A team of researchers from WWF, McGill University, and other institutions studied about 7.5 million miles of rivers worldwide to determine whether they're well connected. They found that only 37 percent are free-flowing — meaning they're largely unaffected by human-made changes to its flow and connectivity. Dams built in the wrong place and climate change are impacting river health worldwide, and the planet's remaining free-flowing rivers are largely restricted to remote regions of the Arctic, the Amazon Basin and the Congo Basin.
Vanishing Free-Flowing Rivers
Long free-flowing rivers are vanishing. Around the world, rivers are becoming increasingly fragmented by dams and other development — such as roads or dikes — endangering freshwater ecosystems and the people and wildlife that rely on them. Free-flowing rivers transport water, nutrients and species that sustain biodiversity and benefit millions of people. To help countries and communities better protect their freshwater resources, WWF and partners came up with a technical definition of a free-flowing river and then created a first-of-its-kind, scientifically backed map — a comprehensive inventory of the world's last free-flowing rivers, rivers with good connectivity and impacted rivers.
1. Mura River — Slovenia
Called the "Amazon of Europe," the Mura River provides critical habitat for endangered and rare species such as otters, Danube salmon and black stork. After urging from WWF and others, in February 2019, the Slovenian government signed an agreement to stop all hydropower plant development that would devastate the Mura.
2. Usumacinta River — Mexico
In June 2018, guided by WWF and partners, Mexico established water reserves across nearly 300 river basins, guaranteeing water supplies for 45 million people for the next 50 years. Ninety-three percent of the water in the Usumacinta — the longest, most biodiverse river in Central America and one of Mexico's — is now federally protected.
3. Bita River - Colombia
The Colombian government named the Bita River basin a Ramsar site — a wetland of international importance — in June 2018, thanks in large part to the work of WWF and partners. Covering 825,000 hectares, it's the largest of the country's 11 Ramsar sites and one of the few in the world to encompass an entire free-flowing river watershed.
4. Paraguay Basin — Brazil
More than 100 dams planned for the Upper Paraguay Basin could hurt water supplies, biodiversity and local communities. After tremendous efforts from a coalition including WWF, Brazil's National Water Agency suspended new dam development there until May 2020. But the suspension only applies to rivers under federal jurisdiction — so just 20 of the 100 dams will be suspended.
5. Luangwa River — Zambia
The Luangwa, which is free but impacted by a dam on a nearby river, is at risk. A proposed dam at Ndevu Gorge threatens this wild waterway, which shelters abundant wildlife and human populations. In Zambia, WWF is advocating on behalf of people and nature, pushing the government to reconsider its energy plans and ensuring that local people maintain their rights to natural resources.
6. Irrawaddy and Salween Rivers — Myanmar
In Myanmar, an in-depth Strategic Environmental Assessment recommended that the main stems of the Irrawaddy and Salween rivers — two of the last long free-flowing rivers in southeast Asia — should remain free of dams. But there is still risk, making alternative energy such as solar and wind power even more important for people, rivers, and the country's economy.
Learn more about free-flowing rivers and WWF's efforts to protect them.
Mapping Downs
Dams provide safe drinking water and electricity to millions of people. But when built in the wrong place — for instance, a river's main stem — they can impede a river's flow, causing drastic declines in biodiversity and affecting fish migration, agriculture and livelihoods. Today there are more than 60,000 major dams around the world — a number that's increasing to meet demand for hydropower. WWF is helping national governments, industries and developers consider both the long-term impacts on local people and habitats and other potential alternative options for meeting water and energy supply needs, as well as helping them identify the best opportunities for river restoration projects. Solar and wind prices are going down, making them attractive alternatives.
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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.
We can learn a lot about the health of freshwater habitats overall by studying the animals that live in them. If freshwater animals are on the decline, that's a sign that the entire ecosystem is in trouble. Freshwater habitats face a host of threats, including increases in the amount of water we take from them; drainage of wetlands; pollution from industry, sewage and farms; invasive plant and animal species; climate change; and infrastructure development in and along waterways.
Perhaps the most urgent threat to freshwater animals and their homes is the dams, bridges, roads and other infrastructure that interfere with the natural flow and connectivity of rivers. Many freshwater fish, for example, rely on free-flowing rivers to eat, reproduce and access nutrients necessary for their survival.
