Solar Energy FAQs

What type of solar panels are they?

The Schoolgen solar panels generate electricity. The Schoolgen solar panels are called photovoltaic panels (PV panels) as they are made up of many individual photovoltaic cells connected together. The Schoolgen PV panels do not just heat water like the other major type of roof mounted solar panel which are solar thermal collectors.

What variety of PV panels are they?

The majority of Schoolgen schools have PV cells made of poly-crystalline silicon. These are thin slices, known as wafers, cut from a larger block (or ingot) of silicon. Another type of PV panel were used in our four South Island schools called thin-film silicon. Thin-film is about 100 times thinner than a crystalline silicon wafer, so a little silicon goes a long way! The type of thin-film we choose was a very clever design called micromorph.The top layer picks up the bluer light and the bottom layer picks up the redder light so it is more efficient than a traditional thin-film cell. However due to the lower efficiency compared with crystalline siliocn more roof area is needed to generate the same power. For a 2 kW installation this is not a problem on a large roof.

Are we collecting the data from all the schools?

Yes. The electricity generation data from the solar panels installed in Schoolgen schools is collected by a modem-like device called the "hot-e box" and sent to the Schoolgen website.

On this website you can see the electricity that is being generated by the solar panels on a daily, weekly, monthly and yearly basis for each school. You can also compare it to other Schoolgen schools on a graph using the 'Solar versus Solar' page , or you can download all of the data in an Excel spread-sheet.

The diagram below shows how this system works.

Technical Diagram: How Schoolgen solar data collection works.

How does the solar panel make electricity from sunlight?

Sunlight or solar radiation is a stream of pure energy composed of tiny packets of energy called Photons. The energy of the photons is transformed (changed) from radiant energy into electrical energy by the PV cells.

When the photons hit the PV cell in the solar panel they may be absorbed by a semiconducting material called Silicon (Si). A silicon atom which absorbs a photon with enough energy can cause an electron to break free. Due to the clever design of the PV cell with two slightly different layers of treated silicon, the free electron is then swept in one direction by a built-in electric field causing an electric current to flow. For more detailed information about how the photovoltaic cell works check out our Schoolgen Level 6-8 poster The Science of Solar Energy.

How long do the solar panels last?

Photovoltaic panels are typically guaranteed to generate power for 25 years.

In general solar panels are expected to last 30 to 40 years after which they can be replaced with the latest technology and recycled. PV panels do experience a gradual decline in their output over time. After 25 years the output is typically guaranteed to not decline by more than 20% from its original value.

How advanced is PV technology?

Photovoltaic's, or PV is a cutting-edge semi-conductor technology which is continually advancing. It is closely linked to the development of silicon chips for computers.

Every year there is a huge amount of research and development to try and improve the efficiency and affordability of PV cells. Since early 2000s, the quantity of solar PV panels being manufactured has doubled every two years! Every time production doubles the price falls by approximately one fifth. For more information about the development of the solar PV cell check out A Short History of the Photovoltaic (PV) Cell

What is the future for solar panels?

Solar energy is abundant and free so it makes absolute sense that we should utilise the sun's resource. Every second as much solar energy hits the face of the Earth as is used in one day by the entire world's electricity networks.

Advances in photovoltaic technology are happening all the time. Some of these are very small advancements but they do help increase the performance of the solar panels and most importantly also reduce the cost. It is quite possible that in the not too distant future nearly every house and building will have some form of solar power.

Does it matter what the weather conditions are like?

Yes. Solar panels work best under direct sun. So on a nice sunny day the solar power system will definitely produce more power! On a dull winters day the amount of power produced is much reduced because of the lack of light. If you have battery storage you can use the stored solar energy that was produced on the last sunny day, however most installations are grid-tied and do not have battery storage. This will change in the future as the cost of batteries is rapidly falling. 

Does the energy output change when it is a cloudy day?

Yes. On a cloudy day the output of a solar system is less than a clear sunny day, however the system will still generate some power. Have a look at the Schoolgen school's electricity generation graphs here and compare it with weather maps to see what difference the weather makes.

What are the environmental impacts of using solar panels?

