The whole world held its breath in awe on Friday watching the Opening Ceremony for the 2016 Olympic Games in Rio de Janeiro. A day later I arrived back in the city that has become my second home while Mayor Eduardo Paes has been C40's chairperson for the last two and a half years. As I sit writing this article while enjoying the extraordinary new space in Porto Maravilha, though many have criticized the city for its Olympic preparations, it's impossible not to be moved by the significance of the first-ever Olympics to be held in South America.
Olympic cities are always criticized while under the world's microscope. Though there are some shortcomings here—mostly in areas that were the responsibility of the state or federal government—it's impossible not to be impressed by the transformation in sustainable transport and public space the mayor has instigated as a direct result of taking on the challenge of hosting the world's single greatest international contest.
The promise of the Olympics has been on the horizon since current C40 Cities Climate Leadership Group (C40) Chair and Rio Mayor Eduardo Paes was elected mayor in 2008. He has worked tirelessly throughout the intervening years not only to produce an event worthy of the global stage, but also to invest in and develop long-term legacy projects that will benefit the city and its inhabitants for years to come. Indeed, Mayor Paes has followed the advice of former Barcelona (also a C40 city) mayor and Olympic host Pasqual Maragall: The Olympics must serve the city, not vice versa.
Mayor Paes speaking at a press conference at Paris City Hall with C40 Mayors in 2015.C40 / Flickr
Mayor Paes has stayed true to that principle: For every one real invested in the Olympics, the city has invested five Reais in sustainable infrastructure and legacy projects. The city's ambitions for the Olympics have always been high and under Mayor Paes' leadership it has made powerful and lasting improvements for the city and its people that will endure far beyond when the last athletes have left town.
- There has been a major expansion of the city's public transit systems, including an incredibly rapid development of bus rapid transit that means the proportion of residents using public transport has risen from under 20 percent to more than 60 percent in just 8 years, a brand new light rail system and more than 450 kilometers of cycle paths (as well as the new subway line, built by the state but for which the mayor has been a major advocate).
- The city has completed a major renovation and revitalization of the Porto Maravilha, the city's historic birthplace. They redesigned the area in terms of mobility to make it more friendly to human-scale transit—removing the brutalist perimetral highway (indeed the first time I met Mayor Paes he apologized for being late with the excuse that he had been blowing up the very same road), adding a light vehicle tram, closing streets to cars, creating facilities for pedestrians and building the arrestingly beautiful Museum of Tomorrow.
- Mayor Paes inaugurated the Rio Operations Center, a digital nerve center of the city in which critical services—from waste management to emergency response and traffic control—are monitored to improve the city's efficiency and emergency response. It is a model that has captured the attention of other cities across the world.
- Though the failure to clean up the Guanabara Bay—which has been a contentious location in the lead-up to the games—falls outside the jurisdiction of the Mayor, the city has invested in a new West Zone Wastewater Treatment Plant that will benefit 430,000 people and treat 65 million liters of sewage that would otherwise be dumped in the bay. This is another fulfilled Olympic commitment and it brings better quality of life for thousands of people.
- More than 70 percent of Olympic facilities were built by converting existing structures and some Olympic venues, like the Handball Stadium, are designed to be converted into community projects, like public schools, after the games.
Hosting an Olympics Games is no mean feat for any mayor, but it is particularly challenging when taking into consideration the political and economic turmoil Brazil has been facing over the past 12 months. Rather than criticizing what has not been done in Rio (and there are still many areas that require improvement and investment), those who care about sustainability should be praising Mayor Paes for delivering an impressive raft of infrastructure improvements, while the rest of the country has been at a virtual standstill.
Moreover, in addition to his job as mayor, Mayor Paes has also been the energetic chair of C40 since December 2013 and has been instrumental to engaging more than 20 new member cities from China, India, the Philippines, Africa and the Middle East, such that we now have a majority of members from the global south.
Under his leadership, Mayor Paes and C40 joined partners in launching the Compact of Mayors, creating a new global standard for urban emissions reporting and creating a program of effective "city determined commitments" to mirror the INDCs being pledged by nation states. Mayor Paes led from the front and Rio became the first city to be compliant with the Compact of Mayors. Rio was also the first Brazilian city to complete a study of its climate vulnerabilities and has mandated emissions cuts of 20 percent by 2020.
