Difference between revisions of "PV system types"
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| − | OSSP is focused on stand-alone PV systems, nonetheless it is important to distinguish the different system types and associated terminology as it will help when designing a system and selecting equipment. | + | OSSP is focused on stand-alone PV systems, nonetheless it is important to distinguish the different system types and associated terminology as it will help when designing a system and selecting equipment. |
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| + | === Direct current coupling vs. alternating current coupling === | ||
| + | There are two overarching categories of stand-alone and multi-mode systems that are presented below - direct current coupled (DC-coupled) and alternating current coupled (AC-coupled). These two terms refer to the way in which the PV charging source is integrated into the system - a DC-coupled system will rely upon a charge controller and a direct connection to the battery bank, whereas an AC-coupled system will rely upon a grid-tied inverter which will convert the PV array output into AC to power the loads, any excess will then be used to charge the battery bank. DC-coupled systems are the most common and versatile design, but AC-coupling carries some advantages in the case of larger systems that supply stead loads during the day. This is because an AC-coupled system passes the energy that the array generates through a grid-tied inverter is then able to directly power loads, which is more efficient (~90-98%) than passing it through a charge controller, battery bank, and then through the inverter (~85-95%) like in a DC-coupled system. AC-coupling generally only makes sense in the case of larger more complex systems and requires additional design considerations to ensure that the grid-tied inverter is able to reduce its output if there are insufficient loads or the battery bank is full. | ||
[[Category:Basics]] | [[Category:Basics]] | ||
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Any connections to a battery bank should run through what is called a ''low voltage disconnect'' which will disconnect loads if the voltage of the battery bank drops too low in order to protect the batteries. Often times, as depicted in the image, a low voltage disconnect is integrated into the charge controller. | Any connections to a battery bank should run through what is called a ''low voltage disconnect'' which will disconnect loads if the voltage of the battery bank drops too low in order to protect the batteries. Often times, as depicted in the image, a low voltage disconnect is integrated into the charge controller. | ||
| − | [[File:Standalone-dconly.png|frame|center|Stand-alone system without an inverter. Components in this image: '''1.''' Solar module/array '''2.''' Charge controller '''3.''' Battery bank '''4.''' Distribution panel to feed loads]] | + | [[File:Standalone-dconly.png|frame|center|Stand-alone system without an inverter. Components in this image: '''1.''' Solar module/array '''2.''' Charge controller '''3.''' Battery bank '''4.''' Distribution panel to feed loads (In practice, typically a far simpler solution than a panel of this type)]] |
| − | === | + | === DC-coupled with an inverter === |
An inverter becomes an essential part of any PV system that is intended to power anything beyond small lighting and appliance loads. A standard inverter enables the use of alternating current appliances. An inverter does have efficiency losses and stand-by consumption losses, but it makes a PV system far more versatile. | An inverter becomes an essential part of any PV system that is intended to power anything beyond small lighting and appliance loads. A standard inverter enables the use of alternating current appliances. An inverter does have efficiency losses and stand-by consumption losses, but it makes a PV system far more versatile. | ||
[[File:Standalone - 2009211.png|frame|center|Stand-alone system with an inverter. Components in this image: '''1.''' Solar module/array '''2.''' Charge controller '''3.''' Battery bank ''' 4. '''Inverter''' 5.''' Distribution panel to feed loads]] | [[File:Standalone - 2009211.png|frame|center|Stand-alone system with an inverter. Components in this image: '''1.''' Solar module/array '''2.''' Charge controller '''3.''' Battery bank ''' 4. '''Inverter''' 5.''' Distribution panel to feed loads]] | ||
| − | [[File:Standalone-invertercharger-200921.png|frame|center| | + | === DC-coupled with an inverter-charger === |
| + | A system with larger energy needs or a system that supplies critical loads, like at a clinic, will often incorporate a generator to ensure that energy needs are met at all times. An inverter charger is capable of ''rectifying'' (the opposite process of invertering) alternating current into direct current in order to charge the battery bank. The inverter-charger can be programmed to automatically start a generator if the voltage drops below a certain value or if the loads increase to a certain value. | ||
| + | |||
| + | [[File:Standalone-invertercharger-200921.png|frame|center|Stand-alone system with an inverter-charger. Components in this image: '''1.''' Solar module/array '''2.''' Charge controller '''3.''' Battery bank '''4.''' Inverter-charger '''5.''' Distribution panel to feed loads '''6.''' Generator]] | ||
| + | |||
| + | === AC-coupled with an inverter-charger === | ||
| + | The array in this configuration is connected to a grid-tied inverter, which will directly supply loads in the distribution panel before passing energy on to the inverter-charger, which will convert it to direct current to charge the battery bank if necessary. Note that there is no charge controller, the inverter-charger will manage the battery bank in this configuration. | ||
| − | [[File:Standalone-accoupled.png|frame|center| | + | [[File:Standalone-accoupled.png|frame|center|Stand-alone system with AC-coupling. Components in this image: '''1.''' Solar module/array '''2.''' Grid-tied inverter '''3.''' Distribution panel to feed loads '''4.''' Inverter-charger''' '''5.''' Battery bank '''6.''' Generator]] |
== Multi-mode systems == | == Multi-mode systems == | ||
Revision as of 01:40, 23 September 2020
OSSP is focused on stand-alone PV systems, nonetheless it is important to distinguish the different system types and associated terminology as it will help when designing a system and selecting equipment.
