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

Eric Cha ericc at xenopi.com
Tue Apr 16 15:34:46 PDT 2013

Hey Gary,

Thanks for sharing that info.  I've had a grid-tied 4kw PV system(and a 
Solar Hot water system which is tied in with our nat gas water heater) 
for about 7 years now, and we just leased a Leaf last November.  For all 
that time, we've been using basic (flat) rate billing.  After reading 
your report, I decided to switch over to TOU rates as well and just did 
so.  (Portland General Electric makes it very easy to do online).  We'll 
see how it goes!



On 4/16/2013 2:58 PM, Gary Graunke wrote:
> 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
> filling).
> 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!
> Gary

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