Gerard Cahill

Have Photovoltaics a Bright Future in Ireland?

Image adapted from www.seai.ie, "Total Primary Energy Requirement 1990 – 2020, Total Primary Energy Requirement 1990–2020"

Ireland today is very much reliant on fossil fuel and as a result Ireland is at the mercy of world supply and demand. Also, the fact that Ireland is an island on the edge of Europe will also lead to higher transportation costs. Ireland needs to remove itself from these unstable markets as materials become scarcer and become independent. However, as our consumption is forecast to increase, future trends would suggest that Ireland's import dependencies would increases even more as our indigenous fossil resources. Hence, by developing Ireland’s renewable resources, Ireland can take steps to ensuring the impact of peak oil or global supply crisis are at a minimum and Ireland can retain some economic competitiveness.

In terms of electricity generation, renewable energy accounted for just 7% of Ireland total electricity generation in 2009 ^[14]. The total annual electricity generation in Ireland is 22,000 GWh ^[20] . From the chart below, we can see that electricity generation in Ireland is based on exhaustible and scarce fossil fuels such as oil, gas and coal.

Image adapted from www.seai.ie, "Input Fuel Mix for Electricity Generation 1990 – 2020 from Total Primary Energy Requirement 1990–2020"

By 2020, as stated in the Irish Governments Energy White Paper in 2007 and in accordance with EU legislation, Ireland aims to achieve 33% of electricity consumption from renewable sources. Outlined in the Energy Forecasts for Ireland to 2020 ^[13] by the Sustainable Energy Authority of Ireland (SEAI), is the road-map to achieve the goal of 33% and beyond. (40% outlined in the report). However, photovoltaic is not included as a means of electricity generation ^[19]. In contrast, global photovoltaic electricity generating technology experienced an impressive annual growth rate compared with other renewable energy generating technologies as shown in the graph below

Image adapted from REN21 ^[15] , "Average annual growth rates of Renewable Energy Capacity"

At the end of 2009, the global power capacity stood at 25 GW, of which 21GW was grid tied and 4 GW was off grid. Germany are the leaders in photovoltaic installations followed by Spain ^[16]. In 2009, Germany added 3.8GW bring their total to 9.8GW by the end of 2009. Despite this impressive growth in other countries, Ireland has an installed photovoltaic capacity of only 0.6 MW at the end of 2009 ^[17]. The majority of the 0.6MW is off-grid (0.5 MW). Growth in Germany has been helped considerably by feed-in tariff mechanism which was introduced by the governments German Renewable Energy Act in order to reach their target of 52-70 GW of installed solar PV capacity by 2020 ^[18]. However, for Ireland it would seem a relative low priority have been given to photovoltaics by Irish Energy Policy. Why compare Ireland to Germany? Both countries have similar solar radiation profiles, see comparison chart 9 in Appendix A.

Images adapted from REN21 ^[16]

While widespread deployment of photovoltaic across Ireland may not make sense just now, it is worth noting that some sector could potentially benefit from installing the technology. The breakdown of electricity consumption in Ireland is as following, residential 34%, industry 27%, transport 0.2%, commercial/public 36% and agriculture 2.2%.

The sector with the biggest increase in electricity consumption since 1990 has been the commercial/public sector. This sector includes schools, offices, retail units, banking who's primary hours of business would be from 9am to 5pm (in line with hourly average solar radiation, see charts 7 and 8 in Appendix A). Solar would be attractive to such consumer if the price was favourable. Also, residential growth predicted globally is highlighted in the chart below, is it possible for the Irish residential sector to follow this trends? In the case study later on in the assignment, we will look at how a PV system currently performs in Ireland and what needs we can expect it to meet and the associated costs.

Why Solar Photovoltaics:

Photovoltaics is emerging as a power source due to it numerous environmental benefits, economics benefits and proven reliability. For centuries we have harnessed the power of the sun but it is only recently that we have been able to trap and store that power effectively, thanks to Photovoltaics! Photovoltaics technology exploits the most abundant source of free power from the Sun, thus can make a significant contribution to ensuring security of energy supply. The primary material used in photovoltaic is Silicon which is the second most abundant material in the Earth crust. Silicon is non-toxic element.

Photovoltaic systems would be considered to be a clean technology. They produce no noise, and emissions they produce over their full life cycle (from manufacturing to operation) are insignificant in comparison to the emissions that they replace ^{[23, 37]} (i.e. coal power plants, see image below). In addition, PV systems consume minimal amounts of water per unit of generation ^[24]. Thus, photovoltaics support efforts to reduce global warming. Moreover, the carbon footprint of manufacturing of photovoltaic systems is decreasing every year ^[5]. Photovoltaic systems reliability is improving with the typical lifetime of photovoltaic systems at twenty five years. Manufactures are now giving guarantee that output will not drop by more than 8% ^[23]. Once installed, photovoltaic systems required very little maintenance and intervention and have low operating costs associated with them. At the end of their lifetime, Photovoltaic systems can be recycled thus saving valuable resources and energy.

