What is a Grid-Tied solar system?

Grid-tied, on-grid, utility-interactive, grid intertie and grid backfeeding are all terms used to describe the same concept – a solar system that is connected to the utility power grid.

Advantages of Grid-Tied Systems

Grid-tied, on-grid, utility-interactive, and grid back-feeding are all terms used to describe the same concept – a solar system that is connected to the utility power grid.
Grid Tied Solar System

1. Save more money with net metering

A grid-connection will allow you to save more money with solar panels through better efficiency rates, net metering, plus lower equipment and installation costs:

Batteries, and other stand-alone equipment, are required for a fully functional off-grid solar system and add to costs as well as maintenance. Grid-tied solar systems are therefore generally cheaper and simpler to install.

Your solar panels will often generate more electricity than you are capable of consuming. With net metering, users can put this excess electricity back into the utility grid instead of storing it themselves in batteries.

Net metering (or feed-in tariff schemes in some countries) play an important role in how solar power is incentivized. Without it, commercial and residential solar systems would be much less feasible from a financial point of view. Many utility companies are committed to buying electricity from users at the same rate as they sell it themselves – not often in South Africa, though. Local authorities are also mandated by NERSA to allow and enable net metering, so we can expect more municipalities to comply in the near future.

2. The utility grid is a virtual battery

Electricity has to be spent in real time. However, it can be temporarily stored as other forms of energy (e.g. chemical energy in batteries). Energy storage typically
comes with significant losses (about 10-15% in and out).

The electric power grid is in many ways also a battery, without the need for maintenance or replacements, and with much better efficiency rates. In other words, more electricity (and more money) goes to waste with conventional battery systems.

According to Eskom data, national annual electricity transmission and distribution losses average about 15% of the electricity that is transmitted in South Africa. Lead-acid batteries, which are commonly used with solar panels, are only 80-90% efficient at storing energy, and their performance degrades with time. (But depending on where you use the electricity, batteries may well be more efficient than power from the grid).
Additional perks of being grid-tied include access to backup power from the utility grid (in case your solar system stops generating electricity for one reason or another). At the same time you help to mitigate the utility company`s peak load. As a result, the efficiency of our electrical system as a whole goes up.

Equipment for Grid-Tied Solar Systems

There are a few key differences between the equipment needed for grid-tied, off-grid and hybrid solar systems. Standard grid-tied solar systems rely on the following components:

  • Grid-Tie Inverter (GTI) or Micro-Inverters
  • Power Meter
  • Grid-Tie Inverter (GTI)

    What is the job of a solar inverter? The inverter regulates the voltage and current received from your solar panels. Direct current (DC) from your solar panels is converted into alternating current (AC), which is the type of current that is utilized by the majority of electrical appliances.

    In addition to this, grid-tie inverters, also known as grid-interactive or synchronous inverters, synchronize the phase and frequency of the current to fit the utility grid (nominally 60Hz). The output voltage is also adjusted to be slightly higher than the grid voltage in order for excess electricity to flow outwards to the grid.

    Micro-Inverters

    Micro-inverters are installed on the back of each solar panel, as opposed to one central inverter that typically takes on the entire solar array.
    There has recently been a lot of debate on whether micro-inverters are better than central (string) inverters.

    Micro-inverters are certainly more expensive, but in many cases yield higher efficiency rates. Homeowners who are subject to shading issues should definitely look into micro-inverter systems that may be better in their situation.

    Power Meter

    To start net metering, clients will need to replace their current power meter with one that is compatible with net metering. This device, often called a net meter or a two-way/bidirectional meter, is capable of measuring power going in both directions, from the grid to your property and vice versa.

    You should consult with your local utility company and see what net metering options you have. In some places, the utility company issues a power meter for free and pays full price for the electricity you generate; however, this is not always the case.

    What is an off-grid solar system?

    An off-grid solar system (off-the-grid, standalone) is the obvious alternative to one that is grid-tied. For users that have access to the grid, off-grid solar systems are usually out of the question. Here`s why:

    To ensure access to electricity at all times, off-grid solar systems require battery storage and a backup generator (if you live off-the-grid). On top of this, a battery bank typically needs to be replaced after 10 years. Batteries are complicated, expensive and decrease overall system efficiency.

    Advantages of Off-Grid Solar Systems

    Grid Tied Solar System

    1. No access to the utility grid

    Off-grid solar systems can be cheaper than extending power lines in certain remote areas, like farms, game lodges, mines and the like.

