1. What is a solar PV system?
Solar photovoltaic system uses solar panels to convert sunlight into electricity. The electricity generated can be stored in the batteries or used directly as DC supply or through an inverter for running Ac appliances. Solar PV systems have no moving part; thus they work silently and there is no mechanical wear and tear requiring regular maintenance. They are ideal for remote locations.
2. How long do the solar PV systems last?
Good quality solar panels are designed to resist environmental conditions such as rain, sun and strong winds. They generally have a 20-25 year performance warranty, but should last even longer. Manufacturers normally assure at least 90% efficiency up to 10 years and 80% up to 20 years.
Standalone PV systems have another important and costly component: the batteries. These are deep discharge cycle batteries, not of the types used in the cars or trucks. The average life of a battery depends on several factors: system design, battery quality, depth of discharge, number of charge-discharge cycles, temperature of battery and maintenance. Quality deep cycle solar batteries like those offered by Exide can last 5 – 10 years.
When the solar DC power is converted into AC inverters are involved. Inverters are also available in various designs, capacity, quality and price. They need to be replaced after some years depending upon the quality. Thus, if a PV system is well designed and good quality batteries and inverters are used, the system is virtually maintenance free.
3. Is my site suitable for solar PV power?
In India (as anywhere in the northern hemisphere) the site must have clear southern exposure during the day. The PV modules must not have shadows of trees, mountains, and buildings at any time of the day, especially during 9 am to 4 pm, during the whole year. The sun travels a lower path during the winter creating the possibility of shadowing even if the modules remain clear of shadows in the summer. Also consider the possibility of the growth of trees and some high rising structure coming up in the future that may cause shading problems. Further, a flat, grassy site is appropriate, whereas a steep and rocky hillside is not.
4. How does weather affect PV module output?
Sunlight is the raw material for the PV power systems. Weather pattern and seasonal factors have directly impact of the sunshine and hence they play crucial role in determining how much power your PV system produces. For any location the potential of PV power generation is given by the annual average “sun hours”. The other important factor is the temperature: in hotter climates panels produce lesser power. Solar modules have a negative temperature coefficient of about 0.40% per degree of rated watt power. Thus, solar panels perform best under bright sun in cooler climates.
5. What is the best way to use solar electricity?
Efficiency is the key word. Before installing a solar power system, it is good to replace current electrical appliances with energy efficient models. Investment in more efficient appliances pays back within months or years. Lights can be replaced with more efficient LED based lighting. Electronic chokes should be used with tube lights. Significantly more efficient fans are available at present; for instance, Crompton Greaves is soon coming up with a 35W ceiling fan (1200 mm size). Already ceiling fans are available in the 45 – 50W range. Star rating system is being used to mark the efficiency of air conditioner and refrigerator. These systems with higher star rating should be used. Laptops consume much less power as compared to desktops PCs (about 70 Watt as against 250 Watt), therefore use of laptops should be promoted.
6. What will determine the size of my solar PV system?
The size of a PV system depends on how much electricity is required. This is usually measured in watt-hour consumption of power. It is obtained by multiplying the wattage of appliances (fans, lights, laptop etc) by average number of hours of daily use and adding them all. For example, if you want to run a 10 watt fan for 5 hours and a 20 watt CFL light for 10 hours every day, then the total daily consumption will be (10 x 5) + (20 x 10) = 250 watt-hours. If you get about 5 hours of average daily sunshine, then a 50 watt panel (250 watt-hours / 5 hours) will be required. This is assuming 100 percent efficiency but there are losses in real systems, so somewhat higher panel wattage will be required. A battery will be required to store the power to run the light and fan after sunset. If AC appliances are to be run, an inverter will be required.
7. What loads can PV run and not run?
With solar Photovoltaic power you can run any electrical load. However, air conditioning and gadgets with electric heating elements (electrical stove, water heater, etc) use large amounts of electricity which will drive the system cost very high. Therefore, it is better to plan for a system that can take care of lighting, fans and laptop, TV etc and continue to run other high power appliances on the regular grid power supply. The solar system cost generally pays for itself within few years and savings on power bill continue for a long time. It will be still better if all lights are replaced with energy efficient LED lights that consume much less power for same illumination.
8. Can I use solar PV power for heating water?
No, it is a bad idea. The photovoltaic mechanism converts sun’s energy into DC electricity with a rather small efficiency of 13 – 16 percent. Therefore, trying to operate a high power electric heating element from PV would be very inefficient and expensive. There are solar water heaters that directly heat water from sun’s energy which is much more efficient and appropriate.
9. Can I use a car battery in my solar system?
It is not a good idea. Automotive batteries are shallow-cycle batteries and are designed to provide very high current for short durations and can be discharged only up to say 20 percent of their capacity. If repeatedly discharged beyond 20% more than a few dozen times, they are likely to be damaged or die down soon.
Unpredictability of electricity generation is inbuilt in the solar systems because not every day is a sunny day or sunny enough! Then there are cloudy and rainy days. Thus, you need the kind of batteries that can withstand vagaries of the panel power output, and hence of the climatic mood. It means, batteries must be able to cope with unpredictable charging and discharging. To provide electricity over long periods, PV systems require deep cycle batteries. These are usually lead-acid batteries and are designed to go through cycles of discharge up to 80% and recharge hundreds (even thousands) of times.
Lead-acid batteries used in solar systems are either low maintenance flooded type batteries which require addition of water every 8-10 month or are sealed type which are spill proof and do not require periodic maintenance (addition of water). Sealed batteries are ideal for remote locations and require no water addition.
Another class of batteries are alkaline Nickel-Cadmium type. Due to high cost they are only recommended where extreme cold (sub zero) temperatures are encountered or for certain critical applications requiring their advantages over the lead acid batteries. Their superiority over the lead acid batteries include tolerance of freezing or high temperatures, low maintenance requirements, and the ability to be fully discharged or overcharged without harm.
10. Can the solar panel be directly connected to the battery?
Batteries need protection against overvoltage and overcharging. Therefore connecting them directly to the solar panel is not a good idea and it is wise to use a charge controller. A charge controller regulates the voltage and current coming from the solar panels going to the battery. Most controllers also control the power to the load, disconnecting it as the battery becomes depleted; reconnect again when the battery is discharged to some low level. A charge controller is an essential part of PV systems with battery storage and keeps the batteries safe for long life.