It has also been through Mayor Paes' personal leadership that we have created the C40 Finance Facility, to address the the startling omission of most of the world's green funds to finance city government's low carbon projects. Starting from initial generous support from the German government, Mayor Paes aims for the facility to unlock up to $1 billion worth of sustainable infrastructure in cities across low and middle-income countries by 2020.
In part because of Mayor Paes' leadership, Latin America is a focal point for city climate action this year: C40 is looking forward to hosting our flagship event, the C40 Mayors Summit in Mexico City at the end of November. Mexico City Mayor Mancera and Mayor Paes will host this gathering where mayors, urban experts, business people and celebrities from around the world will come together to continue positioning cities as a leading force for climate action around the world.
It is with extreme gratitude that we at C40 thank Mayor Paes for his leadership and passion. And is with great excitement that today in Rio we announced the new C40 chair: Paris Mayor Anne Hidalgo.
From left to right: Eduardo Paes, Mayor of Rio de Janeiro and Chair of C40 Cities Climate Leadership Group and Anne Hidalgo, Mayor of Paris.C40 / Flickr
The C40 Steering Committee voted unanimously to elect Mayor Hidalgo, who has maintained a steadfast commitment to urban sustainability throughout her tenure thus far, emphasizing walkability in Paris, spearheading calls to better air quality across Europe and hosting the Climate Summit for Local Leaders alongside the COP21 climate negotiations in Paris last December. She will be an inspiring champion for city voices around the world, leading by example as the C40 chair-elect. She will take over from Mayor Paes after the C40 Mayors Summit in Mexico City later this year.
It is no coincidence, too, that Paris is currently bidding to host the 2024 Olympics, more than half of the cities that have hosted the Olympics are also C40 member cities. And, given that the International Olympic Committee has outlined a commitment to a sustainable future, it's no surprise that C40's member cities—which represent the most powerful and innovative cities in the world—are not only great places to live, work and prosper, but are also make supremely competent Olympic hosts.
Mayor Paes has been an exceptional leader for the last several years and Rio has set an example for other cities around the world seeking a clean development pathway. We look forward to Mayor Hidalgo carrying that charge forward for the critical years to come.
Making the switch to solar energy can help you lower or even eliminate your monthly electric bills while reducing your carbon footprint. However, before installing a clean energy system in your home, you must first answer an important question: "How many solar panels do I need?"
To accurately calculate the ideal number of solar panels for your home, you'll need a professional assessment. However, you can estimate the size and cost of the system based on your electricity bills, energy needs and available roof space. This article will tell you how.
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Factors That Influence How Many Solar Panels You Need
To determine how many solar panels are needed to power a house, several factors must be considered. For example, if there are two identical homes powered by solar energy in California and New York, with exactly the same energy usage, the California home will need fewer solar panels because the state gets more sunshine.
The following are some of the most important factors to consider when figuring out many solar panels you need:
Size of Your Home and Available Roof Space
Larger homes tend to consume more electricity, and they generally need more solar panels. However, they also have the extra roof space necessary for larger solar panel installations. There may be exceptions to this rule — for example, a 2,000-square-foot home with new Energy Star appliances may consume less power than a 1,200-square-foot home with older, less-efficient devices.
When it comes to installation, solar panels can be placed on many types of surfaces. However, your roof conditions may limit the number of solar panels your home can handle.
For example, if you have a chimney, rooftop air conditioning unit or skylight, you'll have to place panels around these fixtures. Similarly, roof areas that are covered by shadows are not suitable for panels. Also, most top solar companies will not work on asbestos roofs due to the potential health risks for installers.
Amount of Direct Sunlight in Your Area
Where there is more sunlight available, there is more energy that can be converted into electricity. The yearly output of each solar panel is higher in states like Arizona or New Mexico, which get a larger amount of sunlight than less sunny regions like New England.
The World Bank has created solar radiation maps for over 200 countries and regions, including the U.S. The map below can give you an idea of the sunshine available in your location. Keep in mind that homes in sunnier regions will generally need fewer solar panels.
© 2020 The World Bank, Source: Global Solar Atlas 2.0, Solar resource data: Solargis.
