How many solar cells would I need in order to provide all of the electricity that my house needs?

f you have read the HSW article entitled How Solar Yard Lights Work, then you can get a feeling for how much power a solar cell can produce. The solar panel shown in that article contains 4 cells, and each of them can produce 0.45 volts and 100 milliamps, or 45 milliwatts. Each cell measures 2 inches by 0.5 inches. In other words, with these solar cells you can generate 45 milliwatts in one square inch (6.45 square cm). For the sake of discussion, let's assume that a panel can generate 70 milliwatts per square inch.
To calculate how many square inches of solar panel you need for a house, you need to know:

How much power the house consumes on average.
Where the house is located (so you can calculate mean solar days, average rainfall, etc.). This question is impossible to answer unless you have a specific location in mind. We'll assume that on an average day the solar panels generate their maximum power for 5 hours.
The first question is actually pretty interesting, so let's work on it.
A "typical home" in America can use either electricity or gas to provide heat -- heat for the house, the hot water, the clothes dryer and the stove/oven. If you were to power a house with solar electricity, you would certainly use gas appliances because solar electricity is so expensive. This means that what you would be powering with solar electricity are things like the refrigerator, the lights, the compute r, the TV, stereo equipment, motors in things like furnace fans and the washer, etc. Let's say that all of those things average out to 600 watts on average. Over the course of 24 hours, you need 600 watts * 24 hours = 14,400 watt-hours per day.
From our calculations and assumptions abo ve, we know that a solar panel can generate 70 milliwatts per square inch * 5 hours = 350 milliwatt hours per day. Therefore you need about 41,000 square inches of solar panel for the house. That's a solar panel that measures about 285 square feet (about 26 square meters). That would cost around $16,000 right now. Then, because the sun only shines part of the time, you would need to purchase a battery bank, an inverter, etc., and that often doubles the cost of the installation.

If you want to have a small room air conditioner in your bedroom, double everything.

Because solar electricity is so expensive, you would normally go to great lengths to reduce your electricity consumption. Instead of a desktop computer and a monitor you would use a laptop computer. You would use fluorescent lights instead of incandescent. You would use a small B&W TV instead of a large color set. You would get a small, extremely efficient refrigerator . By doing these things you might be able to reduce your average power consumption to 100 watts. This would cut the size of your solar panel and its cost by a factor of 6, and this might bring it into the realm of possibility.

The thing to remember, however, is that 100 watts per hour purchased from the power grid would only cost about 24 cents a day right now, or $91 a year. That's why you don't see many solar houses unless they are in very remote locations. When it only costs about $100 a year to purchase power from the grid, it is hard to justify spending thousands of dollars on a solar system.

How I built an electricity producing Solar Panel

Several years ago I bought some remote property in Arizona. I am an astronomer and wanted a place to practice my hobby far away from the sky-wrecking light pollution found near cities of any real size. I found a great piece of property. The problem is, it's so remote that there is no electric service available. That's not really a problem. No electricity equals no light pollution. However, it would be nice to have at least a little electricity, since so much of life in the 21st century is dependant on it.

I built a wind turbine to provide some power on the remote property. It works great, when the wind blows. However, I wanted more power, and more dependable power. The wind seems to blow all the time on my property, except when I really need it too. I do get well over 300 sunny days a year on the property though, so solar power seems like the obvious choice to supplement the wind turbine. Solar panels are very expensive though. So I decided to try my hand at building my own. I used common tools and inexpensive and easy to acquire materials to produce a solar panel that rivals commercial panels in power production, but completely blows them away in price. Read on for step by step instructions on how I did it.

SOLAR ELECTRICITY EXPLAINED

Solar electricity is created by using Photovoltaic (PV) technologyby converting solar energy into solar electricity from sunlight. Photovoltaic systems use sunlight to power ordinary electrical equipment, for example, household appliances, computers and lighting. The photovoltaic (PV) process converts free solar energy - the most abundant energy source on the planet - directly into solar power. Note that this is not the familiar "passive" or Solar electricity thermal technology used for space heating and hot water production.

