Home owners looking to install solar panels on their homes will often receive competing solar bids for different companies some of which sell string inverters and some of which sell microinverters. On more recent times we have also seen the introduction of power optimizers.
But first thing is first, what is the real difference between a string inverter and a micro-inverter.
What is a String Inverter and what is a Micro Inverter?
Both string inverters and micro inverters convert the Direct Current (DC) solar panels generate into an Alternating Current (AC), the type of electricity that is used in your home.
A standard inverter (also known as a string-inverter or central inverter) is a standalone box that is typically installed close to your fuse box and electricity meter. There is typically only one, or possibly two, string inverters on each residential solar installation.
Micro-inverters perform the same basic function but are installed underneath each panel on your roof. Each of these micro-inverters is about the size of an internet router. The big difference is that a solar panel installation with micro inverters will have the same number of micro inverters as there are solar panels.
A string inverter functions in a series circuit with their usually being 6-10 individual solar panels in what is known as a "string".
A micro-inverter functions in a parallel circuit. To simply put, a standard inverter will cap the electricity production of each panel by the lowest producing panel on your roof. A micro-inverter on the other hand, will take full advantage of the production of each individual panel. It will convert the power generated by each panel to the grid voltage.
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Advantages of a String Inverters
The advantage of a string inverter is that you only need one of them. If anything is going to fail in a solar system it is likely to be the inverter and so it is less likely that as an installer you will have to go back to a job.
Cost is another advantage, a single string inverter on a solar panel installation is usually cheaper than installing micro-inverters.
Disadvantages of a String Inverters
No disadvantages of string inverters.
Advantages of a Micro Inverters
The core advantage of using micro inverters is that theoretically you can yield more solar electricity.
The reason for this is that there are slight differences in voltages between solar panels. When solar panels are in a string the voltage is reduced to the voltage of the lowest voltage panel in the string.
If a solar system is facing multiple angles, meaning some panels are facing south, some east, and some west, then micro-inverters are the way to go. Or, if you have shading issues from trees or a large chimney, again micro-inverters would be best. In these situations, the solar panels will be producing different amounts of electricity at different times of the day, but micro-inverters will ensure you harvest all of the energy, while with a standard inverter you will lose some of this production. With solar panels all facing one direction on your system, and you have marginal shading issues, then your best option is a standard inverter. You’ll get about the same production, without paying the higher cost.
To throw more confusion in this, Optimizers are an option for standard inverters as well, which function very similarly to a micro-inverter. With an optimizer, you still have a standard inverter, but you also have optimizers for each individual panel combating production differences.
There are other aspects to consider as well. Micro-inverters typically have 25 year warranties while a standard inverters typically have 5 or 10 year warranties. The reliability of micro-inverters was in questions several years ago, but the technology now has caught up with the industry and the long warranties on the micro-inverters shows the confidence the manufacturers have in their products.
Micro-inverters and the add-on optimizers both offer an additional perk in system monitoring as well. With either of these devices, you have the ability to track the production of each individual panel, while with a standard inverter you only can track the production of the whole system.
If you were to expand your system in the future, micro-inverters are simple to add one at a time. However, with a standard inverter, it would be more costly to add another full unit.
To sum it all up, micro-inverters are definitely a value-add, but are only recommended if you have panels facing multiple orientations or you have shading issues. Otherwise, the less expensive standard inverter is usually more cost effective.
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Disadvantages of a Micro Inverters
The main disadvantage of micro inverters is price. They are typically a $1000 or so more expensive than a string inverter on a standard 5kw residential solar installation.
The second disadvantage is that you have as many inverters on your roof as you have solar panels.
Most micro inverter manufacturers claim very low failure rates but at SolarReviews we remain skeptical of these claims.
The most complex electronics in a solar system is in the inverter and based on my 8 years of experience in the solar installations business the most common thing to fail in a solar installation is the inverter. I would be very reluctant to put 20 inverters up on a job rather than putting one string inverter. I would only do this where there were severe shading issues.
Although micro inverter manufacturers sell the ability to monitor each panel as a benefit of micro's (and it is) they then don't include the monitoring that allows the customer to do this. They only allow the installer to see the panel level data from your system and not you as a customer, unless you agree to buy the higher level of monitoring as an upgrade.
This means you as a customer only see system wide monitoring information not what is going on with each panel. A sceptic would say that the reason they do this is to protect them and their installers from support calls related to broken inverters. It is very difficult with only system wide monitoring data to determine if only 1 or two inverters out of 25 or so have failed.
Having said this, I still like micro-inverters but if I was a client purchasing a system with micro-inverters I would pay the extra money for the level of monitoring that gives you panel level analysis. At least when a string inverter fails the whole system stops and this is easy to notice. My gut feel is that there are a lot of failed micro inverters out on roof tops where the client does not even know they have failed.