Image adapted from World Academy of Science, Engineering and Technology ^[37]

As technology advances even further, it bring with it the capability to create Building Integrated Photovoltaics (BIPV). BIPV can replace conventional building materials (some or parts) such as roofs, skylights and facades. Photovoltaic systems are universal in terms of location. This versatility is a key benefit of photovoltaic systems. These systems can be placed just about anywhere there is sufficient solar radiation. Photovoltaic systems are said to be off-grid or grid-tied. A wide range of applications exist from solar power stations and in buildings (residential and commercial), to stand-alone device (parking meters) and rural electrification. Grid-tied Photovoltaics system can be considered as a distributed and decentralised source of electricity generation. By producing electricity near the place of consumption, transmission losses and demand peaks on the main electricity grid are reduced.

Photovoltaic systems, once installed, will produce electricity over their lifetime (~25 years) at the fixed and known cost. Traditionally, fossil fuel generated electricity prices have increased and will continue to do so as fossil fuels become even scarcer. And of course, jobs! The industry has a broad value chain, covering jobs in science (research and development), engineering, manufacturing, and services many of which require a high level of specialisation in photovoltaics and skilled labour.

Ireland's Solar Potential:

On a global scale, the sun provides more than 10000 times the energy in fuel used by the entire human race. The large yellow cube above represents the amount of energy received from the sun each year. Also own are the world fossil fuel reserves and consumptions.

Image adapted from European Photovoltaic Industry Association,

"Annual Global Solar Irradiation to the earth"

Solar Insolation is a measure of how much solar radiation a given solar panel or surface receives. The greater the insolation, the more solar energy can be converted to electricity by the solar panel. Insolation is expressed as an the irradiance in watts per square meter (W/m²) at any moment or averaged over time as kilowatt-hours per square meter (kWh/m² ). The largest radiation values are over the equatorial zone because the sun's rays are more concentrated, whereas lower values are achieved towards the poles as the solar radiation is projected over a larger area.The intensity of the sunlight that reaches the earth varies with time of the day and year, location, and the weather conditions (i.e. cloud cover can result in reflection and absorption). Air Mass (AM), which is the ratio of optical thickness of atmosphere through which beam radiation passes to optical thickness if sun were at zenith, impacts the solar radiation for Ireland. Outside the atmosphere AM is often termed AM0, air mass 0. For Ireland, this value is typically AM1.5 while it's considered to be AM0 at the equator.

Image adapted from ClimateSanity, "Solar reference spectra"

Using Photovoltaic Geographical Information System (PVGIS) online solar analysis tool, Ireland receives on average 1100 kWh/m² per year or 3 kWh/m² per day [see appendix A, table 1]. This would be considered a moderate exposure level in global terms. Regions closer to the Earths equator would typically receive ~2000 kWh/m² per year. April-September account for 71% of the total, with June, July and August accounting for 37% of the annual total. The PVGIS simulation tool also indicated the optimum inclination angle (I_opt) for each month so as to optimise the PV panel output.

An important parameter to take into account is Ireland's proportion of direct and diffuse radiation. Diffuse radiation is caused by scattering (Rayleigh and Mie) and cloud cover.In Ireland, our skies are completely covered by cloud for over 50% of the time ^[12]. This is due to our geographical position, close to the path of Atlantic low pressure systems which tend to keep us in humid, cloudy airflow's for much of the time.

Overview of Photovoltaic Systems:

A photovoltaic system typically consists of an array of solar modules, an inverter, and sometimes a means of storage (i.e. a battery) and interconnection wiring. As, the solar cell produces only a small amount of power, cells can be interconnected to form modules in order to produce more power, which can in turn be connected into arrays to produce yet more power. Because of this modularity, photovoltaic systems can be designed to meet a wide range electrical requirements.

The solar cell is fundamental component of the photovoltaic system. Photovoltaic systems can be seen everywhere in today's world. Such systems support a wide variety of needs from calculators to motorway phones and from lighthouses to satellites. Solar panels collect solar radiation from the sun and convert that solar energy into electricity

Solar Cell Basics:

The solar cell is a semiconductor device that coverts solar energy into direct current (DC) electricity. This conversion is known as the photoelectric effect. Because the solar cell is a semiconductor device it’s essential to investigate the background theory for a semiconductor. For simplicity, lets limit the theory to the describing the workings of single crystalline silicon solar cells. As we all know, silicon is a group 14 atom meaning that each Si atom’s outer shell contains 4 valence electrons. Silicon atoms can form a solid by covalently bond to other silicon atoms.

As silicon is a semiconductor, this means that in solid silicon, there are certain bands of energies which the electrons are allowed to have, and other energies between these bands which are forbidden called the "band gap". At room temperature, pure silicon is a poor electrical conductor. Using quantum mechanics, we can explain this by the fact that the Fermi level is actually in the forbidden band-gap. In order to make silicon a better conductor, it must be "doped" with very small amounts of atoms from either group 13 or group 15 of the periodic table. These "dopant" atoms then take the place of the silicon atoms in the crystal lattice, and will bond with their neighbouring Silicon atoms in almost the same way as other Silicon atoms do.

However, there as group 15 have 5 valence electrons and group 13 have 3 valence electrons, we end up with either one short or one too many electrons needed to satisfy the four covalent bonds around each atom. Due to this unbalance, these extra electrons, or missing electrons, also known as "holes", are not involved in the covalent bonds of the crystal lattice, these electrons are free to move around within the solid. We can have both n-type and p-type silicon. P-type is doped with group 13 atoms like Al and Ga and the majority charge carriers are the positive holes. For n-type silicon the majority carrier are the negative elections as the silicon is doped with group 15 atoms such at arsenic. It should be noted that both n-type and p-type silicon are electrically neutral, i.e. they have the same numbers of positive and negative charges, it is just that in n-type silicon, some of the negative charges are free to move around, while the converse is true for p-type silicon.

