Will floating PV start trending? NREL estimates its potential in the U.S.

NREL floating PV research

Floating PV being installed in Walden, Colorado. (Photo by Dennnis Schroeder/NREL)

National Renewable Energy Laboratory (NREL) researchers estimate that installing floating solar photovoltaics on the more than 24,000 man-made U.S. reservoirs could generate about 10 percent of the nation’s annual electricity production. Their findings, published in the journal Environmental Science & Technology, reveal for the first time the potential for floating PV to produce electricity in the United States.

While the United States was the first to demonstrate floating PV panels — with the first installation occurring 10 years ago on pontoons on an irrigation pond in Napa Valley, California — the idea has not received widespread national acceptance. The U.S. focus has primarily been on installing large-scale, ground-mounted solar panels, and only had seven floating PV sites as of December 2017. Floating PV sites are being deployed more overseas, however, with more than 100 sites as of the end of last year. Japan, for example, is home to 56 of the 70 largest floating PV installations.

“In the United States, it’s been a niche application; where in other places, it’s really been a necessity,” said Jordan Macknick, the lead energy-water-land analyst for NREL and principal investigator of the project that produced the paper “Floating PV: Assessing the Technical Potential of Photovoltaic Systems on Man-Made Water Bodies in the Continental U.S.” “We’re expecting it to take off in the United States, especially in areas that are land-constrained and where there’s a major conflict between solar encroaching on farmland.”
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Potential and benefits

Macknick and his NREL co-authors, Robert Spencer, Alexandra Aznar, Adam Warren, and Matthew Reese, estimate about 2.1 million hectares of land could be saved if solar panels were installed on bodies of water instead of on the ground. The use of floating PV comes with additional benefits, including reduced water evaporation and algae growth.

Spencer, lead author of the paper, added that in some cases benefits could be greater than those documented in the paper, but that the team used “strict assumptions that would give us a very conservative estimate of the total potential generation and benefits.”

The NREL team also found that operating floating PV alongside hydroelectric facilities yields increased energy output and cost savings because of existing transmission infrastructure.

“Floating solar is a new industry enabled by the rapid drop in the price of solar PV modules,” said Warren, director of NREL’s Integrated Applications Center. “The cost of acquiring and developing land is becoming a larger part of the cost of a solar project. In some places, like islands, the price of land is quite high, and we are seeing a rapid adoption of floating solar.”

— Solar Builder magazine

NREL gets funding to develop low-cost thermal energy storage

NREL thermal energy

The U.S. Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) has been awarded nearly $2.8 million in funding to develop a system for grid electricity storage and power generation that includes a high-temperature charging device, low-cost thermal energy storage modules, a high-performance heat exchanger, and a closed-loop Brayton cycle turbine.

As NREL Principal Investigator Zhiwen Ma explains: “When electric power is cheapest, electric heaters will ‘charge’ the storage modules by heating stable, inexpensive solid particles to more than 1,100 degrees Celsius. And when it’s time to discharge this energy, the hot particles will move through a heat exchanger to heat a working fluid that drives a high-efficiency closed-Brayton combined cycle attached to an electric generator.”

NREL received this competitive award from ARPA-E’s Duration Addition to electricitY Storage (DAYS) program, in which teams will develop energy storage systems to provide reliable, affordable power to the electric grid. NREL’s proposed system will focus on scalability. For example, a 55-gigawatt-hour thermal storage system is enough to power 50,000 homes for 100 hours during an outage. This scalability would not only support the DAYS goals but could also help enhance grid resilience and promote the growth of domestic energy sources.

The project team includes scientists, engineers, and professors from NREL; GE Global Research; Greenway Energy; Allied Mineral Products, Inc.; Purdue University; Colorado School of Mines; and Power Engineers. This NREL-led team will develop the components for the Long-Duration Energy Storage (LDES) system and will verify that it meets specified cost and performance targets for demonstration and commercialization.

— Solar Builder magazine

NREL argues for value of ‘watts per kilogram’ in emerging thin-film, flexible solar technology

NREL lightweight CIGS

This lightweight CIGS photovoltaic cell, on flexible stainless steel, was made by Matthew Reese and his team at NREL. Photo by Dennis Schroeder / NREL

Rigid silicon solar panels dominate the utility and residential markets, but opportunity exists for thin-film photovoltaic and emerging technologies notable for being lightweight and flexible, according to scientists at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL).

Thin films such as cadmium telluride (CdTe) and copper indium gallium selenide (CIGS), along with perovskites and other new technologies, could be ideal for generating the electricity needed for unmanned drones, portable chargers, and building facades. The opportunities and challenges inherent in widespread adoption of these ideas appear in the new Nature Energy paper, “Increasing Markets and Decreasing Package Weight for High Specific Power Photovoltaics.

