Like millions of other Americans, Jonathan Marvel, founding principal at Marvel Architects, remembers watching media coverage stream in from Puerto Rico in September 2017 after Hurricane Maria struck the island. The devastation was extraordinary. As later studies would reveal, an estimated 2,975 people died as a result of the storm and 3.4 million people lost power. It was one of the worst natural disasters to ever strike the U.S.  Now, one year after Maria, Marvel and his partners at Resilient Power Puerto Rico (RPPR) are building a series of solar installations that are bringing emergency power to community centers in informal settlements across the island. Using state-of-the-art Tesla Powerwall batteries, RPPR has enabled these centers to generate solar power during good weather and store it for the blackouts that follow hurricanes and other disasters. Local people can use the centers as shelters where they can charge their phones to find their loved ones, store perishable food, or power life-saving home healthcare devices. The goal of the group was not to rebuild the island's existing infrastructure after Maria, but to provide a new resilient system that would support informal communities when the next storm would inevitably arrive. “When Maria hit," Marvel said, "it hit home.”  Marvel had just returned from Puerto Rico when Maria arrived. He had been helping his mother, who lives on the island, recover from Hurricane Irma, which had blown through only two weeks before. Rather than just sending money to aid organizations, Marvel worked with friends and colleagues Cristina Roig-Morris, ESQ, and José J. Terrasa-Soler, ASLA, to do what architects do best: design a solution to a problem. “Architects jump in,” Marvel said. “We’re the first responders from the professional world. We’re trained to think comprehensively; we’re trained to put the social impact first and foremost.” Rather than tackling the entire enormity of the disaster, Marvel's team focused on power. Electricity, as Marvel put it, "is the basis of all things in the 21^st century,” and according to CNN, the hurricane caused the worst blackout in U.S. history. The goal of the group was not to restore electricity to the whole island; that would be an enormous task and one that a slew of government agencies were already working on. Instead, they looked at how they could create supports in the electrical web to catch the most vulnerable when they fell. RPPR’s solution is straightforward but steps neatly aside of the established way of doing things. “We’ve been very deliberate to stay outside of local politics and federal politics,” Marvel said. Instead, the group looked for creative solutions permissible under existing laws. The sun being an abundant resource on the tropical island, solar power provided an obvious place to start exploring possibilities, but they found there were restrictions on what they could do with private generation. “Before Maria, there was a lot of solar power, but it was illegal to store with batteries,” Marvel said. “After Maria, batteries were allowed without permits, which allowed us to start our system legally. But we still can’t distribute past the property line.” Across the country, small-scale solar generation is tightly regulated by power authorities that have been accused of trying to squash home power generation so that utilities can maintain a monopoly on the electricity market. Puerto Rico allowed domestic power storage in Maria's wake, but still would not allow RPPR to create an alternative power network. RPPR would have to make the most of small-scale installations. Doing a lot with a little is a common practice in Puerto Rico, where resources don't always flow as easily as they do on the mainland. Marvel’s mother, the architect and planner Lucilla Fuller Marvel, had worked extensively with community centers in informal settlements across the island (her book Listen to What They Say presented a bottom-up approach to planning in Puerto Rico), and the group realized that they could focus on powering existing hubs. By installing solar panels and batteries, each community center was able to serve a broad population with relatively little effort. “Each site serves a population about 3,000–5,000 people because of the density,” Marvel said. Thousands of people are able to take advantage of the basic amount of electricity available at each installation during post-disaster blackouts when the central power grid collapses. The focus on informal communities also helped RPPR avoid federal bureaucracy, which, Marvel said, “was completely caught off guard.” While President Trump has recently insisted that his administration got “A Pluses” for their response to the storm, Marvel saw the situation differently: “The federal government does not have a great track record on the lower 48 when it comes to hurricane recovery…but states really help each other out." Puerto Rico, being an island and a relatively isolated territory in the Carribbean, is often forced to go it alone. "Puerto Rico doesn’t have anybody waiting to help. The governor of Puerto Rico was counting on the feds…but the feds didn’t step it up.” When it came to designing the installations, RPPR focused on efficacy rather than looking for a flashy, aesthetically-driven design. Panels are installed in prosaic rooftop setups, but Marvel said that he looked for lessons from what survived the storm when it came time for detailing, and the results have proved resilient. The project’s successes have won new backers and collaborators, and enabled it to broaden its ambitions. Tesla joined the project by providing their home storage batteries, and a variety of foundations have provided hundreds of thousands of dollars in support. Now the project has 28 installations across the island, with 30 more in the pipeline. RPPR and Marvel’s work in Puerto Rico tells the story of a resilient network of communities, badly battered but bouncing back from catastrophe. It’s far from the narrative perpetuated by the current presidential administration, which maintains that the federal government saved a helpless island from impending doom. The project also presents a model for how architects can engage with their communities aside from multimillion-dollar cultural projects or philanthropic endeavors in remote countries. “I think it is very easy for architects to jump into these disasters and think of these solutions. Architects are really well equipped and we do it all the time.” The design’s success comes not out of formal gymnastics or phenomenological effects, but from the social and political structures the project engages and builds on. Ultimately, Marvel credited the served communities for the project’s success. “It’s a generous population,” he said. “They open up their hearts and their houses to each other.” The project shows that when people are willing to lend a helping hand, powerful resilience is possible.

