Renewable Energy and Net Zero Homes

Net zero homes generate as much energy as they use, so the net amount of energy purchased from the hydro company over the year is zero. Net zero homes are designed to be up to 80 percent more efficient than conventional houses. They are built with airtight building envelopes and are super-insulated with thick continuous insulation, triple-glazed windows and ‘thermally broken’ insulated doors. High-efficiency heat pumps, Energy Star appliances, LED lighting and smart electronics help minimize energy consumption.

Net zero homes include at least one on-site renewable energy system that is capable of producing as much power as the home uses in a year. Grid-tied net zero homes will still be connected to the local power grid, to meet changing household energy needs over the days and seasons. Being connected to the grid allows homeowners to supply energy to the power grid during months when heating and cooling energy needs are low, but then draw back from the grid when solar energy may not keep up with winter heating needs.

With a net zero home, not only will your utility bills be minuscule; they will remain low year round. You’re also protected against future energy price increases. If predicted energy price increases do occur, while other homeowners are scrambling to cover enormous hydro and gas bills, your only concern might be covering the monthly cable TV or internet.

Net zero homes are built to a much higher standard than conventional homes. Better insulation and airtightness improve the durability of your home, so there are fewer maintenance costs. Advanced construction methods with superior insulation, heating, cooling and ventilation systems assure you of even temperatures throughout your home. The fresh air system filters out dust, pollen and outdoor air pollution.

Net zero homes are future-proof, carbon-free and built to stand the test of time. It’s not just a “green home” or “a house with solar panels”. Zero energy homes are incredibly comfortable, healthy, quiet, sustainable buildings that are affordable to live in.

Is there a difference between renewable energy and carbon-free energy?

Renewable energy is a naturally replenishing resource that produces zero emissions. When we think of net zero homes we envision roof-mounted photovoltaic (solar) panels, but there are other renewable energy sources like wind, geothermal, biomass and biowaste, and even small stream-fed hydroelectric generators. All renewable energy is carbon-free, but not all carbon-free energy is renewable. To be renewable, the source must be naturally-replenishing.

Carbon-free energy is produced by a resource such as a nuclear plant or hydroelectric dam. These resources generate no carbon emissions and can help reduce greenhouse gas emissions, but they often negatively impact the environment and local economy. The creation of dams to build new hydroelectric energy resources will have a lasting environmental impact on the surrounding ecosystems. And nuclear power plants need to safely store waste long-term, which is a costly proposition.

Renewable energy sources on net zero buildings will reduce the demand for carbon-free energy resources like nuclear plants and hydroelectric dams. But how green are solar and wind power?

Solar panels

Solar energy is already helping thousands of Canadian households reduce their carbon emissions every day, but solar panels have a carbon footprint that needs to be considered. The solar panel carbon footprint created by the manufacturing process is significant. The manufacturing process begins with sourcing raw materials. The factories that produce solar panels are typically powered by coal-powered Chinese power stations, they use large amounts of electricity and this creates a related energy debt that must be ‘paid off’.

Silicon is the second most common element in the earth’s crust. Silica isn’t found in a pure form in nature, but it can be mined from quartzite, mica, talc, and sand. The silica is heated with a carbon material and the oxygen is removed, leaving behind purer, metallurgical-grade silicon, which is further purified into polysilicon, the solar-grade purity of which is 99.999 percent.

There are two types of solar panels being manufactured at present: monocrystalline and polycrystalline. The black panels most of us are used to seeing mounted on the roofs of houses, or in photos of banks of solar panels in major installations are usually monocrystalline. Large silicon ingots are sliced wafer-thin with diamond saws and affixed to solar panels.

Polycrystalline solar cells are also manufactured from silicon, but instead of slicing them from silicon ingots, polycrystalline cells are created by melting silicon crystals together. They may produce less waste, but they are not as efficient as monocrystalline. Dopants phosphorus and boron are added during a doping process, so the wafers can be ionized, through the creation of a positive-negative (p-n) junction.

