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3 EASY STEPS TO ESTIMATE SOLAR SIZE ​

by Ir. Azean Abu Samad.



Solar size (kW)  =

Average energy usage per month

——————————————

Sun hour per month x Derate Factor



STEP 1

DETERMINE YOUR ENERGY CONSUMPTION PER MONTH FROM YOUR ELECTRICITY BILL


There a couple of ways to access your electricity bills. They are:

  1. Printed copies of your electricity bill

  2. myTNB app. Visit App Store or Google play to download the application

  3. Visit www.mytnb.com.my to use the web portal

I would recommend to register your online account through myTNB web or app. It is so easy to use.


Capture the energy usage measured in kilowatt-hour (kWh) for the past 12 months.​


INSTRUCTION: Find the average energy consumption per month


STEP 2

FIGURE OUT YOUR PEAK SUN HOUR​​


What is peak sun hour?

First and foremost, peak sun hours are not the same as hours of daylight. Peak sun hour refers to how much sun exposure that is usable for efficient energy production per area (in meter square) during a typical day of the year. For Malaysia, although the solar panels may receive sunlight from 7AM to 7PM, it does not mean the peak sun hour is 12 hours. The average peak sun hours for Malaysia is between 4.0 to 5.4 hours depending on the location. I will not get into too much theory, but suffice to say that sun peak hours is numerically identical to solar irradiation measured in kWh/m2 as shown below.


INSTRUCTION: Visit www.globalsolaratlas.info to find the peak sun hour for your location


STEP 3

APPLY DERATE FACTOR​​​


What is derate factor?

Every photovoltaic panel has a nameplate with a DC power rating. It is expressed in Watts, and it is rated based on how the panels performs under standard test conditions.

Nonetheless, real life is not like these test conditions. Several factors, called derate factors, can affect how much energy a solar panel may actually produce.  Derate factors may include shading, temperature, as well as losses due to wiring and inverter.

The derate factor will add all potential environmental and system losses into one percentage factor.

According to NREL, typical overall derate factor is 0.77. 


INSTRUCTION: Apply derate factor


BRINGING ALL TOGETHER


Solar size (kW)  =

   848 kWh

—————

133 x 0.77

=    8.3 kW


OTHER CONSIDERATIONS


1. YOUR ELECTRICITY LOAD PATTERN THROUGHOUT THE DAY

As shown in the calculation, the solar PV size will offset 100% of your electricity bill. However, bear in mind that the solar PV system is only generating during the day. If 100% of your energy consumption is during the day, then and only then you can assume that all your electricity demand will be met by solar. If you are at work during the day and only be back to your home in the evening, this would mean your solar electricity generated will not be consumed 100% during the day. So what will happen to the unused energy?

The solution to this problem is simple – enroll in Net Energy Metering Scheme (NEM). Under NEM, for every 1 kWh of exported energy to the grid, TNB will offset 1 kWh of energy consumed from the grid, irrespective of time of use. In short, TNB’s electrical grid acts as your battery storage. If you are totally off-grid, then you need to explore battery storage. 

2. SIZE AND STRENGTH OF YOUR ROOF

You need to take into consideration on the number of solar panel you can fit on your roof. As a rule of thumb, 1 kW is 10 m2. So for a 8.7 kW solar PV size, you need about 87 m2 of roof space. Your solar PV installer will also check how much of additional weight from the solar panels that your roof can hold.

3. SOLAR FINANCING

The solar PV system size will help you determine the cost that you need to invest. You can determine the final size of your solar project according to your budget if you use your own cash.


Otherwise, you can opt for Solar Leasing or Solar Energy Purchase as described in a blog article, in the TNBX website titled under "Solar Financing", or you could also check out our TNBX e-book under resource center, titled "Solar 101 - Your Simple Guide to Go Solar".

4. Regulation

The Energy Commission has set regulation on the maximum size of solar PV system that can be installed on a premise.

The regulations are as follow:


1. For NEM Scheme

  • Residential - 12 kW for single phase and 72 kW for three phase

  • Commercial/Industrial - 75% of maximum demand, or 60% of fuse rating or 60% of current transformer rating

2. For Self Consumption (SELCO) 

  • For a stand-alone system, i.e. off-grid, there is no capacity limit for solar PV system size

  • For a non-stand-alone system, i.e. grid connected, the capacity limit for solar PV system shall be lower than 75% of the maximum demand of the consumer’s existing installation

So there you go. It is easy to estimate the size of your solar PV system. Good luck!

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