By Kevin Kam for Energize Ashland 

A few months ago in this space we discussed the concept of the negawatt, which is the unit of energy that you don’t consume, and that the negawatt—not solar, wind, hydro or nuclear power—is the cleanest unit of electricity.  

Let’s take the negawatt concept one step further by considering that not every negawatt has the same environmental value because timing matters, too. Here’s a chart from the website of New England’s electric grid operator, ISO-New England, showing the total grid-based electricity consumption for the 48 hours starting at midnight Monday June 17.  

The weather that Monday was mostly sunny with a high of 82 degrees, while Tuesday was the first day of a heat wave with high temperature of 92 degrees.  Just from eyeballing the chart, you can see that electricity consumption rose significantly with the air temperature: peak demand on Tuesday was about 26% higher than on Monday, 21,750 versus 17,250 megawatts.

To meet the daily peak demand on Tuesday, the electric grid called on additional gas-fired power plants to run (or for those already on to burn even more gas) and also for an oil-burning plant to come online.  In grid-speak, oil and gas were the “marginal fuels,” meaning each additional unit of electric use caused an equivalent increase in gas/oil consumption, leading grid-wide emissions to peak at 105 metric tons of CO2 per minute compared to about 66 metric tons per minute at the daily low.  In contrast, the peak emissions on Monday were about 88 metric tons of CO2 per minute, and were 44 metric tons at the daily low.  Notice that the emissions graph (the top line represents total emissions, the one slightly below represents emissions from gas plants) is essentially the same shape and magnitude as the power curve.  Imagine that these charts represented traffic on the Mass Pike, and you have a daily commute into Boston.  All else equal, you would avoid the peaks as much as possible, right?  Or, if commuting at peak hours were unavoidable, you would consider alternatives like the commuter rail or shared rides or telecommuting if possible, any way to avoid wasted time (or gasoline!) sitting in traffic.  

Returning the conversation back to household energy, the suggestion here is to intentionally shift electricity consumption away from peak hours (or away from really hot days) by being flexible in running devices such as dishwashers, ovens, and washers/dryers, air conditioners/heaters and charging electric vehicles.  As the emissions chart shows, a negawatt at peak hours results in about twice as much avoided emissions as an overnight negawatt on the same day, and potentially even more if you are able to shift consumption away from a heat wave.        

While each of our individual actions has only a very small impact, intentional actions by a large group can make a difference; after all, what are these graphs but a real-time measure of the choices of our collective decisions to consume electricity?