The Evolution of Solar Power

Improvements in technology have made solar power more efficient and affordable than ever.


New solar panels are more reliable than their predecessors, and financial incentives bring their cost down considerably.

New solar panels are more reliable than their predecessors, and financial incentives bring their cost down considerably.

By: Jill Connors

Solar power for the home has never been more attainable than it is today thanks to recent breakthroughs in technology and pricing innovations — but it has taken a long time to reach this point. Even the term solar power can mean many different things. Here's a look at solar power — past, present and future — for the home.

Solar Power in the Past: Ancient and Recent History

Passive solar power has been used for centuries; indeed, Roman bathhouses in the first century are known to have featured large south-facing windows, and architects today continue the smart practice of orienting a house and its windows to take advantage of sunlight's effect. Solar water, which is heated for household use by a system of rooftop collectors and storage tanks, has also been a recognized technology for many years.

By contrast, solar power that actually provides usable electricity is relatively new. The technology is called photovoltaics (converting light, aka photons, into electricity, aka voltage). Although scientists have been aware of the photovoltaic effect since the 1830s, it wasn't until 1954 that a photovoltaic (PV) cell was developed at Bell Labs with a remarkable characteristic: It could convert sunlight into enough power to run household electrical equipment. The cell relied on silicon, an element found in sand; silicon converts the sun's energy into electricity. As with many cutting-edge technologies, early PV efforts were extremely costly, limiting their use initially to such small applications as wristwatches and calculators — or to such large endeavors as NASA's space program, which used PV cells for spacecraft and satellites.

Solar Power in Homes Today: It's a PV Story

Gradually, solar power has been entering the residential market: Since the 1970s, when the first PV system for a residence was installed, there have been 150,000 PV installations, according to industry experts. Currently, federal and state rebates help promote the use of solar. (You can check what is available in your state at a clearinghouse known as DSIRE, the Database of State Incentives for Renewables & Efficiency.) Even so, only .03 percent of U.S. electricity was generated by solar power in 2010, according to the U.S. Energy Information Administration, while 70 percent of the 4,120 billion kilowatts of electricity generated in 2010 was from fossil fuels (coal, natural gas and petroleum).

For residential use, solar cells are typically grouped into panels, which are then installed on a south-facing rooftop in an arrangement commonly referred to as an array. For example, one solar panel that produces 250 watts might be grouped in an array of 20 panels to create a 5-kilowatt-hour system. Residential photovoltaic systems are typically 3 kwh to 10 kwh, with the appropriate size depending on household use, available rooftop space and sun orientation, among other factors. (An average American household uses 10,000 kilowatts of electricity per year; a 5-kwh system generates an average of 6,000 kilowatts per year.) The array is connected to an inverter inside the home, which then controls the flow of electricity to the house's circuit breaker and also to a utility company that may credit the household if excess power is generated.

New technology continues to create more efficient and reliable PV cells and solar panels — not to mention improved aesthetics — but cost remains the single biggest barrier for homeowners, according to a 2009 report by the Clean Energy Group, a Vermont-based nonprofit group that promotes increased use of clean energy technologies in the U.S. The materials and installation for a 5-kwh system can run $35,000, although federal and state rebates may cut that cost in half.

Solar Panel Installations

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An array of 20 photovoltaic solar panels sits atop the roof of a California house. With each panel producing 250 watts, this array creates a 5-kw system. A south-facing orientation that receives unobstructed sunlight all day is optimal. Photo courtesy of SolarCity  

A photovoltaic array is installed on the south-facing rooftop of a long wing of a California house. A PV array must receive full sunlight for at least four or five hours per day. Photo courtesy of SolarCity  

A gently sloped roof facing toward a home's private pool area offers plenty of surface for an array of 42 photovoltaic solar panels. Photo courtesy of SolarCity  

Two arrays of photovoltaic solar panels are installed on the third-story roof of a traditional brick-and-clapboard house in the Los Angeles area. Photo courtesy of SolarCity  

Three rows of photovoltaic solar panels are installed on the standing-seam metal roof of a California house. Photo courtesy of SolarCity  

A 25-panel photovoltaic array makes maximum use of the shed-style dormer roof on a home in a densely populated neighborhood. Photo courtesy of SolarCity  

A house with multiple wings and an extensive roofline offers more than one place to install solar panels. Photo courtesy of SolarCity  

An array of 22 photovoltaic solar panels is positioned so it receives sunlight without interference from foliage located in other areas of the property. Photo courtesy of SolarCity  

The photovoltaic solar panels on this garden pavilion do double duty: They generate electricity for the property while also creating a shady spot. For houses where the roof is obscured by foliage or is not oriented to the south, the roof of an outbuilding is a good option for a PV installation. Photo courtesy of SolarCity  

Dow POWERHOUSE Solar Shingles, a building-integrated photovoltaic (BIPV) product, combine solar cells directly into a roofing shingle, to generate electricity. The shingles can be installed alongside conventional roofing shingles, as shown on this house. Visit for more information.  

Solar Leasing: The Newest Pricing Innovation

For homeowners who can't afford the initial cost of a solar PV installation, leasing may offer the right economics. SolarCity, a California-based solar installer that operates in 11 states, offers solar leasing options that provide materials, installation, insurance, monitoring and repair for zero money up-front. The homeowners pay a monthly leasing fee of approximately $100 for an average-sized system and will see their monthly power bill reduced by more than the leasing fee. SolarCity's leasing program, introduced in 2008, has been extremely popular. "We have 15,000 residential customers, and 12,000 of them use the financing option," said Jonathan Bass, a SolarCity spokesman. "Solar is a great investment whether you purchase or lease, but initial cost has absolutely been the #1 barrier to adoption," he said.

Solar Roof Shingles: A New Technology

A new product expected to be available this fall may also increase the number of homeowners who are able to utilize solar power. The solar roofing shingle, a building-integrated photovoltaic product (BIPV), is designed to be installed just like an ordinary roofing shingle. Nailed to the roof, the shingle lays flush with other roofing shingles, thereby eliminating the raised structures that hold arrays of solar PV panels. The cost of the solar shingle, plus the fact that it can be installed by a roofing contractor and an electrician, rather than a solar specialist, are expected to make the BIPV shingle an affordable option; a homeowner can benefit from federal and state rebates to lessen the cost, as well. Two Michigan-based companies are currently in final development of solar roofing shingles: Uni-Solar's "PowerShingle" and Dow's "Powerhouse" shingle.

Solar Roof Shingles 03:41

Today's integrated solar shingles are superior to traditional solar panels.

Solar Power for the Home: A Sunnier Future

The renewable-energy industry points to data showing that more than 90 percent of Americans favor solar energy use, a trend likely to remain constant with today's heightened awareness of the benefits of clean energy. Legislation such as the "Ten Million Solar Roofs Act of 2011," recently introduced in Congress, has a stated goal of powering 10 million homes and businesses with solar energy by 2020; the bill's details include rebates that would reduce the $35,000 cost of a 5-kwh system to as little as $7,875. It's been a long time in the making, but more widespread solar use may finally be seeing the light of day.

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