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Deal with summer heat by pre-cooling your home, and other cool news

July 12, 2021

[By Chuck Almdale]

One way to beat summer heat (Source: Wisconsin Life)

Your electrical utility wants you to pre-cool your home. Pre-cooling may save you money and definitely lowers utility managers’ levels of stress. Month after month of torrid days with high peak demand make these people very uncomfortable. Do pre-cooling right* and it won’t be any worse than what you live with now. It may even be better.

*Doing it right means:
Read this posting, check with your local utility, experiment, take notes, be lucky.

What is pre-cooling?

Pre-cooling means cooling your home before you actually need it, letting your A/C “coast” during the worst part of the day, then turning it on again after the high peak if you need it. The worst of the day, utilities say, is during the period of peak demand. This typically is the hottest part of the day as that’s when everyone cranks up their air conditioner. That’s what they want you to stop doing (cranking it up). Thus…pre-cooling.

Figure 1. Six utilities: Time-of-use periods and rates (where available).

Utility Links:
Los Angeles Dept. of Water & Power
Portland Gas & Electric
Sacramento Municipal Utility District
San Diego Gas & Electric
Southern California Edison
Tucson Electric Power

[NOTE: Some utilities such as Southern California Edison – which admittedly serves many localities with differing conditions – hide their rates from the merely curious, partly because they have many options available. Current customers may uncover their options by logging into their accounts.]

Definition: kWh – kilowatt-hour – A measure of electrical energy equivalent to a power consumption of 1,000 watts for 1 hour.
Worth knowing: Water can be stored behind a dam for society’s future use. Electricity cannot. What you’re taking out of the wire must be simultaneously generated and stuffed into the other end of the wire. The closest thing we have to storage of massive quantities of electricity is…water behind a hydroelectric dam.

Utility electrical rates and high-low peak rate differences vary

LADWP high peak rate is 47% higher than their base rate of $0.18386 per kilowatt-hour.
Tucson Electric Power high peak rate is 153% higher than their base rate of $0.023516 per kilowatt-hour. That’s a big increase but from a base rate that’s 87% lower than LADWP.

Utilities differ in their suggestions about how best to do pre-cooling.
What they do agree on is:

  • Smart (programmable) thermostats are very handy. You can “set ‘em and forget ‘em,” which is mostly true.
  • Cool you home before (and after, if needed) the high peak period – at night and/or in morning.
  • If you need some cooling during the peak (e.g. leaky house, poor insulation, it’s really hot outside) set your (smart!) thermostat to 3°F above your preferred setting.

To be more specific:

  • Find out your utility’s peak hour time bracket. For the 3 hours preceding that, set your A/C thermostat to 3°F below your preferred temperature (longer, if necessary). During the peak bracket, set to 3°F above your preferred temperature. At the end of the peak bracket, set it to your preferred temperature.
  • They really want your preferred temperature to be 78°F or higher, certainly not 68° or 72°F.
  • If your utility has three (or more) rates—base, low peak and high peak rates, as does LADWP—you may want to pre-cool during base rate and let it “coast” during all low peak and high peak periods. This may be too long for you to tolerate. This is where experimentation and taking notes comes in.
  • The Sacramento Bee suggested during their 2020 heat wave, “Set the thermostat low each evening after 9 p.m. Cool your house as much as possible until about 1 p.m. the next day. Then, turn the thermostat up to avoid stressing the community’s grid system.” Again: experiment.

Rate schedules options vary

Besides time-of-use (TOU) rate schedules, there may also be:

  • The self-explanatory same-rate-never-changes rate schedules
  • Tiered rates schedules which charge by total electricity used per month: the more you use the more you pay for your usage above the lower tiers. Again, you have to know what your local utility offers. They’re all different.
  • Video on LADWP two residential rate plans: Standard 3-Tiers (R-1A) and Time-of-Use (R-1b) (3 minutes)

Got solar panels?

Lucky you, you’re almost in a different ballpark. Depending on the number of panels and how much it generates versus your usage at high peak, you may be able to ignore everything I’ve written so far. But there are a few things to consider:

  • If you run your A/C or recharge your Tesla (see below) during low light/base rate periods, you’ll be drawing on power from the utility.
  • If you use your A/C or charge your car by drawing on your solar panels, you’ll be doing this during high peak periods.
  • If you’re using your own panel power during high peak, you’re not selling your electricity to the utility at the highest rate possible.
  • You may be better off dollar & power-wise by selling your power during high peak and using their power during base rate periods to cool and charge things. You may also be providing more benefit to your community by doing this.
  • Your utility may not provide many—or any!—price or time-of-usage incentives; they may pay you for your electricity at a rate lower than they charge you for their electricity; or not pay you at all. Always check with your utility.
  • If you use your panels largely to supply power to the utility, they may be more efficient dollar-wise by facing slightly to the west, as the sun is in the western half of the sky during the high peak periods of middle-to-late afternoons.
  • Keep your panels clean. A quick hose washing gets off about 90-95% of the accumulated dust, but avoid spraying cold water on hot panels.

How many homes have solar in your zip code area? Link to: TheSolarNerd.

Net metering

Some states, including California, require publicly-owned utilities to offer net metering to homes with solar panels. Net metering uses the Time-Of-Use (TOU) rates previously discussed. The TOU periods generally follow the curve of daily usage.

