A Net Zero Energy Year : Dec 15, 2010 -Jan 15, 2011


During the past 31 days the house consumed 1810 kWh and produced only 152 kWh. OUCH!

Our total consumption to date (since October 18) is 3986 kWh, with total production at 724 kWh. Since our total annual consumption budget is 8000 kWh, we’ve burned through 50% of our electricity budget.

Sounds pretty bad right? The game isn’t over just yet. We’ve just come through three of the four darkest months of the year. By February 15, we will be getting as many sunshine hours as we do on October 27. Plus, last year we virtually stopped heating the house as of the second week of February (due to a sunny, mild month).

So we are still in the ballpark, but we will definitely need some luck for this to be a net zero energy year.

Some numbers and observations:

December (16-31):

Net Power Consumption: 945 kWh

Total Production (PV Modules): 107 kWh

January (01-15):

Net Power Consumption:  865 kWh

Total Production (PV Modules):  45 kWh

We had a net zero day on January 6:


The negative values represent production (as in, negative consumption).

Thermal Inertia:

With Google PowerMeter, you can really see the thermal inertia that builds up in the concrete slabs:


Very little heat was needed until the latter half of the day on January 7.  After the sunny day of January 6, the concrete in the house retained heat for quite a while.

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Some numbers from Belgravia NetZero. The house is not occupied yet but is being heated. Since winter hit on November 16, I've imported 2769 kWh, produced 216 kWh and exported 125 kWh so my net consumption is 2769 + 216 - 125 = 2860 kWh. That's approaching 30% of my annual energy budget of 10,000 kWh. In that period we've had 2064 heating degree days (base 18C). The average annual heating degree days over the past three years in Edmonton is 5397 (base 18C). Average monthly degree days for November through February are 565, 1010, 892 and 739 respectively so December is the coldest month.

Like you, Conrad, I'm not worried. As the days get longer (and sunnier, I hope) we'll have many days where there are substantial degree days of heating load but where the house will require no active heating.

Average daily production of my 2.4 kW PV system during that period is 3.27 kWh whereas average daily production since I officially became a microgenerator on 2010-06-24 is 7.65 kWh. Average daily production so far in January is 1.4 kWh including 10 days where the modules were covered in snow. B.


Have you ever posted details of the mechanics/engineering that was used to design your solar PV shades? I'd be curious to see how complex the system is.

Not yet John. I'll write something up in a couple of months.


Conrad, Are you tracking the hours of sunlight each day and correlating those numbers to solar gain and PV output?
If so, could you include this info in your readings? - Jim

Hi Jim,

I'm not. I don't know how to, except as a function of PV power production.


I've been trying to find a source of actual measured solar radiation for Edmonton but haven't had any luck so far. For generic information about today's sunrise, sunset and sun path, check out:


I have been very inspired by your project and would like to talk to you about a few business ideas of mine to get a second opinion. I'm currently completing the Construction Engineering program and plan to start a construction company in about 5 years time. I'm may be reaching here... but are production styled NetZero homes (or even LEED certified) always going to be a dream of mine? I think there is a market for it.. and if not today, maybe in five years? The public is becoming increasingly educated on the importance. Of course convincing Albertans that smaller homes for more money will prove challenging, but is it impossible?
I don't know anyone else interested in this matter, nor do I know any construction companies who are completely dedicated to "green construction" so getting people's opinions on the subject would be fantastic.

Comments? brett_garneau@hotmail.com


I think that there will be a huge market in the future for energy-efficient homes. An even bigger market will be retrofits. I think that going into the field is a no-brainer.

The beauty of the construction/renovation business is that your projects can vary from not-so-green to very green, so there is no economic risk in being a "green" builder. You can always take a not-so-green project if you really need the money.

People ask me all the time about contractor who do green renos, so I am particularly convinced that they would line up around the block for a very knowledgeable green contractor.

Good luck!


Conrad, in one of your earlier posts, you mentioned you would not install radiant floor heating because the efficiency of the house, coupled with the solar gain and the thermal mass of the concrete floors, would negate the benefits of radiant floor heat.
In a recent Green Building Advisor discussion, some respondents said concrete floors might feel too cool underfoot. What is your assessment of concrete floors after living in the house for a while?


