Where to put solar for maximal emissions reduction?

Not all places are equal.

Solar energy's potential for implementation is virtually limitless, spanning across nations worldwide—an ongoing trend at a substantial magnitude¹. Among its advantages (though not singular), solar power's standout characteristic is its low-carbon footprint. The act of installing solar panels invariably translates to a reduction in emissions, a concept that was highlighted in the most recent IPCC² report. This emphasis finds clear articulation in the graph below, which illustrates the array of mitigation options available, underscoring the fact that solar has the highest potential for emission reduction.

The mitigation options in the Energy sector. Solar and Wind have the highest potential. Check here for more info.

So, it is clear that solar can contribute to reducing our global emissions. But where should we put solar to maximize carbon reduction?

Attention: in this post, we will only consider carbon reduction for the installation of one kWp³. We do not make any financial or other technical considerations⁴.

How much emissions to produce one kWp?

The manufacturing of solar panels constitutes a notably energy-intensive sector, thereby leading to a non-trivial emission footprint. A captivating exchange regarding the ecological implications of the solar industry recently unfolded on Twitter. The ensuing table underscores the divergence in CO2 emissions stemming from coal-centric regions within China (2614 kg CO2 per kWp) to much cleaner regions (476 kg CO2 per kWp). It is worth acknowledging that China, concurrently engaged in an ambitious decarbonization journey, is poised to progressively lower the uppermost echelons of emissions over time.

Now, armed with an emission estimation for a single kWp, the pressing question emerges: how long does it take to offset or "pay back" these emissions? Addressing this question entails an examination of two pivotal factors: the total output per kWp and the power mix.

Factor 1: total output

The total production per kWp is inherently contingent upon irradiation levels, with pronounced disparities evident across distinct countries, as depicted in the geographical representation below. These disparities span from approximately 1000 kWh per kWp in Germany to a more substantial 2000 kWh per kWp in regions like Algeria, South Africa, and Chile.

Factor 2: power mix

The second critical determinant revolves around the substitution effect: what energy source solar power will supplant or replace within the existing power mix. The spectrum of disparities is depicted in the map below, underscoring substantial contrasts ranging from 882 g/kWh in Poland to a remarkably low 14 g/kWh in Sweden.

Carbon intensity of power generation on 18 August 2023 at 8 AM - GMT.

Actually, it is slightly more complex as we should consider what the solar would displace exactly. As we will see below, it becomes evident that certain instances present unequivocal cases, while others harbor a notably greater degree of complexity. This is particularly pronounced when nations find themselves in states of solar saturation or have important interconnections with neighboring countries.

Let’s explore four different examples.

Example 1: a coal country

The most effective strategy for emission reduction entails a decisive reduction in coal consumption, given its status as the most emitting source of electricity. This fact is unequivocally evident in the South African context, where coal undeniably predominates the electricity generation landscape. The combustion of coal for electricity production emits approximately 950g of CO2 per kWh⁵.

Moreover, South Africa's solar potential is substantial, boasting an irradiation level of up to 2300 kWh per kWp. When these figures are considered, an impressive carbon offset of 2185 kg per kWp installed annually materializes. Even when accounting for solar panels with the highest grey emissions⁶, the net emissions are recouped in just over a year and two months, thereby underscoring the rapid environmental benefit of solar integration in this context.

Coal dominates power generation in South Africa.

Example 2: a gas country

Algeria's electricity generation is predominantly fueled by natural gas, a source that emits considerably less carbon compared to coal, releasing around 400 g of CO2 per kWh. Echoing the situation in South Africa, Algeria also possesses substantial solar generation potential, with irradiation levels reaching up to 2000 kWh per kWp. In this scenario, a single kWp of solar capacity would displace approximately 800 kg of CO2 emissions annually, accentuating the considerable environmental advantage inherent in solar integration within Algeria's energy landscape.

