How to Choose the Right Solar Inverter

When shopping around for solar equipment, people tend to spend the majority of their time researching solar panels; after all, panels are the most expensive part of a PV system.  While solar panels may get all the buzz, the key component that can make or break the success of your solar installation is actually the inverter. A good inverter can mean a difference of up to 20% in your system’s production.  Here is some information that will help you decide which inverter is best for your home solar system.

Solar Inverter 101

An inverter is responsible for allowing the electricity from the solar panels to flow and ensuring that the property is able to interact with the local power grid.  There are 2 types of electricity: DC (Direct Current) and AC (Alternating Current).  Solar panels produce DC electricity, but household appliances rely on AC electricity to function.  This is where the trusty inverter comes in to save the day.  Inverters convert DC electricity to AC power that can be used to power a home or be sent back to the utility grid if there is an excess supply.

Types of Inverters

There are 3 types of inverters commonly used in solar power systems:

String Inverters: This is a common inverter type for both home and commercial solar power systems. PV panels in an array are often installed in strings — several wired in series so that voltage is raised, but the current is kept low. String inverters essentially treat a string of panels as if they were a single large panel, so any problems with one panel will be felt across the entire string. These inverters have traditionally been the cheapest, but prices are now leveling out. Sting inverters are a good choice if your roof has full sun all day, as they are not shade-tolerant and don’t let you monitor each panel’s performance. Generally, string inverters are efficient, robust, and inexpensive compared to other inverter types, but they do not have panel level monitoring, and their high voltage may present a potential safety hazard.

Microinverters:  An alternative to traditional string and central inverters, a microinverter is a small inverter situated close to a solar panel, and allowing each panel to function indepedently, as a stand-alone unit. Such inverters provide a faster and safer plug-and-play installation, as there are no high-voltage DC circuits to handle, and installation time and costs are reduced. A few panel manufacturers even build microinverters onto each PV module, thereby relieving the panel purchaser from buying an extra item. Because they work with single solar panels, microinverters allow your array to continue working even if one panel malfunctions. They are, however, more expensive than other types of solar inverters and require more maintenance.

Central Inverters: These are designed for larger arrays, and they basically function as a more consolidated version of string inverters. They have a low capital price per watt, are highly efficient, and are relatively easy to install. The downsides of central inverters are their size, potential noise pollution, and the fact that if one part of an array fails, the whole system may do so too.

Inverter Systems

Stand-alone System - With this system, an inverter will allow for backup power when the grid goes down. The system consists of a large box that can be installed in a garage or utility closet that uses mechanical rotors to switch the direct current to alternating. These inverters are completely centralized and are connected to a battery which can store and supply electric power during an outage.

Grid-tie system - Modern grid-integrated inverters include many performance-enhancing, safety, and reliability features. The inverter connects your solar panels directly into the grid at your power meter, allowing you to sell excess power back to the utility company. Such systems are often cheaper than standalone inverters because they don’t have a battery, and thus do not offer any backup electricity during a power outage. Grid-tie systems also require “anti-islanding protection,” which shuts off the connection between panels and the grid during a power outage to protect utility workers who may be making repairs in the area.

Hybrid system - Dual-inverter systems are the most expensive as they include both a standalone inverter with a battery and a grid-tied inverter to allow you to sell excess power back to the utility company. A hybrid system appeals to home and business owners because it offers the advantages of both kinds of inverter systems as well as maximum energy security.

Choosing the right inverter for your home

Once you have decided what kind of system you want and what type of inverter you are buying, here are a few more things to consider before making your final decision.

Inverter Capacity - It is best to choose an inverter that has a slightly higher capacity or max output than the peak power your home may need. The best way to estimate your peak power demand is to calculate the power usage of your largest appliances— AC/heater, refrigerator, stove, washer/dryer, television, dishwasher, and all the lights in your home. Though it is not likely that you will ever be running all of these appliances at once, you want to make sure that if ever do, your inverter will be able to handle the load.  Often, when devices are first switched on, they require an additional burst of power. You will want an inverter that is large enough to handle such high-energy bursts of power, so look for an inverter that is labeled “surge compliant”.

Input Power - It is also important to consider the amount of electricity your solar panels can produce to determine the input capacity that you will need.  For instance if you have a 7kW system, you should choose an inverter that can handle the system during those long sunny days with peak production times.

Inverter Warranty - Generally, inverters do not last as long as solar panels, so you will probably have to replace your inverter at least once over the lifetime of your solar power system. A solar inverter warranty typically ranges from five to 10 years, though there are a few companies that offer 12 - 25 year warranties or warranty extension options.