23-07-2012, 01:02 PM
Solar photovoltaic (PV)
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What are PV micro inverters and what are their advantages and disadvantages?
Solar photovoltaic (PV) panels are a hot topic this summer, especially since many expect that the currently very generous financial support under the feed-in tariff scheme will be drastically cut for anyone who installs their PV roof after 1 April 2012, as the government will introduce new tariffs for systems installed after that date.
Apart from the panels themselves, the other major component of a grid-connected PV roof is the inverter.
Modern grid-tied inverters fulfil three roles:
1. they convert the direct current (DC) electricity produced by the PV panels to the alternating current (AC) electricity the grid and our appliances need
2. they ensure compliance with regulations about feeding electricity into the grid, e.g. by immediately disconnecting if there is a power cut – otherwise there would be a risk of sending electricity down the wires while repairs are carried out
3. they maximise electricity production by constantly varying their resistance (load) in a way that ensures that PV panels always operate under conditions optimal for the level of solar radiation at that moment – this is called maximum power point tracking (MPPT)
The most common type of inverters for domestic PV installations in the UK are central “string” inverters: The PV modules on your roof are connected in one or more “strings” and wired to a single central inverter somewhere inside your house.
However, there is another, currently less common approach: Having a small dedicated inverter for each individual PV module, a so-called micro-inverter. Theoretically, this approach should have three main advantages:
1. this allows the inverter to optimize the operation of each panel individually, which should increase performance in cases where some panels on the roof receive more sunshine than others. This could be the case because of shading from a tree or chimney, or because the PV panels are mounted on parts of the roof facing different directions (e.g. SE and SW)
2. micro-inverter systems should be a bit simpler and easier to install, as they avoid the need for high-voltage DC wiring and the installation of a separate inverter box inside your house
3. because each inverter only has to deal with one inverter, the power passing through it is lower. Some manufacturers argue that this makes it possible to build systems that last longer. Indeed, most micro-inverters have warranties between 15 and 25 years.
However, all this is bought at the cost of currently higher capital costs – using micro-inverters will add somewhere between £500 and £2,000 to the cost of a domestic PV roof. Perhaps more critical, though, is the uncertainty about lifetime maintenance cost: While each individual micro-inverter may last much longer than a central inverter, the high number of individual inverters (10-20 in a typical domestic system) may still mean it’s quite likely that there will be dome failures during the life of the PV roof. And while the warranty could cover the cost of replacing the micro-inverter itself, the labour and scaffolding required to change micro-inverters on a roof may still make replacements very expensive.
At the moment, all of this is largely speculation. There simply aren’t enough micro-inverter systems, especially of the latest generation, which have been around for long enough on UK roofs for us to know how they pass the test of time. Anyone installing this technology at the moment should consider themselves an “early adopter” – with all the opportunities and risks associated.
Solar Central Grid Tie Inverters vs Microinverters – Advantages and Disadvantages
Solar Microinverters have opened an entire new category in the traditional Solar Inverter Industry threatening the business model of the incumbent companies which have seen spectacular growth in recent years.Solar Inverter Manufacturers have enjoyed enviable growth of more than 50% CAGR to become a $5 billion industry in 2010.However this industry faces competition from a host of new tiny competitors led by Enphase Energy who claim to reduce costs,increase reliability and add monitory plus flexibility as compared to String Inverters.The threat is the most in residential and commercial solar installations where the advantages of solar micro inverters are more pronounced than in utility applications.Solar EPC Companies in the USA have started adopting this new product though the growing size of the Solar Inverter Industry has managed to temporarily lower the thread.SMA Solar,the biggest solar inverter company in the world recently bought a couple of firms like OKE Services to increase its presence in distributed electronics for the solar panel industry.Here is a list of advantages and disadvantages of Central Inverters and Microinverters.
