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How To Survive A Long-Term Power Outage Solar And How It Works |
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HOW SOLAR WORKS
There is so much information that exists around solar, and with solar becoming more affordable and more available to the consumer for DIY projects, understanding how it works is a big first step before diving into your own solar project.
Basically, solar panels collect the energy from the sun, a charge controller distrubutes the energy to the battery(s) where the energy is saved, the inverter converts the 12v battery DC energy to 110v AC energy to power your devices and appliances. Unless you are comfortable working with electric devices and understand watts, volts, and amps, you should seriously consider a solar system kit which will make your first solar project simple, quick, and safe. Or, consider hiring a solar installation professional. In any event and after your first solar project, you will realize just how simple it really is to purchase and install a working solar system. 1. SOLAR ELECTRICITY BASICS Knowing how to relate power and energy together is a very important concept, but it is also important to have a more in-depth understanding of electricity. Current, Voltage, And Watts Current, Voltage and Watts are all related to electricity. Current is measured in amps. You can imagine current as the amount of electrons. Voltage is measured in volts. You can image the voltage being the amount of pressure pushing those electrons. More electrons or more pressure pushing electrons means more energy, just like more mass or more velocity for an object means more energy. Just like you will need mass and velocity to calculate the power or energy of an object, the same is true with current and voltage. Just having one is not enough. Wattage is a measure of power in an electrical system, and is made up of amps x volts. Watt-Hours is a measure of energy in an electrical system and is made up of amps x volts x run time. Alternating And Direct Current Electricity by default will travel in one direction, which is called Direct Current (DC). In a direct current circuit, electrons flow continuously in one direction from the source of power through a conductor to a load and back to the source of power. Originally electricity traveled by these means. The problem is, DC is not sustainable as it is hard to transfer electricity over long distances without power loses due to the low voltage level. Eventually Alternating Current (AC) was discovered. An AC generator makes electrons flow first in one direction then in another. In fact, an AC generator reverses its terminal polarities many times a second, causing current to change direction with each reversal. AC can create a higher voltage level depending on how you utilize it. This provides advantages for utility companies to transfer electricity over hundreds of miles with little loss by utilizing over a million volts at times, since voltage travels easier than current. Eventually when the power reaches back to your house it is outputted to 100-120VAC, or sometimes 200-240VAC. Because of this, most household appliance are AC. Now that you know the general differences in AC and DC, it is important to understand the difference of power in Direct Current (DC) and Alternating Current (AC). Ignoring efficiency losses from either, power should remain relatively constant in both. For example, we can take a 200W TV and look at it in terms of DC (12V) or AC (110V). In terms of direct current the TV would produce 200W / 12V = 16.6 Amps. In terms of alternating current the TV would produce 200W / 110V = 1.8 Amps. Although the amp and the voltage values differ, the overall power is the same. And the rate of energy consumption, not counting efficiency loses, would be the same. 2. SELECTING SOLAR PANELS Solar Panels in the basic sense work by converting available sunlight into usable electricity. The way we define this power is by watts. Watts are made up of amps and volts. Different panels have different ratings for amps and volts, and it is helpful to understand what these numbers mean when you are looking at a solar system. You can imagine amps as the amount of electrons, and the voltage as the amount of pressure pushing those electrons. Equation: Watts = Volts x Amps or W = V x A Solar Panel Components A solar panel is made up of different components. Not all panels will have these specific components in the specific locations, but generally, most panels have these components:
