How do solar systems produce energy?

Solar power is arguably the cleanest, most reliable form of renewable energy available, and it can be used in several forms to help power your home or business. Solar-powered photovoltaic (PV) panels convert the sun's rays into electricity by exciting electrons in silicon cells using the photons of light from the sun. This electricity can then be used to supply renewable energy to your home or business.

To understand this process further, let’s look at the solar energy components that make up a complete solar power system.

The roof system
In most solar systems, solar panels are placed on the roof. An ideal site will have no shade on the panels, especially during the prime sunlight hours of 9 a.m. to 3 p.m.; a south-facing installation will usually provide the optimum potential for your system, but other orientations may provide sufficient production. Trees or other factors that cause shading during the day will cause significant decreases to power production. The importance of shading and efficiency cannot be overstated. In a solar panel, if even just one of its 36 cells is shaded, power production will be reduced by more than half. Experienced installation contractors such as NW Wind & Solar use a device called a Solar Pathfinder to carefully identify potential areas of shading prior to installation.

Not every roof has the correct orientation or angle of inclination to take advantage of the sun's energy. Some systems are designed with pivoting panels that track the sun in its journey across the sky. Non-tracking PV systems should be inclined at an angle equal to the site’s latitude to absorb the maximum amount of energy year-round. Alternate orientations and/or inclinations may be used to optimize energy production for particular times of day or for specific seasons of the year.

Solar panels
Solar panels, also known as modules, contain photovoltaic cells made from silicon that transform incoming sunlight into electricity rather than heat. (”Photovoltaic” means electricity from light — photo = light, voltaic = electricity.)

Solar photovoltaic cells consist of a positive and a negative film of silicon placed under a thin slice of glass. As the photons of the sunlight beat down upon these cells, they knock the electrons off the silicon. The negatively-charged free electrons are preferentially attracted to one side of the silicon cell, which creates an electric voltage that can be collected and channeled. This current is gathered by wiring the individual solar panels together in series to form a solar photovoltaic array. Depending on the size of the installation, multiple strings of solar photovoltaic array cables terminate in one electrical box, called a fused array combiner. Contained within the combiner box are fuses designed to protect the individual module cables, as well as the connections that deliver power to the inverter. The electricity produced at this stage is DC (direct current) and must be converted to AC (alternating current) suitable for use in your home or business.

Inverter
The inverter is typically located in an accessible location, as close as practical to the modules. In a residential application, the inverter is often mounted to the exterior sidewall of the home near the electrical main or sub panels. Since inverters make a slight noise, this should be taken into consideration when selecting the location.

The inverter turns the DC electricity generated by the solar panels into 120-volt AC that can be put to immediate use by connecting the inverter directly to a dedicated circuit breaker in the electrical panel.

The inverter, electricity production meter, and electricity net meter are connected so that power produced by your solar electric system will first be consumed by the electrical loads currently in operation. The balance of power produced by your solar electric system passes through your electrical panel and out onto the electric grid. Whenever you are producing more electricity from your solar electric system than you are immediately consuming, your electric utility meter will turn backwards!

Net meter
In a solar electric system that is also tied to the utility grid, the DC power from the solar array is converted into 120/240 volt AC power and fed directly into the utility power distribution system of the building. The power is “net metered,” which means it reduces demand for power from the utility when the solar array is generating electricity – thus lowering the utility bill. These grid-tied systems automatically shut off if utility power goes offline, protecting workers from power being back fed into the grid during an outage. These types of solar-powered electric systems are known as “on grid” or “battery-less” and make up approximately 98% of the solar power systems being installed today.

Other benefits of solar
By lowering a building’s utility bills, these systems not only pay for themselves over time, they help reduce air pollution caused by utility companies. For example, solar power systems help increase something called “peak load generating capacity,” thereby saving the utility from turning on expensive and polluting supplemental systems during periods of peak demand. The more local-generating solar electric power systems that are installed in a given utility's service area, the less capacity the utility needs to build, thus saving everyone from funding costly additional power generating sources. Contributing clean, green power from your own solar electric system helps create jobs and is a great way to mitigate the pollution and other problems produced by electricity derived from fossil fuel. Solar-powered electrical generating systems help you reduce your impact on the environment and save money at the same time!

Source: http://www.nwwindandsolar.com/solar-power-in-seattle-and-the-northwest/how-do-solar-systems-produce-energy/

Make Solar Energy Economical

Summary
Solar energy provides less than 1% of the world's total energy, but it has the potential to provide much, much more.

As a source of energy, nothing matches the sun. It out-powers anything that human technology could ever produce. Only a small fraction of the sun’s power output strikes the Earth, but even that provides 10,000 times as much as all the commercial energy that humans use on the planet.

Why is solar energy important?

