Your guide to electricity from Photovoltaic Panel systems

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1 Solar Power Explained: Your guide to electricity from Photovoltaic Panel systems Background Photovoltaic (PV) systems have been in use for over 50 years generating electricity directly from the sun as renewable electrical energy converted from sunlight. Originally a niche product, photovoltaic panels are being seen increasingly as a way to reduce rising energy costs into the future. This locally produced electricity can be fed into the existing grid system anytime when it is not being consumed by appliances within the house, and you will earn credits for it against your regular quarterly power bill. It is most effective for homes with a roof orientated generally northwards, and without shading. Solar power systems generally fall into 2 types, stand alone or grid connect solar power systems. Stand alone Stand alone systems are installed where no conventional electrical power lines are connected from the grid. All solar power generated is either immediately used on site, or stored in large battery banks for use when the sun is not shining (particularly evenings and v. cloudy days). These systems are not so common, and require considerable thought and pre-planning to reduce the electrical demands before installation. They also require users to plan their usage to avoid overloading or draining the batteries, potentially resulting in no power and blackouts! They are generally only used for remote locations where it can become a cheaper option, than long connecting extension lines from the existing national electricity grid. The rest of this explanation will only be relevant to Grid Connect or Feed-in PV Systems. Grid connect Far more widespread and much easier to use and install are the very popular grid connect solar power systems. This is the type of system SLiK has researched and recommends for its Community members. It involves the installation of additional renewable energy generators, usually on domestic rooftops, producing energy on sunny and bright days with thin cloud, which is either used by devices in the house at the time, or is exported or fed into the national grid system (hence their common name of feedin systems), through a 2 way meter which records the energy you have used from the national grid and the renewable energy you feed-in or export to the national grid. It does not account for the energy generated that you have used in the home during the day, but this can easily be calculated by comparing your energy bill to the total renewable energy generated, recorded on your inverter (see explanation in section below). In Tasmania there is no preferential feed-in tariff rate, you are currently compensated for the electricity you produce at the same rate as that you use, typically $0.28/kilowatt hour (kwh) as you are charged for use of electricity by Aurora from the grid. 1 P a g e

2 4 key components required Grid connect systems require 4 key components, a number of photovoltaic panels or modules often mounted on a frame, usually called an array; an inverter to convert the direct current (DC) electricity produced to be usable as alternating current (AC)in our house appliances and the electricity grid; plus a 2 way solar meter to allow unused renewable energy generated, to be exported or flow into the national grid system and be recorded accordingly, but still allow us to draw electricity from the grid as required. Inverters take the electricity produced by the panels which each produce low voltage direct current (DC) and inverts, adjusts or changes it to the required standard alternating current (AC) voltage of V which all our existing domestic appliances use throughout the home, and which we use from the national grid, when we are not using our generated electricity locally. Aurora will install a replacement 2 way solar meter to allow your renewable electricity to flow or feedin to the grid, which also permits you to receive conventional power from the grid as you need it. Aurora will charge you an extra cost, typically around $200 (additional to the PV installer s costs), to fit this new solar meter, replacing your old existing meter to allow the system to work correctly, should you choose to install solar power. The photovoltaic panels or modules comprise a number of individual photovoltaic cells, sandwiched between layers of glass (ideally non-reflective), and plastic or metal backing and edging. A group of these PV cells are connected together to form a solar panel or module, each of which produces typically Watts of electricity. The number and configuration of these generally depends on the size of the system. A number of modules each with its own connections or junction box when grouped and connected together with an inverter form a solar array which is usually mounted on your roof at the correct orientation and elevation, or tilt angle, to minimise shading and maximise electricity generation on your particular house. This array can have a combined power generating output that you can afford, and should contribute to reducing the costs of your power bills. Typical array sizes of 1.5kW, 3kW, 5kW or even up to 10kW are possible, but 10kW usually becomes beyond the affordability of most people. Producing above 10kW classifies the system as a commercial generator, where different and more stringent regulations apply and a feed-in tariif must be separately negotiated. To simplify the options, SLiK suggests a 3kW system is probably the most popular size, although many people already have 1kW or 1.5kW systems which can be added to with extra panels and usually an additional inverter. A reputable Clean Energy Council installer will be able to assist you with specific recommendations for your home and top-up panels if required. It is wise to reduce your power usage as much as possible before installing any PV system. This helps maximise the percentage of your power usage that can be generated yourselves, to keep your future power bills under better control, and reduce the pay-back time for the PV array. How is my electricity measured? The amount of electricity any device uses when it is on, is measured in Watts (W). A standard light globe may use 60W, an energy efficient light globe may use just 11W, but a kettle or plug-in heater may use up to 2,400W or 2.4 kilowatts (kw or thousand Watts). Hard wired heaters like heat pumps, wall heaters and under-floor heating, maybe considerably more up to around 6-8kW. Electricity is used 2 P a g e