“We explore the limits behind power-to-weight ratios and how this can generate value for emerging players in photovoltaics to enable them to reach gigawatt scale without having to directly compete with silicon solar panels,” said Matthew Reese, an NREL researcher and lead author of the paper. The paper was co-authored by Stephen Glynn, Michael Kempe, Deborah McGott, Matthew Dabney, Teresa Barnes, Samuel Booth, David Feldman, and Nancy Haegel, all from NREL.

The market opportunity

Silicon panels constitute 95 percent of the global solar market, generating electricity for utilities, residences, and businesses, but the researchers identified applications that must consider value propositions beyond the standard value triad of cost, efficiency, and reliability used for conventional photovoltaic (PV) panels. Flexibility and portability will be important factors, with the performance of the technology quantified in terms of watts per kilogram.

The researchers identified three high-value markets, each with a potential to cumulatively generate a gigawatt (GW) of electricity—at a price above $1 a watt—over the next 10 years:

Aerospace and unmanned aerial vehicles – Powering satellites is driven by extremely high launch costs; whereas, there is an increasing desire to keep drones aloft for very long periods. For both of these applications, limited space makes efficiency and weight critical and cost secondary. A key player in this market is III-V PV, but while highly efficient it’s also too expensive for many applications.

Portable charging – Making it easy for one person to install or move a portable charger is driving the need for PV technology that’s efficient and flexible. Finding the correct balance between those requirements and cost could put millions of units into service by the military, disaster relief workers, and recreational users.

Ground transportation – The integration of PV in electric vehicles will compete with electricity coming from the grid, but the addition could extend the driving range. The PV would have to use smaller panels and be flexible enough to conform the contours of the roof.

The researchers identified these markets as smaller but significant and ones that will pay a premium for the added value of the technology being lightweight to support initial, low-scale production. As production increases, lower costs will follow.

The NREL team determined the lower limit for a lightweight PV device is between 300 and 500 grams per square meter. Below that would reduce reliability, durability, and safety. A lightweight module on the lower side of that range could generate more than a kilowatt of electricity from something that weighs as little as a six pack of soda. Conventional modules, even without the additional weight from the mounting equipment, might require 150–200 pounds to generate this much power.

— Solar Builder magazine

Shave and a rate cut: How solar + storage solutions are shaving peaks, saving big bucks

shave and a rate cut

Shaving the peaks off commercial and industrial (C&I) electric bills is the top revenue stream for energy storage systems, and given the trend in increasing utility charges for time-of-use consumption, peak shaving can pay for a system in as little as three years, system providers say.

Just how high the peaks need to be in order to justify the investment in an energy storage system varies with geography and jurisdiction, but in general, demand charges of $15 to $20/kW or more are clear candidates, says John Merritt, the director of applications engineering at Ideal Power.

“The vast majority of converters we sold for storage systems in the past year went to California, with eight out of 10 used in applications for peak shaving,” Merritt says. “With the California incentives and the federal tax break, C&I customers can get a payback in as little as three years and in other cases in four or five years.”

A $15/kW demand charge threshold for economic feasibility also necessitates a 50-kW monthly usage level within the peak charge range, suggests Ellen Howe, VP of marketing and corporate development at JLM Energy, based in Rocklin, Calif. Her colleague, Nate Newsom, VP of enterprise sales, says, “Commercial entities that spend 3 percent or more of their monthly budget on electricity and/or experience 40 percent to 50 percent [higher than normal] demand charges typically are a good fit for energy storage.”

The C&I market is virtually untapped

Analyzing the C&I market for energy storage usefulness, the National Renewable Energy Laboratory in Golden, Colo., started with the assumption that demand charges of $15/kW or higher typically result in favorable economics for energy storage projects. Then, counting rooftops, NREL determined that “Of the nearly 18 million commercial utility customers in the United States, almost 5 million of them are exposed to, or could be exposed to demand charges of $15/kW or higher that would indicate cost-effective opportunities for energy storage.”

While not every potential C&I customer will bite the bullet for a stand-alone energy storage system, aggregation through community solar projects, or virtual power plants (VPP), is increasingly an opportunity.

Tesla is among the storage providers that is now active in community solar, with a high-profile October rollout of its commercial-scale Powerpack system at Puerto Rico’s Hospital del Niño, a children’s hospital in San Juan. As of April, Tesla had provided commercial Powerpacks and residential-scale Powerwalls to over 600 locations, with the count rising daily. The company has been quoted stating a goal of providing up to 40 percent of the island’s power storage needs via community solar system build-outs.

