Energy Conversion Efficiency Of Solar Cells

Solar Energy / By

The energy conversion efficiency of solar cells is getting higher and higher.

A new type of cell was recently developed in the US that has a whopping 43% energy conversion efficiency, with experts predicting more to come.

What does this mean for our future?

Will we be able to power all our gadgets on just sunshine?

Is there anything you want to know about solar cells? 

Solar panels are becoming more efficient every day!

The newest type of panel, in development by scientists at Stanford University, can convert sunlight into electrical current at an astonishing 43%.

This is a big step up from previous models which converted only 25% of the sun’s rays into usable electricity.

Table of Contents

What are solar cells and how do they work?

Solar cells is a device that uses the sun’s rays to convert sunlight into electrical energy.

solar cells first appeared in 1876, when a french physicist by the name of Edmond Becquerel discovered that certain materials, like selenium, produce electricity when exposed to light.

By 1883 an italian physicist named Alessandro Volta was able to develop a better design for the solar cell, which he called the voltaic pile.

How do solar cells work? solar cells absorbs photons of light i.e. electromagnetic radiation with different wavelengths, and transfers energy from the photon to an electron in a semiconductor material.

A photon can be thought of as a tiny “particle” of light.

Solar cells is made from semi-conductor materials.

A semi-conductor is a material, usually made from silicon (Si), which has an unusual characteristic.

When the electrons in the atoms of the semi-conductor material are excited by heat or light, they gain enough energy to break free from their atoms.

This means that one electron can become free from each atom.

The energy conversion efficiency of solar cells

The efficiency with which solar cells convert energy from the sun is called the fill factor (FF).

The FF of a typical silicon cell operating under daylight conditions is 25%. This means that, on a sunny day, with the cell facing the sun directly, one photon will free an electron from each atom in 250 silicon atoms.

The energy conversion efficiency of solar cells can be improved by using light which contains more photons per square centimetre i.e. those of shorter wavelengths (higher frequencies).

Edison invented the Carbon filament lamp in 1879 as a practical method for producing such light.

The efficiency of early carbon filament lamps was less than 1%, but this rapidly increased to 2% in 1888 and 5-10% during the 1890s as higher-pressure manufacturing methods were used.

By 1912 Rayleigh scattering (the principle behind blue sky) had been shown to limit the overall efficiency of carbon filament lamps to about 18%.

The energy conversion efficiency of solar cells can be further increased by using multijunction photovoltaic cells.

Multijunction photovoltaic cells are composed of multiple thin film layers, which gives them a much higher FF than single-layer cells, making them especially efficient at converting infrared light into electricity.

The first practical use of multijunction photovoltaic cells was in satellites and space vehicles, where the sun is too distant and dim to excite electrons with visible light.

How much power can a typical household get from the sun?

It depends upon a number of factors: the average insolation (i.e. amount of sunlight) in their region, the area of solar cells on their roof and the energy conversion efficiency of those solar cells.

Depending upon where you live in Australia, and assuming you have enough panels, your household can produce anywhere from a few kilowatt-hours per day to more than 30 kWh.

For example: The capital cost for a typical 5kW* system is between $3,000 -$5,000.

The cost will vary depending on location and size.

How much energy can be stored in a battery?

The amount of energy that can be stored in a given mass of battery depends upon the type of battery and its storage density (energy per unit weight or volume).

If we assume the best “lead-acid” batteries currently on the market, then it would take about 5kg of them to store as much electricity as 1kWh of solar cells.

This means that if you wanted to store enough electricity for all your household’s daily needs, you’d need around 50kg* worth of lead-acid batteries. *assuming an average system size = 5kW

Some drawbacks to using solar cells for home use

The energy conversion efficiency of solar cells is a little lower than the theoretical limit, however the main problem with using solar cell panels for home-use is that they are made from very expensive semi-conductor materials.

The best solar panels currently available have an energy conversion efficiency of about 20% and cost around $5 per watt to manufacture.

For this reason, it is difficult for the average home owner to make a financial return on their investment when selling surplus power back to electricity providers (assuming electricity is $0.20 per kWh).

However, there are other uses for solar cells which do not require an economic return, such as:

(i) To supplement conventional energy sources during peak periods e.g. hybrid renewable generation systems in developing countries

(ii) Flat-rate tariff customers could use their excess power themselves instead of selling it back to retailers at half price (as is currently the case for excess power generated on some tariffs)

(iii) Use solar cells to charge batteries, providing a portable power source.

This could be used for off-grid communications by emergency services and military personnel, or in remote areas with no access to electricity grid.

The chart below shows how long it would take an average household to cover its initial investment (assuming $0.20 per kWh).

The same benefits can be achieved without installing solar cells on your roof if you install a stand alone system (i.e. stand alone solar panels connected to a battery bank).

