[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!

Cheers,

Eric

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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