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Plug in grid tie systems advice? - Page 5

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Posted by Neon John on February 23, 2009, 8:57 pm
On Mon, 23 Feb 2009 11:18:43 -0600, me@privacy.net wrote:

This thread reeks with the stench of ignorance and just plain
stupidity.  How 'bout some thoughts from someone "in the business"?
(retired utility engineer still active in metering and related

First and foremost, you won't be reversing your meter with a toy
system like you're contemplating so none of the ill-informed
discussion about that matters.  For the record, most meters
(essentially all electronic and most mechanical) can do net metering.
Wtih electronic meters it is simply a matter of the utility setting
the appropriate bits during the calibration and configuration.
Mechanical meters naturally run in either direction unless equipped
with a non-reversing ratchet.  This is rare.  

The only metering system that I can think of off the top of my head
that requires two meters is the Turtle AMS.  This is an add-on to
mechanical meters to implement an automatic metering system.  It
counts dial revolutions and cannot distinguish between forward and
reverse events.  Two meters are required, each equipped with a
ratchet.  The company's software automatically subtracts the readings.

Some utilities *as a matter of policy* require two meters.  The reason
is that they want to know how much over-priced power they're having to
buy.  They are forced by law to pay the highest avoided rate (usually
retail) for power that they neither need nor want.  My SWAG is that
there are tax deductions to be had by the utility for these purchases.
In any event, it is a POLICY and not a technical matter.

If your unit is appropriately certified by a testing agency (UL, ETL,
etc) then its use would not be guerilla.  Neither my utility nor any
that I'm familiar with require any sort of paperwork for such
applications.  Others obviously may be different.  You're not going to
generate enough electricity to reverse the meter or even slow it much
so no special metering setup (in accounting or otherwise) is

Instead of guessing, why not find out.  A $0 Kill-A-Watt and a little
time will tell you for sure.  I have a spreadsheet to help streamline
an energy audit.  You can download it here:


Bottom of the page.  It is known to work in both Excel and Open

One of the first things you could do is to post your monthly power
usage, both the kWh and the bottom line dollars, so I can analyze it.
Once those figures are in hand and the cost of your candidate solar
system are also in hand, then we can do an ROI.  I suspect that it
will be very poor compared to other things that you might do.

Also post what kind of comfort heat, water heat, and stove you have
and how much you cook.  Also whether you have AC and what type
(central, heatpump, window units, mini-splits, etc) and the SEER if
you know it.

Something else that you need to do is go to NREL (National Renewable
Energy Laboratory) and look up the average insolation for your
location.  Their numbers are best case.  The constraints of your
apartment orientation and lack of access to the roof will greatly
reduce your available energy.  For example, I should be getting about
6 hours of direct sunlight at this time of year.  I actually get less
than an hour, the result of my cabin's orientation, the terrain and
the forest.

Unless your apartment happens to be south facing and located in a
wide-open space with no trees or buildings to block the sunlight,
you're unlikely to get enough light to matter.  You can go here


and for under $50 can buy a light Hobo that will log the light
intensity falling on it.  Ideally you'd log for a whole year.  At a
minimum you should log during the parts of the year that sunlight is
blocked by local obstacles for a significant period of time.

You could, of course, just toss something up there and see what
happens.  If you have the disposable cash laying around, that's a
valid option.  I'd suggest putting together a meter system like I
picture on my web page above so that you can actually measure what
you're generating.  Not much of an experiment if you don't have any
data at the end.  Most likely the normal variance in your month to
month energy use will mask the change, if any at your revenue meter.


Posted by me on February 24, 2009, 7:40 pm

I plead guilty John!

Basically I have abandoned idea of a
plug in grid tie system and have started
looking at ways to REDUCE power
usage..... i.e. new fridge, etc

Thanks to everyone for advice!!1

Posted by Jim Wilkins on February 25, 2009, 12:39 am
 On Feb 24, 2:40pm, m...@privacy.net wrote:

Harbor Freight's site says item 93519, the Kill-A-Watt for $9.95, has
been discontinued.

Posted by Bob F on February 26, 2009, 6:42 pm
 Jim Wilkins wrote:

They have never been the cheapest place to get it.

Posted by Neon John on February 26, 2009, 1:56 am
 On Tue, 24 Feb 2009 13:40:28 -0600, me@privacy.net wrote:

But that wasn't aimed at you.  You asked a legitimate question and got
everything from the net.lawyer.wannabes on down.

You're welcome. Please follow my advice and measure before you buy. If
your fridge has been made in the last 10-15 years, a new one isn't
going to improve things much.  Older than that and the improvement
will be remarkable, percentage-wise but not on the basis of either the
amount of energy saved or the ROI.  Fridges just don't use that much
power.  My spreadsheet contains actual data from various appliances
that I've measured. I left that data in place as an example.  Even the
very old 2 door fridge, an energy hog compared to modern ones, doesn't
cost much per month to run.

If you have any more questions about doing your energy audit, feel
free to ask.


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