PV Lifecycle Costs

Photovoltaic (PV) emissions are often considered as some of the highest amongst renewable energy systems. This is due to the high levels of energy required for silicon processing in older technologies. Manufacturing techniques have dramatically improved over the years to reduce the energy required and new technologies such as thin film and CdSe with vastly lower embodied energies are becoming more established. In addition to this, as with any energy technology a whole array of factors impact the overall emissions of a system, the most significant of which are listed on this page.

Resource inputs and technology

Depending on the material PV is made from the emissions profiles vary substantially. Of the most established technologies organic panels seem to have the largest footprint with an average of 63.4 gCO2e/kWh, with crystalline silicon an average of 55.3 gCO2e/kWh and thin film technologies the lowest at 20.9 gCO2e/kWh. A few other less well established technologies have much lower values such as Cadmium selenide quantum-dot photovoltaics (CdSe QDPV) which has only 5gCO2e/kWh (value based on only one study (Şengül and Theis, 2011)) (Nugent and Sovacool, 2014)

Location

It makes sense that the higher the solar irradiance the more energy a panel can generate during its lifetime and the lower its CO2e/kWh emissions will be (Nugent and Sovacool, 2014). However intense sunlight also degrades the panels at a faster rate and many sunshine rich desert locations have added problems of dust deposits on the panels surface which can prove troublesome to keep at bay.

Storage

As it stands in most EU countries at the moment there is rarely a period where PV electricity production outstrips demand. As such the requirements for storage is not as pressing as it will be when renewable technologies increase their share of the electricity mix. However the inclusion of storage systems can dramatically affect the overall emissions. Studies on this seem to be lacking and whilst it is clear the embodied energy in batteries must be considered, it is widely acknowledged storage technology is progressing in leaps and bounds and manufacturing techniques and resource management will improve.

Mounting Location

Ground mounting a PV system can reduce the overall footprint required as can tracking devices despite the increase in electrical hardware (Nugent and Sovacool, 2014).

Transportation

In general there is not a significant amount of information on the contribution the distances PV panels travel has on their lifecycle emissions (Nugent and Sovacool, 2014). The only study to consider this on its own put the figure at 6.3 gCO2e/kWh (Querini et al., 2012)

Sizing and Capacity

There is an economy of scale benefit from installation of large PV arrays. This is primarily thought to be down to efficiency gains in logistics and transportation (Nugent and Sovacool, 2014).

Manufacturing

The emissions associated with manufacturing varies a great deal depending on the country of origin. A product manufactured in China could have double the total emissions of the same manufactured in Germany. In the case of crystalline silicon which requires significant thermal processing, the energy mix used can have a significant impact on the lifecycle emissions of the panels (Nugent and Sovacool, 2014).

Longevity

The general trend unsruprisingly is that CO2e emissions are substantially reduced as the lifetime of the installation increases. A 5 year operating lifetime results in very large emissions of over 100 gCO2e/kWh, where as increasing to 20 years drops it to 17.5gCO2e/kWh (Nugent and Sovacool, 2014). PV systems have the advantage that they are almost maintenance free owing to their solid state nature.
An analysis of a PV roof installed in 1997 by the Centre for Alternative Technology (CAT) in 2010 (13 year old panels) found an average of 0.7% decrease per year in output, with the poorest recording an overall 20% drop (CAT, 2010). Modern panels can expect far better performance.

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Biofuels life cycle costs

Biofuels have an enormous potential to contribute to renewable energy around the world. However if critical factors such as Tillage, Nitrous Oxide (N2O) emissions and chemical use are not considered they can easily create more problems than they solve.

Pesticides, Herbicides and Insecticides

Pesticides, herbicides and insecticides are potentially toxic to humans, pollute waterways and have harmful effects on biodiversity (Mole 2011). Neonicotinoids have been linked to the decline of the honeybee (Tennekes 2010)(Vanengelsdorp & Meixner 2010).

Tillage

In agriculture, the preparation of soil for planting and the cultivation of soil after planting is known as Tillage (Tillage 2011). This requires energy and uncultivated soil stores significant quantities of carbon, disturbing the soil to release stored carbon as carbon dioxide (Kemp & Wexler 2010). Surface run off also increases causing nutrient loss, reducing soil moisture, decreasing soil particulate size and increasing soil erosion. In the past 40 years Soil Organic Matter (SOM) has declined, agricultural losses of 50% SOM are not unusual. Growing crops that require less cultivation lowers energy consumption and increases SOM and therefore carbon sequestration (Holland 2004).
Cultivation of Maize causes more soil erosion than that of any other crop (Xu et al. 2011).
If established on marginal/degraded land, or displacing annual agricultural crops, perennial energy grasses and short-rotation tree crops can generate benefits such as reduced erosion, reduced nutrient leaching, increased soil carbon content and increased soil productivity (Berndes 2002).
In conventional farming Non tillage practices have been found to increase yields as well as overall soil quantity (Teasdale & Cavigelli 2008). Perennial crops can be rotated with grain crops to minimise their effect on soil quality (Teasdale & Cavigelli 2008). As an example converting 12% arable land to Miscanthus results in increase in SOC, Short rotation coppice results in loss initially.

