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60 to 72 Cells: Why Photovoltaic Cells Alone Don’t Improve UK EPCs

Close view of interconnected photovoltaic cells

A photovoltaic (PV) cell is a semiconductor device that converts light into electricity using the photovoltaic effect. Each cell produces around 0.5–0.6 volts, most commonly from crystalline silicon, and generates direct current rather than the mains alternating current a home actually uses. A single cell is a building block, not a power source in its own right. It becomes useful only once wired into a module, connected to an inverter and installed as part of a wider system.

TL;DR:

  • The efficiency of commercial photovoltaic modules generally ranges from 20% to 25%, but real-world output is affected by temperature, shading, soiling, and inverter losses.
  • Most residential and commercial systems rely on inverters to convert DC to AC, with inverter performance significantly influencing the system’s overall energy delivery.
  • The placement and orientation of panels, along with shading and degradation over time, limit practical energy yields more than raw cell efficiency.
  • Building-integrated photovoltaics and emerging perovskite or tandem cells promise future efficiency gains, but system-level factors remain critical for performance.
  • Proper site assessment and integration are essential, as system performance depends more on system design and installation than just the type or efficiency of the cells used.
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Table of Contents

What are photovoltaic cells and how do they generate power?

A photovoltaic cell is the smallest working unit of a solar power system, the layer of semiconductor material that does the actual job of turning sunlight into electrical current. Understanding what does a photovoltaic cell do starts with a basic fact of physics: light behaves like a stream of particles called photons, and when a photon strikes a semiconductor with the right amount of energy, it knocks an electron loose. That freed electron leaves behind a positively charged “hole.” Together they form what physicists call an electron-hole pair, and this pairing is the entire foundation of how photovoltaic cells work.

Not every photon that hits a cell contributes to power output. Some pass straight through, some reflect off the surface, and some carry too little energy to dislodge an electron at all. Only the photons absorbed within the semiconductor’s active layer do useful work, which is one reason material choice and cell design matter so much to overall efficiency.

The real trick that makes a photovoltaic cell function is the p-n junction. Manufacturers “dope” silicon with different elements to create two distinct layers: a p-type layer with a slight positive charge and an n-type layer with a slight negative charge. Where these two layers meet, an internal electric field forms. This built-in field is what separates the electron from its hole before they can simply recombine and cancel each other out. The electron gets pushed toward the n-type side, the hole toward the p-type side, and that separation of charge is what creates a usable voltage.

Once electrons are pushed to one side of the junction, they need somewhere to go. Metal contacts on the front and back of the cell collect this flow and route it through an external circuit. That flow of electrons is the electric current, and because the p-n junction always pushes electrons in the same direction, the result is direct current (DC), not the alternating current (AC) used by household appliances.

  • Photon strikes the semiconductor and is absorbed.
  • An electron-hole pair forms inside the material.
  • The built-in electric field at the p-n junction separates the charges.
  • Electrons flow through metal contacts into an external circuit.
  • The circuit delivers direct current, typically at 0.5 to 0.6 volts per cell.

Statistic Callout: A single silicon photovoltaic cell produces approximately 0.5 to 0.6 volts, according to a peer-reviewed photovoltaic technology review. That is why cells are always wired together in strings rather than used individually.

Because a lone cell’s output is so modest, and because it is DC rather than AC, a real installation needs additional equipment before that electricity does anything useful in a home. The U.S. Energy Information Administration confirms that PV systems generate DC current, which then passes through an inverter that converts it to the AC power that runs lights, appliances and everything else on a domestic circuit. Understanding what a solar power inverter does for a home is arguably as important as understanding the cell itself, since a poorly matched inverter can quietly waste a meaningful share of the electricity a roof generates.

What types of photovoltaic cells exist and which materials matter?

Photovoltaic cell technology falls into three broad generations, each with distinct trade-offs between cost, efficiency and maturity. Choosing between them, in practice, usually comes down to available roof space and budget rather than chasing the highest efficiency figure on a spec sheet.

First-generation cells are crystalline silicon, split into two main varieties. Monocrystalline cells are cut from a single, continuous silicon crystal, giving them a uniform dark appearance and the highest efficiency of the mainstream options. Polycrystalline cells are made from multiple silicon fragments melted together, which costs less to produce but sacrifices a little efficiency and gives panels their characteristic speckled blue look. Crystalline silicon dominates the market overall.