3 when we have these devices on and for every hour of use they use their rated kw of electricity. So if we have a device on for an hour, using 1,000 Watts or 1kW of electricity, at the end of the hour it has used 1 kilowatt hour (kwh), which we have to pay for in our Aurora bill. This is the main unit of measure and will be shown on your current electricity bill as units of energy used over a 3 monthly period. This varies seasonally but for a winter quarter maybe around 2,300 kwh (or 25kWh/day) for an average Tasmanian home, perhaps more if you are wasting energy or have additional systems drawing power, or less if you are already being energy efficient. How much electricity can I produce? This will vary for almost every installation because it depends on a number of important factors, including: Size of the solar array Choice of PV Panel and other system components, and their efficiency Orientation of PV panels on roof (true North alignment gives maximum generation) Tilt angle of the PV panels on roof (35-40 degrees in Hobart is the tilt angle calculated to produce maximum annual electricity) Hours of uninterrupted daylight received by the panels each day Seasonal variation in the intensity of solar radiation (irradiance) between summer high and winter low Any shading during parts of the day (any significant shading usually makes these systems unviable) The cleanliness of the panels How hot the panels are while operating (generally the hotter the panels above 25 C, the less efficient they become) What age are the panels (all panels suffer a slow deterioration of output over time) Electrical efficiency of inverter Compatibility of inverter to handle minimum and maximum power generated through the seasons Electrical resistance of wiring due to cable diameter and length In addition one needs to assess how much electricity is currently being consumed each year in the house, how much we may be able to easily reduce that with simple efficiency measures (like turning the heater thermostat down, taking shorter showers, using a low flow shower head, turning off lights and appliances when not in use, using energy efficient appliances etc.), and how much we can afford to produce solar power to help reduce our electricity bill. From this we will be able to determine the size of array suitable for our position. Sustainable Living Tasmania (SLT) in 77, Murray Street, Hobart (above Ecohaven) has a wealth of information and advice available on energy efficiency measures and an easy to read Solar Electricity booklet, available from SLT for just $10 and published by the Alternative Technology Association, For more guidance in this area check out or phone SLT on: P a g e

