The goal of this article is to provide a relative novice everything you need to know about batteries for solar power systems, without inundating you with technical details, so you can make the right choice for your system. To this end, I will list the types of batteries commonly in use at this time (2018) and highlight only the technical aspects germane to performance, cost, and maintenance in the context of a solar power system application.
There are four types of batteries commonly in use for solar power systems. The first three are variants of Lead-Acid technology. This technology has been around for a long time, thoroughly proven in the industry, with a lower up-front cost and a very mature marketplace (easily available from many sources). The fourth is Lithium-Ion. This technology is relatively new to the solar power industry, but far beyond the experimental phase and is growing in popularity as its cost gradually decreases. It has a much higher initial cost, but has some properties that are advantageous for some applications and, over their lifespan, can be fairly competitive with Lead-Acid technology in over-all cost.
Below is a brief overview of these four types. This article will soon be expanded to include more detail for each.
Flooded Lead-Acid (aka wet-cell): This is the most commonly-used type for solar power systems. It has the lowest initial cost and the longest life. However, they require regular maintenance in the form of periodically adding water to cells, cleaning terminals and connectors, and “equalizing charges” to maximize life-span and performance. They also require a well-ventilated area to disperse gases produced during use. They can also be damaged by vibration and can leak electrolyte if tipped.
Absorbed Glass Mat Sealed Lead-Acid (aka AGM): This type costs about twice as much as the flooded type. However, it is maintenance-free, highly resistant to vibration, performs well at low temperature, can store 50% more power, and can be charged and discharged at higher rates than other types.
Gelled Electrolyte Sealed Lead-Acid (aka gel): This type costs about 30% more than the flooded type and thus is considerably cheaper than AGM. It has an additive that gels the electrolyte. This makes it maintenance-free like AGM, good resistance to vibration, resistant to leaking if tipped. However, this type must be charged and discharged more slowly and must be charged at lower voltage than other types.
Lithium Ion: This type costs several times more than lead-acid types. However, it has a longer life-span (more charge/discharge cycles), deeper discharge (80% compared to 50% for lead-acid), it is lighter and smaller for the same capacity, and it is maintenance-free.
You have probably already noticed that the best choice for you depends on the particulars of your system. For example, if the site for your batteries is well-ventilated, easily accessed, and you are available and willing to do the maintenance, the flooded type can be a good choice. If double the cost is not a problem, the no-maintenance and high-performance of AGM is a good choice. If a slower charge/discharge is not a problem, the no-maintenance and lower cost of gel might be best. If your system is portable or if life-span is a major concern, the smaller and lighter lithium-ion may be worth the additional cost.
This basic overview of the types of batteries for solar systems will arm you with enough information and understanding to zero-in on what technology is likely to be best for your system. Very soon, this article will be expanded to include an in-depth look at each, so please check back in a week or two.
This article is one in the series titled “What You Need to Know”, each focusing on one of the six primary topics associated with solar power systems: Panels, Batteries, Charge Controllers, Inverters, Wiring, Sizing, Mounting. This series of articles is intended to convey the essential, practical knowledge necessary to understand and/or build a system – presented in a way that can be understood by a someone with little or no knowledge of the topics.
The primary goal of this article is to provide a relative novice everything you need to know about photovoltaic panels for solar power systems, without inundating you with technical details, so you can make the right choice for your system. To this end, I will list the types of solar panels commonly in use at this time (2018) and highlight only the technical aspects germane to performance, cost, and maintenance in the context of a solar power system application. There are several new technologies that are currently being developed. Most of them are in the research and development stage and, thus, are not available in the marketplace. Some of these new technologies are available in early forms, but are not yet competitive in terms of cost. This discussion focuses on those technologies currently widely in use and cost-competitive.