Pros of Microinverters compared to String Inverters
1. Reliability and Longer Life – Micoinverters are more Reliable as the failure of a single piece affects only that solar panel and not the whole solar array of solar panels in case of Solar Inverters.Also the Mean Life of Solar Inverters are much more than the life of the Solar Panels compared to the 5-10 year life of String Inverters which have to be replaced.
2. Productivity – Microinverters claim to have 5-25% more power production from solar panels as they manage to maximixe the power production from each solar panel (MPTT) compared to string inverters which MPTT the whole solar array.Microinverters give more accuracy If a single panel is operating at a different point, a string inverter can only see the overall change, and will move the MPPT point to match. Shading of as little as 9% of the entire surface array of a PV system can, in some circumstances, lead to a system-wide power loss of as much as 54%
3. Ease of Installation – Installing Solar Panels with Microinverters is easier and faster and leads to lower costs compared to Solar Inverters though there is still some dispute on this.
4. Flexibility – Another benefit of the distributed microinverter design is the potential for installations to be expanded over time. An initial set of solar modules can be installed and additional modules added as needs and budgets grow without requiring the replacement of a large centralized inverter.
5. Reduction in Lifecycle Costs - Installers are no longer limited by string design, marginal designs, co-planarity, and matched modules. Microinverters reduce wiring time, and remove the need for DC switching points.
6. Space and Heat of String Inverters – String Inverters occupy more space (though not a big problem) and generate a lot of heat which has to be cooled by used fans.
7. Higher Power Inverters have to be used - Because of the limited range of power rated inverters availabe,solar panels have to generally use power inverters of greater size for eg. 800 W of Solar Panels will have to use 1 KW solar inverters wasting the 200 W
Disadvantages of Microinverters compared to String Inverters
1) Cost - Traditional Inverters cost between 35-50c/watt depending on the size,technology,brand etc. while microinverters typciall cost between 75-90c/watt again depending on brand,market etc.This is the biggest disadvantage of microinverter compared to solar inverters
2) Placement of Microinverters – Microinverters are place on the rack below the solar modules.This is said to cause problems as it is placed on the hottest part of the solar system and could lead to problems in case of high insolation areas
[attachment=28473]
What are PV micro inverters and what are their advantages and disadvantages?
Solar photovoltaic (PV) panels are a hot topic this summer, especially since many expect that the currently very generous financial support under the feed-in tariff scheme will be drastically cut for anyone who installs their PV roof after 1 April 2012, as the government will introduce new tariffs for systems installed after that date.
Apart from the panels themselves, the other major component of a grid-connected PV roof is the inverter.
Modern grid-tied inverters fulfil three roles:
1. they convert the direct current (DC) electricity produced by the PV panels to the alternating current (AC) electricity the grid and our appliances need
2. they ensure compliance with regulations about feeding electricity into the grid, e.g. by immediately disconnecting if there is a power cut – otherwise there would be a risk of sending electricity down the wires while repairs are carried out
3. they maximise electricity production by constantly varying their resistance (load) in a way that ensures that PV panels always operate under conditions optimal for the level of solar radiation at that moment – this is called maximum power point tracking (MPPT)
The most common type of inverters for domestic PV installations in the UK are central “string” inverters: The PV modules on your roof are connected in one or more “strings” and wired to a single central inverter somewhere inside your house.
However, there is another, currently less common approach: Having a small dedicated inverter for each individual PV module, a so-called micro-inverter. Theoretically, this approach should have three main advantages:
1. this allows the inverter to optimize the operation of each panel individually, which should increase performance in cases where some panels on the roof receive more sunshine than others. This could be the case because of shading from a tree or chimney, or because the PV panels are mounted on parts of the roof facing different directions (e.g. SE and SW)
2. micro-inverter systems should be a bit simpler and easier to install, as they avoid the need for high-voltage DC wiring and the installation of a separate inverter box inside your house
3. because each inverter only has to deal with one inverter, the power passing through it is lower. Some manufacturers argue that this makes it possible to build systems that last longer. Indeed, most micro-inverters have warranties between 15 and 25 years.