4 How soon will I cover my installation costs? Along with the amount of energy being produced, another important measure of a PV system for many is the payback time. How long will it take until the savings made from the system, cover the cost of the installation? To determine this requires clarity on the performance aspects of the system, particularly the efficiency performance of the PV panels being used, and how much energy they produce over a defined period each day or year, for example. Your Clean Energy Council (CEC) approved installer will provide guidance for you. At our latitude the rule of thumb is 3.5 x system rating per day. ie a 1.5kW system should produce on average 5.25kW per day, and a 3kW system should average about 10.5kW/day. From this, one can calculate the estimated kwh generated, of which some is generally used, and the remainder feeds into the grid. Take the energy generated directly from your solar power system, and divide the cost of the system installation by this value to give the approximate number of years it will take to pay for the system installation, assuming the current feed-in tariff remains at the current 28c/kWh. Typically in Tasmania this payback period would currently be around 5-7 years in general. Risk of reduced feed-in tariff could extend pay-back times There are rumours that Aurora may follow other states and reduce this feed-in tariff over the next 2 years, before full contestability arrives in This will remove Aurora s current monopoly by allowing other electricity retailers like Origin, AGL, Momentum etc. to compete for our business, which hopefully should make electricity pricing more competitive and help reduce our power bills. If this happens, it could also adversely affect the payback time, particularly for those families out all day and exporting electricity to the grid during peak sun hours 10am -2pm, while those working from home or retirees who consume PV energy produced during the day, will be least affected. The adverse impacts of this possible change, should it occur, could be minimised by using timers to do clothes and dish washing or use other electrical appliances during the day to use up more solar generated electricity, which minimises export to grid, instead of perhaps as currently, targeting off-peak periods. Were this to occur it would lengthen the payback period considerably. What size solar array should I choose? Often this is determined by your budget, but a 3kW PV system is generally a popular size and delivers a worthwhile amount of energy generation to help make a significant dent in people s energy bills, typically generating around 3,800 kwh/year. Which type of PhotoVoltaic Panel is best? There are 3 basic types of PV panel, monocrystalline, polycrystalline and amorphous thin film (See table below for more detail, on pages 8&9). Monocrystalline are the most expensive but also most efficient (ranging 14-19%), and most reliable with long life and proven over 50 years. They generally produce the most electricity per square metre of 4 P a g e

5 panel area, and 250W panels reduce the number of panels required to generate 3kW, which can help reduce clamps, tracking and wiring required, and slightly reduce installation time. Polycrystalline are often a bit cheaper but also marginally less efficient (typically 10-16%) so may require more panels and a larger unshaded roof area. The better polycrystalline panels have the same footprint as monocrystalline panels of the same rating. Amorphous thin-film are cheapest but also the least efficient (typically 6-8%),least reliable and shortest life, requiring approximately double the number of panels and roof area for 3kW, while deteriorating faster, so we are excluding these from our recommendations. Selecting panels with only positive tolerances is a good indication they will last well. For example a 250W rated panel + x% tolerance (sometimes 2-5%) is recommended over a panel rated at 250W but with ± x% tolerance which can mean increased variability and thereby lower energy production. Each have their strengths and weaknesses as shown in this table, but our research has shown that good quality Tier 1 monocrystalline panels with good efficiency, positive tolerances, long lifetime panel warranties of years, plus 90% of output guaranteed for 10 years and 80% of output guaranteed for at least 20 years, will provide least trouble, deliver good long term power outputs and therefore probably represents the best long term investment for SLiK members. Manufacturer reliability Linked in with this type of panel construction are the panel manufacturers capabilities. Only 2% of Solar PV makers are Tier 1 manufacturers, who are vertically integrated, making their own silicon cells, investing heavily in R&D, using advanced robotic processes to ensure all panels are made equally efficiently and have generally been manufacturing for more than 5 years. This is important as variability in individual cell output, can reduce a whole panel s power generation. These leading manufacturers are generally accepted as making the most efficient and reliable panels that usually generate significantly more power over the life of the panel than most Tier 2 or 3 manufacturers. These panels usually have a positive tolerance on efficiency where every 200W panel generates at least 200W, maybe slightly more by up to 5%. These manufacturers issue the best warranties and are likely to still be leaders in the business after that time. Their temperature coefficients tend to be better, plus panel efficiencies tend to be higher, so slightly more power is generated per panel each day, which over time adds up to be significant. Tier 2 manufacturers are small-medium scale with little R&D investment, little vertical integration but partial robotic production, and have usually been manufacturing for 2-5 years. Tier 3 covers 90% of solar panel suppliers, simply assembling cells for 2 years or less, with all the soldering done by hand which increases cell variability. The lowest output cell in a panel often determines the overall output of the panel, so keeping them all identical is very important and best achieved by robotic control of manufacturing. Such quality control issues may result in a nominal 200W panel only delivering 195W or even less, which seriously erodes the effectiveness of your investment. Their long guarantees are not worth much, as many such producers can go out of business. 5 P a g e