Mono-crystalline Panels: Mono- and Poly-crystalline panels currently comprise more than 90% of the solar panel market, and are roughly equal in their individual market share. Mono-crystalline panels are easily recognized by their monochromatic dark blue or black color and by the rounded edges to their individual cells. Both of these characteristics result from the manufacturing process, which is more complex than that of poly-crystalline panels and thus the cost of mono-crystalline panels is about 10% greater. However, they are also more efficient, that is, they convert a few percent more of the sunlight’s energy to electricity. The increased efficiency means that, compared to a poly-crystalline panel, a mono-crystalline panel is slightly smaller. Mono panels also perform slightly better in partial shade conditions, as well in high temperatures, making them a good choice for the desert southwest.
Poly-crystalline Panels: Poly panels are recognizable by their lighter blue color that has a mottled appearance reminiscent of pressed particle board, and without the rounded corners. These characteristics are also due to their manufacturing process. This simpler process makes them both slightly less expensive and slightly less efficient. Thus, compared to a mono panel, a poly panel of the same wattage will be slightly larger. This type of panel is a little less tolerant of partial shade and performance degrades a little more than mono in high temperatures. It should be noted that the differences mentioned between mono and poly may be significant in some fringe cases, but are small enough that many regard the two as roughly equivalent and both are very durable. Weather, including hail, capable of damaging them would also damage a roof. Both typically come with a 25 year warrantee.
Thin-film Panels: Thin-film panels, as the name suggests, are thin and flat. They can be purchased “framed” and “unframed”. Unframed, they are flexible and very light weight, just a few pounds compared to about 25 for a mono or poly panel. This makes them perfect for curved surfaces and applications in which minimizing weight is important, like RV’s. However, the unframed version cannot be tilt-adjustable to maximize direct sunlight, and is vulnerable to scratches, gouges, and extreme weather. The framed version provides improved durability and rigidity that makes tilting possible. This version weighs more than unframed, but still considerably less than mono or poly. Thin-film panels are typically somewhat-to-considerably less efficient than mono or poly, and usually have 10-year warrantees, but perform a little better in partial shade. In terms of cost per watt, thin-film tends to be about 30% more expensive. For a more technical breakdown of thin-film technologies in common use today, a href=https://www.solar-estimate.org/news/2018-07-14-what-are-thin-film-solar-panels-how-do-they-work-and-why-arent-they-used-for-residential-solar-systems>click here. There are newer thin-film technologies and manufacturing processes that have superior efficiencies to mono and poly, but thus far these are prohibitively expensive for most customers. Nevertheless, for applications in which flexibility and light-weight are critical, these may be considered.
The right panels for you depend on your particular constraints in terms of panel space, budget, weight, mounting surface, and temperature. However, this summary of characteristics for each of the types gives you the basics needed to evaluate the trade-offs involved. See the other articles in the “What You Need To Know” series on SolarEden. Together, they will give you the fundamentals needed to understand a full solar power system.
This article is one in the “What You Need to Know” series, each focusing on one of the six primary topics associated with solar power systems: Panels, Batteries, Charge Controllers, Inverters, Wiring, Sizing, Mounting. This series of articles is intended to convey the essential, practical knowledge necessary to understand and/or build a system – presented in a way that can be understood by someone with little or no prior knowledge of the topics.
The goal of this article is to provide a relative novice everything you need to know about charge controllers for solar power systems, without inundating you with technical details, so you can make the right choice for your system. To this end, I will list the types of charge controllers commonly in use at this time and highlight only the technical aspects germane to performance, cost, installation, and maintenance in the context of a solar power system application. There are new technologies that are currently being developed. Most of them are in the research and development stage and, thus, are not available in the marketplace. Some of these new technologies are available in early forms, but are not yet competitive in terms of cost. This discussion focuses on those technologies currently widely available and in use and cost-competitive.