During Manufacture

Like any industrial scale manufacturing, producing PV panels is energy intensive, resulting in emissions that accompany the use of standard grid electricity. Emissions from manufacture will differ for the same sized PV panel according to the energy mix that is used for generating electricity in that particular location. For example, if the energy used in manufacture mainly came from hydro-electric power stations then the emissions will be much lower than they would be if the energy came from a coal-fired thermal power station. Some PV manufacturers are already using solar panels to make more of them!

It generally takes between one and three years for a PV system to generate the amount of energy equal to that used in production. Thin-film PV which uses a lot less material has a faster payback than crystalline silicon.

Overall, all PV technologies generate far less life-cycle air emissions per unit of energy generated than conventional fossil-fuel based electricity generation technologies.

During Operation

Solar panels do not produce any emissions (fumes, gases) or noise when they are operating so they do not present any environmental impact while they work. As there are no pollutants or moving parts solar panels are extremely safe to birds and other animals in the environment.

Keep in mind that many solar panels connected together generate electricity at quite high DC voltages which are potentially very dangerous. For this reason only qualified electricians should ever work on them.

How much carbon dioxide is prevented by PV panels?

This varies greatly from country to country. Schoolgen calculates kilograms of carbon dioxide (CO2) emissions saved by using solar panels by multiplying the electricity generation (kilowatt-hours) by the official New Zealand emissions factor of 0.195 kilograms of CO2 per kilowatt-hour. This is an average figure for NZ which comes from official figures for the total amount of carbon dioxide emissions from electricity generation over the year, and official figures for the total electricity generation for the country over the same period. This amount varies a lot from year to year and is largely influenced by the amount of hydro electric generation which depends on "wet" or "dry" years. Due to this year-to-year variation an average is taken over a significant number of years. New Zealand has relatively low emissions for electricity generation compared to other countries due to our very large amount of renewable energy. For example Australia which generates a large amount of electricity from coal-fired thermal generation emits nearly 1.0 kilogram of CO2 per kilowatt-hour.

What can you do with 2 kW of POWER?

2 kilowatts is 2000 Watts. The original Schoolgen solar installations only produced up to 2 kW until 2013, but since then they go anywhere from 4 kW to nearly 20 kW. 

Here is a list of some common appliances found in a school and how much power they typically use when switched on.

  • Microwave Oven - 1500 Watts (1.5 kW)
  • Desktop Computer with 17"Screen: 130 Watts (0.13 kW) 
  • Laptop Computer - 40 Watts (0.04 kW) 
  • Fluorescent tube lighting: 60 Watts  (0.06 kW) 
  • So even 2 kW of power generated by the solar panels is a useful amount of power.

  • That's enough to run 15 desktop computers
  • 50 laptops running or charging!
  • Two classes rooms of lighting (though you shouldn't need lights on on a sunny day!)
  • However it wouldn't run many microwave ovens. 

Ok, that's power, but how much ENERGY does it make in a day?

The amount of energy that the Schoolgen PV panels produces over a day depends on the average power (in kilowatts) over that period multiplied by the time in hours. Every time we generate 2kW of energy for one hour we are producing 2 kilowatt-hours (kWh) of electrical energy.

For an appropriately sited and orientated PV system in New Zealand, this works out at around 4 hours at maximum output for a day. 2 kW x 4 hours = 8 kilowatt-hours of electrical energy. For a 20 kW system that is 80 kWh.  

The energy consumption (E) of a device or appliance is equal to the power (P) it draws multiplied by length of time (t) it is on for: (E = P x t) e.g. A television that is rated at 100W is left on for 4 hours it will consume 400 Watt-hours (0.4 kWh).

What is a solar panel made up of?

Typical photovoltaic panels are made up of the following components:

  • Silicon made into photovoltaic or Solar Cells
  • Special light absorption coating so that light is not reflected.
  • Protective, tough and transparent glass
  • Plastic (or glass) backing material
  • Electrical connection cable
  • Metal Aluminium frame

These are assembled in a special process to get a solar module or panel as follows: Silicon (Si) is refined in a special process to create a semiconductor material (like computers chips) called solar grade silicon.

This is melted down and formed into solar wafers.

The wafers are then put through a special wash to give them special layers (P- and N-doped layers) then a special light absorption layer. This gives the cells the blue colour.

Then electrical contacts are applied to the wafer to allow the flow of electrons. We now have a solar cell.

