Off grid solar power systems or stand-alone systems are not connected to the electricity grid and typically are installed in remote areas where there is limited connection to the grid, or areas of low electricity demand. Unlike their grid-connected counterparts, these systems must have batteries or backup generation to provide supply at night. In many cases they will also include a diesel or petrol generator to supplement energy supply.
Stand-alone solar PV systems are solar panel systems that are not connected to the electric grid, they are completely separate and independent form the rest of the electric grid that utilize electric companies to provide them electricity. Typically this type of system is used in a remote location where there is limited connectability and low electrical demand. This type of location makes it difficult for electrical companies to establish a reliable and economical infrastructure. What sets a stand-alone system a part from its counterparts is the battery and backup generation. Essentially, this means that you are provided electricity 24/7. The system provides electricity at all times of the day and may even include a diesel (or sometimes a petrol generator) that supplies energy. The important thing to understand is that a stand-alone solar PV system can be utilized for both small and large homes as well as different sizes of businesses and even entire communities. Stand-alone solar PV systems are not one-size fits all.
A 24/7 Solar Power Solution
The ability to store all of the power generated so that you can use it when you need it – day or night. No feed-in tariff rates, no power bills, no connectivity to the grid. Your system!
It is not surprising that stand-alone solar PV systems are becoming so popular with the rise in electricity costs. Many rural homeowners can invest in their own solar panel systems and save money by producing their own electricity. They actually have more freedom because they become their own green renewable energy company. No longer having to pay an electric company service charges and high electricity bills is something quite refreshing for rural homeowners.
How Does it Work?
The photovoltaic (PV) solar panels are placed on the roof of your home, for example, the array converts the sunlight into direct current (DC) electricity which cannot be used by your home appliances. However, the inverter shown in the picture below is used to convert the DC electricity in to alternating current (AC) which can be used by your home appliances and electronics. The AC is sent to the house through a switchboard. Any excess electricity that is not needed is sent to the battery bank for recharging. If the batteries are full the inverter and charger will stop recharging the batteries. If the stand-alone solar PV system is not producing any electricity, the battery bank will be providing electricity to your home. If the battery bank gets low, the generator will then power the house until the battery bank is recharged.
Benefits of Stand-Alone Solar PV Systems
There are many benefits to owning your own stand-alone PV system such as the ability to cut off owing an electric company a bill every month, remote locations where it is cost-prohibitive instead of having electric lines added, and you are not subject to any regulatory regulations or rules like your electric company is.
Components of Stand-Alone Solar PV Systems
Most stand-alone Solar PV systems will include the solar panels either in a field or roof setting, the panel combiner box with a DC disconnect, breakers, a surge protector to protect the system, and of course ground-fault protection. A wattage meter will be needed along with a charge controller to prevent the battery from overcharging and causing major damage to the entire system. Last, the system will need special high-capacity batteries that are meant for storing the power generated from the panels.
Installer And Designer Accreditation Required
Stand-alone solar PV systems Installers and designers need Clean Energy Council stand-alone accreditation
For an overview of all types of solar power systems read here.
Below is an article that delves into more depth about off-grid solar systems.
This article aims at informing the reader of the numerous social and environmental benefits that Off-Grid Solar Systems have in rural communities. As well as outlining the physics of how these systems work the article outlines the key advantages and disadvantages these systems have. Although parts of this article focused on the solutions Off-Grid Solar Systems provided in developing countries, the range of solutions these systems can solve is extremely broad and versatile.
What is an Off-Grid Solar System
Any electricity system that uses photovoltaic cells to convert the suns heat into electricity and that is not connected to the electricity grid is defined as an: Off-Grid Solar System. Of course, this just means that if you have a Sun in your area (earth has a sun!), a Solar Panel (which harvests energy from the sun), a Battery (which stores the energy, to be used later) and a Solar Inverter (which converts DC into AC current, which I´m sure from physics class you will remember, is an alternating, grid-compliant current) then you have an Off-Grid Solar System. They are common in rural areas where there is no access to a functioning power grid or limited and poor access.
How Does an Off-Grid Solar System work?
There is a degree of complexity involved in the conversion of light to energy via a Photovoltaic (PV) cell. The PV effect is a physics phenomenon that describes the conversion of light to electricity in PV cells. It is impossible to explain in complete depth how this process works, however if we take just the example of a silicon cell as a model we can understand the groundwork of a PV cell.
Silicon is an element, you can find it on a periodic table. It has an atomic number of fourteen. This means that it has fourteen electrons arranged in such a way that the outer four can be given to or accepted from, or shared with other atoms. Because of the electronegativity of silicon, copious amounts of the atom can be bonded together to create a solid. Because each of these solids is bonded together, the silicon shares its four electrons with other silicon solids. This creates a tetrahedral arrangement containing five atoms (the one silicon atom plus the four others it shares electrons with). This regular fixed formation is called a crystal lattice. A silicon crystal lattice has atoms that are located to form the vertices of a cube, this is shown below (Zweibel K and Hersch P, 1984).
