My own Solar Power Plant – part II

My Solar Power Plant – Part II

In my first post, I’ve explained in brief about 100W solar power plant that I set up at my home. In this post, I’ll get a lot more technical in order to explain the issues faced by me after setting up the power plant. (This post is for electrical and electronics students). Here is the solar panel setup for your reference. And here is the raw dump of the log which I did while doing the experiment

#1 Resistance in the wires to inverter:

On the first day, I connected my laptop to the inverter. Here is the schematic for your reference. The battery lasted from 6:50PM to 10:40PM after which the inverter gave a low battery beep and shutdown. I checked the battery voltage and it was high at 11.72V. I thought that the inverter was behaving funny and needed to be checked. The next day, I charged the battery with the solar panels to full(or I thought so) and connected to the load in the night. I finally discovered the problem today. I was using fairly long wires to connect from the battery to the inverter(5m approx) and there was a considerably voltage drop on the wires about 1V! When the battery had 12.38V across it, the inverter had only 11.51 V across it! Measured the voltage at the battery as well as a joint I made with the wires from the battery and a wire from the inverter. Just look at the differences below!

Time Battery Voltage Battery voltage at joint Load type
18:59 12.38V 11.51V Laptop document edit+BB modem Download
19:20 12.32V 11.44V Laptop browsing + BB modem DL
19:47 12.22V 11.36V Laptop browsing + BB modem DL
20:14 12.14V 11.30V Laptop browsing+ BB modem DL
20:49 12.01V 11.12V Laptop document edit + BB modem DL
21:20 11.86V 11.10V Laptop most at rest + BB modem DL
21:42 11.82V 10.99V Laptop mostly idle + BB modem DL
21:53 11.78V 10.64V Laptop mostly idle + BB modem DL
22:11 11.71V 10.66V(!) Laptop browsing + BB modem DL
22:30 11.62V 10.50V Laptop video + BB modem DL
22:40 11.57V 10.46V Laptop video + BB modem DL
22:46 11.54V 10.44V Laptop video + BB modem DL
23:00 11.46 10.35V Laptop video + BB modem DL
Inverter shutdown as it detected a voltage of < 10.4V

If the load were heavier, naturally there will be more voltage drop across the reistance of the wires (V=IR!).

After this, I brought the inverter closer to the battery and shortened the connection drastically. The inverter was able to operate for some more time.

#2 Inverter self Load

I connected an ammeter (unfortunately an AC one which gave inaccurate results for DC) in the battery-inverter wires and found that the inverter consumes about 1A of battery current even while no load is connected. The laptop consumes another 2A and the total load is about 3A. Hence with laptop, 33% of the power(12W) is going to keep the inverter in operation.

#3 Resistance of the wires connecting solar panel.

In the third day I faced a similar problem with the wires connecting the solar panels to the battery. I hadn’t discovered this previously, as I did not have an ammeter then. The solar panels were supposed to give a current output of greater than 5A in full sunshine, but it was giving only 2A. On measuring the voltage generated at the solar panels(18.5V) to the voltage near the charge controller(12.5). I found a 6V difference while supplying 2A of current! Of course the wires were also bad – it was a single strand wire with the thickness of a pin, resulting in higher resistance. When 2 A of current was supplied by the solar panels, the voltage drop across the wires connecting the solar panels and the charge controller was 6V, meaning a resistance of 3ohms. The battery voltage was 12.5V volts. In order to supply more current, the solar panels has to increase their voltage, which is not possible without decrease in current. I then replaced the wires at 4PM and the current supplied by the solar panels considerably improved to 3A 🙂

Time Charging current Battery voltage
08:05 1.12A 12.25V
08:52 1.95A 12.40V
09:20 2.09A 12.45V
11:00 2.18A 12.66V
15:00 2.10A 13.01
16:30 2.96A 13.23V
17:00 1A

At 5:00PM, the solar panels came under a huge shade and it resulted in a drastic drop of output to 1A.

