The math around electricity pricing is very complex, and it used to be most of that complexity was hidden from the end user. That’s not so true today, particularly as more homeowners add solar and electric vehicles to the mix, and utilities offer or demand “time of use” pricing.
I recently did a mathematical analysis of my own situation to decide which electric utility pricing plan to take from Pacific Gas & Electric, one of the largest electric utilities in the USA. PG&E has extremely expensive electricity compared to most of the country. They were responsible for a number of catastrophic wildfires and deaths in California, and their “punishment” has been to be allowed to raise rates for customers to pay for the damage and the infrastructure improvements needed to improve safety. As a result, their prices average from 40 to 50 cents per kWh (compared to a national average of around 13 cents.) EV drivers can get a rate that’s 32 cents at night, but up to 62 cents during the 6pm peak.
That’s a challenge for EV drivers. If you’re paying 32 cents/kWh, that’s 8 cents/mile in a Tesla Model 3, and even more in the heavier cars. That’s the cost of gasoline in a Prius, which is about 8 cents in California, but more than the 17 cents/mile of average cars. The gasoline cars will still pay more per mile for maintenance. This is a big deal. For most people with more normal electricity prices, an electric car is cheaper to buy and operate than any gasoline car, usually a lot cheaper, even though it costs more up front to buy. For PG&E customers (which is a lot of EV owners) it’s now only a little cheaper.
The problem is solved if you get rooftop solar, though that requires you be a homeowner. The price of that continues to drop. You usually pay for solar with a flat up-front fee, though you can finance it. But under $5,000 in solar panels (after tax breaks) will produce enough electricity to run an electric car for 25-30 years. Considering the average Californian pays about $2,000/year for gasoline, or even just $1,000 for the Prius, it’s not hard to see how much of a win the solar panels and EV are.
Or would be, if you could get “net metering” for your solar panels. California ended that last year. Most (42) states still offer net metering, and Californians who ordered before the deadline (such as myself) still have it. With net metering, you can have your solar panels provide power back to the utility in the day, and charge your car at night, and the two are balanced out. Without net metering, you want to use your power as your panels make it, and you are paid only a small amount (like 4 cents or less) for what you feed to the utility. This doesn’t mean there still isn’t a big win for solar with your EV, but it’s not nearly as good a win as it was before.
Without net metering, you can still win if your EV doesn’t stay at the office all day. Cars for people who work from home or otherwise don’t commute can charge during the day, while the panels are generating. There are a variety of tools that will even tell your car to only charge from what’s going spare from the solar panels. Otherwise, your option is to have a household battery, and put the power first into the battery, then into the car when it comes home—that adds a bunch of cost but is often a good idea without net metering.
Picking Pricing Plans
Even with solar, you still connect to the grid electric utility, and you have a price plan with them. They still charge you when you pull power from the utility (for example, at night) and credit you when you send power back. Do it right and your power bill can be at or near zero, or they can even pay a modest amount for your surplus. You still need to pick a pricing plan. For PG&E, you must pick a “Time of Use” plan that has different rates at different times in the day. There’s always a “peak” time (around 3pm to 9pm) which is expensive—sometimes much more expensive—as well as an off-peak and possibly partial peak price for other times.
Without solar, EV users buy a special plan that’s ony for them. It has the best prices on offer off-peak, and very high prices on peak. But if you have an EV, you want this because you can just only charge your car off-peak. Off peak always includes the night, and the night is the most convenient time to charge unless you work the night shift. You also move any other loads you can move into the off-peak, like pumping water in your pool. (The pool and the car are fantastic loads for renewables because you can do them whenever the price is best.)
I made the “mistake” of building a detailed model of all my electrical use and my solar generation. I say mistake because it was a bunch of work and the conclusion turned out to be pretty simple. I was able to download my precise energy use every 15 minutes for the last year from the utility, and the government has a site called PVWatts that will give you an accurate hour-by-hour model of what your solar panels will generate. (If you already have the panels you may have access to a year of real data.) I also have a $140 home monitoring device that gives the data on each circuit in my home.
I do all sorts of tricks, accounting for daylight savings time and more, but the final result was pretty simple. If you expect to generate more solar power than you will use, it doesn’t matter which plan you take, other than you probably don’t want the “EV-2A” plan for EV owners. It’s a great plan if you don’t have solar (or will use far more than you generate) but its virtue there is its flaw for net metering. It has a cheap off-peak price and you generate most solar in its off-peak which lasts until 3pm. So you get less credit for it to use against any peak usage. You never charge your car other than in off-peak on any plan.
PG&E has two other plans, name TOU-C and TOU-D. TOU-D has higher prices, while TOU-C has low prices up to a “baseline” (60% of average) and higher prices past that. If you will generate more than you use, you will stay well under that baseline. In fact, you’ll stay under it even if you go over a fair bit. That makes TOU-C a better choice if you fear you might go over—if you don’t go over, the plans are all the same. You’re less likely to go over on TOU-C, though only slightly less likely than TOU-D. TOU-D has another nice feature: It’s “peak” is only 5pm to 8pm and only on weekdays. So it’s pretty easy to avoid. Don’t charge your car in this short window or pump your pool, and you’re golden. You might enjoy the freedom of not worrying about the time of day. (On EV-2A when the price more than doubles at peak, you want to pay attention, and avoid things like laundry and dishwashers during the peak, and even cutting back air conditioning.)
This changes if you start regularly going over. Most people will go over in winter, and stay well under in summer., but the two are added together in April to balance out. TOU-C is your winner if you go over by a decent amount. If you go over by a ton, you might look at the others. You can only change about 3 times every 2 years.
Your use might change. If you get another electric car, or decide to get AC or a heat pump, there could be big changes. You’ll want to re-evaluate. The man thing is to know your annual solar generation and your expected annual usage, and how close you are to going over.
Stay tuned in future for what to do if you don’t have net metering.