Image adapted from ^[4]

So when a photon of light hits a piece of silicon, one of three things can happen. When the energy of the photons is lower than the band gap energy of the silicon the photon will pass through. The photon can also be reflected. However, when the photon energy is greater than the band gap energy of the silicon the photon is absorbed by the silicon. In the case where a photon is absorbed, its energy is given then to an electron in the valence band of the crystal lattice. Because the electron is in the valence band it’s is tightly bound in covalent t bonds and can’t move far. The energy give to this election by the photon results in the electron been excited into the conduction band. In the conduction band the electron is now free to move. The missing covalent bond left behind by the excited electron is known as a hole. The presence of this hole allows the electron of neighbouring atoms to move into the hole leaving another hole behind. This the hole can move through the lattice. Hence we have a semiconductor with a mobile election-hole pair due to photons absorption.

The photon absorbed only needs to have energy greater than the band gap energy to excite an electron from the valence band into the conduction band. But, given that the solar frequency spectrum approximates a black body spectrum at ~6000 Kelvin , so most of the solar radiance (insolation) that reaches the earth has photons of energies much greater than the band gap of silicon. The higher energy photons will also be absorbed by the solar cell, however the excess energy will into heat (via lattice vibrations - called phonons) rather than into usable electrical energy.

In simple terms a solar cell is a large-area semiconductor p-n junction. So what happens when a piece of n-type silicon is brought into contact with a piece of p-type silicon? Well in reality, the p-n junctions of solar cells are not made in this way. Rather they are made diffusing an n-type dopant into one side of a p-type wafer. So when the contact is made between p-type and n-type silicon there is a diffusion of election for the high electron concentration region into the region of low electron concentrations. (i.e. from n-type region to p-type region). Electrons recombine with holes on the p-type side after they diffuse across the p-n junction. This diffusion does not happen indefinitely due to the electric field created by the imbalance of the charges.There is now a diode created by the electric field across the p-n junction. This diode allows current to flow in only one direction across the junction.

So, once the electron-hole pair has been created by the absorption of a photon, the electron and hole are both free to move off independently within the silicon lattice. If they are created within a minority carrier diffusion length of the junction, then, depending on which side of the junction the electron-hole pair is created, the electric field at the junction will either sweep the electron to the n-type side, or the hole to the p-type side.

Image adapted from Solarnavigator, "Photons absorb into electron-hole pairs, which diffuse to contacts"

Key Solar Cell Parameters:

The key parameters of solar cell are its I/V (current/voltage) curve, short circuit current (which depends on the area of the cell, intensity of the light, optical properties and lifetime of the materials), open circuit voltage and maximum power output, efficiency and the fill factor ^{[27, 28]}.

As seen in the IV curve in the image below, for a given set of operational conditions, a cell has a maximum power operation point on the knee of the orange curve, P_max. The maximum power operating point varies for a give irradiance and temperature ^[29].

Image adapted from Solar Cell Central, "Maximum Power Point Tracking"

The fill factor, FF, a very important parameter in terms of energy yield for the solar cell, is defined as the actual maximum obtainable power divided by the product of the open circuit voltage and short circuit current. Typical commercial solar cells have a fill factor of ~ 0.7 ^[26].

The efficiency, ƞ, of a solar cell is given by the maximum power output divided by power in.

One method to increase the efficiency of a solar cell is to split the spectrum and use a solar cell, Tandem cell, that is optimised to each section of the spectrum.

Photovoltaic cells respond mainly to visible radiation, wavelengths of ~400-700nm) but also respond to some ultraviolet (below 400nm) and some infrared (above 700nm)

Photovoltaic Technologies:

In order to make an efficient solar cell, we must maximize absorption by choosing a material with a high absorption coefficient, minimize reflection and recombination, and maximize conduction. The performance of a solar cell is measured in terms of its efficiency at turning sunlight into electricity. In today's commercial market, a typical solar cell has an efficiency of 15% (about one-sixth of the sunlight striking the cell generates electricity). Improving solar cell efficiencies while holding down the cost per cell is an important goal of the PV industry.

PV technology can be classified into 3 main categories:

• 1. First generation

  2. Second generation

1. Third generation

Basic crystalline silicon (c-Si) is known as first generation, Thin Films technology is known as second generation technology and third generation (emerging technologies) which encompasses concentrator photovoltaic, organics and other technologies that haven’t been release on a large commercial scale.

Crystalline Silicon Technology:

This consists of crystalline silicon cells are made for thins slices of wafer cut from a single crystal or block of silicon. Three main types of crystalline cells can be distinguished:

• • Mono crystalline (Mono c-Si)

  • Polycrystalline (or multi crystalline, multi c-Si)

  • Ribbon sheets (ribbon-sheet c-Si)

Their efficiencies range from 11%-19%. Mono crystalline, which is made from thins slices cut from a single crystal of silicon, provides higher efficiency and thus greater power generation. Crystalline silicon is the most common technology representing 90% of today’s market. In terms of size, the most common cells are 5 x5 inches and produce 3-4.5W. a standard c-Si module is made up of 60-72 solar cells so the nominal power ranges from 120wp to 300wp (wp is Watt Peak) module sizes are typically 1.4m² to 1.7m^{2 [1]}.