On Wednesday May 9, the California Energy Commission will vote on whether or not to require solar panels on new homes. The standard is expected to pass and would apply to all single and multi-family homes up to three stories tall as of January 2020. Exceptions will be made for shaded structures or in situations where it is impractical to install panels and offsets can be used for other solutions, such as re-charging batteries like Tesla’s Powerwall. Homes will not have to reach net-zero status (that is, relying completely on the solar panels for all energy), but is still expected to San Francisco already requires solar panels on all new buildings under 10 stories tall—statewide about 15 to 20 percent of new single family homes rely on solar energy. As California is the world’s fifth largest economy, the massive sales-boost that would result in this measure should not only lower the cost of solar panels in the state, but across the U.S. Installing solar panels will make it approximately $25,000 to $30,000 more expensive to build homes than those built under the 2006 code. However, homeowners are expected to save $50,000 to $60,000 over 25 years. While some have pointed out that this could make California’s housing shortage situation even more dire by raising housing costs, the energy–saving benefits (and California’s increasingly wealthy population) may outnumber the naysayers. This is the most recent of California’s sustainability measures as it continues to push toward a more environmentally friendly future, including filing a lawsuit against the EPA from lowering vehicle emission standards.

Let’s face it: no one has ever characterized a solar panel as being particularly attractive. In fact, they’re eyesores. While the environmental and business cases for photovoltaics are relatively easy to make, their aesthetic dimension has long been a losing proposition. “In states like California, solar is half the price of the local utility, even without subsidies,” explained Ido Salama, co-founder of Sistine Solar. “At the same time, it feels like all solar products look the same: they come in either black or blue, and, while solar panels work great, many people would describe them as ugly. At the very least, they look out of place on a roof,” he added. Rather than attempting to convince people to appreciate solar for what it is, Salama and company set out to build a solar panel that appeals to their sense of aesthetics instead. To that end, Sistine Solar introduced its SolarSkin technology—described on the company’s website as “solar with curb appeal”—in 2013 when its developers won the renewables track of the MIT Clean Energy Prize. Since launching SolarSkin, the company recently introduced its online Design Studio platform to allow anyone to design, customize, and price a solar installation.

How it works

Developed by MIT engineers, SolarSkin is a thin film specially coated with ultra-durable graphics and integrated onto high-efficiency solar panels. The technology employs selective light filtration to simultaneously display an image and transmit sunlight to the underlying solar cells with minimal loss in efficiency. The product is available in any number of colors and patterns, is compatible with every major panel manufacturer, and is available for both new and existing roofs. The end result is essentially a kind of camouflage for the typically drab photovoltaic panel. Sistine Solar’s new SolarSkin Design Studio is an online tool that allows architects, designers, and homeowners alike to design and order a customized solar system from a desktop computer or mobile phone. With a $99 refundable deposit, end users will receive a preliminary system design using LIDAR mapping, a detailed panel layout, guaranteed production figures, a realistic rendering, (where suitable image is available), and guaranteed delivery within 90 days. The Design Studio is intended to get customers more excited about solar, according to Salama. “Homeowners appreciate the transparency, customizability, and especially the ability to match their solar panels to their roof,” he said. “Architects and designers love it because for the first time, they have a product that allows them to showcase solar in a way never before possible—integrated, congruent, harmonious." In spite of the improvement to aesthetics, however, solar technology still faces a number of challenges in terms of market transformation. “Soft costs is one barrier,” he said. “Solar is so complex because every municipality has different rules when it comes to permitting solar.” Noting that it may take one to three days to physically install and wire up a solar system, Salama points out that it can take up to three months to get a permit. “If soft costs could be reduced—like streamlining the permitting process—we would see a radical transformation in adoption,” he suggested. Of course, affordable storage is an ongoing issue with solar technology. “When solar and storage become more economical than buying from the local utility, we will see a huge shift towards distributed generation and plenty of homeowners cutting the cord,” Salama predicted. Now that solar panels are eligible for a makeover, however, there’s one less hurdle to overcome—making the future of solar technology a little more attractive.  

