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Solar Basics

THE TYPES OF SOLAR SYSTEMS AND APPLICATIONS

OFF GRID SYSTEM

OFF-GRID INVERTES: (Standalone system) 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.

NOTE: There`s no need for an inverter if you`re only setting up solar panels for equipment that runs on DC current. You will need an inverter to convert DC to AC for all other electrical appliances.

OFF-GRID: Operating totally off the grid requires a large capacity battery array capable of powering the property during night time and periods of low irradiance in winter and an inverter capable of supplying the maximum load ever required at one time.

This requires a significant investment in PV modules, inverters and especially batteries which cannot normally be justified if there is a good quality grid connection available at the property. An off-grid system is well suited to rural areas with little or no grid connection but is unlikely to be a viable solution in a well-connected urban area.

Should however fixed connection charges for electricity become more common and higher then disconnecting from the grid may become a more viable option in the future.

GRID TIED SYSTEM

GRID-TIED INVERTER (GTI): What is the job of a solar inverter? They regulate 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 50Hz). The output voltage is also adjusted slightly higher than the grid voltage in order for excess electricity to flow outwards to the grid.

Typical Grid-Tied Inverter System

GRID-TIED:  A pure grid-tied system with no storage or load management for a user with fixed rate power charge is a viable option for South Africa but the system will need to be significantly under sized to minimise the wasted energy generation as typically no surplus power can be exported.

Essentially the PV system has to be sized to generate only sufficient power for the base load during the day, i.e. the fridge, freezer, pool pump and other permanently on devices.

The low investment cost of a small PV system with a high self-consumption rate should make them quite attractive especially for households with family at home during the day.

HYBRID SYSTEMS

HYBRID INVERTERS: A Hybrid solar system combines the best from 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 during night time, low irradiance (overcast) or winter seasons. 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.

 

Typical New Hybrid Inverter System

Typical Equipment for New Hybrid Solar Systems

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

  • Solar Panels

  • Charge Controller

  • DC Disconnect (additional)

  • Battery-Based (Hybrid) Grid-Tie Inverter Battery Bank

GRID-BACKUP: If frequent load shedding continues each winter then there will be continued demand for grid-backup systems that can operate with no grid for prolonged periods of time.

Adding a battery inverter or a hybrid inverter along with a battery makes it possible to combine the energy from the PV system with that from the stored battery to power at least the essential loads in the property. 

The size of the battery required depends on the rating of the essential loads to be driven from it at times of no solar power being available.

Load shedding typically occurs during the evening peak in winter from 5:00PM – 08:00PM so there will normally be little or no solar power available to supplement the battery.

Shown below is a typical system layout for a grid-backup system using a Solar PV inverter and a Battery Inverter which gives maximum flexibility in the system design and can be retrofitted to an existing Solar PV system: 

Typical Retrofit System from Grid Tied to Hybrid

 

Typical Equipment for Retro fitting an Existing Grid Tied system to a Hybrid (battery backup) Solar System

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

  • Solar Panels

  • Charge Controller

  • DC Disconnect (additional)

  • Existing Grid-Tie Inverter

  • New Battery-Based Grid-Tie Inverter

  • New Battery Bank

Typical New Hybrid Inverter System

 

WHICH SOLAR PANEL TYPE IS BEST? MONO- VS. POLYCRYSTALLINE

Are you thinking about buying solar panels, but got confused about which type to go for? There are a lot of variables that you should take into account when you are buying a solar photovoltaic (PV) system

Monocrystalline Silicon Solar Cells

Solar cells made of monocrystalline silicon (mono-Si), also called single-crystalline silicon (single-crystal-Si), are quite easily recognizable by an external even colouring and uniform look, indicating high-purity silicon, as you can see on the picture below:

 

Monocrystalline solar cells are made out of silicon ingots, which are cylindrical in shape. To optimize performance and lower costs of a single monocrystalline solar cell, four sides are cut out of the cylindrical ingots to make silicon wafers, which is what gives monocrystalline solar panels their characteristic look.

“A good way to separate mono- and polycrystalline solar panels is that polycrystalline solar cells look perfectly rectangular with no rounded edges”.

Advantages

  • Monocrystalline solar panels have the highest efficiency rates since they are made out of the highest-grade silicon. The efficiency rates of monocrystalline solar panels are typically 15-20%.

  • Monocrystalline silicon solar panels are space-efficient. Since these solar panels yield the highest power outputs, they also require the least amount of space compared to any other types. Monocrystalline solar panels produce up to four times the amount of electricity as thin-film solar panels.

  • Monocrystalline solar panels live the longest. Most solar panel manufacturers put a 25-year warranty on their monocrystalline solar panels.

  • Tend to perform better than similarly rated polycrystalline solar panels at low-light conditions.

Disadvantages

  • Monocrystalline solar panels are the most expensive. From a financial standpoint, a solar panel that is made of polycrystalline silicon (and in some cases thin-film) can be a better choice for some homeowners.

  • If the solar panel is partially covered with shade, dirt or snow, the entire circuit can break down. Consider getting micro-inverters instead of central string inverters if you think coverage will be a problem. Micro-inverters will make sure that not the entire solar array is affected by shading issues with only one of the solar panels.

  • The Czochralski process is used to produce monocrystalline silicon. It results in large cylindrical ingots. Four sides are cut out of the ingots to make silicon wafers. A significant amount of the original silicon ends up as waste.

  • Monocrystalline solar panels tend to be more efficient in warm weather. Performance suffers as temperature goes up, but less so than polycrystalline solar panels. For most homeowners temperature is not a concern.

 

Polycrystalline Silicon Solar Cells

The first solar panels based on polycrystalline silicon, which also is known as polysilicon (p-Si) and multi-crystalline silicon (mc-Si), were introduced to the market in 1981. Unlike monocrystalline-based solar panels, polycrystalline solar panels do not require the Czochralski process. Raw silicon is melted and poured into a square mold, which is cooled and cut into perfectly square wafers.

 

Advantages

  • The process used to make polycrystalline silicon is simpler and cost less. The amount of waste silicon is less compared to monocrystalline.

  • Polycrystalline solar panels tend to have slightly lower heat tolerance than monocrystalline solar panels. This technically means that they perform slightly worse than monocrystalline solar panels in high temperatures. Heat can affect the performance of solar panels and shorten their lifespans. However, this effect is minor, and most homeowners do not need to take it into account.

Disadvantages

  • The efficiency of polycrystalline-based solar panels is typically 13-16%. Because of lower silicon purity, polycrystalline solar panels are not quite as efficient as monocrystalline solar panels.

  • Lower space-efficiency. You generally need to cover a larger surface to output the same electrical power as you would with a solar panel made of monocrystalline silicon. However, this does not mean every monocrystalline solar panel perform better than those based on polycrystalline silicon.

How do they compare

  • Monocrystalline and thin-film solar panels tend to be more aesthetically pleasing since they have a more uniform look compared to the speckled blue color of polycrystalline silicon.

  • Both mono- and polycrystalline solar panels are good choices and offer similar advantages.Even though polycrystalline solar panels tend to be less space-efficient and monocrystalline solar panels tend to produce more electrical power, this is not always the case. It would be nearly impossible to recommend one or the other by not examining the solar panels and your situation closer.

  • Monocrystalline solar panels are slightly more expensive, but also slightly more space-efficient. If you had one polycrystalline and one monocrystalline solar panel, both rated 220-watt, they would generate the same amount of electricity, but the one made of monocrystalline silicon would take up less space.

 

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