Background

I had an idea for a story around solar energy from the perspective of efficient allocation of resources from a land, labor, and capital perspective, and looking at the solar energy ecosystem from energy production to distribution to the customer. (The solar panel and facility supply chain and inputs will be the subject of another article). Charles Diep, Director of Engineering Services for SolarReserve, a utility-scale solar energy developer based in Santa Monica, Calif., and David Sims, Director of Renewable Energy Generation for NV Energy, which provides electricity service to the majority of Nevada, were available to contribute to such an article. This is our attempt at demonstrating the location data connections, influence, and requirements behind delivering solar-powered electricity on a utility scale.

NV Energy has 46 separate renewable energy projects in the production or development phase or in the process of securing necessary permits, including wind, hydro, geothermal, and solar. By 2025, utilities in the state of Nevada will be required to generate 25% of their energy from renewable sources. Currently, NV Energy is on track to reach a 15% renewable energy level by year’s end, most of which is currently generated by geothermal resources. However, with 12 solar projects in operation or under development in the state, NV Energy is seeing a large amount of new capacity from this resource, especially as the price of photovoltaic solar (PV) continues to fall. In addition, solar has become more attractive because PV provides greater siting flexibility, including interconnection at lower voltage transmission levels – where the complexity is not as great, where there are smaller site requirements, and where siting is closer to customer loads.

While NV Energy has explored development of its own facilities, it primarily relies on 3rd party developers to develop, construct and sell electricity to the utility under long-term power purchase agreements, or “PPAs.” SolarReserve is one of the 3rd party developers that NV Energy will depend on for energy production and is responsible for developing what will be NV Energy’s largest solar energy source, a 110-megawatt (MW) solar thermal facility with storage capability.

Solar 101

A variety of technologies exist for converting solar energy to electricity. Photovoltaic, or PV, converts photons from sunlight directly into electricity. Other technologies utilize reflected sunlight to generate heat, which is used to boil water or some other heat transfer fluid to drive a turbine generator. These technologies are typically referred to as “solar thermal,” or concentrating solar power (CSP).

While sunlight may appear to provide an unlimited source of energy, it runs afoul of such things as clouds and dust storms which can interrupt energy production. The reason why the SolarReserve facility will be the largest producer of solar energy is because SolarReserve’s plants do more than just collect solar energy through concentrating mirror units called heliostats. They also store the energy in molten salt so that it can be dispatched on demand, and into evening hours in the summer when the sun is down but demand is still very high. The SolarReserve molten salt concentrating solar thermal power technology provides the reliable solar power needed for a complex electric grid distribution system.

NV Energy and SolarReserve are both in the business of generating electricity, and NV Energy in transmitting and delivering electricity to its customers. SolarReserve relies solely on solar resources. In the case of NV Energy, it relies on a mix of traditional energy sources as well as renewable sources to ensure reliable and consistent supply to its cust-omers. In both instances a number of location-based variables enter the equation that determine a site’s feasibility.

Solar Site Selection

The Role of Renewal Credits

Nevada, with its excellent solar resources, provides excellent opportunities for stand-alone solar facilities in the 20-30 MW range and above. The renewable energy statutes in Nevada also provide some unique opportunities for PV. In Nevada, by statute, if a PV facility is developed on a customer premise and the customer consumes at least 50% of the power from PV facility, their eligible renewable credits are multiplied by 2.4. For example, if one kilowatt per hour of electricity generated earns one renewable credit for a typical renewable energy source, for PV it generates 2.4. This renewable credits incentive has resulted in the development of smaller facilities at some of NV Energy’s customers’ sites, interconnected at the lower voltage distribution level. A typical customer site profile would include a manufacturing facility, a military base, or corporate campus, including both ground-mounted and rooftop installations. Sims noted, however, that the development of such facilities is dependent on the resulting price of the energy and the renewable credits, and the utility’s need for such credits.

