Across the country, how we produce energy is in a huge transition period: with the on-line of renewable energy such as wind and solar energy, coal-fired power plants are being decommissioned. This is happening in Indiana. 

Last week we wrote about a huge solar farm-which will be the largest in the country-coming to northwest Indiana. It will cover 13,000 acres and will have more than 2.5 million panels and power nearly 250,000 homes. 

This may not be surprising, but this story has aroused great interest and many questions from our readers. This is no wonder-solar energy can be tricky. Not all solar energy is the same, and this fact makes the situation even more complicated. Compared to utility-scale solar or things like the Mammoth Solar Project, there is a significant difference between rooftop solar (panels on top of houses). 

Mammoth Solar: Indiana will have the country’s largest solar power plant, covering 13,000 acres

Although it is the same general technology, how it is deployed is "very important" to how the energy is used and who owns and benefits from it. Zakshak of Solar Union Neighbors said that Solar Union Neighbors is a company that helps Indians obtain rooftop solar energy. organization. 

Schalk explained that, more specifically, rooftop solar is usually used on site or behind meters, and unused power on site is directly shared with neighbors on the distribution network. This is different from utility-scale projects that are centrally controlled and plugged directly into the transmission grid.

However, Schalke said: "If we want to decarbonize our energy system as soon as possible, we will need rooftop solar and utility-scale solar."

At IndyStar, we will try to answer some of the most important questions, keeping in mind where the difference between rooftop solar and utility solar applies-so please keep reading. 

In the most basic sense, solar energy is the act of collecting sunlight to generate electricity, and then we can use it to power our homes and businesses. Nick Cohen, president and co-founder of Doral Renewables LLC, the company behind the Mammoth Solar Project, described it as "a one-step process of converting free sunlight into electricity."

Solar panels are composed of so-called photovoltaic cells or PV cells. These batteries are made of silicon. The individual cells are connected together to form a solar panel, usually about 3 feet by 5 feet, and coated with tempered glass to help withstand severe weather. 

Cohen explained that when sunlight hits the panel, the sunlight excites electrons in silicon technology. Those excited electrons generate direct current, which is transmitted from the panel through wires. According to Schalk, in the roof system, the electricity goes into the so-called inverter, which converts it into alternating current that can be used in our homes. 

This largely depends on different factors, such as the amount of electricity the house uses, whether there is good sunlight, and the type of solar panels used. On average, the power of residential solar panels is between 300 and 400 watts. Schalk said it is better to consider the overall size of the system rather than the number of panels. 

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The power of a typical residential solar installation is between 7,000 and 8,000 watts, which Schalke says is enough to meet all the electricity needs of many households. This means that an average home needs about 20 panels to power it. However, for larger households with higher usage rates, the system size can be much larger. 

For Schalke, the answer to rooftop solar is simple: "Of course! Once your solar panels are turned on and generate electricity, you will immediately save on electricity bills." 

He said that how much money is saved over time depends on everyone's situation-how much energy you use and how much your panels are produced-"but there is no doubt that" people's bills will go down, he said. Nevertheless, as long as the homeowner stays connected to the grid, there will be a monthly fixed cost on their bill, even if their panel covers all their electricity consumption. 

Although people save money every month, it takes time to break even after the initial initial investment. Schalk said the monthly bill savings plus federal investment tax credits usually allow many solar owners in Indiana to recover the upfront cost of installing the system in about 10 to 12 years. Since the panels are expected to generate electricity for at least 25 years, the monthly savings will continue. 

Cohen said that besides rooftop solar, utility-scale solar is the cheapest energy source, which helps make the energy prices for any utility company buy or produce electricity more affordable. Cohen said that taxpayers can study their utilities to see how much of their electricity comes from renewable energy, which is expected to come from solar or wind energy. Based on these forecasts, Cohen stated that he will use their renewable energy and hope to achieve savings in this way. 

Cohen said that utility-scale solar farms are a low-risk investor opportunity-the product is predictable and low-risk. Through employment, taxation and payment, this is also beneficial to landowners and their communities, which can really promote the development of a region. 