Monocrystalline Panels vs. Polycrystalline Panels Monocrystalline solar panels are slightly higher in efficiency than polycrystalline panels because each utilizes a different manufacturing technique. A monocrystalline cell consists of a single crystal ingot, whereas a polycrystalline cell consists of a growth containing multiple crystal structures. Both types of cells are made from silicon ingots, but the purity requirement of the silicon is higher on a monocrystalline base. Therefore, monocrystalline panels are more efficient, and thus, more expensive. By using a single cell, monocrystalline based silicon allows the electron greater freedom to move, so less energy is lost and higher efficiency is created. Most monocrystalline cells peak at 22% efficiency, whereas most polycrystalline cells peak at 18% efficiency. Monocrystalline cells are a dark blue almost appearing black, and polycrystalline cells are blue. Even though this is true, there is a common misconception that monocrystalline solar panels will actually perform better than polycrystalline panels even in situations where they have the same wattage. This is not necessarily true. A 100W Mono Panel should perform just as well as a 100W Poly Panel, assuming the electrical characteristics are very close. Your decision should be based on the price, the dimensions, and the color. Also due to common misconception, Poly and Mono panels should perform the same under low light conditions. They also should perform the same under high temperatures. Solar Peak Hours And Irradiance It is important to use the peak sun hours with the wattage of your system to calculate how many watt hours your system produces in a day. You can view peak sun hours as an average, as basing power off the hours of daylight during the day is not sufficient. This is because sunlight in the morning and evening will not produce as much radiation as solar during midday. To calculate each states peak hours, the radiation is averaged based on the highs and lows and also other factors such as what is mixed into the atmosphere. The level of irradiance or W/m2 varies throughout the day. The panels output is directly related to the W/m2 at that given time. Most solar panels are rated at 1000 W/m2. If the irradiance level would be 500 W/m2 at 8am in the morning, then you should expect half the output (50%). The solar peak hours of your state isn't how long the sun is out, but an average from the lows and the highs so that it can be a reliable number in calculating energy generation. SunCalc.org Sun solar position hourly and daily, sunrise, sunset, hours of daylight. 12V vs. 24V Solar Panels Panels come in compatibility of 12V and 24V, and you can wire them in various ways to remain at 12V or wire them up to reach higher voltages. These methods are called series and parallel connections. A series connection will keep the amps the same, but increase the voltage. A parallel connection will keep the voltage the same and increase the amps. Although we label a panel as "12V", the panel doesn't actually produce 12V. The voltage the panel produces is greater than 12V, the higher voltage is necessary for the battery to charge. Batteries must be charged at a higher voltage (like 13V) than what they are nominal (12V), as electricity will travel from higher voltage to lower voltage. How you end up wiring your panels depends on the voltage of your battery bank. The voltage of your panels need to match the voltage of your battery bank in order for it to charge properly (with the exception of the MPPT controller). Most RV and boats have 12V battery banks, so these people will usually use 12V panels to be compatible with the 12V batteries. 100 Watt 12V Monocrystalline Solar Panel
3. SELECTING A CHARGE CONTROLLER Charge controllers generally come in PWM and MPPT types. Different charge controller types have different benefits where a specific charge controller may be better than another in certain situations. Sizing different types of charge controllers is important and an essential component to every off-grid system. An off-grid system should always include a charge controller, and there are a lot of good reasons why. Charge Controller Function The main purpose of the controller is to prevent the batteries from over charging. The charge controller reads the battery level, and once the battery is full, it knows to slow down the rate of solar charge to a float, keeping it from charging the batteries past 100%. This is important as overcharging the batteries can potentially ruin the batteries. Another purpose of the controller is to charge the batteries at the correct voltage level. This helps preserve the life and health of the batteries. Some controllers have special characteristics which allow you to wire your panels in a special way to achieve your charging goals. PWM Charge Controller Function PWM stands for Pulse Width Modulation, which stands for the method used to regulate the charge. PWM controllers have the more basic charging feature in the sense that they mainly just drop the voltage coming from the panel to charge the batteries. This drop in voltage equates to a loss in wattage, in the case of the PWM causing a 75-80% efficiency. PWM Charge Controller Sizing A PWM controller will have an Amp reading for the charger, for example 30 Amp PWM controller. This represents how many amps the controller can handle. Generally the two things you want to look at for a PWM controller is the amperage and voltage rating. First look at the system nominal voltage. Nominal voltage tells you what or which charge controller is compatible with the voltage of the battery banks. Common battery banks for small solar systems are 12V or 24V. Anything higher, such as a 36V or 48V battery bank, this charge controller will not be able to support. Second we look at the rated Charge Current using a 30 Amp rating for a 30 Amp PWM controller. Use a factor of safety of at least 1.25 for