Posted by Luke Fishback

In the world of “clean energy,” projects fall into one of two categories: increasing clean energy generation (supply) or decreasing energy consumption (demand). The energy generation side is developing technologies aimed at displacing the power plants we already have and building additional capacity for our ever-increasing energy appetites. Cool. On the other side, there are those of us focusing on more efficiently using the energy produced, no matter what the source. In this post, I’ll describe why these aren’t just two sides of the same coin.

This is really important: energy saved can have multiplicative upstream impacts. A unit of energy (e.g. a kilowatt-hour) consumed by your television has much more impact than the same unit of energy produced by your local power plant. This is a consequence both of inefficiencies in our system and of the laws and limitations of physics.

Inefficiency in the Home
Let’s look at the power it takes to illuminate a light bulb. We’ll start with a new term, the lumen. A lumen is a unit of measurement used to express the amount of useful (visible) light produced by a light bulb. It is important that we start there because lumens (not Watts) are what we want from our light bulbs. We’ll begin at the lumens and follow the electricity back to the power plant where we’ll discover just how much energy a light bulb wastes along the way.
Let’s say we want to create 1700 lumens of visible light. If we had a perfectly efficient light bulb, it would take about 2 Watts of electricity to produce 1700 lumens. Incandescent bulbs are far from being perfectly efficient. They are about 2% efficient at producing useful light. That means for every 1 Watt worth of useful light produced, 50 Watts are wasted on things like heat and invisible light. For incandescent light 1700 lumens requires a 100W bulb (i.e. 98% of the energy is wasted).

Transmission Inefficiency

Next up, we have transmission losses. This is energy lost between the power plant and our homes (usually the loss takes the form of heat). In the US, our average transmission losses are about 7%. So, a 100W bulb, which makes 2 Watts worth of light, requires 107W of power from the power plant.

Power Generation Inefficiency
Finally, we have power plant losses. Extracting energy from just about any fuel source is an inefficient business. We generally burn a fuel and then use the heat generated to turn a turbine. In the US, across all electricity sources, we’re about 32% efficient (i.e. 68% wasted). So 107W requires 334W of input. All-in-all, it takes 334 W to make 2 W worth of useful light. From coal mine to illuminated living room, we are wasting 99.4% of the energy. Yikes.

So what?
The repercussions of our gross inefficiencies are oft-neglected when it comes to clean energy thinking. We think that adding generation to the grid has the same impact as removing demand from the grid. In reality though, doing without the 2W worth of light is equivalent to removing the upstream need for 334 W worth of input or 107 W worth of generation. Similarly, increasing the end-use efficiency from 2% to 8% like we can do with CFLs, has huge upstream repercussions. Now, we’re still creating 1700 lumens of light, but it only takes a 25 W bulb, 27W of generation, and 84W of input.