Eric's Blog

First month graph of solar power

The solar array was turned on for real 30 days ago; in that time, it’s produced 389 kWh of energy, which covered 96% of our usage for the month.  I’m pretty pleased with this! As compared to household use, it was:

• 389 kWh gross production, of which
• 230 kWh net was pushed out to the grid (meaning 389-230=159 kWh were used directly), and
• 245 kWh net was drawn from the grid

So, we used a mere 15kWh more than we made.  I blame it on my niece’s baking in the electric oven   (and the need to run the dehumidifier a few days; it was very rainy).  404kWh for the month was actually a fair bit higher than the last several months; the other big hitter was running the fans a lot due to the heat.

In terms of daily output, we saw:

• Peak power output of 2185W (I think this is due to a 199W limit on each microinverter)
• Maximum daily energy – 18kWh (on the first day of operation!)
• Minimum daily energy – 5kWh
• Average daily energy – 13kWh

What I really miss now, though, is the whole-house energy monitoring that I had; we climbed in usage last month, and I can point to some causes, but I’m flying blind now.  I’ll have to break down and buy a Ted 5000 if I don’t manage to put together my own monitor with CTs soon.

While the Enphase Enlighten monitoring site is pretty swanky, it’s slow to load and extremely flash-heavy.  It has the advantage of being able to do per-panel monitoring, event log monitoring, etc, but I was hoping for something a little more lightweight.  Enter pachube.com.  Let’s build out the internet of things….

The Envoy system monitor for the Enphase inverters has very basic output monitoring abilities; it shows you current power, and daily, weekly, and lifetime energy production.  So, we can screen-scrape this and upload it to pachube, then do what we like with the data.

I have this script on a 5-minute* 10-minute cron job to get the data.  The Envoy doesn’t seem to update faster than 5 minutes, and it’s such a gutless wonder, doing it any more often than that brings it to its knees, and it stops updating the main site!  If you have problems, you may want to reduce the updates to 15m or more.

To use the script, first get a Pachube API key, and set  up a new Pachube feed.  Add 4 datastreams, for instantaneous power, daily production, weekly production, and lifetime production, in that order.  Edit the script to add your envoy hostname/IP, your API key, and your feed ID.  Then put the script on a 5-minute cron job.  You’ll start seeing the data on a Pachube feed page like this.  Then you can use some of the apps highlighted on apps.pachube.com to create widgets as in the image above, as seen on this page.  You can even get an iPhone app to monitor the data, or create an OSX dashboard widget from the HTML objects!

*Edit: Don’t set the cron job to be more frequent than 10 minutes.  I’ve had trouble with the Enovy unit bogging down and not reporting to Enlighten if you hit it more than every 10 minutes (!)

I got the meters installed today.  It took about 2 minutes of work, after 2 weeks of wait.

The meter on the left is the “production” meter which measures how much power the panels have made over their lifetime, period.  It’s so the utility knows what they got for their rebate money.  (Oddly, it’s the exact same Centron C1SC meter I had previously, for usage measurements!)  The meter on the right is the net meter.  Today it’s running backwards, even though it’s cloudy, because the house is pretty much at base load.

All that’s left is the anti-islanding inspection*, but my installer tells me the utility is OK with having them on prior, so we’re up and running!  On a cloudy day, of course.

I don’t yet have the official Enlighten URL for the array, but my homebrew monitoring is here on pachube.com.

*And one concern about the physical install of the panels & cables, which might possibly require removal and re-fastening of the panels, which would just be awful at this point.

Edit: The official monitoring site is now active.