has estimated it could generate 80% of California's electricity (daytime and nighttime) using CSP/TES at $0.067/kWh (and amazingly low price).
It would only take 3,600 sq. mi. of this to replace all gasoline in the U.S. It would take another 8,200 to 14,000 sq. miles to replace all electric power generation in the U.S. This is far more realistic than biofuels (the best of which take 7 to 40 times more land area than CSP/TES, and the more familiar of which take 100s of times more land area).
How does a system like this compare with a PE system in cost per watt? If you only counted when the sun is shining. I'd like to see a system like this tried in Hawaii.
We are investigating design/use of a CSP system for residential electric power generation & heat. Our selection decision for CSP heating technology is based on sun power, e.g. parabolic trough is generally considered to produce about 100x sun; tower technology [multiple mirrors focused on central tower] is generally considered to produce about 10,000 suns.
The objective is to use the smallest footprint CSP system to produce the most heat; store the heat for use as radiant heating, culinary hot water and low temp power generation.
For turbines, we like the design principal of the United Technologies PureCycle as it generates power using temps as low as 160F.
Installation http://www.yourownpower.com/Power/
PureCycle: http://www.utcpower.com/fs/com/bin/fs_com_Page/0,11491,0173,00.html
For storage, we're still scratching our heads; I suspect we're looking at a generator sized at 15-80kw. Size is dependent on multiple small systems = shorter plumbing runs, or one central system = longer plumbing runs.
The best solution would be 15kw systems installed on each home that use single or multiple parabolic dishes to generate heat; then store the heat for use as power generation & heat with the ability to switch as needs dictate. I wonder if we could circulate heated oil run into a salt storage system, or if the corrosive construction materials issues & cost of this type storage would offset the benefits of thermal storage?
Thermal storage will be key to generate sun-down power and cloudy day heat. I suspect we will use an oil based heat transfer fluid that will circulate from csp dish to storage, with separate closed loops running from a storage to the turbine and heating applications.
Any ideas on storage systems or other low temp power generation systems would be helpful. Actually, we would just appreciate any ideas =)
Thx Steve
snowberryridge@hotmail.com
www.snowberryridge.com
We are investigating design/use of a CSP system for residential electric power generation & heat. Our selection decision for CSP heating technology is based on sun power, e.g. parabolic trough is generally considered to produce about 100x sun; tower technology [multiple mirrors focused on central tower] is generally considered to produce about 10,000 suns.
The objective is to use the smallest footprint CSP system to produce the most heat; store the heat for use as radiant heating, culinary hot water and low temp power generation.
For turbines, we like the design principal of the United Technologies PureCycle as it generates power using temps as low as 160F.
Installation http://www.yourownpower.com/Power/
PureCycle: http://www.utcpower.com/fs/com/bin/fs_com_Page/0,11491,0173,00.html
For storage, we're still scratching our heads; I suspect we're looking at a generator sized at 15-80kw. Size is dependent on multiple small systems = shorter plumbing runs, or one central system = longer plumbing runs.
The best solution would be 15kw systems installed on each home that use single or multiple parabolic dishes to generate heat; then store the heat for use as power generation & heat with the ability to switch as needs dictate. I wonder if we could heated oil run into a salt storage system, or if the corrosive construction materials issues & cost of this type storage would offset the benefits of thermal storage?
Thermal storage will be key to generate sun-down power and cloudy day heat. I suspect we will use an oil based heat transfer fluid that will circulate from csp dish to storage, with separate closed loops running from a storage to the turbine and heating applications.
Any ideas on storage systems or other low temp power generation systems would be helpful. Actually, we would just appreciate any ideas =)
Thx Steve
snowberryridge@hotmail.com
www.snowberryridge.com