On my social media pages, I posted recently about how sunny it gets in tropical regions during dry season, and how I can’t seem to understand why we still can’t have regular power supply. In the past few weeks (precisely 4 weeks now) I have not had electric power supply from the national grid. I was told it has something to do with the transformer and we are to pay so it can be fixed. As if that was not enough, the days has been cloudy recently too (of course we are the raining season), so my solar system has been of little help. This has affected a lot of the things I needed to do including writing here on steemit.
I live in Nigeria (Africa), a developing country marred with so many challenges. However, there are two primary challenges that are of particular interest to me. The first one obviously I will say is educational inequity and the second one, well electricity!
The government is doing so much with respect to these two challenges that we seem to be making little or no progress in these two respects. The citizens are left with no choice than to provide electricity for themselves and I am not left out of this web. I installed a small solar system (actually costing me my total salary for 3 months) due to some personal preferences for solar electric power generation. According to my estimation, although buying a generator as commonly used by many would cost me just a fraction of the money I spent on the solar system, but on calculating the cost of running a generator and fueling it for one year, I realized I would have spent even more than the cost of installing a solar system which has a durability of at least two years.
Well, I am no here to discuss politics or make Nigeria look like the worse country in the world. Every country has its own challenges and I can say of a truth that educational inequity is a global issue.
[image credits: Wikimedia commons under the Creative Commons CC0 1.0 Universal Public Domain Dedication]
The world is also in a quest to get the best out of renewable energy, and in my opinion I think solar energy holds the key to meeting the world’s energy demands. Solar energy is potent for its many uses. However, I will be discussing off grid electric power generation from solar energy, focusing on solar PV system.
The Earth gets more energy from the sun daily than the entire population could use up in a day. So why is solar energy not at the fore front of electric power generation? Before I discuss the advantages and disadvantages of solar electric power generation, I will like to delve more into it so we can all be conversant with what it is all about and the system works.
Simply put, solar energy is the energy generated from the Sun. this energy is harnessed by various technologies such as solar thermal, solar photovoltaic, which forms mainly the technology used for solar electric power generation. Solar photovoltaic (PV) has become very popular in recent time. It has now gained application in the use for the generation of electricity to power homes, commercial buildings, and even cities.
The Sun has been here for quite a long time now (billions of years ago), and will still continue to be here for a couple more billions of years from now by scientific estimation.
Solar electricity is now commonly generated with the use of Photovoltaic cells. Arrangement of photovoltaic cells in cascade is called a module. Photovoltaic cells convert the energy from the sun into electric current which is then used to charge a battery (the storage facility for electricity) through a process known as the photovoltaic effect
Long ago, photovoltaic cells are mainly used to generate electric power for small devices such as calculators. I remember owning on of such calculators in the late 90’s. Nowadays, solar PV’s are not only used by homes, they are also used to generate electricity on a large scale.
Solar energy provides a clean, renewable and readily available source of energy. Its abundance in nature makes it of a potential long term and use. It is also free from political influence; after all, no politician can hold us to ransom claiming ownership and control of the sun.
Solar energy is also pollution free. Even every life on earth owes its existence to the sun. Today we are battling with the menace of climate change and global warming. This is caused by various factors including our energy sources. Solar energy reduces the cost of combating this menace. Solar systems also have the advantage of being cheap to maintain.
Solar radiation reaching the Earth is absorbed by land and ocean. Of course the ocean absorbs a large crunch of the radiation since the earth is vastly water. Solar PV absorbs sunlight and converts it to electric current.
Solar PV systems consist of three major components which I will describe briefly below.
Photovoltaic (PV) panel
[image credits: Wikimedia commons under the Creative Commons CC0 1.0 Universal Public Domain Dedication]
The first one is the Photovoltaic solar panel which comes in different power rating. There is 75W, 150W, 750W e.t.c.
So what does it do?
Solar PV’s traps light and heat energy it receives from the sun, which is then converted to electric current that is used to charge the battery. Solar PV’s are semiconductor material which captures the photons of light falling on it and turns the energy into electrical energy. When photons of sufficiently high energy hit the semiconductor, it transfers energy to free electrons from the valence band and as a result, an electric field is set up which causes current to flow in an external circuit. This is then used to charge the solar battery (batteries).
