Grid Connected Inverters

More on grid-connected solar inverters

Grid-connected solar inverters are the most common and developed in the industry, although hybrid solar inverters are becoming increasingly popular. As their name suggests, they should be used when our solar installation is connected to the grid. These types of inverters can be used for small residential and commercial installations as well as for large solar plants or solar farms.

The main difference between these types of solar inverters is that they need an electrical grid to provide them with the frequency and voltage parameters in order to synchronise with them. Because these inverters are virtually and actually linked to the grid, they must be synchronised to avoid any decoupling or distortion to the internal grid of the house or building or to the general power grid. This means that when there is no grid, these solar inverters cannot operate. To the usual question "If the power goes out at home, will my solar installation be able to supply energy? The answer is NO. In other words, if there is a power cut in the grid, a grid-connected solar inverter stops working (as long as it does not have a specific function to work in "off grid" mode).

The working voltage of these low power inverters (3000W, 5000W and up to 10,000W) on the DC side (solar panels) is variable, but usually ranges between 400V and 1000V and each inverter MPPT input or string usually works in ranges between 80V and 150V. It should be noted that depending on the manufacturer and configuration of the inverter these values may vary. 

Grid connection inverters, as is usual with string inverters, can be oversized on the DC or solar side. This means that we can connect a total power of panels (also called peak) higher than the nominal AC output power of the inverter. Normally, grid-connected solar inverters allow an oversizing of the solar power of between 30% to 50% over the nominal power. 

The output voltage and frequency on the AC side of this type of inverter can vary quite a lot due to the fact that the same model can generally be used in different countries. It is therefore common to see that this type of inverter has variable output frequency values (50Hz or 60Hz) and different voltage values (180V, 220V, 230V, 240V). This flexibility in the output parameters allows this type of inverter to adapt to the different grids to which they are connected.

In the case of Spain we will be working in a frequency of 50Hz and output voltage of 220V/230V. As a general rule, the inverters we sell in Tienda Solar are suitable for use in Spain. If you want to use them in other countries you should check that the electrical characteristics are also valid in your country. If you have any doubts, you can always contact us.

Grid connection inverter monitoring system:

It is very common for grid-connected inverters to have an integrated monitoring system that allows the production of the solar installation and the inverter's operating parameters to be tracked. These systems represent a great advantage for the owner as they provide relevant information on the performance of the solar plant, any faults that the inverter may have and consequently act correctly so that energy production is as efficient as possible.

It is important that grid-connected inverters generate electricity and initially feed it into the internal grid of the house/industry so that it can be consumed instantly. The distribution of the energy via the internal grid and according to the consumption of the appliances is automatic. In other words, the network self-balances the distribution of electricity autonomously to the different consumption points. The monitoring system makes it possible to visualise instantly which loads consume the most.

If the loads consume more than the solar generation, the grid will have to provide the energy deficit in order to keep the loads running. Again, this self-management is done automatically without us having to program or manage anything. The monitoring system also shows the energy balance and allows us to see what percentage of the consumption is covered by solar generation and what percentage is covered by the grid (using a wattmeter).

On the other hand, if the connected loads do not consume the total amount of energy generated by the solar installation, the surplus is automatically fed into the grid. If for some reason we do not wish to discharge our surplus, we can programme the inverter (if it has this function) or add an additional element called a wattmeter if our solar inverter does not have the "zero discharge" function. 

In either case, either by means of the function included in the inverter or the wattmeter, the inverter adjusts its working point (MPPT) to generate the output power corresponding to the instantaneous consumption. In this way the inverter makes sure to match the consumption to the solar production. As mentioned above, the wattmeter, in addition to programming the inverter for "zero discharge" mode, is the element in charge of determining the power extracted from the grid for consumption (home or industry).

How to feed energy into the grid?

In order to feed energy into the grid, it is necessary to have a renewable energy generation system (such as solar panels or wind turbines) and a grid-tied inverter to synchronise the generated energy with the conventional electricity grid.

The general steps for feeding power into the grid are explained below:

• - Power generation: Install solar panels or another source of renewable energy generation on your property. These panels or turbines will convert energy from the sun or wind into electricity in the form of direct current (DC).
• - Grid-tie inverter: Make sure you have a suitable grid-tie inverter for your renewable energy generation system. This inverter converts the direct current (DC) generated by the solar panels or renewable source into alternating current (AC) which is the form of energy used in the conventional electricity grid.
• - Synchronisation with the grid: The solar inverter is designed to synchronise with the frequency and phase of the grid. When properly connected, the inverter detects the presence of the grid and ensures that the power generated is in phase with the grid.
• - Power injection: Once the inverter is synchronised with the grid, it begins to inject the power generated by the solar panels into the grid. The energy flows from the solar panels to the inverter and then to the electrical system of your home or business. If generation is greater than demand as discussed above, the excess energy is dumped into the grid.
• - Metering and balancing: In some countries, there are bi-directional metering systems that record the amount of energy they inject into the grid. Depending on local regulations and compensation policies, you may be able to receive credits or compensation for the energy you feed into the grid at times when you are generating more than you consume.

It is important to note that the process of feeding energy into the grid may be regulated by local or national authorities, and you need to make sure you comply with the requirements and regulations in your area before connecting your system to the grid. It is always advisable to work with qualified professionals for the installation and configuration of the power generation system and the grid-tie inverter.

Each country is different and has its own particularities, but as a general rule it is necessary that the solar inverter used complies with the current regulations of the country in question and in some cases that it has the corresponding certificates requested by the electricity companies or the competent state authority. 

It is important that the grid feed-in and the ease of doing so will usually depend on the nominal power of the solar installation. Countries usually stipulate power ratings for solar installations and the corresponding administrative procedures. For which power range the requirements for solar inverters may vary.

What is the difference between a stand-alone PV system and grid-connected systems?

A stand-alone/isolated PV system and a grid-connected PV system are two different approaches to harnessing solar energy. The main difference is whether the system is connected to the grid or whether it operates independently with local storage. Each approach has its advantages and disadvantages, and the choice depends on the energy needs, location and objectives of the system owner.

What are the characteristics of an On-Grid Photovoltaic System?

The main characteristics that differentiate a grid-connected PV system are:

1. Grid connection: A grid-connected PV system is integrated with the public electricity grid. The electricity generated is first used to meet local needs, and any surplus is fed into the grid.
2. No Storage Requirement: In a grid-connected system, there is no need for storage systems, such as batteries, as the grid acts as a virtual "store". Electricity can be taken from the grid when solar generation is insufficient.
3. Grid Benefits: Grid-connected system owners can generate energy credits or even receive payments for surplus electricity they feed into the grid. This can make the system more economically attractive.
4. Less Dependence on Fossil Fuels: By using solar power, grid-tied systems reduce dependence on fossil fuels and contribute to cleaner energy generation.

At Tienda Solar we have a wide range of grid-tied inverters. From cheap solar inverters to higher ranges with high international prestige brands. If you have any questions please do not hesitate to contact us through info@tienda-solar.es