6 Orientation and elevation Generating electricity, we want to maximise the energy production of the system which occurs during our long summer days, and therefore elevation is set to maximise energy generation during this peak period of the year. At times when we are unable to generate electricity, we can simply import from the normal electricity grid, to maintain our appliances functioning. This maximises our year round electricity generation from the PV system. To optimise energy production your PV system should be specified for the installation to be oriented North or within ±20 either side of true North, and ideally elevated to on the roof (this has been confirmed by calculations done by Sustainable Living Tasmania using NASA solar irradiance data for Hobart, and confirming information from the South Hobart Community group). For those concerned that this is markedly different from their Solar Hot Water System (SHWS), optimised at 55 C, the SHWS is elevated to capture maximum solar gain during the winter when the sun is lower in the sky but higher in summer, since we use hot water all year round, but probably more in winter than summer. With PV panels, we are aiming to maximise energy generation which occurs during the longer summer days. This table illustrates typical electricity generation efficiencies in areas around Hobart Tasmania, depending on elevation angle and orientation towards North (thanks to Sustainable Living Tasmania for these calculations using NASA data). Orientation N Inclination % 78% 78% 78% 78% 78% 78% 78% 78% 78% 78% 78% 78% 78% 78% 5 80% 81% 82% 82% 83% 83% 83% 84% 83% 83% 83% 82% 81% 80% 80% 10 81% 83% 84% 86% 87% 88% 88% 88% 88% 88% 87% 86% 84% 83% 81% 15 81% 84% 87% 89% 90% 91% 92% 92% 92% 91% 90% 88% 86% 84% 81% 20 81% 85% 88% 90% 93% 94% 95% 96% 95% 94% 93% 90% 88% 85% 81% 25 81% 85% 89% 92% 94% 96% 97% 98% 98% 96% 94% 92% 89% 85% 81% 30 80% 84% 89% 92% 95% 97% 99% 99% 99% 98% 95% 92% 89% 85% 80% 35 78% 83% 88% 92% 95% 98% 99% 100% 100% 98% 96% 92% 88% 84% 79% 40 76% 82% 87% 91% 95% 97% 99% 100% 99% 98% 95% 92% 87% 82% 77% 45 74% 80% 85% 90% 93% 96% 98% 99% 98% 97% 94% 90% 86% 80% 74% 50 71% 77% 83% 88% 91% 94% 96% 97% 97% 95% 92% 88% 83% 78% 72% 55 68% 74% 80% 85% 89% 92% 93% 94% 94% 92% 89% 85% 80% 75% 68% 60 64% 70% 76% 81% 85% 88% 90% 91% 90% 88% 85% 81% 77% 71% 65% 65 61% 67% 72% 77% 81% 84% 85% 86% 86% 84% 81% 77% 73% 67% 61% 70 56% 62% 68% 72% 76% 79% 80% 81% 80% 79% 76% 73% 68% 63% 57% 75 52% 58% 63% 67% 70% 73% 74% 75% 74% 73% 71% 67% 63% 58% 53% 80 47% 52% 57% 61% 64% 66% 68% 68% 68% 67% 65% 62% 58% 53% 48% 85 42% 47% 51% 55% 57% 59% 60% 61% 61% 60% 58% 55% 52% 48% 43% 90 37% 41% 45% 48% 50% 52% 53% 53% 53% 52% 51% 49% 46% 42% 37% This fulfils 2 objectives, firstly alignment North to maximise solar gain, particularly during the long summer days, but also elevating the panels above the roof, helps optimise their generating efficiency, keeps them cooler and operating closer to their optimum electricity production temperature of 25 C. Corrugated iron and tile roofs can get very hot in summer which can increase the operating 6 P a g e

