Classification Of Solar Energy Systems

All over the world people are currently moving toward using renewable sources of energy to fulfill their energy requirements. In today's world, there are many examples of the large-scale emergence and implementation of solar energy systems/technologies into society. College students who recently graduated or individuals looking to utilize solar technologies for purposes at home or work will need to be educated about what types of solar systems exist, how they work and their advantages and disadvantages, in order to make informed buying decisions. Solar energy systems can be classified into three types based on:

1) how energy is outputted (technology);

2) how the system connects/works in conjunction with the electric grid (configuration); 

3) a system's size in comparison to other types of systems.

The goal of this article is to provide you with several examples of how we can classify solar energy technology systems into these three categories and to give you detailed descriptions of each one.

The most basic classification of solar energy systems is based on how we are using the sun's energy to power things. There are only two ways to do this: using photovoltaics (PV) or using concentrated solar power (CSP); and then there are the solar thermal systems that create an output of thermal (or heat-producing) energy (heating).

Photovoltaic (PV) Systems

The most common type of solar energy generation usage is Photovoltaic systems. With the aid of the photovoltaic effect, modern Photovoltaic systems transform solar radiation into electrical energy using a semiconductor, most commonly Silicon, which is the industry standard. The semiconductor is 'excited' by the sun's rays, which causes a stream of electrons to move and create a direct electrical current, as opposed to an Alternating Current, which flows in two different directions. In most households and workplaces, this is referred to as direct current (DC). In order to be applicable in most households and workplaces, an inverter is required to convert the direct current (DC) of the cell into an alternating current (AC).

From an installer's or homeowner's perspective, the most practical classification of a PV system is based on its electrical configuration and relationship with the utility grid. There are three main types: grid-tied (on-grid), off-grid (standalone), and hybrid systems.

On-Grid (Grid-Tied) Systems
On-grid systems are directly connected to the public electricity grid and are the most common type of residential and commercial installation worldwide.

How it works: Solar panels generate electricity during the day. This power is used to run the building's loads. If the system produces more power than needed, the excess is fed back into the utility grid. At night or during periods of low production, the building draws power from the grid.

Key Component: These systems do not require battery banks. The grid itself acts as a virtual storage system for excess energy.

Advantages: They are the most cost-effective and simplest to install due to the lack of batteries. They also enable net metering, where homeowners receive credit for the excess power they supply to the grid.

Disadvantage: The primary drawback is that the system shuts down during a grid power outage for safety reasons (to prevent back-feeding electricity to line workers), meaning it cannot provide backup power.

Off-Grid (Standalone) Systems

Off-grid systems function independently from the power utility grid. They're ideal for use in remote areas with no practical grid connection or where grid connection costs are too great.

Operation: Solar panels provide charging of a battery bank for use during the night or when it is not sunny. An inverter functions as a gateway to convert the direct current produced by the batteries into alternate current as it is used in a home.

Central Feature: An battery bank that can provide enough power to support the off-grid system for multiple days without needing to recharge, is the main feature of an off-grid system. For when weather conditions prevent recharging, many off-grid homes will also have a backup generator to provide more than enough power for longer periods of time.

Advantages: Living totally independent from the electrical grid and having access to electricity in a remote area that does not receive electricity from the electrical grid.

Disadvantages: These systems are significantly more expensive due to battery costs. They also require more complex design and diligent energy management by the user to avoid depleting the batteries.

Hybrid Systems
Hybrid systems combine the best elements of on-grid and off-grid technology.

What A Hybrid System Is: A hybrid system connects to the utility grid, just like a grid-tied system, but it also has a battery bank included in the system. The solar energy produced is used to first power the electric loads of the home, then to charge the batteries. Only after the batteries are fully charged will the remaining solar electricity produced be sent back to the grid. During a power outage due to a grid outage, A hybrid system has the ability to island itself from the grid and continue to supply power to the home through the battery bank and through the solar panels.

Key Component of a Hybrid System: Hybrid Inverter or An inverter paired with a battery controller - this component controls the many different components in a hybrid system.

Advantages of Having A Hybrid System: Backup power reliability, the ability to save self-generated energy for use during peak electricity rates, and possibly a smaller battery bank when compared to an off-grid only application.

Disadvantage of Having a Hybrid System: The additional battery costs make the overall cost more than a standard grid-tied system.

Apart from system type, solar installations are also categorized based on their size and their relation to the electrical load they serve.

Distributed Generation (DG): These are smaller systems that are situated closest to the point of consumption. Most systems on residential rooftops and those on commercial buildings are in this category. They are usually integrated into the low voltage distribution grid and can enable consumers to save on their electricity bills.

Centralized Generation (Utility-Scale): These are large solar power plants, usually spread over hundreds of acres, that produce electricity which is then delivered over high voltage transmission lines to far-away end-users. Both large-scale PV solar farms and CSP plants are in this category. Overall, the classification of solar energy systems is complex. Whether classified by the technology involved (PV vs. CSP), the operational configuration (on-grid, off-grid, or hybrid), or the degree of deployment, each classification has an important function in the world's energy system. Knowing these differences is the foundation for those aiming to utilize solar energy.