Shining a light on the true value of solar power

 Beyond the environmental benefits and lower electric bills, it turns out installing solar panels on your house actually benefits your whole community. Value estimations for grid-tied photovoltaic systems prove solar panels are beneficial for utility companies and consumers alike.

For years some utility companies have worried that solar panels drive up electric costs for people without panels. Joshua Pearce, Richard Witte Endowed Professor of Materials Science and Engineering and professor of electrical and computer engineering at Michigan Technological University, has shown the opposite is true -- grid-tied solar photovoltaic (PV) owners are actually subsidizing their non-PV neighbors.

Most PV systems are grid-tied and convert sunlight directly into electricity that is either used on-site or fed back into the grid. At night or on cloudy days, PV-owning customers use grid-sourced electricity so no batteries are needed.

"Anyone who puts up solar is being a great citizen for their neighbors and for their local utility," Pearce said, noting that when someone puts up grid-tied solar panels, they are essentially investing in the grid itself. "Customers with solar distributed generation are making it so utility companies don't have to make as many infrastructure investments, while at the same time solar shaves down peak demands when electricity is the most expensive."

Pearce and Koami Soulemane Hayibo, graduate student in the Michigan Tech Open Sustainability Technology (MOST) Lab, found that grid-tied PV-owning utility customers are undercompensated in most of the U.S., as the "value of solar" eclipses both the net metering and two-tiered rates that utilities pay for solar electricity. Their results are published online now and will be printed in the March issue of Renewable and Sustainable Energy Reviews.

The value of solar is becoming the preferred method for evaluating the economics of grid-tied PV systems. Yet value of solar calculations are challenging and there is widespread disagreement in the literature on the methods and data needed. To overcome these limitations, Pearce and Hayibo's paper reviews past studies to develop a generalized model that considers realistic costs and liabilities utility companies can avoid when individual people install grid-tied solar panels. Each component of the value has a sensitivity analysis run on the core variables and these sensitivities are applied for the total value of solar.

The overall value of solar equation has numerous components:
 

• Avoided operation and maintenance costs (fixed and variable)
• Avoided fuel.
• Avoided generations capacity.
• Avoided reserve capacity (plants on standby that turn on if you have, for example, a large air conditioning load on hot day).
• Avoided transmission capacity (lines).
• Environmental and health liability costs associated with forms of electric generation that are polluting.

Pearce said one of the paper's goals was to provide the equations to determine the value of solar so individual utility companies can plug in their proprietary data to quickly make a complete valuation.

"It can be concluded that substantial future regulatory reform is needed to ensure that grid-tied solar PV owners are not unjustly subsidizing U.S. electric utilities," Pearce explains. "This study provides greater clarity to decision makers so they see solar PV is truly an economic benefit in the best interest of all utility customers."

Solar PV technology is now a profitable method to decarbonize the grid, but if catastrophic climate change is to be avoided, emissions from transportation and heating must also decarbonize, Pearce argues.

One approach to renewable heating is leveraging improvements in PV with heat pumps (HPs), and it turns out investing in PV+HP tech has a better rate of return than CDs or savings accounts.

To determine the potential for PV+HP systems in Michigan's Upper Peninsula, Pearce performed numerical simulations and economic analysis using the same loads and climate, but with local electricity and natural gas rates for Sault Ste. Marie, in both Canada and U.S. North American residents can profitably install residential PV+HP systems, earning up to 1.9% return in the U.S. and 2.7% in Canada, to provide for all of their electric and heating needs.

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On the road to invisible solar panels: How tomorrow's windows will generate electricity

 Five years after the Paris climate agreement, all eyes are on the world's progress on the road to a carbon-free future. A crucial part of this goal involves the energy transition from fossil fuels to renewable sources, such as sun, water, wind and wave energy. Among those, solar energy has always held the highest hope in the scientific community, as the most reliable and abundant energy source on Earth. In recent decades, solar cells have become cheaper, more efficient, and environment friendly. However, current solar cells tend to be opaque, which prevents their wider use and integration into everyday materials, constrained to being lined up on roofs and in remote solar farms.