IKEA, the Swedish furniture giant known for selling cheap, do-it-yourself furniture, is now offering solar energy systems (only these products aren't quite cheap and definitely aren't D.I.Y.).

IKEA has partnered with energy technology company Solarcentury to launch its Solar Battery Storage Solution, which features solar panels and home batteries, in the U.K. Solarcentury, one of the U.K.’s biggest solar panel providers, will produce the panels.

IKEA’s home storage battery works in the same way as Tesla’s Powerwall, storing energy generated from the solar panels instead of selling excess energy back to the grid. The home batteries are compatible with existing solar panels or as a part of a combined storage system.

There is a bit of a sticker shock for those used to IKEA’s affordable prices—the upfront cost for both panels and battery is £6,925 (about $9,034 in U.S. dollars)—but the company estimates customers will make their money back within 12 years and their electricity bills will be cut by up to 70 percent. 

Solar panels and home battery systems have been making big waves thanks to Tesla's recently-announced offering. While still expensive, IKEA's solar system has an advantage in that its starting price is much lower. Just the batteries will cost £3,000 (around $3,900) as opposed to Tesla's price of £5,900 (about $7,684). However, location, type of building, and size of roof, also affect the final cost.

“We believe IKEA and Solarcentury are bringing the most competitive package to the market yet so more people than ever before can profit financially and environmentally by producing their own energy,” Susannah Wood, head of residential solar at Solarcentury, said in a press release.

This news comes on the heels of two big announcements for the U.K.’s energy industry. Just last week, the U.K. government unveiled a plan that will allot £246m of funding (that's around $320.48 million) for battery technology research. British gas owner Centrica also revealed that it would be increasing its energy prices 12.5 percent, despite promises to lower costs.

If you live in the U.K., IKEA’s website offers a free estimate on how much installing its Solar Battery Solution will save you.

While the oil companies struggle to maintain their environmentally disastrous stranglehold on the market and the planet, there are some very realistic technologies that threaten to disrupt the status quo. One of the most dangerous for the oil companies is the Tesla solar roof, an off-the-shelf consumer system of tempered glass tiles. Last week, Tesla began accepting orders for the product and released pricing, which is comparable to normal asphalt roofing. The system is a mix of active solar tiles and inactive simple glass tiles, and as the percentage varies, so does the eventual cost. A 35 percent mix would cost $21.85 per square foot, and according to Consumer Reports, the tiles need to be under $24.50 per square foot to compete with normal tiles. That math doesn't even take into account the energy savings over time, which should allow the tiles to pay for themselves. Tesla released a savings calculator when they announced sales, and they are also offering a lifetime warranty. “We offer the best warranty in the industry—the lifetime of your house, or infinity, whichever comes first,” a Tesla rep told Inverse. https://www.instagram.com/p/BT7HVS3AZ4q/

