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Trends in rooftop solar

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Rooftop solar power in the United States has increased by a factor of ten over the past decade and the majority of that growth has been in the past six or seven years.  At this point, about 7% of American homes have solar panels on their roofs – about 5 million in total. 

Rooftop solar really began experiencing widespread use about 20 years ago.  Over that time period, the amount of electricity that panels are able to produce has grown substantially and the cost of solar power systems has dropped dramatically.

Twenty years ago, the median sized residential solar system generated 2.4 kilowatts of power.  In 2023, the median size was 7.4 kilowatts.  Roofs haven’t gotten bigger; solar panels have gotten better.

More importantly, 20 years ago, the average cost of installing solar power was $12 a watt. In 2023, the cost was $4.20 a watt.

Americans in fact pay considerably more for solar power than citizens in many other countries.  The reason is not the price of the equipment; it is so-called soft costs.  These include labor, financing, and permitting. Driving down soft costs is complicated and difficult. For one thing, it is important for solar industry jobs to have high pay and good benefits.

The cost of solar also varies significantly by state.  California is the leading state for solar power and its median solar cost is the $4.20 a watt, the same as the national average.  Nevada has the lowest cost at $3.40 a watt and Utah has the highest at $5.20 a watt.

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Bigger and Less Expensive: A Snapshot of U.S. Rooftop Solar Power and How It’s Changed

Photo, posted September 18, 2011, courtesy of Team Massachusetts 4D Home via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Powering Britain with sun and wind

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The United Kingdom is quite small in size compared with the US, but its population of 67 million makes it a fairly large country with substantial energy needs.  A recent study by Oxford University looked at the ability of wind and solar power to provide for those energy needs over the course of time.

According to the study, Britain’s energy needs could easily be met entirely by the two sources of clean power.  Wind and solar can provide significantly more energy than the highest energy demand forecasted for 2050 and nearly 10 times the current electricity demand. 

Britain currently requires 299 TWh per year.  The Oxford study found that wind and solar could generate as much as 2,896 TWh per year. Furthermore, the researchers stated that these estimates are intentionally conservative, taking into account concerns around land use and the visual impact of installations.

The analysis assumes that offshore wind would produce nearly three-quarters of the energy required.  Onshore wind would contribute about 7%, while taking up only 0.07% of the country’s land.  Utility-scale solar would add about 19% of the power.  The small remainder comes from rooftop solar.  The researchers do point out that the power grid would require significant upgrades to handle all this renewable energy and that there would need to be appropriate quantities of energy storage. 

According to the authors of the study, achieving these results is a question of ambition rather than technical feasibility.  So far, the UK government has not been aggressive in making the transition to renewable energy.

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Wind and solar power could significantly exceed Britain’s energy needs

Photo, posted November 4, 2021, courtesy of Steve Knight via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

A Big Year For Rooftop Solar | Earth Wise

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The global capacity of rooftop solar power grew by 49% in 2022.  Overall, the installed amount of rooftop solar grew from 79 gigawatts to 118 gigawatts last year and it is projected to reach 159 gigawatts by the end of this year.  By comparison, a typical nuclear power plant can produce 1 gigawatt; a gas-powered power plant is typically half a gigawatt.

Rooftop solar constitutes a relatively small fraction of the total global installed solar capacity, which is dominated by utility-scale solar arrays.  Total installed solar capacity rose from 950 gigawatts to 1,177 gigawatts last year and is projected to reach 1,518 gigawatts this year.  That is enough power to meet more than half the electricity demand of the European Union.

The rapid growth of solar power can only continue if there is more energy storage put in place to manage the peaks and troughs in solar output.  Countries will also need to upgrade their power grids to be able to transport excess solar power from where it is generated to where it is needed.   Bottlenecks in the grids of most of the leading solar-producing nations are already interfering with further solar development.

The overall potential for rooftop solar is based on the number of rooftops that would be suitable for solar power, which depends on the size, shading, orientation, and location of the roofs.  According to the National Renewable Energy Laboratory, rooftops in the United States have the potential for more than 1,000 gigawatts of solar capacity. Currently, only about 4% of US homes have rooftop solar. 

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Rooftop Solar Grew Nearly 50 Percent Globally Last Year

Photo, posted November 16, 2022, courtesy of Oliver Knight via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio

Solar Windows | Earth Wise

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Solar windows are an attractive idea.  It is very appealing to have the vertical surfaces on the outside of almost any building generate electricity.  The challenge is to have a transparent window be able to function as an efficient-enough solar panel.

Most conventional solar panels use silicon solar cell technology, which is not based on a transparent material.  Transparent solar cells use dye-sensitized technology, which has been the subject of research for decades but has yet to achieve widespread use.

Researchers at the University of Michigan have recently published work on a new process to manufacture solar windows that can be large (over six feet in each dimension) and efficient at electricity production.

