[Oeva-list] my first solar year with Leaf EV, solar PV, and TOU

Gary Graunke gary at whitecape.org
Tue Apr 16 14:58:33 PDT 2013

Just over a year ago I switched to TOU rates-three months after I began
operating my new PV array on my garage.

My primary EV was my 2011 Nissan Leaf, though the last month I also drove my
2013 Tesla model S-paying for all those trips to Corvallis and back on one
charge. I put nearly 1000 miles per month on the Leaf, but nearly half was
in long trips, where I obtained free charging. The heavier Tesla uses
electricity to heat or cool the battery even when it is not driven, but
otherwise is rated at 89 mpge vs the 99 mpge of the Leaf.

The solar PV array is 20 245W Solarworld panels feeding two inverters. It is
facing southwest rather than directly south, so its efficiency is only 85%
of ideal for a fixed mounted array. It has a separate meter to count
electricity generated, but not by time period. The installation cost me
~$7000 after Energy Trust and federal and state tax credits. 
The site survey estimated that it would generate 4363 KWH annually, but the
meter difference from April through March is 5479. 

My single level, C-shaped house was built in 1976-long before we cared much
about energy efficiency. However, it has been retrofitted as much as the
usual commercial folks do-no radical improvements. It has a 30+ year solar
hot water system backed up by electricity (now on timers to only heat during
off-peak). The backup hot water is mostly used in the winter. The house has
natural gas heat and a heat pump for AC and heat (but I mostly use natural
gas during the winter). 

Over the year I used 9244 KWH of electricity, 7268 KWH from the grid (796
on-peak, 1405 mid-peak, 5067 off-peak) and 1976 KWH directly from the panels
(435 on-peak, 1239 mid-peak, 302 off-peak). The remaining 3503 KWH generated
was fed into the grid, 771 on-peak, 2196 mid-peak, and 536 off-peak
(Sundays-not at night). 

My non-TOU bill would have been $483.74 for the year, but my TOU bill was
$406.48, a savings of $77.26. Of this, approximately $121.44 is the base
charge, credits, taxes, etc. (The grid is a nice battery I can rent for
$10.12 a month). The electricity charges would have been $362.30 for
non-TOU, and the on-peak TOU cost was $26.42, mid-peak $57.94, and off-peak
$238.79 for a total of $285.04. So TOU saved me $77.26. 

The TOU rate has some interesting complications. PV electricity is counted
as generated on-peak, but is used to offset (in order) on-peak, mid-peak,
and off-peak consumption. PGE gained $25.76 from my generating during high
demand times and consuming during low demand over a system where separate
TOU balances are maintained for each TOU period. In this hypothetical
system, I would have ended the year with balances of 16 of on-peak KWH, 791
of mid-peak KWH, and zero off-peak. (Of course, in net metering any annual
balance is contributed to the fund for those who can't pay their bills each
March, so the real system is better for me-I did not forfeit any remaining
balance). So PV with net metering is not a zero-sum game-we both benefit.
(This shifting in production and demand is called peak shaving and valley

The value of the PV generated electricity directly used would have been
$200.15 under non-TOU, but under TOU it was $300.61. So TOU enhanced the
value of my PV system by another $100 just from direct use. Looking at it
another way, the retail value of the electricity under non-TOU would have
been $554.97, but it was $709.68 under TOU. So it returns 10% ROI less 3.33%
depreciation (PV life of 30 years) or 6.66% tax free interest equivalent for
very low risk-backed by the full faith and credit of the sun. The PV energy
efficiency of converting sunlight to miles on my Leaf is 20% * 80% = 16%--an
order of magnitude better than biofuels.

Bottom line: PV and EV are a great combination. For the after tax investment
of the Leaf, $25000, and PV system, $7000, I spent only $406 for over 11000
miles of travel and all the electrical needs of my house, including winter
hot water.  

Going forward, the Tesla will consume more electricity than the Leaf, the
road tax cometh, and DCQC stations will charge for electricity (though the
free Tesla supercharging is somewhat supported by warranty maintenance fees
relative to the Leaf's amazing $20/year). But I'm still way ahead of paying
well over $770 for gasoline (Prius at 50 mpg, $3.50/gal), and my home
electricity bill is thrown in for free.

Live long and prosper!


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