Water Footprint

Focusing on the Ukraine. The water footprint of maize is marginally above the global average of 1222 m3/ton (Gerbens-Leenes & Hoekstra 2011). Rapeseed is listed as having a green water footprint of 3846 m3/ton , wheat is 1282 – 3954 m3/ton , Barley Green water 1404 m3/ton, Soybeans 2906 m3/ton (Mekonne & Hoekstra 2010).
Sugar beet production in the Ukraine (figure 2) has a Water Footprint far above the sugar beet global average of 133 m3/ton and is causing water stress in the Dnieper Basin. Water from this region flows into the black sea, excessive use of fertillisers and lack of waste water treatment has been blamed for environmental damage to the black sea ecosystem (Gerbens-Leenes & Hoekstra 2011).
Recently research has been carried out into using residual sugar cane/beet biomass to produce ethanol (A. Walter & Ensinas 2010). This may seem like a logical step however it needs to be critically evaluated as these residues are normally left on the ground returning essential nutrients and carbon to the soil and are not necessarily a waste product (Lal 2005).
In 2008 86% of Global freshwater consumption was used for agriculture, in the Central Asian region surrounding Ukraine it is 90% (Gerbens-Leenes & Hoekstra 2011) An increase in biofuels production has the potential to increase water competition, decrease water quality and damage ecosystems (Gerbens-Leenes & Hoekstra 2011).
Virtual water is the water locked up in produce during its cultivation. Between 1995 and 1999 the Ukraine was listed as the 13th largest virtual water exporter in the world (Hoekstra 2003). Delicate regions are highlighted in figure 3.

Estimates of the effect biofuels on worldwide food production vary massively between 2-3% and 70-75% (Dell’ Aguzzo 2008).
Ukraine has a diminishing population and a surplus of land, so competition for food is not thought to be a huge issue (Raslavicius et al. 2011). However in the future there is expected to be a worldwide shortage of food and land may not be so abundant.

Non-exhaust emissions

Emissions from road transport tend to be thought of as primarily from vehicle exhausts or from power stations producing the electricity they use. However a significant proportion is from PM due to tyre, brake and road surface wear, defined as abrasion processes. These particles are emitted directly or re-suspended by other vehicles.

Whatever vehicle we choose to use, some form of wear particulates will be generated. However generally the heavier the vehicle and the greater force required to move and stop it the greater the volume of matter produced. For instance bicycle brake pads and tyres still wear, but as the surface areas and forces involved are far less, much lower amounts of material are involved. Driving vehicles that are appropriate to the environment we occupy is the solution to reducing these emissions. Road surface wear emissions also link with infrastructure costs.

Tyre Wear

Tyre tread wear is a complex physio-chemical process which is driven by the frictional energy developed at the interface between the tread and the pavement. Tyre wear particles and road surface wear particles are therefore inextricably linked. However, for the purpose of determining emission factors, tyre wear and road surface wear must, at present, be treated as separate particle sources due to the lack of experimental data on the emission factors associated with different tyre-road surface combinations. High wear rates may also occur as a result of steering system misalignment and incorrect tyre pressure (Ntziachristos and Boulter, 2013).

Non exhaust elements

Brake Wear

Brake linings generally consist of four main components — binders, fibres, fillers, and friction modifiers — which are stable at high temperatures. Various modified phenol-formaldehyde resins are used as binders. Fibres can be classified as metallic, mineral, ceramic, or aramide, and include steel, copper, brass, potassium titanate, glass, asbestos, organic material, and Kevlar. Fillers tend to be low-cost materials such as barium and antimony sulphate, kaolinite clays, magnesium and chromium oxides, and metal powders. Friction modifiers can be of inorganic, organic, or metallic composition. Graphite is a major modifier used to influence friction, but other modifiers include cashew dust, ground rubber, and carbon black. In the past, brake pads included asbestos fibres, though these have now been totally removed from the European fleet (Ntziachristos and Boulter, 2013).

Tyre elements

Road Surface Wear

Emission factors for road surface wear particles are even more difficult to quantify than those for tyre and brake wear, partly because the chemical composition of bitumen is too complex for quantification with chemical mass balance and receptor modelling, and partly because primary wear particles mix with road dust and re-suspended material. Few studies have provided emission factors for road surface wear according to PM10 or any other metric. It is estimated around 70 % by weight of airborne particles from bitumen range from 0.35 µm to 2.8 µm with a mean below 0.7 µm (Ntziachristos and Boulter, 2013).

External Cost

 

Non exhaust UK

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