Hi,
I've just bought the Solar PV bundle, with a preloaded SD card that I've loaded into a PI with a RFM12Pi attached. Once I figured out that I had to change the frequency in /boot/oemgateway.conf from 8 to 4, so it could talk to the transmitter unit, it's all gone really well and I have both my electricity consumption and PV energy generation appearing on emoncms.
But when I chose "log to feed" for my PV input on emoncms, it first came up as a negative number. So I've since added a multiplyer of -1 to make it positive. That all made sense to my meagre mind, but is that the way to do it? Is there another (better) way? The feed URL is here:
http://emoncms.org/vis/auto?feedid=38105
Thanks.
Steve
Re: Is multiplying Solar Input by -1 correct?
Normally solar production is reported as a positive, I suspect the solar ct needs to be turned around.on the cable.
Paul
Re: Is multiplying Solar Input by -1 correct?
Yup - that worked! Thanks Paul!
Re: Is multiplying Solar Input by -1 correct?
I actually have the inputs come in positive, log them to a feed and then make them negative so I can plot the solar on the multigraph as negative and the power consumption as positive.
http://oem.nicelyweb.com/emoncms/knicely/PowerSumm
Re: Is multiplying Solar Input by -1 correct?
Just for the record and in case someone reading this doesn't fully understand...
When you measure current on its own, you can have no idea of the direction of energy flow. If you know that the current is flowing into a load that only consumes energy, or from a source that only supplies energy, that knowledge will tell you the direction of energy flow, but the current won't.
When you add the voltage measurement and calculate real power, then the phase relationship between current and voltage will give you the direction of energy flow. By convention, we regard import / consumption as positive, and export / generation negative. You can reverse the phase of the voltage by reversing the adaptor (in the case of our standard one), and the phase of the current by reversing the c.t. on its cable. I would argue that "correcting" the sense of the measurement is best done as close to the source of the measurement as possible, so that the rest of the system will be working to a consistent standard.
There's nothing wrong with having your own convention (e.g. Robin's Energy Diverter conventionally uses exported energy as positive), or having one input different if it's not physically possible to do otherwise; as long as you make it clear what your convention is when you ask questions in the forum! Otherwise we'll all get confused.