Solar Energy

Solar Energy Powered HouseImage credit: Jeff Kubina, CC BY-SA 2.0, via Flickr

Solar energy – light and heat energy from the sun – has the potential to meet all of our personal, private and commercial and industrial energy needs, if utilised effectively. The technology used to harness solar energy is advancing all the time, becoming more efficient and affordable. It’s also becoming more popular, as more home and business owners realise the benefits of using solar energy, not least of which include an assuaged eco-conscience, credentials as an eco-warrior and more cash in your pocket.

Additional advantages of solar power for homes, businesses and the world at large include:

  • Energy security, as the sun is a renewable, inexhaustible energy source that is available to everyone and isn’t subject to international relations.
  • Low impact, as solar energy results in less pollution and a smaller carbon footprint than using traditional fossil fuels.
  • Low cost, as sunlight is free the only real costs are the initial set up costs. These can run a bit high, depending on the sophistication of the system used, but they payback period is shrinking rapidly, especially for home solar power systems.
    Not only is solar energy low cost, but it saves money as you no longer have to pay a fortune for electricity or fossil-fuel-driven energy solutions.
  • Job creation, as solar energy technology is still in its infancy and many countries are still investing in the infrastructure, there are plenty of jobs available. Examples of jobs in the industry include those related to research and development, manufacturing, installation, maintenance and policy formation.

It’s not all roses, however, as there are also some disadvantages:

  • Set-up costs are quite high. This can be prohibitive for low- to middle-income earners.
  • Energy can’t be produced when the sun doesn’t shine. So we need efficient storage systems that can save enough energy to see us through long nights and rainy days. Unfortunately, storage systems still have some way to go to reach their full potential.
  • Technology is still not efficient enough to compete effectively with electricity.

Solar power can be used in a number of different private and commercial applications, including:

  • Heating: Solar heating systems can be used in everything from water to air, so applications include commercial heating and air conditioning systems, water heating (geysers and swimming pools) and underfloor heating.
  • Charging: Solar power can be used to charge laptops, mobile phones, solar lamps and the like.
  • Cooking: Solar cookers are great alternatives to ovens, stoves and microwaves that use electricity. They are particularly useful in rural areas where power supply is a problem.
  • Lighting: Solar-powered lights are taking off around the world. You can get anything from solar powered street lights to solar fairy lights for your garden.
  • Transport: Solar-powered cars aren’t yet a fully-realised dream, but charging stations for electric cars can be powered by the sun and some car systems (such as air conditioning) can also be drive by solar energy.

Let’s look at the components of solar energy in a little more detail.

 

Photovoltaic Cells

Photovoltaic Solar PanelImage credit: OregonDOT, CC BY 2.0, via Flickr

If you want to convert solar energy into electricity, you need some photovoltaic (PV) cells. An individual photovoltaic cell won’t generate enough energy to power even a watch battery, so they are connected in modules which are used to create arrays. An array can consist of anything from one to several thousand modules, so you can use them in everything from pocket calculators to the solar panels in a mega photovoltaic park.

Using the photovoltaic effect, PV systems convert solar energy into direct current (DC) so you can use it directly to power small appliances, but inverters are needed to convert solar energy into alternating current (AC) for major commercial or industrial purposes. Photovoltaic systems are usually mounted on roofs or walls (for private or business use) or on the ground, as is the case in solar power parks. Most PV cells are made from silicon alloys, with the most common being crystalline silicon.

The first solar photovoltaic power station in South Africa went online in November 2013. Kalkbult will help supply the national grid from its location in Petrusville, Northern Cape. It’s expected to generate 135 million kilowatt hours a year – or enough to power 33,000 households. It was built by Scatect Solar, a Norwegian company, which is busy on two other solar projects in the country.

 

Solar Inverters

Inverters convert direct current into alternating current. A solar inverter is designed specifically to maximise the energy conversion in a solar power (or photovoltaic) system and will typically include maximum power point tracking (MPPT) and anti-islanding protection. Maximum power point tracking systems monitor PV cell output and adjust the resistance to ensure that the maximum amount of power is always generated given the current environmental conditions. Anti-islanding protection increases the stability and safety around power islands in the grid in the event of a power failure.

Solar inverters allow the power generated to feed into the grid to supplement commercial electricity systems, and allow companies and homeowners to successfully live off-grid.

There are three types of solar inverters:

1)      Standalone inverters are used for off-grid systems. DC energy is stored in batteries and when it is needed, the inverter converts it to AC energy. They’re essential for companies and homeowners who want to operate completely independently off-grid.

2)     Grid-tie inverters are for solar arrays that are connected to the commercial power grid. There is no battery to store energy; instead the DC energy is converted into AC energy and fed into the grid. It’s used when you want to sell energy back to the power company. Users are still vulnerable to power outages, as there are no batteries to store energy.

3)     Dual or backup battery inverters are used in multi-function systems. DC energy is stored in a battery and is converted into AC energy when needed. When the batteries are full, the energy is fed into the power grid. These inverters are great for homeowners in South Africa, as they can sell energy back to Eskom but they are still covered in case of power outages and any other emergency, like flooding or an earthquake.

Solar micro-inverters are becoming increasingly common as tests demonstrate how beneficial they are to solar energy efficiency. Each solar panel module gets its own micro-inverter, which makes it more efficient at capturing and converting energy.

