Assess solar + storage’s value in terms of facility resilience

solar power resilience

The National Renewable Energy Laboratory (NREL) updated its publicly available online solar+storage optimization tool, REopt Lite, which can be used to determine the sizing of resilient power technologies designed to support critical services. Recent disasters in places such as Puerto Rico, where widespread outages contributed to devastating loss of life, underscore how important it is to give building owners and emergency planners straightforward tools to evaluate how to make buildings more resilient with solar and battery storage.

“The updated version of REopt Lite marks a big step in the evolution of solar+storage analysis,” said Clean Energy Group Vice President Seth Mullendore. “It will help many of the organizations we work with every day – affordable housing developers, critical facilities managers, municipalities, and community groups – better understand the potential economic and resilience benefits that solar+storage could bring to their buildings, without having to rely solely on industry representatives and expensive consultants.”

Valuing resiliency

The majority of customer-sited solar+storage installations are designed to meet one of two goals: either to reduce electricity expenses or to increase energy resilience. Cost savings are a key concern for building owners and managers, which is why the economic benefits of solar+storage have made these projects increasingly popular for businesses, schools, nonprofits, and other entities facing significant demand-related charges on their electric bills.

In addition to reducing demand charges and time-of-use energy rates, solar+storage systems also deliver value by providing power to buildings when the grid goes down, whether by allowing a business to stay open or residents to shelter in place; or, in the case of facilities like medical clinics and emergency shelters, potentially preventing loss of life. The economic and social costs incurred due to increasingly more frequent and longer-duration power outages can be avoided with properly designed resilient solar+storage systems.

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With REopt Lite’s newly expanded functionality, users of the tool will be able to compare and contrast economic and resilience goals in a publicly available, easy-to to-use interface. By giving users the ability to assign and adjust a value for resilience benefits and view a side-by-side comparison between resilient system sizing and costs and a system designed to maximize savings, the new version of REopt Lite will help decision-makers identify potential cost gaps and balance what may at times be competing priorities.

“While we have historically measured the benefits of solar+storage in terms of cost and energy savings, resilience is emerging as another critical value,” said Kate Anderson, senior engineer and manager of the Engineering and Modeling Group at NREL. “REopt Lite’s new expanded resilience capability allows users to compare systems designed for maximum economic benefit to systems designed to sustain critical loads during grid outages, and assess the cost-benefit tradeoffs of different options. It also allows users to consider how varying microgrid upgrade costs and avoided outage costs may impact the economics of their system. We hope this will be a useful tool for decision-makers who are considering resilient solar+storage systems.”

Clean Energy Group is also offering free REopt Lite training sessions and analysis support to nonprofit organizations interested in using the tool to evaluate solar+storage projects that would benefit disadvantaged communities. These enhanced resilient design capabilities were developed in collaboration with Clean Energy Group through its Resilient Power Project and supported with funding from The Kresge Foundation and the Department of Energy’s Federal Energy Management Program and Solar Energy Technologies Office.

— Solar Builder magazine

Install Inequality: Nearly half of U.S. residential rooftop solar potential is currently out of reach

poor apartment buidlings

One of the largest barriers to solar adoption on a wide scale is the wealth gap, and it will require more problem-solving than a mandate to overcome it. A new report released by the National Renewable Energy Laboratory (NREL) shows that nearly half (42 percent) of all the United States’ residential rooftop solar technical potential (see pg. 15 for definition) is on the dwellings of low-to-moderate income (LMI) households, representing 330 GW of potential solar capacity — a number the researchers admitted was much higher than they expected at the outset.

“Understanding the potential size of the LMI market in detail offers new insights and opportunities to serve these communities,” said David Mooney, executive director, Institutional Planning, Integration and Development for NREL. “The potential electric bill savings from the adoption of rooftop solar would have a greater material impact on low-income households compared to their high-income counterparts.”

Although residential solar adoption has increased over the past decade, adoption among LMI households (defined as 80 percent or less of the Area Median Income) and affordable housing providers continues to lag.

The obvious issue here is the lack of capital, cash or credit for such an investment among LMI customers, but the NREL report also shows how solar financing strategies and the long-time inability to penetrate the multifamily sector specifically leaves behind the LMI segment.

Segment spotlight

Across the entire U.S., all income levels mushed together, the rooftop potential of residential single-family is much higher than multifamily — 68 percent versus 32 percent — but the high-income category is doing the heavy lifting to get that outcome. Splitting this chunk another way, into owner-occupied and renter-occupied, reveals where the LMI segment diverges from higher income categories. After doing this, the largest modality of potential is single-family owner-occupied (SFOO) at 177 TWh, but is closely followed by multifamily renter-occupied, with 140 TWh of potential.