Already, the sun’s contribution to human energy needs is substantial — worldwide, solar electricity generation is a growing, multibillion dollar industry. But solar’s share of the total energy market remains rather small, well below 1 percent of total energy consumption, compared with roughly 85 percent from oil, natural gas, and coal.

Those fossil fuels cannot remain the dominant sources of energy forever. Whatever the precise timetable for their depletion, oil and gas supplies will not keep up with growing energy demands. Coal is available in abundance, but its use exacerbates air and water pollution problems, and coal contributes even more substantially than the other fossil fuels to the buildup of carbon dioxide in the atmosphere.

For a long-term, sustainable energy source, solar power offers an attractive alternative. Its availability far exceeds any conceivable future energy demands. It is environmentally clean, and its energy is transmitted from the sun to the Earth free of charge. But exploiting the sun’s power is not without challenges. Overcoming the barriers to widespread solar power generation will require engineering innovations in several arenas — for capturing the sun’s energy, converting it to useful forms, and storing it for use when the sun itself is obscured.

Many of the technologies to address these issues are already in hand. Dishes can concentrate the sun’s rays to heat fluids that drive engines and produce power, a possible approach to solar electricity generation. Another popular avenue is direct production of electric current from captured sunlight, which has long been possible with solar photovoltaic cells.

How efficient is solar energy technology?

But today’s commercial solar cells, most often made from silicon, typically convert sunlight into electricity with an efficiency of only 10 percent to 20 percent, although some test cells do a little better. Given their manufacturing costs, modules of today’s cells incorporated in the power grid would produce electricity at a cost roughly 3 to 6 times higher than current prices, or 18-30 cents per kilowatt hour [Solar Energy Technologies Program]. To make solar economically competitive, engineers must find ways to improve the efficiency of the cells and to lower their manufacturing costs.

Prospects for improving solar efficiency are promising. Current standard cells have a theoretical maximum efficiency of 31 percent because of the electronic properties of the silicon material. But new materials, arranged in novel ways, can evade that limit, with some multilayer cells reaching 34 percent efficiency. Experimental cells have exceeded 40 percent efficiency.

Another idea for enhancing efficiency involves developments in nanotechnology, the engineering of structures on sizes comparable to those of atoms and molecules, measured in nanometers (one nanometer is a billionth of a meter).

Recent experiments have reported intriguing advances in the use of nanocrystals made from the elements lead and selenium. [Schaller et al.] In standard cells, the impact of a particle of light (a photon) releases an electron to carry electric charge, but it also produces some useless excess heat. Lead-selenium nanocrystals enhance the chance of releasing a second electron rather than the heat, boosting the electric current output. Other experiments suggest this phenomenon can occur in silicon as well. [Beard et al.]

Theoretically the nanocrystal approach could reach efficiencies of 60 percent or higher, though it may be smaller in practice. Engineering advances will be required to find ways of integrating such nanocrystal cells into a system that can transmit the energy into a circuit.

How do you make solar energy more economical?

Other new materials for solar cells may help reduce fabrication costs. “This area is where breakthroughs in the science and technology of solar cell materials can give the greatest impact on the cost and widespread implementation of solar electricity,” Caltech chemist Nathan Lewis writes in Science. [Lewis 799]

A key issue is material purity. Current solar cell designs require high-purity, and therefore expensive, materials, because impurities block the flow of electric charge. That problem would be diminished if charges had to travel only a short distance, through a thin layer of material. But thin layers would not absorb as much sunlight to begin with.

One way around that dilemma would be to use materials thick in one dimension, for absorbing sunlight, and thin in another direction, through which charges could travel. One such strategy envisions cells made with tiny cylinders, or nanorods. Light could be absorbed down the length of the rods, while charges could travel across the rods’ narrow width. Another approach involves a combination of dye molecules to absorb sunlight with titanium dioxide molecules to collect electric charges. But large improvements in efficiency will be needed to make such systems competitive.

How do you store solar energy?

However advanced solar cells become at generating electricity cheaply and efficiently, a major barrier to widespread use of the sun’s energy remains: the need for storage. Cloudy weather and nighttime darkness interrupt solar energy’s availability. At times and locations where sunlight is plentiful, its energy must be captured and stored for use at other times and places.

Many technologies offer mass-storage opportunities. Pumping water (for recovery as hydroelectric power) or large banks of batteries are proven methods of energy storage, but they face serious problems when scaled up to power-grid proportions. New materials could greatly enhance the effectiveness of capacitors, superconducting magnets, or flyweels, all of which could provide convenient power storage in many applications. [Ranjan et al., 2007]

Another possible solution to the storage problem would mimic the biological capture of sunshine by photosynthesis in plants, which stores the sun’s energy in the chemical bonds of molecules that can be used as food. The plant’s way of using sunlight to produce food could be duplicated by people to produce fuel.

