Off Grid Solar Systems Design:The Beginner’s Guide in 2018

Off Grid Solar Power Systems Design:The Beginner’s Guide in 2018

The off-grid solar system is an array of solar power components meant to run daily operations of electrical devices in absence of electricity. A similar array of solar power is the use of grid-tie solar systems; systems that are required to run electric appliances whenever utility grid is not supplying power.

The grid-tie system is connected to the utility power source and works interchangeably with electric main grid power by having an auto-switch that automatically starts the grid-tie when utility grid is off.

The layout of off-grid solar power is one which is completely disconnected from the utility grid and makes available all needed electricity without extra costs. In other words, the off-grid solar system is a completely stand-alone solar power system that can run all appliance in the house without connection to the main grid power supply.

So, How Do these Solar PV System Work?

Basically, off-grid solar systems operate from a stored electromotive force (e.m.f) in lead-acid solar batteries or battery banks. The stored e.m.f, is obtained directly from photovoltaic solar panels that are erect high up above the ground to capture radiations from the sun then convert to current that is used to charge the battery bank.

The size of the panels to be used is directly proportional to the amount operational voltage required by the consumer. All power supplied for consumption is solely obtained from this battery banks and connected through the normal wiring network. The power can then be supplied around the house for both lighting and sockets.

The components that are used for off-grid system are all similar but with different ratings. These basic components are: Solar Panel (also called PV panel), a power inverter, a charge controller and a battery bank (mostly, lead-acid solar battery). The components should perfectly fit for the whole system to work. Other required components include: Copper wire, monitoring meter, circuit breaker, and fuses. See the diagram below.

Fig. 1. A picture of the off-grid solar system obtained from www.sunvalleysolar.com/au/off-grid-system/

Each of the secondary components stated above have their specific use and the reason they are secondary is because their requirement is not mandatory in the work ability of the off-grid solar power design. The meter is needed to monitor the levels of current flowing through the system so as to moderate it.

The circuit breaker is necessary in controlling over-voltage since it will just switch off the power supply immediately it detects over-volt or under-volt while the fuses will be needed to completely disconnect the power when the current flowing in the circuit is way below the circuit breaker voltage rating but above that of the connected electric device, say a TV.

Load Assessment

Mounting any off-grid solar connection is done carefully to avoid over-voltage and damage of electrical components. The initial step is calculation of the load, that is, the sum total of the current required by all the electrical devices in the house depending on their current/voltage ratings. There are a few guidelines that should be considered when calculating the load which include:

a. The appliances to be run such as TVs, lighting, fan and fridges, and how long they shall be running in hours based on their power ratings which are shown on specification charts of the appliances.

b.You also need to calculate the Watt hours for each appliance and take the sum of the Watt hours for all devices to be run by the power system. That way, you shall know the total voltage required. The calculation of Watt hours is: Rating x number of hours it shall run e.g. 300W x 15hours = 4500Wh = 4.5kWh. Use this calculation for all other appliances and take the sum by adding the resulting product of each calculation.

These load will determine the battery bank rating to be chosen bearing in mind that the DC power produced by solar panels can only be generated during the day. Furthermore, solar panels do not have constant voltage since the amount they generate depend on the sun light.

Stand-Alone Solar Power Systems Design

The solar power design is basically a connection that runs from the PV panel itself to the battery bank connection and around the wiring system. The wiring system done in the house resembles the one from the main grid with main difference being the gauge of the wire used. The main power is drawn from the batteries connected whether is series or parallel depending on the desired output based on the load. The picture below shows the connected system.

Fig. 2. A picture of off-grid solar systems design retrieved from https://salembenmoussa.blogspot.com/2016/02/off-grid-solar-power-systems.html?m=1

The picture above shows the diagrammatic flow chart of the connection design. This design encompasses the main PV panels whose connection leads go through the charge controller, for current/voltage control. The solar panels absorbs solar energy radiations directly from the sun, converts them into electrical energy. The cells of the solar panel are photovoltaic, hence their sensitivity is limited to the daytime solar radiation. In this stand-alone off-grid solar design, the charge controller is self-controlled and it ensures that there is a constant, non-varying direct current (DC) power flowing. The connecting wires from the charge controller are directed to the battery bank whose terminals are arranged depending on the output voltage required.

From the battery, the connecting leads are attached to the power inverter, which is as the name suggests inverts the power from dc format in alternating current (a.c) format. The same inverter steps up the obtained power from 12V a.c, either 115V or 240V a.c which is enough for domestic consumption. The inverter has the capability to run for long and therefore once connected there is no worry of overheating or failure. The inverter now leads the power to the service box, also referred to as circuit breaker box. The breaker actively terminates power flow to the loads whenever power is more than sufficient and can pose a danger to the connected components.

The final leads are the ones emanating from the circuit breaker and headed to the loads. For a house wiring system, it is advised that one should connect the wires from the circuit breaker to the wiring main switch. The main switch can then supply the power to every lighting and sockets connection. However, if one does not have the main switch wiring network, power from the main breaker panel can be connected to extension sockets for direct usages.

Conclusion

The shift, from main grid electricity connectivity to green power is an inevitable phenomenon across the world. As the electric bills are becoming huge and unbearable, many people are turning into installing permanent solar panel power systems that have an initial cost and no bills to be paid. The green energy has also a lot of health benefits since it is purely natural, it has no pollution to the environment and it is highly renewable. The design of the power system that is easily adoptable is the described in this article.