Said another way, although deployment of rooftop has been concentrated on SFOO, about 60 percent of potential is in the other three combinations. This means over half of LMI technical potential for solar is in underrepresented housing combinations, like single-family renter-occupied and multifamily buildings, which means the barriers of solar deployment in these categories is really an additional a barrier for an LMI individual’s access to solar.

The study shows the quantity of residential technical potential is highly concentrated in urban and densely populated areas with more building stock, which makes sense intuitively. But many of these areas with high levels of potential already have significant levels of residential deployment, like California, Maryland, Massachusetts and New Jersey. Several states cited to have high potential with low levels of deployment were Illinois, Ohio, Florida, Pennsylvania and Texas.

RELATED: Solar for All: How to incentivize community solar projects to benefit low-, middle-income customers

At a high level, patterns of LMI potential mirror overall income trends. LMI solar potential percentages are greatest in the lower income communities and higher in rural counties. Spatial trends in the potential for solar to offset LMI consumption most strongly reflected regional variation in per-capita electricity consumed, primarily due to which fuels are used for building heating and cooling loads.

Impact on the future

The Solar Energy Technology Office of the U.S. Department of Energy updated the cost targets of 5 cents per KWh for residential solar by 2030. Using these costs and making forecasts, NREL estimated that achieving them would result in 970 GW of PV capacity 2050, or 33 percent of the generation mix. But can we hit that target leaving the LMI solar rooftop segment in the dust?

Using this data set, NREL examined the feasibility of rooftop offsetting that much in each county in the United States given the technical potential.

Offsetting 33 percent of LMI household electrical consumption (“offset target”) with rooftop solar is technically feasible on a national scale when only considering households in SFOO buildings, although to do so requires buildout on essentially all SFOO buildings — an impractical and unforgiving market challenge. In contrast, on a technical basis, there is more than sufficient roof space to meet the 33 percent offset target when including single-family rental-occupied (SFRO), multifamily owner-occupied (MFOO), and multifamily renter-occupied (MFRO) buildings.

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Using only the popular SFOO segment, 60 percent of counties would have potential to meet 33 percent of LMI electricity consumption. Said in reverse to belabor the point: 40 percent of U.S. counties have insufficient rooftop potential to offset 33 percent of LMI electric consumption in just single-family, owner-occupied. The current path to 2050 will not achieve the target generational mix. But including rental and multifamily there is “more than sufficient rooftop space to meet the 33 percent target.” NREL believes 99 percent of counties would meet the 33 percent threshold in just residential rooftop capacity.

Reaching this potential requires deployment models other than those commonly found today. Such models would need to ensure the rental owner had incentive to install solar on their own buildings, like bundling utility expenses with rent payment as a means of passing the costs and savings along to tenants. These models would also need to address diverging requirements and energy burdens of owners and tenants in multifamily. Here’s a great example of one new concept in our Attack the Tariff Series.

It takes a village

The NREL study shows that most LMI electricity consumption (especially with the LMI segment requiring a lower threshold to offset onsite) can be met with rooftop solar, but again 100 percent deployment is unlikely. To get to these high levels of penetration would require deployment on non-traditional building types.

NREL posits one way to increase LMI access to solar is through the vast network of nonprofits that connect to this segment. What if PV systems on government buildings, public housing, schools, shelters and places of worship were intentionally oversized to benefit their LMI communities with the excess generation? The NREL team estimated this opportunity for three cities — Chicago, San Bernardino-Riverside and Washington, D.C. — based on building size, average electric consumption and solar technical potential for outsizing each of those buildings segments. They found enough gross generation potential on those selected building types to meet between 10 to 30 percent of LMI consumption, but only about 1.5 to 9 percent after accounting for the onsite consumption.

Schools have the greatest opportunity to export to the community because of their typically large flat roofs and lower levels of electrical consumption in the summer when irradiance is highest. Places of worship came next because of low levels of consumption year round and moderately favorable roofs. Public housing sites and homeless shelters likely have insufficient rooftop areas to offset 100 percent on site consumption.

