PV output not correct

Submitted by Lloyd on Sat, 31/03/2012 - 18:32

Moved forward on the next step of my PV monitoring installation this afternoon. Have now got both CT1 and CT2 connected to pv output and consumer unit input. Initial observations are that the PV readings are higher than they should be. And now the sun has just gone down, , I'm still getting a reading of about 200W, even though the inverter has shutdown. (Although as I type it has just fallen to about 45W - ?)

Any clues about where I should look?

Thanks

Lloyd

Re: PV output not correct

Submitted by madmurg (not verified) on Sat, 31/03/2012 - 20:07.

this reading is correct, my solar pv has the same reading on shutdown. this is the power the invertor is using to run.

Re: PV output not correct

Submitted by Lloyd on Sun, 01/04/2012 - 10:04.

The spec sheet for my inverter (SMA SB3300) states that night time consumption should be < 0.1W, so I'm still skeptical. Tonight I'll try and remember to throw the AC isolator on the inverter and see what happens.

Other readings still seem too high. I'm using type 1 connections. Thinking about it, if I want accurate readings, do I not need voltage reference, so I need a hybrid of type 1 and type 2?

Lloyd

Re: PV output not correct

Submitted by robw on Sun, 01/04/2012 - 10:16.

Hi, We have the Sunnyboy 1700 and ours used 0 at night time.. Both energy monitors agree with this so i think something must be amiss with the setup or config.

Rob

Re: PV output not correct

Submitted by Amin Zayani (not verified) on Mon, 02/04/2012 - 03:34.

Modern inverters use less than 1W at standby.

I think your problem is related to noise or so, try recalibrating with a big resistive load (kettle 1500w+).

Re: PV output not correct

Submitted by madmurg (not verified) on Mon, 02/04/2012 - 05:45.

Last night i put a clip on ammeter over the cable to the inverter and it came up at 0.1 amps
So using ohms law i x v = watts. So 0.1 x 251 = 25watts. My unit reads 44 watts so it is not that far out, i am not worried about it being that accurate

Re: PV output not correct

Submitted by glyn.hudson on Wed, 04/04/2012 - 14:06.

Hi Steve,

If your only using a clip-on CT and not using an AC-AC adapter to monitor voltage your monitoring apparent power. When the power factor is less than 1 you will be getting a higher reading than the actual real power. Inverters with transformers in them seem to exhibit a low power factor at night. You will get more accurate results if you use an AC-AC adapter to enable real power to be calculated. I tried to explain this with some screen shots as illustration here: http://openenergymonitor.org/emon/node/448#comment-3321

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