In our previous article “renewable energy sources: solar energy systems” we have reviewed that solar energy systems are classified into three system categories: Solar thermal, passive solar and solar photovoltaic systems. In this article we review the basic operation and advantages and disadvantages of Solar Photovoltaic Systems.
Photovoltaic systems (PV systems) undoubtedly constitute one of the most promising renewable green energy technologies as they are a means to explore the naturally replenishable solar energy and generate electricity.
The basic component of PV systems is the photovoltaic cell which is made from semi-conductor material (mainly silicon, Si) capable of high electron concentrations. PV system operation is based on the `photovoltaic effect’ or ‘photovoltaic phenomenon’ by which part of the energy generated from the impact of solar radiation and sunlight onto the solar cell is being absorbed by the electrons of the semi-conductor. This phenomenon increases the energy level of the electrons forcing them to ‘move’. Continues electron movement is electric current, thus electricity is generated.
Because PV systems generate direct electric current (DC), in cases where this current is transferred onto the electric power grid for distribution, it is necessary to use electrical inverters in order to convert it to alternating current (AC) – fo a complete list of advantages and disadvantages of solar energy and solar energy technologies see our ultimate guide on solar energy pros and cons.
Advantages of PV systems
Photovoltaic systems can be an ideal solution for covering basic energy needs of contemporary and next generation societies. PV systems can facilitate a sustainable energy mix which is friendly to the environment by utilisation of their significant advantages:
- PV systems are environmentally friendly. In contrary to the conventional power generation from fossil fuels, PV systems use solar power, a renewable green energy source, to generate electricity. Thus they help reduce Co2 emissions to the atmosphere which in turn reduces the “greenhouse effect”. Moreover PV systems, as any other renewable green energy technology, avoid or reduce other harmful gas emissions to the atmosphere which constitute a threat to the public health and the environment.
- PV systems are a reliable technology for the exploitation of solar energy. Current industry data shows that PV systems are expected to last for 30 years before any replacement is required.
- PV systems operate autonomous, and do not generate any noise or disturbances, (unlike wind turbines – see wind energy pros and cons) PV systems do not have any moving parts, apart from optional tracker for adjusting to sun radiation, and do not pollute the atmosphere or the surrounding environment by their operation.
- Compared to other renewable green energy technologies, PV systems require minimum maintenance; only minor checking of cable connections and a basic-regular cleaning of the panel surfaces is adequate to keep them operational for several years.
- Because PV systems can be used for remote and ‘small’ power generation plants, they are ideal for distributed power generation. In such networks, energy losses in the power grid due to long distances between point of power generation and power consumption are minimised and network efficiency in increased. Consequently, PV systems can help achieve cost savings in the forms of increased power-network-efficiency and lower capital expenditure for the construction of power lines (e.g. for remote areas).
- An important advantage of PV systems, inherited to all solar power technologies, is that they have peak production of energy when energy demand is at maximum levels (mainly during the summer). This attribute facilitates towards peak-shaving (see related article: Renewable energy facts: Energy storage is Key for RES penetration in to power generation) and ‘smoothing’ of the load curve thus reduce the possibility of a power black-out.
- Last but not least, PV systems, through recent technological evolution, are gradually becoming more popular due to recent achievements in cost-reductions (which are slowly becoming evident in the PV market) but primarily due to their application-diversity, modularity, and ease of installation and expandability (e.g. for small–medium power plants, for residential solar systems and for commercial solar applications on building roofs or facades). However, having referred to cost reductions, it is important to stress that PV systems continue to be expensive and that PV industry has still a long way before PV systems can reach viable costs in the market.
Disadvantages of Photovoltaic (PV) systems
- As already mentioned in no.7 above, the basic disadvantage of solar photovoltaic systems is their cost which remains relatively high. Of course this is relative to the alternatives that PV systems are being compared to. For example, the electrical energy produced by a photovoltaic system is estimated to cost a lot more than the cost of energy produced by a system of Wind turbines or from biomass. Similarly, the cost of PV energy is a lot more than that of energy produced from conventional, non-renewable energy sources (fossil fuels), such as oil or natural gas. Consequently, until anticipated technological progress is realised by achieving further cost reductions and increasing their efficiency, PV systems’ popularity and application rate in the market will be limited. As with all renewable energy technologies, subsidy funding and tax-incentives are of ultimate importance in making their application economically viable (refer to previous article: Renewable energy sources: Why should we subsidise?).
- Another disadvantage of PV systems is that they generate DC current; as already explained, installations for power generation and connection to the power grid require the use of inverters which currently constitute an expensive solution – see micro-inverters vs string inverters. Moreover, reliability issues require the use of energy storage (batteries) increasing even further PV installation costs.
- Compared to other solar energy technologies, PV systems have a low efficiency level, in the range of 8% – 20 % depending on the technology used (monocrystallic, poly-crystallise or thin-film PV panels).
In general, Photovoltaic systems can offer a range of benefits and constitute an important area of technological application for the exploitation and use of renewable energy sources (Solar power). Given the above analysis, it becomes clear that the two main factors hindering their application are high cost and relative low efficiency. Consequently, further technological progress and continuous financial support (through subsidies and incentives provided for all renewable energy applications) will play a crucial role for accelerating the adoption of solar PV systems. – you may wish to refer to our article: Solar Energy facts – Concentrated Solar Power (CSP) Vs Photovoltaic (PV) panels, for a comparison between Photovoltaic systems and Concentrated Solar Thermal Power systems).