Engineering Renewable Energy Supply Chain

What The World Needs, Part 1

I like the communication between myself and my readers and my readers (either random or regular) on the comments section. As such, I’ve decided to try some posts titled “What the world needs” (similar to the “My Hobby” posts over at xkcd). These will supplement, not supplant, my regular posts. So here we go:

What the world needs, part 1…

What the world needs is more energy storage solutions. What we have right now just isn’t going to work. Batteries aren’t reliable enough over the long term, ultracapacitors aren’t developed enough and large scale solutions just aren’t efficient enough. All we keep hearing about at the Detroit auto show are the hybrid and plug-in vehicles (Nov 2010 for the Volt? It’s going to take that long??). While they have the conversion from braking energy back into stored energy, I feel like all of the stored energy solutions right now (within the cars, just are not sufficient). Furthermore, when all those plug-in vehicles are in the driveways of the suburbs and sucking down grid power, there will be a higher need to draw upon reserves of energy, either by cranking on more power plant capacity or tapping stored energy. If we want renewable energy to fill that gap in available power we will need even more storage capability, as renewable sources are not “always on”.

My favorite idea out there is the storage of energy by pumping water up a hill (known as Pumped Storage Hydroelectricity); it’s so simple and beautiful, basically you pump water up a hill and then release it later to be converted through turbines into electricity. The initial concept was developed to help deal with load variations on power lines but also to help sell lower cost electricity produced at night during the high cost hours of the day (a concept the plug-in vehicles also hope to capitalize on). Today we see these hydroelectric storage facilities being targeted as ways to store energy from sources such as solar cells or wind turbines.When the sun isn’t shining and the wind isn’t blowing, renewable sources cannot output power; people do not typically stop consuming energy during those times though, quite the opposite. When the sun is highest A/C units are cranked and when the wind is blowing outside people are cuddled under blankets watching TV or reading by lamp.

Like any engineering problem there are limitations. Evaporation reduces the efficiency in arid climates where large photo voltaic installations are likely. Wind occurs more naturally and is more likely to be harvested in areas with out large inclines to pump the water up and down. The turbines are not 100% efficient so there are losses during any pumping of the water. So the question remains, how else can we store and then harvest energy to take advantage of renewable energy infrastructure?

  1. As the verbiage above suggests, we can actually store energy and harvest it through biofuels; it’s really just a different way of thinking about an existing solution. Corn is a favorite right now, with switchgrass being a potential in the future. Mother nature helps us take sunshine, nutrients from the soil and water to produce plants that can be converted into energy through distillation.
  2. Gravity (in non water forms) could help us store more energy. I think of having lifts that could raise large weights into the air to be released at later times. I know there’s a lamp that uses gravity to temporarily light up LEDs, but I wonder how scalable this idea is.
  3. Spring energy has always fascinated me, ever since I got one of those wind up planes as a kid (you turn the propeller to twist a rubber band which then releases to unwind the propeller as the plane flies). I imagine a huge spring being pushed by some weight and then slowly released later to power a generator, but I doubt the materials would allow this indefinitely (springs eventually lose their “springiness”).
  4. Heat is another storage mechanism but has some serious limitations. You could try and heat up a medium (salt? water? saltwater? I think I saw that somewhere), but then maintaining the heat and retrieving it later provide some serious issues.
  5. Hydrogen is touted as a great storage mechanism; while I like the fact that water is readily available, I don’t think the storage capabilities are reasonable. One of the things I like most about the pumped storage facilities is its simplicity.
  6. Pumping air into a bladder or bag underwater could be a possibility someday. You would pump air into the bag and once the pumping had stopped and you wanted to retrieve the energy, the pressure surrounding the bag would force the air back upwards; when you need it, you direct the air through a turbine to retrieve the energy. Temperature changes as you go down in depth would be a concern (air compresses as it gets colder).
  7. Batteries are still an option…basically taking electrons and squirreling them away into electrolytic solutions (or however you want to do it). These become severely limited in large scale operations though; imagine how many “AA” rechargeable batteries you would need to store the output of a 500 MW wind farm

As a final note, I should point out I found this other Wikipedia article on grid energy storage at the end of writing this post. I still wanted to publish my ideas but only some of them matched.

I get a little frustrated when I try and think of new ways to store energy; however, it’s reassuring that there are many options out there that can still be improved upon. Can you think of any other natural or otherwise methods of storing energy? Let me know in the comments!

Photo by obenson

By Chris Gammell

Chris Gammell is an engineer who talks more than most other engineers. He also writes, makes videos and a couple podcasts. While analog electronics happen to be his primary interests, he also dablles in FPGAs and system level design.

6 replies on “What The World Needs, Part 1”

Over the past five years, I’ve perfected a massive energy storage system. Farms throughout the country produce various goods that are combined into pockets with enough potential energy to produce significant amounts of heat. These “hot pockets” are then ingested by me, and through a complex series of biochemical reactions, a significant percentage of the energy they contain is transformed into a product called “adipose”, which can be stored for many years.

strictly speaking, springs do not lose their springiness unless you exceed their elastic limit. I presume you have never needed to replace a leaf or coil spring in a car because it had lost its springiness, because they are designed to stay within that limit, and you don’t expect a retractable ball point pen to stop retracting after some period, people nervously click them thousands of times without them wearing out.

It’s a great idea to store energy in springs, but I think (although I haven’t really done the math) that the practical considerations of working with gigantic springs as a means of storing serious amounts of energy would be hard to get around. Suppose you want to store….. like…. 100 MJ of energy into a spring, and at its maximum energy, it was 90% of it’s original length (you compress it 10%), and you are willing to use a 30m long footprint on the spring to store it, that gives you 3 m of compression space. At maximum compression, you have to exert 66.7 million Newtons of force on the spring. If something comes loose, that spring is going to break things and hurt people. And really, 100 MJ isn’t much energy compared to those big pumped reservoirs.

So I think it’s possible, but there is a trade between how many springs you want to have, and how much energy you want you store, and how big each spring should be. Maybe someone reading this will have the breakthrough idea on how to get it going, but I agree that a dense storage mechanism for energy is key to both future development in the energy industry, as well as key to making many “green technologies” viable in a broad context. Why haven’t we invented dilithium crystals yet? Somebody get on with it, jeez!

Have you heard about molten salt storage? For power generation such as solar (where you have a disproportionate power generation during the day) it supposedly works well. Basically you heat up salt and store it at temperature, using the heat later to run a steam turbine.

My plan takes the energy storage with spring concept to a much smaller individual size. Each unit portable and…human powered. A charged spring turns a vertical shaft at the top of which are two friction points. Heat from spring-stored human energy.
I think it’s sad that we haven’t developed and put into use systems that can capture and store lightning (static electricity). Time to get that accomplished yesterday.
And WHY aren’t the Active Denial Systems being used on locust swarms and termite infestation?? Sometimes it seems like we’re on Planet Zombie. Hail Humans!

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