How Do Solar Panels Work? A Simple Guide for NI Homeowners

How Do Solar Panels Work?

Solar panels are one of those technologies that seem almost too good to be true. Stick some dark panels on your roof, and they turn sunlight into electricity that powers your home. No moving parts, no fuel, no noise. But how does it actually work?

The simple version: solar panels contain cells made of silicon that generate an electrical current when light hits them. An inverter converts that current into the type of electricity your home uses. The electricity flows into your consumer unit and powers your appliances, lights, and everything else.

If that is all you need to know, you are sorted. But if you want to understand the process properly, and know what each component does and why it matters, read on.

Step by Step: From Sunlight to Powering Your Kettle

Here is the full journey of how sunlight becomes usable electricity in your home:

Step 1: Sunlight hits the solar cells

Each solar panel contains dozens of photovoltaic (PV) cells. These cells are made primarily of silicon, a semiconductor material. When photons (particles of light) from the sun strike the silicon cells, they knock electrons loose from their atoms. This is called the photovoltaic effect, and it was first observed in 1839 by French physicist Edmond Becquerel.

The photovoltaic effect is a physical phenomenon, not a chemical reaction. The cells do not burn fuel or consume anything. They simply respond to light energy by releasing electrons.

Step 2: An electrical current is created

Each PV cell has two layers of silicon that have been treated differently. The top layer is “doped” with phosphorus, which gives it extra electrons (making it negatively charged). The bottom layer is doped with boron, which creates “holes” where electrons are missing (making it positively charged).

When photons knock electrons free, the difference between the two layers creates an electric field. This field pushes the freed electrons in one direction, creating a flow of electricity. This flow is direct current (DC), the same type of electricity you get from a battery.

A single PV cell produces only a small voltage (around 0.5 volts). By connecting many cells together within a panel, and connecting multiple panels together in an array, you build up enough voltage and current to be useful.

Step 3: The inverter converts DC to AC

Your home runs on alternating current (AC), which is what the national grid supplies. The DC electricity produced by your solar panels needs to be converted to AC before your home can use it.

This is the job of the inverter, one of the most important components in your solar panel system. The inverter takes the raw DC output from the panels and converts it into 230V AC electricity that is compatible with your home’s wiring and appliances.

The inverter also performs several other functions: it monitors the system’s performance, maximises the power output from the panels, and ensures the system operates safely.

Step 4: Electricity flows to your consumer unit

Once the inverter has converted the electricity to AC, it flows to your consumer unit (fuse box). From there, it is distributed around your home just like grid electricity. Your appliances cannot tell the difference between solar-generated electricity and electricity from the grid.

Step 5: You use the electricity or export it

If your panels are generating electricity and you are using appliances at the same time, your home uses the solar electricity first. This is the electricity you are generating for free, and every unit you use directly is a unit you do not buy from your energy supplier.

If your panels are generating more electricity than you are using at that moment, the surplus flows out through your electricity meter and into the grid. Under the Smart Export Guarantee (SEG), your energy supplier pays you a small amount for every unit you export, typically between 3p and 15p per kWh.

If you have a battery storage system, surplus electricity charges the battery instead of (or as well as) being exported. You can then use that stored electricity in the evening or overnight when your panels are not generating.

What Are Solar Panels Made Of?

A solar panel is a surprisingly simple piece of engineering. Here are the main components:

Silicon cells

The heart of every solar panel. Most domestic panels use monocrystalline silicon cells, which are cut from a single crystal of silicon. Each cell is typically 156mm x 156mm (about 6 inches square) and is dark blue or black in colour. A standard panel contains 60 or 72 cells wired together in series.

Tempered glass

The front surface of the panel is a sheet of tempered (toughened) glass, typically 3-4mm thick. This protects the cells from weather, debris, and impact while allowing maximum light transmission. Solar panel glass is designed to be highly transparent and anti-reflective.

Aluminium frame

A lightweight aluminium frame surrounds the panel, providing structural rigidity and mounting points. The frame protects the edges of the glass and cells and allows the panel to be securely attached to the roof mounting system.

Backsheet

The rear of the panel is covered by a polymer backsheet (usually white or black) that provides electrical insulation and weather protection. In some modern panels, the backsheet is replaced by a second sheet of glass (known as glass-glass panels), which can improve durability and lifespan.

