SOLAR POWER SYSTEM SIZING: DAILY ENERGY AND PEAK POWER CALCULATION

 Embarking on the journey to harness solar energy requires a thoughtful and meticulous approach, particularly when it comes to sizing a solar power system. The cornerstone of this process is an in-depth understanding of your energy needs, a task that is both foundational and pivotal in charting the course of your solar energy project. This initial step involves a comprehensive calculation of the total electricity usage of your household or the specific application intended for the solar power system. The essence of this evaluation cannot be overstated, as it significantly dictates the scale and capacity of the solar installation required to fulfill your energy requirements.

The decision-making process begins with the collection of electricity bills over the past year, a step that provides a clear picture of your annual energy consumption. This historical data serves as a crucial indicator, revealing the total kilowatt-hours (kWh) expended and offering insights into your energy usage patterns. The relevance of this exercise lies in its ability to translate these figures into an actionable blueprint for the solar power system’s size.

Following the acquisition of annual energy usage data, the next pivotal step is to calculate the average daily energy use. This is achieved by dividing the total annual electricity usage by 365, yielding the average amount of energy consumed per day. This figure emerges as a critical parameter, guiding the sizing of the solar power system to ensure it can reliably meet daily energy demands.

However, in developing countries like Nigeria, the path to sizing a solar power system is nuanced by unique challenges and opportunities. The conventional method of relying on electricity bills to gauge energy needs, while effective in regions with reliable billing systems, often encounters limitations in areas where post-paid services are predominantly estimated. This lack of precision necessitates an alternative approach to ascertain the household's energy needs accurately. Here, the load analysis method becomes invaluable. By itemizing all electrical appliances and calculating the energy requirement for each, households can obtain a detailed and accurate estimate of their daily energy consumption. This meticulous process accounts for each appliance's contribution to the total energy demand, ensuring that the solar power system is sized accurately to cater to the specific energy needs. This reality beckons for a more precise and adaptable approach to understanding and quantifying energy requirements.

Moreover, the concept of load separation becomes particularly relevant in scenarios where detailed energy usage analysis is undertaken. By categorizing electrical loads into essential and non-essential groups, households can prioritize energy allocation to critical systems during the solar power system's design and construction phases. This approach not only enhances the system's efficiency by ensuring that vital functions are maintained but also aids in optimizing the system's size and cost. Essential loads are given precedence, ensuring they are always powered, while non-essential loads can be managed to align with available solar power, thereby tailoring the solar system more precisely to the core energy needs without excess capacity.

Incorporating these considerations—adjusting strategies based on the presence of prepaid meters or the necessity to navigate estimated billing through load analysis and adopting load separation—into the process of sizing a solar power system reflects a deep understanding of the local energy context. It ensures that solar power systems are not only efficient and cost-effective but also precisely aligned with the specific realities and challenges faced in developing countries. With this in mind, let use the load analysis approach to calculate the daily energy requirement of an apartment. 

 

Example

You are tasked with designing a solar power system for an apartment. To accurately size the system, it's crucial to calculate both the peak power requirement, to ensure the inverter can handle the maximum load, and the daily energy needs, to determine the battery storage and solar panel capacity required. Considering the importance of starting surge for inverter sizing, list out the appliances, their power ratings, the number of units, average hours of use per day, and the appliance's surge factor. Using this information:

1. Calculate the peak power requirement, taking into account the starting surge of the appliances.

2. Determine the total daily energy consumption (in kWh) of the apartment.

Appliances Information:

 

- LED Light Bulb

  - Power Rating (Watts): 10

  - Number of Units: 5

  - Hours Used per Day: 5

  - Surge Factor: 1

 

- Refrigerator

  - Power Rating (Watts): 150

  - Number of Units: 1

  - Hours Used per Day: 24 (on-off cycle)

  - Surge Factor: 1.2

 

- Television

  - Power Rating (Watts): 100

  - Number of Units: 1

  - Hours Used per Day: 4

  - Surge Factor: 1

 

- Air Conditioner

  - Power Rating (Watts): 2000

  - Number of Units: 1

  - Hours Used per Day: 8

 

  - Surge Factor: 1.5

- Laptop

  - Power Rating (Watts): 50

  - Number of Units: 2

  - Hours Used per Day: 5

  - Surge Factor: 1

- Use the provided data to compute the peak power requirement, factoring in the starting surge for each appliance.

- Calculate the daily energy consumption for each appliance using the formula:

 

 SOLUTION

APPLIANCE	POWER RATING (WATT)	NUMBER OF UNITS	HOURS USED PER DAY (H)	SURGE FACTOR	DAILY ENERGY COMSUMPTION (KWH)	PEAK POWER REQUIREMENT (W)
LED Light Bulb	10	5	5	1	0.25	50
Refrigerator	150	1	24	1.2	3.6	180
Television	100	1	4	1	0.4	100
Air Conditioner	2000	1	8	1.5	16	3000
Laptop	50	2	5	1	0.5	100
TOTAL					20.75	3430

 

- Sum the energy consumption of all appliances to find the total daily energy requirement for the apartment.

Daily Energy Consumption (kWh) = ∑ ((Power Rating (Watts) x Number of Units x Hours Used per Day) / 1000))

= 20.75KWH

Peak Power = ∑ (Power Rating (Watts) x Number of Units x Surge Factor)

= 3430W

Since the design phase must account for efficiency losses, which are inevitable due to factors such as shading, orientation, angle of the solar panels, and inverter inefficiencies. Addressing these concerns involves adding a margin—typically around 25%—to your calculated energy needs. This adjustment ensures that the system can accommodate losses and still fulfill the energy requirements, highlighting the importance of foresight and contingency planning in the design of a solar power system.

Adjusting based on efficiency losses

Adjusted Daily energy need = Daily Energy Consumption x 1.25

Adjusted Daily energy need = 20.75KWH x 1.25 = 25.94KWH ≈ 26KWH

 

Adjusted Peak Power = Peak Power x 1.25

Adjusted Peak Power = 3420W x 1.25 = 4275W