The windows make use of dye-sensitized cells which are connected to lines of metal so small that they are invisible to the naked eye.  The individual cells are fairly small but the connection technology allows the construction of large windows.

The solar window has an efficiency of 7%, meaning 7% of incoming sunlight energy is converted to electricity.  The researchers believe that 10% efficiency should be attainable with their technology.  Conventional solar panels have efficiencies of 15% or more.

However, the goal is not necessarily to compete with silicon solar panels.  The real opportunity is to be able to generate electricity when rooftop solar is not practical or to produce additional electricity even when there is already a solar roof.

Going forward, the goals of solar window development are to increase efficiency and to reduce costs to where installing the windows is economically attractive.  Estimates are that the windows currently would cost about twice as much as a conventional window but would pay for the difference in two to six years depending on such things as the level of sun exposure.

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Inside Clean Energy: What’s Hotter than Solar Panels? Solar Windows.

Photo, posted April 17, 2017, courtesy of Shelby Bell via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Rooftop Solar Taking Off In China | Earth Wise

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The total amount of solar power generating capacity in the world has been growing rapidly.  In 2008, there was a total of only 15 gigawatts installed world-wide.  By 2012, the total was 100 gigawatts.  As of this spring, there is now 1 terawatt – that’s 1,000 gigawatts – of solar power installed in the world.   About a third of that total is in China, and solar power is really booming there.

Estimates are that China will install 108 gigawatts of solar capacity this year, which is about double the amount installed in 2021.  Much of the growth in solar in China is in the form of rooftop solar, as opposed to utility-scale solar farms.

China is aiming to have 50% of new factory rooftops carry solar installations by 2025.   By the end of next year, China’s National Energy Bureau is aiming for solar panels to cover 50% of rooftops on party and government buildings, 40% of schools, hospitals, and other public buildings, 30% of industrial and commercial buildings, and 20% of rural homes.  This new initiative will drive China’s installed solar capacity to impressive levels in the coming years.

After China, the leading installers of solar energy capacity are the European Union, the United States, and Japan. 

These figures are for generating capacity.  What ultimately matters is solar’s share of total electricity consumption.  In China and the EU, solar provides over 6% of the electricity used.  In the US, that figure is about 3.5%.  In Germany and Australia, solar power provides 10% of electricity needs.  All these numbers will continue to go up rapidly as solar installations grow.

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China Sees Rooftop Solar Take Off as New Policies Bolster Growth

Photo, posted June 17, 2022, courtesy of Nguyễn Mỹ Hoa via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

A Solar-Powered Target Store | Earth Wise

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Many companies have made sustainability commitments of various types. Environmental organizations have urged big-box and grocery stores to install solar panels on their rooftops and parking lots thereby reducing their energy usage and expanding the country’s supply of renewable energy.  These places occupy large areas and therefore are capable of supporting large solar arrays.

According to a report by two environmental advocacy groups, rooftop solar panels on retail stores could generate enough electricity to power the equivalent of nearly 8 million U.S. homes.

Target Stores are one of the retailers that has been making an effort to be a greener company.  Target has installed solar panels on about 25% of its approximately 1,900 stores.  The Target store in Vista, California, about 40 miles north of San Diego, is the company’s most sustainable store.  It already had solar panels on its rooftop, powering a portion of the store.

But now it has installed massive carports topped with solar panels high above its parking lot.  With these panels, this Target can now produce enough renewable energy to power the entire store, from its refrigeration to its heating and air conditioning. Adding in some of the other energy-saving features of the store, Target expects to produce 10% more energy than the store needs, which it will return to the local power grid.  This is Target’s first net-zero energy store.

Target is not the only big retailer going solar.   Home Depot, Lowe’s, and Walmart all have been installing solar panels on some of their rooftops.  Even some restaurants are trying to reach sustainability goals with solar panels.  This is a trend that hopefully will continue to grow.

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Target looks to massive solar panels in a California parking lot as a green model to power its stores

Photo, posted June 30, 2014, courtesy of Mike Mozart via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

A Smart Roof | Earth Wise

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Scientists at the Lawrence Berkeley Laboratory have developed an all-season smart roof coating that can keep homes warm during the winter and cool during the summer, and the coating does not consume any gas or electricity.

Existing cool roof systems consist of reflective coatings, membranes, shingles, or tile that lower house temperatures by reflecting sunlight as well as emitting some of the absorbed solar heat away from the roof as infrared radiation.  The problem with such systems is that they continue to radiate heat during the winter, which actually drives up heating costs.

The new material is called a temperature-adaptive radiative coating or TARC.  It enables energy savings by automatically turning off the radiative cooling in the winter.  TARC reflects about 75% of sunlight year-round, but its thermal emittance is high when the temperature is warm – promoting heat loss to the sky – but decreases in cooler weather, helping to retain the heat in a building.

