Comparing PVWatts Estimates to Actual Solar Production

Click to enlarge

PVWatts is a website run by the National Renewable Energy Lab (NREL) which can be used to estimate how much energy a given solar array might produce, based on historical mesurements of insolation.  If you ever have a site analysis done, the installer will probably use it to estimate your potential for annual production, and you might wonder how close the the mark it’ll be.  Now that I’ve had solar PV for almost 2 years, it’s interesting to look at how close the estimates were for my situation. Continue reading

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Linux Filesystems LOC Update

I did a post last year about how lines of code for some of the primary Linux filesystems were evolving.  It seemed to spark people’s interest, so here’s an update through v3.4-rc4:

(Click to see full size).

I added regression lines this time – btrfs should catch xfs around kernel version 3.8 or so.  :)

Again, I draw no strong conclusions from this – I just think it’s interesting to see how things are moving as these filesystems evolve.

I used CLOC to count lines; the numbers on the graph reflect no blank lines & no comments.  For ext3 & ext4 I included jbd[2] and some of the peripheral files they use; code snippet from the script:

ext3lines=`cloc fs/ext3/*.[ch] include/linux/ext3*.h  fs/jbd/*.[ch] \
           include/linux/jbd.h fs/mbcache.c include/linux/mbcache.h \
           | grep SUM | awk '{print $5}'`;
ext4lines=`cloc fs/ext4/*.[ch] include/linux/ext4*.h  fs/jbd2/*.[ch] \
           include/linux/jbd2.h fs/mbcache.c include/linux/mbcache.h \
           | grep SUM | awk '{print $5}'`;
xfslines=`cloc fs/xfs/*.[ch] fs/xfs/*/*.[ch] include/linux/dqblk_xfs.h \
           | grep SUM | awk '{print $5}'`;
btrfslines=`cloc fs/btrfs/*.[ch] | grep SUM | awk '{print $5}'`;
gfs2lines=`cloc fs/gfs2/*.[ch] include/linux/gfs2* \
           | grep SUM | awk '{print $5}'`;

(Some of the files above no longer exist, but I used the same script to iterate over all the kernel versions.)

Posted in Computers, Linux | 3 Comments

Opower goes social

I wrote about Opower almost 2 years ago, a company which is working to reduce energy use by simply making people more aware of what they use in comparison with others.  At the time of that post, they seemed mostly focused on working directly with utilities, and sending out reports to customers showing them how their energy use compared to similar homes in their area.  The idea seems to be that if you are at all conservation & efficiency minded, seeing where you are in relation to others may actually encourage you to do even better.  They track the results, and apparently, it works.  However, that method works only if the utility is on board to provide the data. Continue reading

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Monitoring boiler temps with an arduino

Ok, so I have a problem; a measurement & charting problem.  The first step is to admit you have a problem; but I don’t yet want to change, it’s too much fun! Continue reading

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pvoutput.org rocks!

(And in other news, I hit 5MWh of lifetime solar production today, woo!)

pvoutput.org is a free service run by a mystery man down under, which can accept solar generation as well as household consumption data, and slice, dice, and graph it just about any way you would like. Continue reading

Posted in Energy, Monitoring, Renewable | 3 Comments

Siri meets wifi thermostat

Oh, man, this is just too cool.  And sadly I just upgraded to an iPhone 4, not 4s (I am both a sucker for a deal, and normally filled with buyer’s regret).  But anyway, this guy used the Radio Thermostat API (which I mentioned in my last post) together with a Siri hack to add voice control to his thermostat.  How awesome is that?  (The thermostat he used is the 3M-50 available at Home Depot, a rebranded version of the CT-30 available at Amazon [amzn]).

Looks like his code is here.

Posted in Computers, Energy | Tagged , , , | 2 Comments

Using a wifi thermostat API


I love it when device manufacturers realize that they can do well by selling a device with documented interfaces, in the hopes that a nebulous community of hackers will invent cool new things for it. So I was pretty happy when the Radio Thermostat Company of America announced that they had an API available for their wifi thermostats (such as the 3M-50 at Home Depot or the CT-30 [amzn] at Amazon). Continue reading

Posted in Energy, Monitoring | Tagged , , , | 18 Comments

Therms per Heating Degree Day

Click for interactive graph

In an earlier post I had tried out a few ways to figure out if our energy-saving efforts with respect to natural gas use were paying off; I did a few bar graphs of therms per day, per heating degree day, rolling yearly averages, etc.  I knew that I needed to normalize for the weather using Heating Degree Days, since natural gas is our primary heating fuel, and I probably needed to find a way to separate space heating from water heating, which have different conservation methods, and which may or may not be weather dependent. Continue reading

Posted in Energy, Monitoring | 30 Comments

Eternal Vigilance is the Price of Efficiency, part 3 – gas

In my last two posts I talked a little about our utility usage for electricity and for water; last up is natural gas usage.  (I don’t think I’ll ever start weighing my garbage, but who knows). Continue reading

Posted in Conservation, Energy, Monitoring | Tagged , , , | 9 Comments

Eternal Vigilance is the Price of Efficiency, part 2 – water

In my last post, I talked about how I keep track of our electricity usage, to be sure that our efforts at efficiency & conservation are staying on track.  But that’s just one of 3 utilities; water has been another focus in our house.  Continue reading

Posted in Conservation, Energy, Monitoring | 5 Comments