Constructing a net zero energy home in Edmonton, Alberta is extremely challenging because this is a cold place. Thankfully, it's also a sunny place. Still, in order to achieve the net zero standard, factors such as energy efficiency, insulating values and solar energy collection need to be maximized.
Peter the builder and I came up with the idea of an adjustable solar awning system that will increase by about 10% the amount of energy that the Mill Creek NetZero Home (MCNZH) produces annually.
I just wrote a proposal to help fund the prototype solar awning that we will put on the MCNZH. Here are some excerpts. Sorry for the formal tone, and warning: the following may be for eco-nerds only.
Passive Solar Energy
The MCNZH is designed to passively collect a large amount of solar heat through its south-facing windows. In fact, the 3642 kWh of solar heat that will be captured through the windows represent 46% of the annual space heating required by the MCNZH. With such a large area of south-facing windows, though, there is considerable risk of the home overheating.
In a home as well-insulated as the MCNZH will be, there are “…severe restrictions in the amount of south windows that can be used without excessive overheating” (CMHC, 2005, p.53). “Increasing the window overhang[, however,] allows for additional south glazing” (CMHC, 2005, p.54). In order to remain comfortable for its occupants, then, the south windows must be shaded by overhangs.
The installation of overhangs presents a compromise between maximum solar energy capture and occupant comfort. HOT2000 simulations show that the MCNZH will capture 314 kWh less annually if equipped with overhangs (HOT2000 is a residential building performance evaluation software distributed by Natural Resources Canada (Natural Resources Canada, n.d.)).
The solar awning prototype will eliminate this compromise, maximizing solar energy capture and providing occupant comfort at the same time.
Photovoltaic Electricity Generation
The MCNZH needs to provide itself with over 8800 kWh of heat and electricity annually. Much of this energy will be provided by an active solar hot water system and a ground source heat pump, but the remaining kWh will need to be provided by photovoltaic (PV) panels.
PV panels produce the most electricity when the sun is striking them at a 90° angle. Because it is so far north, Edmonton experiences a large degree of variation throughout the year in the angle of incidence at which the sun strikes an installed PV panel. On the day of the summer solstice (June 21), a PV panel must be tilted at a XX degree angle (not sure what angle yet) to be producing at its maximum capacity (all other variables considered). Alternatively, on the day of the winter solstice (December 21), a PV panel must be tilted at XX degrees.
When a PV panel is installed in a fixed location on a building in Edmonton, it is usually tilted at an angle of approximately 53°. This represents a compromise between the winter and summer months that maximizes electricity production.
The solar awning prototype will eliminate this compromise by being adjustable. The solar awning prototype will increase the electricity produced by the MCNZH by 10%-15%, or 400 – 600 kWh annually.
Solar Awning
Any design element that has only one function is probably a mistake or a missed opportunity. We ought to strive for multiple and diverse functions of each element so we pay once and get many benefits.
Amory B. Lovins, Rocky Mountain Institute
The solar awning prototype is a system that will provide two functions at once for the MCNZH. Covered in PV panels, the awnings will efficiently produce electricity and provide shade for the windows during the hotter months. They will be installed above the first and second floor windows of the home, and be adjusted four times a year by the homeowner. The solar awning prototype will provide a benefit of 714-914 kWh of energy to the MCNZH. This represents an increase of 8%-10% of energy generated when compared with the same home with regular awnings and the PV panels fixed in place on the roof.
During the summer months, the awnings will be set at an angle of between 25° and 30° (see picture). The summer adjustment will also slide the awnings forward so that they act as shade-providing overhangs for the windows. In addition to providing shade, the PV panels will generate electricity more efficiently because they are properly angled towards the sun.
Solar Awnings in July. The widows are fully shaded and the PV panels are perpendicular to the sun.
During the winter months, the awnings will be set at an angle of between 70° and 90° (see picture). The winter adjustment will pull the awnings up and away from the windows so that they don’t provide any shade. This will maximize passive solar heat capture through the windows, and increase solar electricity production by optimally tilting the PV panels towards the sun.
Solar Awnings in December. The windows are unshaded and the PV panels are perpendicular to the sun.
The solar awning idea is an elegant way to squeeze out an extra 10% of solar energy for this house. Plus I think they look pretty cool. I can't wait to see them in action.
(cross posted at www.raisingSpaces.com)
References
CMHC (2005). Tap The Sun: Passive Solar Techniques and Home Designs.
Natural Resources Canada. (n.d.). Retrieved October 16, 2007 from http://132.156.37.56/residential/personal/new-homes/r-2000/standard/hot2...
Hey, its looking good and the awnings seem to be a good compromise. Will the PV panels/system be the silicone substrate type?
Any thoughts to using rain water for things inside the house (not just for gardening). I've been thinking about the code issues around that for my house. It would seem that an argument can be made for labeling the water going to the toilets/laundry as non-potable and providing a vacuum break so that two supply lines can go to these appliances in case there is no stored water available on site.
Thanks for the pictures/comments.... as tony would say - there Grrrrreat!
Guy Taylor
"Will the PV panels/system be the silicone substrate type?"
Uh, I don't know what that means. They're going to be the most efficient ones that you can buy - rated at 22%, I believe.
As for the water idea, we're going to install a Brac grey water systems (their site is here). It's basically a big tank that you plumb your shower drains to drain to. Then you run your toilet water lines from the tank. It's not legal yet, but we plan on getting the officials on board if possible. If not, we may just go guerrilla with it. It's just too stupid to flush away waste with drinking water.