A PV cell consists of two or more thin layers of semi-conducting material, most commonly silicon. When the silicon is exposed to light, electrical charges are generated and this can be conducted away by metal contacts as direct current (DC). The electrical output from a single cell is small, so multiple cells are connected together and encapsulated (usually behind glass) to form a module (sometimes referred to as a "panel"). The PV module is the principle building block of a PV system and any number of modules can be connected together to give the desired electrical output.

PV equipment has no moving parts and as a result requires minimal maintenance. It generates solar electricity without producing emissions of greenhouse or any other gases, and its operation is virtually silent.

What is PV power used for?

PV systems supply solar electricity to many applications in the UK, ranging from systems supplying power to city buildings (which are also connected to the normal local solar power network) to systems supplying power to garden lights or to remote telecom relay stations.

The main area of interest in the UK today is grid connect PV systems. These systems are connected to the local solar electricity network. This means that during the day, the solar electricity generated by the PV system can either be used immediately (which is normal for systems installed on offices and other commercial buildings), or can be sold to one of the electricity supply companies (which is more common for domestic systems where the occupier may be out during the day). In the evening, when the electrical system is unable to provide the electricity required, power can be bought back from the network. In effect, the grid is acting as a Solar electricity energy storage system, which means the PV system does not need to include battery storage.

Grid connect PV systems are often integrated into buildings. PV technology is ideally suited to use on buildings, providing pollution and noise-free solar power without using extra space. The use of photovoltaics on buildings has grown substantially in the UK over the last few years, with many impressive examples already in operation.

PV systems can be incorporated into buildings in various ways. Sloping rooftops are an ideal site, where modules can simply be mounted using frames. Photovoltaic systems can also be incorporated into the actual building fabric, for example PV roof tiles are now available which can be fitted as would standard tiles. In addition, PV can also be incorporated as building facades, canopies and sky lights amongst many other applications.

Stand-alone photovoltaic systems have been used for many years in the UK to supply solar electricity to applications where grid solar power supplies are unavailable or difficult to connect to. Examples include monitoring stations, radio repeater stations, telephone kiosks and street lighting. There is also a substantial market for PV technology in the leisure industry, with battery chargers for boats and caravans, as well as for powering garden equipment such as solar electricity fountains. These systems normally use batteries to store the solar power, if larger amounts are required they can be combined with another source of power - a biomass generator, a wind turbine or diesel generator to form a hybrid power supply system.

PV technology is also widely used in the developing world. The technology is particularly suited here, where electricity grids are unreliable or non-existent, with remote locations often making PV power supply the most economic option. In addition, many developing countries have high solar radiation levels year round.

Electricity from: Solar Energy

he ultimate source of much of the world's energy is the sun, which provides the earth with light, heat and radiation. While many technologies derive fuel from one form of solar energy or another, there are also technologies that directly transform the sun's energy into electricity.


The sun bathes the earth in a steady, enormous flow of radiant energy that far exceeds what the world requires for electricity fuel.
Since generating electricity directly from sunlight does not deplete any of the earth's natural resources and supplies the earth with energy continuously, solar energy is a renewable source of electricity generation. Solar energy is our earth's primary source of renewable energy.

There are two different approaches to generate electricity from the sun: photovoltaic (PV) and solar-thermal technologies.

Initially developed for the space program over 30 years ago, PV, like a fuel cell, relies upon chemical reactions to generate electricity. PV cells are small, square shaped semiconductors manufactured in thin film layers from silicon and other conductive materials. When sunlight strikes the PV cell, chemical reactions release electrons, generating electric current. The small current from individual PV cells, which are installed in modules, can power individual homes and businesses or can be plugged into the bulk electricity grid.