When light strikes three things can occur. It can be absorbed, reflected or pass through. Let us focus only on what happens when this light is absorbed, but just know that not all the suns heat energy is utilized in a solar panel and just like any energy source technological improvements can be made to minimize these shortcomings.
When light is absorbed by the silicon, it causes this crystal lattice to bend and vibrate (as energy is added). The electrons in the bonds also gain more energy, the electrons cannot escape and so give off this extra energy as heat to return to their original position. But when light of greater energy attacks the crystal lattice, the electrical properties of the crystal can alter (Komp, R.J, 2002). This leaves behind a silicon bond missing an electron, and frees an electron to move about in the crystal. This (bond without an electron) is called a hole. An electron will often jump to fill this hole, leaving another hole. This happens randomly and erratically throughout the solid. The higher the temperature of the material the more aggravated the electrons and holes, and the more of them there are. We use these holes to produce an electric force, this is called the Potential Barrier.
To explain as simply as possible: A PV cell contains a Potential Barrier. A potential Barrier is set up opposite electric charges that face one another. The potential Barrier sends more electrons to one side of the cell, and more holes to the other (Hantula R, 2010). This sets up a voltage difference between either end of the cell, see the image below.
The black line shows the Potential Barrier, just imagine that yellow is positive and green is negative (protons and electrons respectively). This separation creates a voltage. The next step is that we add a negative-dopant (also called the donor). A dopant is an impurity, such as an added phosphorus atom. Basically, we can create a Potential Barrier by creating a dopant and a dopant is just used to alter the silicon by introducing a ´donor dopant´ to produce an internal potential barrier (Phosphorus was chosen as an example because it has 5 valence electrons WHICH IS ONE MORE THAN SILICON). So, repeat this process now with an atom that has one less valence electron than silicon. Thus, we have just added the positive-dopant, such as Boron (Zweibel K and Hersch P, 1984).
Before we move on let’s define two things:
A P-Type Material:
A material where positive charges (holes) are the majority because they far outnumber any free electrons.
A N-Type Material:
A material where the negative charges (electrons) are the majority because they far outnumber the holes.
So, if we put a P-type material and a N-type material together you may have already been able to predict the nature of the reaction. The electrons will jump to fill the holes, this happens on both sides of the material (remembering that they aren´t literal holes that get filled e.g. a hole can just move to the other material, not necessarily be filled). What you might not expect is that although a charge balance exists, there are very few free electrons on the P-type silicon and very few free holes in the N-type material. So, the charge imbalance stays fixed in place. Where the N and P silicon meet is called the P-N junction.
The charges that cross this junction create an electric force. As more carriers cross the junction the force in enlarged, this makes it harder for other carriers to cross and eventually and equilibrium is established. This creates a fixed potential barrier at the junction (The barrier referred to earlier).
How does this create Solar Power?
A conducting wire is used to connected the P-type material to a load, usually a battery the conducting wire will then travel from the battery to the N-type material forming a complete circuit. As the electrons are pushed into the N-type material the electrons move away from each other because they are of similar charge (Komp, R.J, 2002). This wire provides a path for the electrons to move away from each other. This flow of electrons is an electric current and an electric current can be used as electricity. Finally, to increase efficiency a solar cell will usually have a metallic grid to collect electrons from the semiconductor and transfer them to the external load. The image below shows the P-N junction of a typical solar cell (PV cell).
The Solar Invertors function is to convert the direct current (DC) into alternating current (AC). This is important because mathematically a DC circuit is of no use to us. An AC circuit provides a voltage that varies in a sinusoidal manner. The current in an AC circuit is thus oscillating in both direction and magnitude. Because of this oscillation it becomes dramatically easier to transport energy than it would be in a DC circuit, although with new and better semiconductors being invented high voltage direct currents are starting to become more popular. But to put simply, an AC circuit can be stepped up and down in voltage at a cheaper price than DC at this current time. This is because in the laws of electromagnetism, when a magnetic field changes a voltage is created. This is a simple principle to explain. Imagine that you are to construct a machine that rotates a magnetic field about a set of stationary wires while turning a shaft.
Alternator Operation in AC
The polarity of the voltage across the wire coils reverses as the opposite poles of the rotating magnet pass by. Connected to a load, this reversing voltage polarity will create a reversing current direction in the circuit. The faster the alternator’s shaft is turned, the faster the magnet will spin, resulting in an alternating voltage and current that switches directions more often in each amount of time. Hence why AC is more efficient than DC circuitry (cheaper). Therefore, the Solar Invertor is fundamental in the process of creating an energy source that can be used efficiently.
The switchboard is simply a device that optimizes where the electricity goes when it is in your house. The switchboard directs traffic to certain appliances and can be used to control which parts of a household are solar powered (if not all). Any excess of energy is sent to the battery where it is can be used later, this is particularly useful when the climate is not producing an acceptable amount. Some Off-Grid systems will utilize a backup diesel generator in these circumstances.