Link to chart of net metering by state.

Only five states have no policy concerning net metering. Of those five, only Alabama actually levies a charge of $5.41 per kW per month for interconnected solar customers. They really don’t want newfangled solar panels there.

Figure 2. Usage chart for California on 6/14/21, the state-wide highest temperature day so far in 2021. Vertical axis in megawatts, horizontal axis in 5-minute increments. The lowest demand was 21,908 megawatts at 3:40 am, the highest was 35,970 megawatts at 6:40 pm. Average temperature in California ranged 58°-84°F.

Figure 3. Usage chart for California on 2/07/21, the state-wide lowest peak demand day so far in 2021. Vertical axis in megawatts, horizontal axis in 5-minute increments. The lowest demand was 16,382 megawatts at 12:35 pm, the highest was 23,956 megawatts at 6:30 pm. Average temperatures in California ranged 44°-67°F.

Charging electric vehicles

This is unwelcome news, but the electricity it take to charge your electric car doesn’t fall out of the sky like manna from heaven. (Mmmm….manna. Melts in your mouth.) One site said it will likely cost you more than all the rest of your electrical usage combined. The 100 kWh-battery of your Tesla, by design, won’t charge to full capacity; 50 kWh may be the typical charge. Over 120 brands of EVs other than Tesla average 60 kWh of capacity.

Cost to charge that Tesla!   
At local base rate25 kWh50 kWh75 kWh100 kWh

Figure 4. Cost of home charging Tesla battery with three utilities, four charge levels

Fast charging doesn’t take less energy, just less time, so it costs the same. If you’re charging at home, use an appropriate timer to charge at early morning base rate.

Something to think about: Electric vehicle mavens and wonks say things like: “By 2050 50% of all cars in the U.S. will be fully electric.” True or not, I don’t know. I just wonder where all that extra juice is going to come from. If you’re charging at night, which most people using home charging do, solar won’t help, unless you’re importing it from central Asia where the sun shines as Americans sleep. Perhaps we can extract electricity from the temperature differentials at different depths of the ocean?

Common household electrical uses, sorted by cost

Home Appliance Cost at
Energy UsageUsage kWh13¢ / kWh
 kWh / yearCost / year
Xbox One23330.29
Cable box13918.00
Computer tablet121.56
 kWh / monthCost / mo
Water heater380-50050-65
Frost-free fridge 15CF15019.50
Energy star FF fridge 17cf354.55
 kWh / hourCost / hour
Electric furnace10.51.37
A/C Central 3 ton-12SEER30.39
Window A/C 18,000 BTU1.80.23
Hair dryer1.50.20
Space heater (1500W)1.50.20
Baseboard heater 6ft 250W/ft1.50.20
Toaster oven0.750.10
Vacuum cleaner0.750.10
Window A/C 8k BTU0.730.09
TV Plasma0.4< 0.05
Bulb – Halogen 300W0.30.04
Whole house fan0.2-0.4.03-.05
Sleep apnea machine0.20.03
Computer – desktop0.06.01-.03
TV LED 4k  >75″0.18< .02
Fan – pedestal0.03< 0.01
Fan – ceiling.025-.075< 0.01
TV LED 4k 40-50″0.071< 0.01
Computer Monitor 17″ LCD0.04< 0.01
Stereo0.05< 0.01
Bulb – Compact Fluor. 8W0.008< 0.01
Bulb – Heat Lamp0.04< 0.01
 kWh per use or load
Energy star dryer2.28 / load0.30
Dishwasher normal1-2.17 / load.13-.28
Electric blanket king size1 / night0.13
Microwave oven.12 / 5 min0.02
Coffee maker.12 / brew0.02
Toaster.04 / use< .01
Additional information at: 
Silicon Valley Power  

Electricity and water

The closest thing we have to enormous electricity batteries we can flick on and off are large hydroelectric dams with plenty of water piled up behind them. So we also have to think about our water supply. A few fortunate locales can channel ocean tidal flows through gates and generate electricity as the tide flows back and forth. Most places have to capture fresh water behind dams. With more and more people and more and more uses for electricity and less and less rainfall and snowfall, it’s getting difficult to capture enough fresh water to supply either our electrical or water needs. With climate change, there’s no rational reason to expect this situation to significantly improve in either the near or far future.

Speaking of dams, they’re not holding as much water as they use to do.

Lake Oroville in 2014, second-largest state reservoir in northern California, Source: California Department of Water Resources

Peaks and troughs of electrical usage are of critical importance. With more and more hotter and hotter days in our foreseeable future coming at us, demand and electrical rates will continue to rise. Our electrical utilities really want us to think a bit more about the juice we use and when we use it. The well is not bottomless.

So they’re coming up with ideas like time-of-use and pre-cooling—and they’ll be far happier campers if we all play along with them. In the long run, so will we.

When it comes to our supply of fresh water, which generates much of our electricity, we may be “circling the drain,” houseboats and all.

Bridge Bay in Shasta Lake, 23 Jan 2014,
water 100 feet below normal level. Source: The Atlantic

At 247 square miles, America’s largest reservoir, Lake Mead.
Highest level of 1225.44 feet above sea level reached in July, 1983.
Now 152 feet below that.
(Source: Los Angeles Times)

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