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Saturday, July 13, 2024

Heat Waves and Virtual Power Plants

Like many parts of the world, we're having a heat wave; multiple days with highs over 100°F. Luckily we have air conditioning and, during these high temps, it's been running 14+ hours per day. During a heatwave, as you can imagine, there are millions of AC units sucking down kilowatts and pumping cool air into homes and businesses. All of this AC use puts a strain on the grid and there have been some outages. We were recently at a friends house in our neighborhood for a Sunday cookout when they lost power for about an hour.

Luckily, the utility was able to restore the power quickly. An hour is not too bad; the house didn't get too hot and nothing in the freezer/refrigerator went bad. As you can see in the image below, as I write this, my local utility has over three thousand customers without power. 


It's impressive that, even during this heatwave, they have better than 99.7% service reliability. But, if you're one of the 0.28% without functional electricity for fans and AC, it doesn't feel impressive. Checking the outages the next day and there were fewer than 100 customers affected, so more than 3000 were back online in less than (maybe much less than) 24 hours.

So how do you help reduce the load on the grid and prevent outages when there's a heat wave and everyone wants to run their AC at the same time? Our utility has several demand mitigation schemes and, this week, they are using them all. 

Here are the programs: 

Demand Response 

The three residential programs our utility has are Peak Rebates, Smart Thermostat, and Virtual Power Plant (VPP). They use these programs when demand is expected to be high or what they refer to as an "Energy Rush Hour." 

Peak Rebates

With is program, the utility notifies you the day before and asks you to reduce your energy use during a 3 or 4 hour window the next day. You then receive rebates based on how much your usage is below your typical usage during that period. You get paid for "Negawatts." The rate is $1 per kWh that you don't use compared to your usual load for that time. So if that's when you usually do dishes, laundry, or charge your EV, moving these to other times of the day could give you some payback and reduce grid stress for everyone.

Smart Thermostat Energy Rush Hour

With this program you can let the utility have the ability to tweak your air conditioner settings. They pre-cool your house before the peak hours so your AC doesn't have to run as much during the high energy demand period. For any month that you participate in a Rush Hour event, you earn $25. I like this program. With the pre-cooling your home is nice and chilled and you get paid for it. 

Virtual Power Plant (VPP) 

Last on our list is my favorite, and the one I want to spend the most time covering, the VPP. Echoing the Smart Thermostat naming convention, our utility calls this the Smart Battery Program. To participate in this program, you must have an approved residential energy storage battery such as Tesla Powerwalls. When participating, you allow the utility to discharge your battery when the grid needs the energy most. In return, they pay you $1.70 for each kWh dispatched. You can select your participation level at 30, 50, or 80 percent of the nominal storage capacity of your pack. We're participating at the 80% level.

For the recent heat wave, they dispatched our battery 4 times.


Here's one of the dispatches: 

As you can see, the battery is being dispatched at a rate of 10.8 kW. This rate allowed them discharge 80% of the battery capacity during the 3 hour event. During the 4 events they were able to extract a total of 129.6 kWh. At $1.70 per kWh, that's $220. 


As you can see in the chart above, we used 57 kWh and only exported 32 kWh. The point isn't about how much we used but WHEN we used it. As you can see by the tall green bar, we charged the battery at off peak times before 6AM. Then during the Rush Hour event, from 5PM till 8PM, we were exporting solar and battery energy to the grid (shown by the green and yellow in that window of time). 


The Results

Combining the Energy Rush reward and the VPP payment, we earned $245 for our July electricity bill. We'll likely have a negative bill this month. Not bad for our household, but how'd the local grid over all do during these events? 


As you can see in the graph above, grid load was reduced by 109 Megawatts when the Rush Hour started. These programs make a difference and can be a determining factor in keeping the lights on or not.

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