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Bringing solar PV into the mainstream: The Agua Caliente solar PV plant

by Solar Server International Correspondent Christian Roselund
March 13th, 2013


Image courtesy First Solar
Image courtesy First Solar


Place Matters

The 19th - 20th century model of electricity production is essentially removed from the environment. Coal, natural gas and nuclear plants are built in vastly different locations in diverse geographies around the world, with little adaptation to the environment.

Solar and wind, as the technologies of the 21st century, follow a different model, one that involves a dynamic interaction with the land and dependence upon natural conditions. For renewable energy, place matters.

So it is natural that the solar industry should find a home in the hot, dry lands of the US Southwest. The region's deserts have traditionally yielded little agriculture, mostly dependent on irrigation, and sparse habitation between cities.

However, another kind of harvest is taking place in these deserts. 105 km east of Yuma, Arizona, in flat valley of creosote bush at the base of rugged peaks, ten square kilometers of blue-black solar panels reflect the sky and collect the area's most abundant resource – sunlight.

This land, which boasts some of the strongest solar radiation in the world, is the home of the world's largest operational solar photovoltaic (PV) plant, the Agua Caliente Solar Project, which Solar Server has chosen as our March 2013 Solar Energy System of the Month.


Prime desert land

There are several advantages to this location. Given the sparse population and lack of other uses, land is cheap. Substantial transmission lines run between the large cities of the West, and the plant's site lies adjacent to the Hassayampa-North Gila 500 kV transmission line.

The Sonoron Desert offers some of the best natural solar radiation in the world. Image courtesy Highqueue, Wikipedia
The Sonoron Desert offers some of the best natural solar radiation in the world. Image courtesy Highqueue, Wikipedia

NextLight Renewable Energy was the first to choose the location on the former West Wing Ranch north of Interstate 8 for a solar PV plant, and First Solar acquired the project with its acquisition of NextLight in 2010.

While much desert land in the Southwest had little prior commercial value, it has been recently sought after for both solar and wind development. The rush to develop projects on untouched desert to meet renewable energy goals has encountered resistance, with environmentalists and Native American groups fighting and delaying a number of large projects on public lands. Because of this, Agua Caliente's location on previously disturbed, private agricultural land is also an asset.

“The development team did a great job identifying a location on previously disturbed agricultural land, near transmission lines, and even more, being a neighbor to the Yuma County Building and Planning Department,” notes First Solar Project Director Tony Puchta.

“The project itself being on previously disturbed agricultural land really eliminated all of the risks and issues that you may see on a remote site with land that hasn't been previously touched.”


Challenges: floods and sheet flow

However, this land also brings challenges. Cloudy days are rare in the desert, which means weeks on end of direct, uninterrupted sunlight. However, when the rain does come it comes with a vengeance, and can fall heavily for several days in a row in the summer.

Under these rains, the flat valleys which make such easy land to build on lose their innocuous nature, and can host flash floods, which are more severe on graded land. So before First Solar could begin construction, the company had to plan for what to do with the water when it comes.

“The solar plants, they create more of a sheet flow, more than a dense, large quantity of water in small locations,” explains Puchta. “So the sheet flow over the entire project is really the difference between a utility-scale solar project, and say if you were building a building in that same location.”

Puchta notes that First Solar has a “robust” storm water protection plan which it installed at Agua Caliente. “The plan accounts for the heavy sheet flow that a relatively flat site will create, not a lot of undulations in the site, and nearby washes or anything to utilize.”

The lack of natural washes also meant that First Solar had to direct the water to two enormous 11 million liter retention basins at the southern end of the project.


Building on experience

Not every PV module manufacturer has the experience to make an enormous project like Agua Caliente work. However, First Solar has long combined module manufacturing with project development, which gives the benefit of creating a market for its own product.

First Solar has a highly modular process for building PV plants. Image courtesy First Solar
First Solar has a highly modular process for building PV plants. Image courtesy First Solar

This business model has enabled First Solar and other manufacturer/developers to weather the collapse in PV module prices better than pure-play manufacturers.

First Solar has specialized in large PV plants and has built some of the largest in the world, including the 80 MW-AC Sarnia PV plant, which Solar Server chose as its September 2010 Solar Energy System of the Month

So when workers laid hundreds of thousands of posts and installed more than 5 million of its FS Series 3 cadmium telluride thin film modules at Agua Caliente, they implemented a process First Solar had refined on other large PV projects.

“First Solar has a well-defined process and well-defined components, as well as a very modular construction process, which gives us the ability to scale projects down and up and not cause a whole lot of issues,” observes Puchta.