The researchers produced thin-film TARC material that looks like Scotch tape that could be affixed to a surface like a rooftop.  They applied the material to a balcony alongside a sample of commercial dark roof material and a sample of commercial white roof material.

In experiments simulating 15 different climate zones across the US, they found that the TARC material outperforms existing roof coatings for energy savings in 12 out of the 15 zones, particularly in regions with wide temperature variations between day and night, such as in the San Francisco Bay Area, or between winter and summer, such as New York City.

The researchers believe that installing TARC coatings on roofs would save the average U.S. household about 10% in utility costs.

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New Smart-Roof Coating Enables Year-Round Energy Savings

Photo, posted May 18, 2017, courtesy of Damian Gadal via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Solar Power In Australia | Earth Wise

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Historically, the electricity sector in Australia has been dominated by coal-fired power stations.  Even now, coal accounts for about 60% of Australia’s electricity generation.  But since 2005, wind power and rooftop solar have led to a fast-growing share of renewable energy in total electricity generation.

Australia is the second-largest exporter of coal in the world and has proven reserves equivalent to over 1,200 times its annual consumption.  Australia is home to four of the world’s ten biggest coal mines.  But despite this abundant resource, the country is increasing its use of renewable energy.

For just a few minutes on a sunny Sunday afternoon in August, more than half of Australia’s electricity came from solar power.  Low demand and sunny skies resulted in the contribution from coal dropping to a record low of 9,315 MW while solar power provided 9,427 MW.

In 2020, 24% of Australia’s electricity came from renewable energy, up from 21% the year before.  The increase was driven by a boom in solar installation.

Australia is still a long way from meeting its commitments under the Paris Climate Change agreement.  The country ultimately needs 51 GW of new renewable energy generation by 2042 but only 3 GW of new wind and solar projects have been committed to date.

Overall, Australia has promised what has been described as the fastest energy transition in the world.  It is all very ambitious, but Australia has a lot of work to do.

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Solar power in Australia outstrips coal-fired electricity for first time

Photo, posted November 30, 2017, courtesy of D. O’Donnell / European Space Agency via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

30 Million Solar Homes | Earth Wise

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A national coalition made up of more than 230 organizations has launched an initiative called the 30 Million Solar Homes campaign.  The goal is to add enough rooftop and community solar energy to power 30 million homes across the U.S. over the next five years.  That would be the equivalent of one in four American households.

The major focus of the 30 Million Solar Homes initiative is to rapidly and massively scale programs that help low-income families benefit from solar power.  The coalition lists 15 federal policy initiatives including making solar tax incentives more equitable, providing more reliable low-income energy assistance through solar energy, supplementing low-income weatherization assistance with solar energy, and specifically funding solar projects in marginalized communities.

The federal government spends billions of dollars every year to help families to pay their energy costs, but these efforts only serve less than a fifth of the eligible population.  Funding rooftop and community solar access for these households would provide long-term financial relief and reduce the need for annual energy bill assistance.

The more than 230 organizations in the coalition represent organizations focused on energy equity, climate, business, environment, faith, and public health.  The coalition estimates that executing the plan would create three million good-paying jobs, lower energy bills by at least $20 billion a year, and reduce total annual greenhouse gas emissions by 1.5%.

Over the coming months, the campaign will seek to educate lawmakers and the Biden-Harris Administration about the benefits of distributed solar energy.  The vision outlined by the coalition is an ambitious one to say the least.

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30 Million Solar Homes

Supporters of 30MSH

Photo, posted May 20, 2009, courtesy of Solar Trade Association via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

The Largest Renewable Energy Project In The World | Earth Wise

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India has broken ground on what is planned to be the largest renewable energy project in the world:  a 30-gigawatt wind and solar power project in the state of Gujarat.

The renewable energy park will have two zones:  a 122,000-acre hybrid park zone that will accommodate 25 gigawatts of wind and solar power plants and a 57,000-acre zone entirely dedicated to wind power.  Multiple developers will be building the power plants in the hybrid zone.  A single company has been allotted the wind power zone.  The selected developers have to develop 50% of the total generation capacity in the next 3 years and finish the project in five years. The project is expected to create jobs for 100,000 people. Total investment in the project will be about $20 billion.

This is not technically a single standalone project but is rather an aggregation of multiple projects in a single general area.  Nonetheless, it represents the largest renewable energy development ever.  By comparison, the entire United States has a total of 50 gigawatts of installed solar power in large plants – which does not include any rooftop solar.  Total wind power capacity in the U.S. is a little over 100 gigawatts.  So, the 30-gigawatt Indian project is huge by any measure.