Thin Film technology:

Thin film modules involves the depositing of extremely thin layers of photosensitive materials onto a backing panel such as glass, stainless steel or plastic (typically a low cost backing panel). This deposited material is then laser cut into individual solar cells. One of the main advantages of technology is the finished product can be flexible thus can be integrated into buildings or consumer devices. Also, the process of thin film manufacturing results in lower production costs compared to the more material-intensive crystalline technology, a price advantage which is counterbalanced by lower efficiency rates (from 4% to 11%). However, this is an average value and all Thin Film technologies do not have the same efficiency ^[1] .

There are 4 categories of thin film modules that are currently available to the market

• • Amorphous silicon (a-Si)

  • Cadmium Tellurium (CdTe)

  • Copper Indium/gallium Dissidence/disulphide (CIS, CIGS)

  • Multi-junction cells (a-Si/m-Si)

Amorphous silicon can absorb more sunlight than c-Si. However efficiencies are lower. As this technology produces very thin material, the module can be light and flexible which is proving very popular with companies manufacturing the product

CdTe – Cadmium Telluride. Currently the modules cost less to manufacture and have efficiencies of up to 11%. CdTe global market share has risen from 2% in 2005 to 13% in 2010. However, because the two raw materials are by-products of zinc (Cadmium) and copper (Tellurium) the long term availability of these materials and pricing may not be optimum . Also, it should be pointed out that cadmium is a hazardous substance and is restricted in some countries ^[25].

Multi junction cells consist of a-Si cell with additional layers of a-Si and micro-crystalline silicon applied onto the substrate. This can increase efficiencies by up to 10% as the µc-Si layer absorbs more light from the red and near IR section of the light spectrum. These modules are also thicker and more stable

CIS and CIGS – these technologies offer the highest efficiencies (7-12%) but also a more complex manufacturing process. Indium is also used in LCD industry and demand is quite high so from a cost point of view this method is likely to remains high cost for the coming years. recently, efficiencies of over 17% have been reported ^[2].

Image adapted from European Photovoltaic Industry Association, "Solar PV, PV Technologies: Cells and Modules"

Third Generation and other cell types:

Today third generation, emerging technologies, that are been developed are starting to be commercialized. The main ones are as followings: advanced inorganic, organic solar cells and Thermo-PV.

Another technology worth mentioning is CPV, concentrator photovoltaics. In CPV lenses are used to focus the sunlight onto the high efficient cells. The aim is to use as little of possible of the expensive semiconducting PV material while still collecting as much sunlight as possible. CPV systems use only direct irradiation so there is a need for a double axis tracking system to ensure modules are permanently orientated to the sun ^[3]. Also, because CPV's functions only using direct radiation, these would not be favorable for use in Ireland due to our high cloud cover (causing diffuse radiation). In spring of this year, Solar Junction company reported efficiencies of 43.5% ^[8]

Market Trends and Future Roadmap:

For the past decade, the global PV market has experienced vibrant growth with 40% growth rate year on year, see graph below on the right. Crystalline silicon technologies have dominated the markets up to now but new emerging technologies are beginning to enter the market and are expected to account for a significant market share in the coming years. The outlook is positive as the graphs below demonstrate - cell efficiency is increasing as shown on the top, prices are decreasing as show in the bottom left graph. It is important that technology improvements (leading to drop in the system price) increase at rate that is faster than the rate at which incentives are decreasing (if incentives do exist!). With these improvements, one can expect the growth rate of photovoltaic to continue over the next few years.

Image adapted from NREL, "Best Research-Cell Efficiencies" [10]

Images adapted from Navigate Energy [11], Navigant Energy [11]

Manufacturing footprint of Photovoltaics:

The energy it takes to make a photovoltaic system is usually recouped by the energy costs saved over one to three years. Newer generation technologies can even recover the production energy costs within 6 months. Of course, this depends of the location of the system. With lifetimes of at least twenty five years and technology advancing rapidly, photovoltaics systems will generate many times more energy than it did to produce them ^[5]. Recently, advances in nano-coating techniques, which are non-disruptive to the manufacturing process, have been shown to perform with efficiencies up to 18.5% better in early morning and late afternoon, as well as up to 10% better at noon ^[9].

Image adapted from European Photovoltaic Industry Association, "Solar PV, PV Technologies: Cells and Modules"

For comparison and standardisation purposes, PV modules are tested at Standard Temperature Conditions (STC) of 1000 W/m2 and ambient temperature of 25 ^oC. (i.e. a one 1 m² module with an efficiency of 15% is rated at 150 W_p (Watt peak).

Inverter:

The inverter is a key component of the PV system. The inverter converts the DC output from the solar cell to AC current which can then be fed to commercial electricity grid or used locally. Again the efficiency of the inverter is important. Efficiencies currently are 95-96% ^[6]. Some inverters, mainly grid-tied, may have their own Maximum Power Point Tracking (MPPT) capability. The maximum power output tracking is a technique which uses to get the maximum power from the cell, as it adjusts the how much current is drawn by applying a resistance. Inverters, while continuously improving, have, in the past, proven to be of low reliability and high cost. Lifetimes range from 5-10 years ^[30].