Second-generation cells are thin-film technologies: amorphous silicon, cadmium telluride (CdTe) and copper indium gallium selenide (CIGS). These are made by depositing extremely thin layers of photovoltaic material onto a substrate such as glass or flexible plastic, which makes them lighter, more flexible and cheaper per square metre to manufacture. The trade-off is efficiency. A solar cell explainer notes typical thin-film efficiencies in the 7 to 13% range, well below crystalline silicon, meaning thin-film panels need considerably more surface area to match the output of a silicon array. That makes them a sensible choice for large flat commercial roofs or curved and portable surfaces, but a poor fit for a space-constrained UK terrace roof.

Third-generation cells cover the experimental and emerging end of the spectrum: perovskite and multi-junction cells. Perovskite cells have shown remarkably fast efficiency gains in laboratory settings, but stability and manufacturing scale-up remain unresolved problems before they reach mainstream commercial rooftops. Multi-junction cells stack several semiconductor layers, each tuned to absorb a different part of the light spectrum, and this is where the very highest efficiency records come from, though usually at a cost that only makes sense for space and specialist applications.

  • Monocrystalline silicon: highest mainstream efficiency, higher cost.
  • Polycrystalline silicon: slightly lower efficiency, lower cost, wide market share.
  • Thin-film (amorphous, CdTe, CIGS): flexible and cheap per unit area, lower efficiency.
  • Perovskite: rapid lab efficiency gains, still facing durability hurdles.
  • Multi-junction: research-grade efficiency records, used in niche and space applications.

Crystalline silicon accounts for roughly 95% of the global market, according to background reporting on solar cell technology, largely thanks to decades of manufacturing refinement that keeps costs down while efficiency stays competitive.

How are individual cells assembled into a working solar panel?

A single photovoltaic cell only produces about 1 to 2 watts, nowhere near enough to run anything meaningful on its own. Manufacturers solve this by wiring dozens of cells together, and a solar PV factsheet from the University of Michigan notes that a typical panel contains 60 to 72 cells connected in series and parallel arrangements.

Wiring cells in series adds their voltages together, while wiring strings in parallel adds their current. Combining both approaches lets manufacturers hit a target voltage and current for a given panel size. This is the difference between a solar cell vs a photovoltaic cell in everyday language: the cell is the individual unit, while the panel, sometimes called a module, is the assembled, weatherproofed product that actually gets installed.

A finished panel typically measures around 1.7 metres by 1.1 metres and delivers a typical output, depending on cell type and panel size. That output figure, known as the nameplate power, is what most buyers see quoted in marketing material.

  • Cells are laminated between protective layers, usually glass on the front and a polymer backsheet behind.
  • An aluminium frame adds rigidity and allows secure roof mounting.
  • A junction box on the rear houses the electrical connections and bypass diodes.
  • Multiple panels wired together form a PV array, and array capacity scales simply by adding more panels or strings.

Scaling from a single cell to a full array is really just a matter of repeating the same series and parallel logic at a larger scale, right up to utility installations covering many hectares.

How efficient are photovoltaic cells and what affects real-world output?

Commercial photovoltaic modules typically run between 20% and 25% efficiency, while laboratory cells have exceeded 40%, with some multi-junction experimental designs surpassing 47%, according to the peer-reviewed technology review cited earlier. That gap between lab and commercial figures is not a marketing trick. Lab cells are often tiny, expensive, multi-layered devices tested under perfectly controlled conditions, while commercial panels are built for durability, manufacturability and affordability at scale.

Efficiency itself simply measures the portion of sunlight energy a cell converts into usable electricity. Module efficiency, the figure on a spec sheet, is usually slightly lower than the underlying cell efficiency, due to losses at the connections, the glass cover and the spacing between cells within the panel.

How efficient are photovoltaic cells and what affects real-world output? — overview diagram

Statistic Callout: Commercial solar modules generally sit between 20% and 25% efficiency, according to NREL’s photovoltaic research programme, which tracks both commercial and record-breaking laboratory cell performance.

Nameplate power is measured under ideal laboratory test conditions, and real rooftops rarely match those conditions exactly. Several factors chip away at the gap between rated and actual output:

  • Temperature coefficient: silicon panels lose a small percentage of output for every degree above 25°C, so hot summer roofs perform worse than the spec sheet suggests.
  • Shading: even partial shade on one cell in a series string can disproportionately reduce the output of the whole string.
  • Inverter and mismatch losses: converting DC to AC and balancing slightly mismatched panels both consume a small share of generated energy.
  • Soiling: dust, pollen and general grime on the panel surface reduce the light reaching the cells until the next rain or clean.

Estimating annual energy yield in practice means combining a location’s insolation (the amount of sunlight it receives), the roof’s tilt and orientation, and a realistic estimate of these system losses. It is a more involved calculation than simply multiplying panel wattage by daylight hours, which is exactly why a proper solar panel efficiency assessment matters more than the number printed on the box.

