ratcheting cyclometers [RE-wrenches]

Jeffery Wolfe, Global Resource Options jeff at globalresourceoptions.com
Sun Dec 7 21:48:11 PST 2003


Hi Kelly,

Actually, a substantial portion of the PV power WILL flow to the subpanel if
any of the devices powered from it are on.

My understanding of the way the SW works is as follows:

 - If PV power is available, it charges the batteries.
 - If additional PV power is available, it powers the sub panel
 - If even more PV power is available, it goes out the AC1 connection toward
the main electrical feed.

So the amount of PV used by the sub panel has nothing to do with the
duration of outages.

If you've got 100 watts of continuous load on the subpanel, and sun for 10
hours a day (not peak sun, but enough sun to create 100W), that's 1.0
kWh/day that a meter on the AC1 line will not see. So it really depends upon
the backup power loads. Most battery systems that we do want a lot of the
house backed up, so a significant amount of the house runs through the sub
panel. This can easily use up all the PV output on a modest day.

Just no two ways about it. Figuring out RE generation with any type of
battery backup system is not simple.

Jeff Wolfe

-----Original Message-----
From: Kelly Keilwitz [mailto:kelly at whidbeysunwind.com]
Sent: Sunday, December 07, 2003 2:40 PM
To: RE-wrenches at topica.com
Subject: RE: ratcheting cyclometers [RE-wrenches]


Hi Jeff,
Yes, in order to completely measure all of the RE AC output from the system
the throughput to the subpanel loads should also be measured. However,
since these systems are battery backup for a few loads where the grid might
normally be down for 24 hours per year I disagree that the power to the
subpanel is substantial (in these cases). The benefit in accuracy doesn't
seem worth the extra cost and complexity of metering the subpanel AC output
in addition to the grid AC out/input from the inverter to me.

The electronic meters sound promising and must take up less space. However
the utility style meters and sockets are reliable and pretty cheap.(I'll
let the list know when I get a price). I'm not sure about the accuracy,
though.

Yes, the ratcheting meter will allow power flow in both directions, but
measure only one. That's what we want. The customer is paid (extra) for
the "Green Tags" that they produce (send OUT to the grid). Non-ratcheting
meters reverse direction and subtract any energy IN used to charge the
batteries.

Please correct me if MY thinking is skewed!

-Kelly

>
> In order to capture all of the RE power, you need to also measure the
> AC Load output to the battery backed up sub panel. This can be a
> substantial portion of the total power generated.
>
> WE've just started using Davidge Controls electronic meters. They make
> a variety of devices, including one that measures power in each
> direction on a bi-directional line. I believe it's called the
> "Everglades" model. You would need this, plus a "Sequoia" model for the
> unidirectional power to the sub panel.
>
> They are easy to install, although we've had two problems in our first
> application: wrong transducer sent, and then a bad unit. So my jury is
> out still as to whether we'll continue to use it, but it's the cheapest
> method I've been able to figure out so far for actually measuring real
> PV power generation on an SW type installation. Total equipment cost is
> in the range of $300. Each meter has it's own mechanical "odometer"
> type readout (two for the Everglades). There is also an upgrade for
> computer input.
>
> The problems with ratchet meters that I've seen is that although they
> only measure the power in one direction, they will let it flow in
> either direction. Thus, you cannot simply install two opposing ratchet
> meters to measure the power on a bi-directional line. Am I wrong? (It
> would be cheaper if I was wrong!)
>
> Jeff Wolfe
> Global Resource Options
>
> -----Original Message-----
> From: Kelly Keilwitz [mailto:kelly at whidbeysunwind.com]
> Sent: Tuesday, December 02, 2003 5:09 PM
> To: RE Wrenches listserve
> Subject: ratcheting cyclometers [RE-wrenches]
>
>
> Hi all,
>
> We have several battery-based grid-tied solar and wind systems where
> the owners are selling the "green attributes" of their production,
> aside from net-metering with the utility. In order to track total
> production a seperate utility-style meter is required. Because these
> are battery-based systems a ratcheting meter is preferred (so that
> grid-power used to charge the batteries is not subtracted from the RE
> production). Cyclometers (odometer style dials) are easier to read than
> those goofey hands that rotate in opposite directions.
>
> Ideally I would like to find 120volt, ratcheting, cyclometer utility
> style meters. Anyone know where I can find such animals?
>
> Thanks
> -Kelly
>
>
> Kelly Keilwitz, P.E.
> Whidbey Sun & Wind
> Renewable Energy Systems
> 986 Wanamaker Rd, Coupeville, WA 98239
> ph & fax: 360-678-7131
> sunwind at whidbeysunwind.com
> www.whidbeysunwind.com
> Renewable Energy Now!
>
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