#4 Battery sluggishness:

Without knowing much about lead acid battery, I assumed that if I buy a 35Ah lead acid batery then with solar panels supplying 5A of current, I can charge in 7 hours. But I was wrong. The lead acid battery doesn’t like being force fed lot of food in a short amount of time. I went through the site www.batteryuniversity.com and found a lot about the battery which I previously never thought of. It seems that the lead acid battery charges in two stages:

Firstly (like a hungry person) constant current mode during which it takes in lot of currrent and charges upto 70% of the battery capacity. The rate of charge given by many manufactures is 0.15C where C is the Ampere hour capacity of the battery(so for my battery the safe limit is about 4.5A). This stage lasts for about 5-8 hours. The end of this stage reaches at 13.2-13.6V depanding upon the rate of charging and the battery voltage shoots up and has to be regulated by the charge controller to a safe voltage, typically 14.4V. This results in the constant voltage phase.

In the second stage, (like a person who finishes his meal) the battery operates in constant voltage mode where in the battery voltage is maintained at a safe limit(14.4V typical) by the charge controller/ regulator. The battery draws a smaller current that exponentially decreases from the value of constant current stage to zero. When the current drawn reaches 3% of the value, the battery is considered as fully charged. This stage is called “topping charge” and it takes about 60% of the time for completing 30% of the charge! This is important for the life of the battery else the battery will stop accepting full charge.

Thirdly, after being fully charged, the battery should be kept at “float voltage”. This is to compensate for the high self discharge of the battery which is 3-20% per month.

If one looks at the second stage called “constant voltage” stage, the solar panel output is not being used fully resulting in wastage. You cannot skip the stage either, because it will result in reduction of the battery life. I’m currenly doing a project to handle this problem: I want to design a charge controller that will charge two batteries: one battery with low state of charge at constant current stage and another battery at high state of charge in constant voltage phase. This makes sure that the solar panel output is utilized fully.

Any comments on this welcome!

(c) Solarii Knight 2012, some rights reserved Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 2.5 India License.

The Cuboid of God

I often encounter theists who argue over which God is true and supreme. Each have an almost convicing set of arguments which includes quoting from their scriptures and along with reasoning to convince someone about their faith.
Lets look at how God is viewed. Christians, Jews and Muslims view God as a super natural force who created every the universe and the living things in them. The Hindus view God as one true God worshiped in different religions under different names. Needless to say we can see the conflict amongst diffeent religions. Each holding their own God as true and other Gods as false.
Let me explain how I view God. Please look at the cuboid below. Imagine it being hung in a space.

 

 

 

 
If you see it from the front side, you’ll see a rectangle. If you see it from the smaller side, you’ll see it as a square. If you see it slightly tilted, you’ll partially see two or more sides.

My view of different religions is similar: each having a small understanding of God and no one has a complete understanding. However, some might argue their holy scriptures tell them to not worship other Gods. Its simple enough to think how that came: If you are a holy prophet who wrote a holy scriputre, you would only belive in what you saw and not what others saw  isn’t it? That will make you write explicitly not to follow others.

My own Solar Power Plant – part I

I made a major step in implementing renewable energy at home! I setup a small 100W solar power plant(if I may say so) at home. Firstly, I was motivated by my love for renewable energy and the need to reduce dependency on dirty coal energy. That’s been my childhood dream. I used solar energy because it was the easiest. (I’m explaining this to a person who knows somewhat about electicity but not about renewable energy). Here’s what I bought

1. A 40 W panel and a 60 W panel (INR 10,000)
2. solar charge controller (INR 1500)
3. Two 6A diodes to serve as blocking diodes while panels are in parallel.
4. A 12V,35Ah flooded maintenance free lead acid battery.(INR 3800)
5. An inverter (already had one, which cost INR 3.5k)

Solar Panels Image

solar panels - 40W front, 60W back

Battery, CC, Inverter

Battery, DC Ammeter, Charge controller (bottom) and inverter (behind battery)

Now that I’ve bought the inventory, I set about installing the system. I setup the solar panels facing the sun with the help of a few bricks to tilt it 8 degress towards south to compensate for the latitude of my place. I then connected the solar panels in parallel using a blocking diode in each of them to isolate from one another. Then I connected the battery to the charge controller and to the inverter. After that, I connected the solar panels to the charge controller. Here is the schematic in pdf

A charge controller is a device that takes the input from solar panel(17V rated) and feeds it to the battery at the appropriate level(<=14V). Charge controller also gives a DC output taking electricity from either the load or the device. Charge controller cuts off the input from the sun when the battery is fully charged and cuts off the load when the battery levels are too low.