However this approach suffers from problems of scalability because small standalone systems are only viable in very sunny locations, while large systems cost more than connecting them to the grid.

In contrast, you can use your main power points to charge batteries from the existing electricity grid without needing any other hardware or software solutions.

By connecting stand alone systems to the electricity grid, we are creating a new and “dynamic” form of network which could eventually help stabilise fluctuations in energy supply and demand by taking advantage of fluctuations in supply and demand on a local scale (i.e distributed generation).

However there are some difficulties with this approach

(a) The design of the electricity infrastructure must be modified so that it can interface with stand alone power sources

i.e small-scale networks will need distribution boards specifically designed for connecting battery banks .

(b) It is necessary for consumers to become familiar with “smart meters” in order to make informed decisions about energy supply and demand.

With the help of smart appliances, consumers will be able to control their electricity requirements depending upon the changing price at which they can sell/buy excess power .

(c)Stand alone systems connected to the grid would need to have a financial incentive for households to use them (e.g. by including them in pricing tariffs)

3 Ways you can save money by using less electricity

(1) Switching off lights and electrical appliances when not in use

Appliances which are connected to the grid will continually draw current even when switched off, resulting in a waste of energy and increasing your bill.

Switching off electrical appliances when not in use is therefore a cheap and easy way to save money on electricity costs.

(2) Using appropriate light bulbs / setting room lighting timers

Using compact fluorescent (CFL) light bulbs can reduce your power consumption by around 75% while emitting only 25% as much C02  as standard incandescent bulbs.

However, CFLs contain mercury which makes them difficult to dispose of safely, so be sure to recycle them!

Please note that LEDs have an even greater energy savings potential than CFLs (about 90%) but they are still quite expensive right now.

On the other hand, replacing old incandescent globes with modern LED globes will provide around 60% energy savings.

Setting room lighting timers to turn off lights automatically will also help reduce your power consumption.

As an example, if 10 light bulbs are switched on for 1 hour a day in each room of a typical Australian household, this could result in approximately 17 kWh per day being wasted on standby power!

Note that the amount of electricity wasted by switching off lights with a timer depends upon how long they are left switched on before they are turned off again.

It is therefore preferable to use timers which can switch lights off after only 15 minutes .

(3) Using smart appliances and ensuring they operate efficiently

(a) Smart washing machines and dryers

Smart washing machines and dryers can save you money by being able to adjust the temperature of their water/wind according to your usage patterns (i.e. using less hot water when you don’t need it).

It is important that appliances have sensors which are capable of detecting electricity demand required for each cycle, otherwise they will just spin at full speed regardless of whether they are actually pumping out hot air or not in order to achieve desired cleaning results – wasting electricity in the process.

(b) Smart air conditioner controllers

Air conditioners waste a lot of energy when running on higher temperature settings because more electricity is required to cool them off.

It is therefore useful for households with domestic air conditioners connected to the grid to use “smart” controllers which can detect electricity demand and adjust air conditioner settings accordingly – saving you money on your electricity bill.

(c) Smart split systems for heat pumps

Heat pumps require a certain amount of energy (heat/cold) to be pumped out in order to function properly.

Modern split air conditioning systems are designed with sensors that allow them to sense the level of heating/cooling required by their surroundings, thus ensuring they only use enough energy for pumping out the right quantity of heat/cold.

If you do not have a sensor equipped at home, then it may be worth investing in one if your landlord owns a “smart” system nearby because you would be able to switch it on when necessary without paying any additional electrical power.

(4) Turning off lights when not in use and replacing them with low energy lighting alternatives

Using motion sensor switches can be a cheap way to save electricity in areas that you use infrequently.

This is particularly useful for retail shops, bars and other businesses where it is necessary to have the power on during business hours but unnecessary to leave it switched on outside of these times.

As an example, switching off 20 lights over 8 hours could result in 2 kWh being wasted (see footnote [6] for calculation).

(5) Using smart meters to monitor your electricity usage patterns

A “smart” or “advanced” electricity meter tracks your electrical consumption patterns throughout the day (24 hour cycle), rather than just recording only how much power you used at given intervals .

Conclusion

Solar cells are an excellent way to generate sustainable energy that doesn’t pollute the environment.

However, there is a limit on how much power you can get from them and they’re not very efficient when it comes to converting solar radiation into electricity.

If you live in an area without good sunlight or if your home has too many trees blocking the sun’s rays, then getting enough light for solar panels might be difficult.

For those reasons, installing solar cells may not be worth it unless you have other alternatives such as wind turbines or hydroelectric plants since these sources of renewable energy don’t depend on natural conditions like sunshine.

That said, even though people often think about using their homes’ electrical grid most of the time – which is more convenient and comfortable to use – a home solar energy system can be a good alternative to using power from the main utilities company, especially if large electric bills are a problem.