Archive for July, 2013

Second solar anniversary

Last month marked our second solar year. We produced 8,519 kWh and used 6,410 kWh for a net of -2,110 kWh from June 2012 to June 2013.

At $0.04 / kWh that works out to a credit of $86.41 from the electric company.

That’s a 46% decrease from last year when we generated a surplus of 3,650 kWh and a credit of $159.68.

Not only did we produce less this year, we used more.

Note: with the new plug-in hybrid, we’ll be using even more of our surplus, and saving more. We’re spending roughly 13 to 19 cent’s per mile in gas.  We’re saving an estimated $400 to $600 in gas each year by using electricity (13 miles/day * $0.19 = 2.47/day * 250 days) which the electric company would only pay us about $55 (1,400 kWh * $0.04) if we sold it back as surplus.

Why we bought a Plug-in Hybrid

photo of Prius

If you remember one of our early solar posts when building the house, we initially assumed that solar was going to be too expensive for us. Then we ran the numbers and found that the rate of return was actually quite attractive over the log run.

Same goes for our new plug-in hybrid. We had been a one car family since Jill and I met. Our four-wheel drive Ford Escape was both our commuter car and utility vehicle. We made multiple moves in that car. We carted goats and chickens and guineas in that car. We transported a year’s worth of hay. We hoped the Escape would carry us a few more years, but at over 200,000 miles our trusty steed was starting to cost us more in gas and repairs than buying a new car.

We now have a truck to haul goats and other farm trappings when needed, so Jill started researching commute-friendly cars. She drove three hybrids, Honda Insight, Toyota Prius and Ford C-Max. The C-Max had the nicest interior and was more similar feeling to the Escape, but was the most expensive and the mpg reviews were mixed. The Insight had a great price point, but had the worst mpg estimate and interior feel. So we focused on the middle-priced Prius which had the best mpg estimates and a good track record.

With our current net metering plan, it’s better for us to use the excess than sell it back to the utility which pays us very little. It initially looked like a plug-in hybrid was out of our price range (even with federal credits) but when I added up the miles: 19,500, the gas: 970 gallons, and gas dollars: about $3,600 a year, I realized the extra savings in gas might justify the higher cost.

Here’s the breakdown…

The Escape was averaging about 20 mpg. The regular Hybrid Prius averages 50 mpg and would save us 580 gallons of gas and $2,150 per year. Toyota says the Prius plug-in gets roughly 95 mpge (that’s miles per gallon plus electric). We test drove the plug-in for a few days on back country roads and found it was closer to 85 mpge. The plug-in component gives you an extra 13-14 miles before the hybrid engine kicks in.

We estimated conservatively that 70 mpge would save us 690 gallons and $2,560 per year, but use approximately 1,400 kWh per year. That would cost us about $210 in electricity charges if we were paying for electricity, which means we would only be saving $2,350 per year in gas.

The regular Prius is $24,995. Toyota had a special offering interest free loans up to 60 months. So $25k/5 = $5,000/year plus $1,450 in gas equals $6,450/year. Now remember, we were paying about $3,600/year for gas, and $2,000 or more per year in maintenance. So we’d be paying an extra $830/year for a new car.

The plug-in version is $8k more. $33k/5 = $6,600/year. But in addition to 0% interest for 60 months, they were also throwing in a $4,000 rebate for plug-ins. There’s also a $2,500 federal tax credit. That brings the price down to $26,500, only $1,500 more than the regular Prius. That works out to $5,300/year plus $1,030 in gas, plus $210 in electricity equals $6,540. That’s about $90 extra per year for the plug-in, assuming we paid for electricity. Take out the electricity (because we produce excess electricity per year) and the plug-in is cheaper than the regular Prius.

Of course we didn’t start at the $33k price, Jill bargained them down. After rebates and tax credits we’re paying about $100 less a year for the plug-in over the regular Prius. So we are basically paying about $520 more per year (not counting electricity, and assuming gas prices stay the same) for a new car that is easier on the environment. If we get closer to 85 mpge then we will only be paying $330 extra per year. If/when the price of gas goes up, we save more.

The only down side. The Prius is definitely not going to make it up our driveway some days in the winter.

Second quarter 2013 performance

Q2 2013 summary: 13% colder, 44% more usage and 4% less sun.

Now that we are starting to collect our second year of performance data, I’ll be comparing our new data to the same period last year. Year-over-year comparisons should be more illustrative than comparing to previous months. I’m also switching to a quarterly reporting period to look for larger trends, but I will continue to post data monthly at

In Q2 last year our total usage was 1,021 kWh. This year is was 1,468 kWh, a 44% increase. Although it feels like it had rained a lot more this year then last, we only produced 4% less energy in Q2.

Overall, here’s how the first and second quarters compare to 2012.

Q1 and Q2 comparison

2013 Usage Solar PV Net usage
or (surplus)
daily usage
Total 1,468 2,626 (1,158) 16.1 906
528 920 (392) 17.6 571
529 904 (375) 17.1 232
411 802 (391) 13.7 103
2012 Usage Solar PV Net usage
or (surplus)
daily usage
Total 1,021 2,731 (1,709) 11.2 802
387 925 (538) 12.9 535
309 867 (557) 10.0 170
325 939 (614) 10.8 97
All values in kWh (except HDD which is base 65°F).

Interesting note, we used 44% more energy this quarter as compared to 2012, but that was 447 kWh, or about the same as last quarter. We’re consistently using about  5 kWh extra per day than last year. This breaks down to 208 extra watts per hour. 100 watts is a heat lamp for the chick brooder, and the other 108 watts is roughly what my 2 laptops and task lighting use on average per hour.

Our water usage is only up 12%, and our hot water usage is down 3% from Q2 2012.

As for heating, we used the ASHP for roughly 14 hours in April for a total of 7.5 kWh.

In summary, Q2 usage is up compared to last year. That increase is attributed partially to the incubator and brooder box heat lamp (for the turkeys, chickens and guinea fowl), and partially to the increased use of the home office (last year I spent most of the summer building a barn, not staring at computers). We should be retiring the brooder box heat lamp this month, so I predict our next quarter usage will be up roughly 230 kWh from Q3 2012. Let’s see if my prediction holds.

You can see heat maps and detailed charts of temperature and electrical usage at View hourly, daily and monthly values for solar, usage, net usage, temperatures and HDD.

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