Do you know? No more we need the grid to supply electricity to power our residential/commercial loads!
Yes, right! we can avail of this with an “off-grid solar energy system”
At many remote/rural locations such as a farmhouse or cottages, access to the grid is a difficult and costly task, we often experience a frequent power failure and yes we know how irritating it is!
Solar energy ends up being the most productive and solid sustainable power source with a series of economic benefits to cater to all your loads.
The off-grid solar energy system is a popular choice in places with frequent power cuts and remote areas where access to the grid is difficult.
You must be wondering how this solar energy works without connecting to the grid, and what are the pros and cons, is it worth installing this solar energy system, how an inverter works in an off-grid system?
Well in this article we have tried to answer all your questions and enhance your knowledge about the off-grid system.
What is an off-grid solar system?
The off-grid system also known as a standalone PV system proves to be a good alternative for remote places where access to the utility grid is a costly or impractical task. As this system is not connected to the grid, battery plays an important role in energy storage.
The solar panel, battery and inverter forms the basis of an off-grid solar system (In the previous article we have described the components necessary for an on and off-grid system)
How does the off-grid solar energy system work?
- Off-grid solar PV systems work on the basic photovoltaic principle, when solar radiations are incident on the solar panel it generates energy in the form of direct current(DC).
- The generated DC energy is fed to the charge controller which regulates the flow of charge and supplies the regulated power to the battery. To supply power during the night or on non-sunny days, batteries play an important role.
- On a sunny day when the solar panel operates efficiently and produces enough power to cater for the load and also to charge the battery, excess energy is stored in the battery and is retrieved later when required.
- The DC energy from a solar panel or battery is converted into alternating current(AC) energy (as most of the appliances at residential/commercial buildings run on AC supply) with the help of an inverter
- This converted AC energy is supplied to the loads connected with the help of the wiring connection.
How to connect an off-grid inverter?
An inverter is placed between the solar panel and the loads. The inverter is not directly connected to the solar panel, it is assembled with a battery and the charger to control the energy supplied to the inverter from the solar array.
Optional generators such as diesel, fuel etc can be added with the inverter to supply energy in case the battery gets exhausted or if the solar panels operate below the required efficiency level.
How does an off-grid inverter work?
The DC power generated from the solar panel or battery is supplied to the inverter, the inverter consists of a capacitor and inductor circuit that opposes the sudden change in its direction and the current begins to rise and fall thus generating the sinusoidal waveform. The generated waveform is either a pure or modified waveform.
With the basic conversion function, the inverter also functions as a monitoring device, it is used to record and store the solar PV system data.
The advanced inverter is equipped with a maximum power point function to ensure optimum tracking of solar radiation.
For a place where a power halt can cause a huge loss, an inverter can be equipped with a generator and battery to ensure a continuous power supply.
Types of off-grid inverter:
Off-grid inverter depending on the output waveform is divided into the following three types:
- Pure sine wave inverter
- Modified sine wave inverter
- Square wave inverter
1. Pure sine wave inverters: Pure sine wave also known as true value inverter comes with a stable sine wave output i.e. it generates continuous repetitive oscillations in both positive and negative directions. It proves to be a good choice for sensitive electronic appliances. Depending on the frequency it is further classified as :
- Low frequency: This inverter generates a high starting current, hence it proves to be more beneficial for compressors and air-conditioners that can be used for long run time.
- High frequency: These inverters are reliable and efficient with an ability to run both inductive as well as resistive load as compared to modern sine wave inverters. They are free from electromagnetic pollution and offer a higher power conversion rate with minimum losses.
2. Modified sine wave inverter: This type of inverter though is less expensive but comes with a distorted waveformi.e they have a time interval between the maximum positive and maximum negative point. They are also technically termed modified square wave inverters. This inverter is not recommended for an inductive load (this kind of loads run on electromagnetic principles and requires a high starting current) such as compressors, relays, motors, fluorescent lamps etc as it causes excessive heating that may affect the durability of the appliances. Due to its low cost, one can use it for small devices but are not recommended for the renewable energy system.
3. Square wave inverter: These inverters generate poor quality unstable square wave AC output which will affect the durability of the inverter as well as the load. These inverters are not currently used due to their instability and the generation of harmonic distortion.
Confused between pure and modified sine wave inverters? Let us check some basic differences between these two.
From the above discussion, one can surely see that a pure sine wave inverter is a better choice but if the cost is the criteria and you are not a frequent user one can choose a modified sine wave inverter.
Now once you are aware of the difference between this inverter, the other point that might strike you is how to select the inverter, what criteria should one use to select the inverter.
How to select off-grid inverters for your home?
While choosing any inverter one needs to know some basic technical terms (link to be given) like power, energy rating, efficiency etc. Let us consider a few below points that one must check before selecting the inverter.
- Types of target appliance: In the market varieties of inverters are designed depending on the appliance requirement, one should target the required appliances and choose accordingly.
- Power Consumption: After the identification of target appliances, the next task is to calculate the total power consumption by these loads.
- Once the total power consumption is identified a suitable inverter rating is to be selected,if we consider a 100% efficient inverter(with zero losses which is practically not possible) then the power requirement rating is equal to the inverter rating.
But in the practical condition, an inverter with a sufficient higher rating than the total load rating is selected.
- Choice of an Inverter: The present market consists of an inverter with some advanced features such as remote control, inbuilt alarms, advanced cooling fans, etc for better durability and maintenance of the inverter.
- An off-grid solar inverter ranges from less than 1kW for small appliances to more than 16kW for commercial buildings.
- Independent of grid
- The output voltage can be regulated as it is not loaded dependent
- Easy to install in remote areas where connectivity to the grid is a tough task
- Reliable as power can be stored in batteries
- Synchronisation of voltage and frequency between grid and inverter is not required
- Grid connection is not available
- More complex in installation
- Limited backup hours
- Do solar inverters turn off at night?
This is the most common question that comes to the customer’s mind when talking about the solar inverter. As we know the purpose of a solar inverter is to convert the DC energy generated by the solar array into AC power, during the off-solar day and at night the solar array is not capable of generating electricity due to the lack of solar radiation and hence the inverter turns off during this condition.
- Why choose a sine wave inverter over a square wave inverter?
Sine wave inverters have higher efficiency, thus leading to a reduction in electricity bill as compared to square wave inverters. Non-sine wave inverters generally cause harmonics that may cause damage to the coils of the refrigerator, fan etc. Hence it is a good choice to buy a sine wave inverter.
- Does the power outage affect the off-grid solar inverter?
Well no, as your inverter is not connected to your utility grid, power failure will not affect your inverter working.
- Which solar system is better on-grid or off-grid?
Both off-grid and on-grid solar energy systems come with certain pros and cons as we have discussed in this article.
Going for the grid solar power is a good choice until you realise grid failure can halt your connection. Then one might think of an off-grid solar energy system as a good option, but what if we have consecutive cloudy days and the battery gets exhausted?
A hybrid solar energy system can be a solution for the above query, this system comes with the advantage of both on grid and off-grid solar energy systems.
Well to know which system is worth the investment totally depends on the location, requirement and budget.
Don’t worry, if you want to install a solar power system at your location and want to know which system is worthy for your location our design engineers will help you to choose the best.