Why choose Enphase micro-inverters over a conventional string inverter
For grid tie solar systems, there are two choices of power inverters. Traditional string inverters or micro-inverters. Most companies, in Yucatan, still use string inverters and, they will give many reasons for why they are a better choice; however, their reasons just do not stand up when you compare string inverters to Enphase micro-inverters. To help you understand the differences, and why micro-inverters are the best choice, we have developed the following comparison list.
Enphase Micro-inverters
VS
String inverters
No single point of failure – if a micro-inverter stops working the rest of the system continues to work and produce power.
X
One micro-inverter fails, system remains in operation at 90% capacity until micro-inverter is replaced
Enphase micro-inverters have about the same failure rate as string inverters. The argument that is used most often by string inverter installers is “you will have many more points of failure with micro-inverters than with a string inverter”. While this sounds like a good argument, they leave out a key point. A micro- inverter failure shuts down one panel only. The odds of 2 failing at the same time is huge and the odds of more than 2 failing at the same time is astronomical. Not to mention, the cost to replace one micro-inverter (out of warranty) is far less than the cost to replace a string inverter. You can (in most home systems) easily replace at least 90% of your micro-inverters for less than the cost of 1 string inverter. Plus, there is the cost, to the homeowner, for power while the system (in the case of micro-inverters – 1 panel) is out of service.
With a system producing 20 kilowatts per day, the loss of 1 micro-inverter would cost the homeowner as much as $10.00 pesos per day.
Single point of failure – if the string inverter stops working, the entire system stops working.
x
String inverter fails, system is shut down until inverter is repaired or replaced.
0 power production during this time.
When a string inverter fails, it shuts down the entire system. The homeowner is then faced with the cost of loss of production for the entire time it takes to have the string inverter repaired or replaced. Even when the inverter is under warranty, the homeowner is having to pay for the power that was being produced by the system until the inverter is put back into operation.
With a system producing 20 kilowatts per day, the cost would be as much as $100.00 pesos per day while waiting for the string inverter to be repaired or replaced.
Enphase micro-inverters cannot be repaired. They are sealed units that either work or do not work. This means it is very easy to replace a unit. This can be done in under 30 minutes and the system is back in full operation. Even if there is a delay, waiting for a replacement unit, the rest of the system remains in operation.
String inverters can be repaired but, usually not on site. The string inverter needs to be removed from the system (shutting down solar production) and taken back to a service depot for analysis and repair or replacement. This leaves your solar system offline for however long the analysis and repairs take.
Greater power production through the isolation of each solar panel. If one panel is producing less (due to shade, dirt clouds etc.) the rest of the panels are unaffected.
Faster start-up and longer production days. Enphase micro-inverters need less power to start working and, therefore, start producing power earlier in the day and continue to produce power later in the day.
Strings of panels, connected together, means what affects one panel (dirt, clouds, shading etc.) affects every panel in the string. This lowers the power output of the entire string.
Yes, there are special products that can be added to a string inverter system that will separate each panel’s power production; however, they are an additional cost and do not work as well as Enphase micro-inverters. In fact, the addition of power optimizers for each panel in a string inverter system will increase the cost of the system (in most cases) to more than that of an Enphase micro-inverter system.
String inverters need a higher level of power from the solar panels to go into operation and to stay in operation. This means, they begin to produce power later in the morning and stop producing power earlier in the afternoon than micro-inverters.
Direct power conversion. The DC power produced by the solar panels is converted directly at the solar panel and then sent through normal home wiring to the breaker panel for use in the home, or sent as a credit to the electric company.
String inverters use high voltage DC wiring to go from the panels down to the string inverter where the power is converted for use in the home. This is a more complicated and dangerous installation.
Enphase micro-inverter systems are virtually limitless for expandability – if you have the space you can add as many more panels as you need, simply and easily.
String inverters are, usually, sized for the system being installed, with little to no room for expansion of the system. To expand a string inverter system, you, generally, need to either replace your string inverter with a larger model or, add a second string inverter.
Enphase micro-inverter systems are more resistant to power fluctuations than most string inverters. This means that, with our less than stable power grid, Enphase micro-inverters will continue to work when most string inverters are shut down during peaks and valleys of power delivery from CFE.