One new provider of VPP services is solar converter maker SolarEdge Technologies, which in May announced a solution for grid services and virtual power plants, thanks to its recent acquisition of Gamatronic Electronic Industries. The solution includes grid services of aggregative control and data reporting that enable the pooling of PV and storage in the cloud for the creation of VPPs.

demand charge example

Fig 1. Example of the steep savings achieved just through shaving peak demand.

Storage + trackers (plus pumps, plus…)

A relatively new storage configuration for C&I customers is the use of storage with solar trackers, like the 1.1-MW project at the Maharishi University of Management in Fairfield, Iowa. This project will use the NEXTracker NX Flow integrated solar-plus-storage system, in combination with an Ideal Power SunDial Plus converter and a Vanadium flow battery. The project is NEXTracker’s first large-scale installation of the NX Flow solution.

Another budding C&I application for storage is with water authorities, which can typically generate energy from solar for less than it costs to pump water uphill for a discharge to a generator turbine. The San Diego County Water Authority, for example, won $1 million from the California Public Utilities Commission to install intelligent energy storage that will tap the energy from solar panels already installed at the SDWA’s Twin Oaks Valley Water Treatment Plant.

The SDWA energy storage project, being operated by Santa Clara-based ENGIE, is expected to save an estimated $100,000 per year by storing low-cost power for later use during high-demand periods for peak shaving. The storage will help the plant cope with its highest energy use period, during peak afternoon hours. ENGIE acquired majority control of energy storage management software leader Green Charge in 2016.

RELATED: Solar + Sharing: Connect groups of homeowners, renters via one solar + storage network 

The backbone of storage: data crunching

It is tricky enough to coordinate a community solar or VPP operation, providing power on demand to participants and storing the rest until the utility calls for help. But knowing precisely what times, and advising customers as to when it is most optimal to use grid energy, or substitute with storage, is another matter, thanks to U.S. utility rate mayhem.

NREL notes that “There are almost 3,500 electricity providers in the United States, and each one has their own set of tariff sheets, rate structures and pathways for compensating non-utility-owned energy generation.” Add a dynamic dimension of rate evolution arising from rate cases, and it becomes a bit difficult to keep up with when it is most economic to use how much power.

Here the data crunchers enter the fray. Stem, for example, recently launched its Athena analysis product, which uses artificial intelligence to learn, predict and optimize energy in real time. Athena collects data at a rate of 400 megabytes per minute to continually fine-tune its algorithms. The system also has learned from operating systems for over 5 million hours, from processing nearly 200 million data intervals and from running over 35 million project simulations. As a result, the system decides and tells the battery when to store and to discharge power, responds to demand response opportunities and methodically shaves peak utility rates.

Stem has working relationships with eight utilities thus far and expects that number to grow significantly as the company helps shave peak demand, which is costly on both sides of the transformer. Stem has been dispatching batteries into California’s wholesale energy markets where it responded to more than 600 calls from state grid operator CAISO last year, according to the company.

On top of new legislative challenges, the industry has faced high and growing customer acquisition costs over the past few years. According to GTM Research, customer acquisition costs on average now represent a disproportionate 17 percent of the total system cost. This is where a new service from Urjanet, a global leader in utility data aggregation, comes into play. Its new Utility Data for Solar, a data-as-a-service solution that provides on-demand access to residential and commercial energy usage, cost and location data from more than 900 electric utilities in over 15 countries. Urjanet Utility Data for Solar enables a more cost-effective, customized approach to selling solar systems that allows vendors to effectively focus on the needs, requirements and situation of each residential or commercial buyer.

map of demand charges

Fig 2. Here’s where the harshest demand charges are across the U.S., courtesy of NREL.

Storage as a service emerges

When solar leasing became popular, the common knowledge about actual savings from such arrangements was about 15 percent of a residential utility bill, if that. With C&I customers, the savings opportunities are as high as the sky or at least whatever the utility bill looks like pre-storage.

JLM Energy is one of the latest energy storage solution providers that offers financing for energy storage customers through a $25 million project financing fund. The company uses a lease structure to achieve shared savings on a monthly basis for 20 years, with no upfront cost. JLM owns, maintains and guarantees system performance.

Stem has long been financing storage solutions, and now has a $500 million investment pool from which it can draw to finance a project, thanks to a host of private sector investors, including the Ontario Teachers’ Pension Plan.

Wall Street may not have climbed onto the PV wagon when the industry began to mature, but the storage peak-shaving proposition apparently seems as clear and understandable to such investors as the bottom line of the utility bill.

Charles W. Thurston is a freelance writer covering solar energy from Northern California.

— Solar Builder magazine

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