Example 3: a country with relatively low emissions

Let’s consider Spain, an EU country interconnected with Portugal and France. Spain has made commendable progress in the realm of clean power generation, with an average intensity of 217 g of CO2 per kWh in the year 2022. The energy landscape in Spain has undergone a transformative evolution, with coal and oil-based generation nearly phased out. Renewable sources and nuclear energy have assumed a dominant position. Nonetheless, it's noteworthy that natural gas continues to play a significant role within Spain's energy mix.

The intermittent nature of solar power generation introduces a complexity that renders averaging potentially misleading. This complexity is particularly pronounced when the solar cannibalization effect comes into play. As this effect gains traction, instances of remarkably low energy prices become more prevalent, often stemming from the abundance of renewables and nuclear energy sources—both having low emissions profiles. Notably, S&P Global's projections hint at a capture rate dipping below 20% post-2026. This diminishing capture rate implies a surplus of solar generation, potentially diminishing the extent to which additional solar panels displace fossil fuel-based generation. It is pertinent, however, to acknowledge the evolving landscape, where the electrification of transport and heating, as well as the potential for solar energy export to neighboring countries, could offer avenues for broader emission displacement.

Despite the complexity, we can approximate the situation by referencing the average carbon intensity of 2022 alongside the prospective generation potential of 1600 kWh per kWp. This approximation leads to a reduction of 347 kg per kWp. Under these considerations, it becomes evident that the timeline for carbon emissions offset varies significantly. The journey to nullify the emissions associated with manufacturing the most emitting panels would span over 7 years, while the less emitting counterparts could achieve this within approximately 16 months.

Example 4: with hydrogen

Let’s now consider a slightly different case by assessing the extent of CO2 displacement achievable when transitioning from solar energy to hydrogen production, subsequently utilizing this hydrogen for power generation, as opposed to the direct combustion of natural gas. This particular case bears a direct correlation to Germany's aspiration of constructing up to 24 GW of gas power plants earmarked for conversion to hydrogen utilization.

Let’s assume a round-trip efficiency of 30% encompassing the entire process—ranging from power to hydrogen conversion, storage, and the subsequent reconversion of hydrogen to power—we're left with only 300 kWh per kWp from the initial 1000 kWh solar potential. Correspondingly, factoring in the gas-to-power emissions of approximately 400 g per kWh, supplanting gas with locally produced hydrogen would result in the displacement of approximately 120 kg of CO2 per kWp installed. In this context, the timeline for emissions offset is a noteworthy consideration. For the least emitting panels, the payback period amounts to around 4 years, while for those panels with comparatively higher emissions, it amounts to nearly 22 years. This assessment underscores the range of variables at play when contemplating the ecological implications of solar-to-hydrogen power conversion⁷.

Location (and manufacturing) matters in reducing emissions

Undoubtedly, solar power stands as a pivotal technology on our trajectory toward decarbonization. However, it's imperative to acknowledge the pivotal role that location plays. The differential impact becomes apparent when comparing the emission mitigation achieved by placing solar panels in South Africa—where avoidance could reach up to six times that of Spain. Moreover, as evidenced in our previous example, introducing a hydrogen layer in the energy conversion process can dramatically lower the emission reduction potential.

Similar to the influence of location, the manufacturing process also has a considerable influence over our decarbonization journey. Depending on these two variables—location and manufacturing— the emission payback period could range from a few months to two decades.

1. Check out my previous post on the bright future for solar.

2. IPCC stands for Intergovernmental Panel on Climate Change.

3. kWp means kilowatt-peak.

4. We are well aware that emissions reduction is not the main decisive reason for implementing a solar project.

5. Estimation differs depending on the coal quality and the power plant efficiency.

6. Grey emissions are the CO2 emissions generated during the manufacturing and transport of goods.

7. This calculation is of course a simplification but it gives some orders of magnitude. Please note that we did not consider the grey emissions of the hydrogen infrastructure and the potential climate impact of hydrogen leaks, as well as the climate impact of methane leaks.