What is a charge controller?: A charge controller, in the context of a solar power system, is a device that uses electricity produced by solar panels to charge batteries. Solar power systems that do not include batteries do not need a charge controller. When charging the deep cycle batteries used in solar systems, it is necessary to match the applied charging voltage to the current voltage of the batteries in order to maximize the life of, and preserve optimal performance of, the batteries. In a discharged state, a bank of 12 volt batteries wired in parallel may collectively have a voltage of 11 volts. Thus, it is the charge controller’s function to take whatever voltage is being produced by the panels and convert it to 11 volts to match. As the batteries charge, their voltage will gradually increase to at least 14 volts. The charge controller continuously adjusts the voltage supplied to charge the batteries to match. When the batteries are fully charged, the charge controller automatically stops applying charge to the batteries to prevent over-charging, again to maximize the life of, and preserve optimal performance of, the batteries. When the panels are not producing at least as much voltage as the batteries, the charge controller also acts as a one-way gate, preventing charge from flowing back out of the batteries to the panels.
PWM (Pulse Width Modulation) Charge Controllers: This type of charge controller is substantially less expensive. However, there is a negative consequence that accompanies this reduced cost. It does not fully utilize the power produced by the panels. This is because it makes a direct connection between the battery bank and the panel array. This pulls down the voltage produced by the panels to the voltage of the battery bank. This accomplishes the voltage match for effective charging of the batteries, but limits the power produced by the panels. This effectively wastes some of the power from the panel array. As the voltage of the battery bank rises, the voltage output of the panel array rises with it, thus using more of the power produced by the panels. If the nominal voltage of your panel array and battery bank is the same then, depending on charge state of the batteries, the amount of power wasted will between about 20% and 30%. If the nominal voltage of your panel array is greater than that of your battery bank, the power loss can be much larger.
MPPT (Multi-Point Power Tracking): This type of charge controller is significantly more expensive. However, for some applications, the additional expense is justified because it does not waste any of the power produced by the panel array. This type does not directly connect the panel array to the battery bank. Instead, it detects the current voltage of the battery bank and converts the power supplied by the panel array to match. This conversion retains all of the power supplied by the panel array, because current rises in accord with the reduction of voltage. All of the power from the panels is delivered into the batteries regardless of their state of charge, and this is true even if the nominal voltage of the panels and batteries is different.
The question of whether or not the additional cost of MPPT technology is justified in your particular case depends on several factors. For small systems in which the nominal panel array voltage is the same as that of the battery bank, PWM is the best choice. Even if you need more power from your system, it is cheaper to add more panels than to use MPPT instead. MPPT can be the better choice for larger systems or systems in which the panel array voltage does not match that of the battery bank. See the other articles in the “What You Need To Know” series on the Articles page on SolarEden. Together, they will give you the fundamentals of a full solar power system.
This article is one in the “What You Need to Know” series, each focusing on one of the six primary topics associated with solar power systems: Panels, Batteries, Charge Controllers, Inverters, Wiring, Sizing, Mounting. This series of articles is intended to convey the essential, practical knowledge necessary to understand and/or build a system – presented in a way that can be understood by someone with little or no prior knowledge of the topics.
The goal of this article is to provide a relative novice everything you need to know about Inverters for solar power systems, without inundating you with technical details, so you can make the right choice for your system. To this end, I will define what an inverter is and list the types of Inverters commonly in use at this time and highlight only the technical aspects germane to performance, cost, installation, and maintenance in the context of a solar power system application. There are new technologies that are currently being developed. Most of them are in the research and development stage and, thus, are not available in the marketplace. Some of these new technologies are available in early forms, but are not yet competitive in terms of cost. This discussion focuses on those technologies currently widely available and in use and cost-competitive.
