[SGVLUG] Off-topic - for Tom - plug-in car that can power yourhouse

[Robert Leyva]

Well!

...If I don't take into consideration any financial return on investment
and just focus on the geek factor as well as being able to keep your
fridge running next to your Wii and big monitor having fun as you sip your
nice cold "free as in beer" beer when the next Enron-like company causes
the next big power outage

...then it's priceless.


> I think this calls for some back-of-the-napkin calculations...
>
>
>
> Tom mentioned:
>
> Hmmm... As much as I'd like to agree with you and your "smiley",
> something doesn't add up here...
>
> The buyback for a $10k add-on would (naturally) be $10k of gasoline NOT
> purchased over the lifetime of the vehicle.  The third generation prius
> (which is what we're talking about here) nominally gets 50-60mpg, this
> add-on boosts that to 100+mpg.  Let's use 50 as that makes the figuring
> easier -- you effectively have to buy half as much gasoline with this
> addition to drive the same distance without it.  Though the price
> fluctuates, in the long run it has been hanging around $3/gallon.  At
> that price, $10k buys 3,333.3333 gallons (plus a drop or two...), and at
> 50mpg that pushes your car around the 1-mile oval 166,666.665 times.
>
> In order to SAVE $10,000, you would have to drive the car that much IN
> ADDITION TO the miles you "pay" for with direct gasoline purchases, or
> 333,333.333 miles overall.  In other words, for $20,000, you could drive
> a prius this far.  For $10,000 in gasoline PLUS $10,000 for the add-on,
> you could drive a prius exactly the same distance (though you've done
> the planet a "favor" by burning half the fuel).
>
> For comparison, I've **just** recently rolled past the 80k mile mark in
> my 2001 prius -- at that rate, I'll have to drive it another 15 years to
> have spent $20,000 in fuel (provided fuel really does stay at $3/gallon
> for that long -- all this goes out the window when the price of gasoline
> say TRIPLES from what it is now...)  That is without the "benefit" of
> this add-on
>
> Now, for the discussion at hand: the site talks about "selling" the
> excess energy in your vehicle as a "profit center" for joe average.
> Unfortunately, this doesn't take into account that if you sell off this
> "excess" energy, your MPG rating drops back down to 50mpg since you stop
> getting the benefit of using it to push your car around.  (actually,
> your mpg will probably drop BELOW what you would get without this add-on
> for two reasons: it's heavier, and with the battery "depleted", the
> on-board computer actually runs your car at idle longer to re-charge the
> battery)
>
> But that is a red herring :)
>
> You see, what the story is REALLY telling people to do is to "sell" the
> excess energy in your car DURING PEAK HOURS, then "buy" cheaper
> electricity at night to recharge the battery for your morning commute.
> You still get (better than) 50 mpg since (at least in the morning) you
> are running with a charged battery.  Presumably, "at work" your car will
> be used as a source during the peak period, so you'll either have a
> partial-charge or a depleted battery, so your evening commute will be
> back at 50mpg or less.
>
> BUT... Why bother going to this much trouble?  If the "deal" is to buy
> low/sell high by storing electricity in a battery for about 12 hours,
> why not just skip the part about having wheels on it?.  Or to put it as
> is often seen on slashdot:
>
>    1) buy "cheap" electricity during off-peak hours
>    2) charge a battery with it
>    3) ??? [or in this case, "wait 12 hours"]
>    4) sell back "expensive" stored electricity
>    5) profit!
>
> Unfortunately, this will only work if nobody else does this.  If
> "everybody" were to put a car-sized battery in their garage, "buy" cheap
> electricity off-peak, and "sell" it during peak, eventually the
> "off-peak" demand will reach or exceed the "peak" demand...
>
> Note: I was going to leave it is as an exercise for the reader to
> determine how long you would have to do this to make any measureable
> dent in your own electricity costs, but figuring out these things is so
> much damn fun :)
>
> Per this website, for our area, so cal edison charges about $130 for a
> "megawatt/hour"
> [http://www.jea.com/services/electric/rates_quarterly.asp]  but this is
> kind of lump-sum (i.e., doesn't take into account peak vs. off-peak)  It
> does, though, work out as an "average" of 13 cents/kwh which is about
> right -- A little more digging finds this site,
> http://www.riversideca.gov/utilities/resi-urate.asp, which shows "peak"
> rates at 20 cents and off-peak at 5 cents. (gratuitisly rounded)
> Averaging (20+5)/2 gets 12.5 cents/kwh, so we're in the same ballpark.
>
> HOWEVER, the real gem here is noting that there is a 15 cents "profit
> margin" per unit (well, kilo-unit ;) )  If your "normal" usage of
> electricity is evenly balanced between peak/off-peak periods, you'll pay
> the same regardless of whether you use the "average" rate or per-period
> rate.  If, in addition to that, you "buy" 1kw per hour off-peak and
> "sell" it all back, you'll be making 12*$0.15/day, or $1.80/day, or
> $54/month.  If your electric bill is less than that, your making a
> profit.  Of course, you do need to figure in the initial cost and
> depreciation of a battery capable of storing 12kwh -- if your "bill" is
> $50/month, it may take longer than you'd like to "pay off" this purchase
> with only $4/month to show for it...
>
> OK, it's time for me to head for the meeting -- expect this discussion
> to continue at BC tonight...
>
>


-- 
"Knowledge is Power" -- Francis Bacon

Robert Leyva
mrflash818 at geophile.net