Solar Inverters

A Solar Inverter, also known as PV Inverter, is an essential component of a Photovoltaic Solar System. Its purpose is to convert the low voltage DC power (variable Direct Current) output of PV solar panel into AC power (Alternate Current) that can then be used by commercial or residential electrical systems (a house in the electrical grid) or simply by an autonomous system (off the electrical grid).

There are three major types of inverter installations. The Grid Tie Power Inverters, the Stand-alone Inverters and the Micro-Inverters.

Grid Tie Power Inverters

Grid Tie Power inverters, also known as Sine Wave Power Inverters, are used in the cases where you want to connect your solar panels to the electrical network (on grid installation). This has to be done in agreement with your electricity utility provider. In this case, whatever electricity your solar panels produce will be sent to your electricity provider. This is required in order to provide current stability both to your house electricity system and to the grid (they are specifically designed to precisely match the voltage and frequency of the grid). Then your electricity provider will deduct the electricity you provided from the electricity you produced (in a pre-agreed formula which may differ from country to country) and you will only pay the difference of the two. In the case you produce more power than you consumed you may sell the extra power to your utility provider (again according to the agreement you have). In the case of a Grid Tie Power Inverter there is no need to install any batteries to store the produced electricity. In this way you save a lot of money from the batteries and a lot of maintenance costs. For safety reasons, Grid Tie Power Inverters will automatically shutdown as soon as the power supply from your electricity provider is lost (anti-islanding protection).

In the cases where you have often power outages in your area you can use Battery Backup Inverters. These types of inverters can provide AC supply during power outage. They are used to charge the batteries and send any excess power to the electricity provider. Because they are connected to the grid they still require to have anti-islanding protection. Battery backup inverters are more expensive than Grid-Tie power inverters and are only used in the cases where you need a backup power system.

Stand-alone Inverters

These types of inverters are used in off-grid installations (isolated solar power systems). In this case batteries are an integral part of the system, so in many cases stand-alone inverters are provided in conjunction with the batteries. Because these systems are not connected to the grid you do not need any agreement with your local electricity provider and you do not need to have an anti-islanding protection system. They are mostly used in remote areas where it is not possible to connect with an electricity provider or for small commercial applications where an AC input is required.

Micro-inverters

Micro inverters are small inverters that are installed at the back of each panel, one for each panel. The advantages of micro-inverters are the following:

• The performance of each panel can be monitored separately so that you can quickly identify problems in any panel.
• The system is easily expanded by adding another panel with its micro-inverter. In single inverter installations you need to verify that your inverter can support the expansion.
• The system has greater reliability because when a micro-inverter fails it will not affect the whole system.
• A micro-inverter is simpler in design and manufacturing and so it has longer lifetime (same as the lifetime of the panels) than single larger inverters which you are typically expected to replace them once during the lifetime of the panels.
• The panels do not need to have the same characteristics between them.
• Performance of the whole system is not affected by degradation of the performance of any single panel.

The main disadvantage of micro-inverters is that it is relatively new technology with less expertise and higher cost per watt than a single inverter.

Solar Power Inverters Cost

The cost of solar power inverters can vary a lot depending on quality, technology used and size of inverter (in KW). A typical price for a solar power inverter for residential use is around $2000 – $3000 (USD) for systems between 3KW and 10KW. Solar panel inverters lifetime is around 8-10 years. So it is expected that during the lifetime of your solar panels you will need to replace the inverter once (unless you use micro-inverters which have longer lifetime).