From the time i took a pledge to be a little green in my living, i wanted to run my house on solar power. I am a great believer that Solar, wind and small hydro power are really a sustainable solution for the energy crisis that we are facing.
Solar power, however is an expensive technology and does not yield economic returns in the short to medium term. But i still feel its affordable for the middle class. It is because of subsidized grid power that solar power has not gained popularity and its a general feeling that solar power technology does not break even at all. Also the environmental costs of producing conventional power (Coal, Large scale hydro) is never captured in our calculations.
The idea of this post is not to argue for an economic case for solar but its about my efforts to put up a solar power plant on my rooftop. We designed and installed the rooftop power plant in our house in March 2014.
Below i try to put down my experience in designing and installing the power plant.
Energy Requirement:
The First step in designing the system is to carefully examine one's Power requirement.
The power you need is the instantaneous intensity of electricity required to power the appliances you use; this is measured in kilowatts. The more appliances that are used at the same time, the more power required. Energy is a measure of the length of time you have used a given amount of power. It depends on the power required by the appliances and on how long and how often you use them. Electrical energy is measured in kilowatt hours (Kwh). You need to know the electrical power and energy requirement for lighting, heating, cooking and other uses for your home. How large a system do you really require is a function of Power requirements which is not very easy to measure .
To estimate how much electricity you need:
• List all your electrical appliances and lights and note when and how long they are used.
• Note the power that each appliance consumes. An appliance’s power rating is usually written on the back of the appliance and is measured in watts or kilowatts.
• Record the number of hours each appliance is used in a typical day.
• For each appliance, multiply the power rating in watts by the number of hours used each day to obtain the number of watt hours (or kWh) that the appliance uses per day.
• Energy-use patterns change with the seasons (e.g., lighting is generally used more in monsoon/winter).
• Add up the watt hours for all your appliances. This total is an estimate of your electrical energy consumption per day. Then you can calculate how much energy you would need per month.
The above exercise was done for the lighting loads of my house (Excluding heaters, refrigerators, microwave oven and iron).
The table below are the results
Sl No
|
Utility
|
Power rating
(W)
|
No
of Hrs
|
Watt Hours Consumed (Wh)
|
Units (Kwh)
|
| 1.00 | Fan 1 (Office) | 70.00 | 8.00 | 560.00 | 0.56000 |
| 2.00 | Fan 2 (Hall) | 80.00 | 4.00 | 320.00 | 0.32000 |
| 3.00 | Fan 3 (Room) | 70.00 | 7.00 | 490.00 | 0.49000 |
| 4.00 | LED 1 (Office) | 7.00 | 5.00 | 35.00 | 0.03500 |
| 5.00 | LED 2 (hall) | 10.00 | 4.00 | 40.00 | 0.04000 |
| 6.00 | CFL 1 (room) | 14.00 | 2.00 | 28.00 | 0.02800 |
| 7.00 | CFL 2 (kitchen) | 14.00 | 2.00 | 28.00 | 0.02800 |
| 8.00 | CFL 3 (utility) | 8.00 | 0.50 | 4.00 | 0.00400 |
| 9.00 | CFL 4 (Bathroom) | 5.00 | 0.25 | 1.25 | 0.00125 |
| 10.00 | CFL 5 (Toilet 1) | 5.00 | 0.50 | 2.50 | 0.00250 |
| 11.00 | CFL 6 (Toilet 2) | 5.00 | 0.25 | 1.25 | 0.00125 |
| 12.00 | CFL 7 (Toilet 3) | 5.00 | 0.25 | 1.25 | 0.00125 |
| 13.00 | Computer 1 | 90.00 | 9.00 | 810.00 | 0.81000 |
| 14.00 | Computer 2 | 90.00 | 6.00 | 540.00 | 0.54000 |
| 15.00 | Television | 100.00 | 6.00 | 600.00 | 0.60000 |
| 16.00 | Set top box | 5.00 | 10.00 | 50.00 | 0.05000 |
| 17.00 | Misc | 0.25000 | |||
| Total | 3,511.25 | 3.76 |
So i need to generate about 3.8 Units of power per day to power all my non inductive loads.
The next step is to choose the type of system. That is to design an optimum configuration where the solar power, the battery power (Charged from solar and grid) and the grid power is used in the most efficient manner. Broadly there are three configurations.
1. Off Grid System: Off Grid or stand-alone system refers to being independent of the state grid. The design would support all the loads and sufficient back up can be provided to cater to the power needs worst conditions.
One can go off-grid for low intensity loads. In other words, all equipments having a power rating lesser than 500W can be taken off grid.
2. Grid Tied System : In grid tied systems, the system is interfaced to the state power grid. Here, Solar takes the first priority to run the loads. The excess power, if generated will charge the battery bank. The excess from the battery bank is fed into the state power grid. Grid tied system can be configured without battery bank also.
In case there is deficit of solar power, the differential power is drawn from the state power grid.
In case of grid tied system, a meter to record the net power (Net metering) will be installed.
3. Hybrid System or Grid interactive system: Hybrid system is a smart system involving, solar, grid , battery bank. A DG can also be added if required. Here, Solar takes the first priority to run the loads. Excess power generated will charge the battery bank. During night battery will support the loads till a safe battery voltage. System will switch over to grid automatically below battery safe voltage. (If GRID is not available and battery has been discharged, PCU can command DG to start and supply power to the loads till Grid or solar is restored).
Hybrid systems can also be configured as grid interactive systems where only solar and grid are present. Here, the first priority is given to solar. Excess power generated will charge the battery bank. During night battery will support the loads, till a safe battery voltage. System will switch over to grid automatically below battery safe voltage. This would extend the battery life and provide seamless power supply. There will be no power exported to grid.