For example, sunlight could power the electrolysis of water, generating hydrogen as a fuel. Hydrogen could then power fuel cells, electricity-generating devices that produce virtually no polluting byproducts, as the hydrogen combines with oxygen to produce water again. But splitting water efficiently will require advances in chemical reaction efficiencies, perhaps through engineering new catalysts. Nature’s catalysts, enzymes, can produce hydrogen from water with a much higher efficiency than current industrial catalysts. Developing catalysts that can match those found in living cells would dramatically enhance the attractiveness of a solar production-fuel cell storage system for a solar energy economy.

Fuel cells have other advantages. They could be distributed widely, avoiding the vulnerabilities of centralized power generation.

If the engineering challenges can be met for improving solar cells, reducing their costs, and providing efficient ways to use their electricity to create storable fuel, solar power will assert its superiority to fossil fuels as a sustainable motive force for civilization’s continued prosperity.



References

Beard, M.C., et al.  2007.  Multiple Exciton Generation in Colloidal Silicon Nanocrystals.  Nano Letters 7(8): 2506-2512.  DOI: 10.1021/nl071486l S1530-6984(07)01486-5

DOE (U.S. Department of Energy).  2007.  Solar America Initiative: A Plan for the Integrated Research, Development, and Market Transformation of Solar Energy Technologies.  Report Number SETP-2006-0010.  Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Program.  Washington, D.C.: DOE.

DOE.  Solar Energy Technologies Program Multi-Year Program Plan 2007-2011.  Office of Energy Efficiency and Renewable Energy.  Washington, D.C.: DOE.

Lewis, N.S.  2007.  Toward Cost-Effective Solar Energy Use.  Science 315(5813): 798-801.  DOI: 10.1126/science.1137014

Ranjan, V., et al.  2007.  Phase Equilibria in High Energy Density PVDF-Based Polymers.  Physical Review Letters 99: 047801-1 - 047801-4.  DOI: 10.1103/PhysRevLett.99.047801

Schaller, R.D., and V.I. Klimov.  2004.  High Efficiency Carrier Multiplication in PbSe Nanocrystals: Implications for Solar Energy Conversion.  Physical Review Letters 92(18): 186601-1 - 186601-4.  DOI: 10.1103/PhysRevLett.92.186601

Source: http://www.engineeringchallenges.org/challenges/solar.aspx

Generate cheap, green electricity from sunlight

The benefits of solar electricity

• Cut your electricity bills. Sunlight is free, so once you've paid for the initial installation, your electricity costs will be reduced.
• Get paid for the electricity you generate. The UK government’s Feed-in Tariff scheme pays you for the electricity you generate, even if you use it.
• Sell electricity back to the grid. If your system is producing more electricity than you need, you can sell the surplus back to the grid through the Feed-in Tariff scheme.
• Cut your carbon footprint. Solar electricity is green renewable energy and doesn't release any harmful carbon dioxide or other pollutants. A typical home solar PV system could save over a tonne and a half of carbon dioxide per year – that's more than 30 tonnes over its lifetime.

How do solar panels (PV) cells work? 

PV cells are made from layers of semi-conducting material, usually silicon. When light shines on the cell it creates an electric field across the layers. The stronger the sunshine, the more electricity is produced. Groups of cells are mounted together in panels or modules that can either be mounted on your roof or on the ground.

The power of a PV cell is measured in kilowatts peak (kWp). That's the rate at which it generates energy at peak performance in full direct sunlight during the summer. PV cells come in a variety of shapes and sizes. Most PV systems are made up of panels that fit on top of an existing roof, but you can also fit solar tiles.

Solar tiles and slates 

Solar tiles are designed to be used in place of ordinary roof tiles. A system made up of solar tiles will typically cost about twice as much as an equivalent panel system. Solar tile systems are not normally as cost-effective as panel systems, and are usually only considered where panels are not considered appropriate for aesthetic or planning reasons.

Cost and savings

England, Scotland and Wales

A 4kWp system can generate around 3,800 kilowatt hours of electricity a year in the south of England – roughly equivalent to a typical household's electricity needs. It will save nearly two tonnes of carbon dioxide every year. A 4kWp system in Scotland can generate about 3,200 kilowatt hours of electricity a year – more than three quarters of a typical household's electricity needs. It will save more than a tonne and a half of carbon dioxide every year.

The average domestic solar PV system is 4kWp and costs £5,000 - 8,000 (including VAT at 5 per cent). 