    2. Become energy self-sufficient

    Living off the grid and being self-sufficient feels good. For some people, this feeling is worth more than saving money. Energy self-sufficiency is also a form of security. Power failures on the utility grid do not affect off-grid solar systems.
    On the flip side, batteries can only store a certain amount of energy, and during cloudy times, being connected to the grid is actually where the security is. You should install a backup generator to be prepared for these kinds of situations.

    Equipment for Off-Grid Solar Systems

    Typical off-grid solar systems require the following extra components:

  • Solar Charge Controller
  • Battery Bank
  • DC Disconnect (additional)
  • Off-Grid Inverter
  • Backup Generator (optional)
  • Solar Charge Controller

    Solar charge controllers are also known as charge regulators or just battery regulators. The last term is probably the best to describe what this device actually does: Solar battery chargers limit the rate of current being delivered to the battery bank and protect the batteries from overcharging.

    Good charge controllers are crucial for keeping the batteries healthy, which ensures the lifetime of a battery bank is maximized. If you have a battery-based inverter, chances are that the charge controller is integrated.

    Battery Bank

    Without a battery bank (or a generator) it’ll be lights out by sunset. A battery bank is essentially a group of batteries wired together.

    DC Disconnect Switch

    AC and DC safety disconnects are required for all solar systems. For off-grid solar systems, one additional DC disconnect is installed between the battery bank and the off-grid inverter. It is used to switch off the current flowing between these components. This is important for maintenance, troubleshooting and protection against electrical fires.

    Off-Grid Inverter

    There`s no need for an inverter if you`re only setting up solar panels for your boat, your RV, or something else that runs on DC current. You will need an inverter to convert DC to AC for all other electrical appliances.

    Off-grid inverters do not have to match phase with the utility sine wave as opposed to grid-tie inverters. Electrical current flows from the solar panels through the solar charge controller and the bank battery bank before it is finally converted into AC by the off-grid-inverter.

    Backup Generator

    It takes a lot of money and big battery banks to prepare for several consecutive days without the sun shining (or access to the grid). This is where backup generators come in.

    In most cases, installing a backup generator that runs on diesel is a better choice than investing in an oversized battery bank that seldom gets to operate at its full potential. Generators can usually run on LPG, petrol, diesel and many other fuel types – even bio-diesel.

    Backup generators typically output AC, which can be sent through the inverter for direct use, or it can be converted into DC for battery storage.

    What is a Hybrid Solar System?

    Hybrid solar systems combine the best advantages of grid-tied and off-grid solar systems. These systems can either be described as off-grid solar with utility backup power, or grid-tied solar with extra battery storage.

    If you own a grid-tied solar system and drive a vehicle that runs on electricity, you already kind of have a hybrid setup. The electrical vehicle is really just a battery with wheels.

    Advantages of Hybrid Solar Systems

    Grid Tied Solar System

    1. Less expensive than off-grid solar systems

    Hybrid solar systems are less expensive than off-grid solar systems. You don`t really need a backup generator, and the capacity of your battery bank can be downsized. Off-peak electricity from the utility company is cheaper than diesel.

    2. Smart solar holds a lot of promise

    The introduction of hybrid solar systems has opened up many interesting innovations. New inverters let users take advantage of changes in the utility electricity rates throughout the day (time of use tariffs).

    Solar panels happen to output the most electrical power at noon. Your home and electrical vehicle can be programmed to consume power during off-peak hours (or from your solar panels).

    Consequently, you can temporarily store whatever excess electricity your solar panels in batteries, and put it back into the utility grid when you are paid the most for every kWh.

    Smart solar holds a lot of promise. The concept will become increasingly important as we transition towards smart grids in the coming years.

    Equipment for Hybrid Solar Systems

    Typical hybrid solar systems are based on the following additional components:

  • Charge Controller
  • Battery Bank
  • DC Disconnect (additional)
  • Battery-Based Grid-Tie Inverter
  • Power Meter
  • Battery-Based Grid-Tie Inverter

    Hybrid solar systems utilise battery-based grid-tie inverters. These devices combine can draw electrical power to and from battery banks, as well as synchronize with the utility grid.

    The bottom line is this: Right now, for the vast majority of homeowners, tapping the utility grid for electricity and energy storage is significantly cheaper and more practical than using battery banks and/or backup generators.