Grid-Direct, Off Grid and Hybrid Solar Electric Systems
There are three types of solar electric systems: grid-direct, off-grid, and hybrid. Each system has its own distinct features that
set it apart from the others, and each has its pros and cons. The most common installation of new solar electric systems belongs to the grid-direct category.
The grid-direct system is the simplest and most affordable of the solar electric system installations. That is partly because it connected to a main power grid. And whether it is a new installation or a retrofit system, it can redirect much or all of the excess electricity that your PV panels generate.
How a grid-direct system works
The installed PV panels function to generate DC electricity, which is converted to AC current via a home-installed inverter. There are many sizes of inverter on the market to choose from, and they come in different watt sizes. You may choose to install a single main inverter or have multiple units of inverters for a large PV array installation.
Alternatively, you can choose a micro-inverter that comes in the same size as a single PV module electricity generator, or you can string together a few micro-inverters in an AC branch circuit, which allows for the addition of PV modules into your existing array at any time. One benefit of using micro-inverters is their ability to continue to generate electricity even when one or two pieces are shaded and prevented from generating electricity. This is the reason why central inverters tend to perform more poorly -- their electric modules are strung up in series. When one module is shaded, it cannot generate power. Its non-performance hinders the performance of other modules.
When the generated DC current is inverted to AC, it is sent to the home-based AC service panel that has breakers. This “control center” then pushes out the electricity to various parts of the home for various applications. Excess electricity will be passed to the utility meter, spinning it back before sending out the excess to the electric grid. But if the PV array does not generate enough electricity to meet the home’s demands, power will be extracted from the main electric grid, which flows into the meter for costing purposes. This net metering causes the meter to spin back and forth which may end up with a zero payment for you at the end of the day (not literally).
For this reason, net metering measures only net production and consumption activities though various utility regulations and state laws that apply to the actual computation to produce the net figure. Instead of one meter that spins backward and forward depending on power throughout, a homeowner can install two meters: one for electricity production, and another for electricity consumption. This is not felt to be a significant factor in a solar system installation.
The main issue with a grid-direct system is its inability to generate electricity when the PV system inverter shuts down due to a blackout or lack of sunlight. Utility regulations are set up to prevent anti-islanding when