Introduction to Solar PV Basics
Solar PV Introduction 1. Solar PV Theory a) Photoelectric Effect b) What is a Solar Cell c) How do Solar Panels work d) What are solar panel basic components e) Types of solar cells (types of solar panels ) f) Module Efficiency g) Temperature coefficient effect of temperature on solar panels 2. Basic components of solar systems a) Panels b) Mounting equipment c) Inverters d) Isolators e) Wiring
Solar PV Introduction 3. Not all panels are the same 4. Battery systems a) DC coupled b) AC coupled c) Hybrid 5. Battery types a) Lead Acid b) Lithium Ion 6. Calculating solar yield 7. Site survey Pre-Installation checklist
Theory 1. Solar PV Theory Photovoltaic Solar Panels get their name from two words. Photo meaning light, and Volt being unit of measure for electricity. As the name suggests, Photovoltaic (or PV) panels convert light directly into electrical energy. a) Photoelectric Effect - PV solar panels produce your electricity using something called the photoelectric effect. - Certain materials would produce a small electric current when you exposed them to light.
Theory b) What is a Solar Cell - Solar cells are small devices which can convert sunlight into electricity. - One cell on its own will only provide a very small amount of power. - Several cells connected together and fixed in a frame make a solar panel (or a module), this will produce a larger, useful amount of power. - When several panels are connected together this creates a solar array. Example: To achieve a 5kW solar array you will require 19x 260W modules (4.94kW) or 19x 265W modules (5.03kW) etc.
How it works c) How do solar panels work - Inside a solar cells have two wafer-thin layers of silicon crystal, placed on top of each other to make a sort of silicon sandwich. - The top layer has been specially treated so that its atoms are unstable they have one too many electrons that they need to get rid of. - The bottom layer has also been treated, but this time the atoms have a few empty spaces that need an electron to fill them. - This setup puts everything is in place for electricity to be produced, all that s needed is the sunlight: the electrons within silicon crystal will not move around freely until the solar panel is exposed to light.
How it works - When sunlight hits the top silicon layer, it excites the electrons and gives them enough energy to move. - The electrons begin to flow from the top layer to the bottom. - When electrons move in the same direction, this is electricity. - When placing two metal contacts on either side of the silicon sandwich and we have electricity moving through a circuit.
Solar panel components d) Solar panel basic components - Frame structural component for strength and rigidity and to allow for module fixing - Glass rigid protection from elements - Laminating (encapsulant) x2 - adhesion between different layers - Cells main active components of solar panels - Backsheet protection from UV, weather, moisture and acts as an electrical insulator - Junction box main electrical connection with external devices
Monocrystalline e) Types of solar cells, types of solar panels. Majority of the World s photovoltaics today are based on some variation of silicon - Crystalline Silicon (c-si) or Amorphous Silicon (a-si). These are the main types: Monocrystalline Silicon Solar Cells - most efficient - Monocrystalline cells are made by growing a single crystal. - The way they are cut gives them recognizable appearance - missing corners - The crystals structure is even so they do not show grain marks - Most efficient, but also the most expensive
Polycrystalline Polycrystalline Silicon Solar Cells best value - efficiency levels close to monocrystalline panels, but at a lot less cost - Polycrystalline solar is made by pouring molten silicon into a cast. - The crystal structure forms imperfectly, creating boundaries where the crystal formation breaks. - Impurities in the crystal mean the polycrystalline silicon is slightly less efficient when compared with mono. - Polycrystalline is sometimes called multicrystalline
Thin film Thin-Film Solar PV - portable and light weight The technology with the lowest market share, but while it has several disadvantages, it is a good option for projects with lesser power requirements but needs for light weight and portability. Please note we do not supply Thin Film Modules.
Module efficiency f) Module Efficiency - Module efficiency is a mathematical equation of maximum power output of module divided by total surface of the module - a 1638 x 982mm module with max power output of 265W will have efficiency of approx 16.48-16.5%. - This is calculates as: Module surface area = 1.638 x 0.982= 1.608m 2. Which means power of 265 divided by surface of 1608. 265/1608= 0.1648 = 16.48% - Cell efficiency will always be higher than the whole module efficiency. - Not all of the module area is active, some of it is the frame or spaces between the cells plus electrical connections between the cells create losses. - When comparing modules its important to distinguish the two values.