Producing Reliable Solar Energy

To engineers, collecting photons and moving the electrons to create electricity is pretty straightforward. Collecting solar energy through photovoltaic panels is one thing; generating consistent reliable energy to the grid is a whole other complex matter. “While storage of solar power for effective grid management is the key technical component of a utility-scale solar energy facility, there are many location-based variables that determine the efficiency of any particular facility,” said Charles Diep.

Once a site has been identified using requirements such as regional market demand, access to transmission lines (which includes distance to an interconnection point or substation), regulatory requirements and water availability, a performance analysis based on other location-based parameters ultimately determines the feasibility of a particular SolarReserve project. These parameters include: solar resource pattern, other atmospheric conditions, as well as site topography. Weather and atmospheric conditions include temperature, water, wind, humidity, air density, and visibility patterns.

Did you know that Spain has the highest number of solar facilities in the world? Why? Not because it has the greatest solar resources (lots of sunny days) but because it receives the most government subsidies for solar energy production. With the ability to store solar energy, even regions with mediocre solar resources can produce reliable electricity.

For solar thermal technologies, temperature, for example, has an impact on the steam cycle efficiency. The higher the temperature, the more cooling needed resulting in the increased loss of efficiency. Lower temperatures will cause additional heat loss and require additional insulation. Temp-erature also impacts other solar technologies such as the PV panel; as temperature rises, the output of the panel declines.

Temperature issues create a bit of a challenge as areas consisting of high solar resources are generally warmer. Every project deserves its own treatment and attention to these variables, which requires a temperature distribution profile to analyze time of day and year in order to design a system based on the site’s specific temperature range. For each proposed facility, a projection of the average solar resources over the next 20-25 years is required to determine impact on yield and to guarantee production over the life of a 25-year purchase agreement by the contracting utility.

The siting process starts with knowing where substations and transmissions lines are located. This process is similar to traditional power plants’ site selection process. The locations of natural gas and water lines are also important to siting traditional power plants. Water is particularly important to large power plants for process water and cooling purposes. Water requirements depend on the size of the plant for steam cycle water, the choice of cooling systems and other ancillary uses.

Due to the scarcity of water at sites that SolarReserve considers, it has proposed and been able to incorporate air cooling into the process. Other options that SolarReserve considers include use of local gray water and/or hybrid cooling. NV Energy also focuses on minimizing water use at its proposed facilities wherever possible.

Production to Distribution	Solar Power Production SolarReserve	Renewable Energy Generation NV Energy
	Charles Diep, Director of Engineering Services for SolarReserve, is responsible for providing solar resource assessments for the company, and for performance analysis to determine electrical power yield per location. He works with developers, the finance department once a project is ready for financing, and supports contracting and project construction.	David Sims, Director of Renewable Energy Generation, is responsible for developing renewable energy projects at NV Energy and is primarily focused on solar projects.
End Product	Power to the grid from solar resources	Power to the customer (residential, business, or government) from a variety of renewable energy sources.
Cost	Up-front capital cost to build the plant but because there are no fuel costs, costs remain relatively constant once the plant is built depending on environmental factors that impact the efficiency of the operations.	The more remotely located the facility is from the substation and transmission lines, the more complex and costly it becomes to transmit the electricity. There are costs associated with adding load to transmission lines and connecting at different transmission levels.
Location Data	Topology, flood plains, BLM lands and development zones, water data, transmission lines, substations, solar resource and other weather data, and sensor data (GPS chips in solar collector, for example).	Associated land uses, zoning, roads, transmission lines, water pipelines and available water resources, easements and rights of way. Location of generation assets and distribution network are needed to ensure the balanced and stable delivery of sustainable power to customers.
Challenges	Long development and permitting process is on average a 2-3 year process, with different requirements per state.	Approximately 90% of the state of Nevada is controlled by various agencies of the federal government, typically prompting a review of the proposed land use under NEPA (National Environmental Policy Act). The BLM (Bureau of Land Management) has established special teams to help renewable projects through the NEPA process.

