Walt at Random

I’ve mentioned our photovoltaic (“solar,” but for electricity–most solar installations in our neighborhood are water-heating systems) system before, installed last November. I’ve also mentioned that it’s easy to start obsessing about power usage and generation–particularly when SolarCity provides a web page I can check that shows generation by half-hour on a daily graph (along with some other information).

There are two, maybe three, kinds of milestones that come into play here:

1. Days on which the next integer of kiloWatt-hours (kWh)  generated is reached, as the days get longer and the sun gets more direct.
2. The first month in which PG&E’s “true-up” report shows a negative number–that is, the first month you actually feed net electricity back into the distribution system when totaled over an entire month.
3. Percentage milestones for overall usage–e.g., points at which we’ve generated 60% of all the electricity we’ve used, 65%, 70%…I don’t really track those (and it’s going to be damnably difficult to get from 70%, where I think we are now, to 75% and 80%).

We hit two milestones this week:

• Daily generation: After reaching 12 kWh on February 14, 13 kWh on February 22, 14 kWh on March 10 and 15 kWh on March 13 [there were a lot of cloudy/rainy/foggy days, so the small gap between 14 and 15 isn’t too surprising], we reached 16 kWh on April 6…and, finally, reached 17 kWh on April 24. I’m guessing it will be 3 weeks before we reach 18 kWh; we really don’t know what the maximum daily output’s likely to be (presumably around June 20), but if we hit 20, I’ll be delighted. (We have a relatively small system–2.5 kW, with an inverter rated for 2.8 kW–because our power consumption isn’t very high anyway.)
• Net generation: For March 17-April 17, we generated more energy than we used. Not a lot more (42 kWh), but more. We’re expecting to see net generation for the next five or six months, unless our (new, super-efficient) AC gets a lot of use come summer.

And my wife is suggesting that, when our already-old clothes dryer finally needs replacement, we should run gas to the utility room (which should be easy–it’s about a 4′ extension) and replace it with a gas dryer. Which would probably make us negative on electricity throughout the year–at least on an annual basis–after we did that. (Natural gas is relatively cheap around here, and there’s a LOT of natural gas available, enough so that too much of it is still burned off as a waste product in oil production. And converting natural gas to heat is, I suspect, considerably more efficient than getting the heat from electricity generated in gas-fired plants…)

I must admit, I find myself reading some product reviews–particularly high-end stereo, which I read just for amusement–and thinking “I wonder what the power consumption, particularly standby consumption, is like?” I was astonished by one item where a company redesigned one amplifier slightly, one of these amps that’s supposed to be left on in standby all the time, reducing its standby consumption to one watt (the equivalent of three LED nightlights or one-third of a regular nightlight)…from, gasp, 360 watts.

360 watts. To do nothing at all. Our  household’s “idle usage” [clocks, pilot lights, appliances in standby, etc.] is between 40 and 80 watts. If that amplifier sits idle all the time, it uses 259 kWh a month–which is about two-thirds of our household’s entire electricity consumption. And when I read about the auditory wonders of Class-A amplification (which is incredibly inefficient and uses full power no matter how softly the music is playing), I’d really like to see the line-draw numbers. Not that it would matter to most high-end stereophiles.

[I was surprised and delighted when we picked up a cheap Sony DVD player a few weeks ago as an inexpensive way to make our partially-broken Denon music system work for a few more years, by using the Sony as a CD player feeding into the Denon’s aux. input. The Sony brochure, touting the Energy Star seal, explicitly noted that the standby power consumption–that is, “off,” but able to respond to the remote control–is less than 0.1 watt. There is, to be sure, no pilot light in that mode. This tells me that remote readiness doesn’t have to involve significant parasitic power.]

Another clear, beautiful day. Wonder if we’ll pass 17 kWh again today?

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Update 4/26: No, we didn’t quite hit 17 kWh on Sunday…but close. More significantly, in noting our house’s “idle power,” I omitted what’s probably a significant chunk of that 40-80 watts…namely, the DSL modem, wifi router and secondary wifi router (used only for SolarCity’s monitoring).

This entry was posted on Sunday, April 25th, 2010 at 10:28 am and is filed under Stuff. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.