What is the ultimate potential of renewable energy use?

• Limitless! US solar resources are many times greater than US energy consumption: For example, the sunlight energy falling on White Sands Missile Range alone is roughly equivalent to the entire US energy consumption! Similarly, developable wind power resources, that is, sites that have adequate winds and located such that wind farms would not adversely affect birds or create visibility problems, are estimated to be able to provide between two to ten times the entire electricity needs of the US.

What are the basic types of solar energy systems, and how much do they cost?

• Electricity can be produced from renewable energy resources in several ways: The most flexible way is "photovoltaic", or "PV" systems, which employ semiconductor technology to convert sunlight directly into electricity. PV costs about $10/watt to install (a standard home requires between 600 to 3000 watts, depending on efficiency, hence $6000 to $30,000 - roughly the cost of a car). In terms of energy produced, PV costs between 20 to 50 cents per kilowatt hour (for comparison, grid power typically costs around 10 cents per kilowatt hour retail).
• Solar hot water systems generally cost $2000-$5000.
• Designing a home with Passive solar attributes can cost anywhere from $0-$4000.

How long do solar power systems take to "pay back" their initial investment?

• Grid power, although usually very dirty (if produced from coal or nuclear), is very cheap. Therefore, it takes PV systems several decades to "pay" for themselves on this basis alone. This is much faster than was the case 20 years ago, however, and in particular, not bad at all if the system is simply included in a mortgage. For many off-grid homes, however, PV is immediately cheaper because it often costs thousands of dollars to extend grid power lines for even a fraction of a mile. Renewable electricity can also be tied into the local utility grid in a system called NET-Metering, which feeds your excess energy back into the grid - turning your meter backwards, and improving the economics.
• Solar hot water systems tend to pay for themselves in roughly a decade (and shorter if there are spikes in gas or propane prices, as has occurred in recent years). Good passive solar home design tends to pay for itself in zero to several years.

Are renewable resources too intermittent for practical use? How can the energy be stored?

• Some sources, such as geothermal, hydro, biomass, and wave power, are not significantly intermittent to begin with. Solar power in the Sunbelt is quasi-intermittent: it works well almost every day. Wind power is significantly intermittent, producing between 25% to 40% of the time at good sites (utility scale wind power has achieved its low cost despite this fact - if the wind blows constantly at a site, wind power becomes dirt cheap). Present day technologies for storing renewable electricity include batteries, which can be used for home power applications, and molten salt heat storage, which can be used effectively to shift the output of large solar thermal electric plants to peak load times. In the future it is likely that energy storage problems will be solved completely through production of a fuel such as hydrogen. This can be done with an overall life-cycle efficiency of at least 50% if fuel cells are used to convert hydrogen energy back into electricity.
• Passive solar design, on the other hand, functions very well using thermal mass, i.e. thick masonry surfaces, to absorb and store heat for the nighttime or a cloudy day.

Do renewable energy collectors take up too much land area to be used widely?

• No! There are several ways to see why: A single utility scale wind turbine can provide enough energy to completely power more than 300 homes (assuming the wind only blows 30% of the time), yet has a footprint smaller than that of a single home! The fraction of roof area required to provide the electricity needs of an energy-efficient home in the Sunbelt with PV is approximately the floor area of a single bedroom; Overall, it is estimated that all the energy needs of the US could be provided with a land area impact of less than 0.5% of US land area — which is much smaller than the land area used by agriculture, for example. Moreover, much of the land area used can be integrated with existing land uses (wind farms integrate well with agriculture, and solar integrates well on rooftops). On the other hand, strip mining for coal, over a century, affects up to five times as much land area as that needed to produce the same energy with solar, and these impacts are much more severe and continue to grow indefinitely (coal mining has already affected approximately 24 million acres in the US alone: roughly enough land area to completely power the US with solar!).