I have seen very useful discussions over the forum. The experiences you people have shared is of high value and compelled me to conduct a feasibility report for solar solution implementation in Pakistani Market (especially Lahore). Summary is pasted below while detailed report is attached along-with. Please feel free to discuss and share your suggestions for further improvement. Many thanks.
Poly Crystalline Or Mono Crystalline:
In mature solar markets, the domestic rooftop market starts to demand good looking solar panels, and has settled on solar panels with black cells and black frames with improved aesthetics. For this market, your choice of solar panel will be far more about choosing a quality brand that you trust than worrying about whether those panels followed a polycrystalline or mono-crystalline manufacturing route.
As a bottom line, since the system cost is a key driver for fast return on investment, most people prefer poly-crystalline modules. Mono-crystalline modules are often chosen for solar projects in which space is very limited, due to their higher efficiency.
- A battery is an electrical storage device. Batteries do not make electricity; they store it.
- Part - or most - of the loss in charging and discharging batteries is due to internal resistance. This is converted to heat, which is why batteries get warm when being charged up. The lower the internal resistance, the better.
- Slower charging and discharging rates are more efficient.
- The lifespan of a deep cycle battery will vary considerably with, How it is used, How it is maintained and charged, Temperature & Other factors.
- A battery "cycle" is one complete discharge and recharge cycle. It is usually considered to be discharging from 100% to 20%, and then back to 100%.
- Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD (Daily Depth of Discharge).
- Battery capacity (how many amp-hours it can hold) is reduced as temperature goes down, and increased as temperature goes up.
- The standard rating for batteries is at room temperature 25 degrees C (about 77 F). At freezing 0 C, capacity is reduced by 20%. At approximately -27 C, battery AH capacity drops to 50%. Capacity is increased at higher temperatures at 50 degrees C, battery capacity would be about 12% higher.
- The higher the temperature the lower the voltage, due to high internal resistance.
- Even though battery capacity at high temperatures is higher, battery life is shortened.
- For every 8C over 25, battery life is cut in half. This holds true for any type of Lead-Acid battery, whether sealed, gelled, AGM, industrial or whatever.
- The faster a battery is used (discharged), the LOWER the AH capacity. Conversely, if it is drained slower, the AH capacity is higher.
- At around 10.5 volts, the specific gravity of the acid in the battery gets so low that there is very little left that can do. In a dead battery, the specific gravity can fall below 1.1
- Do not put a new battery in a pack which is more than 6 months old or has more than 75 cycles.
- Do not have more than two parallel strings (Recommended). If you must use three or more strings in parallel be sure to tie them together with equal length cables and equalize a little more frequently than usual.
- Do not try to get away with the minimum amount of batteries. Trying to save money in the beginning by installing the bare minimum battery bank will always end in disaster.
Recent industry experience indicates that a 4 to 7 year VRLA battery life is more likely, regardless of cell size or warranty claims.
- Temp plays an important role in battery life. Controlled temp gives an incredible battery life. And finally FLA lead acid battery performs the best out of all other similar competitors with best cost estimates over 25 years under 20C temp and 60% DOD.
INVERTOR & CHARGE CONTROLLER:
- Inverters convert DC electricity into AC electricity. Solar panels (and most small wind turbines) produce DC electricity. That electricity is used to charge a battery bank in off-grid systems or sent directly to an grid tie inverter which feeds the electricity directly to the electric grid.
PWM or MPPT?
- PWM and MPPT charge controllers are both widely used to charge batteries with solar power.
- The PWM controller is in essence a switch that connects a solar array to the battery. The result is that the voltage of the array will be pulled down to near that of the battery.
- The MPPT controller is more sophisticated (and more expensive): it will adjust its input voltage to harvest the maximum power from the solar array and then transform this power to supply the varying voltage requirement of the battery plus load.
- When using an MPPT charge controller there are two compelling reasons to increase the PV voltage (by increasing the number of cells in series). 1) Harvest as much power as possible from the solar array, even at high cell temperature. 2) Decrease cable cross sectional area and therefore decrease cost.
- An MPPT charge controller is therefore the solution of choice:
1) If cell temperature will frequently be low (below 45°C) or very high (more than 75°C).
2) If cabling cost can be reduced substantially by increasing array voltage.
3) If system output at low irradiance is important.
4) If partial shading is a concern.
Generally speaking under controlled temperature conditions, a 24 hr independent solar solution will take 2 yrs 11 months (35 months) to cover the fixed cost. For overall system, it will take around 9.5 years to cover the entire cost of 25 years of the solution.
While a solution with no battery backup that works in day only will take 2.5 yrs to cover the fixed cost. For overall system, it will take 3.7 yrs to cover the entire cost of 25 years.
Thus looking at ROI comparison, solar solution without batteries is 3.5 times better than the one with batteries backup.
Note: Solar solution with battery backup and under uncontrolled temperature conditions can be extremely costly. The cost can double or even tripple and will take many more years to break-even.
Solar Solution Feasibility Report RA1.pdf