What is an inverter?:An inverter is, primarily, a device to convert Direct Current electricity into Alternating Current. The simplest and cheapest form of an inverter produces square wave AC output or modified square wave output (which is a stepped square wave and constitutes a modest improvement over straight square wave). These are now becoming rare in the marketplace, as not all devices will work properly with this kind of AC, and some devices will be damaged by it. These kinds of inverters may also be euphemistically, or even deceptively, called “modified sine wave” or “altered sine wave”, so do not be fooled by this terminology. Most users will want an inverter that produces a “true sine wave”, also called “pure sine wave”, output. This output will operate all AC devices properly and safely. Inverters come in a wide variety of power ratings up to 10,000 watts, and can typically accommodate DC voltages of 12, 24, 48 volts. Inverters consume a small portion of the power they convert, typically about 4% to 10%.
Low Frequency vs. High Frequency Inverters: There are two categories of inverters with regard to conversion of DC to AC, “low frequency” and “high frequency”. Low frequency inverters are less common and more expensive because they are specifically designed for heavy loads and commercial applications. They use a large, central transformer (and thus are larger and heavier) that better handles the demands of high-surge mechanical devices like motors, compressors, and pumps. Most residential applications are better served by high frequency inverters, which are less expensive, smaller, and lighter.
Secondary and Optional Inverter Functionality: Inverters are available with a variety of additional functionalities, depending on the application. Each of these is explained below.
Multi-Point Power Tracking Functionality: Most inverters implement MPPT, which optimizes voltage vs. current to maximize power output.
”On Grid” (also called “Grid Tie”) Functionality: Grid tie inverters implement what is generally referred to as “grid current control”. All grid tie inverters produce a pure sine wave, because their output must be consistent with power on the grid. These inverters are capable of injecting surplus current back into the grid. Thus, when your system is producing more power than you are using, your power meter effectively runs backward and you save money on your grid power bill. These inverters also have an automatic grid disconnect when grid power fails. This is called an “anti-islanding” feature and prevents your system from energizing the grid when it is down and endangering line workers repairing the grid.
Charge Controller Functionality: Some inverters include an integrated charge controller for charging batteries. Of course, this would only be useful and desirable if your system includes a battery bank. Charge controllers are of two types, PWM and MPPT. PWM is less expensive but also less efficient, and MPPT is more expensive and more efficient. For more information about charge controllers, Click Here to see another article in the “What You Need To Know” series dedicated to charge controllers. Charge controllers are also available as separate devices. The advantages of an integrated charge controller are a simplified system design and easier installation. The disadvantage is that if either the charge controller or the inverter fails, both may need to be replaced.
Monitoring Functionality: Most inverters include monitoring functions to display and/or record performance characteristics. This can be very helpful to track the performance of your system and detect any problems. The monitoring functions available vary greatly by manufacturer and model.
Types of Inverters:
Central Inverters: Central inverters are used for large, utility-scale systems. They are highly efficient and can range into the hundreds of megawatts.
String Inverters: String inverters are the least expensive option for residential applications. As the name implies, the panels are arranged in “strings” and the combined output is wired to the inverter. This type of inverter works best for systems in which the panels are of uniform type and orientation (that is, all in the same direction and angle), and that are unlikely to change (that is, unlikely to expand number of panels), and that are always fully exposed to the sun (that is, never partially shaded by obstacles). When panels in a string are oriented in different directions or angles, the panel producing the least power at any given time will bring down the entire string to that level. Similarly, if a panel in a string is partially shaded, it will bring down the entire string to its level. It can be more difficult to expand this kind of system by adding more panels because the inverter is usually designed to match the output characteristics of the string, which will change if you add more panels to it. Monitoring of a string-oriented system can only be done at the string level, not the panel level.
MicroInverters: In a system that uses microinverters has one microinverter mounted with each panel. Orientation and partial shading of panels is not an issue with this kind of system because each panel’s power is converted to AC individually and one panel producing less power does not affect the others. Also, this type of system is easy to expand. Panels, each with its own microinverter, can be added at will with no negative consequences. Monitoring of systems using microinverters is at the panel level, providing much more detail and making it easier to track down any problems.
See the other articles in the “What You Need To Know” series on the Articles page on SolarEden. Together, they will give you the fundamentals of a full solar power system.