At this point every cell is tested under a special light know as a flasher or artificial sun. The flasher powers up the cell as though it was exposed to intense sunlight and lets the scientists make sure every cell is ready to go to work.

Once tested, several cells are then connected electrically to form strings of cells. This is what determines the power of the solar module. The electrical connections of each string of cells are then all joined to two points known as the positive (+) and negative (-) poles. The strings of cells are now placed on special highly transparent glass (low iron - high transmissivity/ low reflectance glass).

A protective backing is then applied. This may be another layer of glass or more commonly a special plastic layer called Tedlar.

A special box to protect and house the electrical connection point is glued in place over the positive and negative connection points. This keeps the solar module and electrical connection points waterproof and is called the Junction Box.

Finally, a strong metal frame is usually fixed around the outside of the module to give it strength and to make it easier to mount. This is typically made from aluminium as it is both strong and light. The complete solar panel is then run through a tough testing process to check electrical performance and ensure it is waterproof and ready to use for at least 25 years.

What is the difference between PhotoVoltaic and Solar Hot Water systems?

Photovoltaic panels absorb solar radiation and transform this energy into electricity. Solar hot water systems use a form of Solar thermal collector which absorbs solar radiation (light) and transform this energy into heat. Solar hot water panels are a simpler technology than photovoltaic panels and use a very dark coloured layer of absorption material under a glass cover. Water or fluid passing though the solar thermal collector absorbs this heat energy and gets much hotter. The hot water is then stored in a cylinder ready to use.

Where is the best place to locate the panels and why?

This depends on what part of the world you live in. In the Southern Hemisphere where we live in New Zealand/Aotearoa the sun always shines from the northern sector of the sky- rising in the east in the morning and setting in the west at sun-set. For this reason you should always face your solar panels toward the north when in the Southern Hemisphere. A north facing roof with a slope angle of about 10 to 40 degrees is a good surface to mount solar panels in New Zealand.

In the Northern Hemisphere the sun of course also rises and sets in the same directions, however the suns path tracks through the southern sector of the sky, so you need to face solar panels south in these areas.

What are the costs of a solar panel? Is it cheaper than normal electricity?

PV panels have come down drastically in price in recent years, dropping by 50% alone in 2011! As production of PV increases, roughly doubling every two years, the price will continue to fall. Since electricity costs from power companies is always increasing, the time is coming when the cost of electricity generated by roof mounted solar PV panels will be equal to or less than conventional electricity. This is called grid parity. In some parts of the world where electricity is expensive, such as where it is generated by diesel, this is already the case.

Can you use the solar energy at night?

Solar energy systems only generate their energy when the sun shines. At night, when the sun goes down the solar power system will rest waiting for the next day's sun. When the sun comes up it starts work again.

If we want to use power at night that has been generated during the day by the sun we need to store this energy. Energy is typically stored in batteries although there are other ways to store solar energy that are used in some situations- this includes fly wheels and making and storing hydrogen. Batteries are not used in most of the PV systems in the Schoolgen programme because they are connected to the national power grid. In this case we say that "the grid is the battery".

Can you put them on your house?

Yes. Solar panels are used in all kinds of places. They can be used on almost anything like houses, bus stops, camper vans, cars, boats, signs, lights, billboards, parking meters and high-rise buildings.

In the future many buildings will use solar energy for both electricity and heating. Keep an eye out for solar panels on top of speed warning signs by your school.

Are solar panels enough to save the planet?

Solar panels are one part of the solution, but many other innovations will also be needed to really "save the planet" and create a sustainable world for humans and all other living things. Anything that reduces or eliminates greenhouse gas emissions is part of the solution to the problem of Climate Change.

First we need to make the most of what we have already and make sure we use it wisely. If we all start with some simple steps we can go a long way to helping save our planet. Some things you can do around your home and school are:

  • Reduce your energy consumption - turn off appliances when you're done, unplug chargers.
  • Reduce your waste and use of materials- for example you could use the same shopping bags when you go shopping to reduce the amount of plastic waste.
  • Buy items with less packaging and those that have recyclable packages.
  • Skate, scooter, bike or walk to school. If your parents insist on driving you, ask to get out a few blocks away from school and walk for the last five minutes.

How is the electricity generated by the panels used within the school?

