In the comment sections following articles about big solar projects in the desert, you’ll typically find the claim that we should put solar only on rooftops, citing studies like this from NREL, that stated: “New analysis nearly doubles previous estimates and shows U.S. building rooftops could generate close to 40 percent of national electricity sales.”
But claims that we can get all the solar that we need from rooftops overlooks one key fact. They give the reader the sense that ‘could’ equals ‘would.’
In practice, going solar is up to the roof owner. All homeowners do not necessarily want to go solar or can go solar, even when their roof is perfect. Solar industry insiders estimate that out of 50 or so leads, about one in 10 of those who agree to get a quote will go solar.
Fresco Solar CEO Sean Kenny abandoned residential sales by 2011 because of the 10 to one lead to sale ratio.
“I’d say it’s a bit more than 10 percent today,” he said. “Because now people know they can approach companies online. On the other hand, it is much less for the guys at Home Depot; more like only 5 percent.”
If only 10 percent of viable solar rooftops owned by just solar-receptive owners will actually go solar, we’ll actually average just 4 percent from solar rooftops from cities nationwide, based on NREL’s 40 percent of suitable roofs.
Four percent is inadequate to prevent climate change on its own. So we can’t get there with rooftop solar alone. We need to remain open to desert solar too.
Desert Solar Could Last Forever
Unlike the solar arrays on rooftops that can be removed, a utility-scale solar site, once it is generating power, could potentially keep generating forever.
Any big desert solar project initially has a set contract for about 25 years with a utility like PG&E to supply clean power.
Once its first power purchase agreement (PPA) ends, there are commercial incentives to renew the contract for another 25 years, because once a desert solar project is in a place chosen for its excellent solar insolation and access to transmission to high load centers, and it has paid off the capital costs, it remains commercially attractive for any new buyers in the future.
Demand will grow. The utilities have an every-growing mandate to purchase more clean energy for an ever-growing population and economy, to meet climate goals, to meet future electric vehicle demand, and to replace eventually dwindling — or hopefully one-day illegal — fossil energy.
So the most likely decision by every subsequent owner over the centuries will be to periodically upgrade any aging solar equipment and renew energy contracts. For these reasons; once a solar project begins, chances are it will send clean energy to the grid forever.
We already see this happening with the first solar in California, built in the 1980s. The SEGS solar project built in the 1990s, has now begun its second 20-year PPA with SCE, at around 6 cents/kWh, having completed its first contract at about four times that amount, during which time it paid off capital costs.
Mandates Drive Renewable Growth
Renewable Energy Standards (RES) are mandates that drive growth in utility-scale clean energy. Most states require that utilities include more and more renewables. Penalties for failure to meet the percentages kept utilities steadily growing their renewable energy purchases.
Currently, California utilities PG&E, SCE and SDG&E all have enough contracts in place to generate 33 percent from renewable energy by 2020. Developers are currently building the utility-scale projects due online at that time, and planning the additional projects due online the following year, and so on.
The three utilities are now delivering about 27 percent renewable energy in 2016, having achieved their requirements to generate 25 percent by 2015.
One way of understanding this would be to say that for more than a quarter of each year, renewable power alone powers an economy that is the sixth-largest in the world. Mandates work.
So Why Don’t We Look at Mandates Like the RES for Rooftop Solar Too?
Until now home owners have not been required to install and keep growing the amount of renewable energy that they generate on their roofs.
While California’s rooftop solar industry has grown fast based on market incentives, rooftop solar does not come close to generating 27 percent of all eligible rooftops, like utility-scale solar, with its renewable energy mandates.
But that could change. In April 2016, the California Public Utility Commission entertained the idea of utilities owning solar arrays on customer rooftops — and offering discounts to homeowners hosting them.
And a few years ago, California required that all new roofs must be “solar ready” — i.e., have large enough unobstructed areas available to install solar, with not too many little triangular gables, for example.
First Rooftop Solar Mandates Are Beginning
Now there is a bigger move towards the first actual solar mandates — at least for new buildings.
In 2013, the inland industrial city of Lancaster, Calif., was the first in the nation to mandate solar on all new homes. Since taking effect in 2014, commercial homebuilders must now add at least 1 kW of solar per home. They could comply by putting 5 kW on every fifth one, for example, as KB Homes has done.
San Francisco has mandated that all new buildings under ten stories must add solar.
Santa Monica requires solar at a rate of 2 kW per 1000 sq. ft. of all new low-rise residential buildings like apartment buildings and motels and 1.5 kW per 1000 sq. ft. for new single family homes. Since taking effect a year ago, 11 new buildings have met the new code.
The small town of Sebastopol made re-roofing the trigger for its mandate, which could potentially affect a larger percentage than just new homes. If you replace more than three quarters of the roof in Sebastopol, you must add solar.
Carlsbad in Southern California is also considering a solar mandate as part of meeting its climate goal.
Of course, only if all buildings, not just new but existing ones, were mandated to include solar, could the studies that influence opinion, like the NREL study, be a meaningful indication of how much solar we really could generate from rooftops?
If every solar-capable roof was mandated to switch to solar, then we could get the 40 percent from distributed generation that the study claims. But even these trailblazing cities are applying the law only to new buildings or to roof replacements, which are relatively rare events.
But Too Little, Too Slow for Climate
Given the 50 or 60 years it takes to entirely replace housing stock, that might take too long to have an effect. Even within a few years, new owners might take the solar system off the roof.
By putting all our eggs in that “rooftop only” basket, we would foreclose getting off fossil fuels. This is why we can’t afford to make a mistake about the ability of rooftop solar to meet climate goals on its own. We need big solar projects in the desert as well.
Sir Thomas Stern first sounded the alarm in 2006 on the cost of not switching the global economy to clean energy before we destroy our climate. This week he said that this cost has risen, because we have been unable to move fast enough in these 10 years.
“We have been too slow in acting on climate change,” Stern told The Observer this month. “In particular, we have delayed the curbing of greenhouse gas emissions for far too long.”
When he first published his review 10 years ago, we were collectively pumping 40 billion metric tons of CO2 into the atmosphere annually. Now it is 50 billion.
So let’s not kill off desert solar in the meantime, by arguing that rooftop can do it instead. Utility-scale solar takes houses off the grid and is more likely to keep them off. We need both.
Lead image credit: First Solar.