[ausev] Residental Solar Power ROI

[Brian Lasseter]

On Thu, Aug 7, 2008 at 10:16 AM, Aaron Choate <achoate at gmail.com> wrote:
> Have those of you with solar arrays who have EVs experimented with using
> your traction pack as backup power during grid outages?  One of my strongest
> interests in solar + EV is that I can be offsetting the power that my
> vehicle is using with what is being generated off of my roof.  Having the
> pack available for emergancy power would be very cool.  Just curious if
> anybody has been working to hack a solution together.

What you ask for is very complex... but doable...

* "grid-tie" - As Greg stated, most solar installations are
"grid-tie"... meaning that the power goes into the power grid and
nowhere else.  Since the inverter must sync to the phase of the power,
when the city power goes... the solar inverter turns off too.  This
has a 95% efficiency.

* "battery" - The other normal option is "battery" system inverters...
meaning that the solar panels directly charge batteries, and then the
DC from the batteries is inverted to power your house.  With this
system, the local power utility will not let you connect to the grid,
since your power would not be phase-locked to the local utility.
This system, since it has to go through the batteries, has a much
lower efficiency, around 80%.  You could install an automatic transfer
switch to use a local utility power, but your efficiency will be low,
and you can't sell energy back.

Most of the time... you can't have your cake and eat it too... However
a new option has emerged from a leading Austrailian company, Outback
Power Systems:

* "grid-interactive" - This is slightly more expensive... but it does
what you would expect.  It charges the batteries to full, then
phase-locks to the grid power, and dumps the excess power back into
the grid.  At night, you can configure it to pull back from the grid
(more efficient) or to use your batteries (more self sufficient).  In
either case, it will switch from one power supply to the other if one
of the power supplies goes out.  (Switching to battery when the grid
fails, or switching to the grid when the batteries run out.)
http://www.outbackpower.com/applications/residential/grid_interactive/

I... alas... did not figure this out until I had already bought my
first inverter, but if my inverters die (which is the only component
in a solar system ever likely to fail), then I will get some of the
outback inverters.


Back to your question Aaron... as this is a question I have
pondered... With an Outback GTFX or GVFX inverter, you could run high
voltage DC power lines from the inverter sitting on the side of the
house to where ever your car is sitting, and when you park your
electric car, then you would hook up the high voltage DC lines to the
car.  The Outback inverter would sense them, and either charge or use
the batteries as it saw fit.

The downside of this set up... is that you would likely have low car
batteries each morning as you want to go to work if you have the
inverter set up to use the battery power before using the grid power.
You would have to disconnect the car from the Outback inverter and use
a regular A/C battery charger if you wanted to be able to use the car
for driving.  You would also have to be very careful how you displayed
such a system to Austin Energy.  They will only refund systems which
are connected to the grid.  If you wholly disconnect from the grid...
they reserve the right to come after you for money.

The upsides are enormous, as you get a higher efficiency charging the
electric car from the DC electricity of the solar panels instead of
the AC electricity in the house.  You also get the ability to not care
about a power outage (so long as your car is at your house).


-- 
TTFN,
Brian "Lasso" Lasseter

"No Sane man will dance." -Cicero (106-43 B.C.)