Over the last few years, solar capacity in the United States has truly taken off. Over 58 gigawatts (or million kilowatts) of solar capacity are currently installed across nearly 2 million projects, and at least 3.7 gigawatts more are in the pipeline as of late 2018. At the same time, the fate of nuclear power in the country is at a crossroads. Only one single nuclear unit has been completed in the U.S. since the 1990s, and the two most recent projects are experiencing delays, cost overruns, and ultimately cancellations.
With both nuclear and solar energy making headlines recently, it’s worth a deeper dive into how each power source stacks up against the other. While both are carbon-free sources of electricity, the big similarities end there. This article compares how much each power source costs, how much energy they produce, how long they last, and importantly, how long each resource takes to build.
The biggest differences between solar and nuclear power are the cost and time it takes to build each type of generating facility. Nuclear power is much more expensive and takes much longer to bring online.
The recent history of nuclear power construction in the U.S. provides a useful point of comparison. Only a single nuclear power plant has been completed in the U.S. in the last 30 years: the two-unit Watts Bar Nuclear Plant in Tennessee, which required 23 years for one reactor to be operational and 33 years for the other. What’s more, the two most recent nuclear projects under construction — the Vogtle Electric Generating Plant and the V.C. Summer Nuclear Station — received approval in 2012 from the Nuclear Regulatory Committee (NRC), and are both over budget and far from completing construction. For instance, a revised cost forecast for the Vogtle plant projects a total project cost of $25 billion, which is a 75 percent increase over its original $14.3 billion estimate.
In the six years since the approval of the Vogtle plant and V.C. Summer station, the Solar Energy Industries Association lists 57 utility-scale solar projects of at least 100 megawatts (MW) that have come online, with 14 additional 100-plus MW projects currently under construction. One such project currently under construction, the 250 MW Phoebe Solar Project in Texas, is scheduled to cost $397 million and take less than one year to bring online.
These stark differences are echoed in the most recent Levelized Cost of Energy Analysis by Lazard, a leading financial advisory and asset management firm. Their findings suggest that the cost per kilowatt (KW) for utility-scale solar is less than $1,000, while the comparable cost per KW for nuclear power is between $6,500 and $12,250. At present estimates, the Vogtle nuclear plant will cost about $10,300 per KW, near the top of Lazard’s range. This means nuclear power is nearly 10 times more expensive to build than utility-scale solar on a cost per KW basis.
Interestingly, Lazard also forecasts the construction time required to build the different facilities and finds that utility-scale solar takes nine months to complete, while nuclear may take 69 months to build. Given the recent experience of building nuclear power in the U.S., 69 months (or slightly less than six years) might be optimistic. In fact, the revised estimated operational dates for the two units of the Vogtle plant are now 2021 and 2022, a full decade after the plant received approval from the NRC.
Deciding to build solar vs. nuclear power
Consider a hypothetical scenario where an energy developer must decide to begin construction of a new nuclear power plant or to build utility-scale solar farms. The developer can decide to build one single 2,430 MW nuclear unit in 10 years or to build as many 250 MW solar farms as possible within that same 10-year time period. If the goal is to add as much carbon-free electricity to the grid as possible, which option should they choose?
The clear choice is utility-scale solar. Because one new 250 MW solar farm can be built every nine months, a total of 14 utility-scale solar farms could be built sequentially and back-to-back within the same decade it takes to build one nuclear power plant. The result of these 14 solar projects would be 3,500 MW of utility-scale solar, which equals 46 percent more carbon-free generating capacity per decade of construction. What’s more, whereas the nuclear power plant comes online all at once, building utility-scale solar generates nine additional years of solar electricity while waiting for the one nuclear facility to finish construction (see graph).
Importantly, this hypothetical scenario assumes that only one utility-scale solar facility is built at a time, as opposed to the nearly sixty 100-plus MW solar farms that have been completed since the Vogtle plant received its approval in 2012. From a cost perspective, the 3,500 MW of solar capacity will cost around $3.3 billion, which is less than one-seventh of the cost of the $25 billion dollar Vogtle nuclear plant.
There’s more to the comparison of solar vs. nuclear power than costs, capacity, and construction timelines. One of the most important factors to consider is how much energy each produces per year.
Power sources have two key characteristics: capacity, which is a measure of the power that a source can output in megawatts, and generation, which is a summation of the amount of energy that a power source can supply to an electric grid in a given time period (measured in megawatt-hours, or MWh). For instance, an incandescent light bulb requires 60 watts of power, and keeping that light on for an hour requires 60 watt-hours of energy.
A measure of how much energy a certain power source puts onto the grid is its “capacity factor,” which calculates how close to the maximum amount of possible annual generation a source produces. For instance, a nuclear power plant will run at its max until it needs new fuel, which may be six or twelve months later. As such, nuclear has a capacity factor of close to 100 percent because it typically produces as much generation as possible during every hour of the year. Solar power, on the other hand, can only produce electricity when the sun is out. This means that over the course of the year, solar power plants will produce their maximum amount of generation in just 17 to 20 percent of total hours, on average.
In other words, the 2,430 MW Vogtle nuclear plant could be expected to generate 21 million MWh per year, enough to power about 1.75 million residential households. The 3,500 MW of hypothetical solar power from the example above would produce just under 6 million MWh of electricity per year, enough to power 500,000 homes.
For solar to produce as much electricity as is generated by the 2,430 MW Vogtle nuclear plant it would require about 13,000 MW of utility-scale solar capacity, nearly four times as much as built in the above example. However, the cost to build that capacity would be $12.4 billion, which is still just 50 percent of the cost of the $25 billion Vogtle nuclear plant.
As this hypothetical scenario explains, solar projects can be built in substantially less time and at a much lower cost than a single nuclear project. Even when accounting for capacity built and energy produced from a nuclear facility, large-scale solar farms remain much less expensive and quicker to bring online than nuclear. As governments and utilities across the U.S. plan for the next century of power generation, utility-scale solar easily bests nuclear as the leading source of carbon-free power.