Which Inverter Do I Choose? Central Inverters Versus Micro Inverters

You have an interest in going solar, and you’ve decided on a grid-tie system. You’ve already determined your house is a good fit, and who doesn’t want to see their electric bill cut drastically? You’ve already found a great deal on panels; however, now you’re asking yourself which inverter best suits my goals and budget? The good news is that whichever route you choose, it is not as complicated as it may first appear.

The main function of an inverter is to convert the direct current (DC) your solar panels produce into alternating current (AC) so you can power home appliances and feed excess energy back into the utility grid. Both central and micro inverters perform this DC to AC conversion. Because they have different benefits and drawbacks, the inverter that suits you best depends on your project and budget requirements.

Central Inverters

A solar system with a central inverter has a single large inverter. All your solar panels feed into this inverter so the DC - AC conversion can take place at a single, central location. This inverter then supplies your home’s AC’s energy needs while feeding extra energy back to the grid in a process called “net metering”.

How do you size an appropriate inverter for your panels? Some say it is a good rule of thumb to try to match your solar array wattage to the wattage of the inverter (ie. a 5kW solar array matches a 5kW inverter). Since inverters are not one-hundred percent efficient at converting DC to AC and are rated based on their AC watt output, this is not always the case; there will be some losses in energy. This is why generally an inverter can handle a higher solar array wattage than the watts it is rated at.

For example, the Sunny Boy 5000 is described as a 5kW inverter; however, it can handle an input from your solar array of up to 6,250 watts. The 5,000 watts is the maximum it can put out given this 6,250 watt input.

Pros:

• Central Inverters are usually more cost effective
• Highest efficiency in the right conditions (facing south; no obstructions or shading)
• Wide variety of options to choose from
• Ease of installation

Cons:

• Shading and/or mismatched panels lower a system’s overall power
• Growing to a larger system may be restricted by inverter size
• Monitoring is available, but not as granular as micro inverters.

Micro Inverters

Micro inverters take a different approach to DC - AC conversion. One inverter is installed on each solar panel in the array, and the actual conversion is performed right there. The AC generated is then transported via trunk cabling to your junction box. From here, like with central inverters, the AC generated powers your home while the excess is fed back into the grid.

Sizing a micro inverter is very simple; you simply need one per solar panel. You will need to find one with an input wattage range that matches your solar panels; for example, an M215 can handle most 60-cell panels from 190 - 260 watts.

Pros:

• MPPT technology allows each solar panel to produce to its maximum ability, regardless of shading issues elsewhere in the array
• Isolates and controls the output of each panel so you can mix and match panels
• Easy to upgrade to a larger system - you can build as you go
• Superior System Monitoring - track each panel’s status and production

Cons:

• Higher cost: one inverter per panel and one cable per micro inverter adds up when systems grow
• Can be less efficient than central inverters in optimal conditions
• Currently, there are only a few options