Green IT #1 - Data centres are not light bulbs

Will green data centres increase energy use?
The industry press has a never ending stream of “green” announcements from ICT vendors telling us how much energy their new product will save or how good the “Design PUE” of their new data centre is. The problem is that all this green may actually increase data centre energy use.

Light bulbs
When a 100W light bulb fails you may well replace it with a new, green, high efficiency lamp that consumes only 20W but provides the same amount of light.
 

This saves energy because we selected the original 100W light bulb based upon the amount of light we required in the room, not on the capital or operational cost of the bulb. The purchase and power costs of light bulbs are so low that they are not a significant selection factor. When we choose a new low energy bulb to replace the old one we generally choose the same light output and therefore a lower energy consumption bulb.

The Jevons paradox – Price elasticity
In his 1865 book an economist, William Stanley Jevons made an observation which came to be known as “the Jevons paradox”.  In the preceding years the much more efficient James Watt design of steam engine had replaced the earlier Thomas Newcomen designs. Jevons observed that far from the expected result of reducing the consumption of coal this improvement had actually increased total consumption. This was because the new, more efficient steam engine lowered the price of doing a given amount of work with coal, therefore unlocking further demand such as the flooded tin mines in Cornwall which had been too expensive to pump dry with horses or Newcomen engines but became viable with the new Watt engine.

This, counter-intuitive effect is now known as price elasticity and well understood in economics. The elasticity is basically expressed as the change in demand (or consumption) of a given item divided by the change in price of that item.

For our light bulb example it is clear that the elasticity against energy cost is low as we generally buy the equivalent light output lamp so there is a small change in demand divided by a large change in cost.

Price elasticity in the data centre
In the data centre it is well understood that there is continuous demand from the business for more, faster or better featured software services. As we improve the efficiency with which we deliver ICT services from the data centre this inevitably reduces the cost of a given unit of service delivered. Jevons tells us that this decrease in cost will increase demand, if our elasticity is high then we may actually increase the total energy consumed by the data centre by unlocking sufficient demand.

This large elasticity of demand in the data centre is a distinct change from the light bulbs and presents us with a bit of a problem in selling “green” IT.

Aren’t we supposed to be saving energy?
One of the goals of “Green” IT was to save energy in addition to cost however there are a number of factors which may mitigate this demand growth.

Firstly there is the substantial cost of software and management of the systems which will become a larger proportion of the overall cost as we reduce the data centre plant, power and IT equipment costs.

Secondly, we need to consider the ICT energy consumption in context, if the growth in ICT energy displaces more energy consumption elsewhere than ICT consumes then we still have a net reduction and there are countless case studies of exactly this happening. One example is the logistics system for UPS choosing right turns over left turns (across traffic) to reduce waiting time saving 3,000,000 gallons of fuel. We don’t need to see their data centre power bill to work out whether this is a net saving.