The energy produced by the solar panels is introduced to the school distribution network as it is produced. Given that this is generated inside the schools distribution network it is used prior to and in conjunction with any "imported" energy.

Why do we use Inverters?

Solar panels always generate electricity in the form of DC or Direct Current. DC or Direct Current goes in one direction only, from positive (+) to negative (-).

However, the National Grid and most things plugged into it (like your school and your house and your parents work) use AC or Alternating Current. AC goes back in forth, rapidly changing direction many times each second. To change DC from the solar panels into AC we need a special type of converter called an INVERTER. The inverter takes the DC from the solar panels typically at about 400 volts for many of the Schoolgen PV systems and converts it into AC at 230 volts for use in the home, school or if you make more than you need it can exported and sold to the National Grid. Here is one of our Schoolgen inverters:

Bayswater Inverter

Inverter Diagram

In the case where you are able to export any surplus electricity to the National Grid, the inverter "looks" at the grid and judges how to time (or synchronise) its pulses of energy into the power lines. This is to make sure it delivers the exact same voltage (230 Volts) and frequency (50 times per second) as the grid. If we do not generate enough from the solar power system then we simply get our power from the grid in the normal way. The imported power simply combines with the solar power we have generated so we can reduce how much power we bring in from the grid.

Will the PV system installed in Schoolgen schools export electricity to the Grid?

The PV system that is installed in Schoolgen schools can ideally generate anywhere from 2 kW to 20 kW (as of 2015). Schools generally use a lot of energy (even during weekend and holidays!) so most of the time, most of the energy will be consumed within the school. For small schools which are trying very hard to be energy efficient and reduce their energy costs it could be possible to sometimes have excess electricity to export to the Grid.

Where are the panels made?

Solar panels are made in many countries around the world. Increasingly however many solar PV panels are made in China.

A company called Schott Solar in Germany made the solar panels we installed on most of our first 42 schools. We used these panels because the process for their manufacture requires less energy than other similar companies; they are made to catch lots of sun and to last a long time. The 2012 round of Schoolgen schools trialed a form of thin-film solar panel called micromorph.

What are thin-film panels?

Thin-film is a type of PV which uses a much thinner layer of material than is used in crystalline silicon wafers. Thin-film panels can be made from a variety of semiconductor materials and in some cases can be printed onto a surface. Because of the way it is manufactured and the reduction of material it is less energy intensive than crystalline silicon and therefore cheaper. The efficiency of thin-film per square meter is lower than crystalline silicon so more area is required to produce the same amount of power. Thin-film has been claimed to perform better in low light conditions than crystalline silicon.

What is micromorph thin-film?

This is composed of two very thin layers of different forms of silicon - microcrystalline and amorphous- creating what is called a tandem cell. The amorphous silicon forms the top layer of the solar cell and most effectively targets the blue part of the visible solar spectrum. The lower microcrystalline layer most effectively targets the red and infra-red part of the solar spectrum. The combination of these two layers means that a broader part of the solar spectrum can be captured and converted to electricity than for single layer thin film panels. 

Schoolgen installed micromorph panels at 4 schools in 2012 partly to evaluate the performance of these type of panels compared to the more conventional crystalline ones. Claims had been made that they produce more energy 'watt-for-watt' than conventional crystalline silicon cells because they are more efficient in low light. Is this actually true? Time will fully tell, but at this stage the production is no more than standard crystalline ones.  

How are solar panels better for the environment?

One big advantage of solar panels is that they use renewable energy so they do not emit greenhouse gases such as CO2 (carbon dioxide) while in operation. Non-renewable energy sources such as coal emit large amounts of greenhouse gas pollution which is definitely causing Climate Change and the problem will get much worse if we don't act very soon. Photovoltaic solar panels are very reliable and require very little maintenance and they have little visual impact. There is also a lot of roof space through the world which is a great place to install solar panels. Compared to other forms of renewable energy like hydro and wind solar panels are not that noticeable and have less impact on their surroundings.

Why do we need solar panels?

To reduce our greenhouse gas emissions which are causing Climate Change (this is due to the trapping of heat by these gases which very slowly raises the average temperature of the planet). To have more options in the ways we can make electricity. To provide more security of supply for homes and businesses if there is disruption to the national grid. To reduce demand for building expensive new power stations.