One of the few criticisms of photovoltaic panels has been put to rest by a new study that looks at total energy output from solar 1975-2014, compared with the oil used to make them.

Here's an excerpt:

"PV electricity has large social and governmental support, as during its operation no harmful emissions are released. Over the whole life-cycle of a PV system, it pays back the energy invested and greenhouse gas (GHG) emissions released during its production multiple times..

As PV systems operate over a period of up to 30 years, there is a significant time-lag between the investments, in terms of cumulative energy demand (CED) and GHG emissions, and the benefits obtained due to delivery of electricity and replacement of high-environmental impact electricity from fossil fuel sources.

Coupling the rapid growth of PV with this context of upfront investments has led to some concerns, regarding the PV industry’s environmental sustainability. A fast growth of installed PV capacity could result in the creation of an energy sink, as the PV industry could embed energy in PV systems at a rate outpaced by these system’s ability to deliver it back. The same can be true for GHG emissions, when the production of PV systems releases more GHG emissions than the electricity produced with PV can offset by replacing more GHG intensive electricity. Although there is evidence that shows that CED and GHG emissions are correlated10, this is not necessarily the case.

To avoid the creation of an energy and/or GHG sink, in general, the growth of the industry should be limited by 1/PBT11,12, where PBT (payback time) is the time in which upfront investments in either CED or GHG emissions are paid back. However, energy and GHG sinks from periods of growth exceeding 1/PBT can be offset by decreased growth rates (or decreasing PBT) in later stages. Thus, the dynamics of growth need to be taken into account, rather than always aiming for a 1/PBT limited growth, as is discussed by Emmott et al.13 The concept of the PV industry as an energy sink, and more recently GHG sink is well known in the PV community. Grimmer et al. have been one of the first to address this issue in terms of energy, stating that to maximise the (positive) impact of solar technologies, they should have short energy payback time (EPBT) and long lifetime. When the growth of the PV industry started to accelerate, others indicated the necessity of strong decreases in energy payback time12. Others have also analysed the relation between industry growth and EPBT and concluded that for mono-crystalline PV, a sustainable growth rate should be limited to around 7% (ref. 14), however this result was based on a static measurement of the energy footprint of PV systems, and thus did not account for the decrease of the energy footprint of PV systems over time. More recent studies have also analysed GHG sinks."

The report continues:

"Our results show that from 1975 onwards, there are clear trends in reduction of cost, CED, and GHG emissions, concurrently with a rapid growth of installed PV capacity. While cost decreases with 20.1% for each doubling in capacity, CED decreases with 11.9–12.6% and GHG emissions with 16.5–23.6%. The rapid growth of the PV industry has resulted in the creation of a temporary net primary energy sink, as well as it being a temporary net emitter of GHG emissions. However, because of the trend of decreasing environmental footprint concurrent with the growth of CIPC, according to the ‘Increasing PR’ scenario, this debt was likely already repaid in 2011 for both CED and GHG emissions. For the worst case scenario, which is the ‘Low PR’ scenario, the 95% confidence interval shows break-even during 2017 for CED and 2018 for GHG emissions."

The study was published in Nature Communications, and is available for reprint under a Creative Commons 4.0 license.