The Carbon Payback Period of Solar Panels in NZ: Yay or Nay?
By Aniket Bhor on in Solar Power New Zealand
There is a considerably large group of people that likes to believe that solar panels are a scam, just as there is a group that believes the Earth is flat. A major argument that poorly supports this belief is that the net effect of solar panels on the environment is bad — because of their mining requirements, energy use during manufacturing and logistics, and lastly their end-of-life waste generation.
In other words, the cradle-to-grave implications of solar photovoltaics is often a concern that certain groups raise. While multiple studies worldwide have time and again proved that solar panels are overall beneficial for the planet, despite their use of resources, there hasn’t been a comprehensive study of the New Zealand scenario — until now!
New Zealand’s First Proper Carbon Payback Study for Renewables
Studying the net effect of solar on the environment, using sophisticated tools and methods, is not only important to shut down critics. It helps us truly understand the suitability of solar to certain locations, especially in comparison to other energy sources.
Recently, researchers Alan Brent and Isabella Pimentel Pincelli of Te Herenga Waka — Victoria University of Wellington conducted life cycle assessments of multiple renewable energy technologies in New Zealand.
What did they find? Their study clearly showed that ‘the carbon and energy footprints are quite small and favourably complement our current portfolio of renewable electricity generation assets.’ Simply put, yes, solar energy and other key renewables in New Zealand are great choices for cutting our carbon emissions significantly.
Finally, to the online skeptics claiming “solar panels use more energy to make than they’ll ever produce” or “they’re only green if made with green energy” — the facts say otherwise. Modern solar panels in New Zealand have an energy payback period of just 0.7 to 1.6 years. With lifespans of 30 years or more, that’s decades of clean energy generation, far outweighing the emissions from manufacturing and shipping.
The Cradle-to-Grave Analysis of Solar Power Systems
Researchers conducted assessments on multiple distributed solar energy systems as well as a 10 MW utility-scale power plant in Waikato. On the broader level, researchers measured the energy used in the component manufacturing and the system installation, along with the carbon emissions, as these are the key things of interest. But besides that, they also used a bunch of other, more specific metrics for a deeper understanding of the implications of these solar power systems.
Before we dive into the results, here is a quick summary of the specific metrics:
- Global Warming Potential (GWP): As you can guess from the name, GWP is the measure of how much carbon emissions a power plant causes per unit of energy generated. The overall GWP of a solar plant is obviously smaller than, say, coal-fired plants. But understanding the exact numbers helps us understand how much better a solar plant is compared to a coal-fired plant, or even a wind energy farm.
- Carbon Payback Time (CPBT): We’ve all heard about the financial payback period, which signifies how fast the monetary investment in a system is recovered. Similarly, carbon payback tells us how many months or years it takes for the avoided carbon emissions to equal the emissions in the manufacturing and installation of a system. The faster the CPBT of a system, the better it is for the environment, as the system will then have more life remaining to avoid emissions. In other words, a system begins to be truly emission-free only after its carbon payback time is crossed.
- Cumulative Energy Demand (CED): As the name suggests, CED shows us how much energy a solar power system utilizes over its entire lifespan, starting from the component manufacturing all the way to its waste management and recycling.
- Energy Payback Time (EPBT): Here comes another payback metric. The EPBT is an indicator of how many months or years a system needs to operate to generate an amount of energy that equals the amount of energy it uses in its lifetime, AKA its CED (cumulative energy demand).
- Energy Return on Investment (EROI): Just as the financial return on investment, the energy ROI (EROI) compares the overall energy generation from a system to its cumulative energy use (CED). In other words, it quantifies the ‘profit’ in the context of energy generation.
Alright! Now that we understand some of the key fancy terms of this topic, let us look at a table showing the study’s results:
| Metric | Utility-scale Solar | Distributed Solar |
|---|---|---|
| GWP (gCO₂eq/kWh) | 23.3 – 26.2 | 24.2 – 45.7 |
| CPBT – avoiding grid (years) | 6.8 – 7.3 | 7.0 – 13.0 |
| CPBT – avoiding CCGT (years) | 3.6 – 4.0 | 4.0 – 7.0 |
| CED (MJ/kWh) | 0.28 – 0.31 | 0.33 – 0.64 |
| EPBT (years) | 0.7 – 0.8 | 0.8 – 1.6 |
| EROI (dmnl) | 38 – 43 | 19 – 37 |
The first row shows the global warming potential of both utility-scale and distributed solar, which lie well below 50 gCO2-equivalent/kWh. In comparison, a coal-fired plant has a GWP of nearly 1,000 gCO2-equivalent/kWh. This means a typical solar power plant in Aotearoa New Zealand is responsible for only about 5% of the emissions of a typical coal power plant.
The second metric is the carbon payback period (CPBT), which ranges from 6.8 to 13 years when you consider avoided emissions from the grid. But New Zealand’s grid is already a low-emissions grid, thanks to a large proportion of renewables in our mix.
When you calculate the CPBT using avoided emissions from a combined cycle gas turbine (CCGT) plant, the carbon payback time drops to a range of 3.6 to 7, which is quite impressive. Most solar power systems, whether residential or utility-scale, will last well over 30 years. This means multiple decades of zero-emission energy generation.
Next comes the cumulative energy demand (CED), which lies between 0.28 and 0.64 MJ/kWh (mega-joules per kWh). This is way smaller than the CED of a typical coal power plant, which has a CED of 10-15 MJ/kWh.
After that, we move to the energy payback period (EPBT), one of the most important metrics for understanding whether and how much of the solar energy produced is free of emissions. The assessed Kiwi solar plants have an impressive EPBT of 0.7-1.6 years. Suppose a plant uses 0.3 megajoules (MJ) from its component manufacturing stage to the installation and all the way to the waste management. With a typical EPBT of 1, the plant will generate 0.3 MJ by the end of one year, and keep generating way, way more energy over the next 30 or more years of its life. Looking at the study’s results, even the longest calculated EPBT value of 1.6 years is still about just 5% of the system’s lifespan — a glorious number!
We asked Alan Brent whether the carbon emissions calculations in the study included shipping and distribution, or if they focused solely on the manufacturing phase, his response:
"Yes, we did including the transportation. For example, with distributed solar we assumed shipping from China to Auckland and then distribution over the country from there. There is much variability with the distribution of course (and it’s much easier to quantify this aspect for utility-scale solar), but it has a very small contribution to the overall results."
That brings us to the last metric of the energy ROI (EROI). Researchers found the EROI for the analysed solar power systems to be between 19 and 43. Experts say that an EROI of 7 can be considered sustainable in terms of development, which means our solar energy systems have excellent EROI values.
Final Thoughts
As our world slowly inches closer to the threat of an uninhabitable atmosphere, it becomes ever more important to scrutinize our energy systems, even those that we’ve long thought of as highly sustainable.
Particularly solar energy, which is set to completely dominate our energy mix, needs to be extremely sustainable. This is why it is a great step to conduct proper life cycle assessments of the solar energy systems in New Zealand. Such assessments not only provide us with factual, quantitative data against half-baked narratives criticising solar panels, but also gives us insight into the net effect of solar on the environment.
The research by Te Herenga Waka - Victoria University is welcome news, and its results are beyond satisfying. New Zealand’s solar power systems that were chosen for the study, and which were representative of the overall national solar capacity, have shown excellent results on all the key metrics, whether we’re talking about energy demand or net emissions or the return on investment.