My Perfect Green Data Centre (1) My Perfect Green Data Centre (3) – AC/DC

My Perfect Green Data Centre (2) – Storing Energy

The idea is to build a clean data centre: less energy, cleaner energy, and fewer nasty things. As the first two concern energy, I’ll first set the scene on what energy is.

Data centres are energetic beasts. They not only consume huge amounts of energy, but must also store huge amounts of energy. The obvious example is the battery pack of a UPS system, but that diesel fuel in the tanks for the generator sets is also a form of stored energy, and air-cooling systems are full of pockets of stored energy, too.

Energy takes many forms, but the form which computers need is electrical. And this is the first difficulty with data centres. Nature is set up to store heat, movement (kinetic) energy and so forth, but not for storing electricity. Take heat. The atmosphere which protects this planet from the frigid reaches of interplanetary space is a natural heat storage system, and the rock crust of Earth which keeps the mantle contained, another. A vacuum flask is not natural, but it’s cheap, easy to make, and stores heat.

Another form of natural energy storage is kinetic. Set a (fly)wheel in motion and, absent of friction, it will spin until the end of time. Kinetic storage can also be combined with gravity: lift something up using kinetic energy, and the energy used to lift it will be stored until that thing is dropped. (As one of nature’s clumsier individuals, I often see downwards kinetic energy realized by the breakage of a cup.)

Electricity is an altogether different beast. Electricity is free electrons in motion. For those who remember school chemistry, atoms consist of a nucleus of protons and neutrons, surrounded by outer shells of electrons. Those electrons spin round and round the atom. So, in a sense, potential electricity is everywhere – in the pages of the books in the shelves to the right of where I sit typing, in the precarious cup in front of me. But, in the other sense, it’s nowhere, because like people, electrons are creatures of domesticity. They only leave if pushed; they don’t just wander away.

When an electron is knocked off its atom, it seeks a home. To do this, it must move and, when it does this – and only when it does this – does it become electricity. Hence the problem: you can’t store things that are moving.

Nature, therefore, doesn’t store electricity per se and neither do we. We convert electricity to another form, and convert it back again when we need it. The predominant ways of doing this are electromagnetic induction, photonic bombardment, and the quantum equivalent of a foster home.

Induction (I won’t pretend a detailed understanding of the physics) is the traditional method of generating electricity: stored or generated kinetic energy is used to turn a turbine, which in turn rotates a magnetic field in a dynamo or alternator, which produces electricity. Turbines are turned indirectly by steam by burning coal, oil, LPG, diesel, recycled waste and creating sub-critical masses uranium, and directly in hydroelectric plants and wind turbines.

Photonic bombardment is the essential physics behind all photovoltaic (PV) cells. Photons, those bearers of light - mostly from the sun but in principle from anywhere – knock the electrons out of their homes.

The foster home is the battery: an electron is given temporary accommodation on the outer ring of an atom that doesn’t really want it, and runs free as soon as it’s offered a place to go.

So, that preliminary out of the way, on to where it all starts: the back of the computer.

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