As nonrenewable fossil fuels (oil and gas) become depleted, price shifts will move the world toward more use of renewable energy sources, such as solar energy, wind-generated power and plant-based fuels. The most cost-effective options for homeowners now are passive solar design, geothermal heat pumps and solar water heating.

Rapidly emerging technologies for homes include fuel cells and photovoltaics, both having the potential to take homes “off grid,” (no use of electricity from a centralized power generation plant) or create “zero energy homes” that are connected to the grid yet use zero net energy over the course of a year. Zero-energy homes produce and sell enough excess power back to the utility to balance out the amount of power consumed. In either case, a home must first be highly energy-efficient to minimize the need for power.

Fuel cells: Residential fuel cells are an emerging technology that can meet some or all of a home’s need for electricity. A fuel cell is an electrochemical device that combines hydrogen (from a hydrogen pipeline or derived from a fuel such as natural gas, propane or others) with oxygen from the air to produce electric power without combustion.

Because power is produced without burning fuel, fuel cells have almost no polluting emissions. Fuel cells are expected to be an economical and reliable means of providing electric power to households in remote locations. As the technology advances and costs drop, they will become a viable and attractive option for more homeowners.

Photovoltaics: Photovoltaic (PV) modules convert sunlight (a free, clean energy source) into electricity. They can be installed on the south side of an unshaded roof or on free-standing tracking devices that follow the sun and therefore capture more sunlight per day. A typical PV system consists of solar cells connected electrically to form a module that can measure 2-4 feet wide and 4-6 feet long. Some solar modules look just like traditional roof shingles. Many interconnected PV modules are called an array.

Until recently, a PV professional needed to “build” the system, and not all of the components had the same level of market readiness, code approval or availability for residential installations. Now, there are components of each type that are fully developed, widely available and compatible; and there are many firms that offer residential package systems with all components fully integrated and warranted. Also, today’s PV systems are reliable, durable (hail and severe-weather resistant) and may last 30 years with minimal maintenance.

Technological breakthroughs continue to reduce the costs of PV ownership. Depending upon where you live, local utility costs and government incentives offered, PV power can be competitively priced with other energy sources. The current cost of PV power is equivalent to around 30 cents per kilowatt-hour (kWh), considering initial cost spread over the lifetime of the system plus maintenance costs. As utility rates rise and PV advances reduce its cost, solar power will become an increasingly practical option. PV systems can be less costly than extending power lines to homes far from utility services (in some cases, a half mile or more) or replacing these lines after a disaster.

A PV system needs unobstructed access to the sun's rays for most or all of the day throughout the year. Most residential systems require from 50 square feet (for a small "starter" system) up to 1,000 square feet for larger systems. The more energy-efficient your home is, the less energy you will need to produce. A one-kilowatt system would occupy from 80 to 360 square feet.

Most residential systems consist of a PV module, battery storage and an inverter to convert PV current (DC) to standard household current (AC). Small, affordable home PV systems may be attached directly to appliances or lighting systems (and serve the additional purpose of backup power for essentials during a power outage). Larger systems can supply all power for the home.

Solar water heating is considered the most cost-effective and affordable residential solar option. Solar air-conditioners are now available. PV-integrated roofing materials have been developed to replace traditional PV modules that are mounted on rooftop racks. The result is a solar system that is hardly noticeable and replaces part of the roofing (offsetting some of its cost). For more information, visit http://www.eere.energy.gov.