Zach Says, let’s keep the conversation simple… so even Elmo can understand it!
Question: How much electrical energy can we move off the electrical grid and store in an Electric vehicle? For the sake of our conversation, we’ll use the standard electrical outlet normally found in your home as the source of electrical energy.
Before you answer, we will assume you have exactly 10 hours to make the energy transfer, and we’ll also assume you have zero electrical losses in any kind of transformer or rectifier necessary to condition the energy for storage.
Since units of energy can be converted, we’ll use BTUs, and we’ll compare our stored energy to a gallon of diesel fuel, and use a typical value OF 147,000 BTUs a gallon for our calculations.
So here’s the Quiz Question and multiple choice Answers.
Q: How much energy can we transfer from a >standard< 120VAC electrical outlet into a storage device during a 10 hour window of time? Pick an answer closest to your calculation.
A. An amount equal to 10 gallons of diesel fuel.
B. An amount equal to 3 gallons of diesel fuel.
C. An amount equal to one third of a gallon of diesel fuel.
How about posting your answer? you need not use your real name.
Following are some musings about EVs and the road ahead..
How do we consider making an informed decision as to when we’ll invest?
Among those giddy about pure electric vehicles of the future, I meet few who will make time to run their own pencil.
As I look over the glossy EV ads, I see marketing at it’s best. There she is, a well dressed Babe with her makeup perfect and high heels on. She’s plugging in her Electric Vehicle into the standard household electrical outlet.
If we study the standard house of today, we note most all the outlets are now wired with 14 gauge wire. If we visit the household breaker box; we see our 120VAC outlets are fed by 15 amp circuit breakers. Before we design our EV charger, we best start with the power source. We know that 15 Amp breaker needs to be considered in our design or we could have a huge liability on our hands. Opening the brochure that comes with a breaker, we see they are typically rated to carry 80% of the current on a continuous basis.
Here’s the math, check me out.. … 120VAC x 15Amps =1800VA, we apply our 20% derate and end up with 1440 VA max that we can safely transfer from the grid to our load (our EV) over this typical circuit.
We’ll be generous here, and assume zero losses between the outlet and the input of our energy storage device. This allows us a maximum of 1440 watts of electrical power. Since a watt is a power figure, we can convert it to BTUs, Calories, or other common units of energy we are familiar with. A constant 1440 watts provides us with 4913 BTUs an hour. If we multiply by 10, We transfer 49,130 BTUs of energy into our EV in a 10 hour period, which might be a realistic overnight charge period of time.
If we compare this energy to kerosene or diesel, we see that we are able to transfer the equivalent of one third of a gallon of energy over our standard plug in over a period of 10 hours. This might give you some idea as to how much energy is in these fuels, and why the Russians use Kerosene in their booster rockets when they put payloads into orbit. Energy density has a lot to do with how much you can take with you, and how much work can be done.
Now that we know what amount of energy we can transfer into our EV, we shouldn’t expect to use it all, we don’t get everything back we put in.. We have losses of several kinds between the energy storage unit and the rear wheels and we need consider that on many days we might use far more energy than our transfer rate allowed just to keep the inside of our car warm or cool, and the windows defogged enough to safely see out. Consider that day in heavy traffic, stop and go traffic demands a lot from a battery, but keeping the car warm or cool can take far more energy than our home electrical outlet can deliver.
Certainly, there is hope! All you need do is call in the electrician and buy the more advanced charger and enjoy a fuller state of charge over the 10 hour window. In some cases, there’s little need to call in the gang, as the breaker box might be close, and you could have your new charging station installed for less than $3000.00 dollars.
Recently, we saw Prince Charles’ Aston Martin DB6 put to work as part of the Royal Wedding Ceremony hauling William and Kate. Some of the AE enthusiasts praised Prince Charles for having converted the car to run on clean ethanol made from excess wine. We skeptics might ask just how much excess wine there is in UK, and how might the effort ‘scale up’? Maybe we simply command more wine to be made?
Our homes have been designed to carry the electrical loads we normally carry, and of course our electrical grid is designed to carry what’s typical, we barely squeak by on peak load days in many areas.
When it comes to the Grid and rebuilding it to meet the new increased EV demand, those who are most optimistic will tell you the grid isn’t used much at night when the charging will be done. They have no concept of how energy is made or stored. In reality, the grid is far more dynamic than many understand.. there are energy reserves that are charged during off peak hours, and these same reserves are used to cover peak loads. The difference in cost between a peak KWH and an off KWH can be huge. In the wholesale market, a KWH might trade for five cents or well over a dollar during the hours or minutes of high peak loads brought on by a number of circumstances. An example of some of these energy reservoirs can be studied at hydro facilities and Power South’s ‘CAES’ compressed air energy storage system is a great example, and more of these solutions are under study to meet future demands.
This huge variability in price per KWH is seldom seen by the consumer, but if we decide to remove a good portion of our off peak production hours, we should expect the price per KWH to go up dramatically, fact is, what proponents of EVs call cheap electrical energy today might become far more expensive. If we were to convert half the cars on the road to EVs, we create a mind boggling need to increase capacity in electrical power generation and capacity to haul that energy to the point of use. How does that get paid for? Remember… A subsidy is paid out of your back pocket.
What did I get wrong?