Where are photovoltaic cells actually used?

The benefits of photovoltaic technology show up across a surprisingly wide range of settings, from rooftops to satellites to pocket calculators. The common thread is simple: anywhere light is available and a wire can carry electricity somewhere useful, a PV cell can, in principle, do the job.

Residential rooftop systems are the most familiar application, generating electricity for self-consumption within the home and exporting any surplus to the grid. Commercial rooftops follow a similar logic at larger scale, often on flat industrial buildings with generous unshaded area. Utility-scale solar farms take this further still, covering large tracts of land with thousands of panels feeding directly into the electricity grid.

  • Residential and commercial rooftop self-consumption.
  • Utility-scale solar farms feeding the national grid.
  • Space applications, including satellite and spacecraft power systems.
  • Remote and off-grid installations powering equipment far from any grid connection.
  • Portable electronics, from garden lights to calculators and camping chargers.

Space applications represent one of the oldest uses of photovoltaic technology, powering satellites since the earliest days of the space programme, where reliability and weight matter far more than cost per watt. Remote and off-grid systems serve a similar practical purpose closer to home, powering everything from rural telecommunications equipment to narrowboats and cabins with no mains connection. At the smallest scale, portable devices use tiny PV cells for calculators, garden lighting and battery chargers, where a modest trickle of power is all that is needed.

The Centre for Sustainable Energy’s guide to solar PV notes that UK residential adoption has been driven largely by self-consumption economics and export arrangements such as the Smart Export Guarantee, which pays homeowners for the surplus electricity they feed back to the grid.

What can’t a photovoltaic cell do on its own?

A photovoltaic cell only generates direct current, and a home cannot run on DC electricity. Every grid-connected residential system needs an inverter to convert that DC output into usable AC, and inverter efficiency directly affects how much of the generated electricity actually reaches household appliances. A cheap or poorly sized inverter can quietly erode a system’s returns for years without an owner ever noticing.

Photovoltaic generation is also inherently intermittent. Cells only produce electricity when light is available, which means output drops to zero overnight and falls sharply on heavily overcast days. The Energy Saving Trust points out that most PV systems cannot store electricity without an added battery, so households either use generated power immediately, export the surplus to the grid, or invest in battery storage to smooth out the mismatch between generation and use.

Siting imposes its own constraints. Roof orientation, pitch and shading from chimneys, trees or neighbouring buildings all limit how much of a roof’s theoretical potential is actually usable. And panels degrade slowly but steadily over their working life, typically losing a small fraction of a percent of output each year, which is why manufacturers issue separate performance and product warranties rather than a single blanket guarantee.

  • Inverters convert DC to AC and their efficiency affects total usable output.
  • Without storage, generation and consumption must roughly line up in time, or surplus power is exported.
  • Roof orientation and shading cap the practical (not theoretical) output of any given site.
  • Degradation is gradual, but it is cumulative over a 25 to 30 year system lifetime.

Pro Tip: Before assuming a shaded roof rules out solar entirely, ask an installer about micro-inverters or power optimisers. Unlike a single string inverter, these limit the damage a shaded panel does to the rest of the array’s output.

An extension guide on solar PV system considerations makes the point plainly: system integration, not cell selection, is usually where real-world performance is won or lost.

How are photovoltaic cells actually manufactured?

Silicon cell production starts with purifying raw silicon and growing it into large cylindrical ingots, either as a single crystal for monocrystalline cells or as a cast block for polycrystalline versions. These ingots are sliced into thin wafers, and each wafer then goes through a doping and diffusion process that creates the p-type and n-type layers forming the cell’s p-n junction.

Metallisation follows, where thin metal contacts are printed onto the wafer surface to collect the current the finished cell will generate. Each step demands tight tolerances, since even small defects in the wafer or contact printing measurably reduce a cell’s eventual efficiency.

Thin-film and perovskite manufacturing takes a different route entirely. Rather than slicing wafers, manufacturers deposit extremely thin layers of active material directly onto a substrate, using vacuum deposition or, for some perovskite methods, solution-based printing techniques closer to inkjet printing than traditional semiconductor fabrication. This is part of why thin-film and emerging cell types can, in theory, be produced more cheaply once manufacturing matures.

  • Silicon ingots are grown, then sliced into wafers.
  • Doping and diffusion create the p-type and n-type layers.
  • Metal contacts are printed onto the wafer to collect current.
  • Thin-film and perovskite cells are deposited directly onto a substrate rather than sliced from an ingot.

