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.

Photovoltaic Solar Systems Types & Germany practice

The most developed method to generate electricity from renewable energy sources is photovoltaic solar systems.

There are two types of photovoltaic systems:

(1) Stand Alone System: at this type the total electricity generated from the solar photovoltaic panels should meet the demand at all times during the day. But this is impossible since we haven’t sun at the nigh, So PV systems should be supported by either two means:

First: by additional electricity power source like wind turbine, diesel generator or cogeneration engine. This type is called photovoltaic stand alone hybrid system.

Second: by a storage systems (batteries). This type is called photovoltaic stand alone with storage system.

(2) Grid connected system: at this system PV panels work in parallel with the public electricity grid in the condition that in case of grid electricity outage, PV panels will automatically switched of until the electricity of the public grid is returned back.

Germany Experience:

Germany consider as a leading country in using PV systems. Most of PV systems present in Germany are of the type grid connected system which present all over residential, commercial and industrial sectors due to the premium feed-in tariff  as all the energy generated is fed to the public electricity grid . Germany government predicts that after 30 year one third of electricity power supply will be generated from photovoltaic systems.

We hope that all countries will do like Germany government does in order to meet the increasing demand of electricity.

Why Solar Electricity?

Friends, all of us now that we can generate electricity from the solar energy by two means, the first one is by photovoltaic systems (PV) which convert the sun radiation directly to electricity and the second one is by solar thermal energy systems (CSP) which convert the solar radiation to a thermal energy then to electricity .   In the year 2020 the installed power of solar energy systems used to generate electricity will exceed the installed power of hydropower, wind and nuclear systems which used also to generate electricity.

Of course it is a matter of time until solar electricity will be the number one of electricity generation technology, let us see why ??:

First:

Solar radiation is available at all places on the earth and in a high abundance as the amount of energy that arrives to the earth is about larger than ten thousands times the total energy required for all the humans .In the same time solar energy is the largest energy source available of renewable energy sources.   

Second:

Solar electricity is a clean electricity generation source, so no environmental side effects which lead to dangerous earth warm due to green house gases.

Third:

For solar photovoltaic electricity systems there will not be a high cost of maintenance and operation. They represent a fraction comparing to other fossil fuels electricity generation systems cost.

Fourth:

Building anew renewable energy plants like hydro or nuclear and even fossil fuel plants require large investment. In the same time using photovoltaic system can be installed decentralized i.e., every one can use its building roof to install PV system and generate electricity for its home need and when he needn’t this electricity , he can buy it to the electricity utility . By this mean, we can face our increased requirements of electricity without the need to such high capital cost required to establish anew electricity power plant.

We believe that solar electricity is the coming revolution that will change our electricity generation landscape especially photovoltaic solar electricity systems that will be the force behind this revolution due to its high growth rate in most of world countries.