7 temperature of the panels, and thereby reduce their power generating efficiency, during really sunny days. Installers usually do not recommend framing unless the roof is less than 20 degrees or greater than 60 degrees, as it adds time and cost and increases wind loading. Often when mounted flush there is still adequate room for this important venting. Inverters There are several types of inverter, older style larger ones with transformers, which use power to run the inverter and give off waste heat, which are less efficient. These are largely replaced by transformerless (TL) inverters to which a number of panels are connected in one or more strings. Only problem here is that if one panel is shaded or not working correctly, the whole string is not producing energy until they are all un-shaded. More efficient yet are those High Frequency inverters having Maximum Power Point Tracking (MPPT), where they optimise the power produced from specific panels, and only the part shaded panel will cease to produce electricity. The latest inverters have 2 MPPT facilities, which can use 2 strings to optimise production from difficult roof configurations. MPPT can also improve output efficiency on variable cloud cover days, which can boost electricity generation from the PV panels by 1.5% or more, so it is an important technological advance. More recent but more expensive micro-inverters are now becoming widely accepted as potentially the most efficient and reliable option, but these have not been in the market long enough to determine their long term reliability and benefits. Here a micro-inverter is connected to each panel and should maximise its power performance by tracking each cell on the panel, so if one fails or is shaded, the other cells in that panel will still produce electricity instead of the whole panel ceasing production. This reduces DC cabling requirements where integrated on the panel, and should also speed up installation time. The downside is that most inverters will need to be replaced after years. With a single inverter you know when that is because the whole system shuts down. With micro-inverters, each may fail at a different time, requiring each to be replaced independently by a specialist, and it may take several to fail before you notice a significant drop in power production since each is responsible for less than 10% of total production, adding to the system maintenance costs. On balance we have therefore decided to recommend proven inverters with MPPT technology from a reputable manufacturer for SLiK members, to maintain generating efficiency and reliability over time. Having a single inverter to change during the life of the system, rather than many micro-inverters, could also prove more cost effective, over the system lifetime. Unless your CEC approved installer provides good reasons why micro-inverters may be a more cost-effective answer for your particular home. New meter required During the installation, your CEC approved installer will provide the necessary forms required to instruct Aurora to change the meter (at extra cost to the householder of around $200) so it can record the generated electricity exported to the grid from your Solar PV system. It will not record the power that is used in the house as it is generated, so there will be a disparity between the exported power shown on your bill and the total power generated by the system, as recorded by the MPPT inverter. Both readings are correct! The difference is what you have used, before it could be exported to the grid. 7 P a g e

8 Panel type Strengths and weaknesses STRENGTHS WEAKNESSES Monocrystalline Panels Proven technology in use for over 50 years. Made from slices of large single crystal ingots (hence mono crystalline) which reduces variability Most efficient type of module or panel, typically 13-19% efficient in real conditions This means more power is generated over the peak sun hours each day Marginally more expensive than polycrystalline or amorphous thin film modules Uses more embodied energy in production, than cheaper panels Output efficiency decreases by approx. 0.5% per degree C above the standard test temp of 25 C Often used where space is limited as fewer panels needed on roof Have very slow degradation (typically % per year) Usually provide best warranties typically 25 years,with best over 90% power generation output for 10 years and 80% output to 20 years. Most panels are pre-tested against damage from high winds, hail, snow, torrential rain etc., some also for coastal locations. Cooler Tasmanian climate means maximum efficiencies often achieved By-pass diodes usually supplied to allow current to flow through panels when cells are shaded to minimise risk of cell damage and maximise energy output 8 P a g e

9 STRENGTHS WEAKNESSES Polycrystalline panels Usually a little less expensive than monocrystalline modules By-pass diodes usually supplied to allow current to flow through panel when cells are shaded, to minimise risk of cell damage and maximise energy output Best panels are pre-tested against damage from high winds, hail, snow, torrential rain etc., some also for coastal locations. Produced from multiple crystals which may make them less efficient than monocrystalline modules, but panel is rated before sale to confirm output Sometimes require more modules on roof to derive the same amount of energy Less efficient than monocrystalline modules, typically 10-16% efficient in real conditions Cooler Tasmanian climate means maximum efficiencies often achieved Output efficiency decreases by approx. 0.5% per degree C above the standard test temp of 25 C Amorphous thin film panels Cheapest to produce and buy Lighter weight than either mono or polycrystalline modules Amorphous silicon is a common thin film technology but efficiencies are always lower than crystalline modules, typically just 6-10% Some are less susceptible to hail than glass covered monocrystalline modules Considerably more modules on roof needed to derive same amount of energy Less affected by heat so operate more effectively in hot conditions Often degrade in output by up to 10% when first exposed to sunlight. Use less embodied energy in production, than crystalline panels Output efficiency decreases slightly less than crystalline panels above the standard test temp of 25 C Lower lifetime guarantees Government incentives STCs As with the SHWS bulk purchase, those taking up this Solar PV recommendation will gain a number of Small Scale Technology Certificates (STCs) in recognition of its renewable energy production over the 9 P a g e

