Intergovernmental Panel on Climate Change’s new report, Special Report Renewable Energy Sources (SRREN), is due out soon. The summary for policymakers (pdf) is available now.

The questions this report addresses are important: how much electricity and other energy can be supplied by renewables? At what cost? This report (more so the full report and technical summary) will help us make sense of conflicting claims today. All policy experts agree that renewables are needed, along with other low-carbon forms of energy, but what is their potential in the coming decades?

How much energy comes from renewables today?
Currently, world primary energy is 492 exajoules (the joule is the metric unit of energy. 1 exajoule = 10^18 joules = 1 billion billion joules = 278 terawatt hours (trillion watt hours or billion kWh).

Renewables supply 12.9% of this energy, of which 60% is traditional biomass, eg, wood, used for cooking and heating. 10.2% of all energy, 80% of all renewables, is biomass of some kind. Of the remaining 2.7%, 2.3% is hydro, 0.4% is other.

The graphs are a little confusing; energy sources are placed on different graphs because there is so much more of some than others. Recent gains in solar are impressive—photovoltaics, solar panels are up by almost a factor of 10 in 4 years, but the absolutely increase in exajoules pales compared to increases in other forms of renewables, from hydro to municipal solid waste. Also, information is often given in capacity, or GW—capacity tells us how much power is produced, at a maximum—rather than in GWh, total energy produced. [For example, German photovoltaics, with their 9.5% capacity factor, produce half as much electricity per GW as do PV in California, where the capacity factor is twice as large. Wind generally does better, but German wind has a capacity factor of less than 20%, while American wind is more than 30%. (To compare, American nuclear power capacity factor is >90%). So 1 GW of German solar produces half as much electricity as 1 GW of CA solar or German wind, and less than 1/3 as much as US wind.]

Most renewables except hydro and geothermal are more expensive than non-renewables. The costs of many are expected to decline.

How much energy can come from renewables by 2030? 2050?
The full report examines 164 scenarios. The use of renewables increases under all scenarios, no surprise. In the most ambitious scenario, renewables supply up to 43% of energy in 2030 and 77% in 2050. Half of scenarios show a contribution of >17% in 2030 and >27% in 2050.

Bioenergy appears to supply half or more of renewables in both Annex I and non-Annex I countries. Here are the median (half are higher, half are lower) estimates for 5 types of renewables (Annex 1/non-Annex 1), read from the graphs:
• bioenergy: 30 EJ/70 EJ
• hydro: 10 EJ/15 EJ
• wind: 10 EJ/15 EJ
• solar: 8 EJ/12 EJ
• geothermal: small
Marine energy is thought to be relatively unimportant in 2050.

The highest estimates assume a combined 430 EJ/year, considerably more than the median. Bioenergy, solar, and wind are much higher than the median in some scenarios.

The cost, depending on how ambitious the goal, would be $1.4 – 5.1 trillion between now and 2020, and $1.5 – 7.2 trillion between 2021 and 2030. For some renewables, there would be savings later because fuel costs are less. Costs of the renewables themselves are uncertain, and there are additional costs:

The costs associated with RE integration, whether for electricity, heating, cooling, gaseous or liquid fuels, are contextual, site-specific and generally difficult to determine. They may include additional costs for network infrastructure investment, system operation and losses, and other adjustments to the existing energy supply systems as needed. The available literature on integration costs is sparse and estimates are often lacking or vary widely.

So costs depend. Also, maintaining system reliability will become more difficult, but having a portfolio of renewables reduces risks and costs of grid integration.