National nonprofits GRID Alternatives and Vote Solar updated their Low-Income Solar Policy Guide which explains some proven strategies for expanding solar access being used in states and cities across the country. In multifamily, for example, successful strategies include:

  • Net metering or other incentives to ensure full value of solar
  • Financial incentives to reduce upfront costs, overcome split incentives scenarios and ensure benefits reach tenants
  • Measures to reduce barriers to financing
  • Technical assistance to affordable housing providers, participating contractors and service providers
  • Pairing solar with energy efficiency programs
  • Facilitating waivers from regulatory utility and rent allowance requirements to maximize tenant benefit. (Under a utility allowance formula, a resident’s rent plus utilities equate to a certain percentage of the resident’s income. When a resident’s utility bills decrease, as can happen with solar, the rent portion will automatically increase under the formula)
  • Integrating job training and employment opportunities in the solar energy and energy efficiency sectors of the economy

California and Washington D.C. are the only examples of active programs in place specifically targeted to deploying solar for multifamily affordable housing. California has an incentive program dedicated to affordable housing multifamily, with requirement that half of energy generated on site be used to serve tenants loads. Other states have included incentives for multifamily solar adoption in their broader solar programs. In Colorado, the Denver Housing Authority’s 2-MW LMI solar garden model has shown a scalable model through utility partnerships for offsite generation. In Massachusetts, the SREC II program has awarded a higher price for solar renewable energy credits that are generated by projects that are considered community shared solar projects or that serve affordable housing. When the SREC II program ends, it will be replaced by the new Solar Massachusetts Renewable Target (SMART) program that will award a higher incentive for solar projects that serve affordable housing.

Final thought

It is a big opportunity, though there are clear market and economic barriers. Ignoring this segment and these potential barriers could significantly limit the long-term size of the rooftop solar market.

“Solar can have tremendous benefits for low-income communities in addition to diversifying and de-carbonizing our national energy mix,” said Tim Sears, chief operating officer for GRID Alternatives. “We hope this research will give more states the data they need to develop effective low-income solar programs and build a more equitable clean energy economy.”

The report is accompanied by a web application (maps.nrel.gov/solarforall) that enables users to assess solar technical potential for their communities. This tool makes it possible to visualize the amount of low-income solar potential in a specific neighborhood, for example, while also enabling identification of neighborhoods with both high solar potential and high electricity costs where rooftop solar could provide cost-effective electricity generation. Check it out and see if it sparks any new ideas. The potential is there, it just needs to be tapped.


Methodology

Using LIDAR data from Homeland Security to examine 23 percent of U.S. building stock, the researchers inferred the solar potential of building footprints and unshaded roof area, azimuth, tilt and roof plane. Age cannot be detected so was not considered. This was then matched with socio-economic demographic data from the Census and building stock data to understand total usable rooftop area for LMI households. A statistical model was then created to make estimates of areas not covered by the available LIDAR data (stuff like household counts, number of suitable buildings, etc.) They then dove into three representative regions to infer more in-depth information.

— Solar Builder magazine

Solar wealth gap: New reports show size of low-income solar market, solutions to boost installs

solar low income incentives

Something that’s not talked about enough: one of the largest barriers to solar adoption and a game-changing move into a distributed generation future is the wealth gap. A new report released by the National Renewable Energy Laboratory (NREL) shows that nearly half of all the United States’ residential rooftop solar technical potential is on the dwellings of low-to-moderate income (LMI) households, representing 320 GW of potential solar capacity. Although residential solar adoption has increased over the past decade, adoption among LMI households (defined as 80% or less of the Area Median Income) and affordable housing providers continues to lag.

Given that solar lowers the cost of electricity, and that electricity is a public utility, solutions to bridge this gap and make lower cost electricity available to homeowners that need it most should be a top priority.

The issues

The Institute for Energy and the Environment (IEE) at Vermont Law School released “Low-Income Solar Ownership in Vermont: Overcoming Barriers to Equitable Access,” a report prepared for the Vermont Low Income Trust for Electricity (VLITE), Inc. The report examines how to give low-income customers equitable access to the benefits of distributed solar as the renewable energy resource becomes an increasingly cost-effective option to meet clean energy goals. The authors examine four categories of barriers: upfront capital costs; unsuitable housing; lack of information, time and trust; and existing incentives.

“Vermonters should have equal access to the benefits of solar and it is clear in looking at both federal and state policy that is not the case, particularly when it comes to access to solar ownership among low-income Vermonters,” said IEE Director Kevin B. Jones. “In order for our state and nation to meet our clean energy and climate goals, in an equitable fashion, we need both our legislators and our regulators to help level the playing field. There is much work to do to remove the barriers to low-income solar ownership.”

