I also have an interesting table of energy equivalents per gallon of
gasoline which I will try and upload for the group.
But they are quite complex (worse, I think, than cell phone plans).
First the "baseline" usage is dependent on where you live, even within
the south bay there may be multiple different baseline values.
Then the cost of power is on a progressive scale based on
average daily usage in a billing period.
So a simple question like: "How much does it cost to run
a particular electrical device" cannot be answered even
approximately without knowing:
1) Where do you live?
2) How much power do you use per month?
and possibly also (if you have time-of-use metering)
3) When will you use it?
My cost per kWh could vary by a factor of 5 (from $0.09 for
baseline off-peak usage to $0.45 for >300%baseline
That $0.45 rate is from the time-of-use (E-6) tariff and only applies
to 1pm to 7pm summertime (May-October) usage. Unless my solar
panels break, I should not only never hit the +300% baseline level
in that period, I should be collecting $$$ from PG&E during that
time period each day as my net usage will be negative. Sadly I
don't think that they'll credit me at $0.45/kWh (even if I give them
+300% of the baseline usage) ... but they will pay at the peak-time
baseline rate of $0.20865 which is a two-for-one deal against the
The normal residential rate is the E-1 tariff which maxes out at a
mere $0.36434 per kWh.
Akeena provided a bunch of numbers in their bid ... the bottom line
was payback of the installation cost at about the 11-12 year mark. I
can dig up the folder and find some more of the details on how they
got to that number (I've been meaning to do so for a while, I want to
put more stuff on my solar web page, comparing the predicted with the
Unfortunately, we don't have any data on how many SVP customers use air conditioning.
>>> "John Allen" <johna...@gmail.com> 3/19/2007 10:40 AM >>>
John A Allen
http://solar.sippelhouse.com but right now it just has graphs showing
power and energy produced today (which are pretty sad today with 100%
cloud cover ... but at least the panels are getting the dust rinsed off by
the rain), a last 60-days graph, and a link to a page with some basic
> No rush, but I would lke to see the numbers and more especially the
> formula(s) for ROI.
I'll dig out the predictions from the Akeena sales pitch together with
the assumptions on which they were based.
> Perhaps the most fundamental is the ratio between total initial cost and
> yearly energy savings. After that there are a lot of details that are
> different for different people, like tax rate, cost of capital, and
> predicted energy inflation.
I'm planning on adding some predicted vs. actual numbers.
I wrote the logging software, and used "gnuplot" to make the graphs.
The inverters produce other data (such as heat-sink temperature, and
some mysterious MPPT data) that I may add later if I find an interesting
way to display it (especially if in summer I find that excessive inverter
temperature is affecting the yield of AC-watts).
> What does sippel refer to?
We are the third owners of our 1909 craftsman house. The first owner
(from 1909 to 1979) was Effie Church-Sippel ... hence we refer to our
house as "The Sippel House" as it might have been known in its early
years ... but for the minor historical detail that she started out as
"Effie Church", and only added the Sippel to her name when she
married ... but "The Sippel House" sounds a lot cooler than "The
> http://solar.sippelhouse.com/daylen.png , can you tell
> me why there is sharp transition on the sun rise and set times twice a year?
Either there is a giant black-hole in our solar system that periodically
stops or boosts the rotation of the earth ...
> Is that the damnable daylight savings time?
Ah, yes ... that seems a lot more likely :-)
> Imagine all the programming time
> that has gone into factoring that out of things.
In this case it was programming time to put that *in*. The
software that generates sunrise/sunset times for me does
so in UTC, but I usually think in local time.
The inverters have rs232 ports for data (and some programming, but
most of the programmable things are factory-set stuff). I have an old
pentiumII system that is the house Linux server (way too many watts,
but better than a modern desktop). That system collects the data
every minute while the sun is up. Every 15 minutes it makes a new
graph and uses ftp to push to the website (hosted by Yahoo!).
> Cool history about your house. How about a tour?
Since you were so gracious as to open your house for me to
see, how can I refuse? I'll be up and out of the house early this
weekend (my daughter has a swim meet). But I think I'll be
home in the late afternoon).