A growing number of Oahu solar farms have found homes on hilly terrain and lower mountain slopes instead of planted like crops in neat rows on flat, even fields.

In the works, for example, is a 30-megawatt West Oahu solar project by Virginia-based AES Corp, a sweeping portion of which would be sited on the lower slopes of the southern Waianae Mountains.

As the state strives to grow more food and produce more green energy on an island chain with finite land available for development, competition for land threatens to upset goals to expand the agriculture and renewable energy industries.

While tightening restrictions on farmland development could serve to preserve ag land for food production, a new report argues that it might also send renewable energy developers looking to alternate technologies, such as offshore wind farms or biofuels, to achieve the state’s energy goals. These alternative renewable energy projects would likely be more expensive to construct — a cost that affects the price for energy paid by consumers.

But if solar developers grow more willing to build their projects on steeper land — a strategy endorsed in a new white paper by the Ulupono Initiative — the state could continue to make progress on its goal to produce all electricity from renewable sources by 2045 without eclipsing its goal to double local food production by 2030.

This is the key finding of the white paper, published Monday, by the impact investment firm that supports projects focused on locally produced food, renewable energy, clean transportation and waste and water management.

“While solar developers may be apprehensive to developing on higher-sloped lands,” says an excerpt from the white paper, “a willingness to develop solar facilities on sites with <20% slope, at a slightly higher per project cost, will allow for most, if not all, of Oahu’s agricultural lands to be protected.”

The white paper is based on the work of Matthias Fripp, a University of Hawaii electrical engineering professor who evaluated how different land use strategies could affect land availability, electric generation costs and the makeup of the technologies powering Oahu’s grid.

“If we cast a little bit wider net and consider these more moderate slopes, it’s one way of stretching what is a very limited land bank.” — Matthias Fripp, University of Hawaii engineering professor

“If we only consider unrestricted agricultural land and limit ourselves to flat land and low slopes that are the easiest for solar development, then there’s probably not enough (land) to provide as much solar power as we would want,” Fripp said. “On the other hand, if we cast a little bit wider net and consider these more moderate slopes, it’s one way of stretching what is a very limited land bank.”

If nothing more is done to protect agricultural lands from development, the white paper predicts that Oahu is poised to lose half of its Class B agricultural lands and up to 20% of its Class C agricultural lands to solar development.

Yet more restrictive land use rules could have the effect of accelerating the adoption of more costly renewable energy technologies, such as wind turbines, that the public may be less willing to support on the landscape when compared to solar panels.

But if solar energy projects are developed on higher-sloped lands, the report concludes that the most valuable agricultural lands can remain available for farming.

The white paper acknowledges that siting solar projects on steeper slopes can translate to higher development costs, but in an interview Fripp underscored that it’s already being done.

Fripp said his analysis found that two-thirds of AES’s West Oahu solar project and 10% of the EE Waianae Solar project are situated on a slope of at least 15%.

There are alternative sites for solar projects, however, that the white paper doesn’t consider, such as military-owned land or residential and commercial rooftops, Fripp said.

There are also other competing interests. State Land Use Commission Chairman Jonathan Likeke Scheuer pointed out that acreage best suitable for food and solar farms also overlaps with lands where housing is cheapest to build.

Wren Wescoatt, director of development for Longroad Energy’s proposed Mahi Solar project in Kunia, said he is looking for ways to ease competition between the state’s sustainability goals by incorporating farming and ranching in between and underneath the solar panels that would power the equivalent of some 37,000 homes.

On defunct sugarcane fields on Oahu’s north shore, a strategic marriage to produce both food and renewable energy is in the works at Clearway Energy Group’s Kawailoa Solar, the state’s largest solar project that allows local ranchers to graze their sheep between nearly half of a million panels.

“Solar and farming, they like the same kind of land — flat and sunny with lots of dirt,” Wescoatt said. “Especially on Oahu, we have a very limited amount of land. But I think there’s opportunity to further the goals of both sectors and it doesn’t have to be this zero sum paradigm.”

Yet while Wescoatt said he supports Ulupono’s attempt to find more ways for agriculture and energy projects to coexist, he said siting solar farms on steeper slopes is easier said than done.

Locating a solar project on a slope, he said, can make construction more challenging, which, in turn, can significantly raise the cost to build it.

“It can be done, but it’s very challenging to build solar on steep slopes,” he said, noting that the maximum industry standard is a slope of about 10 to 15%.

“Hawaii Grown” is funded in part by grants from the Ulupono Fund at the Hawaii Community Foundation, the Marisla Fund at the Hawaii Community Foundation, and the Frost Family Foundation.

The Ulupono Initiative is a venture of The Omidyar Group. Pierre Omidyar is a co-founder of The Omidyar Group and is also CEO and publisher of Civil Beat.