Plugging computers, televisions, and other electronic devices into a power strip instead of a wall receptacle allows power to be completely shut off with a single switch. May devices plugged into the wall continue to draw a small amount of power even when they are turned off. The trickle of wasted energy adds up.
Once decisions have been made about the house - insulation, windows, solar orientation, mechanical systems and the like - it's time to work in renewable energy. And here, there is no magic, just a methodical accounting of how much electricity will be consumed day by day over the course of a year. Energy modeling software, such as Energy-10 developed by NREL, can be a huge help.
Appliances and heating and cooling equipment are major energy consumers. Planners can check specifications provided by manufacturers to see how much electricity a particular appliance will use. Washing machines, heat pumps, dishwashers, and refrigerators all come with government-mandated labels showing predicted energy use.
Note: Planners may want to dive deeper than that and do more thorough calculations.
Estimating the amount of electricity the house will use in a year is simply a matter of adding up the numbers, and taking a few educated guesses along the way.
Plug loads are a wild card, not only because phantom loads (the electricity surreptitiously used to power electronics and other devices when they are turned off) can be substantial but also because we kind finding more stuff to plug in.
Adding up the Numbers
In an all electric-house, a renewable energy system can be sized once these values have been determined. When other fuels are used, however, there's one more step: producing enough surplus electricity to compensate for the firewood, natural gas, liquefied petroleum, or other fuels that might be used for space heating or cooling.
Homeowners who watch their use of electricity carefully, who remember to turn out lights when they're not needed, and unplug the TV instead of just turning it off, will get by with less renewable energy capacity than an energy spendthrift.
Renewable Energy Options
For the moment, photovoltaics, wind energy, and solar hot-water collectors are the basic tools that designers and builders have at their disposal to get a house to zero energy performance. The exact mix of energy sources for a home depends greatly on the site, the house specifications, and the habits of its occupants. The one constant - a super-efficient building envelope - well-insulate and well-sealed.
Deciding where to spend the building budget can be a challenge. Paul Norton, a senior research engineer at NREL, says, "the critical question" in net zero building is how much money to invest in renewable energy and how much to invest in improving the energy performance of the building itself.
Making energy improvements to the building is relatively inexpensive. Air sealing, for instance, is relatively less expensive than triple-glazed windows and thick layers of sprayed-in polyurethane foam insulation. It's more expensive to make the building more efficient than it is to add renewable energy capacity.
Norton believes this crossover point occurs when 50-60% of total energy savings have been reached. The first half of the journey toward zero energy takes place on the building side and the rest with renewable energy. As the cost of renewable energy continues to fall - either through more generous government subsidies or basic improvements to the technology - the equation will change as well.