The Final Product
The image below shows the processes of an Off-Grid Solar System.
Off-Grid Solar System in a Rural Household
Advantages and Disadvantages of Off-Grid Solar Systems
|· Photovoltaic systems are well suited to off-grid electricity generation applications, and where costs of electricity generation from other sources are high (such as in remote communities) (Australian Energy Resource Assessment, Page 261).
· A low-cost solution to decentralize a power supply (easy to take Off-Grid because they can be used everywhere).
· They require few resources and help combat climate change.
· Off-Grid Solar can aid developing countries bypass the fossil fuel era.
· No noise is produced in the operation of this renewable energy source (Assuming no diesel backup generator is used).
· The solar panels can shield and insulate roofs from the suns heat. They have high power-to-weight ratio (Kadar, 2014).
· PV cells are made from silicon, which is a highly abundant resource (U.S Department of Energy, 1982).
· A rough optimistic estimate by the University of Colorado stated that solar can supply 30% of domestic energy needs within a decade.
· New technology continues to produce more efficient solar panels at a more economical cost.
|· Solar radiation is intermittent, meaning that because of daily and seasonal variation they are not always at peak efficiency. A secondary power source may need to be used in these situations.
· If the system is not used regularly the electrical battery may wear out.
· Although the cost is low, the families who need access to Off-Gird Solar would typically be of lower income and thus the cost may be unmanageable, particularly in 1st world countries where the cost is inflated because industries optimize profit rather than community and environmental advantages (HushEnergy, 2017).
· Not all homes are optimized to benefit from solar panels as effectively as others, just as not all areas of the world are as effective at generating solar energy.
Why are Off-Grid Solar Systems Important?
In remote towns and urban community centers the access to an affordable grid connected energy system is not always possible. Electricity is a fundamental component to our high standard of living, electricity is used to pump water, generate warmth and provide lighting. Communities without access to an electrical grid suffer from a crucial lack of the essential and modern needs that electricity provides. In these rural communities, many attempts have been made to install Off-Grid Power Systems to enhance the standard of living. In recent years an affordable solution to the electrical-grid problem has been the installation of Off-Grid Solar Powered Systems.
Developing countries such as India and China have large rural slum communities, and often their houses are ‘lit’ by kerosene fueled lamps. The Health Protection Agency published in 2006 a report compiling the effects these kerosene lamps have on individual health. They state that: along with ocular and dermal issues inhalation of the chemical causes headache, drowsiness, incoordination and euphoria (HPA, 2006). Many social organizations challenge this increasing problem by providing communities with Off-Grid Solar Power. Pollinate Energy is a social organization that has provided clean energy to over 880 communities in India and is estimated to have saved approximately 6.5 million kg of CO2 emissions just by replacing kerosene lamps with small scale solar powered lights (PollinateEnergy.org, 2017).
The lack of safe drinking water in developing countries has been in recent years another major challenge. One Tenth of the world’s population is without clean drinking water. However Off-Grid Solar Systems have been utilized to tackle such an issue. One type of Off-Grid Solar system for example is the Solar Still. The materials needed to build this water purification system are estimated to cost only $1.60 (for a system that can purify 1 liter of water per hour). Researchers at the University of New York stated that this was four times faster than a regular commercially available water purification system (Robert Service, 2017).
Besides providing solutions to specific sets of problems in the 3rd world, Off-Grid Solar Systems have can be used to power entire villages and communities. The image below highlights how a Central Off-Grid system can provide energy to an entire remote community.
A large scale solar panel is connected to a battery bank to store and accumulate energy so that the community can share a centrally controlled power supply. There are clearly paramount benefits to using solar power not only regarding economic efficiency, but also environmental sustainability. Health, education and clean drinking water are all dependent on electrical power. Rural communities will often attempt to use diesel generators and transport copious amounts of fuel to generate them, however with the added and increasing cost of fuel transportation these systems are not efficient in solving these solutions. But, Off-Grid Solar Systems are and our ability to utilize them has always been in our reach, it is just a matter of supporting largely positive change.
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Websites and Journals:
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Kádár, P. (2014). Pros and Cons of the Renewable Energy Application. Acta Polytechnica Hungarica, [online] 11(4), p.14. Available at: https://www.uni-obuda.hu/journal/Kadar_50.pdf [Accessed 22 Jun. 2017].
Michael, K. (2017). Presentation from the 2014 World Water Week in Stockholm. [online] http://programme.worldwaterweek.org. Available at: http://programme.worldwaterweek.org/sites/default/files/kuteesa_solar_energy_secures_safe_drinking_water_for_school.pdf [Accessed 22 Jun. 2017].
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Service, R. (2017). Sunlight-powered purifier could clean water for the impoverished. [online] Science | AAAS. Available at: http://www.sciencemag.org/news/2017/02/sunlight-powered-purifier-could-clean-water-impoverished [Accessed 22 Jun. 2017].