Quality control runs throughout, with electrical testing (flashing each cell with a calibrated light source to measure its actual output) catching underperforming units before they reach final module assembly. Manufacturing scale is a major reason crystalline silicon remains dominant: decades of production refinement have driven costs down in a way newer technologies have not yet matched.

What do the numbers on a solar panel label actually mean?

Reading a module specification sheet is easier once a handful of terms are clear. Pmax is the maximum power output under standard test conditions, usually the headline wattage figure quoted in marketing. Vmp and Imp are the voltage and current at that maximum power point, the values the panel actually operates at in real use. Open-circuit voltage (Voc) and short-circuit current (Isc) are theoretical extremes, useful mainly for installers sizing inverters and wiring rather than something a homeowner needs to dwell on.

The temperature coefficient, usually expressed as a percentage loss per degree Celsius above 25°C, matters more in the UK than it might seem. Even though British summers rarely hit extreme heat, panels sitting on a dark roof in direct sun regularly exceed that 25°C baseline, so a lower temperature coefficient genuinely translates to slightly better real-world yield across a typical UK year.

  • Pmax: the headline rated power output.
  • Vmp and Imp: real operating voltage and current at maximum power.
  • Voc and Isc: theoretical extremes used for system design, not everyday output.
  • Temperature coefficient: how much output falls as the panel heats up.

Warranties come in two distinct types, and installers prioritise low degradation over marginal efficiency gains for good reason. A product warranty covers physical defects, typically for 10 to 12 years. A performance warranty guarantees a minimum output level, often 80 to 90% of original capacity, over a much longer span of 25 years or more. Reading both carefully tells a buyer far more about long-term value than the efficiency percentage on the front of the box.

How do photovoltaic cells affect EPC ratings and the Home Energy Model?

Installing PV generation on a property directly influences its Energy Performance Certificate outcome, because on-site electricity generation is factored into the overall energy performance calculation an assessor produces. A larger or better-oriented array typically improves a property’s modelled performance, though the actual effect depends on system size, orientation and how the assessment methodology treats generation versus consumption.

How PV system details affect EPC modelling

PV installation should be flagged and evidenced whenever an assessment is carried out on a property, whether that is a standard EPC or a report under the incoming Home Energy Model methodology set to replace SAP calculations. Assessors typically need documentation of panel specification, orientation, tilt and inverter details to model the system’s contribution accurately, rather than relying on an estimate.

For UK property owners weighing up whether solar makes sense, the practical route is straightforward: request a proper assessment, ask specifically how the proposed PV system is likely to affect the resulting EPC band, and consider pairing generation with other efficiency measures rather than treating solar as a standalone fix. A well-specified home solar setup paired with fabric improvements tends to move the needle on a rating far more than panels alone.

Historical development and evolution of photovoltaic cells

The photovoltaic effect was first observed by French physicist Alexandre-Edmond Becquerel in 1839, though it would take more than a century before the phenomenon became a practical power source. Bell Labs produced the first practical silicon solar cell in 1954, achieving roughly 6% efficiency, a figure that seemed remarkable at the time but pales against today’s commercial panels.

Early photovoltaic technology found its first serious application not on Earth but in orbit. Space programmes throughout the 1950s and 1960s adopted PV cells to power satellites, since solar generation offered a reliable, low-maintenance energy source with no moving parts and no fuel to carry into orbit.

Terrestrial adoption accelerated much later, driven by a combination of environmental policy, manufacturing scale and steadily falling material costs. Crystalline silicon cell efficiency crept upward decade by decade, while thin-film alternatives emerged from the 1970s onward as researchers looked for cheaper ways to cover large areas. The steepest cost declines came more recently still, as Chinese manufacturing scale drove panel prices down dramatically over the 2010s, transforming solar from a niche, subsidy-dependent technology into one of the cheapest sources of new electricity generation in much of the world.

Perovskite cells represent the newest chapter, first demonstrated as a viable PV material only in the late 2000s, yet already rivalling decades-old silicon technology in laboratory efficiency tests.

Environmental impact and sustainability of PV production and disposal

Manufacturing photovoltaic cells carries a genuine environmental cost, even though the electricity they generate over their lifetime is far cleaner than fossil alternatives. Silicon purification and wafer production are energy-intensive processes, and the manufacturing supply chain for some thin-film technologies involves materials, such as cadmium in CdTe cells, that require careful handling and disposal.

Life-cycle analyses generally show that photovoltaic systems recoup the energy invested in their manufacture within a few years of operation, after which every additional year of generation represents a net environmental benefit. Over a typical 25 to 30 year lifespan, this makes solar one of the lower-carbon electricity sources available, even accounting for manufacturing emissions.

