When people ask me how if they can install solar, they generally mean solar photovoltaic or solar PV. To help you get solar on your home, let’s explore some of the common technologies and common terms to help you be an informed solar designer or owner.
First off, let’s talk terminology. This way you know what you are looking for when you are getting quotes.
A solar panel, which creates electricity, is called a solar “module.” It is made up of solar “cells.” The solar cells can range from 24-72 cells (in 12 cell increments) and operate at roughly 0.5VDC each when running. We tie these cells electrically in “series” by hooking them from the negative side of one cell to the positive side of an adjacent cell till we reach the end of the cells. Then we have one side that is positive and one side that is negative to get the desired output of either 12VDC (24 cells) to 36VDC (72 cells.) These cells are then housed between a piece of aluminum frame and tempered glass.
As solar professionals, we hook up the modules in series, just like we did with the cells, to increase their voltage which feeds into a device (called an inverter) that converts the electricity from DC (direct current) into AC (alternating current.) This way, it can be used it in a home, business or even to power up the utility grid. If you hook up multiple modules in a series, it is called an PV array.
From the inverter, it sends the AC electricity into your service panel (breaker box) to power the house, or business and then it can be sent out to the grid to provide power outside the home or business.
This system is called “grid tied” or “interactive.”
You may have heard the term “off-grid.” This refers to a system that is not connected to the utility “grid” at all. This system works by having solar modules hooked up to a device called a “charge controller.” This device charges a set of batteries, and those batteries are “inverted” with an inverter to take the batteries DC power and convert it into AC power. This AC power goes into your service panel to power your home. It is rare to see any businesses use this model; however, it is readily seen in subsistence homesteading.
SO HERES THE RUB – Off-grid systems use different components, even down to the solar panels than what is used in interactive systems. Interactive systems are cheaper, easier to install and the components are more available than off-grid. They also take up about 98% of the solar PV market. The other big deal is that if you hook your system to the grid, you can receive a tax break. In the USA, this equates to 30% from the federal government plus any state incentives for the next several years. If you are not connected to the grid, you receive no incentives.
The choice is obvious as a business decision: less costly, easier to install, significant savings … go with interactive! But this system has one downside, it does not provide power to your home or business if the grid has an outage. I repeat, no power from the grid, no power from your system even to your home on a sunny day. The reason we do this is so that your do not electrocute the lineman who could potentially be working on the down power line someplace.
So, if the components are different, how can I hook to the grid, get incentive AND provide power when the grid goes down? I want to have backup power. Our new system is called AC coupled.
AC COUPLED SYSTEMS
AC coupled systems use a standard interactive system setup (presumably from a previous installation that happened.) Then it utilizes the off-grid components such as the charge controller and batteries; however, it brings in a new piece of technology called an AC coupled inverter. This component is made a few different ways but usually, it is part grid tied inverter, part charge controller, and has a new electronic component installed called an automatic transfer switch (ATS.) The ATS has been used with generator backup for decades. It is reliable, efficient, switches a parallel circuit to the grid to your home or business, and activates a generator. We use this to switch the power line going to the grid to a disconnected state and then routes the power from the solar PV to the batteries as well as use the batteries to power your service panel.
These systems are much more complicated, more expensive, but do qualify you for tax incentives, either in part or completely, and provide all the sexiness people want when they think about going solar.
So, which one is best for you? That is a bigger question based on locations shade, budget and needs for your system. Stay tuned for our next article that goes into a business case on these topics.
For the past 20 years I have been advocating and teaching about Renewable Energy and Alternative fuels. I worked in IT for 9 years and ran a few IT businesses during that time. I have worked wind turbines and in fuel cell technology and I currently teach college courses full time in Renewable’s and Alternative fuels. I am passionate about technology, building things, family and having fun outdoors. I love sharing and helping to make the world a better place in my own way.