Inverter is a device that converts DC power of the battery into AC power required by my laptop or any other device. I can either connect the input of the inverter to the output of the charge controller or to the battery itself. I choose battery terminals as I found inverter itself had the capability to cut off the battery from the load when the batter level was too low.

Now with the arrangement done, I put it into action! The solar panels absorbed the divine energy given by the sun and then transformed it into electricity, feeding the batteries! But here, the battery was already pre-charged in the factory shipped state and it did not take much time to charge it fully. Only about 2 hours. I decided to be cautious and not operate the inverter to supply the load during day. Hence, I waited for the night.

At night, I turned on the inverter and connected the laptop to it! It was so exciting for me know that my laptop was being powered by the sun! I was able to power the laptop for about 5 hours before facing some trouble. I will tell more about that in the next post. On the second day, I was able to power for another 5 hours, though the lead acid battery can power the laptop for nearly 10 hours. I’ve explained more about that in the next post, where I learnt a lot about the nature of the lead acid batteris that caused the problem. Until then, good bye! 🙂

NOTE: My next post contains more information for a person who’s an electrical engineer.

(c) Solarii Knight 2012, some rights reserved Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 2.5 India License.

Religion and Infallibility

We all need something – or someone always caring, prefect, all knowing and a friend. The most common such source is God. God is all knowing, caring and perfect in  all aspects. Men who had come across this supernatural force have always tried to understand God and they have written down or spoken their experiences with this supernatural forces. This has resulted in rise of various religions.

However, here’s the catch. Can men, whose powers are limited fully understand God? They may understand better than most, but its not full. If they are fully able to understand God, then they have to be equal to God. We know that is not true. Yet many follow holy scriptures like the Bible, the Quran or the Gita and each one assumes the one scripture  that they follow to be the ultimate truth. If we end up blindly following everything they say about God, we can be wrong in many ways – may be as wrong as the ancient men who thought that the earth was flat.

I believe that we might be able to understand a part of God which the religious Gurus like the disciples of Jesus Christ(or even Jesus Christ, but he never wrote a book so we don’t know!), Prophet Muhammad, etc never looked into. We will be able to understand God fully – only bits and  pieces but the journey will be exciting one as we will be treading on a path unknown.

Computers and Humans

I intend to express what computers means for humans

To me computers are devices that are meant ot assist humans in their work. They can do few things which humans can do, but much faster and more efficient than humans can do. For example, your computer can do tens of millions of calculations per seconds, while an average person can only do one addion in few seconds. Cell phones can carry our voices to someone very far off. If we were to do that we’d have to travel upto the place where the person is and then talk with them.

But there is are also things that computers can’t do. For example, omputers can’t feel anything. They don’t have hapiness, joy or sorrow. Also they can’t help is effectively in communicating the same over Internet. If we are make the person at the other end really know how we feel, we must meet them face to face. Also, computers can’t invent or think in new dimensions like us. A pentium 3 processor did not invent pentium 4, it was due to humans entirely.

I feel we must use computers to assist us in whatever we do and not entirely depand on it. We have more abilities than computers overall.

How Listening Helps

Today a person approached me with an issue in his computer.  His laptop’s touchpad was not working. He told that the had accidentally disabled it somewhere and was unable to enable it. I did not ask him further for anything more. Being a good solver of problems, I set out armed with my considerable knowledge on computers. I reinstalled the touchpad in his computer and it worked. However, when the computer was restarted once, the old problem returned again. This left me scratching my head. Now I asked him whether there was any way to enable/disable the computer’s touchpad. He said he did not know. I looked through the function keys of the keyboard and all of a sudden he said that the option to disable the touchpad came when he was trying to increase the volume of the computer. I looked at the volume increase button in the keyboard. Nearby was a function key combined with the touchpad symbol. I pressed that key and the option came up to disable the touchpad. I enabled the touchpad, thereby solving the problem permanently.

From this I learned that listening to others helps. Here, had I asked him more questions instead of plowing into solving the problem, I would have known exactly when the problem had occurred and solved the problem more quickly.