In Florida, solar power advocates defeated a major amendment cleverly crafted to thwart the expansion of solar energy within the Sunshine State. Amendment 1, known as Solar Energy Subsidies and Personal Solar Use, was rejected last week after it failed to accumulate the 60 percent of voter support required to pass. There was a particularly heated battle around this bill, given the use of rhetorical spin encouraged by Sal Nuzzo of the James Madison Institute—a think tank with close ties to Florida utilities and funding from Koch Industries, who also financed the amendment’s sponsor group, Consumers for Smart Solar. According to Christian Science Monitor, Nuzzo was caught on tape encouraging what he called “‘a little bit of political jiu-jistu’” that would “use the language of promoting solar” while building in “protections for consumers that choose not to install rooftop [panels].” With current net metering policies that exist in every state, including Florida, utilities companies are required to purchase excess energy from solar-powered homes, offsetting the cost of power taken from the grid at night. The amendment “establishes a right under Florida’s constitution for consumers to own or lease solar equipment installed on their property” a right Floridians already have, but only in order “to generate electricity for their own use.” If passed, residents would not be able to sell their cheaper, excess electricity back to the grid. Utilities companies argue solar homes—in selling their excess energy to the grid—make use of transmission lines and grid infrastructure without paying a fair share, according to Mother Jones. This amendment would've also ensured that the cost of maintaining the grid wouldn't be shifted onto non-solar users. The amendment also didn’t seek to legalize leasing solar panels through third party groups (such as SolarCity and Sunrun) which have installed approximately 72 percent of residential solar in the nation since 2014, according to Greentech Media. Florida residents must continue to go through one of the four existing utilities companies, which maintain exclusive rights to selling power in Florida, to arrange for solar power. When the Nuzzo recordings leaked toward the end of October, it gave the opposition the boost it needed to defeat the amendment. It became clear that the amendment was “an attempt to destroy all free market energy in the state along with solar energy in general,” Tory Perfetti, chairman of Floridians for Solar Choice told The Huffington Post. Moreover, according to the legal brief filed by Earthjustice, if passed, “solar users could end up paying twice as much as other customers pay to buy power from the utilities.”  Former Florida senator and governor Bob Graham blasted Amendment 1, Jimmy Buffett recorded a video about it, and Elon Musk tweeted about it, calling it a “calculated attempt to deceive Florida voters about solar.” While solar expansion in the Sunshine State still has a long way to go, the amendment’s rejection was a bullet dodged.

March 11 marks the five-year anniversary at the Fukushima nuclear power plant in Japan. After the disaster, officials have been on the hunt for alternative energy solutions. Now, Japanese electronics firm Kyocera has begun construction on what will be the world's largest floating solar farm, just outside Tokyo. The Yamakura dam power plant will use more than 50,000 solar photovoltaic panels covering nearly 2 million square feet. Japan is a country short on space, so energy solutions that aren't built on land are a welcome sight to many. As the Guardian recently reported, the country is increasingly dependant on imported fossil fuels, to the detriment of its carbon footprint goals. The solar array is being constructed upon a reservoir with hopes of providing enough energy for roughly 5,000 homes when finished in 2018. Despite its size, the plant is comparatively small to land-based solar farms. Expected to produce 13.7MW when complete, this more than 28 times smaller than the 392 Ivanpah Solar Power Facility in San Bernardino, CA. According to Kyocera TLC Solar, "the project will generate an estimated 16,170 megawatt hours (MWh) per year — enough electricity to power approximately 4,970 typical households — while offsetting about 8,170 tons of CO2 emissions annually. This is equal to 19,000 barrels of oil consumed." "With the decrease in tracts of land suitable for utility-scale solar power plants in Japan due to the rapid implementation of solar power, Kyocera TCL Solar has been developing floating solar power plants since 2014, which utilize Japan’s abundant water surfaces of reservoirs for agricultural and flood-control purposes," the firm added.