However, all this is bought at the cost of currently higher capital costs – using micro-inverters will add somewhere between £500 and £2,000 to the cost of a domestic PV roof. Perhaps more critical, though, is the uncertainty about lifetime maintenance cost: While each individual micro-inverter may last much longer than a central inverter, the high number of individual inverters (10-20 in a typical domestic system) may still mean it’s quite likely that there will be dome failures during the life of the PV roof. And while the warranty could cover the cost of replacing the micro-inverter itself, the labour and scaffolding required to change micro-inverters on a roof may still make replacements very expensive.
At the moment, all of this is largely speculation. There simply aren’t enough micro-inverter systems, especially of the latest generation, which have been around for long enough on UK roofs for us to know how they pass the test of time. Anyone installing this technology at the moment should consider themselves an “early adopter” – with all the opportunities and risks associated.
Solar Central Grid Tie Inverters vs Microinverters – Advantages and Disadvantages
Solar Microinverters have opened an entire new category in the traditional Solar Inverter Industry threatening the business model of the incumbent companies which have seen spectacular growth in recent years.Solar Inverter Manufacturers have enjoyed enviable growth of more than 50% CAGR to become a $5 billion industry in 2010.However this industry faces competition from a host of new tiny competitors led by Enphase Energy who claim to reduce costs,increase reliability and add monitory plus flexibility as compared to String Inverters.The threat is the most in residential and commercial solar installations where the advantages of solar micro inverters are more pronounced than in utility applications.Solar EPC Companies in the USA have started adopting this new product though the growing size of the Solar Inverter Industry has managed to temporarily lower the thread.SMA Solar,the biggest solar inverter company in the world recently bought a couple of firms like OKE Services to increase its presence in distributed electronics for the solar panel industry.Here is a list of advantages and disadvantages of Central Inverters and Microinverters.
Pros of Microinverters compared to String Inverters
1. Reliability and Longer Life – Micoinverters are more Reliable as the failure of a single piece affects only that solar panel and not the whole solar array of solar panels in case of Solar Inverters.Also the Mean Life of Solar Inverters are much more than the life of the Solar Panels compared to the 5-10 year life of String Inverters which have to be replaced.
2. Productivity – Microinverters claim to have 5-25% more power production from solar panels as they manage to maximixe the power production from each solar panel (MPTT) compared to string inverters which MPTT the whole solar array.Microinverters give more accuracy If a single panel is operating at a different point, a string inverter can only see the overall change, and will move the MPPT point to match. Shading of as little as 9% of the entire surface array of a PV system can, in some circumstances, lead to a system-wide power loss of as much as 54%
3. Ease of Installation – Installing Solar Panels with Microinverters is easier and faster and leads to lower costs compared to Solar Inverters though there is still some dispute on this.
4. Flexibility – Another benefit of the distributed microinverter design is the potential for installations to be expanded over time. An initial set of solar modules can be installed and additional modules added as needs and budgets grow without requiring the replacement of a large centralized inverter.
5. Reduction in Lifecycle Costs - Installers are no longer limited by string design, marginal designs, co-planarity, and matched modules. Microinverters reduce wiring time, and remove the need for DC switching points.
6. Space and Heat of String Inverters – String Inverters occupy more space (though not a big problem) and generate a lot of heat which has to be cooled by used fans.
7. Higher Power Inverters have to be used - Because of the limited range of power rated inverters availabe,solar panels have to generally use power inverters of greater size for eg. 800 W of Solar Panels will have to use 1 KW solar inverters wasting the 200 W
Disadvantages of Microinverters compared to String Inverters
1) Cost - Traditional Inverters cost between 35-50c/watt depending on the size,technology,brand etc. while microinverters typciall cost between 75-90c/watt again depending on brand,market etc.This is the biggest disadvantage of microinverter compared to solar inverters
2) Placement of Microinverters – Microinverters are place on the rack below the solar modules.This is said to cause problems as it is placed on the hottest part of the solar system and could lead to problems in case of high insolation areas