How many solar panels are needed to power a house?

The average Indian family of four needs 10 to 13 solar panels to power your house in 2022.

(That can run your appliances like a TV, fans, LEDs, a Fridge, an A/C, a heater, and other small electrical appliances.)

It is based on their average energy use of 500 kW-hr per month.

And installing these number of solar panels may cost you between Rs. 2,00,000 to Rs. 3,00,000.

Read: What is the average cost of 5 kW solar power system in India?

There are fair chances that your energy needs may not fall in the average that is just discussed above.

Well, it depends on a number of factors.

How exactly do you find out how many solar panels you need to meet your daily energy needs?

I have got covered all for you in this amazing post.

Solar Panels

The solar panels are the most important component of any solar power system and are the first interphase between the sun and your energy needs.

They convert sunlight into direct current.

Their proper sizing can solve your energy needs and you enjoy smooth electricity for decades.

Online Solar Course: Learn to design the complete solar power system and know its financial feasibility

Factors that decide the solar panels you need

1. Your energy needs

The sizing of the panels depends on your solar energy needs that we learned in the previous post and the amount of sunlight falling on the place where you live.
 
Let us see how these variables are related to the sizing of the panels?
 
One easy way to figure out your daily energy needs is to look at the last month’s electricity bill.

• Divide the last month’s units consumed by 30 to get the daily energy needs.

But we consume more in summers and winters. While the consumption is moderate in other months.

Then how to get the fair idea of your average consumption?

• Add the total units consumed in the last 12 months and then divide the total by 365.

You get your average daily consumption.

For example,
 
On using the above methodology, my average daily energy need is 22 units.

Solar Panel sizing conditions

I further found that I consume nearly 16 units in the day time when there is sunlight and the remaining 8 units in the night.
 
Now, 2-panel sizing conditions arise.

One when I want to limit my solar energy needs to 16 units (daytime only).

Another when I need complete 22 units from Solar Power.

First Condition: It is the simplest configuration when you restrict your solar energy needs to daytime only (16 units). I don’t need any storage system as my energy needs are fulfilled by the solar panels only.
 
Second Condition: The panels can produce current in the daytime only.

But I need 8 more units in the night and solar panels cannot work.
​Therefore, I need an add-on system (solar batteries) that can store some energy for night use.

How I should do it?
 
Here is the answer,
 
I will size my panels so that they produce whole 22 units in the daytime.
 
I’m going to consume 16 units in the daytime as it is my daytime energy needs.

The remaining 8 units from the panels will go inside the batteries and they will store them.
 
In the night, these batteries will produce these 8 units and fulfill my night energy needs.
 
My night time energy needs are indirectly fulfilled by Solar Power through batteries.
 
Therefore, the batteries are required if you want to fulfil your night-time energy needs.
 
It is understood that if my energy needs are more than my panel size will also be more.

2. Sunlight

Now, coming to the second variable, the sunlight.
 
If your region or area receives good amount of sunlight then you need fewer solar panels than the area with not so good sunlight.
 
In short, good sunlight less panel size.
 
Let me share Sun Peak Hours (amount of sunlight per square meter area in a day) of some of the major cities:

Sunlight is inversely proportional to the panel size.

The ideal formula is:

Panel Size = Daily Energy needs/ Peak Sun Hours

If I say that my daily energy needs is 22 units and I live in Delhi where the average sun peak hours are 5.35.

In that case, my panel size would be = 22 kWhr/5.35 hr
= 4.11 kW
 
But when you live in Arizona with the same energy needs then your panel size would be:

= 22/6.44 = 3.42 kW

Now, you can see that increase in the Peak Sun Hours reduces the panel size.

Here is the panel size chart of the 4 major cities which we have discussed right now:

3. Losses

What you think you divide your energy needs by sun peak hours, you get the right size of the panels that will fulfil your energy needs.
 
Well,
 
That would be an ideal system with no losses.
 
Let me share the diagram of a solar power system with battery backup:

You can see that sunlight falls on the solar panels and they convert it into direct current.
 
This direct current is get stored inside the batteries in the form of chemical energy.
 Also, when D.C. current passes into the inverter gets converted into A.C. current that finally run our electrical appliances.