Solar panels’ carbon footprint is approximately 20 times less than the carbon output of coal-powered electricity sources. 44 – 50g of CO2 per kilowatt-hour is produced during the first years of operating a solar energy system. It takes three years for solar panels to pay off their carbon debt, becoming carbon neutral. Your home’s solar power system will then remain carbon neutral for the rest of its service life. The life expectancy of solar panels is about 30 years before decommissioning and replacement.

Wind turbines

Like solar panels, wind turbines create energy without carbon emissions, but there is also an energy debt incurred during the mining and production of materials, and the manufacturing process. Building and erecting home-based wind turbines typically involves hundreds of pounds of materials, including steel, aluminum, concrete, fibreglass, copper, epoxy resins, and more exotic items like neodymium and dysprosium used in permanent magnets. Mining metals and rare earths consumes a lot of diesel fuel. Producing steel requires the combustion of metallurgical coal in blast furnaces. And the manufacture of concrete, generally used in the foundation, emits plenty of carbon dioxide.

Wind turbines average just 11 grams of CO2 emission per kilowatt-hour of electricity generated. When compared with 44g/kwh for solar energy, 450g for natural gas, and 1,000 for coal, the carbon debt for wind power is incredibly low; just slightly above 9g/kwh for nuclear energy. Suppliers are advertising that it can take as little as one year to pay off a wind turbine’s carbon debt. The good news is that, like solar panels, the emissions are nearly all front-loaded.

Hybrid homes: solar / wind renewable energy systems

Producing your own clean, renewable energy is one of the fundamental aspects of owning a net zero home. Most net zero homeowners believe they must choose between solar panels or wind turbines. The problem with choosing between solar and wind is that you limit the amount of energy that your home can produce.

With solar panels, you obviously will not be generating electricity during the nighttime. Extended cloudy periods will significantly reduce the power your home can use, store or feed to the grid. And wind turbines can produce energy at all hours of the day, but only when there’s wind present. During seasonal periods where there’s little wind, there will be virtually no energy produced.

Hybrid renewable energy systems combine two or more sources. A hybrid system diversifies and increases your chances of successful year-round energy collection, so the approach just makes sense. You can produce energy nearly around the clock, every single day of the year.

If your home is not grid-connected, by adding a wind turbine to your solar panels you will be able to decrease the size of the battery system needed to power your home during the night. And for grid-connected renewable energy systems, you will be able to decrease your reliance on the energy grid. Most grid-connected renewable energy systems push energy to the grid during the day when it is sunny and then pull some energy back from the grid during the night. In areas like the Sea to Sky Corridor, along BC’s West Coast, where both sunshine and wind are abundant, it should be possible to more than achieve net zero with a hybrid system, becoming net-positive.

Can an existing home be retrofitted to net zero?

Yes, the net zero building concept isn’t limited to new homes. Net zero renovations include sealing the building envelope, boosting the insulation levels to exceed code standards, installing triple- or quad-glazed windows, replacing forced-air furnaces with heat pumps, perhaps orienting windows to take better advantage of the sun, installing the latest Energy Star appliances and LED bulbs, and adding a renewable energy source. It’s a big project, but it can be done.

What is net zero ready?

A net zero “ready” home is essentially a net zero house without energy generation. It’s so efficient that it could become fully net zero with the installation of a renewable energy source. For Part 9 homes and buildings, the BC Energy Step Code describes five performance levels or “steps” that exceed the base BC Building Code. Step 5 on the staircase timeline describes a home that has been constructed as net-zero energy ready (NZER).

The BC Energy Step Code is currently adopted by municipalities voluntarily. Between 30 and 40% of all of the primary energy used worldwide is consumed in buildings. As people are gaining a better understanding of the impact building homes has on our planet, governments at the local, provincial and federal levels are taking the initiative to make new homes more sustainable with a step approach.

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