Slacy’s Blog

I’ve updated my solar stats pages with 30-day and 90-day reports. Take a look!

I’d been struggling to find time to debug the problems I’ve been having with my solar monitoring system. Well, after filling up my hard drive with 60+GB of logs, I finally have deployed a fix to production, and the new service is running 24/7. (thats a bit of work-speak for everybody) It’ll take another week for the system to collect a nice set of 7-day logs, but thats to be expected. I may dork around with it a bit more and try to fill in some of the gaps, for which I actually have logs sitting in a super secret location.

Oh, and as of yesterday, I’m net -17kWh for the last month. That means that I’ve produced more energy than I’ve used, by just over 1 day’s usage.

One of the interesting questions about having a solar system is how does the weather affect solar production. Specifically, how does temperature effect the panel output. If I ever had spare time and money, I’d get one of these WMR918 units, and run wx200d to collect the data, and compare that to the solar output.

Unfortunately, I’ve had some issues getting data collected right from the solar system. I actually found the missing data, and may try to re-insert it today.

I’ve set up rrdtool to collect and graph the output of my solar system, as well as some other interesting numbers. Check it out!

As of 3:15pm today, my solar system was only 17W shy of its theoretical maximum output. I was shocked when I looked at the inverter and meter, which both confirmed the same numbers.

Theoretical output is:

22 panels * 175 Watts each * 95% inverter efficiency = 3657W

The system was outputting 3640W just a few minutes ago. Thats 99.5% of the theoretical maximum. Wow, I was shocked! I didn’t think it would ever get that high! I think its the combination of a nice cool day, and the panels having just been washed off by a rainshower this morning.

I’m not too worried about having over-built the system, since we’ve got a kid on the way, and that means more energy usage (more laundry, more lights on in the middle of the night, baby monitors, and just another person around in general.) Our net usage over the last few days is still positive at 7kW for the last 4 days (1.7 kW/day), but we’ve had a few cloudy days. We’ll see how things change when the weather is more consistent. I think I’ll be massively over-producing during the summer, and under-producing during the winter, and thats exactly what the net metering is for!

PG&E came out and installed and inspected my NEM (Net Metering) system today. This means that I can (and have!) turn on my solar system for good!

The NEM E7 meter records total usage as well as “peak” usage in kWh. PG&E has approved only 5000 of these E7 style meters for the whole year of 2007! (see link) They then calculate peak & off peak usage (or generation) and total them up in a monthly bill. Credits can carryover to the next month, and we’ll only receive a traditional “bill” for electricity once a year! The meters start out reading 50000 kWh used, so that they won’t go negative when you start to generate electricity. I’ll report back after a day or so of production and see what they look like…

Oh, and the other cool thing about the meter is that its digital and reads out the instantaneous whole house usage. This means I can see how much electricity the TV, refrigerator, dryer, etc. are all using, and I’ll be able to compare the day & night numbers too. Right now, the solar is on, and it was reading about -1.5kW. (yeah, thats negative) and we were pushing power back into the grid!

Stephen Lacey is the host of “Inside Renewable Energy” which is supposedly the #1 Renewable energy podcast! Here’s a big shout out from one Steve L. to another!

Today, I filled out the form on solar-nation.org. It sent e-mails for me to Dianne Feinstein, Anna Eshoo and Barbara Boxer. Boxer & Eshoo sent generic “thanks for your feedback” e-mails, but the awesome Dianne Feinstein sent this:

March 26, 2007

Mr. Stephen Lacy
Mountain View, California 94041

Dear Mr. Lacy:

Thank you for writing to express your support for
the “Securing America’s Energy Independence Act of
2007″ (S. 590). I appreciate hearing from you on this
important topic.

I believe renewable energy sources hold a great
deal of potential to reduce air pollution, combat global
climate change, increase economic competitiveness and
reduce our nation’s dependence on oil. As you may
know, the Federal government plays an important role in
supporting the development of renewable energy sources.
S. 590 has been referred to the Senate Committee on
Finance, of which I am not a member. Please know that I
will keep your comments in mind should this legislation
come before the Senate.

You may be interested to know that I am taking an
active role in supporting renewable energy legislation.
Senator Olympia Snowe (R-ME) and I have to
introduced the “EXTEND the Energy Efficiency
Incentives Act of 2007,” which builds on the incentives
for efficient buildings adopted in the Energy Policy Act
of 2005. The principal purpose of the bill is to extend
temporary tax incentives for energy efficiency buildings
so that the business community can make rational
investments in complying with the ambitious
requirements of the incentives. The “EXTEND Act”
establishes solar energy tax incentives and extends other
energy efficiency tax credits, such as those for home
retrofits that save energy.

I also plan to introduce the “Energy Efficiency
Improvement Act of 2007,” which would establish a
national energy efficiency program modeled after
California’s energy savings programs. This bill would
not only require electricity and natural gas distributors to
implement energy efficiency measures, but also mandate
strict energy efficiency standards for Federal,
commercial, and residential buildings. The revised
building codes would save 13 million metric tons of
carbon dioxide emissions by 2020 from new homes and
buildings, a reduction of 25% below projected levels.

Again, thank you for your letter. I hope your will
continue to write to me on issues that are important to
you. If you have any additional comments or questions,
please feel free to contact my Washington, D.C. office at
(202) 224-3841.

Sincerely yours,

Dianne Feinstein
United States Senator

http://feinstein.senate.gov

You Rock, Dianne!

So, in my last post, I postulated that the average solar production for the year was equal to the production on the equinox. After pondering this for a while, I realized something else. The issue is the angle of the sun. The panels are oriented to be about perpendicular to the summer sun at noon, to maximize energy production. What this means is that an hour of sun in the summer at noon will produce more energy than an hour of sun in the winter at noon. (All weather effects aside). Thus, 4 hours of winter sun are less productive than 4 hours of summer sun.

Thats all well and good, but the question now remains: Is the energy produced by 1 hour of noon sun on the equinox exactly half way between the summer (solstice) and winter (solstice) production? I think the answer is that its not. The factor is panel “tilt” (relative to the sun) and this is a non-linear function, and I’ll guess that summer sun is a lot more productive than winter sun.

We’ll just have to wait and see, I guess.

I know. I’m not supposed to have the system turned on until the PG&E and city inspections are complete, but I couldn’t resist leaving it on for the day (or for the weekend) to see how much electricity it produced. Its not quite sunset right now, but its close, and we just broke the 13.0 kWh mark.

Because the solar equinox was just 4 days ago, one may assume that the average yearly production of the system will be approximately equal to its production on the equinox times 365. (right?)

And, our average yearly electricity consumption for the previous 24 months was 17 kWh per day.

But, we just replaced all our lightbulbs with compact flourescents, and we have 2 refrigerators, and I’m tempted to turn the second one off. I think if I do those two things, we can get our electricity consumption below 13 kWh/day, and which point we’ll have a zero sum electricity bill.

I’ll see what it produces tomorrow.

Oh, and yes, I’ve been thinking of modding a WRT54GL, adding a serial port, hooking it to the Xantrex GT3.8, sending the results over the network to my desktop, and running rrdtool there to generate stats and graphs of production. I love stats!