The Location Analysis

Various layers of data from solar resources and weather patterns, to transmission and water data, need to be overlaid and correlated. With the heavy analytics involved in site-specific performance assessment, SolarReserve needs a “friendly platform to build on that can grow with the organization, and allows for rapid expansion of the platform with 3rd party sources,” said Charles Diep.

Google Earth Pro is SolarReserve’s development tool of choice. “This is a friendly web-based platform on which an organization can layer additional distributive web services to meet a specific organization’s needs.” Particularly important to SolarReserve in managing their engineering resources is a common platform that requires developers to need very little training, and enable them to easily add services on top of it and develop custom tools that makes the company successful.

SolarReserve’s location data analysis starts with developers who are tasked with identifying a potential site. The developer sends a KMZ file for the proposed project location to the engineering team. With the KMZ file, the team starts the performance analysis of the referenced location parameters. Once the performance analysis is complete and the site is deemed feasible, it moves on to the permitting process. The permitting process is equally location-intensive with all sorts of environmental conditions to evaluate. Location data such as topography is continually leveraged through the detailed engineering design and the financing phases. All the background data that goes into justifying the project is location-based.

There is far more data available in the U.S. for siting and performance analysis. When evaluating projects in some other countries, such as the Middle East, there is relatively less data available, which makes the process challenging. Most of SolarReserve’s facilities are in the southwest United States, with international developments in Europe, North and South Africa, the Middle East, China, South America and Australia. Anywhere the solar resources are adequate and with sufficient government support, a solar power plant is possible.

Distributing Electricity: Solar Back-up Generator

“The biggest operational issue for an electric utility is making sure that consistent power is delivered to customers,” according to David Sims. That means making sure that there is always sufficient capacity on the grid to follow changes in customer load and plant output. As more renewable energy comes on line this may be a challenge, as some sources of renewable energy are intermittent. For a wind turbine, if the wind drops down, or if a PV panel is temporarily covered by a cloud, the result is reduced power generation and capacity to the grid. For PV solar, NV Energy is participating in several studies with DOE and other agencies to model the impact of such intermittency on its system.

In the case of thermal solar with storage capability, SolarReserve’s plants collect energy all day, store it in molten salt, and then can deliver electric power to NV Energy customers at times when the need is still high. It is critical for utility operators to have control over the dispatch of power. With the ability to dispatch solar power as needed, a SolarReserve facility effectively acts as a solar-powered backup generator. This becomes a critical procurement factor.

If you could wave the wand, what would make your job easier?

David Sims: A tool that will provide high-level screening of site suitability and the attendant cost of renewable energy.

Charles Diep: A screening process or a tool that will actually spit out a list of high value sites, that meet all of the environmental and performance attributes, that acts as a standardized baseline that regulators and 3rd parties in the process can reference.

See Figure 2 for location of the SolarReserve Tonopah Solar Facility in Nevada. While not particularly close to Las Vegas, it is close to a substation and transmission lines. It would have been more efficient for the plant to be located closer to Las Vegas, but the plant was developed where feasible.

The cost of delivering renewable energy is still considerably higher than traditional coal or natural gas plants. At current fuel prices, coal and natural gas both have variable cost of around 3 cents per kwh, wind is 6 or 7 cents, and solar is about 10 to 20 cents depending on the type of solar technology. While solar energy is free when it hits the ground, the upfront cost of solar collectors, receiver(s) and thermal storage is still currently more expensive. There are efforts to bring these costs down, but in the meantime the upfront investments are high. The complexities of solar power generation are still evolving, and the National Renewable Energy Laboratory (NREL) is providing key analyses – particularly as it relates to the costs and value of thermal energy and thermal energy storage – to better educate the public. Location data plays a critical role in helping them understand such complexities and costs, and in streamlining the permitting process. More importantly, as the public starts to better understand solar energy, they also will need to change their perception of energy consumption – from the cost of production to the cost of investment in a renewable power future. But that is the subject of another article.