the charge current, meaning you would multiply the current from your panels by 1.25 and then compare that to the 30 amps. For example: 5 x 100 Watt panels in parallel would be 5.71 x 5 = 28.55 Amps. 28.55 Amps x 1.25 = 35.68 amps and would be too much for the controller. The reason for this is the panel can experience more current than it is rated for when insolation is above 1000 Watts/m^2 or tilted. Third we will look at the Max. PV Open circuit voltage. This tells you how many volts you can have going into the controller. This controller cannot accept more than 50V. For example: 2 x 100 Watt panels in series for a total of 22V (open-circuit voltage) x 2 = 44 volts. In this case, it will be alright to wire these four panels in series. Fourth we can look at the Terminals. Each controller will usually have a maximum gauge size for the terminal. In the case of this PWM controller, it can handle up to # 6 AWG. This is important when purchasing wiring for your system. Fifth we can look at Battery Type. These tells us what batteries are compatible with the charge controller. This is important to check as you do not want to have batteries than cannot be charge by the controller unit. Low voltage reconnect / disconnect: This only applies to controllers that have a load terminal. The low voltage disconnect is the battery voltage level at which the load cuts off. The low voltage reconnect is the battery voltage level where the load turns back on. For those charge controllers with or without this feature, a low voltage reconnect / disconnect device can be added between your battery and load to help protect your battery from over discharging. MPPT Charge Controller Function MPPT stands for Maximum Power Point Tracking, which stands for the method used to regulate charge. MPPT charge controllers use this method to find the maximum operating point for the panels current and voltage. With this method, MPPT controllers are actually 94-99% efficient. MPPT controllers have two special features: they can accept a high input voltage and step this voltage down to match your battery bank voltage for a correct charge and even though they lower the voltage, they are able to recover any potential lost power via a boost current, which increase the amperage to make up for the lost voltage. MPPT Charge Controller Sizing MPPT charge controllers will have an Amp reading for the charger, for example 40 Amp MPPT Controller. They will also have a voltage rating, but unlike PWM the input voltage rating is much higher than the battery banks it will charge. This is due to the special property of the MPPT controller being able to lower the voltage to the battery bank voltage and then increase the current to make up for lost power. You do not have to utilize the high input voltage if you want to avoid series connections in small systems, but it is very beneficial in larger systems and this controller can handle 12V or 24V battery banks. For example: an MPPT-40 charge controller is rated for 40 amps of current where the Max Solar Input Voltage, is 100 Volts. This particular MPPT Controller can accept 100 Volts input. It will then take this (up to) 100 Volts and step it down for a 12V or 24V battery bank. Another example: A 400W system in series consisting of 4 x 100 Watt panels, each with an open-circuit voltage of 22.5V. Those 4 in series will be 4 x 22.5 V = 90 Volts, which the controller can accept. Now if we ignored boost current, we would see that string only has 5.29 amps, so then if the controller is 40 amps, couldn't we have (40/5.29 = 7.5) 7 strings, bringing us 2800 Watts? Why does the spec sheet say 520 Watt maximum? To answer this, we need the boost current. Boost current can be calculated by taking the system array wattage divided by the battery bank voltage. In the case of 2800 Watts, we have 2800 Watts / 12 V = 233 Amps, which would destroy the controller. Realistically we find that 520 Watts / 12V = 43 Amps. We can ignore this result as 12V is a voltage you will probably never see. More accurately you would divide by boost voltage which is more common, 520 Watts/14.4V = 36 Amps. We can now see why the boost current is an important part of sizing the controller. Boost Current = Solar Array Wattage/Battery Voltage Charge Controller Models As your panels charge your battery bank, your controller will adjust what voltage level they are being charged based on the voltage level of the battery. These different voltage levels represent different charging stages. Equalization charging voltage: An equalization voltage is one you will most likely never see. It occurs roughly every 20 to 30 days, and it temporarily over-charges your batteries to desulfate the battery cell. This helps with the battery cell health and allows them to last longer. The equalized voltage will vary based on the battery type. You can also set the equalization voltage, which is beneficial for certain batteries that require a custom set parameter. Boost charging voltage: A boost charge is a majority of what you will see when your battery is being charged. This is what does the majority of the charging of the battery. Boost charging voltage can vary for each battery type and the user can usually set the voltage level. Float charging