The battery
[image taken by me: [my apartment personal solar deep cycle battery]
Solar batteries are specialized deep cycle batteries which stored the electric charges supplied by the photovoltaic system. Unlike starter batteries like car battery, they are designed with the ability to discharge their total energy storage up to 75% which makes them suitable for solar power use. They are usually lead acid batteries. Nothing can be 100% efficient so is deep cycle battery. Some energy is lost in form of heat and chemical changes during the process of charging and discharging. The heat loss in the battery is mainly due to the internal resistance. Deep cycle batteries also have high efficiency. They also offer best power to price ratio. They are durable, and can last for up to 2 years. So, whenever you consider installing a solar PV system for your home or office use, ensure you insist on the use of deep cycle battery.
The Inverter
[image taken by me: [my apartment personal inverter]
A key element of a solar PV system is the inverter. The inverter converts DC to AC. Most of the electrical equipment/ household facilities use an AC power source. So the main duty of the inverter is to convert the DC from the battery to useable AC to power the appliances. Inverter comes in various capacities, depending on the intended use. For my relatively small PV system, I used a 1.5KVA inverter which puts a limit on the number of panels that can be installed for the solar system. So, my system can only take a maximum of 1050W solar panel.
Inverters have low voltage shut off which is mainly to protect the inverter from damage. The inverter should be connected to a charge controller to avoid over discharge of the battery which can damage the battery in no time. In my case, my inverter has an in-built charge controller. When buying an inverter, you can request for the one with an in built charge controller to save you some stress.
I know you might, by reading this article or even before now planning to install a solar system for a specific use. Before you do this, there are some factors you need to consider.
The purpose of a solar collector is to absorb and retain solar energy as much as possible and transfer it to storage. It must therefore have high optical efficiency. But all this will not be achieved if there is limited sunshine in your area.
So, first thing to consider is the sunshine hour you get. This determines the insolation an area receives in a day. Also, the angle of tilt of the panel to sunlight is very important. The Sun peaks between 12noon-3pm and you don’t want to lose getting significant energy this time. Costing is also an essentially important factor. You have to determine the load requirement before you can install an efficient PV system.
I am going to put you through solar PV design using my own solar system as an example. You really have to count your cost before going ahead with your installation.
My solar system is powered by 12Vdc, 150Wp (Wp=peak power) PV module.
Load Estimation
- Two 18W bulb used for 4 hours per day = 18×4 = 72Wh/day
- One 65W TV set used for 4hours per day = 65×4 = 260Wh/day
- One 60W electric fan used for 6 hours per day = 60×6 = 360Wh/day
- One 65W computer (laptop) used for 4 hours per day = 65×4 = 260Wh/day
Total load requirement per day = 952Wh/day
After determining the load requirement, it is now time to determine the solar panel needed for the system. Thus:
The total load estimation is multiplied by 1.3 to account for energy loss in the system. Therefore, the total panel energy requirement for the load will be:
952×1.3 ( factor for energy loss in the system)
=1237.6Wh/day
This is then divided by the Panel generation factor which varies for different location. The panel generation factor I used for Nigeria is 3.41.
Therefore, the total Wp of PV panel capacity required = 1237.6/3.41
=362.9Wp
Finally, the number of PV panels that should be installed is:
362.9/150
=2.4 (Approximately 2 PV panels, but using 3 will be a good idea)
(150W is the capacity of one PV panel used)
Inverter size
It is advisable that the inverter used for a PV system be larger than the total Watt of the load. In my case, a 1500W will do just fine.
Battery size
The battery size is also important. I want my solar system to serve for just a day. Of course I leave it to charge the whole day and only make use of it at night.
Nominal battery voltage = 12V
Days of autonomy = 1
Battery capacity = (Total appliances used × number of days)/ (0.85 for battery loss)(0.6 for depth of discharge)(battery voltage)
Therefore, battery capacity = 952/ (0.8×0.6×12)
= 165.27Ah
So, the rating of the battery should be 12V, 200Ah for one day autonomy.
I did not worry about charge controller since my inverter comes with an in built one.
In my experience so far, apart from cloudy days which has become prevalent this period (raining season). The PV system really meets up to my expectations.
Summary
Solar energy is an abundant source of energy that when fully harnessed could end the electricity crisis being faced by many developing countries of the world. Although the technology is still on the high side, especially for low- income individuals, I would advise government of countries to consider solar energy and make necessary investment in it, especially for on-grid electric power generation.
References
Solar Photovoltaic system design basics
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