Design Off grid Solar Photovoltaic System to Generate Electricity

With simple, brief and accurate method, Many People ask me about how can they feed their homes or commercial buildings with electricity from the off grid solar photovoltaic system . Kindly permit me to introduce you the answer in six steps as following:

 Step one: Calculate load kWh requirement for DC and AC electricity per day and indicate battery days of autonomy required by customer, which mean the number of days that our electrical load can be fed from batteries without the aid of the solar radiation

 Step two: Divide kWh for AC electrical load on inverter efficiency (let it 0.90) and add the result to kWh for DC electrical load then divide the result on 0.85 (efficiencies of batteries and charge controller), so the result is DC kWh that required from the solar photovoltaic array per day.

 Step three: Divide DC kWh required from the solar photovoltaic array which resulted from step 2 on sun hours per day for the location of the array (city and country), let it 5 hour for Egypt country , you will get minimum  DC kW required from array, select module power and calculate Isc & Voc incase of parallel and series modules connection. But try to select connection that will introduce low electrical current in order to reduce electrical losses

 Step four: Charge controller is a DC to DC converter and its selection is depending on photo voltaic array current and voltage. Voltage and current of array (Isc, Voc) mustn't exceed the voltage and current max input ranges of charge controller in order to achieve MPPT (maximum power point tracking). Charge controller specifications are briefly comprise (max current, max voltage, operational voltage (24/12 v) and if it precedes MPPT or not).t

 Note:charge controller have (2 inputs) from the solar photo voltaic array, 2 outputs to DC load continued to the 2 inputs to the inverter , 2 outputs to the batteries and it's duty is to regulate charging and discharging of the battery. Usually the output voltage of the controller is 12/24 V

 Step five: Select any battery spec and start to determine AH (ampere hours) of the batteries by dividing total daily DC kWh required by the total load on (battery depth of charge (let it 0.6) * controller charging voltage 24/12) and multiply the result by days of autonomy, for example let it 2 days

 Hint: AH of the total series batteries is the same for the one battery but if the batteries are connected in parallels, AH of the totals is equal to the sum of all. Also Battery depth of charge 60% mean that you can get 60% of battery charge without affecting its life time or its safety

:Step six : Indicate minimum inverter power rating, it will be depending on the AC kW load and equal to (AC kW load / efficiency)

At the end if you want to design off grid solar photovoltaic system to generate clean and reliable electricity, you can simply precede the six steps mentioned above and I will be very happy to answer your question and inquires.

How Can Solar Cell Work to Generate Electricity ?

As we know that solar cell is a semiconductor material that converts light to electricity, this semi conductor material may be silicon or gallium or cadmium telluride but the crystalline silicon solar cell is the most commonly used to generate electricity representing 95 % of the market share.

How solar cells work?

Regarding crystalline silicon cell, the silicon atom has 4 bonding electrons at the outer shell and all silicon atoms is connecting to each other by sharing electrons to complete the outer shell for each cell to 8 electrons and hence the result is silicon lattice.

To generate the solar cell we introduce impurities (doping atoms) into this silicon lattice to form to type of crystalline silicon:

Type one called : N- type silicon : impurities are phosphorus atoms with (5) electrons in the outer shell so we have one electron more for each connection between one silicon cell and one phosphorus cell so at N – type crystalline silicon we have abundant of negative electrons.

Type two called : P- type silicon: impurities are boron atoms with (3) electrons in the outer shell so we have one electron less (hole) for each connection between one silicon cell and one boron cell so at P – type crystalline silicon we have abundant of positive holes .

If we bring p-type silicon layer together with n-type silicon layer a p-n junction is formed, at this junction the abundant electrons and abundant holes will start to diffuse in opposite directions to each other but fortunately some positive charge atoms remain at n-type layer (at transition region) and some negative charge atoms remain at p-type layer (at transition region), this create a region known as space charge region with an electric field that opposed to the movement of the transition and that result in stopping the diffusion of holes and electrons.

If the solar cell two contacts are externally connected to each other by an outer electrical wire the electrons will flow in wire generating electrical current in the condition that it will be enough energy to motivate electrons.

Now if the solar cell (p-n semiconductor) is exposed to the light (input energy) photons and electrons diffusion will occur and the space region will formed and hence a voltage will present on the solar cell contacts and if the electrical circuit is closed , the current will flow…this process as whole is called photovoltaic which mean converting sun light to electricity.