RELATED: Solar for All: How to incentivize community solar projects to benefit low-, middle-income customers

“It is particularly difficult for any Vermonter, particularly low-income Vermonters, to make the numbers work and truly purchase net-metered solar with the punitive $0.06/kWh REC [renewable energy certificate] adjusters put in place by the Vermont Public Utility Commission in opposition to what many Vermonters requested,” Jones said. “If the commission does not change this shortsighted, punitive policy, then the legislature should.”
According to Energy Fellow for Climate Justice Christa Shute JD’13, in addition to environmental benefits, solar is about stabilizing energy costs over the next 40 years.

“Increasing access to net-metering for low-income Vermonters is an equity issue that deserves attention,” Shute said. “This Vermont Law School report on increasing access to low-income solar ownership highlights challenges and proffers potential solutions. There are answers if we consider the problem from the perspective of those facing the challenges. I have faith that our state can come together and be a leader to find energy solutions that work for our most vulnerable.”

Solutions?

To inform the report, the Energy Clinic at the IEE explored how Vermont’s low-income residents are participating in the solar net-metering program, identified challenges faced in procuring solar energy, and developed policy proposals that will help lower barriers to and encourage low-income customers’ participation in these programs. Researchers interviewed local financial institutions, community action agencies, affordable-housing developers, and others involved in the industry. They also researched what other states and regions are doing to promote diverse solar ownership opportunities.

Proposed solutions consist of improved incentives, financing and education and training—all with an eye toward long-term policy. Solution highlights include:

1. Incentives

  • Create low-income specific adders to net-metering projects.
  • Reversal or modification of harmful 2017 changes to net-metering, including the punitive REC adjuster.

2. Financing

  • Legislative mandate for the Public Utility Commission and utility implementation of an on-bill tariff program that lends to the meter instead of the person. This addresses three primary barriers: the split incentive in rental homes, access to financing, and an aversion to risking additional debt.
  • Support existing financing programs with increased access to loan guarantees and funding sources.

3. Informing

  • Collaboration with community partners, utilities and providers is necessary to create a successful program that is promoted statewide.
  • Identify and inform targeted demographic based on volunteer answer to one question on state tax return.
    Motivate citizens to inform neighbors on ways to save money and stay warm.

“Vermont has an opportunity to advance its energy and climate goals, strengthen the economy, and assist those with the highest energy burden,” Jones said. “We can bring the benefits of solar ownership to a larger portion of the population by creating market-specific incentives, leveraging that investment through financing, and informing them of opportunities.”

— Solar Builder magazine

NREL update: The puzzle of scaling perovskite solar cells (and possible solutions)

perovskite solar cell

As perovskite solar cells set efficiency records and the nascent technology becomes more stable, another major challenge remains: the issue of scalability, according to researchers at the Department of Energy’s National Renewable Energy Laboratory (NREL).

“It is scalable,” said Kai Zhu, a materials science researcher at NREL. “We just need to demonstrate efficiency and yield at a large-scale to move the technology beyond the laboratory.”

Lead author of a new Nature Reviews Materials paper titled, “Scalable Fabrication of Perovskite Solar Cells,” Zhu and his colleagues at NREL reviewed efforts to move perovskites from the laboratory to the rooftop. Zhen Li, Talysa Klein, Dong Hoe Kim, Mengjin Yang, Joseph Berry, and Maikel van Hest are the co-authors.

Most solar panels on the market today are made of silicon, but perovskite solar cells have the potential to accelerate the growth of photovoltaic (PV) manufacturing in the United States because they’re much cheaper to make and have shown performance potential in the lab. Perovskites have achieved record efficiency levels faster than any other solar cell technology with the current record—certified last summer—now standing at 22.7 percent. But efficiency in a perovskite solar cell declines as the cell and module area increases. A combination of factors is attributed to the decline, including the non-uniform coating of chemicals in the cell. Also, when any type of solar cells are joined together to create modules, inactive zones form between cells where sunlight isn’t converted to electricity, leading to efficiency declines.

RELATED: Module Evolution: What big-time PV improvements will boost panel efficiency?

To make a perovskite solar cell in the laboratory, scientists deposit chemicals onto a substrate. The perovskite material forms as the chemicals crystallize. The most commonly used deposition method in the laboratory, called spin coating, produces devices with the highest efficiency, but the process wastes more than 90 percent of the chemicals used, the so-called perovskite ink. Spin coating also works best on cells smaller than four square inches, but there isn’t an easy way to enable this technology to be used on a larger surface.