Number of Residents and Amount of Energy You Use
Households with more members normally use a higher amount of electricity, and this also means they need more solar panels to increase energy production.
Electricity usage is a very important factor, as it determines how much power must be generated by your solar panel system. If your home uses 12,000 kilowatt-hours (kWh) per year and you want to go 100% solar, your system must be capable of generating that amount of power.
Type of Solar Panel and Efficiency Rating
High-efficiency panels can deliver more watts per square foot, which means you need to purchase fewer of them to reach your electricity generation target. There are three main types of solar panels: monocrystalline, polycrystalline and thin-film. In general, monocrystalline panels are the most efficient solar panels, followed closely by polycrystalline panels. Thin-film panels are the least efficient.
How to Estimate the Number of Solar Panels You Need
So, based on these factors, how many solar panels power a home? To roughly determine how many solar panels you need without a professional assessment, you'll need to figure out two basic things: how much energy you use and how much energy your panels will produce.
According to the latest data from the U.S. Energy Information Administration (EIA), the average American home uses 10,649 kWh of energy per year. However, this varies depending on the state. For example:
- Louisiana homes have the highest average consumption, at 14,787 kWh per year.
- Hawaii homes have the lowest average consumption, at 6,298 kWh per year.
To more closely estimate how much energy you use annually, add up the kWh reported on your last 12 power bills. These numbers will fluctuate based on factors like the size of your home, the number of residents, your electricity consumption habits and the energy efficiency rating of your home devices.
Solar Panel Specific Yield
After you determine how many kWh of electricity your home uses annually, you'll want to figure out how many kWh are produced by each of your solar panels during a year. This will depend on the specific type of solar panel, roof conditions and local peak sunlight hours.
In the solar power industry, a common metric used to estimate system capacity is "specific yield" or "specific production." This can be defined as the annual kWh of energy produced for each kilowatt of solar capacity installed. Specific yield has much to do with the amount of sunlight available in your location.
You can get a better idea of the specific yield that can be achieved in your location by checking reliable sources like the World Bank solar maps or the solar radiation database from the National Renewable Energy Laboratory.
To estimate how many kW are needed to run a house, you can divide your annual kWh consumption by the specific yield per kilowatt of solar capacity. For example, if your home needs 15,000 kWh of energy per year, and solar panels have a specific yield of 1,500 kW/kW in your location, you will need a system size of around 10 kilowatts.
Paradise Energy Solutions has also come up with a general formula to roughly ballpark the solar panel system size you need. You can simply divide your annual kWh by 1,200 and you will get the kilowatts of solar capacity needed. So, if the energy consumption reported on your last 12 power bills adds up to 24,000 kWh, you'll need a 20 kW system (24,000 / 1,200 = 20).
So, How Many Solar Panels Do I Need?
Once you know the system size you need, you can check your panel wattage to figure how many panels to purchase for your solar array. Multiply your system size by 1,000 to obtain watts, then divide this by the individual wattage of each solar panel.
Most of the best solar panels on the market have an output of around 330W to 360W each. The output of less efficient panels can be as low as 250W.
So, if you need a 10-kW solar installation and you're buying solar panels that have an output of 340W, you'll need 30 panels. Your formula will look like this: 10,000W / 340W = 29.4 panels.
If you use lower-efficiency 250-watt solar panels, you'll need 40 of them (10,000W / 250W = 40) panels.
Keep in mind that, although the cost of solar panels is lower if you choose a lower-efficiency model over a pricier high-efficiency one, the total amount you pay for your solar energy system may come out to be the same or higher because you'll have to buy more panels.
How Much Roof Space Do You Need for a Home Solar System?
After you estimate how many solar panels power a house, the next step is calculating the roof area needed for their installation. The exact dimensions may change slightly depending on the manufacturer, but a typical solar panel for residential use measures 65 inches by 39 inches, or 17.6 square feet. You will need 528 square feet of roof space to install 30 panels, and 704 square feet to install 40.
In addition to having the required space for solar panels, you'll also need a roof structure that supports their weight. A home solar panel weighs around 20 kilograms (44 pounds), which means that 30 of them will add around 600 kilograms (1,323 pounds) to your roof.