voltage: A float charge is used when the battery is full to prevent overcharging. A float charge will still charge a battery, but reduce the voltage and current equal to the batteries natural discharge rate, which depends on the battery bank size. Low voltage reconnect / disconnect: This only applies to controllers that have a load terminal. The low voltage disconnect is the battery voltage level at which the load cuts off. The low voltage reconnect is the battery voltage level where the load turns back on. Additional Features Some controllers have extra features that can be beneficial and worth mention. Load terminal: The load terminal comes with some controllers and allows you to attach a DC load to the controller, rather than having to attach it to the battery. It is usually noted with a light bulb symbol and sometimes used for the timer function. You can program the load to turn on at sundown and off at sunlight. This is particular useful for lighting. LCD Display: An LCD display can display different characteristics of your system and give you a more accurate portrayal of what is going on in your system than from the LED lights. This controller in particular will have icons that show what is happening in your system. It also displays numerical values for the panels and batteries voltage and amperage that your system is producing. Keep in mind, not all controllers have an LCD display and this is usually included on more expensive controllers. RTS Interface: Connection for a RTS (Remote Temperature Sensor) to remotely detect battery temperature. Battery temperature detection can help improve charge controller battery maintenance more accurately. RS485 Communication interface: Monitor controller by PC, remote meter MT50 or APP and update controller software via RS485 (RJ45 interface). MT50 can display various operating data and fault of the system. The information can be displayed on a backlit LCD screen, the buttons are easy to operate, and the numeric display is readable. There are a variety of charge controllers each with different features that sets them apart from one another. When choosing which charge controller is right for you, keep the following in mind. If you like to know what the system is producing throughout the day, we recommend choosing the MPPT charge controller with LCD Display or PWM controller . If the controller will be mounted outside then a PWM controller might be the one for you. Many MPPT controllers offer load terminals and a PC Monitoring Software. The PC Software allows you to customize the controller charging parameters and load terminal. You might like the MPPT controller or PWM controller if you like knowing every little detail about your solar system. If you just want something simple without all these extra features , the cheapest charge controller might be your option. One of the most important features when choosing a controller is making sure it can charge the type of battery you have. Most charge controllers are capable of charging Sealed, Gel and flooded batteries but if you will be charging a Lithium battery only the Voyager or Rover MPPT types are compatible. 4. SELECTING SOLAR BATTERIES The most important part of the off-grid system is the solar battery/battery bank, which stores the energy generated from your system. There are many different types of batteries on the market for various applications. Solar systems work with deep cycle batteries and not common cold cranking amp (CCA) automotive batteries. Deep cycle batteries can be charged and discharged at a slow rate and are ideal for solar setups. Battery Purpose The main purpose of the battery is to store energy produced by the solar panel(s). Without this component, an off-grid system will be incomplete. Batteries are generally rated by a voltage level, most common are 6V or 12V, and an Amp-Hour rating. This Amp-Hour rating is important to know the capacity of the battery. Most small systems are 12V. RV and boats are usually 12V systems. A set of batteries connected together is called a battery bank. Battery Sizing To understand battery sizing, we must understand the capacity of the battery. Batteries being measured in Amp-Hours and Volts, need to be calculated into Watt-Hours to tell you the energy. It is important to know both the Amp-Hours and Volts of your batteries. Example: 2 x 100AH batteries, one being 6V and the other being 12V. The 6V battery will be measured at 6V x 100 AH = 600 Watt Hours. The 12V battery will be measured at 12V x 100 AH = 1200 Watt Hours. As you can see even though they have the same Amp-Hours, their energy is different. To size a battery, we need to first understand your consumption. We can calculate consumption as Wattage of Appliance x Hours of Run Time. Once we get this Watt-Hour value, we can divide it by 12V to get the battery in terms of Amp Hours. We also prefer to double this value, as we recommend a depth-of-discharge of only 50% to help preserve the life of the battery. You should never drain the battery below 50%. Another example of a 35 Watt fan running for 6 hours. We have 35 Watts x 6 Hours = 210 Watt Hours. We then do 210 Watt-Hours/12V = 17.5 Amp-Hours. We then want to double the value for depth of discharge (DOD) of 50%, so we