What is a life cycle assessment?
A life cycle assessment (LCA - also called a 'life cycle analysis') examines every aspect of a product’s life from the gathering of raw materials right up to its disposal and eventual breakdown. Even environmentally 'friendly' technologies like solar panels have some impact on the environment, and it's well worth considering how much energy goes into their manufacture. A proper LCA will by necessity be as specific as possible to measure the total influence of the product - especially taking into account things like how and where materials and components are produced, and what sorts of emissions are associated with transport.
What’s in a solar panel?
Solar panels start out as raw quartzite rock, which is processed in a number of different ways to into a single silicon crystal (monocrystalline). This is then sliced into wafers, coated and prepared with electrical contacts to produce a solar cell. In addition to the cell itself, glass for the covering, aluminium for the framing and copper for the wiring as well as various rubbers and plastics all go into making the completed kit. As well as the solar panels themselves, a complete assessment also needs to take into account other supporting hardware like DC to AC inverters.
What does a solar panel’s lifecycle look like?
First the quartzite is mined and refined into silicon, then further processed to make a silicon cell. Components are then assembled and shipped in bulk around the world to individual retailers. From there, the products are purchased and installed in people's homes where they will begin to pay back the energy used in their production. At the end of their lives - normally somewhere between 25 and 30 years, some components may be recycled, negating any energy used in the initial gathering, and others will need to be scrapped.
Full details about the long term effects of disposing of all of the components in solar panels aren't yet available, since this is still a fairly recent technology and the rated lifetime for most residential systems is between 25 and 30 years. Despite this, the expected impact is fairly small because most of the constituent materials are either recyclable, or essentially composed of rock and sand.
Where is most of the energy used?
Nearly all of the energy 'consumed' across a solar panel setup's life cycle (close to 85%) comes from turning the quartzite rock into a silicon wafer. More specifically, about half of this energy is consumed turning the silicon from metallurgic grade silicon (MG-Si) into a refined solar-grade silicon (SoG-Si) required in solar cells.
The amount of energy used in the production of a 1kW solar PV system creates nearly two tonnes of greenhouse gases. The next largest contributor to energy use is the production of the inverter, but at only around 7% of the total, it pales in comparison to the production of the solar panels.
How long does it take solar panels to pay off their own production?
Solar panels are relatively quick to generate enough energy to offset the amount used in their own production, so they're considered to be quite efficient. The time it takes for solar panels to offset the energy used in their own production depends on how big the panels are, how much sunlight's available, and how efficiently the panels work.
Andrew Moore, a Life Cycle Consultant, conducted a full LCA study based on a 1kW system in Australia. According to his study the time to offset the emissions created during production (the 'energy payback time' - EPBT) at 1.7 years for Darwin or Perth to 2.3 years for Hobart, where there's less sun1.
Similar studies differ slightly in their projections, but most point to the fact that solar panels are relatively quick to pay back the energy used in their production, and over the course of their lifespans generate many times this amount.
How much greenhouse gas emissions will solar panels offset over a lifetime?
The amount of greenhouse gas emissions that will be saved over the course of a solar installation's lifespan will again depend on its size, efficiency and usage - but the biggest difference is measured in terms of the emissions produced by different power suppliers in different states.
According to Andrew Moore's study, in most states the savings over the 30 year lifespan of a 1kW system will range between 37 and 49 tonnes. The exception is Hobart, where the savings amount to about 7 tonnes, thanks to the fact that much of the grid power's already supplied by renewable hydroelectric generation. The biggest reduction in greenhouse gas emissions is likely to be in Victoria.
These figures have the potential to change with developments in more sustainable grid power, of course - but for the foreseeable future, solar panels will continue to offer the chance to seriously reduce your greenhouse gas emissions.
1. Andrew Moore. "The solar lifecycle test". Issue 109 (pp 46-48), ReNew Magazine, Alternative Technology Association 2009