Tracker systems:

Solar panel efficiency can be optimized by using dynamic mounts that follow the position of the sun in the sky and rotate the solar panel to get the maximum amount of direct exposure during the day as possible. Such devices are known as solar trackers. Single axis tracker provide the capability to adjust the tilt angle or the azimuth angle (orientation with respect to due south) of the PV panels while double axis trackers provide the capability to adjust both the tilt angle (optimum tilt angle, I_opt of Ireland is shown in Table 1 in Appendix A) and the azimuth angle. The adjustments can have different types of drivers: chronological tracker (timed based on earth rotation speeds), active tracker (uses motors and gear trains to direct to direct tracker as commanded by a controller responding to solar direction) and passive tracker (movement of acompressed gas fluid due to solar heating caused the tracker to reposition the PV panel). Improvements due to a dual tracker system for Dublin are shown in Chart 8 in appendix A. Improvements are of the order of 30% for daily capture for the month of July,

Image adapted from http://www.mpoweruk.com/solar_power.htm

Ground-Mounted, Roof-Mounted and Building Integrated Photovoltaics:

Photovoltaic panels can be installed in 3 main forms - ground mounted, roof mounted or building integrated. Each has pros and cons in terms of optimising orientation, area usage, easy of access, ventilation for cooling, need to bury wiring, cost and visual appearance. Building Integrated Photovoltaics (BIPV) have been replacing conventional building materials (some or parts) such as roofs, tile, skylights and facades. An example of commercial options currently available can be found at homepower ^[31]. It's worth noting that some countries offer incentives for BIPV (i.e. France, Belgium, Italy, Germany ^[32,42]). One benefits of BIPV is the that cost elements they replace can be offset against the photovoltaic cost for new building structures and designs can be visually impressive.

Grid-tied, Off-Grid and Storage:

Depending on the scale (residential, commercial, utility-scale power plant, stand alone or off-grid), location and intended use of the photovoltaic system, it may make sense to have the system grid-tied or install local storage (or even both where possible). Neither may not be needed, where consumption demand matches or is less production but that is rarely the case.

Photovoltaic systems typically have a Capacity Factor of 17% ^[33], however this would be slightly less for Ireland as measured recently by Dublin Institute of Technology ^[34]. For a photovoltaic system, the capacity factor is ratio of the actual output over a period of time and its potential output if it had operated at full capacity the entire time. The capacity factor of photovoltaic system would be low compared to other sources of energy ^[33]. The profile of daily solar radiation, which drives electricity production in the photovoltaic system, is shown in chart 7 in Appendix A. of course, there is no solar radiation at night so no electricity will be produced. Also, we can see that solar radiation varies throughout the course of the day and the overall hours of solar radiation varies over the course of the year. Also, as mentioned earlier Ireland is subject to cloud cover which vary throughout the year. Therefore, due to intermittent supply, there is a need for connection to the grid or some form of storage in order to ensure security of supply during times of no electricity generation or where electricity generated doesn't meet the consumption demand or demand peaks.

Residential and commercial systems would typically be grid tied. As most homes and business are in developed areas, connections can be made to the local electricity grid and excess power can be feed back into the system. Feed in Tariffs (FiT) schemes provide an incentive for owners to fed electricity back into the system. Industrial and utility-scale power plants, which could produce several hundred kilowatts or even megawatts, are also grid tied. Industrial building, such as warehouses, can server a double use of urban space and supply electricity to the grid where at a point where demand is located and avail of the feed in tariffs.

Current storage options used across the world are shown in image below.

Image adapted from electricitystorage.org, "Worldwide installed stored capacity for electrical energy" ^[35]

Because of the low capacity factory of photovoltaic systems, storage is of great importance. The provision of cost-effective electrical energy storage remains one of the major challenges for the development of improved and grid independent PV power systems^[36]. For off-gird and stand alone photovoltaic systems batteries would typically be the preferred choice of storage.