have 17.5 Amp-Hours x 2 = 35 Amp Hours. Your battery size would be 35AH at 12V. Keep in mind this is in 12V. To see this same battery in 24V, you would do 210 Watt-Hours/24V = 8.75 AH. You can then double this to 17.5 Amp Hours. This battery would be 17.5 AH at 24V. You can utilize multiple batteries in series, parallel, or series-parallel to get a desired battery bank size. Battery Types The most common and recommended battery type for storage is Lead Acid Batteries. Most common is a Sealed or Flooded Lead Acid battery. It is important to make sure that your controller is compatible with your battery type. Other types of compatible deep cycle batteries are: AGM, Gel, and Lithium-Iron Phosphate. The AGM and GEL batteries have very similar characteristics whereas the Lithium-Iron battery is vastly different. You should research the various battery types to see which type is best for your application as they range in efficiency, size, weight, and cost. Once you choose a battery type and size, you can then start putting your system together. The battery is where all the energy is stored in the system and following all the safety precautions and guides is necessary. 5. SELECTING AN INVERTER The inverter gives you the ability to run AC powered devices through your 12V battery. The inverter charger acts as an inverter and gives you the ability to charge your 12V battery from an AC power hookup. You can choose different size 12V inverters and inverter chargers depending on your application and use. Inverter Purpose The purpose of the inverter is to convert DC energy to AC energy. Since batteries are DC, the inverter exists to allow you to run your AC appliances. They will come with an AC outlet(s) to plug in things such as your computer, or fridge. Inverters come in sizes of Watts and Volts, and can change DC (12V) to 100-120 Volts or 200-240 Volts. It is important to make sure the voltage of your inverter matches the voltage of your battery bank. The inverter charger acts as an inverter and gives you the ability to charge your 12V battery from an AC power hookup. Common sizes are 500W to 2000W inverters and 1000W and 2000W inverter chargers. Inverter Sizing When sizing for an inverter you need to look at 3 factors: wattage, DC voltage, and AC voltage. Wattage Inverters will be rated by a wattage value, telling you how many watts it can run at one time. For example: a 500 Watt Fridge and 800 Watt Air Conditioning. These two items combined would be 1300 Watts and would require an inverter with a slightly higher wattage value than 1300W. DC Voltage The DC voltage rating on the inverter will tell you what battery bank it is compatible with. For example: a 24V battery bank, will require an inverter that is compatible with 24V. AC Voltage The AC voltage rating on the inverter will tell you what kind of AC appliances it will run. Most of the time a 100-120VAC(Volts AC) inverter will be alright as most household items use that voltage. Sometimes very large loads will run on 200-240VAC so it is important to know this for special items you want to run. The inverter size is solely dependent on what devices are going to be running on the inverter. If you are running multiple devices, then you will have to add the wattage consumption of those devices together. For example, if you want to run a television (800 Watts) and a Blu-ray player (400 Watts) at the same time, you would add those values together (800W + 400W = 1200W) and that tells you that you need an inverter that is capable of handling 1200W at the same time, in this case a 1500W or higher inverter. Inverter Types Inverters come in modified and pure sine wave types. Modified sine wave inverters are usually much less expensive, produce unclean energy and are very limited to what appliances you can run. Pure sine wave inverters produce very clean energy and are compatible with most devices including most sensitive electronics, best to use these pure sine wave inverters. How To Connect The inverter is separate from your solar system and does not require a solar system to run. The inverter runs directly off a 12V source or battery bank and is very user-friendly to set up. Note: It is important to be mindful of what is running through the inverter. Inverters are great for running AC devices on a DC battery but are not very efficient. Running most devices through an inverter will put a large drain on your battery, that's why it's important to keep track of what you're running and how long you are running them. With that in mind, you can now enjoy using your inverter to run your household devices through your battery bank. 6. SOLAR SYSTEM SETUP Before and while you are setting up your solar system, the panels should be out of the sun or covered for safety reasons. Before connecting your panels to the charge controller, the battery should be connected to the charge controller. You can use your tray cable or any general stranded copper core wire to connect the battery to the charge controller. Make sure that the wires from the battery terminals and charge controller match the + and - on both. Connect the exposed wires tightly inside the charge controller terminal. Then, connect the battery rings to the battery. A reversed or crossed connection can damage your battery or charge controller. At this point, your charge controller will display battery information. Then, connect your solar panel wires to your charge controller. Connect the adapter kit to your panel first, then follow the + or - sign coming off of the leads of the panels and match it with the + and - sign on the charge controller. Make sure the panel leads are inserted into the correct slots, you can have reverse polarity and short the system causing damage to the panels or controller. Now, you can connect your inverter to your battery by using battery ring cables and by matching the + to + and - to -. 