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Recently had a solar array put in, and the information available is ... lacking...  I went looking for an energy monitor, and found several, but the one that caught my eye was eguage.net.  Holy crap, $500 ?!?!?  Seems like a job for...  Arduino!

I've seen a number of projects around this, but none seem to directly fit my needs.  I think it'll need to monitor voltage, and then (seperately) monitor current-transducers.  Neither should be all that difficult as far as hardware goes.  The software could simply post the data to Google Powermeter, or some other API...  Ideally I want to monitor (with a seperate CT), every circuit in the house, plus the main, plus the solar production.  But I'd be happy with seeing just the main and solar at this point.

Has anybody done something like this?
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Holy crap, $500 ?!?!

Well - how much did you spend on the array?

Normally, $500.00 is a drop in the bucket compared to the total cost of the array, installation, inverters, charge controllers, battery bank, etc...
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Even if it cost me £50, i'd be looking at doing it with a microcontroller.  smiley-wink
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The array is on a lease, third-party-developer basically...  Zero down (actually they're going to give me a $700 incentive, plus I got a rebate from the city on the sales/use tax.  You might argue I should use those kickbacks to invest in the e-guage, but that didn't go over so well with my wife :-) ), zero-buyout, 20-year lease, for $87 a month and I own all the power it generates.  Plus they insure it, maintain it, and repair it.  Sunrun will also "monitor" it, but their "real time monitoring" is more like real-week monitoring, or maybe real-day at best, plus they don't show my usage, only my production.

So needless to say, the Arduino comes to mind.  Seems like there should be a project around this, but all I've found is the openenergymonitor, which looked a bit lacking...  Maybe thats what the E-Guage guys were thinking, so they built a good one.
« Last Edit: November 16, 2010, 02:34:43 pm by msturtz » Logged

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Have you asked them about what you want to do, and how that may impact any warranties?

Also - how old is your roof? If you are roof mounting the system, you might want to get it replaced first; otherwise, when you need to replace your roof, you will need to hire a contractor (or "Sunrun") to come out, remove the system, then re-install it - on your dime, most likely.

As far as what you are looking to do, it won't be easy - the openenergymonitor site is a place to start - I am sure others have done something similar using PICs or other systems (you might look into old projects by Steve Ciacia of Circuit Cellar fame - he's had a "wired house" since the 1970's). You might also look into old back-issues of Nuts and Volts magazine.

Basically, you can monitor current flow on your circuits via inductive "taps" which are small coils that fit around the neutral or hot lines of each circuit, and generate a voltage proportional to current draw (which then needs to be rectified and converted to 0-5 volts to monitor via the Arduino). Monitoring the solar array can be done in a similar manner (although a hall-effect system might be better - depends on the current output of the array - and you have to tap into the circuit for this).

Something else to keep in mind: If you install a homebrew setup like this, and it causes a fire or injury, your homeowners insurance may deny any claims. It may also void any warranty on the array. You may want to do some further research on this before going much further...

 smiley
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The array is already in, and the roof was replaced immediately before, but that's very good advice for a solar noob.

I'm aware of current transducers or CT's, the current sensors you mentioned, although I wasn't aware of the other requirements for getting the Arduino to read them.  Still need to read line voltage, too, in order to calculate power.  I suppose the ideal would be an arduino with an ethernet shield which could send data to Google Power Meter, or another API, since obviously the Arduino doesn't have enough horsepower to store, let alone deal with the data its collecting.
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since obviously the Arduino doesn't have enough horsepower to store, let alone deal with the data its collecting.
It doesn't require any "horsepower" to store data. Just a big barn. Which the Arduino doesn't have.

Collecting data will hardly tax the Arduino's capabilities. You haven't said anything about how you want to deal with that data. With a 16MHz processor, there will be loads of time to process (whatever that involves) the data, before any significant change to the data occurs. How fast will the temperature be changing, after all? Of the level of energy being produced/consumed? How often do you need to sample those items? Once a second?
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I'm thinking once a second, maybe more...  If its just collecting data and sending it to an API, it probably needs to buffer up (average) a minute worth, maybe more, and send it to the API only that often.  By "API", I'm thinking Google Power Meter, or a PHP/MySQL application hosted elsewhere.

By "processing", I mean the ability to store the data over some period of time (like, at least a day in order to be useful), which as you point out, the Arduino isn't likely to be able to do, and display it in a meaningful way.  That probably means a chart or graph of some kind, but a simple table would be nice to have, which again isn't really the Arduino's forte.  Given that limitation, as I said, I suspected the Arduino would be responsible for collecting the data and handing it off to somewhere else to be stored and displayed.  That could be done by serial, Xbee, ethernet, whatever.  The goal of the project is not only to see point-in-time usage, but also to visualize that usage over time.

Keep in mind my original question wasn't just limited to consumption vs. production...  Given enough inputs (Mega, or an external AtoD), I should be able to monitor every circuit seperately.
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I'm thinking once a second, maybe more...  If its just collecting data and sending it to an API, it probably needs to buffer up (average) a minute worth, maybe more, and send it to the API only that often.  By "API", I'm thinking Google Power Meter, or a PHP/MySQL application hosted elsewhere.
Easily done, even for several circuits. Sending the data after every collection (once a second) via XBee to a PC would be trivial. The PC can stuff the data in a database, produce real-time graphs, etc.
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I've been wanting to do a similar project, but unfortunately I don't have a fancy new solar array to monitor - just my usage :'(

I think it would be really beneficial to have the arduino send off all the info to the API as it's collected/processed - even if that means fewer data points.  If you have to have a computer store it locally 24/7 - it's just going to burn up more energy, defeating the purpose of the project.
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If you have to have a computer store it locally 24/7 - it's just going to burn up more energy, defeating the purpose of the project.
Depends on whether the computer is already running 24/7, or not. If it is, I doubt that you would be able to measure the extra energy it requires to record the data.
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Good point Paul.  I don't however have a computer running at home 24/7 for this exact reason.

There is a less expensive commercial option for simpler installations such as mine.  Though, I don't think it would work for the OP.  And not as much fun if you can't build it yourself.

http://currentcost.net/

They have an available web bridge that can post data to Google Power Meter, and have recently opened up an API for posting to whatever else.  Some really good stuff on their technical blog here: http://currentcost.posterous.com/

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If you want simple and easy, look at The Energy Detective (TED) -- http://www.theenergydetective.com/

I wanted something ... Different...  Although the price is better than E-Guage.
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A few people - including myself - have tried to get the Black & Decker Energy Monitor or the (very similar) Blueline PowerCost Monitor to talk to Arduino. Success has been ... limited.

Both units read pulses from the utility meter, so don't suffer from CT/ADC inaccuracy. They transmit on the 433MHz range, but I don't know of anyone who's successfully deciphered the data.
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Hah, well, for most people that would work, but if you have a solar array, that only helps measure the *net*, and only accurate to the kwh.  My array, because it was done by a "third party developer" has a net meter and a seperate production meter, which I could measure.  They both have the IR window at the top.  But again, that still isn't what you'd call real-time.
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