Solar Panel Inverters 

The Conversion Process:

Solar panel inverters are a crucial component of a solar energy system, responsible for converting the direct current (DC) electricity generated by solar panels into alternating current (AC) electricity, which is suitable for use in homes and businesses. The conversion process involves several key steps:

Step 1: DC Electricity Generation

• Solar panels, also known as photovoltaic (PV) panels, capture sunlight and convert it into DC electricity through the photovoltaic effect. When sunlight strikes the solar cells within the panels, it excites electrons, creating an electric current. Watch our video 'How do solar panels generate electricity' here.

Step 2: DC Electricity Collection

• The DC electricity generated by individual solar panels is collected and combined at a central point, often through a combiner box or junction box. This consolidated DC electricity is then sent to the solar inverter for conversion.

Step 3: Inverter Input

• The DC electricity from the solar panels enters the solar inverter, where the conversion process begins. Inverters are typically connected to multiple solar panels in an array.

Step 4: DC to AC Conversion

• Inside the solar inverter, electronic components, including semiconductor devices like transistors, capacitors, and transformers, work together to convert the incoming DC electricity into AC electricity. This conversion process involves rapidly switching the DC current to create a sinusoidal AC waveform that matches the grid's frequency and voltage requirements (e.g., 50 Hz in the UK).

Step 5: Synchronization with the Grid

• One of the critical functions of a solar inverter is to synchronize the AC output with the electrical grid. This synchronization ensures that the electricity generated by the solar system is in phase and in harmony with the grid's electricity supply. A stable and synchronized output is vital to prevent disruptions or damage to the grid.

Importance of Synchronization with the Grid and Maintaining a Stable Output:

1. Grid Connection: To effectively utilize solar energy in homes and businesses, the AC electricity generated by the solar inverter must seamlessly integrate with the local electrical grid. This synchronization allows surplus energy to be fed back into the grid, potentially earning homeowners or businesses credits through net metering or feed-in tariff programs.

2. Preventing Voltage Fluctuations: Maintaining synchronization with the grid helps prevent voltage fluctuations and ensures a stable supply of electricity. Inconsistent or unstable electricity can damage appliances and electronics connected to the grid.

3. Safety: Proper synchronization with the grid is essential for safety reasons. It prevents "islanding," a situation where the solar system continues to generate electricity during a grid outage, posing a risk to utility workers trying to repair the grid. Solar inverters are designed to disconnect from the grid during an outage to ensure the safety of workers. You can install a manual changeover switch to physically disconnect your home from the grid in the event of a power cut so that your home can be run using the inverters Emergency Power Supply - allowing the batteries and solar panels to power your home in the event of a powercut. A Tesla Powerwall will do this automatically.

4. Grid Stability: Solar inverters can also provide grid support functions by stabilizing voltage and frequency, contributing to the overall stability and reliability of the electrical grid.

In conclusion, the conversion process carried out by solar panel inverters is a crucial step in the generation of usable electricity from solar energy. Ensuring synchronization with the grid and maintaining a stable AC output is fundamental for the safe and efficient operation of solar energy systems and their integration with the existing electrical infrastructure.

The first thing to bear in mind is that the UK receives less sunlight/solar irradiance than the US or Australia so the standard advice cannot be copied over and applied here.

Australia average solar irradiance: 1825 kWh/year/m2 (climatebix)

US average solar irradiance: 1817 kWh/year/m2 (EPA.gov)

UK average solar irradiance: 949  kWh/year/m2 (Wikipedia)

We would recommend a 2:1 ratio between AC output of the solar inverter and DC capacity of the solar array. But make sure you adhere to the solar inverters maximum voltage per MPPT and maximum amps when stringing the array.

The standard approach when sizing the inverter is to typically not let the solar panel array capacity exceed 1.3x of the solar panel inverter AC output. The US and Australia recieve roughly the same solar irradiance, however the UK receives almost half as much. 

On average, a solar panel inverter in the UK would be generating half as much electricity than an inverter in the US or Australia.

This is significant as solar panel inverters are least efficient when operating between 5-15% of their maximum. As you can see from the graph on the right, typically an inverter would be 70-85% efficient at 5-15%. Efficiency jumps to 94%+ when operating at 20%+.

The goal of your solar panel inverter should always be to maximise generation over the course of the year, not merely to have the highest peak generation in the summer (and then have poorer performance for 90% of the year).

Sticking to the maximum voltage per MPPT and maximum Amps - we'd recommed a 2x ratio. E.g a 10 kW array should have a 5 kW (hybrid) solar inverter.

