There are different elements involved in the designing of a solar street light system. It is highly important to make an accurate measurement of the required values of all the elements for the smooth operation of the system. The two most important elements involved in the designing of battery powered street lights system are the calculations of battery and solar panel. The ratings of these panels depend upon the solar street light that they have to operate. Therefore, people should first purchase a solar street light, which is capable of meeting their lighting requirements. We recommend our readers to carry out extensive research before purchasing the solar light since it will affect the parameters of all the other elements of the system. People can check the luminosity of the solar lights and its power consumption ratings before making the investment.

Once they have purchased the street light then they can move ahead with designing an appropriate battery and solar panel as per their requirements. In this article, we will explain how users can calculate the ratings of battery for battery powered street lights.

Important concepts to understand

Battery capacity and power

The capacity of a battery is a measurement of the maximum amount of energy that it can store. Batteries having large capacity can store more energy as compared to those that have lower capacity. The capacity of a battery is determined in terms of kilowatt-hour or kWh. In simple terms, it is the amount of energy that a battery can provide in an hour.

Similarly, the power of the battery is given in terms of watts and it is known as the power rating of the battery. The power rating is the measure of the multiplication of voltage (V) and current (I) supplied by the battery to the load.

Ampere-hour (AH)

It is also a measure of the capacity of the battery. However, in these criteria, the capacity of the battery is represented in terms of the multiplication of the total current that it supplies in a number of hours. For example, if a 12-volt battery supplies a current of 5 amperes for a period of 5-hours then the capacity of the battery will be 25 ampere-hours.

The capacity of battery = 5A x 5h = 25 AH.

This representation of the capacity is necessary because usually, the specifications of the batteries are in terms of ampere-hours.

Depth of discharge or DoD

It gives an account of the energy in a battery that can actually be used by the load. It is possible that a battery may not be able to make use of all the energy that it has stored. Therefore, the amount of energy in a battery that can be used for productive purposes is represented in terms of the depth of discharge of the battery. In common terms, it is the energy that a battery supplies when it discharges from full capacity to the lowest capacity.

For example, if a battery has a depth of discharge (DoD) of 80% then out of one hundred per cent, only 80% of the energy will become available for the load while 20% energy will not become available for the load. In quantitative terms, if a battery has a capacity of 50-kilowatt hours and depth of discharge of 60% then, only 30 kilowatts hours of energy will be productive.

The working temperature of a battery

It is also one of the most important factors that affect the performance and parameters of a battery. The battery should have an optimum temperature of around 27 degrees, as it might not perform well above or below this temperature.

Calculations of the battery requirements for a battery powered street lights

In this section of the article, we will explain a step-by-step process with the help of which people will be able to calculate the requirements of a battery.

Step 1

The first step in the calculation of requirements for the battery is the collection of relevant data that is necessary for the process. The data necessary is the power rating of the street light, which has to be operated using the battery, the working voltage of the street light, the brightness requirements, supported rainy days for the operation of the street light, and the Depth of discharge (DoD) of the battery.

The rated power and voltage of a street light are available in its specification sheet.

The brightness requirements of the street light have to be determined by the users. it is probable that they may be able to get decide is there with 60%, 70%, 80% of the brightness of the light instead of operating it at 100%.

Users will also decide the requirement for the number of rainy days support.

The depth of discharge of a battery will also be available on its specification sheet. We recommend users to consider 80% of depth of discharge (DoD).

Step 2

In the second step, juices have to calculate the daily consumption of the battery-powered street light. Daily consumption of the street light will also be in terms of amperes-hour (Ah). The formula for calculating power consumption is as below:

PC = Power Rating/Voltage x Time

Step 3

In the next step, users should account for the requirements of rainy days for which they require a battery to supply power to the load. On the other hand, in case, uses required support for rainy days for up to three days, then they will have to multiply the power consumption of load with this factor. Therefore, the formula for accounting rainy days support in battery calculations is as follows:

Power consumption (PC) x number of rainy days

This is the ratings of the battery that uses will require in order to support the load. However, there is still a need to account for the depth of discharge (DoD), which means that a battery of higher rating will be required depending upon the DoD percentage.

Step 4

The next step is to account for the depth of discharge (DoD) of a battery, which can reduce its overall capacity. In order to account for DoD, users need to divide the values obtained from step 3 by the DoD percentage. In case, the power consumption of load with three days support is 100 AH, and users want to consider 80% DoD then the requirements of the battery will be 100/80% = 125Ah.

Therefore, in order to support the load, users will require a battery of 125 Ah ratings.

Conclusion

We have discussed that the ratings of a battery depend upon a number of different factors and people should consider all these factors for making accurate calculations. Some of the factors on which the ratings of the battery depend upon are the required capacity/rating of the load, depth of discharge, and working temperature of a battery. People can follow the steps above in order to calculate requirements for battery powered street lights.