Building a zero-energy home isn't simply a matter of throwing in a solar-power system and the highest-efficiency refrigerator on the market. A ZEH is built from the ground up with energy efficiency in mind. It starts with the most basic design and construction elements, focusing on two major areas: reducing energy requirements for the systems that account for most of a home's energy use and increasing the home's built-in energy-generating capacity.
A ZEH incorporates:
- A solar-photovoltaic system for generating electricity
- A passive solar-thermal system for heating water (passive systems have no electrical parts -- see How Solar Water Heaters Work to learn more)
And it minimizes energy needs for:
- Space heating, space cooling and ventilation
- Water heating
- Lighting and appliances
There are lots of tricks builders and architects use to accomplish these goals. For instance, the walls, roof and foundation, and the interaction between the three, can be designed to most efficiently manage water, vapor and heat flow. The roof coating may have a high solar-reflectance value. Eaves and awnings can be strategically placed and sized to block summer sun and allow winter sun. Other design elements may include:
- Extra-thick windows and insulation
- Built-in temperature and ventilation monitoring systems
- Strategically placed skylights to reduce lighting needs
- Orientation to take full advantage of sun exposure for solar panels
- High-performance attic sealing to reduce cooling needs in summer
Even with the highest-efficiency design and appliances, a ZEH still uses power, and it's still connected to the electrical grid. So how can it be "zero energy?" That has to do with the installed solar photovoltaic system. The solar panels sometimes provide as much energy as the home uses. And when they don't, they have a payback plan.