# Selection of solar panels and batteries

• subakumaran
In summary, when selecting the power rating of solar panels and ampere hour rating of batteries, it is important to consider the application and the operating time of the motor. A minimum requirement for the battery is calculated by multiplying the power and time, but it is recommended to have more capacity and a safety factor for cloudy days. The required peak power rating of the solar cells also depends on the amount of sunshine and the battery capacity. Matching the voltage is crucial to avoid conversion losses. In the given scenario, a 20W solar panel and a 24Ah battery would be more than enough, considering 5 hours of intense sunshine per day. However, a controlled way to charge the battery is necessary. A 12V 10A charge
subakumaran
is there any procedure ( formulae ) to select the power rating of solar panels and ampere hour rating of batteries ?

It depends on the application.

mfb said:
It depends on the application.

it is to charge a battery which inturn provides the supply for a 12 V 100 W DC motor ... the operating time of the motor is 5 minutes intermittent cycle of 4 cycles in a day

Well, that helps a bit, but it is still a bit vague:

100W for 5 minutes are 100W*300s= 30kJ = ~8.3Wh. This is the minimum requirement for your battery, unless you want to rely on sunshine directly at the time of the motor operation.
8.3Wh at 12V correspond to 8.3Wh/(12V) = .69 Ah.

In general, your battery won't get fully charged between cycles, so I guess you'll need more capacity. If your solar cells are sufficient to provide the power for a day even if it is cloudy, a capacity for 4 cycles could be sufficient. Otherwise, you could need more capacity.

The required peak power rating of the solar cells depends on the amount of sunshine you get, and the battery capacity. The average energy per day has to be at least the required energy for the motor operation, but there should be some additional safety factor for cloudy days/weeks.

Matching the voltage is another thing you have to take care of - if the output voltage of the solar cells is not 12 Volts, you get some conversion losses.

mfb said:
Well, that helps a bit, but it is still a bit vague:

100W for 5 minutes are 100W*300s= 30kJ = ~8.3Wh. This is the minimum requirement for your battery, unless you want to rely on sunshine directly at the time of the motor operation.
8.3Wh at 12V correspond to 8.3Wh/(12V) = .69 Ah.

In general, your battery won't get fully charged between cycles, so I guess you'll need more capacity. If your solar cells are sufficient to provide the power for a day even if it is cloudy, a capacity for 4 cycles could be sufficient. Otherwise, you could need more capacity.

The required peak power rating of the solar cells depends on the amount of sunshine you get, and the battery capacity. The average energy per day has to be at least the required energy for the motor operation, but there should be some additional safety factor for cloudy days/weeks.

Matching the voltage is another thing you have to take care of - if the output voltage of the solar cells is not 12 Volts, you get some conversion losses.

can a 20 W solar panel and a 24 Ah battery will be more than enough for this operation ? considering our place in India we get a minimum 5 hrs of intense sunshine a day ...

20W*5h = 20J/s*5*3600s = 360kJ. Should be more than sufficient, especially with the large battery that can store enough energy for a few days.

Just keep in mind that you need some controlled way to charge the battery with the right voltage and current range.

mfb said:
20W*5h = 20J/s*5*3600s = 360kJ. Should be more than sufficient, especially with the large battery that can store enough energy for a few days.

Just keep in mind that you need some controlled way to charge the battery with the right voltage and current range.

hmm yes ... i'll be using a 12 V 10 A charge controller ...
can i go for a 12 V 12 Ah or a 12 V 24 Ah battery ?

Sorry for the late reply: both should work.

## 1. How do I determine the right size of solar panel for my needs?

The size of solar panel you need depends on your energy consumption and the area available for installation. Calculate your average daily energy consumption and multiply it by the number of days you want to run on solar power. This will give you the total energy requirement. Next, check the wattage of the solar panel you are considering and divide the total energy requirement by the wattage. This will give you the number of panels you need.

## 2. What is the difference between monocrystalline and polycrystalline solar panels?

Both types of panels are made from silicon, but monocrystalline panels are made from a single crystal of silicon, while polycrystalline panels are made from multiple crystals. This makes monocrystalline panels more efficient, but also more expensive. Polycrystalline panels are more affordable but have slightly lower efficiency.

## 3. How do I choose the right battery for my solar panel system?

The right battery for your solar panel system depends on your energy needs and the type of solar panels you have. For smaller systems, lead-acid batteries are a cost-effective option, while lithium-ion batteries are more efficient and have a longer lifespan. Make sure to also consider the battery’s depth of discharge, voltage, and cycle life when making your selection.

## 4. Can I connect different types of solar panels and batteries?

It is not recommended to mix different types of solar panels and batteries in a system. This can lead to issues with compatibility and performance. It is best to stick with one type of solar panel and battery to ensure optimal efficiency and performance.

## 5. What is the lifespan of solar panels and batteries?

The lifespan of solar panels and batteries varies depending on the quality of the products and the maintenance of the system. On average, solar panels have a lifespan of 25-30 years, while batteries have a lifespan of 5-15 years. Regular maintenance and proper usage can help extend the lifespan of both components.

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