Archive for the ‘Renewable Energy’ Category

500W Solar System

Last year, I made a 100W solar system. The system was good enough in the end only to power up a 12W LED tube for 6 hours. Add to the fact I broke 40W out of the 100W because I didn’t mount it properly. So this year I decided to go big to power something significant, which happened to the LED lights at the reception in my mother’s hospital. My primary motivation for setting up a solar system has and will always be to combat Global Warming. Secondary motivation is that it’s fun to generate your own power.

I had already made LED lights for the hospital’s reception with the foresight of mixing that with a solar system. There were about 10 LED downlights totalling to 110W of which all lights had to remain powered on for 3-4 hours in the night and 2 LED downlights totalling to 18W had to remain powered on for the remaining 8-9 hours. Added to this is the 40W LED floodlight that remains in operation for 12 hours, taking the total energy requirement to 1080Wh of loads. I decided on 500W,24V system which generates approximately 2000Wh per day. The excess power compensates for inverter losses and previous dull days. Here are the panels, in my roof:

 Two 250W Panels (60 cell)

Two 250W Panels (60 cell)

I bought the 20A PWM phocos charge controller to charge batteries of 24V,150Ah that can store 3600Wh ideally, but practically only 2800Wh can be used. The batteries are Su-kam tall tubular make and turned out to be a bad choice as well as a bad product. Firstly, they only gave a capacity of 75Ah. I think it was due the fact that battery was 3 months out of the factory when I bought it and lead acid batteries may not survive without degradation for that long. Additionally it seems normal tubular batteries cannot survive solar application. Within 2 months, the battery regressed to 50Ah and I had to replace them. I ordered and bought 2 Nos of 150Ah Exide Solar tall tubular battery. This battery, which has the ability to go long periods in partial state of charge, has turned out good so far, though I haven’t pushed the battery to full discharge and see its capacity.

The inverter I chose initialy was 1500VA,24V su-kam shiny UPS and not a solar hybrid inverter as I wanted a separate charge controller. But this turned out to be a bad choice too, as the inverter has 36W of self consumption losses and more importantly it did not have no load shutdown feature, which means someone has to manually turn off the inverter whenever there is no load connected in the output. I looked for a new inverter. I didn’t want an inverter with bulky iron core transformer as it was heavy and decided to try a inverter with high frequency transformer. I bought 1KVA,780W Sinex Solar PCU by Electronet Systems from GoGreenSolutions. It turned out to be fair. This solar inverter (aka solar PCU) has an no load shutdown and automatic wakeup feature. It has an disappointing self consumption of 24W when in operation and 6W when on standby mode, but still better than the pervious one due to no load shutdown. It is light and weighs 4.5kg, unlike the previous one that weighed 16Kg. It has poor dynamic characteristics, but since the load is LED lights that have SMPS and my laptop which has SMPS too, it is not a problem. But my desktop which I rarely use turns off when I subject the inverter to a new load. The inverter has an good fan control that varies depending on load.

Sinex solar PCU and Exide Solar tubular battery

Sinex solar PCU and Exide Solar tubular battery

Now for the overall power consumption of the system. The total energy requirement is 1080Wh, but inverter efficiency is 90%, taking the consumption to 1188Wh. Additionally, the inverter has self consumption of 24W for 12 hours and 6W standby for 12 hours adding upto 1548Wh. The power generation during a sunny day is 2000Wh and hence there is a surplus of 450Wh that can be used to compensate for dull days. The battery has a Depth of Discharge rate of 45% (1548Wh of 3600Wh) and manufacturer Exide claims that it can last for 3000 cycles(8.21years) at this Depth of Discharge.

The system serves well powering the reception lights of hospital. It is most useful during the time between power cut and when generator is turned on or when generator is down due to technical problems. The hospital does not remain in total blackout.

Economics of it

Two nos of 250W solar panels = Rs.27500

Charge controller = Rs. 3000

1KVA,24V Sinex Solar PCU(pure sine wave) = Rs.10200

Solar panel Mounting = Rs.4500

30m 4sqmm copper wire = Rs.1200

2Nos of 12V,150Ah Solar Tubular Battery = Rs.31600

sub-total = Rs.78,000


Su-kam Shiny HUPS = Rs.10000

2Nos of 12V,150Ah Su-kam Battery = Rs.30000

Grand Total = Rs.1,18,000

Overall the system cost is Rs.78,000. Generating 1.5 units per day and operating for 8 years with no failure, it translates to Rs.17.8 per unit (excluding cost of Investment). However, if I can find ways to reduce the cost of the system, especially by consuming the generated power instatnly, then I may have an answer to my mother’s hospital’s Diesel generator, which operates at 8-12 hours per day, producing power at Rs.20 per unit.

LED lights and Solar system mix

The use of LED lighting reduced the system size by 50%. Had I used CFL downlights and halogen floodlight, the system would have been atleast twice the size, costing an additional Rs.78,000. The cost incurred for the LED lights were Rs.23,000. So I realized that whem I’m generating my own power, every Watt hour of energy saved matters.

An audacious plan for the Future

I live in a state where power cuts are frequent and lasts upto 12 hours per day depending on the time of the year. Upto 50KWh is supplied for 12 hours by Diesel Generator. Currently the generator in my mother’s hospital produces power at the rate of Rs.20 per unit approx. That’s higher than what I acheived with my solar system. If I can make a big system that cuts costs then I might be able to bring down the cost of electricity supply while making the hospital contribute less to climate change.

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Economics, environment and the disjoint – I

We have a problem here. A serious one. Select a tree in your house and ask a employee from a sawmill: what would be the cost if he were to cut the tree and sell it for you? He’d say Rs.X for the sale and Rs.Y for the cutting charges etc. And that’s the value of the tree. Now ask him or anyone else: what is the money value of the benifit to the society if it were to be left alone. You will be left with blank stares. We have learnt that the most important function of a tree is to take in carbon dioxide and provide oxygen, which is responsible fot the life of the entire animal kingdom. So what’s the money value of that? The answer is that we simply didn’t consider that in our economics. Our economics only cared about consumption of the tree for producing goods or clearing it to make way for cities. And that narrow mindedness is where we’re having trouble when dealing with environmental issues. Economics simply hasn’t taken into consideration the environemental effects.

Lets extend this to renewable energy and fossil fuels. The fossil fuels based power plans and vehicles are cheaper than renewable energy ones. Commercial rates of electricity in Tamil Nadu is Rs.7/KWh and is mostly produced by coal powered plans. If it were to be replaced by solar power plants, then the cost would be Rs.15-Rs.20KWh (and higher for standalone rooftop solar systems). If one were to look at the economic point of view, then it would make perfect sense to stay with coal powered plans. Again. What are the factors that we did not consider? Did we consider the problems caused by emission of carbon dioxide and other harmful gases/particles? CO2 causes global warming which has been causing cyclones to become more and more severe each year. But the average railfall keeps falling. So, the total cost of power produced by coal is Rs.7+Rs.X and it is very difficult to model and bring about the value for ‘X’. But our scientists tell us one thing – if we don’t do something soon then global warming will go out of control and lead to horrible disasters.

This economic paradigm which we live in needs change. It is incompatible with the environment.

(to be continued)

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 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.

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.