Encapsulant

Between the glass, cells, and backsheet, layers of EVA (ethylene-vinyl acetate) encapsulant bond everything together and protect the cells from moisture and mechanical stress. The encapsulant is transparent so light can reach the cells.

Junction box

A small junction box on the back of the panel is where the electrical connections are made. This box contains bypass diodes that help maintain output if part of the panel is shaded, and it is where the cables connect the panel to the rest of the system.

Types of Solar Panel

There are three main types of solar panel technology used in domestic installations:

Monocrystalline

Monocrystalline panels are made from single-crystal silicon and are the most common type installed on UK homes today. They are recognisable by their uniform dark appearance (usually black or very dark blue).

Efficiency: 18-22% Advantages: Highest efficiency, best performance in low light, longest lifespan, most space-efficient Disadvantages: Slightly more expensive than polycrystalline

For most NI homeowners, monocrystalline panels are the best choice. Their higher efficiency means you get more electricity from a smaller roof area, which matters when space is limited.

Polycrystalline

Polycrystalline panels are made from multiple silicon crystals melted together. They have a distinctive blue, speckled appearance.

Efficiency: 15-18% Advantages: Lower cost per panel Disadvantages: Lower efficiency, less consistent appearance, slightly worse performance in low light

Polycrystalline panels were popular when they offered a significant cost advantage, but the price gap has narrowed considerably. Most installers now recommend monocrystalline as standard.

Thin-film

Thin-film panels use a thin layer of photovoltaic material (such as cadmium telluride or amorphous silicon) deposited onto a substrate. They are lightweight and flexible.

Efficiency: 10-13% Advantages: Lightweight, flexible, can be applied to curved surfaces Disadvantages: Much lower efficiency, requires significantly more roof space, shorter lifespan

Thin-film panels are rarely used for domestic rooftop installations in Northern Ireland. They are more commonly found in large commercial or ground-mounted applications where space is not a constraint.

Which type is best for NI?

Monocrystalline panels are the best choice for Northern Ireland homes. Their higher efficiency is particularly valuable in our climate, where maximising output from available daylight is important. They also perform better in overcast conditions and at higher temperatures than their polycrystalline counterparts.

The Role of the Inverter

The inverter is often described as the brain of a solar panel system. It does much more than simply convert DC to AC.

Types of inverter

String inverter: The most common type for domestic systems. A single inverter is connected to all the panels, which are wired together in one or more “strings.” The inverter is usually installed in the loft, garage, or near the consumer unit. String inverters are reliable, cost-effective, and easy to maintain. The main limitation is that shading on one panel can reduce the output of the entire string.

Microinverters: Small inverters attached to the back of each individual panel. Each panel converts its DC output to AC independently, which means shading on one panel does not affect the others. Microinverters are more expensive but can deliver 5-15% more energy in situations where partial shading is an issue. They also make it easier to monitor individual panel performance.

Hybrid inverter: A string inverter that also manages a battery storage system. If you plan to add a battery (now or in the future), a hybrid inverter is worth considering, as it handles both the solar panels and the battery in a single unit. This avoids the cost of installing a separate battery inverter later.

Where is the inverter installed?

The inverter is typically mounted on an internal wall, away from direct sunlight and extreme temperatures. Common locations include:

• The loft or attic space
• The garage
• A utility room
• Near the consumer unit

The inverter needs to be accessible for maintenance and should be positioned where you can hear it during operation (it produces a very faint hum). Most modern inverters also connect to your home Wi-Fi, allowing you to monitor your solar generation via a smartphone app.

How Solar Panels Connect to Your Home

The physical connection between your solar panels and your home’s electrical system is straightforward:

1. Panels to inverter: DC cables run from the panels on your roof, through the roof space, and down to the inverter. These cables are typically routed through existing voids and clipped neatly to avoid any visual impact inside the property.

2. Inverter to consumer unit: An AC cable connects the inverter output to your consumer unit (fuse box). The solar supply is connected via a dedicated circuit breaker, just like any other circuit in your home.

3. Consumer unit to appliances: Once the solar electricity reaches the consumer unit, it is distributed to your appliances through your existing wiring. No changes to your home’s internal wiring are needed.

4. Consumer unit to meter and grid: Your electricity meter records both the electricity you import from the grid and (with a smart meter) the electricity you export. When your panels generate more than you use, the surplus flows back through the meter to the grid.

A generation meter may also be installed to record the total electricity your panels produce. This is separate from your main electricity meter and is used for monitoring purposes and, in some cases, for SEG payment calculations.