However, for most PV systems it would seem that grid-tied would be the preferred option.This is currently the trend globally. In the US, grid-tied systems (commercial, utility, and residential) represent 98% of demand for the PV industry. This demand is also driven mainly driven by incentives ^[38]. Germany also has a similar profile, of which a significant amount of its success can be attributed to it's feed in tariff. Incentives play a major roll in the success of photovoltaic system installations and eventual "grid parity" (the point in time when the generation costs of solar photovoltaic electricity equals the cost of conventional electricity sources). incentives come in 3 main forms, up front investment subsidies, Feed in Tariffs (FiTs) and Solar Renewable Energy Certificates. For Ireland, investment subsidies (Accelerated Capital Allowance, or ACA ^[39]) are available but only to companies paying corporation tax. This a tax incentive, not a grant, and allows companies to write-off 100% of eligible equipment cost against profit in the first year It is not available to the residential sector. (though there is a grant available for solar heating) Germany's renewable energy policy (EEG) is regarded as been very successful and many other countries have model their model. The EEG guarantees owners of photovoltaic system a fixed feed in tariff for 20 years (between 21.11 and 28.74 cents/kWh subject to type and size of system in 2011) ^[40]. Changes to the policy in 2010 saw photovoltaic installed capacity grown by 43%^[40]. The benefits of FiTs are 3 fold to the photovoltaic system owner - the owner receives payment for all the electricity produced, even if consumed by the owner, additional bonus payments for electricity exported to the grid and reduction on standard electricity bill (from using energy produced be the owner). Also, addition premiums are given by some countries (i.e. Germany, Belgium, France ^[42]) for BIPV. In some regions/countries (Arizona, USA ^[43]), net metering has been established. Net-metering means that the price the owner receives for exported electricity is equal to the utility company's retail rate. So as a results of the benefits, a FiT means that the pay back time is considerably shorter and makes photovoltaics systems more attractive. However, in Ireland no Feed in Tariffs currently exist for photovoltaic generated electricity under the Renewable Energy Feed In Tariff (REFIT) scheme ^[44]. As part of the Renewable Energy Directive and National Renewable Energy Action Plan, FiTs exist for wind, hydro and biomass but not photovoltaics. This is a major drawback to the development of photovoltaic capacity in Ireland. However, export payments of 9-19 cents/kWh are available from ESB Customer Supply for under the Micro-Generation Scheme ^[45]. (current rates are due to expire 31^st December 2011!) Solar Renewable Energy Certificates (or often simply SRECs) allow generators of renewable energy to sell credits to utility companies who need them in order to comply with government regulations. These credits accrue automatically to photovoltaic system owners and can be offset against consumption or refunded (depending on utilities supplier).

How much electricity can we generate in Ireland using Photovoltaics:

Solar panels function best when placed in direct sunlight, away from obstructions that might cast shade and in areas with high regional solar insolation ratings. As per analysis of Ireland's solar irradiation the annual average is given as 3.020 kWh/m²/day (at the optimum tilt angle, see H_opt in Table 1 in Appendix A). Thus, if one were to use a solar panel of 1 m² with 15.7% efficiency the total output would be 474 kWh/day (before conversion from DC to AC).

Case Study : Photovoltaic system in Dublin, Ireland

In a recent photovoltaic system performance test in Camden Row, Dublin ^[47], it was observed that a 1.72 kW rooftop grid connected photovoltaic system produced an average annual electricity yield 885.1 kWh/kWp. The system consisted of 8 solar panels (SanyoHIP-215NHE5, 17.2% efficiency) covering 10m², an a inverter and supporting structures. The PV installed cost was €13,200,this was made up as follows - PV modules 62%, inverted 11%, installation 10%, mounting structures 12% and accessories 5%. The cost of land was not included.

A wide range of measurements were taken with the tilt angle set of 53^o and the azimuth angle of 0^o (facing directly south). A performance ratio of 81.5% was measured. Performance ratio is a measure of the quality of the PV system - how to ideal performance is a PV system during real operation. It allows comparison of PV systems and metric is independent of location, tilt angle, orientation and their nominal rated power capacity. An annual average capacity factory of 10.1% was observed with a range of 5% in December to 15.5% in June.

The impact of low ambient temperature and high wind speed ^[48] was shown to provide good operating condition by keeping the average PV module operating temperature lower than the standard operating condition temperature, this making Ireland more favorable compared to other locations (i.e. Berlin, Germany). Season variation showed that average daily values varied from 1.08 kW h/m2/day in December to 4.22 kW h/m2/day in July. The overall system efficiency was 12.6%, while for individual components the efficiencies of the module was recorded at 14.9% and the inverter 89.2% ^[49] as per the chart on the right below. Cloud cover impact, as per the chart on the left below, was shown to significantly reduce the PV module efficiency ^[50]. Seasonal performance of the system show that Spring and Summer each accounted for 32.5% of the annual output, Autumn accounted for 21% while the made up the remaining 14%. Comparisons against other regions show the performance of the PV system in Ireland was similar to that of other Northern European locations (Germany) but lower than that of locations in Southern Europe (Spain).

Images adapted from ^[48,49,50]

The average Irish home uses about 5,000 kWh of electricity per year ^[46]. The system described above would deliver 1,522 kWh of electricity annually, so would in order to meet the need of an average household 3 to 4 systems would be needed. This equates to approximately 28 solar panels covering an area of about 35 sq meters at a cost of €40,000 (using 2009 rates and assuming pricing decreases and economies of scale)

.

When will can we expect photovoltaic to compete in the Irish Energy Sector:

The projected costs and environmental performance of the PV system discussed above are studied ^[51]. In the calculation, some key assumption are made - current Feed in Tariff (9 to 19c/kWh) will exist through the lifetime of the photovoltaic system, CO2 emissions due to manufacture of the PV is zero as the components are not made in Ireland, cost of land is excluded, PV module maximum power degradation of 0.82% per year and the lifetimes of the PV modules and inverter are 25 years and 10 years respectively.

The Net Present Value, NPV, mechanism is used to calculate the cost viability of system and if/when return on investment will be achieved. NPV is given by the total life cycle cost of the systems (sum of capital and installation costs plus repair costs) minus the revenue from the generated electricity (sum of on-site consumption and exported to grid, analysis showed on-site consumption accounted for 96% of electricity generated). Four scenario are analysed using combinations of a learning rate (technology improvements of 15% and 20%) and growth rates ^[53] (moderate, meaning low level of support from Government policy, and advanced, meaning continuation of existence support mechanism and addition of others (FiT, grants, etc)). A range of PV module costs are take but we will just use the average cost, €5,700, of the purpose of this analysis. However, a negative NPV shows for installation in 2009 for all scenarios for the PV investment for this given module cost.