7. SOLAR SYSTEM KITS A complete solar kit consists of all of the components needed to charge and discharge a battery bank. In general, solar system size and components are determined based on your energy requirement. You will need enough batteries to provide your energy requirement or expectation. Next, you will need enough solar panels to provide enough energy to sufficiently charge and maintain those batteries, then you can select a charge controller to charge and maintain those batteries. The inverter size will depend on the highest amount of wattage needed to operate your devices and appliances. Unless you are keen at managing your energy usage, you should consider to buy a solar system kit where solar panels and solar batteries can be added to upgrade your energy usage. For many reasons, it is a good idea to purchase a slightly larger solar system (and expandable) than anticipated. You won't be sorry. There are two types of solar kits: On-grid kits and off-grid kits. Depending on your application and power requirements, will determine which kit is for you. On-grid or grid-tied kits tie into your electrical company's grid and typically work best with larger applications such as residential and commercial buildings. Grid-tied systems require professional installation and city permits. Off-grid systems are commonly used for smaller applications such as sheds, barns, RVs, vans, boats, and tiny homes. Off-Grid kits are user-friendly, DIY kits that require a battery bank for energy and they do not connect to the electrical grid. The first step in setting up your solar system is to determine which type of solar system is necessary for your application. If you are trying to power a house, cabin, commercial building, or a large-scale structure, it will be more practical to go with an on-grid grid-tied system than an off-grid system. If you are looking to power smaller applications such as sheds, barns, RVs, vans, boats, or tiny homes, an off-grid system with a battery bank will probably work for you. The second step is determining the size of the solar system. For on-grid applications, your monthly electrical bill contains all your electrical usage information. Off-grid systems require a little bit more work. To size a system that will best fit your needs, make a list of all the devices you plan on running. Get the wattage information, or the amps and volts of the product, and provide an average run time per device. With that information, you can size an appropriate system that will run effectively and efficiently. The third step is setting up your new solar system correctly. For an on-grid system, it is necessary to contact your local electrical company to inform them that you are planning on going solar and contact a licensed installer/contractor for the installation of the system. They will be able to walk you through the rest of the process. For off-grid kits, you may or may not consult with an installer or electrician for guidance and support. Most off-grid kits are DIY ready with a user-friendly installation process; usually installation guides are available online. Once everything is set up, your system will start generating power as soon as the sun comes up. 8. SERIES AND PARALLEL PANELS Why Parallel Panels? Parallel panel connections are mostly utilized in smaller, more basic systems, and usually with PWM charge controllers, although there are exceptions. Connecting your panels in parallel will increase the amps and keep the voltage the same. This is often used in 12V systems with multiple panels as wiring 12V panels in parallel allows you to keep your charging capabilities at 12V. The downside to parallel systems is that high amperage is difficult to travel long distances without using very thick wires. Systems as high as 1000 Watts might end up outputting over 50 amps which is very difficult to transfer, especially in the systems were your panels are more than 10 feet from your controller, in which case you would have to go to 4 AWG or thicker wire which can be expensive in long runs. Also, paralleling systems require extra equipment such as branch connectors or a combiner box to connect all of the panel wires to one wire connecting to the charge controller. The upside to parallel systems is shading. When panels are wired in parallel, they do not depend on each other. If one panel is shaded it will not affect the whole string. This is not true with a series connection. Why Series Panels? Series panel connections are mostly utilized in smaller systems with a MPPT charge controller. Connecting your panels in series will increase the voltage level