Energy: All About the Flow

Energy: All About the Flow

How to get, use, save or avoid the need for energy are compelling topics today. So many of our products since the Industrial Revolution have relied so heavily on energy rather than those other two key parameters, information and structure. This dependence has led to a costly burden on the environment, but the living world offers hope of solutions. It's important to first understand the dynamics of energy in nature.

In describing the natural world we talk of energy flows, material cycles and food webs as key components. Energy is described as a flow rather than a cycle because of how we frame the phenomenon. Sunlight, our ultimate source of energy, flows through our world and out into space, whereas carbon is recycled endlessly within our biosphere.

On its way to dissipation in space, this sunlight suffuses an entire world with the ability to do work and the living creatures in that world can be divided by how they use it. You either make your own food with the sun (autotrophs) or you don't (heterotrophs). If you don't make your own food, you can eat others (herbivores, carnivores) or their waste products (decomposers). The autotrophs convert sunlight into chemical energy in photosynthesis and make the sugar and oxygen that we all depend on. Sugars are burned through cellular respiration in order to do work, and we animals also exhale carbon dioxide, which is just what the autotrophs need to make their sugars. Very neat; very complete.

What can we learn from this?

1. First there is a constant flow of energy from one source, the sun, and access to it is universal.

2. This energy is made useable by the production of a standard unit: ATP, a sugar phosphate molecule that is the basic widget of biological energy use. You can store it, transport it, use it at will whenever you like, and easily and quickly recycle it for reuse.

3. The standardized component of ATP is made and spent endlessly in an elegant complementary and continuous exchange of raw materials between the autotrophs and the heterotrophs. Each party's voided byproduct is the feedstock for the other's production of both energy and materials.

4. While energy flows through the system toward entropy and the vacuum of space, the biological world is busy building itself, essentially heading in the opposite direction towards more order, rather than less. This strikes a principle balance in the overall system.

Have we yet designed an energy system that comes even close to this? No…but let's not be too hard on ourselves. Much of these processes are still a mystery, and we simply do not have the technological capability to produce similar organic (and information rich) materials, let alone control them for our use. There have been important strides made in emulating this miraculous cycle, however, and I will mention two of them here.

Photosynthesis, as complex as it is, might be described, in part, as splitting water. A plant takes in water (H2O) and carbon dioxide (CO2) and wants to combine a part of each molecule to make its sugars. It therefore needs to split the hydrogen out of water and combine it with the carbon from the carbon dioxide. Thankfully for us, it throws out the leftover oxygen.

Daniel Nocera, a professor of energy and chemistry at the Massachusetts Institute of Technology, has spent most of his career looking at this phenomenon. Recently his lab has come up with a way to cheaply and efficiently split water into hydrogen and oxygen, and they propose that we incorporate this ability into solar panel arrays. During sunlight, the excess electricity from photovoltaic panels would be used to split the water, and the two components would be recombined in a fuel cell. At night, the fuel cell would power appliances and electric cars. Excess water from the fuel cell would feed back into the system for further splitting the next day. The advance is in the relatively cheap catalyst, a phosphate/cobalt electrode that can act at room temperature, normal atmosphere and neutral pH.

Nocera and colleagues would also like to produce fuels from this process. Just as the plant combines hydrogen and carbon to make sugars, they would like to combine the two elements to make hydrocarbons like methanol to fuel your car. Since the carbon used as feedstock for the fuel would be from existing CO2, when the fuel was burned it would be carbon-neutral. One source; many products.

Another team at MIT, this one a student design team, has also advanced the practical application of solar-based energy systems. This team, Heliotrope, has devised a passive structure for tracking the sun, as plants do, in order to optimize solar panel exposure. No motors, no electricity, no whirring noise. Just a brilliant design using the different expansion properties of two metals to bend a thin panel toward the light. A similar bimetal strip is used in your furnace thermostat to bend away from electrical contact and shut off the boiler when it gets too hot. Both are passive control systems making use of simple feedback. Here the designers used the information in the material to replace the energy of motors to position their panels automatically.

Both of these examples show that scientists and engineers are progressing toward putting the pieces together for a more integrated solar energy collection system, and that we are coming closer to that wonderful model all around us.


Tom McKeag teaches bio-inspired design to at the California College of the Arts and University of California, Berkeley. He is the founder and president of BioDreamMachine, a nonprofit educational institute that brings bio-inspired design and science education to K12 schools. 

Photo CC license by jam343