Everyone loves rooftop solar panels. But there’s a problem.

Over the past decade, millions of solar panels have been installed on homes from California to Massachusetts. These solar panels allow their owners to cut down on their bills, pull electricity directly from their rooftops, and sometimes even store it in home batteries to use later in the day.

But are those solar panels the best way to reduce fossil fuel emissions?

The answer is more complicated than it seems. Researchers argue that home solar panels are raising the price of electricity and reducing the need for cheaper large solar farms - making the entire transition to clean energy more expensive. And as more and more homeowners turn to solar, thanks in part to more generous government incentives, that could actually make it harder for the United States to meet its overall climate goals.

Jesse Jenkins, a professor of mechanical and aerospace engineering at Princeton University, said that rooftop solar is an example of the “crises and mismatches” that occur when electricity is billed in the wrong ways. “Some people are going to pay more than they should, and some people are going to pay less than they should,” he said. “It’s going to cause unnecessary costs.”

The issue is that solar, unlike other energy sources, only produces power during a particular time of day - when the sun is shining. Solar panels can provide a ton of power between the hours of 9 a.m. and 5 p.m.; in states like California during the spring, solar can almost provide all of the state’s energy during those hours.

That means that solar on peoples’ homes is partly competing with large solar farms run by utilities. “I call it a ‘solar-shaped hole’ in the electricity grid,” Jenkins said. “The more rooftop solar you have, the less valuable utility-scale solar is.”

At some level, that’s not a big problem: As long as there are solar panels producing power, why does it matter whether they come from a big farm in the desert or the rooftop of a suburban home?

But rooftop solar costs much more than a giant solar farm. Installing solar panels on the roof of a house or apartment building will cost a homeowner around $4.20 per watt before tax breaks and incentives - while installing them in a large solar farm costs closer to $1.16 per watt.

“Pooling together private and federal money, it’s just going to be a lower cost way to get kilowatt-hours of solar, if it’s utility-scale,” said Duncan Callaway, a professor of energy and resources at the University of California at Berkeley.

Rooftop solar groups counter that the cost of utility-scale solar doesn’t include all of the other expenses involved in building big solar farms.

“They are not adding in the cost of what it takes to deliver that electron to your home,” said Bernadette del Chiaro, the executive director of the California Solar and Storage Association.

At the moment, about 28 percent of all solar installed in the country is on the rooftops of homes and businesses, according to Wood Mackenzie and the Solar Energy Industries Association. By 2035, the country needs around 1,000 gigawatts of solar power to hit climate goals - if more of that is rooftop solar than utility-scale solar, the country could spend billions of extra dollars on the transition to clean energy.

Some of that cost is covered by the individuals installing systems on their homes; but part of it is covered by government tax credits and lower electricity rates faced by those customers. At the moment, homeowners can receive a federal tax credit for 30 percent of the cost of installing solar panels; avoided costs of paying electricity bills can be in the hundreds of dollars per year.

Rooftop solar does have other benefits. Advocates say that it can help lower other costs - solar panels on a home don’t require long-distance, large power lines to carry energy from a faraway desert solar farm to major cities. (The nation’s slow build-out of power lines is one of the major factors holding back a transition to clean energy; it can also take a long time to connect solar farms to the larger electricity system.)

Panels on the roofs of big box stores or suburban homes also save space; they won’t interfere with prairie ecosystems or endangered species. Large-scale wind and solar farms can take 10 times the space of coal and gas-fired power plants - although some developers have experimented with combining solar farms with grazing cattle or growing crops.

“These installations benefit everyone by taking strain off the grid,” Abigail Ross Hopper, the president and CEO of the Solar Energy Industries Association, said in an email. “We need massive increases in solar deployment at all scales in order to decarbonize the grid.”

“This is clearly an apples to oranges comparison,” said Amy Heart, senior vice president of public policy at Sunrun, a home solar and battery storage company. Heart says that half of all the systems Sunrun is currently installing include battery storage, alleviating the problem of solar all being generated at the same time.

Callaway says that it depends on what people value: cleaning up the grid cheaply or saving land. “Some people prefer to leave open space open,” he said. “If that is the value, then rooftop solar makes sense.”

Rooftop solar in the United States also costs more than in other places around the world. In other countries, rooftop solar and large solar farms cost approximately the same amount per watt. In America, high costs for advertising and the sheer difference of American homes ramp up costs.

“We have local counties and cities that have their own building codes,” said Joachim Seel, a policy researcher at Lawrence Berkeley National Laboratory. “There are local permitting procedures and inspections.” Even the variety of American homes - ranch houses, townhouses, multistory colonials - can drive up costs compared to other countries. “I don’t think there’s an easy way around it,” he added.

Heart says that the United States has 40,000 jurisdictions and red tape that solar providers have to go through - much more than in other countries. “We make it so complicated,” she said.

Researchers say that part of the issue is that many states and utilities provide very lucrative deals for users of rooftop solar - often compensating owners of home panels more than the value of their solar to the grid. In states like California and Arizona, Jenkins said, in the middle of the day homeowners might get 20 cents back for each kilowatt-hour they send to the grid. But for a grid already flooded with solar, the value of that extra energy is close to zero.

The result is that richer homeowners who can afford solar get cheap electricity bills - while poorer residents see higher bills to compensate. In California alone, researchers at UC Berkeley and the California Public Advocates Office estimated that rooftop solar will between $4 billion and $6.5 billion to customers’ bills in 2024. One solution is to match the tax breaks and benefits of rooftop solar more closely to the value it actually adds to the electricity grid.

Some groups dispute that this cost-shift is taking place. The California Solar and Storage Association argues that solar has helped avoid peak middle-of-the-day demand in the state - and that most of the growth in electric bills has come from high utility spending. Utilities say that they need higher rates to protect their infrastructure from wildfire and other climate extremes.

“The utilities view rooftop solar as competition - it directly conflicts with their business model,” del Chiaro said. “We see it as very convenient scapegoating.”

Few scientists or researchers want to abandon home solar panels entirely. Research has shown that solar panels are contagious - the best way to predict whether a household will install them is whether their neighbors already have. Taking individual steps to change your lifestyle can also encourage people to take other steps: installing climate-friendly heat pumps, buying electric cars and eating less meat.

“Having your own solar system on your own rooftop - I think for many people it helps them think about energy consumption and energy efficiency in general, and take ownership of that,” Seel said. “From that perspective, it’s important.”