and keep the amperage the same. The reason why series connections are utilized with MPPT charge controllers is that MPPT charge controllers are able to accept a higher voltage input, and still charge your 12V or more batteries. Many MPPT charge controllers can accept 100 Volts input. The benefit of series is that it is easy to transfer over long distances. For example you can have 4 x 100 Watt panels in series, run it 100 feet and only use a thin 14 gauge wire. The downside to series systems is shading problems. When panels are wired in series, they all in a sense depend on each other. If one panel is shaded it will affect the whole string. This will not happen in a parallel connection. Why Series And Parallel Panels? Solar Panel arrays are usually limited by one factor, the charge controller. Charge controllers are only designed to accept a certain amount of amperage and voltage. Often times for larger systems, in order to stay within those parameters of amperage and voltage, we have to be creative and utilize a series-parallel connection. For this connection, a string is created by 2 or more panels in series. Then, an equal string needs to be created and paralleled. 4 panels in series need to be parallel with another 4 panels in series or there will be some serious power loss. There is not really a downside to series-parallel connections. How To Set Up Your System With Parallel Panels A Parallel connection is accomplished by joining the positives of two panels together, as well as the negatives of each panel together. This can be accomplished by different means, but usually for smaller systems this will be utilized via a set of two branch connectors. A branch connector has a Y shape, where one branch connector has two inputs for positive into one connector and another branch connector with two inputs for negative into one connector. The one negative out and the one positive out will be connected to the charge controller using a solar PV cable. Example: You have 2 x 100 Watt solar panels and a 12V battery bank. Each panel is 12V and the battery bank you want to charge is 12V, and you want to parallel your panels to keep the voltage the same at 12V. The operating voltage is 18.9V and the operating current is 5.29 amps. Paralleling the system would keep the voltage the same and increase the amps by the number of panels paralleled. In this case you have 5.29 Amps x 2 = 10.58 Amps. Voltage stays at 18.9 Volts. To check math you can multiply 10.58 amps x 18.9 volts = 199.96 Watts, or pretty much 200 Watts. How To Set Up Your System With Series Panels A Series connection is accomplished by joining the positive of one panel to the negative of the other panel together. With this you do not need any additional equipment except for the panel leads provided. Example: You have 2 x 100 Watt solar panels and a 24V battery bank. Each panel is 12V and the battery bank you want to charge is 24V, then you need to series your panels to increase the voltage (and not the amps). For safety, use the open circuit voltage to calculate series connections, in this case the 100 Watt panel has 22.5 Volts open circuit, and 5.29 amps. Connection in series would be 22.5 volts x 2 = 45 volts. Amps would stay at 5.29. The reason we use open circuit voltage is we have to account for the maximum input voltage of the charge controller. To check the math will not work with the open circuit voltage. You can use the operating voltage to multiply 18.9 volts x 2 = 37.8 volts. 37.8 volts x 5.29 amps = 199.96 Watts, or pretty much 200 Watts. How To Set Up Your System With Series And Parallel Panels A series-parallel connection is accomplished by using both a series and a parallel connection. Every time you group panels together in series, whether is 2, 4, 10, 100, or more is called a string. When doing a series-parallel connection, you are essentially paralleling 2 or more equal strings together. Note: A 40 Amp MPPT Controller can accept up to 1000 Watts of power, but only up to 100 Volts. Therefore panels all in series may not work. Paralleling 8 panels as well would cause too high of an amperage. For this example, you would use the open circuit voltage of 22 Volts and the operating current of 5.71 Amps. Creating a string of 4 panels, you will have a voltage of 22 Volts x 4 = 88 volts, which is under the 100 Volt limit. Then by paralleling on the other string, the voltage will stay at 88 volts and the amps will double, so 5.71 amps x 2 = 11.42 Amps. Note: There is usually another factor to be taken into account when sizing for the MPPT Controller called the boost current. To check math will not work with the open circuit voltage. You can use the operating voltage to multiply 17.48 volts x 4 = 69.92 volts. 69.92 Volts x 11.42 amps = 798.49 Watts, or pretty much 800 Watts. 