But what if next-generation solar panels could be integrated to windows, buildings, or even mobile phone screens? That is the hope of Professor Joondong Kim from the Department of Electrical Engineering at Incheon National University, Korea. In a recent study published in Journal of Power Sources, he and his colleagues detail their latest invention: a fully transparent solar cell. "The unique features of transparent photovoltaic cells could have various applications in human technology," says Prof. Kim.

The idea of transparent solar cells is well known, but this novel application where scientists have been able to translate this idea into practice is a crucial new finding. At present, the materials making the solar cell opaque are the semiconductor layers, those responsible for capturing light and translating it into an electrical current. Hence, Prof. Kim and his colleagues looked at two potential semiconductor materials, identified by previous researchers for their desirable properties.

The first is titanium dioxide (TiO2), a well-known semiconductor already widely used to make solar cells. On top of its excellent electrical properties, TiO2 is also an environment-friendly and non-toxic material. This material absorbs UV light (a part of the light spectrum invisible to the naked eye) while letting through most of the visible light range. The second material investigated to make this junction was nickel oxide (NiO), another semiconductor known to have high optical transparency. As nickel is one of the mist abundant elements on Earth, and its oxide can easily be manufactured at low industrial temperatures, NiO is also a great material to make eco-friendly cells.

The solar cell prepared by the researchers was composed of a glass substrate and a metal oxide electrode, on top of which they deposited thin layers of the semiconductors (TiO2 first, then NiO) and a final coating of silver nanowires, acting as the other electrode in the cell. They ran several tests to evaluate the device's absorbance and transmittance of light, as well as its effectiveness as a solar cell.

Their findings were encouraging; with a power conversion efficiency of 2.1%, the cell's performance was quite good, given that it targets only a small part of the light spectrum. The cell was also highly responsive and worked in low light conditions. Furthermore, more than 57% of visible light was transmitted through the cell's layers, giving the cell this transparent aspect. In the final part of their experiment, the researchers demonstrated how their device could be used to power a small motor. "While this innovative solar cell is still very much in its infancy, our results strongly suggest that further improvement is possible for transparent photovoltaics by optimizing the cell's optical and electrical properties," suggests Prof. Kim.

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New solar panel design could lead to wider use of renewable energy

 Designing solar panels in checkerboard lines increases their ability to absorb light by 125 per cent, a new study says.

Researchers say the breakthrough could lead to the production of thinner, lighter and more flexible solar panels that could be used to power more homes and be used in a wider range of products.

The study -- led by researchers from the University of York and conducted in partnership with NOVA University of Lisbon (CENIMAT-i3N) -- investigated how different surface designs impacted on the absorption of sunlight in solar cells, which put together form solar panels.

Scientists found that the checkerboard design improved diffraction, which enhanced the probability of light being absorbed which is then used to create electricity.

The renewable energy sector is constantly looking for new ways to boost the light absorption of solar cells in lightweight materials that can be used in products from roof tiles to boat sails and camping equipment.

Solar grade silicon -- used to create solar cells -- is very energy intensive to produce, so creating slimmer cells and changing the surface design would make them cheaper and more environmentally friendly.

Dr Christian Schuster from the Department of Physics said: "We found a simple trick for boosting the absorption of slim solar cells. Our investigations show that our idea actually rivals the absorption enhancement of more sophisticated designs -- while also absorbing more light deep in the plane and less light near the surface structure itself.

"Our design rule meets all relevant aspects of light-trapping for solar cells, clearing the way for simple, practical, and yet outstanding diffractive structures, with a potential impact beyond photonic applications.

"This design offers potential to further integrate solar cells into thinner, flexible materials and therefore create more opportunity to use solar power in more products."

The study suggests the design principle could impact not only in the solar cell or LED sector but also in applications such as acoustic noise shields, wind break panels, anti-skid surfaces, biosensing applications and atomic cooling.

Dr Schuster added: "In principle, we would deploy ten times more solar power with the same amount of absorber material: ten times thinner solar cells could enable a rapid expansion of photovoltaics, increase solar electricity production, and greatly reduce our carbon footprint.

"In fact, as refining the silicon raw material is such an energy-intensive process, ten times thinner silicon cells would not only reduce the need for refineries but also cost less, hence empowering our transition to a greener economy."

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