Besides lower electricity costs, an added bonus
The
study defines the value of solar, or VOS, as household-level financial benefits
from electricity bill savings plus revenues from selling excess electricity to
the grid—minus the initial installation costs.
For
many U.S. households, increased earnings from residential rooftop solar could
total up to hundreds of dollars annually by the end of the century, say the
authors of the study, which was published April 19 in the journal Nature
Climate Change.
“Given the average 25-year lifespan of a rooftop solar installation, a system built today will nearly experience 2050 weather,” said study senior author Michael Craig, assistant professor of energy systems at the U-M School for Environment and Sustainability and of industrial and operations engineering at U-M’s College of Engineering.
“So,
it’s important for households to think of future value when building solar. If
households do so, our findings indicate they would see even greater value from
solar, and might decide to build more.”
Public
awareness of the increased future value of rooftop solar could spur greater
adoption of the technology, which in turn could accelerate efforts to
decarbonize the power-generation system in the United States and globally, the
study shows.
The
expected financial gains seen in the study were driven largely by increased
demand for residential air-conditioning as the climate warms. The other key
factor affecting the value of rooftop photovoltaic systems, the researchers
say, is future solar-panel performance in response to climate change.
Craig
and colleagues analyzed data from 2,000 households in 17 U.S. cities and
estimated air-conditioning demand and solar-panel performance under future
climates using a moderate climate-warming scenario called RCP-4.5.
The
value of rooftop solar panels increased in nearly all the cities, in both warm
and cold locations. Miami saw the largest increase in value, while only
Minneapolis saw a decrease in the financial benefits of rooftop solar for
households.
“This
is the first study to quantify the value of rooftop solar under climate change,
and we show that households across the U.S. will realize greater cost savings
from rooftop solar under future weather than under historic weather,” said
study lead author Mai Shi, a former U-M visiting doctoral student now at
Tsinghua University in Beijing.
As
home-cooling demands rise, a greater proportion of solar-generated electricity
will be used to cool the home, rather than being sold to the electrical grid,
benefiting owners of rooftop solar systems, according to the study.
That’s
because—in many states—solar energy used to power a home reduces the
homeowner’s electric bill by the full retail cost of electricity, while
electricity that is sent to the grid is credited at a lower rate.
“Greater
cooling demand means more solar power is consumed at the household rather than
sent back to the grid,” Craig said. “And it’s generally more valuable for a
rooftop photovoltaic owner to consume the power generated by their PV panel,
rather than exporting it to the grid.”
Under
the moderate RCP-4.5 climate scenario, demand for residential space cooling is
expected to increase in all 17 cities studied. Cooling demand will increase by
an average of 35% by mid-century and by an average of 64% by the end of the
century, across all households in all of the cities, the researchers say.
The
other key factor affecting the future value of residential rooftop
photovoltaics is solar-panel performance in response to rising air temperatures
and changes in cloud cover.
Solar
panels work best in cool, sunny weather. As air temperature or cloud cover
increase, the amount of electricity generated by a solar panel declines. The
study found that future solar-panel performance will vary from place to place
across the U.S., depending on weather conditions.
In
cities such as Ann Arbor, Austin, Chicago, Dallas, Detroit, Houston, Louisville
and Milwaukee, rising air temperatures will decrease solar panel efficiency,
but reduced cloud cover will likely increase the amount of sunlight reaching
panels, on average. The two factors “are opposing but roughly comparable,”
meaning they cancel each other out, the researchers say.
But
cities such as Baltimore, Boston, Los Angeles, Minneapolis, New York City and
Phoenix are expected to be both warmer and cloudier in response to climate
change, which will “significantly decrease” the electrical output of rooftop
solar.
Even
so, increased cooling demand in all 17 cities will likely outweigh changes in
panel electrical output, resulting in financial gains for owners of rooftop
solar in nearly every case, according to the study. Minneapolis, where limited
future increases in cooling demand will combine with decreased electrical
output from rooftop solar panels, is an exception.
While
future financial gains from rooftop solar will be reaped mainly by households
that can afford to install panels, various programs are in place to increase
accessibility, so that more people share in the anticipated benefits, Craig
says.
For
example, there are programs that defray the costs of solar, opening it up to
lower-income individuals. Governments can also install rooftop solar on public
buildings, such as subsidized housing, to cover the capital costs while
providing solar benefits to tenants. And community solar programs can benefit
entire communities, including households that lack the means or ability to
access rooftop solar themselves.
In
addition to Craig and Shi, the other author of the Nature Climate Change paper
is Xi Lu of Tsinghua University.
The
study was supported by the National Key R&D Program of China, U.S. National
Science Foundation, National Natural Science Foundation of China and Carbon
Neutrality and Energy System Transformation Project.
Study: Climate change will impact the value and optimal
adoption of residential rooftop solar (DOI
10.1038/s41558-024-01978-4)
