Thriving On Low Carbon

Self-cleaning ovens

For the first time in my sheltered life, I have a range with a self-cleaning oven. After over a year which included roasting a number of chickens (which we've been raising the past few years) we had an oven covered with enough spattered grease to cause the smoke detector to go off any time we turned the oven on. The manual that came with the range cautioned against using the usual oven cleaners and recommended the use of the self-cleaning feature. This process locks the oven and heats it up to a very high temperature - Wikipedia among others says 900F. I was curious what this would be like - would the range feel really hot to the touch; how much would it smoke; woudl it actually clean the oven; how much energy would it use?

You have to clean any serious accumulations of stuff out first, perhaps so it doesn't combust. Also, you're not supposed to leave the racks in - they warn against the high temps destroying a finish that makes them slide easily. This was a major bummer since we'd been dumb enough to leave the plethora of racks this range comes with in the oven while we only needed one to roast the chicken :-( Duh - they were really grimy and we (OK, not we, Jill) cleaned them by hand. Note to self...

Once we started the process, the oven heats up quickly and smoke comes spewing out the vent. We had windows open and the range hood running. In the first hour of the three hour cycle the visible smoke stopped. I didn't abort the cycle because I thought I should go through it at least one time. The front and sides of the range felt surprisingly un-scary in terms of temperature - there might actually be some reasonable insulation in there

Once it turns off, the door stays locked and it indicates on the display that it's still hot for close to another hour, until it cools down. It did get pretty clean, and there was some ash remaining. And the entire process used 8 kWh of electricity. That night we had friends come to share homemade pizza, so we added another 3 kWh. The day's total of 11 kWh exceeded the usage in some months!

One Year PV Production

Phil Forest flipped our 4.76 kW Sunpower PV system on during the afternoon of June 9th, 2011. At the end of the day June 8th, 2012, the system had produced 6,694 kWh. On the following day, it made 22.5 kWh, so take half of that for a full year's worth of production - afternoon to afternoon - and the total is 6,705 kWh. I'm really pleased and not a little surprised at this total, it's significantly over what we predicted. The system has some winter shading, too. Nonetheless, the yield was 1.41 kWh/W/year, and during the time when I had a small (1.06 kW) system at my NH home in the late 1990s/early 2000s, that system never made over 1 kWh/W/year. Likely a cloudier climate, and I know this past year has been sunny (Eliakim's Way PV production is up 6% over the first year), but some of this has to also be technology improvements. Sunpower claims their technology is more productive in low light conditions and high temperature conditions than their competitors, and just maybe they're right!

Two years of energy usage at Eliakim's Way

It's now two full years since the eight households moved into their new homes at Eliakim's Way that South Mountain Company designed and built. We've continued to read the sub-meters monthly and now have two full years of data. Here's the comparison between the two years, by house and by end use:

Some observations:

- Heating energy was down due to the mild winter

- PV output was up -  1.42 kWh/W!

- House 4 got within 300 kWh of zero net energy

- Most households increased their use of energy once heating is disregarded

- House 8 used an amazingly low amount of heat

Our meter reader has said Enough! so from now on out we'll be looking once a year at these totals.

Measuring stuff

Eric Sandeen asked how are all these measurements taken. The embarrassing truth is, with very simple hardware, that requires manual reading.

The 240 volt loads - PV inverter output, range, minisplit heat pump, electric resistance water heater - are metered via re-manufactured old-style glass front electromechanical meters that I get from Hialeah Meter. I read them daily. The refrigerator and freezer and HPWH are 120V loads and they are on Kill-A-Watt EZ meters. The EZ model has battery back-up, useful so all data isn't lost in a power failure, or when you unplug it. The Kill-A-Watt logs kWh and elapsed time, as well as providing instantaneous readings of Watts, Volts, and Amps.

The utility meter from NSTAR has cumulative usage as a net, kWh delivered to the house, kWh exported by the PVs, and peak demand in kW. I read this daily also.

I measure hot water usage with a water meter from watermeters.com on the cold water inlet to the Marathon water heater. Mine is a DLJ75. We recently installed a couple of meters from this company that also have pulse output (DLJ75C), and we set them up with a Hobo UX120 pulse logger from Onset computer. This way we'll get cumulative water use and will be able to see usage over time, in order to be able to see peak demand as well as usage.

For ease of monitoring, the web-enabled products such as the eMonitor are great. You get circuit by circuit energy data, and no one has to read any meters! They have a nice interface. The downside is there is an initial cost, of course, but there is also an ongoing monthly cost for the service.

Finally, I am datalogging temperature and relative humidity in the basement and on both levels of the house, and outdoors, using Hobo dataloggers, both the simplest U10 logger for Temperature and TH, and U12-013 which have internal temperature and RH and two external sensor ports, which I am using for additional temperatures (such as inlet and outlet water temperatures to the water heater.) I have current transformers that also can plug into these external ports, for measuring current draw to various devices.

May energy data

May was a lot cloudier than April - 577.5 kWh vs. 802.5 kWh in April. We still used some heat in May, so not quite down to the summer baseload of 200-225 kWh/month. The energy used pattern (blue columns below) is much smoother than the solar electricity produced pattern, which shows the variations in weather overlaid upon the typical seasonal pattern of production.



Here is the energy usage by end use:

Energy used by the Geyser heat pump water heater is beginning to drop as the basement temperature and the incoming well water temperature both rise: