

Ask HN: Does plugging an electric car affect household electric consumption? - Mustafabei

Does anybody know about the possible effects of it to the grid?<p>Read this today:<p>http:&#x2F;&#x2F;www.technologyreview.com&#x2F;news&#x2F;518066&#x2F;could-electric-cars-threaten-the-grid&#x2F;<p>And it says: &quot;Plugging in an electric vehicle is, in some cases, the equivalent of adding three houses to the grid.&quot;<p>What? Really? It couldn&#x27;t possibly be that! Anyone?
======
lutusp
> And it says: "Plugging in an electric vehicle is, in some cases, the
> equivalent of adding three houses to the grid."<p>What? Really? It couldn't
> possibly be that! Anyone?

I'm a former NASA electrical engineer, and I can tell you it's so. A charging
electric car requires an enormous amount of energy, and a suitable charger
will greatly increase household power consumption for the duration of the
charging cycle.

The Tesla model S has two battery types, let's use the larger battery for this
example -- it has a capacity of 85 kilowatt-hours (KWh). Assuming 25% system
losses, to fully charge this battery requires about 106 KWh. That translates
to 8.83 kilowatts for twelve hours.

8.83 kilowatts at 240 volts requires about 36.9 amperes. A typical household's
electrical system can handle this current level if it's been set up properly.

Okay, so for 12 hours each night, the electric car requires 240 volts at 36.9
amperes to top off its battery. How does this compare to a normal household's
power usage? Here's an online reference:

[http://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3](http://www.eia.gov/tools/faqs/faq.cfm?id=97&t=3)

Q: "How much electricity does an American home use?"

A: "In 2011, the average annual electricity consumption for a U.S. residential
utility customer was 11,280 kWh ..."

An annual usage of 11,280 KWh divided by the number of days in a year gives
30.88 KWh/day. Compare this to the daily energy required by the electric car
-- 106 KWh. The bottom line is that the electric car's power usage is about 3
1/2 times that of the remainder of the household, and a household with an
electric car uses 4 1/2 times as much power as a household without an electric
car.

Returning to the original quote:

> "Plugging in an electric vehicle is, in some cases, the equivalent of adding
> three houses to the grid."

That's just about right.

~~~
pfbz
Not exactly... but this isn't rocket science.

First, the P85 has an ~280 mile range, so you would only need a full recharge
every night if you were driving about 100,000 miles a year.

It will recharge on a standard NEMA 40A outlet at ~35 miles/hr using 9.6 kW,
or ~70 miles/hr using the optional 16.8 kW high speed charger.

So to go a typical 12,000 miles per year, that takes ~3,300 kWHs, less than a
tenth of your analysis. It's about a 25% increase in average household energy
consumption, not 350%

------
mchannon
Let's set the FUD chow aside for a second.

It takes more electricity to refine a gallon of gasoline than an EV uses to
travel the equivalent distance. That means if oil had zero energy content or
environmental footprint, you're still using more electricity filling your
SMART car up at the pump that plugging your EV in at home.

So I ask you to do the math- if it uses less electricity to charge at home
than the refinery uses, how is our grid destined for failure?

On a house-by-house scale, I'll grant that maybe you'll need a new transformer
or electrical box if you're interested in fast-charging 100mi of range in one
hour (less than 5% of EV owners would consider that necessary or worth the
expense). Far more Americans have been adding bigger and bigger refrigerated
air systems to their homes for years requiring these same electrical service
upgrades (adding a 200A load to a 60A service installed on the cheap in the
'40s), and nobody is handwringing about that.

Turn on your electric oven to bake some cookies and odds are you're using
three houses' worth of electricity, depending on the houses and the time of
day.

The real question is how many refineries are we taking off the grid by
switching to EV's?