Image adapted from ^[52]

However, the earliest economic viability is predicted for 2023 for learning rate of 25% with advanced economic policies^[53].

Image adapted from ^[52]

If a 4.5% increase in grid electricity prices year on year is assumed then grid parity is attained in 2019 for learning rate of 25% with advanced economic policies ("advanced 25" scenario) while for the "moderate 15" scenario, grid parity is achieved in 2030. Further improvements suggested would to use a dual tracker systems. This can increase the solar radiation capture by up to 30% for summer months, see Hourly Average Solar Radiation for Dublin Airport - Dual Tracker System Impact chart 8 in Appendix A. This would help move us closer to grid parity. The report shows the potential for CO₂ emission reduction, over the course of the lifetime of the photovoltaic system, each kWp of installed PV capacity would typically save about 15.3 tCO₂ if green house gas emissions associated with conventional electricity remain at 2007 levels as PV systems consume minimal amounts of water per unit of generation ^[24].

Conclusion:

The two most obvious benefits of photovoltaic systems is that it's source, the sun, shines for free every day and no C0₂ emission are generated during operation. From a green house gas emission point of view, the installation and deployment of photovoltaic systems to generated electricity as opposed to conventional method using fossil fuels is a "no-brainer". We should be installing photovoltaic systems sooner rather than later. However, as with all things in life there is a cost element that needs to be considered. Capital cost are high and need to decrease significantly. Even with advances in technology, more competitive market and falling prices, there is still a need is more regions across the global for support mechanisms.These support mechanism are need to eventually lead photovoltaic to grid parity. Once grid parity is achieved photovoltaic will be seen as a viable energy source. On some regions across the world, grid parity is just around the corner. Some forecasters predict that Germany, who's solar irradiation profile is similar to that of Ireland, will achieve grid parity in 2 year or so. Overall on a global scaled the photovoltaic industry is growing rapidly but this not the case in Ireland.

In order to achieve widespread adoption of photovoltaic systems within the domestic sector, and indeed other sectors such as the commercial sector, in Ireland, a series of policy options will have to be explored to make them more attractive to potential investors. Some of these policies should include

• facilitating access to dump excess electricity into the national grid

  • grid connection made simple, generation-based incentives which include feed-in tariffs, net metering

• financial incentives such as capital cost subsidies, soft loans, income tax incentives to help cover up front investment

  • tax rebates, reduced value added tax, zero interest long term loans, etc

Implementation of one or some of these polices might be the trigger need to kick off photovoltaic in Ireland. Without such policies it's hard to see photovoltaics making headway in Ireland especially in the current economic conditions. However, global markets may certainly help us, especially as market development occurs in other counties leading to further decreases in prices. A major breakthrough in storage technology, thus solving of security of supply challenge due to intermittent issues, could possibly drive an even greater photovoltaic boom across the global and in Ireland. Until the support mechanisms are in place or the right price is upon us, Ireland needs to ensure that the correct educational plans are in place to raise awareness of photovoltaics.

Have photovoltaics a bright future in Ireland? Yes.

Hopefully Ireland will leave the "oil age" and enter the age of the sun very soon

Acknowledgements:

The author is grateful to Dublin City University for access to journals and papers via Engineering Village for the research and writing of this paper, work colleagues for their support and friends for their positive encouragement.

References:

Energy is measured in Joule,kilowatt hour (kWh) and the British thermal unit (BTU). One kWh is equivalent to exactly 3.6 million joules, and one BTU is equivalent to about 1055 joules.

• 1. European Photovoltaic Industry Association , "Solar Photovoltaics competing in the energy sector – On the road to competitiveness", September 2011

1. http://www.renewableenergyfocus.com/view/22425/cigs-thinfilm-sets-174-efficiency-record/

   1. Renata Reisfeld (July 2010). "New developments in luminescence for solar energy utilization". Optical Materials 32 (9): 850–856. doi:10.1016/j.optmat.2010.04.034

   2. http://2.bp.blogspot.com/_H7ONwTvnNP0/S__rYQ6_XZI/AAAAAAAAAUw/WD6Hdpfl7go/s320/solar-photovoltaic-system.png, accessed December 2011

   3. European Photovoltaic Industry Association , "Solar Generation 6, Solar Photovoltaics Electricity Empowering the World", February 2011

   4. James Worden and Michael Zuercher-Martinson, "How Inverters Work", May 2009 http://solar.gwu.edu/index_files/Resources_files/How-Solar-Inverters-Work-With-Solar-Panels.pdf

2. Dave Freeman (Texas Instruments), "Introduction to Photovoltaic Systems Maximum Power Point Tracking", November 2010 http://www.ti.com/lit/an/slva446/slva446.pdf

3. http://www.greentechmedia.com/articles/read/solar-junction-setting-new-cpv-efficiency-records/

4. Solarpa-inc.com, http://www.solarpa-inc.com/Benefits.html accessed on 5^th December 2011

5. National Renewable Energy Laboratory (NREL), Data compiled by Lawrence Kazmerski, "Best Research Cell Efficiencies"

6. Navigant, source Urbanomics "The solar power convergence", April 2011

7. Met Eireann, http://www.met.ie/climate-ireland/sunshine.asp?prn=1 accessed 5^th December 2011, see chart 6 in Appendix A for actual data