French authorities have announced that it plans to lay over 600 miles of solar roads within five years. Research from a five year study in collaboration with highway company COLAS indicates that the roads could provide power to up to 5 million people, or 8 percent of France's population. However, some claim that the French government is merely subsidising French companies and not following the best road for alternative energy solutions. Project "Wattway," as it is being called, was launched last October with the French Agency of Environment and Energy Management stating that just over 13 feet (4m) of solar road (215 square feet to be precise) could meet the energy demands (except heating) of one home. On that basis, 5,000 residents could draw on their energy supplies from as little as 0.62 miles of solar road. https://twitter.com/RoyalSegolene/status/693861761179611136?ref_src=twsrc%5Etfw Five years of research deduced that French roads are only occupied by vehicles "10 percent of the time" and that the solution could pave the way for solving future energy demands. Looking at the specs, the surface uses polycrystalline silicon cells, which are "encapsulated in a substrate," forming high yield solar panels. Only 0.28 inches (7mm) thin, the panels have an extremely high strength-to-weight ratio which allows them to deal with the weight of pretty much all motor-vehicles. For those thinking that driving on solar panels has the potential to be hazardous, fear not. Snowplow tests have been passed and the panels com equipped with all-weather skid-resistant coating. “These extremely fragile photovoltaic cells are coated in a multilayer substrate composed of resins and polymers, translucent enough to allow sunlight to pass through, and resistant enough to withstand truck traffic,” said COLAS. It's not just homes the roads could potentially power. Outlining the possibilities for "intelligent roads," COLAS said how they could be used for real time traffic management, self-driving cars, charging moving electric vehicles and eliminating black ice. What's more, COLAS said that the panels can be "directly applied to existing roads, highways, bike paths, parking areas, etc., without any civil engineering work." On top of that, the panels can last up to 20 years in areas that see infrequent traffic, meanwhile COLAS estimates the lifespan of the panels in regular traffic conditions to be 10 years. For example, if the quickest route from Caen in the North of France down to Marseille were to be covered, residents in both cities could be powered for 52 years if the panelled road lasted 10 years (and was removed afterwards). How Legitimate are COLAS's claims? France gets 1,600–2,000 sunlight hours per year. Taking the minimum of that, and subtracting 10 percent (road occupancy from vehicles) that leaves 1,440 sunlight hours per year. Interestingly, COLAS's claim of powering one home every 13 feet arose from the presumption of roads receiving only 1,000 sunlight hours per year, indicating that they are being extremely stringent with their study. Unsurprisingly, COLAS's panels have a lower percentage yield than current photovoltaic market solutions, offering 15 percent solar yields compared to 19 percent, but one can presume that this is a byproduct of making the panels roadworthy and their altered angle of incidence. This equates (by COLAS' calculations) to the panels costing $6.73 per Watt. However, according to Olivier Danielo of DDMagazine, this is "six times the cost "of large-scale photovoltaic cells." Danielo has reason to be skeptical. COLAS specialize in highway construction and by creating an "energy efficient" solution actually implement roads that have a shorter lifespan than regular roads, thereby giving themselves more work. Surely it would be far more efficient to equip houses who can utilize the optimum angle of incidence in conjunction with the most efficient photovoltaic (PV) technology? Jenny Chase, head of solar analysis at Bloomberg New Energy Finance ("Solar Insight Team") backs Danielo's claims up.  https://twitter.com/solar_chase/status/696658947252609024 Danielo and Chase aren't the only ones concerned, either. French engineer Nicolas Ott said that the energy payback from rooftop PV's is 7.5:1 compared to Wattway's 1.6:1. COLAS also claim to have "invented" the solar road when this is not the case. SolaRoad, a bike path in Krommanie in the Netherlands produced better than expected yields. However, when compared to three rooftop PV systems in the same area of the prototype road, data showed that rooftop PV's was double that of the SolaRoad per square meter over the same period. https://www.youtube.com/watch?v=6-ZSXB3KDF0 Nonetheless, installation of the French solar road panels is set to start soon with funding coming from raising taxes on fossil fuels. https://www.youtube.com/watch?v=8ZNJhcNq9q4

Last week Cincinnati officials lauded the opening of a new police station that they're calling one of the nation's greenest buildings devoted to public safety. Cincinnati-based emersion DESIGN led design on the new Police District 3 Headquarters, which will be LEED Platinum and net-zero, producing as much energy on site as it consumes, according to city officials. The building's design/build team also included Messer Construction, CMTA Engineering, Human Nature Landscape Design, Strand Associates, and Genesis Design. Geothermal heating and cooling complements the building's tightly sealed envelope, as well as other efficiency measures that cut its energy demand in half relative to similar 24/7 public safety buildings, while solar photovoltaic panels offset its electricity consumption. At 39,000 square feet, the new headquarters more than doubles the previous Warsaw Avenue facility, which first opened in 1907. The new building at 2300 Ferguson Road in Westwood will house roughly 200 employees. Following the playbook of Cincinnati Public Schools, the new district HQ will also incorporate public art and host community events in an attempt to soothe a sometimes fraught relationship with police. In 2001 Cincinnati grabbed national headlines when widespread protests seized the city following the police killing of unarmed Timothy Thomas. (Cincinnati police have also earned national media attention for substantial reforms since the riots.) “It used to be that when cities built civic buildings like this, they were places the community could come together,” said Mayor Mark Mallory at the building's groundbreaking in 2013. “With District 3, we’re doing that again. We want people to come here and feel comfortable coming here with their neighbors.”