What might interfere with some of the more ambitious plans?
First, hydro and bioenergy availability is less certain in the future:

Climate change will have impacts on the size and geographic distribution of the technical potential for RE [renewable energy] sources, but research into the magnitude of these possible effects is nascent…Because RE sources are, in many cases, dependent on the climate, global climate change will affect the RE resource base, though the precise nature and magnitude of these impacts is uncertain. The future technical potential for bioenergy could be influenced by climate change through impacts on biomass production such as altered soil conditions, precipitation, crop productivity and other factors. The overall impact of a global mean temperature change of below 2°C on the technical potential of bioenergy is expected to be relatively small on a global basis. However, considerable regional differences could be expected and uncertainties are larger and more difficult to assess compared to other RE options due to the large number of feedback mechanisms involved. For solar energy, though climate change is expected to influence the distribution and variability of cloud cover, the impact of these changes on overall technical potential is expected to be small. For hydropower the overall impacts on the global potential is expected to be slightly positive. However, results also indicate the possibility of substantial variations across regions and even within countries. Research to date suggests that climate change is not expected to greatly impact the global technical potential for wind energy development but changes in the regional distribution of the wind energy resource may be expected. Climate change is not anticipated to have significant impacts on the size or geographic distribution of geothermal or ocean energy resources.

[The following were not mentioned in the SPM, though they may be included in the main report:
• A study just published in Science says that the climate already may be affecting worldwide wheat and maize (corn) production.
• There is a likely link between hydro and the Sichuan earthquake which killed 70,000. Worries about earthquakes could reduce the addition of hydro.
MIT analysis suggests wind turbines could cause temperatures to rise.]

The report emphasizes that the potential for renewable energy is large. However,

Factors such as sustainability concerns, public acceptance, system integration and infrastructure constraints, or economic factors may …limit deployment of renewable energy technologies.

There are some steps between here and there:

A variety of technology-specific challenges (in addition to cost) may need to be addressed to enable RE to significantly upscale its contribution to reducing GHG emissions. For the increased and sustainable use of bioenergy, proper design, implementation and monitoring of sustainability frameworks can minimize negative impacts and maximize benefits with regard to social, economic and environmental issues. For solar energy, regulatory and institutional barriers can impede deployment, as can integration and transmission issues. For geothermal energy, an important challenge would be to prove that enhanced geothermal systems (EGS) can be deployed economically, sustainably and widely. New hydropower projects can have ecological and social impacts that are very site specific, and increased deployment may require improved sustainability assessment tools, and regional and multi-party collaborations to address energy and water needs. The deployment of ocean energy could benefit from testing centres for demonstration projects, and from dedicated policies and regulations that encourage early deployment. For wind energy, technical and institutional solutions to transmission constraints and operational integration concerns may be especially important, as might public acceptance issues relating primarily to landscape impacts.

There can be challenges integrating the renewables into the grid.

The characteristics of different RE sources can influence the scale of the integration challenge. Some RE resources are widely distributed geographically. Others, such as large scale hydropower, can be more centralized but have integration options constrained by geographic location. Some RE resources are variable with limited predictability. Some have lower physical energy densities and different technical specifications from fossil fuels. Such characteristics can constrain ease of integration and invoke additional system costs particularly when reaching higher shares of RE.

Water availability could affect hydropower, bioenergy, and thermal plants (such as solar thermal or biomass).

Modeling GHG emissions from biomass is particularly difficult because of land use change. In order to grow plants for electricity or fuel, the land is converted from another use (such as forest).

And it could be even better
Potentially, the use of biopower with carbon capture and storage may reduce atmospheric carbon. This is because plants take carbon dioxide out of the air, and release it back when burned to make electricity or fuel. CCS could be used when making electricity, so that the carbon dioxide goes into long-term storage.

By 2050, renewables may be more attractive than other low-GHG forms of energy, such as nuclear or carbon capture and storage.

Many combinations of low-carbon energy supply options and energy efficiency improvements can contribute to given low GHG concentration levels, with RE becoming the dominant low-carbon energy supply option by 2050 in the majority of scenarios.

[Note: more will be known in a decade or three on the costs of the various renewable technologies, as well as the costs of nuclear and carbon capture and storage. And more will be known about the pitfalls of all technologies.]

This report is a welcome addition to IPCC policy analysis. Please find a link to the policy summary here.

Photo by xedos4.