In this article we will explain in a very simple way and a few steps how a photovoltaic system can be integrated to your home when your home is connected to the national grid.
The system is widely applicable to all grid-connected properties, warhouses or commercial buildings. Our turnkey solution is designed for grid-connected installation (single or three phase) with the ultimate goal to reduce the dependence on the supply of the grid and to maximise the self-consumption for the energy produced by the solar panels.
It is obligatory and all the DNOs require a certified product with export limitations, for the UK market, the inverter should G98/99 compliant.
The primary goal of a self-consumption system is to optimise the use of solar and/or wind power. The major obstacle in such a system is that power generation times do not match
the actual times of power use. This results in a system being forced to import energy from the grid and export it when there is a surplus. In an optimised self-consumption system, surplus energy is stored locally for local on-demand use. Such energy storage is becoming an increasingly attractive proposition, especially with feed-in tariffs decreasing and grid supplies becoming less stable and more expensive.
It is important to mention that the system is always connected to the grid but the grid supplies in parallel with the inverter/solar panels the energy demand of the household.
It is important to explain that a hybrid inverter will power the AC-loads but if the energy demand exceeds the capacity of the inverter or the batteries are not fully charged, the surplus energy will be withdrawn from the grid. In simple terms if the load is 5kW but the inverter can only supply 4kW then 1kW will be supplied by the grid.
This is a major difference between off-grid inverters and hybrid grid inverters, the off-grid system will go into bypass mode if the power demand exceeds the rating of the inverter and all the energy will come from the grid (read more about off-grid set up here)
We collected some pictures from real installations, the energy from the photovoltaic system is converted to 230VAC single or three phases, and the output is connected directly to the switchgear of the property using a standard MCB 32A or an RCBO (with integrated RCD).
The picture with current sensor (clamps meter, C.T) and digital energy meter feeding data back to Solis 5kW 5G hybrid inverter
Similar setup with single phase consumer unit connected to the hybrid inverter.
Voltacon Hybrid 5.5kW inverter AC input is connected to the consumer unit.
Let’s see now using our simple but very useful diagram of how the system behaves during in 24 hours. The graphs are easy to understand, we used the most informative and meaningful quantities to plot the results. One diagram is adequate to proof without any doubts that solar is the way to become power independent. The key points of our graph:
Below, there is another scenario with the night battery charger switched off. There was energy reserves into the batteries around 70% and next days was expected energy generation from the sun. 11.4kWh of free energy was produced from solar panels. Below is the Solis monitoring platform view of the power generation and consumption. The blue line represents the PV generation and the doted red light represents the homeowners power consumption. This system has the 24-hour feature enabled.
When upgrading the grid-tied system to an energy storage system the only part that changes is the AC Coupled battery inverter add-on. The existing solar PV system doesn’t need to change at all. The AC coupled battery inverter is installed alongside batteries which is then connected directly to your panel or mains. If the customer wants critical load backup, then those loads will be moved to the backup port (ac output for off-grid mode) . This will give customers the opportunity to select loads that they define as “critical”. Critical loads will remain online during a grid failure until the solar PV generation is null and/or the battery state of charge is null. Examples of critical loads would be refrigerators, hot water tanks, emergency lighting, etc.
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 what you are capable of consuming. With net metering, homeowners can put this excess electricity onto the utility grid instead of storing it themselves with batteries.
Net metering (or feed-in tariff schemes in some countries) play an important role in how solar power is incentivized. Without it, residential solar systems would be much less feasible from a financial point of view.
Many utility companies are committed to buying electricity from homeowners at the same rate as they sell it themselves.
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.
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 EIA data, national, annual electricity transmission and distribution losses average about 7% of the electricity that is transmitted in the United States. Lead-acid batteries, which are commonly used with solar panels, are only 80-90% efficient at storing energy, and their performance degrades with time.
Additional perks of being grid-tied include access to backup power from the utility grid (in case your solar system stop 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.
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:
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 60Hz). The output voltage is also adjusted slightly higher than the grid voltage in order for excess electricity to flow outwards to the grid.
Micro-inverters go 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 suspect to shading issues should definitely look into if micro-inverters are better in their situation.
Most homeowners 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 meter, is capable of measuring power going in both directions, from the grid to your house 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 pay full price for the electricity you generate; however, this is not always the case.