India already gets over 30% of its electricity from renewable sources, making it one of the largest renewable energy markets in the world.  The country has a goal of 60% renewable energy by 2030, amounting to 450 gigawatts of capacity.  This will require the country to double its already substantial renewable capacity in less than 10 years.  The Gujarat energy park will represent substantial progress towards that goal.

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Largest Renewable Energy Project In World Will Be 30 Gigawatt Solar–Wind Project In India

Photo, posted October 16, 2019, courtesy of Jonathan Cutrer via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Community Solar With Storage In New York | Earth Wise

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Community solar allows members of a community to share the benefits of solar power even if they cannot or prefer not to install solar panels on their own property.  There are several models for how community solar works, but all of them allow members to benefit from solar power being generated by an offsite solar array by effectively allocating a portion of its output to them.  In any event, community solar can save money on electric bills and allow people to make use of renewable energy for their needs.

A next step in the evolution of a decentralized energy system is incorporating energy storage into community solar projects.  The first one of these in New York State has now been completed in Yorktown Heights in Westchester County.  The project consists of 557kW of rooftop solar in the form of nearly 1,500 solar panels paired with 490kW of four-hour Tesla Powerpack battery energy storage.  The system is expected to provide 150 participants with approximately 10% savings on their monthly electric bills over 25 years, as well as providing power to 12 Tesla electric vehicle charging stations.

The project was funded by NYSERDA, under its Retail Energy Storage Incentive program, which currently includes 50 community solar-storage paired projects across New York State that are expected to be installed in the next two to three years.

New York has been actively promoting community projects in support of goals announced by Governor Andrew Cuomo to install 6,000MW of solar in the state by 2025 and 3,000MW of energy storage by 2030.

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First community solar-storage project completed in New York

Photo, posted June 21, 2017, courtesy of Franck Michel via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

More Solar And Wind Power In The U.S.

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According to the U.S. Energy Information Administration, both wind and solar power are contributing more and more to total electrical generation in the United States.  For the first 8 months of 2019, the combination of wind and solar power accounted for almost 10% of U.S. electrical generation.

Solar, including small-scale PV systems on home rooftops, grew by almost 14% compared to the first eight months of 2018 and accounted for more than 2.7% of total electrical output.  In fact, small-scale solar generation increased by 19% and provided nearly a third of all the solar power in the country. 

Wind energy in the U.S. increased by 4.4%, accounting for almost 7% of the country’s electricity.

Overall, renewable energy sources – which include biomass, geothermal, hydropower, solar, and wind – accounted for 18.49% of net domestic electrical generation during the first 8 months of 2019.  The non-hydro renewable sources actually accounted for over 11% of total electricity production and saw a year-over-year growth of 6%. 

Outside of renewables, nuclear-generated electricity declined by 0.6% and coal power dropped by almost 14%.  Much of the coal generation was replaced by natural gas, which grew by 6.5% compared to the previous year.

Renewables now accounting for nearly 20% of overall electricity generation in the US represents significant progress.  But the variations by state continue to be substantial.  For example, while Vermont gets 99% of its power from renewables, Ohio gets only 2%. 

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Solar and wind energy provide almost 10 percent of total generation in the US in 2019

Photo, posted April 8, 2019, courtesy of City of St. Pete via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Schools And Solar Power

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A new study from Stanford University looked at the benefits of installing solar panels on the rooftops of schools.  According to the study, taking advantage of all the viable space for solar panels could allow schools to meet up to 75% of their electricity needs and reduce the education sector’s carbon footprint by as much as 28%.

Given the long list of spending priorities for schools, solar power seems like a luxury item.  But the Department of Energy estimates that K-12 schools spend more than $6 billion a year on energy and, in many districts, energy costs are second only to salaries.  In the higher education sector, yearly energy costs add up to more than $14 billion.  In total, educational institutions account for approximately 11% of energy consumption by U.S. buildings and 4% of the nation’s carbon emissions.

The Stanford study suggests that investments in the right solar projects combined with the right incentives from states could free up much-needed money in school budgets.

To no surprise, the study finds that three large, sunny states – Texas, California, and Florida – have the greatest potential for generating electricity from solar panels on school rooftops.

Apart from measurable effects on air pollution and electricity bills, solar installations at schools can also provide new learning opportunities for students.  In fact, some schools are already using data from their on-site solar energy systems to teach students basic ideas about fractions, as an example, as well as more sophisticated concepts such how shifting solar panel angles can affect power production.

According to the study, nearly all states could reap value from school solar projects.

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What happens when schools go solar?

Photo, posted February 28, 2011, courtesy of Black Rock Solar via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Transparent Solar Panels

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 It is now commonplace to see solar panels on the rooftops of homes and businesses.  There are more than a million solar homes in the US alone.  But a new generation of see-through solar technology has the potential to also turn the windows of buildings and cars, as well as other glass-coated objects, into electricity generators.

[Read more…] about Transparent Solar Panels

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