Remember, a 5 kW hybrid solar inverter can also charge the batteries using DC electricity, therefore it can send 5 kW to the AC side plus 3.6kW+ to the batteries - giving a maximum solar generation of 8.6 kW.

You should not install a hybrid inverter with a lower AC output than the batteries as this would reduce the battery charge/discharge potential. Therefore a 3.6 kW - 5kW hybrid inverter would cover most residential installations in the UK.

A Maximum Power Point Tracker (MPPT) is an essential component in many solar photovoltaic (PV) systems, especially those with varying solar conditions like changing sunlight intensity and temperature. Its primary function is to optimize the power output of solar panels by continuously tracking the Maximum Power Point (MPP) of the panel's current-voltage (I-V) curve, ensuring that the solar panel inverter operates at its peak efficiency and produces the maximum possible energy. Here's how an MPPT works:

1. Understanding the I-V Curve: Each solar panel has a unique I-V curve that describes the relationship between the voltage (V) and current (I) it generates under different operating conditions. This curve typically exhibits a distinctive "knee" point, which represents the maximum power point (MPP) where the panel generates the most power.

2. Measurement and Data Collection: The MPPT continuously measures the voltage and current of the solar panel in real-time. It collects data points from the I-V curve, including voltage and current at any given moment.

3. Calculating Power: Using the collected data, the MPPT calculates the instantaneous power output of the solar panel using the formula P = V x I, where P is power, V is voltage, and I is current.

4. Searching for the MPP: The MPPT employs an algorithm, often a perturb and observe (P&O) algorithm or an incremental conductance algorithm, to analyze the power output and adjust the operating voltage of the solar panel. It incrementally changes the voltage and observes how the power output changes.

   • Perturb and Observe (P&O): This algorithm slightly increases and decreases the voltage around the current operating point and compares the resulting power outputs. It adjusts the voltage in the direction that increases power, effectively "perturbing" the operating point and "observing" the power response.

   • Incremental Conductance: This algorithm considers both the change in voltage and the change in current simultaneously, adjusting the voltage to maintain the highest possible ratio of ΔP/ΔV, where ΔP is the change in power, and ΔV is the change in voltage.

5. Tracking the MPP: The MPPT continues to adjust the voltage until it reaches or gets very close to the point on the I-V curve where the power output is maximized, which is the MPP. At this point, the solar panel is operating at its peak efficiency, and it is generating the maximum possible power for the given environmental conditions.

6. Output to the solar Inverter: Once the MPPT has identified and locked onto the MPP, it regulates the voltage and current to match the requirements of the connected inverter or load, ensuring a consistent and efficient supply of electrical energy.

In summary, an MPPT is a critical component in a solar PV system that optimizes the performance of solar panels by continuously tracking the maximum power point (MPP) on the panel's I-V curve. It adjusts the operating voltage to ensure that the solar panel operates at peak efficiency, allowing it to generate the maximum possible power under varying environmental conditions, such as changes in sunlight intensity and temperature. This optimization increases the overall energy yield of the solar system and maximizes its efficiency.

Solar optimisers achieve the decoupling of panels and maximize energy production by implementing the following key mechanisms:

1. Individual MPPT Control: Each solar optimiser is equipped with its own Maximum Power Point Tracking (MPPT) circuit. This circuit continually monitors the electrical characteristics of the specific solar panel it is connected to, including voltage and current.

2. Calculating Individual MPP: The optimiser calculates the maximum power point (MPP) for that specific panel based on the real-time data it collects. The MPP represents the optimal operating point where the panel generates the most power under its unique conditions, such as shading, temperature, and panel age.

3. Adjusting Voltage and Current: The solar optimiser adjusts the voltage and current at the output of the connected panel to match its calculated MPP. This adjustment ensures that the panel operates as close to its peak efficiency as possible, even if other panels in the array are experiencing different conditions or limitations.

4. Independent Panel Operation: Because each panel is equipped with its own optimiser, they can operate independently of one another. This means that the performance of one panel does not affect the performance of the entire array. If a panel is partially shaded or underperforming due to any reason, the optimiser for that panel can make real-time adjustments to optimize its output.

5. Optimizing Energy Production: By allowing individual panel-level optimization, solar optimisers maximize the overall energy production of the entire solar array. Even in cases where some panels are affected by shading, soiling, or other issues, the unaffected panels can continue to operate at their full potential, mitigating energy losses.

In essence, solar optimisers function as intelligent electronic devices that enhance the performance of each solar panel by ensuring it operates at its individual maximum power point. This not only boosts the overall energy yield of the solar PV system but also reduces the impact of factors like shading, panel mismatch, and variable sun angles, making the system more resilient and efficient.