Apple Looks For New Renewable Energy Procurement Methods
According to this article by Renewable Energy World’s Meg Cichon, Apple is replacing a great deal of the energy it consumes with renewables. That’s hardly shocking; the company’s entire brand is built around living harmoniously with its customers. What surprised me is a) that they have apparently patented a proprietary form of energy storage (an area far outside of their core business), and b) the description of this patent sounds extremely inefficient. Check this out:
Apparently Apple is not settling with its current renewable procurement methods. This week, Apple Insider reported a wind energy storage patent that the company hopes will help mitigate renewable energy intermittency issues. The patent describes the technology as converting the friction from rotating turbine blades into heat. This heat is then stored in a “low-heat-capacity” fluid, such as mercury or ethanol. When wind is at a lull and more energy is necessary, the stored heat can then be transferred to a “working fluid” that is brought to a boil to create steam. The steam is then directed to a turbine that is connected to a generator.
You have inefficiencies in generating the heat, storing it, and transferring it, all the while bumping up against the Carnot limit. My strength isn’t thermodynamics, but this sounds like a mess to me. Maybe I’m wrong, but the way I read this, by the time you get finished, you’re not going to have enough heat left to take a warm bath. Perhaps one of the Dotys (or some other senior scientist) could comment.
I would say you are not wrong!
If you make heat using excess power then it is usually best to use it as heat – space heating, hot water, and in the hotter regions to run a heat pump chilling a large tank of slush ice / salt mix to run the air conditioning for the next few days. (Preferably using both the hot and cold sides of the heat pump simultaneously)
This thermal storage system need not be at the site of the wind farm, and can be used to firm up power production from wind and make use of excess production. Thermal load with storage can be switched on or off at any time, or throttled to balance supply and demand.
This strategy will lop off a large part of peak demand by moving heating and chilling loads to low demand times – greatly reducing the need to have peaking plant and large spinning reserves, and cutting the grid associated costs of large scale wind power.
Notes on thermal storage –
Either hot water or slush ice is suited to holding around 60 kWh(thermal) per thousand litres.
The cost and efficiency of a store for hot water or slush ice varies with size. Take a tank in the shape of a cube, the volume of a tank increases in proportion to the cube of its sides whilst its surface area increases as the square.
As a result, double the length of the sides and surface area increases 4 times and volume 8 times.
With 8 times the volume and 4 times the surface area, specific heat loss is halved with the same thickness of insulation. It also becomes more viable to increase the thickness of insulation.
Very large thermal stores such as are found in district heating, or which are suited to hospitals, universities, and other large buildings can be very economical per thousand litres of storage.
The following article puts the cost of a 1 million litre tank at around $250 to $500 per thousand litres or around $4 to $8 per kWh of thermal storage with costs dropping further for larger systems.
http://www.rhc-platform.org/fileadmin/Events/4_-_Kerskes_seasonal_TES.pdf
By comparison, even lead acid batteries are around $150 to $200 per kWh of electrical storage.
Use of Money. ..at it’s best
I wonder how much of this is Apple trying to cash in on it’s reputation to sell something questionably efficient and how much of this is Apple trying to patent something it thinks will work for the sake of owning a patent it thinks it can sell.
As for the specifics of thermal storage, that is very interesting but how long would something like that hold a usable level of heat? When the wind blows around here, it usually blows pretty steadily for several hours a day, but then when it’s idle it’s light to idle for several days in succession.
I realise that some people will be skeptical about the storage duration of heat.
Storage efficiency is a function of scale and insulation. The very largest thermal energy stores on district heating networks are big enough and efficient enough to hold around 85% of the heat put into them on an inter-seasonal basis (with some use of heat pumps for upgrading). That is, 85% of heat stored in the summer is available for use in the winter.