End-of-life disposal is the area receiving growing attention as the first large wave of panels installed decades ago reaches retirement. Panels contain recoverable materials including glass, aluminium and silicon, but established recycling infrastructure for solar panels remains less mature than for other electronics streams. Industry and regulators in several markets are working to build out dedicated recycling pathways, since the volume of retired panels is set to climb sharply over the coming decade as early installations age out.

Responsible disposal and a mature recycling supply chain matter as much to the technology’s long-term sustainability credentials as the generation itself.

Perovskite technology sits at the centre of most near-term innovation discussion. Laboratory efficiency gains have arrived faster for perovskite cells than for almost any prior photovoltaic material, but durability under real-world sun, heat and humidity remains the barrier between laboratory promise and rooftop reality. Much current research focuses on stabilising these cells for a commercially viable lifespan rather than chasing further efficiency records.

Tandem cells, which stack a perovskite layer atop conventional silicon, aim to capture the best of both: silicon’s proven durability and perovskite’s ability to harvest a different part of the light spectrum than silicon alone can absorb. Early tandem prototypes have already demonstrated efficiencies exceeding what silicon-only cells can achieve.

Building-integrated photovoltaics, where solar cells are built directly into roofing tiles, facades or even windows rather than mounted as separate panels, continues to develop as a way to add generation capacity without the visual footprint of a conventional array. Floating solar installations on reservoirs and flexible, lightweight panels for unconventional surfaces both point toward photovoltaic technology expanding into spaces that traditional rigid panels could never occupy.

Manufacturing efficiency is likely to matter as much as cell breakthroughs. Continued gains in production scale, automation and material use are expected to keep driving costs down, extending solar’s reach into markets and applications where it previously made little economic sense.

A straight answer on what actually matters here

The single most useful thing to understand about a photovoltaic cell is that it is a component, not a complete solution. Get fixated on cell type or efficiency percentages and it is easy to miss the factors that actually determine whether a solar installation performs well: inverter matching, roof orientation, shading, and how the whole system integrates with a property’s actual energy use. A slightly less efficient panel on a well-oriented, unshaded roof with a properly sized inverter will consistently outperform a premium cell poorly sited.

For anyone genuinely weighing up solar, the practical next step is not to obsess over spec sheets but to get a proper assessment of the property itself, including how PV interacts with UK energy ratings. That system-level view tells you far more than any single cell’s datasheet ever will.

— Danny

How Home Energy Model can help you understand solar’s real impact

Choosing a panel type is only half the picture. What actually determines whether solar improves a property’s energy performance is how the whole system, generation, fabric and rating methodology, works together, and that is where a proper assessment earns its keep. Guidance and assessment services built specifically around UK compliance standards, including how photovoltaic generation feeds into EPC outcomes and the incoming Home Energy Model methodology replacing SAP, are available.

Rather than selling panels or installation kits, Homeenergymodel focuses on the advisory side: helping property owners and landlords understand exactly what an assessor will need to see, and what effect a proposed PV system is likely to have on a rating before money changes hands. If solar is on the table for a property, requesting a home energy assessment is the sensible starting point, giving a clear, documented picture of where the property stands before any generation is added to the equation.

Sources

FAQ

What’s the difference between solar panels and photovoltaic cells?

A photovoltaic cell is the individual semiconductor unit that converts light into electricity, while a solar panel (or module) is the assembled product containing 60 to 72 of those cells wired together, according to the University of Michigan’s solar PV factsheet.

Is photovoltaic better than solar?

“Photovoltaic” and “solar” are not competing technologies. Photovoltaic refers specifically to the electricity-generating effect used in PV cells, while “solar” is a broader term that also covers solar thermal systems that heat water rather than generate electricity.

Are photovoltaic cells in solar panels?

Yes. A solar panel is simply a weatherproofed assembly of dozens of individual photovoltaic cells wired in series and parallel to produce a usable combined voltage and current.

What are the disadvantages of photovoltaics?

Photovoltaic cells generate DC electricity that needs an inverter for household use, produce no power without sunlight, and gradually degrade over a 25 to 30 year lifespan. Real output is also reduced by shading, high temperatures and soiling, so actual yield rarely matches the nameplate rating printed on the panel.

How efficient are commercial photovoltaic cells compared to lab records?

Commercial modules typically achieve 20% to 25% efficiency, while laboratory cells have exceeded 40%, with some experimental multi-junction designs surpassing 47%, according to NREL’s photovoltaic research programme and the peer-reviewed technology review.

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