Solar Photovoltaics in the Energy Transformation

In the early 1950s, scientists at Bell Laboratories invented the first modern silicon photovoltaic cell – a semiconductor crystal that could convert sunlight directly into electricity, using one of the most abundant materials on the earth.¹ Some time either this year or next (2022 or 2023), the world will cross the threshold of having one trillion watts of solar cells installed,² roughly equivalent to the combined capacity of all the electric power plants of the United States.³ It took 70 years to reach the first trillion watts of solar photovoltaic cells; the next trillion watts will likely be built within about seven years.

Industrial products tend to follow a general rule that the cost of manufacturing an item decreases on average about 10 to 30 percent for each doubling of cumulative units produced.⁴ This has lead to about a 500-fold decrease in the cost of solar cells,⁵ which is about 5,000-fold reduction if the effect of inflation is removed. As a result, in the best conditions, solar cells are capable of producing the cheapest electricity available today.⁶

While this is a landmark achievement, solar photovoltaics still only accounts for about 4 percent of global electricity supply, and at current rate of installation would take over a century to generate the total amount of electricity the world now uses. This does not include demand growth, which has been averaging near 3 percent per year in recent history,⁷ implying doubling electricity consumption by mid-century.

A complete conversion to electrification of transportation, building heat, and industry, could cause an additional doubling (or more) of electricity demand, profoundly challenging those who want to move to 100 percent renewable energy very quickly, relying primarily on solar photovoltaic panels, while “electrifying everything.”

The conclusion should not be despair, but rather should motivate inquiry into the means and goals of the energy transformation. To address the climate crisis, guidance is provided by the Intergovernmental Panel on Climate Change (IPCC) report on limiting warming to 1.5 degrees Centigrade over pre-industrial average temperature,⁸ in accord with the Paris Agreement between nearly all nations of the world.⁹

For that report, climate scientists modeled 89 “pathways” between 2020 and 2050, each of which includes a different combination of assumptions about the development of energy demand, shares of various energy resources, electrification (of industry, transportation and heat), land use, and carbon sequestration. Fifty of the pathways limited warming close to 1.5º C, which included starting with a quarter of world electricity from renewable energy in 2020, increasing to half by 2030, and an average slightly over three quarters by 2050.¹⁰

Prioritizing reduction of the most carbon-intensive fuels is an important complement to increasing renewable energy. Nearly all coal used for electric generation is phased out by 2050, while an average of about 9% of electricity is still produced by fossil fuel, mainly natural gas, in these scenarios.

By 2050, world electricity demand in these pathways a little more than doubles, which is roughly the current trajectory of demand growth for electricity without additional burden from electrification of transportation or building heat. In other words, it is crucial in these pathways to limit growth of energy demand in order to limit warming.

Rather than focusing on only one renewable resource, the pathways have various blends of energy resources. The maximum scenario for solar photovoltaics is just over half of electricity from a combination of solar and wind by 2050. Through limiting demand growth, blending different resources and approaches, and balancing different essential goals (sustainability, feasibility, affordability, reliability, etc.), following the IPCC model pathways for solar photovoltaics out to 2050 becomes much more feasible. Nevertheless, reaching the scenarios limiting warming to 1.5º C over pre-industrial global temperature, will require roughly tripling the current rate of installing renewable electric power, including solar photovoltaics.

Widening the scope of available tools can help a lot, using the concept that “many hands make light work”. Photovoltaics is just one of a number of methods for using solar energy, which can also provide hot water, space heat, lighting, cooking, industrial processes, air conditioning, refrigeration, generate electricity from heat, and produce renewable fuels.

Some of these applications already exist at a large scale, with half a trillion watts of solar thermal (mostly solar hot water) panels installed in the world today.¹¹ However, this is a small fraction of the potential, providing about one percent of building heat.

Direct use of solar energy – where it is possible – is usually far more efficient than solar photovoltaics. For example, converting sunlight to electricity, then using the electricity to power a lightbulb, wastes at least 90 percent of the captured solar energy.

Looking at California, solar photovoltaics has grown dramatically from one percent of the state’s electricity in 2011,¹² to over 20 percent today.¹³ Total renewable energy provides half of the state’s electricity, if customer solar and large hydroelectric power plants are included.¹⁴ California electricity has already reached the IPCC pathways average share of renewable energy for 2030 to limit warming to 1.5º C, almost a decade early, while Greenhouse Gas emissions in the  state’s electricity sector have been reduced by about half since 2008.¹⁵

This dramatic success has been accomplished through a coordinated set of policies all pulling in the same direction:

• The Renewables Portfolio Standard (RPS) requires an increasing share of retail sales of electricity to be from state qualified renewable sources, rising from 20 percent a decade ago, to 33 percent in 2020, and 60 percent in 2030; there is also a planning goal for 100 percent renewable and zero carbon electricity by 2045.^16,17
• The California Solar Initiative/Million Solar Roofs program set a target of 3,000 megawatts of customer solar photovoltaics by 2016, with the aim to transform this technology into a standard product; today over 10 percent of California homes have solar, and over 12,000 megawatts of customer sited solar has been installed.^18,19
• State law (SB 350) set a target for additional energy efficiency that is projected to reach over 80,000 gigawatt-hours per year of annual electricity savings by 2029 compared to a 2015 baseline.²⁰
• The power plant Emissions Performance Standard requires that new contracts with baseload power plants limit carbon dioxide emission rate to no higher than a natural gas power plant, which is effectively phasing out coal generation in California’s electricity supply.²¹
• The Cap and Trade program places a price on carbon dioxide emissions, including coverage for electric distribution utilities that sell carbon pollution permits (called “allowances”) to power plants.²²
• Local government procurement of renewable energy beyond what state law requires, for residences and businesses in their jurisdiction, through Community Choice Aggregation.²³

Despite long standing concerns about the aggressive renewable electricity law, its targets are so far easily being met, with the large utilities and most other retail sellers reaching or exceeding the 33 percent requirement for 2020.²⁴ While historically, biomass, geothermal, and hydropower where the main sources of renewable energy, in recent years at first wind and then solar photovoltaics have dominated new development.²⁵

By 2019, half of California’s renewable energy was solar photovoltaics. (In the graph, “BTM Solar” means solar photovoltaics that is behind customer meters, while “Solar” refers to utility scale solar projects contracted by retail sellers of electricity) This emerging pattern is true not only in California, but also in the United States as a whole, where 90 percent of new power generation is renewable, primarily solar and wind.²⁶