8. SEAI, "Energy Forecasts for Ireland to 2020", December 2010

9. SEAI, "Energy Forecasts for Ireland to 2020", December 2010, Table 17

10. REN21, Renewables 2010 Global Status Report (Paris: REN21 Secretariat), 2010, Page 15, Figure 2

11. REN21, Renewables 2010 Global Status Report (Paris: REN21 Secretariat), 2010, Page 19, Figures 7 & 8

• 1. EUROBSERV’ER, "PHOTOVOLTAIC BAROMETER", APRIL 2011, Page 5, Table 2

  2. EUROBSERV’ER, "PHOTOVOLTAIC BAROMETER", APRIL 2011, Page 6

12. SEAI, "Energy Forecasts for Ireland to 2020",Table 16 December 2010

13. SEAI, "Electricity Generation, Distribution and Supply in Ireland", 2003

14. European Commission, Eurostat, "IRELAND – Energy Mix Fact Sheet", 2007

15. SEAI, "Energy Forecasts for Ireland to 2020", December 2010, Table 7

16. Fthenakis V. et al. , "Emissions from Photovoltaic Life Cycles", 2008

17. NREL, "A Review of Operational Water Consumption and Withdrawal Factors for Electricity Generating Technologies", Page 22

18. http://www.solarserver.com/solar-magazine/solar-news/current/2011/kw22/eu-maintains-exception-for-pv-modules-in-rohs.html, acceded on 6^th December

19. http://www.solarfreaks.com/what-is-the-fill-factor-of-a-solar-panel-t138.html, accessed on 10^th December

20. National Instruments, http://zone.ni.com/devzone/cda/tut/p/id/7230 accessed on 10^th December

21. http://www.pveducation.org/pvcdrom/solar-cell-operation/short-circuit-current accessed on 10^th December

22. E. Radziemska and E. Klugmann, "Photovoltaic Maximum Power Point Varying with Illumination and Temperature", 2006, http://dx.doi.org/10.1115/1.2147586

23. NREL, "A Review of PV Inverter Technology Cost and Performance Projections", 2006

24. http://homepower.com/view/?file=HP130_pg38_Mync accessed on 11^th December

• 1. CLER, "Les tarifs d’achat de l’électricité produite par les sources d’énergie renouvelables", August 2011

25. NEI, "U.S. Capacity Factors by Fuel Type", 2010

26. Dr. A. Duffy, Dr. S.J. McCormack, Dr. M. Conlon, Dublin Institute of Technology, "Economic and environmental performance analysis of PV systems for domestic applications in Ireland", 2009

27. EPRI, "Electricity Energy Storage Technology Options", December 2010

28. Shi-cheng Zheng1, "Research on Charging Control for Battery in Photovoltaic System", June 2011, Page 5

29. M. Sedighizadeh, and A. Rezazadeh, "Comparison between Batteries and Fuel Cells for Photovoltaic System Backup", 2007, Table 3

30. Paula Mints (Navigant), "Solar PV in perspective 2011", December 2011

31. http://www.seai.ie/Your_Business/Accelerated_Capital_Allowance/

32. Germany Inventment and Trade, "The Photovoltaic Industry in Germany", Issue 2011/2012

33. Wind Works, "Snapshot of Feed-in Tariffs around the World in 2011", September 2011

34. GTM Research, "Building-Integrated Photovoltaics: An emerging market", July 2010

35. Database of State Incentives for Renewables & Efficiency (DSIRE), http://www.dsireusa.org/

36. SEAI, REFIT ,http://www.dcenr.gov.ie/Energy/Sustainable+and+Renewable+Energy+Division/REFIT.htm accessed on 11th December 2011

37. Commission for Energy Regulation, "ESBCS DOMESTIC MICRO-GENERATOR EXPORT TARIFF", December 2010

38. SEAI, "How much electricity can wind turbines and other renewable energy facility produce?", accessed 14th December 2011

39. L.M. Ayompe a,, A. Duffy a, S.J. McCormack b, M. Conlon c, "Measured performance of a 1.72 kW rooftop grid connected photovoltaic system in Ireland", August 2010

40. L.M. Ayompe a,, A. Duffy a, S.J. McCormack b, M. Conlon c, "Measured performance of a 1.72 kW rooftop grid connected photovoltaic system in Ireland", August 2010, Fig 5

41. L.M. Ayompe a,, A. Duffy a, S.J. McCormack b, M. Conlon c, "Measured performance of a 1.72 kW rooftop grid connected photovoltaic system in Ireland", August 2010, Fig 9

42. L.M. Ayompe a,, A. Duffy a, S.J. McCormack b, M. Conlon c, "Measured performance of a 1.72 kW rooftop grid connected photovoltaic system in Ireland", August 2010, Fig 10

43. L.M. Ayompe a, A.Duffy a,n, S.J.McCormack b, M.Conlon c, "Projected costs of a grid-connected domestic PV system under different scenarios in Ireland,using measured data from a trial installation", March 2010

44. The Greenpeace/EPIA, "Solar Generation V – 2008", Part Three - Solar Generation Scenarios, Page 30