Being that it’s Friday evening here, I think a bit about the weekend to come.
The weather this weekend is a mixed bag, but I’m going to need to hang a door on the chicken run, and start working on the inside of the chicken coop, so that we can put those ladies to work! Now then…
Today I was starting to look over application notes and data sheets for a home power meter that I can use to measure power that we’re buying from PG&E and measure the power we’re not buying, but rather selling to PG&E. Being the early adopters that we are, we defied the tin-foil hat wearing residents of Sebastopol and went ahead with getting our Smart Meter installed.
It’s pretty. It’s digital. It’s the future, people. I don’t understand how you can deny that there’s already freakish amounts of RF coursing through your body every minute of the day as you shout into your Bluetooth headset jammed into your ear canal, which is linked to your wireless phone tucked in your pocket (mere millimeters from your flesh, mind you), sitting in front of your computer, and you’re upset about a meter on the side of your house causing you harm? Seriously?
Anyhow, we now have a smart meter that runs both ways. Unfortunately, and partly due to the fact that our neighbors all cower in fear of progress, we can’t actually go to PG&E’s website to see how much power we’re using on a real-time basis. Thanks, neighbors!
[And don’t get me started on the solar array we had installed using Enphase Energy microinverters. They have a subscription-based web site called Enlighten that will show you — Ruby on Rails style — how much energy you’re generating. But they lock up the transceiver (that you bought) nice and tight, and expect only that you will obediently plug it into your home broadband network so it will transmit your power generation data to them, so they can turn around and sell you your data back to you. Ridiculous.]
So, I’m left with the option of measuring and logging it myself. There are some very well worn Arduino forum posts and even some cool European-oriented open source hardware websites where folks have set this up (that’s not exactly being fair. There is a growing community of people on that site, it’s just that it takes a very 230VAC non-split single phase view of the world). And now there’s even someone in the U.S. who has helped figure out the nuances of split-phase current transformers for us lay people.
So if I was fully equipped, here is my power meter wish list:
- Accurate to +/- 1% from 1A to 200A (which is the size of my residential service)
- Powered by it’s own 240VAC circuit, to ensure voltage reference for each half of the single phase.
- Wifi or XBee or some other RF transmission for the short distance of getting the signal into my house. Don’t forget the tin-foil hat.
- Actual measurements will be taken by a circuit I’ll design that uses two separate Analog Devices ADE7753 tied over SPI to an Arduino-compatible MCU.
- I will likely use two split core current transformers (200A) that meet my desired accuracy for the mains.
- I will need to find two smaller current transformers (20A) that will work for the solar microinverter lines.
- My biggest problem here is finding CT’s that will perform well enough under low-load conditions (< 1 amp) as well as full load conditions. And as long as I’m not spending a fortune to do it.
- One of the ADE7753’s will measure the incoming service from the utility.
- The other ADE7753 will measure the “incoming service” from the solar array microinverters.
- Together, I should be able to work out my net metering myself.
- The MCU will retrieve measurements from the ADE7753 and store it until it periodically forwards a collection of the data to a waiting RF receiver, hooked up to a real computer (well, okay, a Mac Mini, but it’s cute anyway) that will properly compile it into a database of sorts. Alternately, it will upload the data using a RESTful web service to a cloud-based web app that I write myself. Yeah, okay, keep it simple.
- From there the data is stored on servers that I control (assuming I don’t go with Google AE, that is), and the data is mine to use as I wish. Enphase be damned for their closed-source, closed-minded approach.
Simple, right? We shall see about that. I’m figuring it’s my 2011 on-the-side project for getting on top of our energy usage.
My biggest problem right now is that I don’t have any of this equipment (except perhaps the Arduino). Sigh.