Step 2. Solar Capture
Solar's contribution to the Zero Energy goal
The average Auckland house consumes 7,970 kWh of electricity from the grid each year1, with 30% used for heating. The Zero Energy House building envelope (framing, insulation, and glazing) eliminates the need for heating, effectively getting us 30% of the way towards our Zero Energy goal.
Solar takes care of the rest. The solar hot water system contributes 25% by providing almost all of our water heating needs. The last 45% is met by the solar photovoltaic (PV) panels, which generate enough electricity to power all of the appliances and lights in the house and run the hot water cylinder for the remaining water heating needs.
Why we went solar
The choice to go solar is tightly linked with the reasons why we've chosen to pursue Zero Energy. Building a house like this protects two things:
The average Auckland family could pay $80,000 in electricity bills over a 25-year period. Our solar system cost a fraction of that.
- The environment. Most of the country's electricity supply comes from hydro-electric power, with a portion coming from coal-powered plants. Coal pollutes the atmosphere and hydro-electric power requires infrastructure that infringes on the natural environment. And regardless of the source, electricity gets shifted all around the country on a massive transmission grid that costs money to maintain and results in energy loss. Generating electricity via solar on-site is clean, efficient, and, we believe, elegant.
- Our finances. When you factor in long-term electricity costs solar makes financial sense. The average Auckland home pays $2,000 a year in electricity bills2, equating to $50,000 over a 25-year period. But that doesn't take into account energy price increases. Since 2000 inflation-adjusted prices have risen by 3% per annum3. If they continue to do so the average home could face $80,000 in electricity bills over a 25-year period; our solar system cost a fraction of that.
What the system looks like
On a typical house the roof is there simply for protection from the elements. We decided to make our roof work for us. With our architects, we designed the roof size, shape, and pitch (along with orientation and placement of the entire building) to capture the amount of solar energy we needed to achieve our Zero Energy goal. The entire north-facing side of the roof is covered in energy-generating panels, both solar hot water and PV.
Using both systems means we can meet all of our energy needs. Heating water with a solar hot water system is far more efficient than doing so via electricity generated from PV so it is important to have both.
The C21 photovoltaic panels
The C21 is different to any other PV panel you'll see in New Zealand. In fact, the Zero Energy House is the first building in the southern hemisphere to have these panels fitted.
What makes the C21 different is that it replaces the building's roof. Whereas traditional PV panels are fixed to a steel or tile roof, the C21 performs as both a panel and a roofing tile. Eighty-eight of them cover most of the north-facing side of our roof, fixed onto battens like a normal roofing tile.
While this is the first time an integrated solar roof tile has been used in New Zealand, they are becoming increasingly common overseas. The C21 product is in its third generation, has been installed in the UK for seven years, and last year won the Queens Award for innovation. We believe the elegance and simplicity of panels like the C21 will make them standard in New Zealand for new houses built with solar in mind.
SolarCity is the exclusive supplier of C21 panels in New Zealand.
Like other PV, the C21 converts the sun's energy to electricity which is then either used in the house or sold to the grid. We've chosen to be grid-connected because on-site storage of energy using batteries is currently too expensive and batteries contain toxic elements such as lead and acid. By selling surplus electricty to the grid, and buying it back on days when we may not produce enough, we're effectively using the grid as a storage solution.
The system we've installed will produce much more energy than we need. Our models show we can expect to have surplus electricity throughout nine months of the year, with a small deficit in May, June, and July. Over a year, this will mean a Zero Energy (or better) balance.
For more information about our PV system, we have a dedicated page here.
Solar hot water
We're using an Artline solar hot water system from SolarCity. Eight panels, insulated and covered by protective glass, are laid out next to one another to run the full length of the roof-line.
Artline panels are manufactured in Christchurch, and are being made available as standard on a 2,200 property subdivision in the Canterbury rebuild.
Our models suggest the system will provide around 80% of our water heating needs. The remainder will come from a standard hot water cylinder powered by electricity generated by the PV panels.
For more information about the solar hot water system, we have a dedicated page here.
We don't have performance data yet because the house is still under construction and the solar systems won't be turned on until it is completed in late-August.
But we've got a good idea of how the house will perform. You'll see that we've mentioned modelled data a few times. We're both engineers and work full-time in the sustainability field; we work with building performance and solar models like these on an almost daily basis.
But you shouldn't just take our word for it, and you won't have to. During construction we have embedded forty sensors throughout the home that will monitor energy generation and consumption, temperature, humidity, and water usage. Once the house is switched on we'll publish results from those sensors on the website for everyone to see - along with the cost to build and cost to operate.
If you want to hear how the house performs, the best way is to subscribe via eMail, Facebook, Twitter or Google+ in the sidebar. We'll let you know when everything is up and running.
Why go solar with SolarCity?
We chose to install systems from SolarCity, partly because the PV panels we wanted to use are not available from any other solar company. But there are other reasons why SolarCity is a good choice for people considering solar:
- Experience. SolarCity has a 30-year track record and has installed over 8,000 systems on buildings throughout New Zealand. Their clients range from home owners to government agencies and large businesses.
- Full service. SolarCity is New Zealand's only full-service solar company. They design and manufacture systems, provide financing, have a nation-wide network of installers, and monitor systems once they're installed to ensure they run as efficiently as possible.
- Sustainability and jobs. Sustainability is at the heart of SolarCity's business. The company was founded by its CEO, Andy Booth, who was previously a board member of Greenpeace. It is the first solar company in the world to achieve CarboNZero™ certification. And many of its systems are manufactured in New Zealand, providing a growing source of green jobs for the economy.
1 Building Research Association New Zealand (BRANZ). (2006). Energy use in New Zealand households: Report on the year 10 analysis for the household energy end-use project (HEEP). p18.
2 This is based on the 2010 rate of 25.5c per kWh in, Ministry of Economic Development. (2011). New Zealand energy data file: 2010 calendar year edition. p130-131.
3 Based on calculations from data in the MED report above. The non-adjusted average annual increase is 7%, as we state in the video.