Solar Cells: From Einstein to Modern Advancements in the Built Environment

Solar cells being installed onto a roof

From Einstein to satellites and green energy, the development of solar cells has a rich history. It was once believed that they might revolutionise the way we generate electricity, creating a permanent source of renewable energy. Solar cell development has advanced dramatically in recent times, but how effective is solar power today? And what role will it play in helping deliver net zero to the built environment?

In 1839, a 19-year-old physicist named Edmond Becquerel developed the first photovoltaic cell in his father’s laboratory. 46 years later, the first solid-state solar cell was built by Charles Fritz, his device had a now meagre energy conversion rate of about 1%. Later, Einstein’s explanation of the photoelectric effect would lay out the basic principles for effective solar energy that would be used to create the first practical solar cell in 1954.

20 years later, amid an energy crisis, Congress passed the Solar Energy Research, Development and Demonstration Act, which initiated a massive wave of funding and interest in the potential of harnessing solar energy. This saw the first practical integrations into the built environment. Hopes for widespread public use were high and many believed it was the energy of the future. Although at the time, cells were expensive, inaccessible and inefficient.

Today, the solar cell industry has changed radically. Typical modern cells have an energy conversion rate of around 15-20% and have declined in price astronomically, but is this the energy of the future people hoped for?

The Declining Price of Solar Power

Graph showing the price of solar modules since 1976

The price of solar cells experiences an interesting phenomenon known as Swanson’s law. As the efficiency of photovoltaic technology increases with the expansion of the industry, the price of solar modules per watt of energy decreases. For every doubling of cumulative installed solar capacity, there is a 20% drop in price per watt of solar modules.

At current rates, costs decrease an impressive 75% every 10 years. In 1977 the price per watt of crystalline silicon cells was $76.67; in 2014, they were as little as $0.37.

The constantly reducing costs of solar panels have increased their accessibility as a product significantly over the last decades. As a result, Modern solar cells are far more economically viable as an energy source than ever before.

Modern Advancements in Efficiency

Solar cell technology is very complex. There are multiple types of solar cell efficiency, such as thermodynamic and conductive efficiency, but the overall efficiency is the product of them all. Some solar cells in laboratory settings have recorded energy conversion rates of more than 40%, although these figures are realistically not achievable in more practical applications.

There are significant variances in the types of solar cells available and their aptitude for different applications. For example, some cells, such as multijunction cells, have varying energy conversion rates dependent on the intensity of sunlight exposure. In lower intensity, more diffuse light conditions, the energy conversion rate reduces and the cost-benefit of using multijunction cells often decreases, making them unviable. Some cells require more complicated manufacturing processes, more expensive materials and sometimes rarer materials, all of which can affect their appropriate application range.

Today most solar cells available for general use offer a conversion rate of around 18-22%. Advances in efficiency are also likely to slow significantly in years to come. Crystalline silicon cells are the most commonly used type of solar cells in the built environment and are approaching their theoretical limit of power efficiency, known as the Shockley-Queisser limit.

However, this does not mean the end of efficiency improvements as new materials are being researched and tested constantly. Solar cells that use perovskite as their semiconductor material show immense promise and could have major effects on the cost benefits of solar energy installations.

Perovskite Solar Cells

Perovskite solar cell | Credit: National Energy Laboratory

Perovskite solar cells get their name from the unique crystal structure of the perovskite materials they use. This structure consists of a metal cation (usually lead or tin) at the centre, surrounded by an anion framework.

One of the key advantages of perovskite solar cells is their compatibility with solution-based processing techniques. This means that perovskite layers can be deposited onto various substrates using relatively simple and cost-effective methods like spin-coating, inkjet printing, or spray coating.

Perovskite materials also offer the advantage of a tunable bandgap. By altering the composition and structure of the perovskite, researchers can adjust the bandgap to absorb specific wavelengths of light. This allows for better matching of the solar spectrum and potentially higher efficiency in converting sunlight to electricity.

While perovskite solar cells hold great promise, they also face challenges. One major challenge is their stability over time, especially in humid and high-temperature conditions.

Researchers are actively working to improve the long-term stability of perovskite materials and made a breakthrough earlier this year. A study conducted at California State found that altering the ion diffusion network of a perovskite module can drastically improve its durability.