Solar-thermal technologies are, more or less, a traditional electricity generating technology. They use the sun's heat to create steam to drive an electric generator. Parabolic trough systems, like those operating in southern California, use reflectors to concentrate sunlight to heat oil which in turn creates steam to drive a standard turbine.

Two other solar-thermal technologies are nearing commercial status. Parabolic dish systems concentrate sunlight to heat gaseous hydrogen or helium or liquid sodium to create pressurized gas or steam to drive a turbine to generate electricity. Central receiver systems feature mirrors that reflect sunlight on to a large tower filled with fluid that when heated creates steam to drive a turbine.

What are the environmental impacts?

PV systems operate without producing air, water or solid wastes.
When constructed as grid-connected central station systems, they require significant land, which can impact existing ecosystems. Nevertheless, most PV installations come in the form of distributed systems that use little or no land since the panels are installed on buildings.

Manufacturing PV cells involves the generation of some hazardous materials. Nonetheless, appropriate handling of these small quantities of hazardous material reduces risks of exposure to humans and to the environment.

Like PV, solar-thermal technologies generate zero air emissions, though some emissions are created during the manufacture of both technologies. Water use for solar thermal plants is similar to amounts needed for a comparably sized coal or nuclear plants.

The biggest concern with solar technologies may be land use...
...since five acres of land are often needed for each megawatt of capacity. PV can eliminate the land use impacts by integrating the generators into building construction, eliminating the need for dedicating land use to PV generation.

How Do You Produce Electricity From Solar Energy

The answer to the question of how do you produce electricity from solar energy is fairly easy to understand once you have a slight knowledge of the subject.
Before you are able to produce electricity through solar energy, there needs to be some form of solar cell or panel.The solar panels are made of a semi-conductive material, the most common material is silicon.The semi-conductive material contains electrons which are quite happy just sitting there.When photons (contained within the suns rays) hit the solar cells, the electrons absorb this solar energy, transforming them into conduction electrons.If the energy of these photons is great enough, then the electrons are able to become free, and carry an electric charge through a circuit to the destination.Any electrons that do not receive enough energy simply warm up, which heats your cell or panel, resulting in lowering the efficiency of the cellThe lowering in efficiency is down to two main factors and they are; that the cell is not working to its full potential (e.g. some electrons may be lost), the second factor is when the electrons release heat, the panel also becomes warm, interfering with other aspects of the solar cells.

Flexible solar cell implant could restore vision

The first flexible retinal implant could restore some vision to people with certain forms of visual impairment.

Conditions such as age-related macular degeneration occur when some of the photoreceptors in the eye stop functioning properly. But as other parts of the eye still work, it should be possible to restore vision using an implant that mimics the photoreceptor layer, says Rostam Dinyari at Stanford University in California.

To achieve this, an implant needs to convert a light signal into an electrical pulse – in other words, perform like a solar cell.

But most solar cells are rigid, which makes them far from ideal for use inside the eye. "If you have a lens, the focal plane is always curved and the best picture forms on a spherical surface," Dinyari says. This is why the retina is curved.

Rigid implants

Using rigid chips, a large number of small implants must be fitted in order to approximate the curve of the retina. A flexible implant would simplify matters.

"You would need a lot of surgery to implant a large enough number [of rigid implants] to cover the retina," says Dinyari. A flexible implant "would use just one surgical procedure".

While several companies are developing rigid implants, Dinyari and colleagues have designed a flexible silicon implant. They did so by carving deep grooves into the silicon between adjacent solar cell pixels that are each just 115 micrometres across.

The implant would be inserted over the most damaged part of the retina. A glasses-mounted camera would capture video, convert it to near-infrared signals and project it directly onto the implant.

Projecting images

When hit by the light, the solar cells inject current patterns corresponding to the projected images into neural tissue, which ultimately arrive at the visual cortex via the optic nerve. Near-infrared signals are used as they do not interfere with the surrounding intact photoreceptor cells, which send signals to the brain as normal.

