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Our NESEA Zero Net Energy Building Award Submission

Presentation Board

Click to view the presentation board (PDF, 5.4 MB)

We submitted our entry materials for the NESEA Zero Net Energy Building Award yesterday. We didn’t quite have a full year’s worth of data for last year’s competition. So we were excited to apply this year. You can find out more about the requirements for the competition on the NESEA site.

In putting together the data for the competition, I realized I needed to update a few items on our About page.

First, square footage. We had listed the house as 1408 sf. This is the outside dimension of the house (32*22) times two floors. Technically we should include the basement, which would bring the total to 2,112 sf. Total conditioned space remains the same at 1,200 sf.

Second, price per square foot. We had estimated $142 per square foot. When we added up the final tally last year, I divided by the 1,408 number rather than the 2,112 number, so we ended up with an actual of $208/sf. But when I went through all the numbers again I found a few extra expenses and realized I divided by the wrong number. So using the revised numbers, we end up with $142/sf, strangely what we estimated originally. (In hindsight, that had to be total luck.)

That $142/sf does not include significant site work. We didn’t pick a nice easy flat site next to the road to build our house. But if you built this house to similar specs on a nice flat lot near the road and didn’t have to drill your own well or install your own leach field, then this about what what you would pay if you did a lot of the design and labor yourself.

One last thing. The submission requirements included calculating the Energy Use Intensity (EUI). This is measured in kBTU per square foot per year. The fun part is converting kWh to kBTU. This is problematic for an Air Source Heat Pump, because the kWh required to create BTUs increase as the temperatures decrease. But as a general measure I suppose this is helpful. It might also be a trick question to check if the person submitting the entry knows what they are doing. Hmmm, hope I answered correctly.

Here’s how I determined our EUI. Our total energy use for the last 12 months was 6,898 kWh. To convert to BTUs we multiply kWh by 3412.14163312794 BTUs which gives us 23,536,952.9853165 BTUs. Divided by 1,000 to get kBTUs is 23,537 kBTUs. Now divide by square footage. It doesn’t specify whether this is conditioned space or total enclosed space, so I chose conditioned space. That gives us an EUI value of 19.6. If we use the larger enclosed space value then we get 11.1. The lower the value the better. Maybe I should have used the 11.1 value.

The winners are announced at the BuildingEnergy Conference in March. Wish us luck!

P.S. If you have built a net zero house in the larger New England area and have a year’s worth of energy data to prove you’re net zero, then apply soon. The deadline is December 15.  Good luck!

Third quarter 2013 performance

Q3 2013 summary: 36% cooler, 38% more usage and 2% less sun as compared to Q3 2012.

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 netplusdesign.com

In Q3 last year our total usage was 927 kWh. This year is was 1,283 kWh, a 38% increase. Although it feels like it had rained a lot more this year then last, we only produced 2% less energy in Q3.

Overall, here’s how this quarter and the first three quarters compare to 2012.

Q1-3 comparison

2013 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 1,283 2,826 (1,544) 14.0 294
Jul
384 929 (546) 12.4 18
Aug
447 961 (514) 14.4 58
Sep
452 936 (484) 15.1 218
2012 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 927 2,871 (1,944) 10.1 216
Jul
319 970 (651) 10.3 17
Aug
316 1,018 (702) 10.2 31
Sep
292 883 (591) 9.7 168
All values in kWh (except HDD which is base 65°F).

We used 38% more energy (356 kWh) this quarter as compared to 2012. That’s about  3.9 kWh extra per day, or 161 watt hours per day more than last year. The last two quarters we’re been running about 5 kWh higher. Last quarter I predicted this quarter usage would be up roughly 230 kWh from Q3 2012. It was actually up 356 kWh. I didn’t take into account the fact that we would be buying a plug-in hybrid car.

However, we used a lot less cooling this quarter. We used the ASHP for roughly 5 hours in September for a total of 3.7 kWh, a 93% reduction. Third quarter last year the ASHP used 50.6 kWh. We used the air conditioner a lot last year mainly for dehumidification because the house was still drying out and we didn’t want any buckled floors. The house seemed to cope well with the humidity this year.

That means we used roughly 403 kWh more than last year if you factor out cooling. That’s about 4.4 kWh per day. I’m using about 432 Wh per day for the home office. If the Prius is using about 3.8 kWh per day as predicted, that means there’s another 200 or so watt hours unaccounted in there per day in comparison to last year.

Our water usage is down 13%, and our hot water usage is down 12% from Q3 2012. More rain equals less watering the garden. Less barn building this summer equals less showers.

Predictions for next quarter? Will we use 4 or 5 kWh more per day than least year? Stay tuned!

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

20 Megawatt-hours

20,000 kWh meter pic

Today we generated our 20th megawatt-hour.

It took 837 days to generate 20,000 kilowatt-hours, or roughly 28 months.

Since we moved into the house January 1, 2012, we’ve generated 15.3 MWh and used 10.6 MWh.

 

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 netplusdesign.com

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)
Avg.
daily usage
HDD
Total 1,468 2,626 (1,158) 16.1 906
Apr
528 920 (392) 17.6 571
May
529 904 (375) 17.1 232
Jun
411 802 (391) 13.7 103
2012 Usage Solar PV Net usage
or (surplus)
Avg.
daily usage
HDD
Total 1,021 2,731 (1,709) 11.2 802
Apr
387 925 (538) 12.9 535
May
309 867 (557) 10.0 170
Jun
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 netplusdesign.com. View hourly, daily and monthly values for solar, usage, net usage, temperatures and HDD.

72% of our usage is grid supplied, even though we produced more than we used!

Supply Mix

In the last year (April 1, 2012 to March 31, 2013), we used 6,046 kWh of electricity and produced 8,576 kWh for a net surplus of 2,530 kWh. That’s awesome right?

But 72% of the electricity we used was supplied by the grid when solar could not supply enough power to cover the need at that moment, like at night or on a cloudy day*.

Or another way to look at it, although we produce more than we use, most of what we produce we don’t really use directly. We only use 28% of what we produce. The rest goes back to the grid to pay back what we used when the sun wasn’t shining and to build up a surplus for a rainy day.

So even with all that sun, we still draw a lot of power from the grid that requires coal and other nasties to be burnt to serve our electricity needs.

It makes sense, most of our heavy use, hot water for showers, cooking, washing dishes, all occurs early in the morning or evening when the sun is not at it’s brightest or best angle. The more we time our usage to occur when the sun is shining, the less we demand of the grid.

There has to be a common industry term for this? Anyone know? Percentage of power supplied by the grid as compared to total usage when solar or other renewable is in the mix?

To me this seems like a much more important number to track if you have solar and are concerned with your direct carbon producing footprint.

* In order to find how much energy we used from the grid I added up all the usage values on an hourly basis that were greater than what was being produced by solar. For example from 5-6am, total demand was 1000Wh. The sun was just coming up and the system was only producing 200Wh. That means the grid was supplied 800Wh during that time. 80% is grid supplied for this hour. Now do that for every hour in a year. Hint, it helps if all your energy values are stored in a database.


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