Before the project can begin construction, it must sign a long-term sales contract with an investment-grade electricity buyer—usually called a power purchase agreement. This ensures that the power will be used and paid. Cohen said that construction costs are also locked in by investment-grade suppliers, which helps to reduce costs as much as possible. 

Although some subsidies are sometimes available for these projects, companies and private investors often bear the upfront costs, and they are confident that they can get a return by selling the energy they produce. 

"Investors are looking for predictable returns," Cohen said, which is consistent with the returns they get through typical low-risk utility investments. 

Schalk said this issue is important to distinguish between rooftop solar and utility-scale solar. 

Cohen said that for the scale of the utility, the main advantage is that it is usually the cheapest source of electricity on the market today. This is because with the advancement of technology, the cost of solar panels has dropped rapidly, and once solar panels are installed, the sun is free. It also has the benefit of generating reliable electricity without any carbon emissions. 

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Rooftop solar has the same advantages: it generates clean electricity and reduces carbon emissions that help combat climate change. However, one of its main benefits is that rooftop solar allows solar owners to control their power source, Schalke said. This means that they can directly reduce electricity bills and improve grid efficiency by generating electricity close to the actual location of use. 

Nick Cohen added another aspect: "It's simple and easy to maintain." 

Schalke said this is a difficult question to answer, "There is no need to ask another question: Compared to what?"

Schalk said that one of the main disadvantages of solar energy is that it is essentially related to the cycle of the sun, and its exact output depends on factors such as weather and cloud cover. Without the larger and more advanced battery storage options being developed, it is impossible to generate electricity at night. This means that solar energy “cannot be an independent source,” Cohen said, and some supplementary power generation is needed—usually from fossil fuels. 

Cohen added that solar energy, especially on a utility scale, also requires a larger footprint to produce the same amount of electricity output as some other sources (such as traditional fossil fuel power plants). Sometimes it may be difficult to find that much total space to build a solar farm, or find an area where the grid is strong enough to handle new energy. 

However, Schalke said he believes these are differences from traditional energy sources, not shortcomings. 

"Solar energy is different from our traditional energy sources," he said, "but I think these differences are an opportunity to shape our energy system into a clean, just and fair opportunity." 

When some people think of solar energy, they think of toxic materials and leaks. But modern panels are harmless, Cohen said. The same is true for batteries that help store solar energy, so they can be used at night or in bad weather. Cohen said that most of these batteries are lithium-based, like those used in smartphones, and have no history of leaks. 

For utilities and rooftop solar, some people also don't want to look at the panels-they think they are an eye-catcher. But many times, panels can be hidden in setbacks, landscapes or different films to make them less noticeable. 

Schalk said that another major problem with rooftop solar is that not everyone has the ability to install panels on their roofs. This may be because there is not enough space, the roof is facing the wrong direction of the solar panels, or the homeowner's association has restricted the ability to install solar panels. It may also be someone who cannot afford the installation cost or lives in a building without a roof. 

"The good news is that many obstacles can be lowered through good policies," Schalke said. 

Cohen said that most manufacturers in the industry have recycling programs for solar panels-aluminum and other valuable components make recycling an economical option. Nevertheless, the recycling process is not easy to separate all the different parts of the panel. 

Scrub Hub: Will wind turbines and solar panels go to landfills or can they be recycled? 

Schalke said the reality is that very few solar panels in the United States have not reached the end of their useful life, especially in Indiana. This is because the solar industry is still in its infancy, and panels are expected to reliably generate electricity for 25 years. Since there are very few panels decommissioned at this time, the United States is still in the early stages of developing a strong solar panel recycling industry. 

Schalke said that other parts of the world, such as Europe, have more advanced solar markets and are one step ahead of us, "so we may learn from them in the next few years."

Correction: An earlier version of this story stated that "a typical residential solar installation ranges from 7,000 to 8,000 kilowatts..." The correct measurement unit is 7,000 to 8,000 watts. 

Please call 317-444-6129 or email sarah.bowman@indystar.com to contact IndyStar reporter Sarah Bowman. Follow her on Twitter and Facebook: @IndyStarSarah. Connect with IndyStar's environmental reporter: Join The Scrub on Facebook.

IndyStar's environmental reporting project has been generously supported by the non-profit organization Nina Mason Pulliam Charitable Trust.