A Data-Driven Approach to Determine When to Run Your Dishwasher
Why you should run your dishwasher @ 2pm (or 2am) on sunny days in California
I never understood why my dishwasher had a Delay Start feature. It’s like teaching a dog how to play dead — a fun party trick? cute? also completely useless?
Aside from the age-old debate as to whether to pre-rinse dishes before putting them in the dishwasher (hint: def don’t pre-rinse), I’ve spent very little time thinking about my home appliances. Especially my dishwasher.
Dirty dishes go in. Clean dishes come out. Why delay?
Turns out that delay feature can teach us a lot about how energy and utility markets work. And it may be a helpful tool to help us solve climate change.
Let’s take a peek into our dishwasher and see what we see.
What makes dishes clean?
So how do dishes get clean? There are a few ingredients you need.
Dirty dishes. Soap. Water for rinsing. Air for drying.
And to make the rinsing water hot and drying air hot, you need energy. Dishwashers require electrons.
Dirty dishes. Soap. Water for rinsing. Air for drying. Electrons.
And those electrons need to be generated somewhere, using some sort of fuel. That fuel could be the sunlight kissing your solar panels, a warm western breeze turning a windmill, the cool waters of Lake Eerie falling over Robert Moses Hydroelectric dam…or pile of coal being shoveled into a coal furnace in Kingston, Tennessee.
And because the electric grid requires supply and demand to be balanced, the electrons that your dishwasher is using have been generated very recently (within ~5 minutes).
So the beauty of this Delay Start feature is that it allows you to control when those electrons get consumed. In the words of General Electric, “The benefit of the Delay Start option is that it allows you to run your dishwasher when its hot water demands will not conflict with those of the family. It also lets you take advantage of off peak utility rates.”
The general concept here is known as Demand-Side Management, or Load Shifting.
Between the time I load my dishwasher and am ready to unload my dishwasher, I don’t really care when the dishwasher runs. Which means we have flexibility to control when these electrons are consumed. And if we’re optimizing for minimizing our personal carbon footprint1, that means we can consume the electrons that are generated by the least carbon intensive fuel.
How many electrons are we talking about?
By looking at my home energy usage, we can get to an estimate of the load profile for my dishwasher. We see on nights that we run our dishwasher, our energy consumption spikes by +0.5 kWh for 2 hours. We have a GE Adora dishwasher has a 118 minute “normal” runtime and is estimated to consume ~1.12 kWh per load. So the EnergyStar estimates and reality are looking pretty close.
When’s the carbon-optimal time to run my dishwasher?
Let’s answer this question for an individual.
First, let’s start by finding the worst time to run your dishwasher. The worst time to run your dishwasher is when the incremental demand directly correlates to the most carbon-intensive fuel is being burned to generate the electrons to power your wash cycle.
In California, because solar provides such a large supply of clean energy during the day, the worst time to run your dishwasher would be when demand is highest and renewable supply is lowest. At these points, every incremental ask for more electrons need to be supplied by carbon-intensive fuel.
On most days in California, that’s around 6-7am or 7-8PM, when the sun’s down and everyone is at home cooking, showering, watching TV, doing laundry, and…considering washing their dishes.
So the optimal time is the inverse of this, in which the most renewable supply is available and demand is the lowest. Most days in California, that’s appears to be ~2-3PM.
Of course, this assumes no real-world constraints, like when your dishes get dirty and whether you need dishes to eat your dinner. If you want to run the dishwasher overnight, 2AM seems like the sweet spot when net demand is lowest.
What if you were a Dishwashing Demigod?
Now let’s pretend you are an almighty Dishwasher Demigod. No, you weren’t blessed with control over the Sky or Sea or War. But you have one very important superpower — ultimate and final control over when to run all dishwashers in the universe.
Let’s constrain our analysis to California and assume there are 7.2 million dishwashing machines that need to run every day2. How will you, as all powerful Dishwasher Demigod, allocate this 8MWh load?
The answer is almost certainly to schedule all dishwashers to run between 11a-4pm. This is when net demand is at it’s lowest, which means incremental demand can be serviced with low-carbon alternatives3. 8MWh, while sizeable, is And by creating predictable demand, CAISO could include this demand in its forecast models to ensure optimal capacity.
Clean ya dishes at 2PM
There are obviously a lot of other factors to consider when thinking about when the optimal time to run the dishwasher. Grid-scale batteries, renewables fuel mix for your region, weather, and water levels can all play a role. And it’s fair the assume that the least carbon-intensive dishwasher cycle is the one that never happens. So if you can skip a cycle or enjoy a crusty patina of last night’s dinner on your bowls, do that.
But if you must run your dishwasher, think about using that delay start feature to schedule the cycle when net load is at it’s lowest. That’s usually 2am or 2pm!
Thanks to Baker Shogry, Calvin French-Owen, Chris Nixon, Alexia Niparko and Simon Greenberg for reading drafts!
There are many things that consumers can be optimizing for. Cost, hot showers, carbon, convenience. For the sake of this post, we assume Best Climate Intent.
Based off 13M households, 68% dishwasher penetration, and the shocking stat that 20% of dishwashers run less than 1x per week
There’s actually a fair amount of nuance to thinking about incremental demand/supply. We are going to add the load at some point, we need to pick the points in which incremental demand consumes from already running, high-efficiency energy plants. By “filling in the trough”, we can potentially keep plants running (reducing carbon cost of bringing a plant on/offline) and ensure that we aren’t consuming from lower-efficiency (but more flexible) plants that come online during afternoon ramp.