You will notice that some solar panels are described as residential, while others are described as commercial. Residential panels have 60 individual solar cells, while commercial panels have 72 cells, but both types will work in any building. Here are a few key differences:
- Commercial solar panels produce around 20% more energy, thanks to their extra cells.
- Commercial panels are also more expensive, as well as 20% larger and heavier.
- Residential 60-cell solar panels are easier to handle in home installations, which saves on labor, and their smaller size helps when roof dimensions are limited.
Some of the latest solar panel designs have half-cells with a higher efficiency, which means they have 120 cells instead of 60 (or 144 instead of 72). However, this doesn't change the dimensions of the panels.
Conclusion: Are Solar Panels Worth it for Your Home?
Solar panels produce no carbon emissions while operating. However, the EIA estimates fossil fuels still produce around 60% of the electricity delivered by U.S. power grids.
Although the initial investment in solar panels is steep, renewable energy systems make sense financially for many homeowners. According to the Department of Energy, they have a typical payback period of about 10 years, while their rated service life is up to 30 years. After recovering your initial investment, you will have a source of clean and free electricity for about two decades.
Plus, even if you have a large home or find you need more solar panels than you initially thought you would, keep in mind that there are both federal and local tax credits, rebates and other incentives to help you save on your solar power system.
To get a free, no-obligation quote and see how much a solar panel system would cost for your home, fill out the 30-second form below.
7,100 Cities From 119 Countries Join Together in Historic Collaboration to Accelerate Climate Action
When UN Secretary-General Special Envoy for Cities and Climate Change Michael R. Bloomberg suggested creating a Compact of Mayors to mirror the UN program for national commitments on climate change, it was not possible to guess how central the idea would become to putting mayors at the heart of global climate action. But it turned out to be a game changer.
Just five months on from the "Abu Dhabi Ascent" conference where we first discussed the idea, in September 2014 at the UN Secretary General's Climate Summit in New York City, three global city networks, C40, ICLEI and UCLG joined forces to help activate the compact. We hoped to better quantify the collective magnitude and potential for cities and towns to deliver emissions reductions. Working quickly, decisively and collaboratively under the compact, the networks helped to inspire ambitious commitments from more than 500 cities of all sizes around the globe; just as nation states registered commitments to emissions reductions in the lead up to the COP21 climate summit.
The effort demonstrated the unprecedented scope and degree to which local governments were already engaged in meaningful, collaborative climate action and, importantly, gave a voice for them at a high level in the UN, through the leadership of Special Envoy Bloomberg and engagement of the Local Government and Municipal Authorities (LGMA) constituency. As a result, cities were crucial in shaping and advocating for a strong Paris agreement on climate change—and city leaders will be crucial in delivering on its ambition going forward.
Now cities are making another great and historic stride: bringing together the Compact of Mayors and the EU Covenant of Mayors to form a new Global Covenant of Mayors for Climate & Energy, announced Wednesday in Brussels. This new initiative will be even more important for its ability to unify existing commitments at all levels, including thousands of European towns and villages and hundreds of major global metropolises—altogether more than 7,100 cities from 119 countries and six continents and representing more than 600 million residents, more than 8 percent of the world's population.
To give a sense of the magnitude of the impact these cities can have: as of December 2015, cities and towns signed on to the Compact of Mayors had already made commitments that could deliver half of the global urban potential greenhouse gas (GHG) emissions reductions available by 2020. At the same time, actions by EU Covenant of Mayors signatories accounted for 15 percent of the EU-28 CO2 emissions reduction 2020 target. Under one unified banner, these city climate leaders will demonstrate the vast power of cities to effect global change.
Aligning efforts will allow for greater collaboration between cities across the world to tackle the biggest challenge humanity has ever faced, bridging gaps and building connections, as well as increasing funding to support and empower cities to do more. The merger will harness the convening power and investment of the European Union and the UN Secretary General Special Envoy for Cities and Climate Change, generously supported by Bloomberg Philanthropies—critical ingredients to unlocking the potential of cities to take action. We hope many other donors will follow suit to support local climate action that can be scaled up, with support of the city networks. Moreover, a merged initiative will ensure more consistent and comparable data—giving investors the ability to see that the actions cities have been taking are having lasting and verifiable impact.