Temperature coefficient g) Temperature coefficient effect of temperature on solar panels Each module data sheet quotes temperature characteristics as per below: - Silicon modules become less efficient as temperature increases their voltage and power will drop as per the values specified on data sheets. - The -0.31% value above means that for every degree of temperature increase, the module will loose 0.31% of its power. - Standard test conditions are at 25deg, the actual temperature on the roof on a hot summer day will be considerably higher - The smaller the numbers on the spec sheet (so the closer they are to zero) the better the module will perform at high temperatures.
2. Basic components of solar systems. Components of solar systems
Components of solar systems
Components of solar systems a) Panels - PV panels are the single biggest expense of a PV system. Their placement and mounting affect your system performance more than any other part of the job. As cells above, these can be Mono, Poly or Thin film.
Components of solar systems b) Mounting equipment - Critically important - Mount for maximum sunshine over the year - Mounting kit should be strong enough to hold the system for its lifetime - Roof must be structurally sound and not compromised by the solar array - Not advisable to install on a roof that has asbestos - Seek an expert survey if in doubt
Components of solar systems c) Inverters DC-to-AC grid connected inverters. - Panels create DC (direct current), appliances in properties use AC (alternating current - Inverters convert DC from panels to usable AC - All inverters need to be sized correctly to the size of the pv array - Pv strings need to be correct length (No of panels) to keep within the manufacturer recommended inverter voltage range - Inverters tend to be the weak point in PV system, so quality is a must
Components of solar systems d) Isolators - - Isolators are important safety feature - Need to be mounted within easy reach - Need to be sized according to max voltage, current and power of all relevant parts connected and adjusted with following safety factors - For Mono or Poly crystalline installations all d.c. components must be rated, as a minimum, at: - Voltage: Voc(stc) x 1.15 - Current: Isc(stc) x 1.25
Components of solar systems e) Wiring - Cables, conduit and connections are considered low initial cost outlay, but they comprise a big chunk of labour when installing - All DC and AC components (cables, isolators / disconnectors, switches, connectors, etc ) need to be sized for voltage, current and power of all parts connected and should also include safety factors - Attempt to cut cost at this stage, to try to save money is not advisable, as the whole PV system is only as good as its weakest link
Choosing a solar panel 3. Not all panels are the same. When choosing module for your 25 or more years investment you should ask the following questions: a) Warranty length what is the length of warranty? b) Financial stability of manufacturer - will the manufacturer be there to honour the warranty in a few years, 20 years? c) Plus tolerance of module are the modules plus tolerance or plus / minus tolerance? d) Quality of used components will the panels last the predicted 20-25 years of its life on the roof e) Automated manufacturing process are the panels made using robots or humans? Robots tend to make less mistakes and be more accurate so the panel should last longer f) Does the panel manufacturer make the own cells as well? g) How long has the manufacturer been making panels for?
Batteries 4. Battery systems a) DC coupled System DC DC Charger This system is installed between the solar panels and the standard grid connected pv inverter. It takes the solar power and uses the excess energy to charge the solar panels. It outputs in DC to the normal Solar Inverter to convert to AC for use in the property. b) AC coupled system AC DC Charger This system fits between pv inverter and consumer unit it takes AC then converts this to DC to charge the batteries. It also takes DC from the batteries and output AC c) Hybrid System This Unit combines a standard grid connected PV inverter with DC DC battery charger. It charges the batteries and outputs in AC this may have a secondary output for essential goods
Batteries 5. Type of batteries The two types of batteries most commonly offered for solar PV storage in the home are: a) Lead Acid (similar to the ones used in cars) Cheaper Typically used for off-grid properties where more storage is required Heavier and larger Need good charging and discharging routine to maintain battery
Batteries b) Lithium Ion (commonly found in electronic devices such as laptops and mobile phones) More expensive Increasingly common in domestic grid-connected solar PV storage systems Lighter Require integrated controller, which manages charge / discharge More efficient Can discharge more stored energy Longer expected lifetime
Solar Yield 6. Calculating solar yield Solar PV yield depends on following variables: -Base Irradiance values for specific geographical location (in kwh/kwp) Bloemfontein 1900 Cape Town 1600 Johannesburg 1650 Port Elizabeth 1500 -Deviation from a north-facing orientation (in the southern hemisphere) -Deviation from optimal module inclination -Shading
Site survey Pre-Installation checklist 7. To be able to prepare an accurate quotation you will require the following information: Type of roof (pitched or flat, tiled or metal or standing seam) Usable roof dimensions (size available for solar panels) Orientation and pitch of the roof Roof substructure (wood, steel) Type / brand of panels required if known Type / brand of inverter required if known