SolarCity : These 3 maps show the absurdly large growth potential of home rooftop solar in America

Solar power in America is on a roll.

Over the last decade, the cost of solar installations in the U.S. has fallen by more than 70 percent, and every year has had more solar installed than the last. Since 2010, the nation's solar power capacity has grown fifteen-fold. And employment in the U.S. solar industry recently surpassed 200,000 people - that's more than the oil and gas extraction industry, and three times more than the coal-mining industry.

It's really just the beginning though. To grasp solar's enormous untapped potential, we can start by looking at home rooftop solar. There are already more than 1.1 million home solar rooftops in the U.S. today - including more than 300,000 SolarCity installations - but the coming years are likely to make that look small.

Using publicly available data, we've produced the three maps below to convey the absurdly large growth potential of home rooftop solar in America.

Map #1: Which states today have a meaningful amount of homes with solar rooftops?

First, let's see which states today have at least some meaningful amount of homes with solar installed. Each tiny square in Map #1 represents enough home rooftop solar to power ~3,000 homes. (Three thousand homes is roughly the number of homes in a small town with a population of less than 10,000 people.)

The map shows the states that currently have roughly enough residential solar to power ~3,000 homes or more.

Map #1 reveals that more than half of the states have enough residential solar to power at least a few thousand homes. Some states are clearly leading the pack. However, if residential rooftops are to become a major energy source across America, then powering a few thousand homes here and there isn't enough. Thinking on a larger scale is required, where residential solar can power tens of thousands, hundreds of thousands, or even millions of homes in any given state.

The next map helps us think on that larger scale….

Map #2: Which states today have enough residential solar to power a significant number of homes?

Map #2 enables thinking on a larger scale. Each tiny square in Map #2 represents enough home rooftop solar to power ~80,000 homes. (Eighty thousand homes is roughly the number of homes in a single midsize US city, such as Irvine, CA or Salt Lake City, UT.)

This map shows the states that currently have roughly enough residential solar to power ~80,000 homes or more.

Map #2 reveals that only a small handful of states (CA, NY, NJ, MA, AZ) currently have enough residential solar to power a significant number of homes. This is not to say that home solar installations aren't producing big benefits in other states; indeed, many households from New Mexico to Vermont are successfully lowering their utility bills, reducing pollution, and gaining more energy independence thanks to solar. But so far, it's happening at a far smaller scale than in the leading states, where a combination of policy and other factors has catalyzed solar growth.

The question for the future is: what growth potential does home rooftop solar have across the country? And can home rooftop solar become a major energy source in all states? Which brings us to our third map….

Map #3: Which states have the potential for residential solar to power a significant number of homes?

The potential for home rooftop solar to become a major energy source is enormous - in every state.

The map below shows the potential of home rooftop solar for each state, using the same scale as above, where each little square represents enough residential solar to power ~80,000 homes. The data comes from the National Renewable Energy Laboratory (NREL), which has calculated how much energy could be generated by rooftop solar panels in each state, if installed on all suitable roofs. NREL's analysis of 'suitable roof area' takes into account factors such as shading, roof tilt, roof position, and roof size.

Map #3 reveals that in every state, home rooftop solar could be a major energy resource. NREL's analysis suggests that America's total home solar capacity can increase 100 times over, and each state could meet 10-45% of its electricity needs from residential solar alone. You can hover over the map above to see approximately what percentage of electricity demand in each state could be met by residential solar.

In total, residential rooftops could provide around 25 percent of all the electric demand in the continental United States, according to NREL's analysis. If you add in the roofs of medium and large buildings, that number rises to 40 percent. By comparison, all rooftop solar today combined provides less than 0.5 percent of the nation's electricity.

More than 1.1 million American homes have gone solar so far. It's just a hint of what's possible.

There's no doubt that home solar power is already spreading contagiously. But the maps above suggest that American communities have just scratched the surface of what's possible. A new solar installation goes up every 2.5 minutes in the U.S. today, but that pace could vastly increase, given solar power's record-low costs and strong bipartisan popularity.

The animation below contrasts the 'Current' and 'Potential' views of home rooftop solar, to give a sense of what America's energy future looks like. The sooner that homes across the country become a part of that future, the more years they'll have to enjoy its benefits.

Methodology Notes:

Current state-by-state installation data for home rooftop solar comes from state fact sheets published by GTM Research and Solar Energy Industries, as of September 2016.

Conversion of how many homes can be powered by 1 megawatt of solar panels is based on SEIA's current national estimate of 164 homes per MW. Rounding procedures and inclusion thresholds for each map are described in their lower left corners.

State-by-state home rooftop solar potential is roughly deduced from NREL's 'Rooftop Solar Photovoltaic Technical Potential in the United States ' (2016). The data in this post draws upon NREL's analysis of 'small buildings' (those with a footprint of less than 5000 square feet), which does include some non-residential buildings. However, NREL states: '…the national building stock is estimated to contain 78 million single-family households, but only 3.2 million commercial buildings with a footprint less than 5,000 ft.' This suggests that 96 percent of the 'small buildings' analyzed by NREL are single-family households. Since this represents nearly all the 'small buildings' considered, we make the simplifying assumption that NREL's 'small building' classification is interchangeable with single-family residential buildings.

The maps focus on the continental U.S. because NREL's solar potential analysis is confined to the continental U.S. Although Hawaii is a leading solar state, the maps still provide a fairly complete national picture, as the continental U.S. represents >99.5% of all US electricity generation (http://www.eia.gov/electricity/state/).

The estimate that rooftop solar currently accounts for less than 0.5% of U.S. electricity comes from EIA's Electric Power Monthly, Table 1.1, computing [(Distributed Solar PV Generation) / (Total Generation at Utility Scale Facilities + Distributed Solar PV Generation)] for 'Rolling 12 Months ending in September 2016.