Thanks for commenting.
Basically the ones that are not using silicone are not as efficient, but much less expensive. Therefore you have to have more area for the same required wattage, but the panels are less expensive. I am assuming A) you went with the silicone because you didn’t have the additional area to work with? B) Efficiency was more important than payback time etc?
What is the total electrical load that you anticipate for a year? Remember there is a third child on the way, and Rach is committed to washing cloth diapers.
With respect to "Brac"; are you intending on supplying all the toilets with only the grey water that comes from inside the house (showers only?)? Will that be enough? I guess with the Brac system if additional water is required then potable water is used. I guess you could add other grey water supply lines later if needed (rain water etc.)?
I haven't looked into it yet, but our builder Peter says that the more efficient ones are a similar cost per watt as the others. And yes, we do want to cram as much wattage in as little area as possible.
We're expecting the house to consume 9,000 - 10,000 kWh per year in all. With tenants, the usage will obviously increase.
Yes, all toilets with just showers. I'm pretty sure it will be enough. We could add the washing machines if it isn't. The best side benefit is the 1000 kWh of free heating that we'll gain by keeping the warm shower water in the house until it gives up its heat.
I counted 24 Pv panels and 7 solar heating panels, is that right?
What is the panel size and type you will use? what is the wattage output for all 24 panels (under perfect conditions of course) and how many hours of sunshine can you assume per year?
I like the different angles that you can get from the awning, can the roof ones be adjusted too?
I ask, because the fellow I visited in Boyle , AB. said it makes a huge difference to his (off-grid) system and he adjusts it almost once a month.
Guy
I believe that they will be 220 W panels. So that would be 5280 Watts.
From the Riverdale NetZero home technical specification:
"A 24-module, 5.3 kW grid-dependent solar photovoltaic (PV) system
generates 5667 kWh of electricity per year, which meets all the electrical energy
required by the house on an annual basis."
That number is from Gordon Howell, so it's reliable. Plus, the Mill Creek NetZero Home (MCNZH) has a better orientation than the Riverdale project. So, I think we can safely conclude that we'll get at least 5667 kWh of electricity annually.
3740 Watts of PV capacity will be on the awnings, and they get a 15% (Gordon says 20%, but let's be conservative) boost because of their adjustability. So I think that a boost of 600 kWh from the solar awning is reasonable.
That gives the MCNZH 6200 - 6400 kWh of electrical energy per year to play with.
The MCNZH is currently modelling at 8000 kWh of energy consumption per year without any solar hot water or heat pump. That number includes electricity from the HRV and assumes that we'd be using a dryer (we won't be). It assumes two adults and two children, with 50% occupancy.
With solar hot water for our hot water needs during summer, taking into account the heat recovered from our grey water recovery system, and if we added, say, a geothermal system, we could easily shave 3000 kWh off of that number, which leaves us with a very healthy surplus of 1200 -1400 kWh of energy per year.
This is a cool website, thanks so much for your efforts to spread the information you're learning around.
Your moving awnings look like a great idea. There's just one thing: other green builders I've recently read about (fellow from Saskatoon working for Sask. gov't, sorry don't have his name) said that complex - bad, simple - good. Your system will move, and have bearings and structural engineering. Can you provide any details? How will it move, and what sort of bearings will you use? Can one person do it?
You're talking about Rob Dumont. He hasn't been negative about the awning idea, but he isn't jumping for joy either. There are moving parts, which are to be avoided if possible. Still, they only need to be moved four times a year...
In the end we decided to go with building the awnings because they provide four benefits. The two main ones I've already documented - increased passive solar heat capture, and improved electricity generation. In addition to these, the awnings will automatically shed snow in winter because they will be at such a steep angle. Finally, we are using sanyo bifacial modules for the awnings. These module produce electricity from both sides, thereby making them a perfect fit for an awning application. They will be the first bifacial modules installed in Canada, and they will perform up to 15% better than regular modules would.
An no, we don't have details yet. One person will be able to do it, but we're still designing the awnings. Stay tuned!
Yes, the solar PV modules (not panels) will be of single-crystal silicon (not silicone). We are using Sanyo 180 W 15% bi-facial PV modules for the awnings and Sanyo 190 W 16% efficient mono-facial modules for the fixed PV array. All the Sanyo modules will have their HIT® (Heterojunction with Intrinsic Thin layer) PV cells. HIT cells are hybrids of single crystalline silicon surrounded by ultra-thin amorphous silicon layers.
Hello Conrad, I was studying your computer images of the movable awnings. If you have any pictures of details of the installed units, could you post them? Could you explain the mechanics of the supports?
In your post about steel roofing, I mentioned some drawbacks of steel roofing. Could you update us if there are any issues with snow and ice on your awning solar panels or falling from the roof.
Thanks Jim.
I have yet to see a solar home utilize the "pop can" heater in their designs. While classed as active they are so simple they could be treated as passive. Has anyone that you know calculated the energy gain per ft2 compared to glass? Unlike glass, there is no energy lost when the sun is not shining. The only drawbacks are you can't see through the units and the radiant energy captured transfers directly to the air before being asbsorbed by any thermal mass inside. I would like to see a design incorporating vac tubes for solar water heating (& thermal storage); pop can units (instant heat) and glass (view & thermal storage)& PV (when prices drop)
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