Most string inverters have narrower limits for what range of power delivery they can operate under. When the voltage being delivered from CFE is higher (or lower) than these limits, the string inverter shuts down and the system is not producing power.
Enphase micro-inverters are designed for the outdoors. They have gone through over 1 million hours of testing in harsh environments ranging from Alaska to the Australian Outback. They have been subjected to high humidity, extreme high and low temperatures, sand blasting, complete water emersion and more..
String inverters are designed for inside installation and are subject to far lower operating conditions.
CFE power delivery
270 volts
Enphase micro-inverters have the highest level of monitoring available. Each micro-inverter monitors and reports the power production from each panel and many other conditions, including even the current operating temperature of the panel. This is all coordinated through the Envoy monitor and transmitted to Enphase, the installation company and, the system owner. Issues with production are relayed by e-mail to the installation company, with recommendations for corrective action. This means that most issues can be dealt with electronically – no need for a service call. If there is need for a service call, the technician will already know what the problem is, what to do to correct the problem and even the specific location of the problem micro-inverter. In many cases the issue (if covered under warranty) will already have been authorized for repair or replacement.
Enphase micro-inverter systems can also monitor power consumption. With the add on feature of power consumption monitoring, you can see exactly how much power you are using at any point in the day or night.
String inverters are restricted to basic reporting of either the entire system, or an individual string of panels and is provided to the system owner only.
If there is a problem, the homeowner will need to contact the system installer for correction. The technician will need to come to the site and investigate to, first – identify the problem, second – locate the problem and, then affect repairs.
The technician may also need to contact the manufacturer to report the problem and then get authorization for a warranty replacement.
Power consumption monitoring is not available with most string inverters. There are other companies that do offer both production and consumption monitoring (for any string inverter system), however, this adds substantially to the cost of the system.
Enphase micro-inverters have an international 10-year warranty (this can be increased to up 25 years through Emerald Coast Solar).
There have been a number of studies conducted comparing power production of Enphase micro-inverters and string inverters, by both Enphase and independent researchers. Every study has shown Enphase micro-inverters outperform string inverters and do so by a large percentage.
Enphase micro-inverter systems are cost effective and in many cases are less expensive than string inverter systems. When you compare overall power production of an Enphase micro-inverter system to a string inverter system (using the same panels and mounting equipment), the string inverter system will require more panels and a larger mounting system.
String inverters range from inexpensive brands that have as little as a 2-year warranty, most brands have a 5 year warranty and some brands are 10 years, or more.
There have been no studies done that show any string inverter outperforming Enphase micro-inverters for overall power production.
String inverters (compared head to head with the same panels and mounting systems) require more panels and a larger mounting system to produce the same overall power. This equals a higher materials cost and higher labor costs for the same production system.
An Enphase micro-inverter system takes up little room in your home and is designed to be mounted almost anywhere. All it requires is a connection from the panels (we install a small subpanel), a connection to a 220-power supply and a wi/fi connection.
String inverters are large bulky units that need to be mounted on a wall. They require certain clearances around the unit to ensure it remains cool and they need to be easily accessible for servicing, as well as to monitor production of the solar system. Special electrical wiring is required and special connections both on the roof and at the inverter. As well the entire system is required to be separately grounded to minimize the electrical hazard.
One final point - Enphase systems do not depend on getting the maximum potential out of each solar panel. Panels rarely produce to their maximum rated wattage in the first place. What Enphase does, is produce more power earlier in the day and later in the afternoon and by individualizing each panel avoids the affects of clipping, shading, dirt etc. that on one panel will affect the entire string on a conventional string inverter system.
Conventional String inverter systems count on this upper area to calculate total production for the panel and the system. Here is the kicker - as panels age, they become less efficient and in a string inverter system, this reduces the actual performance of the system. This loss of power comes right off the top. Over the life of the system, this can be as much as a 15 - 20% loss of system production.
With an Enphase system - since Enphase is not harvesting the top of the production curve per panel - the power production loss over the life of the system is minimized. The power you get, on average, from your system with Enphase micro-inverters in year 10 or even longer, will be about the same as it is on day one.