You know that when energy undergoes conversions while traveling from one component to another, it suffers losses at each conversion.

In short, what is produce at the source will not reach the same at the destination.

You will receive a diminished or decreased value.

If your requirement at the destination is 22 units then the source (Solar Panels) must produce more than 22 units so that you get the desired value.

Units from Solar Panel = Units at the destination (Energy needs) + losses

Therefore, we need to over-size the panel to compensate for the energy losses and you get the required units to run your electrical appliances.
 
Let us see the different types of losses:

a) Shade Loss

Loss in energy due to shading of the panels due to trees or nearby building.

b) Temperature loss

Due to the change in the temperature or to be more precise when the temperature of the solar panel increases, it efficiency starts decreasing.

c) Dirt loss

When the dirt gets accumulated on the surface of the panel, its output decreases.

d) Transmission loss

When energy travels from one point (source) to another (destination), some of the energy gets lost in the form of heat.

e) Inverter and battery loss

The loss in the energy due to its conversions in Inverter and the battery.

I have taken the following de-rating factors (when the loss is subtracted from the value, it is called the de-rating factor) to know how much my solar panels should produce so that I get 22 units daily to run my appliances.

Solar Panels should produce = My requirement/ (all the de-rating factors)
 
= 22 units/ (Temp. de-rating factor x Dirt de-rating factor x Transmission efficiency x Shading de-rating factor x Power tolerance de-rating factor x Inverter efficiency)
 
= 22 units/ (0.95 x 0.95 x 0.97 x 0.95 x 0.95 x 0.95)
= 22/ 0.75
Or
= 22 x1.33 (multiplying factor)
= 29.3 units

My solar panels must produce at least 29 units so that I get 22 units for running electrical appliances.

The real solar panel sizing formula

Solar Panel Size = 1.33 x (Your daily energy needs/Peak Sun Hours)
(1.33 is the multiplying factor that we have just derived. It is used to compensate for the system losses).
This multiplying factor may change depending on the amount of losses.

Using the above formula, my solar panel size would be:

= 1.33 x 22 units/5.35

where,

• 22 units are my daily energy needs
• 1.33 is the multiplying factor
• 5.35 is the PSH of Delhi/NCR

= 5.5 kW

Therefore, I should install 5.5 kW solar panels to meet the daily energy needs of 22 units.
 
Simple 🙂 

Space required by the solar panels

We all have limited space.

The efficient solar panels produce more power than the less efficient ones in the same space.

If you have a space-constraints, go for efficient solar panels.

Read: The most efficient solar panels in the world

A typical 320 watts solar panel occupies nearly 20 square ft. of roof space.

The average number of solar panels based on system size

Size	Units Produced/day	Space Required
1 kW	4 to 5 units	63 sq. ft.
2 kW	8 to 10 units	125 sq. ft.
4 kW	16 to 20 units	250 sq. ft.
6 kW	24 to 30 units	375 sq. ft.
8 kW	32 to 40 units	500 sq. ft.
10 kW	40 to 50 units	625 sq. ft.

The direction of the solar panels

We live in northern hemisphere.

Therefore, the solar panels should face towards the south.

And the tilt (angle with the ground) of the panels depends on the latitude of the location:

Let me share the tilt of a few different places in India.

City	Fixed Tilt
New Delhi	24.32o
Mumbai	16.21o
Chandigarh	26.12o
Thiruvananthapuram	7.24o
Bengaluru	11.02o
Bhubaneshwar	17.25o

Key Takeaways

• The average number of solar panels for a family of 4 or 5 is 10 to 13 solar panels ( 1 solar panel = 320 watts)
• The main factors that decide the number of solar panels are: energy need, sunlight, losses, and efficiency
• Add the units consumed in the last 12 months and divide the sum by 365. You get your average daily energy need.
• The formula for panel size = Your daily energy needs/PSH x (1.25 to 1.4) depending on the losses
• If you have high energy needs then you need more panels.
• Good Sunlight reduces the panel size (fewer panels are required) and improves the financial feasibility of the system.
• The amount of sunlight received depends on your location.
• Extra units produced will go inside the battery and it will produce current at night.
• Panels need to produce a bit extra to cover the losses and meet the energy demand.
• Efficient solar panels occupy less space than the less efficient ones.