9. SOLAR ENERGY AND POWER One of the most important concepts to understand when sizing a system or figuring out how much your panel produces is Power and Energy. Power Power is defined as rate of doing work. It essentially tells you how quickly you can produce energy. Power takes on different forms, but when dealing with electricity or solar, you will define power as a Watt (Watts = Volts x Amps). Multiplying the panel's voltage by amperage will give you a value in watts. This is also true for an appliance. Energy Energy is the capacity for doing work. It essentially tells you how much work can be done. Energy can take different forms, but when dealing with electricity or solar, you will define energy as Watt Hours (Watt Hours = Watts x Hours). Multiplying an appliance's wattage times how long it will run, will give you its energy value. Multiplying a panel's wattage by the peak solar hours will give you its energy value. Energy In Panels For Solar Panels, the energy produced is dependent on how much sun you get in your location. Sun hours will vary from state to state, but it is important to have an idea of what your state's peak solar hours are. For example, let's look at a 100W panel in Texas vs. Nevada. Using Texas's low value of 4.5 peak hours and Nevada's low value of 6 peak hours we can calculate the energy or Watt-Hours produce by the panel. For Texas, 100 Watts x 4.5 Hours = 450 Watt-Hours. For Nevada, 100 Watts x 6 Hours = 600 Watt-Hours. As you can see the state location does have an impact on energy production, in this case by 150 Watt Hours. Energy In Appliances For appliances, the energy produced is dependent on the wattage value of the appliance along with the hours of run time. It is very important that you have the wattage, not just the voltage or amperage as those aren't complete power values. For appliances, you can take the voltage and multiply it by the amperage. For example, an 8 Amp refrigerator at 110V will be 8 Amps x 110 Volts = 880 Watts (when running). Let's take two 35 Watt fans. One we will run for 2 hours and the other for 5 hours. The first fan consumes 35 Watts x 2 Hours = 70 Watt Hours and the second fan consumes 35 Watts x 5 Hours = 175 Watt Hours. As you can see, given the same fan, the second one takes more energy since it is ran for longer. Energy In Batteries We can also relate energy to batteries as well. Knowing only your battery voltage is not a complete form of energy, this information alone is not enough to determine how much your batteries can store. You must find the Watt-Hours value. Luckily most batteries are rated in a term called Amp-Hours. Although this has hours in it, it still isn't energy. To get Watt-Hours we must multiply Amp-Hours x Volts. Amp-Hours x Volts = Watt-Hours For example two batteries, one 6V and one 12V. The 6V battery is rated at 100 Amp-Hours (AH) and the 12V battery is rated at 75 Amp-Hours (AH). The energy of the first battery is 6V x 100AH = 600 Watt-Hours. The energy of the second battery is 12V x 75AH = 900 Amp-Hours. As you can see even though the first battery has more Amp-Hours, it does not have more energy or storage. 10. SIZING A SOLAR SYSTEM Step 1: Load sizing Sizing your system starts with what loads or devices you want your solar system to run. It is important to get the wattage of each item you are planning to run along with how long you plan on running them for. You will multiply the watts by the hours to get Watt-Hours. If you have more than one appliance, you add them all together to get the total Watt-Hours. Step 2: Solar Wattage Sizing Determine your state's peak solar hours. Then, take the load Watt-Hours and divide it by your state's peak solar hours to get Watts. This will be the Watts you need to run those items before efficiency loses occur. Since your system will run through a controller, there will be efficiency losses. For a PWM controller you will have around a 79% efficiency and an MPPT will be around 94% efficiency. Then take the Watt value from before and divide it by the efficiency to get an actual wattage value. If you are using an inverter, you want to do this again by dividing the value by the inverter 90% efficiency. Now, you have the wattage needed to run your appliance(s). Step 3: Controller Sizing Find a controller that can accept the wattage you need. You can check the controller specification sheet to see the wattages they can handle. For example: a 30 Amp Controller can handle 400W on 12V, so you know you can have up to 400 Watts. Step 4: Battery Sizing To size your battery, double your initial Watt-Hours value so your loads only drain the battery down 50%. Then take new Watt-Hours value and multiply it by 2 and divide by the battery voltage, either 12V, 24V, or 48V based on what controller you plan to use to find the Amp-Hours needed. Step 5: Inverter Sizing Add up all the wattages of all the items you want to run to choose an inverter capable of more wattage than your total wattage needed. Make sure your inverter matches your battery bank voltage. 11. FUSING A SOLAR SYSTEM When hooking up your solar system, the best way to add protection is by using fuses or circuit breakers. Fuses and circuit breakers are used to protect the wiring from getting too hot and also protect all devices connected in the system from catching fire or getting damaged if a short circuit occurs. They are not necessary for the system to run properly, but it is always a good idea to use fuses or circuit breakers for safety purposes. There are three different locations to install fuses or breakers:
Note: There are other aspects such as cable size/length and fuse/breaker types, when amperage increases, that are important as well. |
