Question

In: Civil Engineering

2:Discuss the economics and environmental considerations with PV systems.

Expert Solution

Answer

Solar photovoltaic systems, commonly referred to as solar PV systems, convert sunlight directly into electricity. This is different to the solar thermal collectors for solar water heaters. A solar PV system can help reduce carbon emissions and your electricity bill by producing sustainable electricity from the sun instead of burning fossil fuels. Economic and Environmental aspects are two main vital factors which are assessed for any PV project. Following are the key points which are considered in both the aspects:

Environmental impact and safety

The environmental impact of photovoltaic energy is probably among the lowest of all electricity generating systems.

This is because:

· In normal operation PV energy systems emit no gaseous or liquid pollutants and no radioactive substances.

· Crystalline silicon PV cells contain only minuscule quantities of dopants such as boron and phosphorus. (However CIS or CdTe modules include very small quantities of indium, cadmium and tellurium, so there is a slight risk that a fire in an array might cause small amounts of toxic material containing these elements to be released into the environment and it is important that these cells are properly recycled at the end of their working life.)

· PV modules have no moving parts, so they are also safe in the mechanical sense, and they emit no noise.

· The electrical hazards of a well-engineered PV system are no greater than those of other comparable electrical installations.

PV arrays do, of course, have some visual impact. Rooftop arrays will normally be visible to neighbours, and may or may not be regarded as attractive, according to aesthetic tastes. Several companies have produced special PV modules in the form of roof tiles that blend into roof structures more unobtrusively than conventional module designs.

PV arrays on buildings require no additional land, but large, multi-megawatt PV arrays will usually be installed on land specially designated for the purpose, and this will entail some visual impact.

Environmental impact and safety of PV production

The environmental impact of manufacturing silicon PV cells is unlikely to be significant – except in the unlikely event of a major accident at a manufacturing plant. The majority of PV cells are made from silicon, which is not intrinsically harmful although it is important that workers not be exposed to dust produced during the manufacturing process.

The chemicals used in silicon production must also be treated with care. Silane gas, SiH4, from which pure silicon is produced, is inflammable and waste silicon tetrachloride (SiCl4), which is highly toxic, can also be produced. Sulphur hexafluoride and nitrogen trifluoride, which are both potent greenhouse gases, are used for cleaning purposes and must not be released into the atmosphere.

Cadmium is obviously used in the manufacture of CdTe modules and very small amounts of cadmium may also be used in manufacturing CIS and CIGS modules – although zinc may potentially be substituted.

As in any chemical process, careful attention must be paid to plant design and operation, to ensure the containment of any harmful chemicals in the event of an accident or plant malfunction.

PV arrays are potentially very long-lived devices, but eventually they will come to the end of their useful life and will have to be disposed of – or, preferably, recycled. Since 2014 EU recycling regulations under the Waste Electrical and Electronic Equipment (WEEE) directive make it compulsory for manufacturers to take back and recycle at least 85% of their PV modules free of charge.

Energy balance of PV systems and potential materials constraints

A common misconception about PV cells is that almost as much energy is used in their manufacture as they generate during their lifetime. In the early days of PV production, manufacturing processes were very energy-intensive, and the efficiency of the cells was relatively low, leading to low lifetime energy output.

However, modern cells are more electrically efficient and the use of modern PV production processes and thin film cells has made the energy balance of PV much more favourable. The time it takes for a PV array to produce as much energy as was used in its production (its energy payback time) varies depending on the array type and the conditions. For new multicrystalline silicon PV rooftop systems in northern European conditions it is about 2.1 years. This falls to only 1.2 years for systems in southern Europe, while cadmium telluride PV systems pay back their energy investment in about 0.6 years in southern European conditions (Fraunhofer ISE, 2017).

Concerns have also been expressed over the availability of ‘rare earth’ elements such as indium and tellurium, used in thin film PV. PV cell manufacture was, in 2015, using about 5% of the world’s silver production for cell contacts (Wirth, 2015). Given that this is expensive, there is commercial pressure to reduce the amounts used.

Economic analysis

Once the technical requirements of a PV application have been stated and a PV system design completed, the economic analysis can be carried out. The economic assessment includes both costs and benefits of the system. It considers many aspects of the problem including the energy and economic ones. Actually, even if it is important to evaluate the energy cover factor of a PV system, it could happen that the PV system does not harvest economic advantage from the operational phase. The combined analysis of energy and economic aspects is of basic importance for evaluating real outcomes of investments. To reach this result the proposed methodology follows the following economic aspects like:

a. evaluation of costs of the PV systems (investment costs and costs for maintenance, servicing and insurance against damage) and benefits due to the gains for the avoided bill costs, the incentives and the sold electricity

b. analysis of cash flows

c. evaluation of the economically effective and ineffective roofs

d. estimation of the energy cover factor related to the results of the economic analysis

e. sensitivity analysis for the most significant physical and economic parameters.

After you know all this information, it is best to determine the payback period. A payback period is the length of the time required to cover the cost of an investment. Here is an quation that can be used to determine the payback period for you specific solar system:

Simple Payback Period= Total installed cost of Project- tax credits, grants, and subsidies

(Estimate of annual produced kilowatt hours) * (grid price per kilowatt hour)

Simple payback period is only a simplistic measure and gives the number of years needed for a system to pay itself off.

Economic considerations on PV installations

The revenues obtained by connecting the plant to the grid during the useful life of the plant itself (usually 25 years) are constituted by the following elements

a. incentive tariff on the produced energy (supplied for 20 years);

b. non-paid cost for the energy not drawn from the grid but self-consumed and possibly sold (sale contract).

The installation of a PV plant requires a high initial investment but the running costs are limited: the fuel is available free of charge and the maintenance costs are limited since, in majority of cases, there are no moving parts in the system. These costs are estimated to be about from 1 to 2% of the cost of the plant per year and include the charges for the replacement of the inverter in the 10th-12th year and an insurance policy against theft and adverse atmospheric conditions which might damage the installation.

In spite of the technological developments in the most recent years, the costs for the erection of a plant are still quite high, especially when compared to electric generation from fossil sources and in some cases also in comparison with other renewable sources.

It must be realised that no manmade project can completely avoid some impact to the environment, so

neither can photovoltaics. Potential environmental burdens depend on the size and nature of the project

and are often location specific. Most of these burdens are associated with loss of amenity (e.g., visual

impact or noise in the case of central systems). However, adverse effects are generally small and can be

minimised by appropriate mitigation measures, including the use of the best available abatement

technologies.

In the module production process hazardous gases are used. The handling of hazardous gases in

the module production should be a point of attention, especially where large scale production is

concerned.

Research should be carried out as to how recycling of 80% to 95% of the modules can be

achieved.

Because availability, completeness and quality of the data on materials and processes is far from

ideal, future research for LCA-studies should include the development of a database with data

from both national and international (material) processes.

It is up to the involved factors (investors, developers, and permitting authorities) to make the

appropriate decisions by taking environmental issues into serious consideration. To that end, an

Environmental Impact Assessment for central systems, which should estimate the magnitude of potential

environmental impacts and propose appropriate mitigation measures, can play a significant role to proper

project design and to a subsequent project public acceptance.