The challenges of renewable energy: solar

Today, Chilean mining giant Antofagasta Minerals announced that it had sold its minority interest in the Javiera photovoltaic solar power plant (though it will continue to off-take electric energy from it).  Looking at the photo provided with the press release, one can’t help reflect on the challenges facing renewable energy sources, solar in this case.

The most obvious is that solar takes a lot of space!

The Javiera plant shown here has an installed capacity of 69.5 MW, yet it covers hundreds of acres.

The largest solar plant to date is in Kamuthi, India; its capacity is 648 MW and it reportedly covers a very tight 10 sq. km (2,470 acres) for a land to capacity ratio of 3.8 acre/MW.  The most efficient large scale one in the US, the 550 MW Topaz Solar Farm, occupies 25 sq. km for a 11.2 ratio.

Concentrated Solar Power (CSP) plants use parabolic mirrors to heat a fluid which then generates steam to drive traditional turbines.  They are more efficient than the photovoltaic types.  Yet even in the most favorable environments they still occupy a lot of ground:  Mojave One with a nameplate capacity of 280 MW covers1,765 acres for a 6.3 ratio.  The ratio is 6.8 at Solana, 15 at Crescent Dunes and 4.5 at SEGS.

In comparison, a 56 MW GE LM6000 combined cycle gas-fired power plant has a much smaller footprint than Javiera, as evidenced by the photo on the left.

Nuclear plants too are far more space efficient.  And they generate a lot of electricity.  The Millstone Nuclear Plant, CT, has a capacity of 2,037 MW on a 500 acre site for a ratio of 0.25 acre/MW.  The ratio is 0.16 at Peach Bottom, PA, and 0.4 at Susquehanna, PA.

Clearly, the desert of Northern Chile is ideal to find ample space for a solar farm, but not all lands are so devoid of potential use.

The second great challenge is capacity utilization.  In the US, nuclear plants produce energy more than 92% of the time.  By contrast, solar photovoltaics average 18% and CSP types can exceed 30%.  Javiera is probably in the mid 20s ballpark given the extremely favorable climate of Northern Chile.  But how many places in the world offer ideal climatic conditions and a ready customer (in the case of Javiera, a copper mining concern)?  Instead, generators in desolated places will need to build hundreds of miles of transmission lines to connect with populated areas.

Finally, there is the cost factor.  A popular methodology is the “levelized cost of electricity” or LCOE whereby initial capital costs, operating costs and fuel costs are combined over the useful life of a generating plant to calculate a lifetime cost of generating a MWh.

In the US, the EIA has the following LCOE estimates for plants entering service in 2020:

(in US$/MWh)	Minimum	Average	Maximum
Solar- photovoltaic	97.8	125.3	193.3
Solar- CSP	174.4	239.7	382.5
Advanced Nuclear	91.8	95.2	101.0
Coal-conventional	87.1	95.1	119.0
Coal-IGCC	106.1	115.7	136.1
Natural gas-advanced	68.6	72.6	81.7

It should be noted that these projections depend on the assumptions made, in particular, the future price of fossil fuels.  Nevertheless, some patterns are apparent:

1.     Natural gas is by far the cheapest fuel for electricity generation,

2.     Solar energy is cheap in places like the Mojave Desert and Arizona because of exceptional climatic conditions, not so elsewhere,

3.     Coal, natgas and nuclear plants costs don’t vary much with location.

However, the above LCOEs are imperfect in two fundamental respects:

1.     They do not include the cost of standby plants for solar, which is substantial since solar capacity utilization averages under 20%, and

2.     They assume that all plants sell their electricity at the same price.  In reality, an intermittent producer like solar doesn’t have the luxury to pick when to sell electricity and could well be stuck with off-peak demand and prices more often than fossil fuel fired power plants.

Still, solar technology has made great progress in the last decade.  It likely will continue to do so.  However, it is crucial for these producers (and the taxpayers) that energy storage technology advance to improve the economics of the system.  Rather than paying out excessive subsidies, the states and the federal government should invest, or encourage more investment, in R&D.