Initial trials using retinas extracted from pigs showed that the implant could be inserted without damaging the fragile solar cell array. The team hope to implant the device into a live pig soon, before testing it in humans.

Jason Dowling at the Australian eHealth Research Centre in Herston, Queensland, thinks the approach is interesting. "To the best of my knowledge I think this is the first implant which is shaped to the curved surface and this [approach] makes a lot of sense," he says.

Dinyari presented his work at the 2009 IEDM conference in Baltimore, Maryland, last week.

Thin film solar cells

The high cost of crystalline silicon wafers (they make up 40-50% of the cost of a finished module) has led the industry to look at cheaper materials to make solar cells.

The selected materials are all strong light absorbers and only need to be about 1micron thick, so materials costs are significantly reduced. The most common materials are amorphous silicon (a-Si, still silicon, but in a different form), or the polycrystalline materials: cadmium telluride (CdTe) and copper indium (gallium) diselenide (CIS or CIGS).

Each of these three is amenable to large area deposition (on to substrates of about 1 meter dimensions) and hence high volume manufacturing. The thin film semiconductor layers are deposited on to either coated glass or stainless steel sheet.

The semiconductor junctions are formed in different ways, either as a p-i-n device in amorphous silicon, or as a hetero-junction (e.g. with a thin cadmium sulphide layer) for CdTe and CIS. A transparent conducting oxide layer (such as tin oxide) forms the front electrical contact of the cell, and a metal layer forms the rear contact.

Thin film technologies are all complex. They have taken at least twenty years, supported in some cases by major corporations, to get from the stage of promising research (about 8% efficiency at 1cm2 scale) to the first manufacturing plants producing early product.

Amorphous silicon is the most well developed of the thin film technologies. In its simplest form, the cell structure has a single sequence of p-i-n layers. Such cells suffer from significant degradation in their power output (in the range 15-35%) when exposed to the sun.

The mechanism of degradation is called the Staebler-Wronski Effect, after its discoverers. Better stability requires the use of a thinner layers in order to increase the electric field strength across the material. However, this reduces light absorption and hence cell efficiency.
his has led the industry to develop tandem and even triple layer devices that contain p-i-n cells stacked one on top of the other. In the cell at the base of the structure, the a-Si is sometimes alloyed with germanium to reduce its band gap and further improve light absorption. All this added complexity has a downside though; the processes are more complex and process yields are likely to be lower.

In order to build up a practically useful voltage from thin film cells, their manufacture usually includes a laser scribing sequence that enables the front and back of adjacent cells to be directly interconnected in series, with no need for further solder connection between cells.

As before, thin film cells are laminated to produce a weather resistant and environmentally robust module. Although they are less efficient (production modules range from 5 to 8%), thin films are potentially cheaper than c-Si because of their lower materials costs and larger substrate size.

However, some thin film materials have shown degradation of performance over time and stabilized efficiencies can be 15-35% lower than initial values. Many thin film technologies have demonstrated best cell efficiencies at research scale above 13%, and best prototype module efficiencies above 10%. The technology that is most successful in achieving low manufacturing costs in the long run is likely to be the one that can deliver the highest stable efficiencies (probably at least 10%) with the highest process yields.

Amorphous silicon is the most well-developed thin film technology to-date and has an interesting avenue of further development through the use of "microcrystalline" silicon which seeks to combine the stable high efficiencies of crystalline Si technology with the simpler and cheaper large area deposition technology of amorphous silicon.

However, conventional c-Si manufacturing technology has continued its steady improvement year by year and its production costs are still falling too.

The emerging thin film technologies are starting to make significant in-roads in to grid connect markets, particularly in Germany, but crystalline technologies still dominate the market. Thin films have long held a niche position in low power (<50W) and consumer electronics applications, and may offer particular design options for building integrated applications.