Connected rivers help people, too. Free-flowing rivers move sediment to floodplains and deltas downstream, providing nutrients and soil for floodplain agriculture, allowing for healthy fisheries and supporting the resilience of delta habitats under a changing climate.
Keeping Rivers Connected and Flowing
There are currently nearly 60,000 large dams on rivers around the world and more than 3,700 more hydro dams—structures that give us energy from the flow of water—are planned globally. While hydropower plays an important role in today's renewable energy revolution, it must be carefully planned so as to minimize loss of river health.
This means considering the health of an entire river basin to find energy opportunities with the least amount of impact on the environment and people. Into the future, the dropping prices of wind and solar power, along with innovations in the ability to store power, provide the possibility for countries to meet energy demands with less hydropower and therefore fewer dams.
We can also set aside a certain amount of water in a river basin exclusively for the protection of nature and for people. Called a "water reserve," this concept requires a careful calculation of how much water people can use for energy, agriculture and other purposes and how much must remain in the river to sustain a healthy ecosystem.
This summer, Mexico authorized water reserves in nearly 300 river basins, including in one of the country's longest remaining free-flowing rivers, the Usumacinta. WWF worked with Mexico's National Water Commission to calculate how much water could be allocated to human activity and how much water should remain in the river to sustain a healthy ecosystem. This science-based planning and policies backing it up ensure water quality and quantity for 45 million Mexicans for the next 50 years—all while protecting the river's plants and wildlife.
You Can Help
The decline in groups of freshwater animals is staggering, but we can help reverse the trend. Join WWF's Freshwater Force to take action to stop bad dams and infrastructure development in freshwater habitats, raise awareness of the importance of freshwater, and champion the wildlife and communities that depend on free-flowing, clean rivers for survival.
Earth Hour 2018: Globe Unites to Celebrate People’s Connection to Planet https://t.co/B66o5zcVjS @GreenpeaceUK @wwwfoecouk— EcoWatch (@EcoWatch)1522149013.0
The historic decision came this week during a World Heritage Committee meeting in Bahrain, just five months after the Belizean government imposed a moratorium on oil exploration and drilling in all of Belize's offshore waters—a landmark piece of legislation that protected critical ecosystems and established the country as a new world leader in ocean conservation.
"At time when we are seeing numerous threats to World Heritage sites, Belize's government has taken real action to protect one of the world's most special places," said Marco Lambertini, director general of WWF International. "We have seen an incredible turnaround from when the reef was being threatened by seismic testing for oil just eighteen months ago."
Comprised of seven protected areas, Belize's Barrier Reef System is the second-largest reef system in the world and is home to nearly 1,400 species, from endangered hawksbill turtles to West Indian manatees, sting rays, coral and six threatened species of sharks.
Nearly 200,000 people—more than half Belize's population—rely on the reef to live. Reef-based tourism and recreational activities provide vital sources of income and account for an estimated $200 million of Belize's GDP, while commercial fishing contributes about $15 million. The reef also provides important natural protection against damages from extreme storms along the coast.
The Belize Barrier Reef System was first inscribed as a UNESCO World Heritage site in 1996 in recognition of the site's incredible biodiversity and cultural significance. But in the last decade, exploration for oil, development along the coast, and a lack of strong regulations have posed increasing threats to the fragile ecosystem. The reef site was added to UNESCO's List of World Heritage in Danger in 2009 due to the threat of irreversible damage from harmful coastal construction and oil exploration.
Last year, more than 450,000 people from around the world joined WWF and other organizations—including Oceana, the Belize Tourism Association, Belize Audubon Society and Belize Institute for Environmental Law and Policy—to campaign against proposed oil exploration near the World Heritage site. They signed petitions, wrote letters, and used social media to urge the country's government to secure the long-term protection of the barrier reef.
Antonio Busiello / WWF-US
Their hard work payed off.
In December 2017, Belize agreed to put an end to oil exploration in its waters and began to secure the region against immediate threats—a critical step towards protecting the reef, its species and the people who rely on it. Belize is now just one of three countries in the world with such legislation.
"Belizeans stood up to protect their reef, with hundreds of thousands more globally joining the campaign to save our shared heritage. In taking swift collaborative action, Belize has shown that it is possible to reverse nature loss and create a sustainable future," added Lambertini.