Location	System size	Feed-in-Tariff generation payment (£/year)	Feed-in-Tariff export payment (£/year)	Electricity bill savings (£/year)	Carbon dioxide savings (kgCO2/year)
		Valid between 1st October- 31th December 2015
London, South England	4kWp	£475	£95	£65	1,870 kg
Aberystwyth, Wales	4kWp	£445	£85	£65	1,750 kg
Manchester, North England	4kWp	£420	£80	£65	1,650 kg
Stirling, Scotland	4kWp	£400	£75	£65	1,560 kg

If your system is eligible for the Feed-in Tariff scheme, you could generate savings and receive payments of £540 - £635 a year depending on your location if you register before the end of December 2015 (based on a 4kWp solar PV system eligible for a generation tariff of 12.47p/kWh). You will get paid for both the electricity you generate and use, and what you don't use and export to the grid. 

Note that the Department of Energy and Climate Change (DECC) has released a consultation on a review of the Feed-in Tariff scheme. This consultation proposed a number of changes to the scheme including changes to generation tariffs. For more information visit our FITs page.

Northern Ireland 

A 4kWp system can generate around 3,400 kilowatt hours of electricity a year – roughly equivalent to a typical household's electricity needs. It will save over a tonnes and a half of carbon dioxide every year.

Location	System size	NIROCs payment (£/year)	Export tariff payment (£/year)	Electricity bill savings (£/year)	Carbon dioxide savings (kgCO2/year)
Belfast, Northern Ireland	4kWp	£560	£85	£80	1,700 kg

If your system is eligible for the NIROC (Northern Ireland Renewable Obligations Certificates), you could generate savings and receive payments of around £725 a year (based on a 4kWp solar PV system eligible for a generation tariff of 16.32p/kWh, using a ROC rate of 4.08p/kWh). You will get paid for both the electricity you generate and use, and what you don't use and export to the grid if you register before September 2015.  When applying for NIROCs you will need to apply through Power NI if your system is below 50kW.

If you know your system size, you can get a tailored estimate of FIT payments for your system using our Solar Energy Calculator. 

Costs can vary between installers and products, so we recommend getting quotes from at least three installers. 

Other factors that affect PV installation costs are:

• The more electricity the system can generate, the more it costs but the more it could save.
• Larger systems are usually more cost-effective than smaller systems (up to 4kWp).
• PV panels are all about the same price per kWp, but PV tiles cost much more than a typical system made up of panels.
• Panels built into a roof are more expensive than those that sit on top.

Financial support 

Solar PV is eligible for Feed-in Tariffs and you will earn a tariff for each kWh of electricity generated by your system. You will also receive another tariff for each kWh of electricity you export. You can visit our Solar Energy Calculator to find out how much you can save and earn through Feed-in Tariffs.

Find out more about financial support for renewables.

Maintenance 

Solar PV needs little maintenance – you'll just need to keep the panels relatively clean and make sure trees don't begin to overshadow them. In the UK panels that are tilted at 15° or more have the additional benefit of being cleaned by rainfall to ensure optimal performance. Debris is more likely to accumulate if you have ground mounted panels.

Once fitted, your installer should leave written details of any maintenance checks that you should carry out from time to time to ensure everything is working properly. This should include details of the main inverter fault signals and key trouble-shooting guidance. Ideally your installer should demonstrate this to you at the point of handover. Keeping a close eye on your system and the amount of electricity it’s generating (alongside the weather conditions) will familiarise you with what to expect and alert you to when something might be wrong.

The panels should last 25 years or more, but the inverter is likely to need replacing some time during this period, at a current cost of about £800. Consult with your installer for exact maintenance requirements before you commit to installing a solar PV system.

Source: http://www.energysavingtrust.org.uk/domestic/solar-panels

Scientists are developing an invisibility cloak for solar panels

Current solar panel technology has enough trouble as it is converting sunlight into useable current, what with their paltry 20 percent average efficiencies. And it certainly doesn't help matters that up to a tenth of every solar panel's active collection areas are obscured from the sun by electrical leads called "contact fingers." But researchers at the Karlsruhe Institute of Technology (KIT) have developed a novel workaround: they're wrapping the finger contacts in little invisibility cloaks.

Like other invisibility cloaks, this system works to wrap light around the object. The fingers are still visible to the human eye -- I mean, they're not really invisible -- but the light that hits the top of the contacts is redirected to the solar panel underneath through some tricky physics. The team is currently looking at two alternative methods for accomplishing this feat. The first method involves wrapping the fingers in a polymer coating with a precisely tuned refractive index. The other involves etching grooves into the fingers themselves that refract light around the components. Current computer models of both methods suggest that panel efficiencies would increase by about 10 percent should the contact fingers be made to disappear.

[Image Credit: KIT]

Source: http://www.engadget.com/2015/10/01/scientists-are-developing-an-invisibility-cloak-for-solar-panels/