Work is currently underway on a new mixed-use development at Ohio's Oberlin College that, once complete later this year, will include one of only a handful of hotels pursuing LEED Platinum certification in the United States. The hotel operator is Olympia Companies, based in Portland, Maine. In addition to 70 guest rooms, the building features a restaurant focused on local food, 10,000 square feet of retail, a conference center, and a basement jazz club. Rounding out the facility's 105,000 square feet will be offices for the college's admissions and development staff. The Peter B. Lewis Gateway Center, developed by Cleveland's Smart Hotels, was planned to be “the cornerstone of Oberlin's Green Arts District,” at the intersection of North Main Street and East College Street. Chicago architects Solomon Cordwell Buenz designed the project, which will draw on Oberlin's existing 13-acre solar photovoltaic farm adjacent to campus. Smart Hotels' Christopher Noble said the design team worked with the New York office of Germany's Transsolar on the development of that solar farm, and the new building will not throw Oberlin off its target of purchasing 100 percent renewable energy for electricity by the end of 2015. Mechanical engineers KJWW helped finesse the building's fully radiant heating and cooling, which employs no forced-air ventilation—although some back-of-house areas will still use some water-source heat pumps, Noble said. “We're relying on nonconventional HVAC systems,” said Noble, who added that heating and cooling needs will be fulfilled fully from geothermal wells on site. The building is expected to be certified LEED Platinum after opening early next year. While the design team hasn't assessed the payback period for the building's sustainable features, Noble said Oberlin made energy efficiency a project priority. “It wasn't a cost issue,” he said. “It was a design issue—we were going to make a statement and do this.” Of the $35 million total project cost, $12 million came from outside donors, including $5 million from the building's namesake, the late philanthropist and chairman of Progressive Insurance Company, Peter B. Lewis.

A luminous, arched pavilion in Ohio aims to highlight the potential of 3D fabrication techniques, and to so it's mounting a Promethean stunt. The so-called Solar Bytes Pavilion grabs sunlight during the day and radiates light when it gets dark, recreating the day's solar conditions minute-by-minute throughout the night. Brian Peters helped found DesignLabWorkshop in 2008, eventually settling in Kent, Ohio. Their latest project is the Solar Bytes Pavilion, a continuum of 94 unique modules (“bytes”) 3D printed in ceramic bricks covered with white, translucent plastic. Peters and his team then put solar-powered LEDs in each of the bytes, snapping them together in a self-supporting, arched pavilion just big enough for a few people to huddle inside. 3DPrint.com got some detail on the fabrication process:

...he used a 6-axis robot arm located at the Robotic Fabrication Lab at Kent State. A hand welding extruder, called the Mini CS, was attached to the robot arm to serve as the 3D printhead, and it extrudes plastic material in a sort of FDM-style process. The technology, provided by Hapco Inc. and called BAK/DOHLE, is employed by universities, government agencies, and concerns like the University of Michigan, Oak Ridge Laboratory, the US Department of Energy, and the University of Tennessee.

The pavilion debuted at Cleveland's Ingenuity Fest.

According to the San Francisco Chronicle, David Chiu, president of the San Francisco Board of Supervisors, is proposing legislation to mandate that all new buildings in the city contain solar panels, rooftop gardens, or both. The resolution, called Solar Vision 2020, would form a permanent program (extending the work of the pilot GoSolarSF) to help building owners pay to install solar arrays, set a goal of doubling the city's solar energy production, and install 2 megawatts–worth of panels on residences citywide each year. “Many landlords have told me that if we just had the right financing mechanisms, they’d be interested in doing this,” he told the Chronicle. In addition to the local plans, a statewide bill called the Solar Permitting Efficiency Act—which would streamline the permitting processes around solar power and save customers up to $1,000 each—has passed the legislature and is now waiting for Governor Jerry Brown's signature. Meanwhile the California Solar Initiative and the Federal Residential Renewable Energy Tax Credit both provide rebates to would-be solar energy installers. In Los Angeles, the Department of Water and Power offers the Solar Incentive Program, which provides rebates on photovoltaic installations, and supports Go Solar LA, established to reduce customers’ cost of installing solar PV systems.