Does the solar power you enjoy use photovoltaics? Or is it a collector system? Does it generate electricity or heat? While it’s great enjoying the benefits of this clean power source, it is always helpful knowing what type of solar power is going to serve you best, its relative costs, and how it works.
Here According to the Solar Energy Industries Association (SEIA), there are three primary technologies by which solar energy is commonly harnessed:
- Photovoltaics (PV), which directly convert light to electricity
- Concentrating solar power (CSP), which uses heat from the sun (thermal energy) to drive utility-scale, electric turbines
- Heating and cooling systems which collect thermal energy to provide hot water and air conditioning
Before we proceed further, I add a fourth category for solar power: passive solar. While this is not a technology, it is a design technique long used by architects and engineers to take full advantage of available sunshine, or to shield yourself from it in order to stay cool. You can find many useful books which can help designers, builders, and others in putting available sunshine to its best use.
But for now, let’s look at the three primary technologies for using solar energy.
This solar technology directly produces electricity which can be used, stored, or converted for long-distance transmission. PV panels can be manufactured using a variety of materials and processes and are widely used for solar projects around the world, including travel in space.
SolarCity provides this overview concerning the process and the equipment needed to generate clean and affordable energy.
How photovoltaic solar panels function
- Solar panels are made with PV cells, which convert sunlight into direct current (DC) electricity during the light of day.
- An inverter converts the DC electricity generated by the solar panels into alternating current (AC) electricity.
- The AC electricity is sent from the inverter to your electrical panel to power your lights and appliances with solar energy. The electrical panel is often called a breaker box.
- The utility meter measures electricity use. It goes backward when the system generates more power is needed.
- If your state utility has a net metering policy, excess energy is returned to the grid and the revenue you receive offsets the electricity you use at night.
SolarCity, as well as other companies, provide customers with monitoring tools. SolarCity offers a PowerGuide Monitoring System.
“Our exclusive PowerGuide monitoring system continuously tracks your energy production and ensures that your solar power system is running smoothly. It will even alert our repair crews in the rare event that problems arise.”
Storing solar electricity
While storing solar electricity may be desirable, it isn’t always necessary. In fact, many calculators with solar cells never need batteries. As long as there’s enough light, they seem to work for a long time. Solar panels in space, emergency road signs, call boxes, buoys and parking lots deploy similar technologies to power lights.
Howstuffworks SCIENCE reports photovoltaics — which were once used almost exclusively in space, powering satellites’ electrical systems as far back as 1958 — are being used more and more in less exotic ways. “The technology continues to pop up in new devices all the time, from sunglasses to electric vehicle charging stations.”
Solar cells, which are the foundation of solar panels, are produced from thin wafers of silicon. When light falls on the cells an electric current is produced. A collection of solar cells connected together forms a module.
Most homes or commercial buildings will need around 10 square meters of unshaded roof space to mount the modules for a 1kW solar system. Ideally the modules should be tilted towards the sun at around 30 degrees to maximize the solar collection.
An inverter converts the direct current (DC) power collected by the solar panels into power for your home, or power to send back to the electricity grid. It can be placed inside or outside your home and can give you information about the amount of electricity being produced.
Meters and the grid
Unless you have large battery storage, you need to be connected to the electricity grid to ensure having electricity at night and when there is heavy cloud cover. A meter (net metering) enables you to sell back excess electricity. This will require having a digital smart meter fitted to your solar system during installation.
For safety reasons, when your electricity supply from the grid is interrupted, your solar PV system must automatically and immediately turn off.
Photovoltaics & Photons: Terms & History
- A photon is an elementary particle of light and a carrier of electrical energy.
- An electron is a particle in an atom with a negative electrical charge.
- Silicon, a chemical element, is a key ingredient in solar cells; it works well because of its semi-conductor properties.
- A solar cell turns sunlight directly into electricity through the photovoltaic effect.
- A solar panel is a collection of solar cells arranged on a flat plane.
Writer John Perlin has credited Albert Einstein with understanding and articulating the photovoltaic effect:
“E=hv, where E is energy, h is Plank’s constant, and v is the frequency of light. In his simple equation, containing only two variables, he showed that light waves carry packets of energy he called light quanta and presently referred to as photons.
“In 1923, 18 years after Einstein published his light quanta piece, American physicist, Arthur Hailey Compton, created a collision between a stationary electron and a short wave of light. Just as in billiards, when the cue ball strikes its target, the light wave transferred some of its energy and momentum to the electron. This is exactly what happened in Adams and Day’s experiment: sufficiently energized photons radiating from the candle’s flame struck electrons in the selenium. They transferred energy and momentum to the electrons. Science defines electricity as the movement of energized electrons. After the Compton Experiment, the reality of Einstein’s photon and the photovoltaic effect gained universal acceptance in the scientific community.”
From Physics to Applications: How Solar Panels Turn Sunlight Into Electricity
Jeff McIntire-Strasburg states a pool table serves provides a a good metaphor for the type of chemical/physical action that takes place within a solar cell. When the sun “shoots” a photon into the top layer of the cell, that layer has been infused with phosphorus to set electrons free from silicon atoms.
“Those photons strike the electrons, and knock them into another layer of silicon that’s been “doped” with boron,” he writes. “This chemical composition creates an absence of electrons: these are the pockets at which those electrons are aimed.
“The movement of particles between cells creates an electric field: the phosphorus layer becomes positively charged, and the boron layer becomes negatively charged. The electric insulating quality of the silicon helps maintain this field. The field provides order to all of this chaos, driving the particles into a moving current.”
His conclusion? “This is the photovoltaic effect in action: essentially, sunlight uses its own particles to set electrons in motion.”
Remember, photons require light to exist. The solar panel array must have completely unblocked sunlight available for it to work.
Solar Heating & Cooling (SHC)
These technologies generate thermal heat energy which is used for water, pool, and space heating. Such systems have also been used for hot water heating. SHC technology can also be used for cooling. Solar heating technologies provide cost-effective solutions for people in a variety of climates. We will write more on this technology later.
Concentrating Solar Power (CSP)
Using reflective materials like mirrors and lenses, these systems concentrate sunlight to generate thermal energy, which is in turn used to heat water and produce steam to turn a turbine which can generate electricity. Similar to traditional power plants, many CSP plants are hundreds of megawatts (MW) in size and some can continue to provide power after sunset. To get more information on CSP visit here.