continuing from part 2:
Monitoring hardware to public display database interface
Another aspect of the project that has been interesting and I have learned quite a bit from has been connecting the different monitoring hardware up to the display database, We are doing this via three routes:
1) Direct access to the SMA Inverters webbox via a cleaver bit of code Carlos has written. Carlos has kindly documented his work and put it up on the website here, have a look: http://openenergymonitor.org/emon/node/89
2) Via a JSON string fetched across the network from a script on the proprietary SCADA pulse counting system. With the JSON string being decoded and the data being inserted in the database via the method documented here: http://openenergymonitor.org/emon/node/88
3) For the pulse output meters: total grid import, chp generation and backup diesel generator that are located on a different part of site were there was no existing pulse counting hardware: I used an arduino to read the pulses and an ethernet shield to send a JSON string with the power and energy data to the public display server. I have documented the Arduino pulse counting here http://openenergymonitor.org/emon/node/79
Finding out about JSON strings was really useful. A JSON string is a string structure that allows you to send a variable key along with its value. It is possible to use this key to automatically register new devices by checking if the device already exists in the database with the same key and also send data from multiple devices in no particular order to the same script on the server.
Learning about and using pulse output kwh meters has also been very interesting. It is a nice way of monitoring large systems and there are pulse output meters for all sorts of measurement applications: water, gas etc. Many smart meters are pulse output meters, if they dont have the wired pulse output they probably have the flashing led output that you can bolt a sensor on to as many people are doing.
part 4: next steps and the PV lab project...To engage in discussion regarding this post, please post on our Community Forum.