The floors are cold in winter. There is no getting around that. They are also very hard in all seasons. We wear slippers all of the time indoors, and we knew that that would be the case (we did so anyway on our hardwood in the other house).

The floors are also comfortably warm during the swing seasons, and nicely cool in the summer.


Hello Conrad.

We are in the process of building a home and have a goal to make the home as energy and cost efficient as possible. I would be interested in knowing the following if possible (per square foot cost is sufficient):

1. The capital equipment cost difference between heating your home with natural gas and your current heating sources (ie. gas furnace v. photovoltaic panels etc.).
2. The capital cost difference between framing and insulating your home as you did versus standard stick frame construction and minimum code insulation?
3. Did you insulate the exterior of all levels of your home and, if so, what did you use and its r-value?
4. The cost to heat your home using natural gas versus electricity since you have occupied your home?
5. Have you done a financial and environmental (ie.CO2 emissions for instance) analysis of the heating system you are currently using versus natural gas since you have occupied your home (ie. coal fired generated electricity v. natural gas)?
6. I have spoken to a few mechanical engineers and they all have indicated that ICF walls can provide a very high insulating value ie. r50 and higher insulating value, no thermal bridging and very air tight; i am specifically talking about the walls themselves and not how they are sealed to windows, doors etc. as this variable applies to any type of wall construction. I was wondering about your ICF comments on your website about them that they do not provide the insulating values they claim?
7. When selecting the lot for your home did you take into consideration current/future trees and homes etc. that may block the natural solar gains through your windows and your photovoltaic panels? Please elaborate how you did this for the future?

Thank you for your time and consideration and I look forward to hearing from you.



1. The two gas furnaces (one for a suite in the basement) would have cost $10,000+. Our electric baseboards cost us $900, installed. Plus roughly $50,000 for the PV system, but that cost isn't related only to heating.

2. 4% increase over conventional construction with 8" studs

3. Yes. R56 walls above grade, R50 basement walls, R24 under the slab, and R90 in the ceiling.
4. I don't know.
5. No.
6. ICF homes are very tight, but the R50 number is, pardon me, complete bullshit. The amount of insulation is about R22. Some places try to claim a benefit from the thermal mass inside of the forms, but that is complete bunk.
7. We did, and we just used a best guess. The row of houses across the alley is zoned for maximum 8.6 metre houses, and we have no way of knowing if that zoning will change. Also, neighbours can plant trees if they want. There are no solar access rights as of yet.


Dean, I have also heard the outrageous claims about the R value of ICFs. The Oak Ridges National Laboratory (ORNL) assessed a variety of wall types. A nominal 2 x 6 wall stud wall is usually defined as R 20, but the ORNL found it performed at about R13 because about 20 to 25% of the wall's area is lumber (window frames, top & bottom plates and studs. Thermal bridging reduced the performance value in a whole wall assessment.
Most ICFs have about 2.5 inches of foam inside and outside of the concrete core. 2.5 to 2.8 inches of expanded polystyrene (EPS) is rated at about R10. ICFs which were defined as R20 performed at R 20 to 21 in the ORNL lab tests.
Larsen Truss walls or double stud walls which were rated at about R 42 performed in the lab at about R 38 or better. ORNL and the NRC have determined that Larsen Truss walls and double stud walls deliver the best performance at the lowest cost per square foot of wall per R value.

Great comment Jim. Thanks. As you pointed out, ICF walls have virtually no thermal bridging, and they do make for very tight homes. However, the embodied energy in said homes is MASSIVE.

Concrete is very, very hard on the planet. If we can find another way (wood-framed walls), we should avoid using it when we can.


Conrad and Dean,
As luck would have it, today the Green Building Advisor website posted a blog about a home Thorsten Chlupp has built in Alaska. The web address for the blog is:
It appears that Mr. Chlupp has built a modified Larsen Truss wall with the exterior trusses held off of the home's structural wall by plywood gussets. Unfortunately, the article does not go into great detail about the wall configuration except to say that the insulation was R75 cellulose, (probably about 18 inches thick and dense-packed).

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