Parts and pieces: making logistics work

However, even First Solar had not built a project this size before, and the sheer scale of the project meant logistical challenges. “A (10 kilometer) site with many  pieces requires a very detailed and well-planned logistics plan,” recalls Puchta.

In order to meet this challenge of scale, Puchta set up multiple lay-down areas at the south, middle and north ends of the site, distributing materials based on the needs of the subcontractors. He notes that these challenges affected the speed of development.

“The more parts and pieces that you have on the site, the larger area that you need to control, and contain those parts and pieces,” explains Puchta. This meant not only the five million modules, but posts, mounting system, cables and other ancillary equipment, with as many as 450 workers on site at one time.


30 MW a month

These logistical challenges were met so well that First Solar has consistently beat project deadlines, building as much as 30 MW of the plant per month at periods of peak construction.

Agua Caliente will comprise more than 5 million First Solar PV modules when complete. Image courtesy First Solar
Agua Caliente will comprise more than 5 million First Solar PV modules when complete. Image courtesy First Solar

“The construction process and the schedule were so efficient that we had enough plant build ahead of us that we could commission at a record pace,” notes Puchta.

The company has been building the massive project year-round over the last three years, commissioning the plant in phases. In January 2012 it commissioned the first 30 MW-AC phase, to reach 100 MW-AC in April 2012, and 200 MW-AC in July 2012.

“If we have the ability to construct at a higher velocity, we would have the ability to commission at a high velocity, typically,” observes Puchta.

In September 2012 First Solar reached 250 MW-AC of capacity with more than 4 million modules, more than ¼ the electricity generation capacity of a standard nuclear reactor. This made Agua Caliente the largest single-site solar plant in the world.


Meeting demand

This large scale means that Agua Caliente and other large PV plants begin more and more to resemble conventional generation. This is a stated goal of First Solar, to help move solar generation from a niche to a mainstream power source.

First Solar Americas PR Director Alan Bernheimer notes that this means not only scale, but designing the electrical system to optimize output to the grid as well.

“(Agua Caliente) incorporates some technology that makes it look to the grid like a conventional generating facility, in order to provide for grid stability and reliability from what is basically an intermittent resource,” notes Bernheimer.

The plant includes technology to make it look to the grid more like a conventional power plant. Image courtesy First Solar
The plant includes technology to make it look to the grid more like a conventional power plant. Image courtesy First Solar

This includes regulation for voltage, frequency and power factor, as well as control of active and reactive power, ramp rates and the ability to curtail power when necessary.

It also includes weather forecasting, so that First Solar can alert the grid operator that output may be decreasing with cloud cover or increasing after clouds have passed. First Solar monitors conditions at the plant remotely from its Operations Center, where it reports  changing conditions to local grid operators to ramp up and down other resources, so that such fluctuations do not impact grid stability.

“We tend to incorporate this kind of technology into all of our large-scale projects,” notes Bernheimer.


The most precious resource

But for all of the intended similarities, First Solar's PV plants do not resemble conventional power plants in one key way: Water usage.

Coal, natural gas and nuclear plants use copious amounts of water in the process of generating electricity, with a typical coal plant consuming 1 - 4 billion liters annually. And while PV plants usually use a much smaller amount for cleaning, after initial water use for dust suppression during construction, First Solar's PV plants do not consume water.

“Between the occasional rainfall, the fact that our modules are frameless, and the fact that our technology is tolerant of somewhat more diffuse light conditions, we typically do not use water for cleaning,” notes Bernheimer. “So that is very hospitable to the desert environment.”


Coming home to the mainstream

Agua Caliente is a landmark project not only because of its scale, but what it represents, which is the way that solar PV has come from a niche product for wealthy environmentalists to a mainstream source of power for Americans. When complete, the plant will be 290 MW-AC in capacity, supplying enough power for roughly 100,000 homes, with electricity sold to Pacific Gas & Electric Company in Northern California.

But perhaps the most important test of this acceptance is the investor community. In that, First Solar and Agua Caliente have passed with flying colors.

In January 2012, MidAmerican Renewables, owned by billionaire investor Warren Buffet's Berkshire Hathaway, acquired a 49% interest in the Agua Caliente project from NRG Energy, as one of several very large PV projects which the company has invested in. This means that the largest operational solar plant in the world sits in the portfolio of one of the world's wealthiest and most respected investors.

PV has come a long way in the last decade, and in many ways it is coming home to where it always belonged – not only the Sonora Desert, but the mainstream of American life.

Image courtesy First Solar
Image courtesy First Solar