What Happens to Excess Electricity?

When your solar panels generate more electricity than your home is using at that moment, the surplus has to go somewhere. There are three options:

Export to the grid

Without a battery, surplus electricity flows automatically into the national grid. Under the Smart Export Guarantee, your energy supplier pays you for each unit exported. The rate varies between suppliers (typically 3-15p per kWh), but it is always less than what you pay for imported electricity (around 24p per kWh).

This is why self-consumption matters. Every unit of solar electricity you use directly saves you the full retail rate. Every unit you export earns you only the export rate. The more of your own generation you can use, the more money you save.

Battery storage

A home battery system stores surplus solar electricity for use later. Typical domestic batteries have a capacity of 5-13kWh, which is enough to power an average home’s evening and overnight electricity needs.

Battery storage increases your self-consumption rate from around 40-50% (without a battery) to 70-80% (with one). This significantly improves the financial return from your solar panels, as you are using more of your free solar electricity and buying less from the grid.

Battery costs have fallen considerably in recent years. A typical home battery system costs between £2,500 and £5,000, depending on capacity and brand.

Self-consumption strategies

Even without a battery, you can increase your self-consumption by timing high-energy activities to coincide with peak solar generation. Running your washing machine, dishwasher, tumble dryer, or immersion heater during the middle of the day (when your panels are generating most) means more of your solar electricity is used directly.

Many modern inverters and smart home systems can automate this, turning on certain appliances when solar generation exceeds household demand.

Do Solar Panels Work at Night?

No. Solar panels need light to generate electricity, and they produce nothing at night. This is a fundamental limitation of the technology.

However, this does not mean you are left without electricity after dark. Your home simply switches to drawing electricity from the grid, just as it did before you had solar panels. The difference is that during the day, your panels have been reducing (or eliminating) your grid consumption and potentially charging a battery.

If you have a battery storage system, you can use stored solar electricity during the evening and overnight. A well-sized battery (8-13kWh) can often cover an average household’s electricity needs from the end of solar generation (typically 6-8pm) through to the following morning.

During winter months, when days are shorter and solar generation is lower, you will rely more heavily on grid electricity. This is normal and expected. The financial savings from your panels are calculated across the whole year, with strong summer generation offsetting reduced winter output.

How Much Electricity Do Solar Panels Produce in NI?

Northern Ireland receives approximately 900-1,000 kWh of solar irradiance per square metre per year. While this is less than southern England (which receives around 1,100-1,200 kWh/m2), it is more than sufficient for solar panels to be a worthwhile investment.

Here is what you can expect from different system sizes in Northern Ireland:

System Size	Number of Panels	Annual Generation	Daily Average (Summer)	Daily Average (Winter)
2kW	5-6 panels	1,700-1,900 kWh	8-10 kWh	1-3 kWh
3kW	8-10 panels	2,550-2,850 kWh	12-15 kWh	2-4 kWh
4kW	10-12 panels	3,400-3,800 kWh	16-20 kWh	3-5 kWh
5kW	13-15 panels	4,250-4,750 kWh	20-25 kWh	4-6 kWh
6kW	16-18 panels	5,100-5,700 kWh	24-30 kWh	5-7 kWh

These figures assume south-facing panels at an optimal tilt angle (30-40 degrees) with no significant shading. East or west-facing panels will produce approximately 15-20% less than south-facing equivalents. An experienced installer will assess your specific roof orientation and provide accurate generation estimates during their survey.

To put these numbers in context, the average Northern Ireland household uses approximately 3,800-4,200 kWh of electricity per year. A 4kW solar system can therefore generate roughly the equivalent of an entire household’s annual electricity consumption, though the timing of generation and usage means you will still import some electricity from the grid (and export some to it).

Understanding Your Solar Generation

Once your system is installed, you can monitor its performance through the inverter’s app or web portal. Most modern inverters provide real-time data showing:

• Current generation (in watts)
• Daily, monthly, and annual generation totals
• Self-consumption versus export ratios
• Historical performance comparisons

This data helps you understand your system’s performance and adjust your electricity usage habits to maximise self-consumption. Many homeowners find it genuinely interesting to see how their panels respond to different weather conditions and seasons.

The technology behind solar panels is well-proven, reliable, and remarkably low-maintenance. Once installed, your panels will quietly generate clean electricity for 25 years or more, with no fuel costs, no moving parts, and no ongoing effort required from you.