 

Solar Updraft Tower

The full potential of solar updraft towers hasn’t yet been properly explored, primarily because set up costs are quite high. However, a small pilot project in Spain proved that they can be surprisingly effective and very reliable.

The other disadvantage to solar updraft towers is the space required. While exact measurements vary according to the desired energy output, projects need between 500m to 10km in diameter of land. They also need from 100m up to 1km of clear air space above.

The massive land space is used to house a collector – a transparent membrane that is suspended off the ground to encourage solar radiation, like a greenhouse. The solar updraft tower rises from the middle of the collector.

The hot air generated in the collector flows towards the tower, which is the lowest point of pressure. The movement of the air powers a wind turbine located at the tower’s base. The air flow is maintained as long as there is a temperature difference between the air in the collector and the air outside. This means that power is still generated for at least a few hours during the night.

When used on their own, solar updraft towers are not that efficient, but they have very low operating and maintenance costs and the power they generate is reliable and consistent. They can also be used in conjunction with other solar technology (thermal collectors and PV cells) to increase efficiency. Additional pilot projects are required to fully test their potential.

 

Solar Tracker

Solar trackers increase the efficiency of other solar devices (like solar panels, reflectors and lenses) by adjusting their angle and orientation, effectively allowing them to follow the sun. By adjusting the angle at which they lie, trackers expose solar panels to more direct beam sunlight, which produces more energy than diffuse sunlight. Solar trackers can increase the efficiency of solar panels by as much as 30%.

There are two broad types of trackers:

1)     Single-axis, which track the sun from east to west.

Single-axis trackers can be further subdivided into horizontal single-axis trackers (HSAT), vertical single-axis trackers (VSAT), tilted single-axis trackers (TSAT) and polar-aligned single-axis trackers (PSAT).

2)     Dual-axis, which track the sun from east to west and north to south.

Dual-axis trackers can be further subdivided into tip-tilt dual-axis trackers (TTDAT) and azimuth-altitude dual-axis trackers (AADAT).

The type of tracker required is dependent on the size of the solar installation, latitude and prevailing weather. As a rule, trackers are better suited to commercial solar power systems than residential ones. However, if you really want a tracker for your home, then a dual-axis tracker will deliver more bang for your buck.

 

Solar Thermal

Solar thermal energy (STE) is solar power that is used specifically for residential, commercial and industrial heating requirements. Special collectors are used to absorb the energy. Different types of collectors are used for different applications. There are three main types of solar thermal collectors, at least according to the U.S. Energy Information Administration.

1)     Low temperature collectors

Low temperature collectors are typically glazed or unglazed flat plate collectors that can be used for space heating and water heating. Glazed collectors tend to be used in residential space-heating applications, while unglazed collectors are used in commercial and industrial heating and air conditioning systems, as well as to heat residential and public swimming pools.

2)     Medium temperature collectors

Medium temperature collectors are used primarily in residential and commercial solar water heating systems. They consist of flat plates that are also used in air heating systems.

3)     High temperature collectors

High temperature collectors are used in industries with high heat requirements (called concentrated solar thermal – CST), as well as in the production of electricity (called concentrated solar power – CSP). They use mirrors or lenses to concentrate and increase the heat.

 

Solar Collectors

Man Solar - NAITImage credit: NAIT, CC BY-ND 2.0, via Flickr

Solar collectors absorb the heat from direct and diffuse sunlight. Solar panels are the most commonly known type of collector, as they can be used for residential, commercial and industrial applications. Other collectors include solar parabolic troughs and solar towers, which tend to have larger, commercial applications, including electricity generation.

Solar collectors can be divided into two categories, based on the collector area vs. the absorption area.

1)     Non-concentrating collectors

The collector area is the same size as the absorption area. Flat-plate and evacuated-tube collectors are prime examples of non-concentrating collectors, as the entire plate or panel is used to collect sunlight.

2)     Concentrating collectors

The collector area is bigger than the absorption area. Mirrors or lenses are used to concentrate the heat. A parabolic trough is a concentrating collector.

 

Solar Chargers

Solar chargers, very simply, allow you to charge batteries and appliances (and even cars) using the power of the sun. Some electric car charging stations are at least partly solar powered, but most solar chargers come in small and portable kits for maximum convenience. This means you can take them with you when you go camping, for instance.

Portable solar chargers tend to be made from monocrystalline panels, which are more efficient than other thin film varieties. Modern portable chargers tend to include a battery, so solar energy is stored and the charger can be used even at night.

The facts are undeniable; we’re running out of fossil fuels, which are becoming increasingly expensive. This places a great deal of importance on any and all renewable energy projects, from the solar panels on your roof to the solar farm in the Northern Cape.

There are many ways in which you can bring solar power into your life. For instance, you might just be able to afford a portable solar charger kit, and that’s great. Or you might try your hand at a DIY solar water heating system, and that’s also great (DIY kits with easy-to-follow instructions and step-by-step pictures are readily available). Or your budget might extend to a state-of-the art, top-of-the-line residential solar power system, complete with inverters, trackers and batteries, and that’s wonderful.

How many uses you find for solar energy is up to you, all that really matters is that you are prepared to give it a go. Once you see the benefits in one application, it’s almost guaranteed that you’ll be motivated enough to find more.

 

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