Additionally, toxicity concerns related to lead-based perovskites have led to research into alternative materials that maintain the beneficial properties of perovskites while reducing environmental impact.

Perovskite solar cells are still in the research and development stage, but they have shown rapid efficiency improvements in a short period. As stability and scalability challenges are addressed, perovskite solar cells could potentially offer a more cost-effective and versatile alternative to traditional silicon-based solar cells. They may find applications in building-integrated photovoltaics, portable devices, and other areas where lightweight and flexible solar panels are desirable.

Building Integrated Photovoltaics (BIPVs)

Building Integrated Photovoltaics

BIPVs are photovoltaic materials that are used to replace conventional building materials on building exteriors. They are commonly used in the construction of new buildings but can also be installed in retrofitting projects.

There are many advantages to integrated systems other than just a seamless aesthetic. The cost saving on the initial building materials that would be used with a non-integrated system is definitely something to note.

BIPVs offer greater design flexibility and space utilisation, so they cut down on the risk of an inconvenient and expensive installation process. Being able to place the cells more freely allows for more efficient panel locations, which can contribute to lower energy transmission losses across the system. They also increase property value and are likely to attract more environmentally conscious buyers or tenants.

The main aspect of these integrated systems is, of course, green energy. The renewable source provides considerable carbon footprint reductions and gives heightened energy independence to buildings in the face of power cuts and rising electricity tariffs. Applying BIPVs to company buildings is a major step towards net zero targets and more sustainably oriented infrastructure.

How cost-effective are they?

The greatest obstacle to implementing solar energy sources in the built environment is cost. The main concern is that they offer little to no cost saving on energy consumption in a foreseeable period and have high upfront costs in addition to regular maintenance requirements.

This is in part true; solar energy installations are not cheap. A mid-range 4kw system will typically cost £4500 in an average three-bedroom home. On the other hand, financial savings are now better than ever, especially with Smart Export Guarantees (SEG). SEGs are a government-backed initiative launched in 2020 that requires all electricity suppliers with over 150,000 customers to pay small-scale generators for low-carbon electricity which they export back to the National Grid, providing certain criteria are met. This allows users to sell the excess electricity they generate back to the grid for greater cost savings.

Using SEG, the average returns estimate of photovoltaic systems sits at around £400 a year.

These cost savings are highly variable: the size and efficiency of your installation, household energy consumption, panel location and SEG tariff all affect the final monetary benefits.

The main issue with SEGs is the tariffs. Most energy suppliers buy your energy at well below half its actual value, severely limiting any financial benefits. On a positive note, pressure is rising on energy suppliers to offer fairer tariffs as more people install solar energy systems and add to the group of underwhelmed customers. The energy market is still particularly tough at the moment after the October energy price cap sees a rise in the price of electricity of 69%. As a result, improving the condition of SEG prices is likely to be a slow process.

There is an alternative option that can massively boost financial savings. Buying a solar battery allows owners to store and use a much greater percentage of the energy they generate. The catch is that solar batteries are also expensive, typically costing an additional £4500. They can however, more than double the efficiency of your system, potentially increasing annual savings to £900 in a standard 3-bed house. This could cover installation costs in as little as 10 years and potentially cover the entirety of a house’s energy needs from there on out.

Are they Worth It?

A definite yes, if you can afford them. The environmental benefit of solar energy over non-renewable forms is tremendous. Global emissions need to be reduced drastically in order to meet 1.5℃ targets and every possible transition to more circular, lower carbon solutions is desperately needed.

As the price of non-renewable energy rises in the face of the global climate crisis, independent energy sources are going to become more and more valuable.

From a business perspective, photovoltaic installations can contribute greatly to net zero goals, which are becoming more essential as sustainable reporting regulations and stakeholder requirements become more stringent. The initial investment for solar installations will always be a short-term financial hit, but in the long run, they will always offer a net reduction in energy expenses.

With a projected CAGR of 6.9% in the global solar energy market, consistent growth and decreasing solar module costs are poised to render BIPV installations increasingly viable. Couple this with revolutionary advancements like perovskite technology, the future of solar power shines brightly.

Firstplanit will soon be adding BIPVs to our material database, keep an eye out for any new additions in the future.

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