Belize also recently adopted critical regulations to protect the country's mangroves and announced that it would begin to phase out single-use plastics like plastic bags, utensils, and take-out containers that threaten species and delicate ecosystems.
But there's still more work to be done to ensure that Belize's barrier reef and the rest of the World Heritage sites—and the 11 million people they support worldwide—continue to be protected for future generations.
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"Once again, the people have spoken through Earth Hour," said Marco Lambertini, director general of WWF International. "The record participation in this year's Earth Hour, from skylines to timelines, is a powerful reminder that people want to connect to Earth. People are demanding commitment now on halting climate change and the loss of nature. The stakes are high and we need urgent action to protect the health of the planet for a safe future for us and all life on Earth."
From Colombia to Indonesia to Fiji, Earth Hour 2018 mobilized people to join efforts to protect forests and mangroves. In Romania, hundreds of people showed their commitment to safeguarding nature by writing symbolic letters to rivers, forests and wildlife. In Africa, 24 countries celebrated Earth Hour to highlight the most pressing conservation challenges they face such as access to renewable energy, freshwater resources and habitat degradation.
Earth Hour 2018 celebrations in ScotlandWWF
This Earth Hour, for the first time, people across the globe also joined the conversation on connect2earth to share what nature means to them, in the places they live in and care about. The platform, created in partnership with the Secretariat of the United Nations Convention of Biological Diversity and supported by Germany's Federal Ministry of the Environment, Nature Conservation, Building and Nuclear Safety with funding from the International Climate Initiative, aims to build mass awareness on the values of biodiversity and nature to our lives, health and well-being.
"The science is clear: the loss of nature is a global crisis. Wildlife has declined by close to 60 percent in just over 40 years. Our planet is at a crossroads and we cannot have a prosperous future on a depleted, degraded planet. Together as a global community we can turn things around. People must mobilize and join governments and companies toward stronger action on biodiversity and nature—the time to act is now," added Lambertini.
The impacts of accelerating biodiversity loss and climate change on the planet are profound, as are the consequences for humanity. As French President Emmanuel Macron stated in a special message for Earth Hour, "The time for denial is long past, we are losing our battle against climate change and the collapse of biodiversity. If this trend continues, our planet's ecosystems will collapse, along with the clean air, water, food and stable climate that they provide."
To drive further global awareness and action on nature and the environment, WWF has also joined forces with the World Organization of the Scout Movement this Earth Hour. The energy and voices of 50 million scouts worldwide send a resounding message to decision-makers worldwide that the time to act on nature, for nature is now.
WWF and Earth Hour teams around the world will continue to empower individuals, communities, businesses and governments to be a part of environmental action. In his video statement for Earth Hour, UN Secretary-General António Guterres reiterated the need for people to work together to build a sustainable future for all. Strengthened by the support shown, teams will renew the charge to tackle issues such as sustainable lifestyles, deforestation, plastic pollution and ocean conservation across continents.
Earth Hour 2018 celebrations in RussiaWWF
Earth Hour 2018: Facts and figures (based on initial estimates on March 25, 2018):
- 188 countries and territories focused on environmental action and issues such as protecting biodiversity, sustainable lifestyles, deforestation, plastics and stronger climate policy;
- Lights out at around 17,900 landmarks including the Sydney Opera House (Sydney), Big Ben and the Houses of Parliament (London), the Tokyo Sky Tree (Tokyo), the Empire State Building (New York), the Pyramids of Egypt (Cairo), Sheikh Zayed Grand Mosque (Abu Dhabi), Christ the Redeemer statue (Rio de Janeiro) and the Eiffel Tower (Paris);
- 3.5 billion + impressions of official campaign hashtags between January and March 2018. Related hashtags also trended in 33 countries;
- Around 250 celebrities and influencers worldwide also raised their voice for the planet including Andy Murray, Jared Leto, Ellie Goulding, The Killers, Amitabh Bachchan, Li Bingbing, Park Seo-joon, Claudia Bahamon and Roger Milla;
- Earth Hour partners include Zinkia Entertainment Ltd, creators of popular cartoon character Pocoyo, and crowdsourcing platform Userfarm.
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