In view of economy and ease of use, the grid interactive system is the best. One can slightly under design the system also if budget is a constraint.
In my house, i decided to go in for a grid interactive system. The system consists of
1. Solar Panels
2. Battery Bank
3. PCU or Power conditioning unit.
In bangalore weather conditions, one kilowatt peak (KWp) will generate about 2.5 units of power per day on an average bright day. So if my requirement is 3.8 units per day, i would need 1.52 KWp.
So i would need a power conditioning unit (PCU or inverter) that can support 1.6 KW. However, it is prudent to go for slightly higher PCU to account for accidental higher loads (or in event of guests at home).
The battery bank is designed to cater to maximum night loads. Also many PCUs needs a basic minimum voltage to even start. As such for a 2KW system that i decided to put, i had to connect 4 batteries of 12 V each in series to give 48V.
So my final configuration was
1. 6 modules of 230Wp solar panels (total of 1380Wp)
2. 4 numbers of 100Ah, 12 V deep discharge batteries in series.
3. 2KW PCU (i decided to go with a PCU with transformer).
The mounting structure proved to be the most difficult part of the installation. There were two riding considerations for mounting structure.
1. The structure has to be non penetrative. That is we did not want to drill the roof to fix the structure.
2. We wanted to keep the cost to care minimum without compromising on quality and safety.
1. The structure has to be non penetrative. That is we did not want to drill the roof to fix the structure.
2. We wanted to keep the cost to care minimum without compromising on quality and safety.
The mounting structure was designed in view of economy and wind loads. The design we arrived was a very simple "Z" section of 3mm thickness, web length of 6 inches and flange length of 9 inches with oblong slots. We got the same fabricated with powder coating. 6 such sections were fixed to each panel.
The panels were just anchored to the mounting angles with nuts and bolts. The panels with angles were placed on the roof. A rubber pad was placed between the angle and the RCC roof to minimize friction caused by wind. A simple clay brick counter weight was placed for additional safety.
For the DC wiring, we got double sheathed DC cables specifically designed for solar purposes. We got the right switches and the wires.
After all the electrical and structural design, we had aesthetics to care of . Thanks to power tools from Bosch we did and re-did the wiring (DC and AC) thrice before we were happy with the aesthetics. It took full three days for three people for installation. All in all it was a terrific time designing and installing the system. (A short video is at the end of the post).
The final phase of the work was to check the system and measure the efficiency. So after about two weeks of installation, we measured the key parameters. A graph of array current and array voltage against time was prepared to study the system. Below are the results.
| Time | Array voltage (V) |
Array Current (A) |
Total Power Produced (W) | O/P current (%) |
O/P Voltage (V) | Battery Current (A) | Battery Voltage (V) |
| 09:00:00 | 54 | 2.9 | 156.600 | 10 | 231 | 1.6 | 51 |
| 09:30:00 | 53 | 3.2 | 169.600 | 4 | 231 | 0.1 | 54 |
| 10:00:00 | 54 | 5.3 | 286.200 | 6 | 231 | 0.5 | 51 |
| 10:30:00 | 59 | 13.8 | 814.200 | 9 | 231 | 7.3 | 56 |
| 11:00:00 | 59 | 12.8 | 755.200 | 5 | 231 | 7.9 | 57 |
| 11:30:00 | 59 | 12.2 | 719.800 | 6 | 231 | 7.3 | 56 |
| 12:00:00 | 60 | 12.6 | 756.000 | 5 | 231 | 2.1 | 56 |
| 12:30:00 | 61 | 13.9 | 847.900 | 7 | 231 | 9.5 | 58 |
| 13:00:00 | 61 | 15.6 | 951.600 | 8 | 231 | 2.8 | 58 |
| 13:30:00 | 65 | 6.6 | 429.000 | 8 | 231 | 0.9 | 54 |
| 14:00:00 | 62 | 4.9 | 303.800 | 6 | 231 | 2 | 54 |
| 14:30:00 | 63 | 6.5 | 409.500 | 5 | 231 | 3 | 54 |
| 15:00:00 | 54 | 3.1 | 167.400 | 5 | 231 | 1 | 52 |
| 15:30:00 | 63 | 5.7 | 359.100 | 6 | 231 | 2.3 | 54 |
| 16:00:00 | 62 | 4.7 | 291.400 | 5 | 231 | 1.7 | 54 |
| 16:30:00 | 54 | 2.1 | 113.400 | 6 | 231 | 1.1 | 52 |
| 17:00:00 | 53 | 2.1 | 111.300 | 4 | 231 | 0.7 | 51 |
Key metrics from the above table are.
|
Maximum units produced 2.67 Kwh
(after all losses)
(after all losses)
The power production was actually less than expected. There are two reasons for that.
1. The day was not that bright. We had few spells of cloud cover.
2. There was a tree shadow on one of the panels after 2 PM. Since the modules were made of polycrystalline cells, practically the whole panel will not function if there is shadow on any portion of the panel.
However for a 1.38Kwp power plant we can easily expect about 3 units of power on a moderately bright day.
Since it is a grid interactive system, the balance power requirement for the day was met by state utility grid power.
Installation Video
2.67 units out of 3.76 = ~70% is quite good. Do you have cost estimates for the same?
ReplyDeleteIt costed me about 1.65 Lakh(With Emerson inverter). It can cost about 30 K lesser if one goes for a MRO-Tek Inverter.
ReplyDeleteWhat is total cost to apply solar panels for home bangalore
ReplyDelete