1. Basic Grid-Tied System
A system is said to be “grid-tied” when the output of the system inverter connects directly to your utility service.
The house wiring is not aware of the source of the power it is using. It can come from the array if there is sufficient energy being generated to meet the building’s needs, or from your utility’s grid, or a combination of both. All of this is handled automatically and transparently by the grid-tied inverter.
The transparency is possible because of the inverter design. Before the inverter can turn on and produce power, it senses the presence of power from the grid. It must match the frequency and phase of the grid signal before it can turn on its output. In this way, your solar panel output matches your utility power precisely.
The illustration above shows a “string inverter.” This inverter requires a “string” of panels to be connected in series and wired to its input. The electrical characteristics of the string must be carefully matched to the inverter or the system efficiency will suffer. A well-matched string system is the most cost-effective system in terms of cost per Watt. A typical string includes 12-14 panels.
One important consequence of this is that if the grid goes down for any reason (storm damage, power outage, etc.) the grid-tied inverter must shut off. If your goal is to offset your conventional energy usage, the grid tied system is completely appropriate and the most cost-effective option. If your goal is to have a source of energy in the event of a power outage, you should consider a battery-backup system.
2. Off-Grid System
An off-grid system needs no grid present, as the name implies.
While the electronics on an off-grid system are less complex than a battery back-up system, the system design of an off-grid system requires great attention. In an off-grid system there is less margin for error in sizing a system since it is the sole source of power. Efficiency is not optional!
To go off-grid is a lifestyle commitment, but it *can* be done!
3. Battery Backup System
A battery backup system operates just as a grid-tied system does, as long as grid power is available. In the background, the system is also maintaining the state of charge of a bank of batteries. If the grid does go down, the system switches automatically to be powered from the battery bank. The inverter fed by the batteries can then supply power to all the household circuits which have been wired to the separate breaker panel.
This system requires careful planning to select which circuits to feed in the event of power outages. It also requires significantly more complex hardware. The inverter is more complex than a basic grid-tied inverter. There is also a charge controller required to extend the life of the battery bank.
As with all renewable energy systems, it is important to note that if you plan a battery back-up system, it should be done after or in conjunction with improvements in your energy efficiency.
An inverter takes the electricity from your solar panel and allows you to store or use it. There are three types of inverter setups that we sell:
You system will need an inverter, and the grid-tied inverter is the most common type. Inverters take the DC voltage from the panels and convert it to standard household AC voltage. The inverter is also the place where the decision to push power to the grid is made. A standard grid-tied inverter will disable its output whenever you lose power from the utility. This prevents any linemen from being exposed to electrical shock while repairing a downed line.
Battery Backup Inverters
A battery-backup inverter has the same primary function as a grid-tied inverter. The difference is that a battery-backup inverter adds sophisticated electronics that can sense when the grid goes down and switch its own input power to run from a battery bank, at least for a subset of the building’s circuits that are pre-wired to the inverter.
An off-grid inverter uses only a battery bank as an input power source. It has no ability to sense the grid or push power to the grid.
When we talk about solar energy, all systems start with the “Panels” or “Modules,” which do the actual conversion of sunlight to electricity. That is what most people can see, and often the only thing people think about. But there are other major components that are absolutely necessary to allow the output of the panels to be used:
Since panels include a plate of glass and brittle silicon cells, there needs to be a robust means of holding the panels in place regardless of wind and weather. Twisting the frame is the worst thing that can be done to a panel. A well-engineered and installed mounting system can add years to system life.
Mounting systems are available for both roof and ground mount. On a roof, system design differs depending on whether the roof is a pitched metal or asphalt covered surface, or a flat membrane-covered surface. Generally, a roof-mounted system will be less costly to install than a ground-mounted system, since it will rely on the structure of the host building for much of its rigidity.
Use of a monitor system is optional. However, they provide great benefits. With a monitor, you can track your system production, both at the given moment, and daily/monthly/annually since the first day you turned it on. This allows your installer to make periodic checks on system production. Most can also be configured to send an email alert to you and your system installer if a fault is detected.
Balance of System
The Balance of System (BOS) is the unglamorous stuff that is absolutely necessary for system function: wire, conduit, breakers and service panels, hardware and fasteners – you get the idea.
Yes. Indiana state law requires Investor-Owned Utilities (IOUs) to allow for distributed energy generation (e.g., solar, wind) to be able to connect to the grid in system sizes up to 1 MW peak ac power. Municipal utilities and REMCs are not bound by the same regulations, but all allow some form of interconnection.
Not typically. Some REMCs do charge for the new meters required, otherwise it is usually only a paperwork exercise.
No, not in the way that you are probably thinking. While there are programs for large systems where you can negotiate a power purchase agreement with the utility, most small-medium systems use net metering. “NET METERING” agreements are used by the IOUs, and in these arrangements money never changes hands. Rather, if your system ever makes more than you are using at any instant, the energy flows in the opposite direction that it normally does, going out to the utility lines. This outward flow of energy can be considered as “turning your meter backwards.” (If you have a mechanical meter, this is literally what happens.) That in effect means that you get 1-for-1 credit for power produced. When you again use more than you produce, the meter goes forward again, consuming the overproduction that was recorded earlier.
This does not apply for most municipal and REMC power customers. Most of those agreements are referred to as “NET BILLING”. The meters for net billing are capable of measuring incoming and outgoing energy independently. Properties that push power back to the grid are given credit for that energy at wholesale energy prices (usually 2 to 3 cents/kWh), and the total of that credit every month is subtracted from your bill.
Your contractor should be able to help you. If GAI is your solar partner, we make this process almost completely painless for you!