Solar Power - Environment
Frequently Asked Questions about Solar Power
Why go solar?
Because solar energy is clean and renewable. It not only lowers the cost of your electricity bills, but also
reduces negative impact on the environment. What's more, photovoltaic (PV) modules have no moving or wearing
parts, and require no maintenance other than an occasional cleaning.
What are the benefits of solar power?
PV technology brings many benefits. It's a quiet, clean source of energy, is reliable requiring minimal
maintenance, and lasts for decades. It is not only competitive with other sources of energy in terms of costs,
but directly contributes to reduction in greenhouse gases. What's more, it's an effective back-up power source
in case of emergencies.
What are photovoltaics?
Photovoltaics (PV) are solar cell systems that convert sunlight directly into electricity. PV modules
consist of semi conducting material that absorbs sunlight in a way that frees electrons from atoms.
Electricity is produced as the electrons flow through the semi conducting material. A group of PV modules
are typically combined in an array to generate electricity for a single structure. Large numbers can be
combined to form a power plant.
How do PV modules convert sunlight into electricity?
Sunlight is made up of photons, or particles of solar energy. Photons contain various amounts of energy,
corresponding to the different wavelengths of the solar spectrum. When photons strike a PV cell,
they may be reflected or absorbed, or they may pass right through - only the absorbed photons generate electricity.
When this happens, the energy of the photon is transferred to an electron in an atom of the semiconductor PV cell.
With its newfound energy, the electron escapes from its normal position in an atom of the semiconductor material and becomes
part of the current in an electrical circuit. By leaving its position, the electron causes a hole to form.
Special electrical properties of the PV cell-a built-in electric field across the PN junction -provide the voltage
needed to drive the current through an external load (such as a light bulb).
The part of the spectrum used by silicon PV modules is from 0.3 to 0.6 micrometers, approximately the same wavelengths
to which the human eye is sensitive. These wavelengths encompass the highest energy region of the solar spectrum.
Are there any effects other than producing electricity?
A heat shielding effect can be anticipated, with an associated reduction in air-conditioning load in the heat of summer.
How long do photovoltaic (PV) systems last?
A PV system that is designed, installed, and maintained well will operate for more than 25 years.
The basic PV module (interconnected groups of PV cells) has no moving parts and can last more than 30 years.
The best way to ensure and extend the life and effectiveness of your PV system is by having it installed and maintained properly.
Do the PV modules need to track the sun?
The power output of a PV array is maximized when the array is pointed directly at the sun.
Single-axis tracking of the array will increase the energy production, in some locations, by as much as 35 percent annually.
The most benefit comes in the early morning and late afternoon when the tracking array will be pointing more nearly at the
sun than a fixed array. Generally, tracking is more beneficial at sites between 30° latitude North and 30° latitude South.
For higher latitudes (like NZ) the benefit is less because the sun drops low on the horizon during winter months.
The cost of the tracking system is likely to outweigh the energy production benefit and it is usually more cost effective
to increase the size of the PV array instead.
What's the difference between PV and other solar energy technologies?
- Photovoltaic (PV) systems, which convert sunlight directly to electricity by means of PV cells made from semiconductor
materials.
- Concentrating solar power (CSP) systems, which concentrate the sun's energy using reflective devices such as troughs
or mirror panels to produce heat that is then used to generate electricity.
- Solar water heating systems, which contain a solar collector that faces the sun and either heats water directly or
heats a "working fluid" that, in turn, is used to heat water.
- Transpired solar collectors, or "solar walls," which use solar energy to preheat ventilation air for a building.
How much energy savings can be expected?
In the case of Japan, a 3.12kW PV system will generate annual energy savings equivalent to around 770 litres
of oil. (Savings may vary in other parts of the world depending on local conditions.)
What does energy conversion efficiency mean?
Energy conversion efficiency is an expression of the amount of energy produced in proportion to the amount of energy available
to the device. The sun produces a lot of energy in a wide light spectrum, but we only capture a small portion of that
spectrum and convert it to electricity using photovoltaics. So, today's commercial PV systems are about 7% to 17% efficient.
Most PV systems also degrade a little bit (lose efficiency) each year upon prolonged exposure to sunlight, typically degrading
about 1% per annum. Some PV substrates have been produced that have an efficiency up to 40% however these are very expensive
and not readily available other than for Satellite or Power station applications.
How are watts (W) different from watt hours (Wh)?
Watts are units of power measured over one second. If one watt of electric power is used for one hour, the total
volume of power consumed is expressed as one watt hour, or 1Wh. Similarly, 1,000 watts of power is expressed
as one kilowatt (1kW) and 1,000 watt hours as one kilowatt hour (1kWh). If a 2kW system produces power
continuously for five hours, the total volume of power generated is expressed as 10kWh.
Do PV modules work on cloudy or rainy days?
PV modules produce power anytime the sun is out. On cloudy days power output is considerably reduced.
On sunny days...
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On cloudy days...
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On rainy days...
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| Power is generated in proportion to the strength of the sunlight. If connected
to the utility grid, the amount of excess power sold to the utility company is higher. |
On cloudy or rainy days power is still produced from any
sunlight absorbed. If connected to the utility grid, the volume of power purchased from
the utility company increases. |
What happens if the PV module is covered by leaves?
If fallen leaves, shadows or the like cover a PV module, resistance increases at the affected area and overall power output
decreases significantly. Mitsubishi Electric PV modules incorporate a Bypass Diode function that minimizes the effect of
shadows on the unit's surface area.
Does PV work well in cold weather?
As photovoltaics generate electricity from light, not heat, PV technology is highly suitable for cold weather environments,
on the whole even generating more power at lower temperatures. This is because they are electronic devices, and like all
electronic devices operate more efficiently at cooler temperatures.
Does the PV module surface require cleaning?
In most residential areas no cleaning is necessary, as rainfall will remove the majority of grime.
How popular are PV systems?
As the cost of PV has fallen drastically since the early 1970s— as much as 90 percent— photovoltaics have become an
increasingly attractive option for a variety of both small- and large-scale uses. They are in use in outer space, at
the polar caps, and are a desirable source of electricity in rural areas of developing countries. Although PV is still
a small part of the energy make-up of any given country, more and more homeowners are turning to PV systems to supplement
their conventional power utility.
How does the manufacture of PV modules affect the environment?
Mitsubishi Electric has developed environmentally friendly composite materials and manufacturing processes, including
the use of lead-free solder. We have also been able to reduce the energy required for production.
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