The NREL researchers examined potential scalable deposition methods, including:

• Blade coating, which uses a blade to spread the chemical solution on substrates to form wet thin films. The process can be adapted for roll-to-roll manufacturing, with flexible substrates moving on a roller beneath a stationary blade similar to how newspapers are printed. Blade coating wastes less of the ink than spin coating.

• Slot-die coating, which relies on a reservoir to supply the precursor ink in order to apply ink over the substrate. The process hasn’t been as well explored as other methods and so far has demonstrated lower efficiency than blade coating. But the reproducibility of slot-die coating is better than blade coating when the ink is well-developed, so this is more applicable for roll-to-roll manufacturing.

• Ink-jet printing, which uses a small nozzle to disperse the precursor ink. The process has been used to make small-scale solar cells, but whether it is suitable for the high-volume, large-area production will depend on the printing speed and device structure.

Other methods exist, such as electro-deposition, but there haven’t been any reports of that being used to make direct deposition of halide perovskites in perovskite solar cells.

Despite numerous challenges, impressive progress is being made toward scaling up production of these solar cells, the NREL researchers noted in the paper. The new paper outlined research that needs to be addressed to scale-up the technology. One area in particular that needs more attention is the ideal architecture of a perovskite solar module.

Several studies have estimated perovskite solar cells could generate electricity at a lower cost than other photovoltaic technologies, although those figures are based on hypothetical research. But one conclusion that can be drawn from the studies is that the highest input costs for perovskite modules will come from substrates and electrode materials, which points to a range of opportunities for innovation in these areas.

— Solar Builder magazine

NREL promotes new solar tool to accurately calculate PV module degradation rates

How long a product can be expected to perform at a high level is a fundamental indication of quality and durability. In the solar industry, accurately predicting the longevity of photovoltaic (PV) panels is essential to increase energy production, lower costs, and raise investor and consumer confidence. A new software package developed by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and industry partners SunPower and kWh Analytics is making the measurement of PV system expected lifetime performance more reliable, consistent and accurate.

RdTools

RdTools results show time-series data along with a year-on-year degradation distribution. The same system is analyzed with the clear-sky method (a), and sensor-based method with a poorly maintained sensor (b). In this case, high reported degradation is likely caused by sensor drift, rather than a degrading PV module

RdTools combines best practices with years of NREL degradation research to deliver new methodologies that change how solar field production data is evaluated. The software package makes it possible to accurately evaluate PV systems faster, despite common challenges with performance data.

“There’s a high level of interest in this software because it provides user-friendly, accurate, and objective assessments that can help owners make sense of their data,” said Dirk Jordan, engineer and solar PV researcher at NREL. “We spent years building consensus in the industry around a common set of analytical rules. Now PV stakeholders can learn much more about the performance of their technology and improve decision-making on multiple fronts.”

How it works

PV module and system degradation have been historically difficult to assess in the PV industry. Field performance can be impacted by many confounding variables including ambient weather conditions, seasonal changes, sensor drift, and soiling, to name a few. Extracting system degradation rates previously required years of production data, high accuracy instrumentation, and the presence of staff scientists to conduct the evaluation.

RELATED: How OMRON reduces solar module PID potential through its inverter topology 

The RdTools software package solves these problems by providing a robust and validated software toolkit for calculating and analyzing PV system performance and degradation over time. The tool can deliver valuable insights for manufacturers, engineers, investors and owners who have a stake in system performance, such as identifying under-performing sub-arrays, and quantifying system performance relative to neighboring systems.

For co-developer SunPower, the results of its own data analysis were compelling. “The RdTools method was used to analyze energy generation from 264 PV systems at locations across the globe, revealing that degradation rates were slower than expected,” said Greg Kimball, a senior performance engineer at SunPower. “The result prompted improvements to and extension of our warranty coverage to customers.”

According to Adam Shinn, a data scientist for co-developer kWh Analytics, RdTools is valuable because of the information it provides to the solar investors with whom they work. “As more and more solar is deployed, there is an ever-increasing amount of PV performance data available to analyze,” Shinn said. “For solar investors who seek to understand the long-term financial risks of their energy-producing assets, analysis RdTools will help them quantify PV durability.”

RdTools was led by a NREL team of researchers: Michael Deceglie, Chris Deline, Dirk Jordan, and Ambarish Nag and funded by the U.S. Department of Energy Solar Energy Technologies Office. The software is actively being developed as a set of open-source Python scripts and usage examples on GitHub and is publicly available to interested users who can access, download, and customize the software.

— Solar Builder magazine