As city networks, we have long been committed to the principle that working together helps cities go farther, faster. We therefore welcome the Global Covenant of Mayors for Climate and Energy. We look forward to engaging new partners and a broader coalition of city leaders committed to taking concrete, measurable and transparent action on climate change. United, we can lead the drive to peak global emissions by 2020 and enhance climate change adaptation and resilience in our communities.
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C40 released a report Monday that provides a roadmap for specific climate action that cities should take in 2016 and beyond. C40 and partner Arup released the report, Potential for Climate Action, at an event at Le Bourget alongside the COP21 climate negotiations.
This report is significant because it both analyzes the most important specifications that major cities can take to cut carbon emissions and it identifies the barriers that need to be removed if mayors are to achieve them. The member cities of the C40 represent a combined population of more than 600 million people and a quarter of world economic output. What happens in these cities will significantly dictate whether or not the world can tackle climate change.
The key findings are that, while C40 cities have already taken 10,000 climate actions between Copenhagen COP15 in 2009 and Paris COP21 in 2015, the potential for further delivery is much greater—a pool of 27,000 actions. The report analyzes each of these potential actions against three factors, the opportunity learn from their peers (ie has another city already done it), having mayoral power to deliver and scale of potential GHG reduction impact. This allows us to identify 2,300 priority actions which, if fully implemented, will cut GHG emissions by 450Mt CO2 in the next few years and will cost $6.8 billion to catalyze. This is a relatively modest sum, but this analysis shows that access to funding is the single biggest obstacle to cities delivering greater climate action.
Thanks to our speakers & panelists @MayorOfTshwane @ArronWood @mpencharz @paula_kirk #RoadFromParis #COP21 https://t.co/VXt4XhrdzX— C40 Cities (@C40 Cities)1449579541.0
The report finds that fully three-quarters of the barriers to taking these potential actions require city leaders to partner with other actors—chiefly national/regional governments or private companies. It provides further evidence that a collaborative approach is essential to tackling climate change—the essence of C40's work. Finally, it will serve as a building block from which we can engage many other partners in this endeavor. Published against the backdrop of the crucial COP21 talks, it provides a positive reminder of the significant potential for climate action in addition to that which the Paris agreement will, hopefully, unlock.
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Come December, all eyes will be on Paris for the COP21 climate negotiations, which will determine our post-2020 climate future. But what about the next five years?
New research released today from my organization—C40 Cities Climate Leadership Group (C40)—and Stockholm Environment Institute (SEI) shows that cities hold the key to ensuring we don't exceed the world's remaining safe carbon budget: in fact, urban policy decisions before 2020 could determine a third of the remaining global carbon budget that is not already "locked-in" by past decisions.
This is cause for great hope. Instead of leaving our global future to be determined by intricate international policy negotiations, we now know that mayors and local leaders in office today have the opportunity—and the responsibility—to help determine whether or not we have a realistic path to a climate safe world.
And these decisions have positive economic implications as well: previous research has shown that investing in low carbon infrastructure in the next five years will be four times less expensive than making the wrong decision now and having to replace carbon-intensive infrastructure in the future.
The report calculates that if cities around the world pursue low carbon urban development over a business as usual scenario, we could save 45 Gt CO2 by 2030, or roughly eight times the current annual emissions of the United States.
For context, scientists have previously calculated that we can emit a "carbon budget" of just 1,000 Gt CO2 without creating an unacceptable risk of run-away climate change, and that much of this budget may be locked-in by infrastructure investments that have already been made.
Previous research also suggests that decisions about the remaining infrastructure will happen by 2020. Fortunately, our new analysis shows that a third of the decisions will be made in cities, many of which are already demonstrating leadership on climate change.
More than half of C40's 80 member cities, for instance, have committed to the Compact of Mayors, a global platform where cities publish their current emissions inventories and commit targets and action plans to cut future emissions. Hundreds more cities around the world—representing nearly 300 million people—are following suit and making ambitious commitments.
Even though cities are taking decisive action to combat climate change, this report highlights the need for national governments to support climate action at a local level, such as the Our Cities, Our Climate international exchange program in the United States, a joint effort between the U.S. Department of State and C40 partner Bloomberg Philanthropies.
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