Why should I set an end timer?
[UPDATE: 10/1/17 – Updated to include information about charge rates and times with L1 and L2 EVSE]
All electric cars and many EVSEs (electric vehicle supply equipment) come with a timer that offers the ability to set a start time, end time, or both to enable you to charge your electric car within a specific time window. This article offers a sound reason to use the end timer function provided for your use.
A recent study by a company called Opower has highlighted the fact that a western US region showed higher electrical power usage by electric vehicle (EV) owners than non-EV owners, and specifically a sharp spike in power usage at midnight with usage dropping dramatically after 1:00 AM (found here). While Opower is picking on Tesla owners in the title of this blog post, they are actually targeting all EV owners. Based on their findings, there is some reason to.
Many energy companies offer time-of-use (TOU) rates for EV owners. These TOU rates may run from midnight to 5:00 AM or they may be as broad as 11:00 PM to 7:00 AM, depending upon the market and the utility company. Energy costs are significantly less during these non-peak hours as the utility companies generally have much lower demand for electricity during these times. By encouraging EV owners to charge their EVs in the middle of the night rather than in the evening when they come home, the utility ends up selling just as much power, but managing their power generation more evenly.
The challenge for the grid is that as EVs gain popularity, if everyone sets their charge timer to kick on at midnight, it can cause a huge surge in demand all at once. The way to alleviate this is to set the end time rather than the start time. Depending on the vehicle or equipment the timer may read as “Start” and “End”. Or it may read as “From” and “To”. It doesn’t really matter what the words are, but it does matter that you understand your vehicle or your equipment.
As we have learned with our range remaining indicators, there is much wiggle room in the proclamation of these numbers. The same can be said for the end time settings – these are rough estimates rather than precise determinations. Most electric cars will stop charging well before the end charge time is reached. For our purposes as EV drivers, this is fine. We still have a fully charged car so we can go where we need to go. As importantly, for the utility company, there is no large spike in demand at midnight. Rather there is a more even demand spread out throughout the the night as EV driver’s vehicles recharge with varying start and end times. The end result is that this works well for everyone involved. Do not set a start or from timer at all. The use of an end timer will provide you with the same result as using the start timer, but it works out better for the utility. Which means it will probably work out better for you when it comes time for your state’s public utilities commission to review utility rates.
Using the end timer on a LEAF
Let’s say your super off-peak electricity rates are from 11:00 PM to 7:00 AM. This provides an eight hour window to charge your car. If you use the 120 Volt trickle-charge cable that came with your LEAF, it will charge at a rate of about five miles of range for every hour plugged in. The math shows that you will gain about forty miles of range in this eight hour period. If you drove over forty miles, the car cannot be fully charged in an eight hour window. It will stop charging at 7:00 AM, but you will not have a full charge. If you have your end-time set and the car charges beyond the end-time, take it into your dealer for inspection. If you need a full charge, don’t set the end timer.
If you have driven more than forty miles and want a full charge in the morning, you will need to plug in prior to 11:00 PM. Your car will start charging before your super off-peak rates kick in, but you will have a full charge when you wake up. Your are now faced with the dilemma of saving time or saving money. Analyze whether you really need that 100 percent charge every day. If you are not arriving home with an empty battery each day, perhaps you can recharge forty miles each night and go to a 100 percent charge on the weekend. Or you could buy a 240 Volt EVSE.
Even the slowest 240 Volt EVSE (portable or wall-mounted) will charge in less than half the time of the 120 Volt unit. Many residential garages already have a 240 Volt dryer outlet installed. If not being used for the dryer, this could supply your LEAF assuming an appropriate breaker is installed. Since the LEAF S has no start timer, when you plug in the EVSE, the EVSE and the car communicate via the charge plug. The car then determines the capabilities of the EVSE and will start charging accordingly. You do not need to wait until 11:00 PM to plug in your car.
Check the amperage rating on any 240 Volt EVSE that you buy. The higher the amperage rating, the faster the charge. Low cost 240 Volt EVSE units typically operate at only 16 amps and take almost twice as long as units that operate at 30 amps. Most dryer breakers are 30 amp breakers, so they will support this EVSE use.