Incidence meters [RE-wrenches]

[Bill Brooks]

Windy and Kurt,

Don't bother sending it back to the factor for calibration until you check
it for yourself. All you need is a good PV module with a known Isc at 1000
W/m2. Test the Isc of the module and compare it to the Daystar in the same
orientation.

A module with an Isc of 4.7 Amps at 1000 W/m2 will produce 4.0 amps at 850
W/m2. This is a routine test that every Wrench should have in their back
pocket. Isc is almost perfectly linear with irradiance for crystal silicon
down to at least 300-400 W/m2. All the Daystar is doing is measure Isc of
the small cell on top.

God often gives us more than 1000 W/m2 in the summer and fall so don't blame
God or the meter until you know that the meter is wrong--then send it back.

Bill.


-----Original Message-----
From: Windy Dankoff, Dankoff Solar [mailto:windy at dankoffsolar.com]
Sent: Tuesday, February 18, 2003 8:18 AM
To: RE-wrenches at topica.com
Subject: RE: Incidence meters [RE-wrenches]


>Greetings Larry,
>
>Due in part to a series of posts on this list, I bought a Daystar hand
>held meter.  If I remember correctly it was around $130 delivered
>(www.raydec.com/daystar).
>
>I would like to hear about other experiences with this meter.
>
>I must say I have been impressed, or maybe even a little concerned, at
>how frequently the Daystar meter indicated a watts/m2 above 1,000 this
>last summer.  On a number of days where it felt really hot from a
>human/solar perspective, I pulled out the Daystar and it indicated we
>were receiving on the order of 1,200+ watts per sq. meter (Northern most
>point in WI, sometimes 4 hours past solar noon).  Is this what we should
>be seeing up here or might the meter be somewhat optimistic?
>
>Kurt Nelson


Kurt -- I'd be suspicious too, unless you were in a period of very
low humidity. I suggest you send it back to the factory and ask them
to recalibrate it if necessary.

Ours reads a bit over 1200 on a dry clear mid-day here in New Mexico.

I like the meter very much. It uses a polycrystalline silicon PV cell
as its sensor, so it sees what a PV array sees.

Windy

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