10 next 15 years. The Government announced (16 th November2012), that the 2x multiplier that was to apply to the first 1.5kW system capacity until 1st July 2013, would only apply for systems fully installed before 1 st January This means that the number of STCs for a 3kW system will be reduced from 79 to 53, reducing the Government assistance typically from $2,370 to $1,590 depending on the price at the time for each STC (remember they are traded a bit like shares, hence their value can rise or fall from the typical current $30/unit value), so you will be receiving approximately $780 less government subsidy than we expected when doing this research. We still believe it is worth investing, as there is a current over capacity of PV panels, and the Australian dollar is trading high against other currencies, so prices are as attractive as they are likely to be for quite some time. Likely costs and payback Detailed prices and specifications will vary depending on your specific situation and complexity of install, but we would anticipate nett installed costs to be typically around $7,400 for a 3kW system (after your STC contribution). Based on a continuing 28c/kWh feed in tariff and 53 STCs for a 3kW system, payback is likely to be around 7-8 years. With electricity prices expected to rise by around 25% over the next 5 years (Australian Energy Market Operator s Economic Outlook Information Paper 2012), if feed-in tariffs do not drop this could bring the payback period down further to around 5-6 years. This is conservatively only about ⅟ 4 of the way through the life expectancy of the system, so still pretty worthwhile as a longer term investment. This document necessarily only provides an overview. For more details we suggest you download the Clean Energy Council s Solar PV Consumers Guide from : Suggested Checklist: 1. Identify whether your roof faces true North (±20 ). Does it get shaded at any time(s) of day... if so how long and when? (any more than a small area for over an hour will have quite a detrimental impact, particularly in the peak generating hours in the middle of the day). Might be worth investigating whether the shading can be removed eg. by trimming shrubs or trees perhaps? 2. Identify your current electricity usage year round. What does this average each day in kwh? 3. You could save up to 30% on your current power bill by taking simple energy efficiency actions without installing a Solar PV system Identify those actions you can quickly implement and reduce your power usage further, for example: turn off appliances at socket (avoid standby) use low energy lights and turn off when not in use turn your heater thermostat down to 19 C check your shower flow and use a low flow version take shorter showers 10 P a g e

11 dry your clothes outside whenever possible rather than use the dryer wash clothes on cold wherever possible only use the dishwasher when full! 5. Now, once that is all done, review your likely power usage again. What does this average each day in kwh? What contribution will your proposed solar PV system generate (3kW system based on average 3.5 multiplier = 10.5kWh/day). 6. Identify what you can afford to spend on a PV system, and what roof area you have available that faces generally N. 7. A 3kW system could take up around 20m 2 of roof area (but having panels in 2 groups is feasible providing they both get good sun. The suitability of such options can only be determined by a site visit from an approved CEC installer). 8. If this represents a good value investment for you, then it is worth gaining quotes from local installers to meet your requirement. Disclaimer: This document has been prepared by SLiK and all information and data provided is intended to assist the reader in their own evaluation to gain a good quality, long lasting, reliable photovoltaic system. While every care has been taken to provide accurate information and impartial analysis, it is inevitably quite general in nature. We recommend you should seek specific advice from a Clean Energy Council approved installer in the area, who should provide: a cost-effective system design for your home estimate of annual electricity generation for any proposed system a firm quotation, including the offer of crediting you against his trading of the STC certificates generated by this renewable energy system, on your behalf. Ensure you are satisfied, before proceeding with any purchase. We wish you good luck, and hope this research has proved useful in achieving the PV system satisfaction you deserve. Author: Mike Willson. SLiK contact details: Mel Staples e:mstaples@kingborough.tas.gov.au SLiK February P a g e