Contents
Direct current coupling vs. alternating current coupling
There are two overarching categories of stand-alone and multi-mode systems that are presented below - direct current coupled (DC-coupled) and alternating current coupled (AC-coupled). These two terms refer to the way in which the PV charging source is integrated into the system - a DC-coupled system will rely upon a charge controller and a direct connection to the battery bank, whereas an AC-coupled system will rely upon a grid-tied inverter which will convert the PV array output into AC to power the loads, any excess will then be used to charge the battery bank. DC-coupled systems are the most common and versatile design, but AC-coupling carries some advantages in the case of larger systems that supply stead loads during the day. This is because an AC-coupled system passes the energy that the array generates through a grid-tied inverter is then able to directly power loads, which is more efficient (~90-98%) than passing it through a charge controller, battery bank, and then through the inverter (~85-95%) like in a DC-coupled system. AC-coupling generally only makes sense in the case of larger more complex systems and requires additional design considerations to ensure that the grid-tied inverter is able to reduce its output if there are insufficient loads or the battery bank is full.
Grid-tied PV systems
PV systems installed that have a grid connection are called grid-tied systems. The inverters that come with these types of systems are called interative as they are capable of interacting with the grid by matching its voltage and frequency. As a system of this type produces energy, it must either be consumed on the presmises or it will be fed back into the grid - through a meter - to be used by other customers. These systems cannot store energy and do not provide backup power in the case of a power outage. The majority of PV systems installed globally are of this type.
Stand-alone systems
PV systems installed in areas that lack a grid connection are called stand-alone systems, but are also commonly referred to as battery-based or off-grid systems. These systems take many different forms, but they almost always incorporate some type of storage, typically a battery bank, and one or more charging sources. In addition to solar PV, these systems may include a generator, wind, or hydro as well. These systems with multiple charging sources may also be referred to as hybrid systems. Stand-alone systems can use alternating current and direct current as charging sources and can supply alternating and direct current for loads. The various different stand-alone system types are depicted below.
Direct current only
A common system in less developed off-grid areas - common with systems less than 100W of PV. An economical option to provide lighting and energy for small appliances. Using only direct current has the advantage avoiding energy losses due inefficiencies created by an inverter (inverters are typically only around 85%-95% efficient) and the energy that is required to power an inverter when it is standing by. The disadvantage of not having an inverter is that most appliances are designed for use with alternating current, therefore the available DC appliance market is often much smaller.
Any connections to a battery bank should run through what is called a low voltage disconnect which will disconnect loads if the voltage of the battery bank drops too low in order to protect the batteries. Often times, as depicted in the image, a low voltage disconnect is integrated into the charge controller.
DC-coupled with an inverter
An inverter becomes an essential part of any PV system that is intended to power anything beyond small lighting and appliance loads. A standard inverter enables the use of alternating current appliances. An inverter does have efficiency losses and stand-by consumption losses, but it makes a PV system far more versatile.
DC-coupled with an inverter-charger
A system with larger energy needs or a system that supplies critical loads, like at a clinic, will often incorporate a generator to ensure that energy needs are met at all times. An inverter charger is capable of rectifying (the opposite process of invertering) alternating current into direct current in order to charge the battery bank. The inverter-charger can be programmed to automatically start a generator if the voltage drops below a certain value or if the loads increase to a certain value.
AC-coupled with an inverter-charger
The array in this configuration is connected to a grid-tied inverter, which will directly supply loads in the distribution panel before passing energy on to the inverter-charger, which will convert it to direct current to charge the battery bank if necessary. Note that there is no charge controller, the inverter-charger will manage the battery bank in this configuration.
Multi-mode systems
