What can you run with a 150-watt solar panel?

You can run a fan, T.V., Laptop, LED, and more with a 150-watt solar panel.

We find our energy needs and then size the solar panel.

For knowing my energy needs.

I will look for the number of electrical appliances and note down their power.

Then I will find the average number of hours I want to run on solar power.

Then finding the energy consumption by multiplying their power by the number of hours.

This is the approach for sizing the solar panel.

In this post, we’ll do the opposite.

I have a 150 watts solar panel.

I will find how many electrical appliances I can run and for how many hours.

Let us start it.

Understanding the power of the solar panel

The solar panel in consideration has 150- watt power.

We know that power is the product of voltage and current.

For solar panel producing Pmax 150-watts, the voltage and current values are:

Vmp = 18 volts
Imp = 8.35 ampere

Making a power of (18 volts x 8.35 amp) 150 watts

This value is written on the back of the solar panel.

What does it mean?

Is it going to produce 150 watts in every situation?

No, it will produce 150 watts only when certain conditions are met.

These are called the Standard Test Conditions (STC).

When the sunlight is 1000 W/m² and it falls perpendicular to the solar panel.

(1000 W/m² = 1 Peak Sun Hour)

And the cell temperature is 25ᴼ C.

Air mass index: 1.5

In other words, I can say that my 150 watts solar panel will produce 150 w-hr when the sun rays are falling perpendicular with a PSH intensity of 1.

Some people mistook it for the number of hours the sun is in the sky.

If the sun shines for 11 hours in a day in a particular location.

Then they multiply the power of the solar panel power by 11 to get the energy produced.

For 150 watts, they do 150 watts x 11 hours = 1650 W-hr.

This is the wrong approach.

“Peak Sun Hours (PSH) and the time for which sun is in the sky are the two different things.”
1 PSH = 1000 W/m²

Let us understand it in more detail to clear up this confusion.

The energy produced by the solar panel

We know that the relative position of the earth and the sun is changing every moment.

The two main phenomena that make this happen are:

Rotation around its own axis

The revolution of the earth around the sun.

Rotation gives us day and night.
Revolution gives us seasons.

Both these phenomena bring variation in the sunlight intensity.

If I take a particular day, I observe sunlight variation from sunrise to sunset.

It first starts increasing.

And reaches the maximum around.

Then starts reducing and reduces to the minimum during the sunset.

If I am given the task of finding the total sunlight intensity for a whole day.

I will first find the sunlight intensity every hour from sunrise to sunset.

Then add them all to get the total sunlight intensity.

Assuming the following chart.

Adding all the values, I get 5000 W-hr in a day.

Let us find the Peak Sun Hours of this day.

As discussed, 1000 W/m² is 1 PSH.

I divide total sunlight intensity by 1000 W/m² to get the PSH for that day.

These are:

PSH = 5000 W-hr/1000W/m²

= 5

It is clear that PSH and the number of hours of sun in the sky are two different things.

A 150-watt solar panel with 1 PSH sunlight intensity will produce 150w-hr energy.

Therefore, with 5 PSH, it will produce 5 x 150 watts = 750 W-hr.

What are PSH in my region?

For a common man, it is difficult to find the PSH in the region in which s/he is living.

Don’t worry, our scientists, engineers, and solar experts have made our work easy.

They have collected the PSH data for decades and provided us for finding energy from solar panels.

When I talk about my region that is Delhi/NCR.

The average PSH in my region is 5.35.

5.35 is the average of daily PSH for 12 months including all the seasons of winter, summer, spring, monsoon, and autumn.

This value becomes the basis for the amount of energy produced by the 150-watt solar panel.

The energy produced by the solar panel is directly proportional to the PSH.

The energy produced by my 150-watt solar panel would be:

150-watt x 5.35

= 802.5 watt-hr

If I place the same 150-watt solar panel in a different location.

The amount of energy produced would be different.

For example, Karnataka is near to the equator than Delhi/NCR.

It receives more sunlight.

The average PSH in the state is 6.12 hours per day.

when I place the 150-watt solar panel in Karnataka.

The energy produced would be:

150-watt x 6.12

= 918 watt-hr

Which is 918 – 802.5 = 115.5 W-hr more.

I suppose the concept is clear.

Coming back to the region of Delhi/NCR.

I am rounding off the average PSH of 5.35 to 5.

It is to make a conservative estimate.

In that case, the energy produced by a 150-watt solar panel would be:

150-watt x 5

= 750 Watt-hr.

There are losses in the system

Like any other machine or instrument.

The solar panels do suffer from various losses such as:

Dirt loss
Shading loss
Temperature loss
Conversion loss
Transmission loss
Efficiency loss
Aging of the solar panels
And many other losses

If I sum up all the losses then they can eat up to 30% of the power produced by the solar panel.

“Quite surprising”

Despite this, the solar power system is a financially attractive option.

The real energy produced by 150-watt solar panel

The real energy would be when I deduct the above losses from the energy produced by a 150-watt solar panel.

That is:

750 watt-hr – 30% of 750-watt-hr

= 750 – 225 watt-hr

= 525 watt-hr.

This is the usable energy for me from the 150-watt solar panel.

And I will utilize this energy for running my electrical appliances.

The battery backup

My 150-watt solar panel is producing 525 watt-hr of usable energy in the daytime when placed in Delhi/NCR.

I want to use this energy at night or in the evening.

As I am out during the day.

I need a system that can store energy from the solar panels produced in the daytime.

For this, I need a battery backup.

But before this, I need to size the solar charge controller.

Solar Charge Controller

It is a semiconductor device that is placed between the solar panel and the battery.

The solar charge controller regulates the battery charging.

When the battery is empty, it allows the full flow of the current from the solar panel.

when the battery is full, it passes a trickle charge to the battery.

It prevents the backflow of the current to the solar panel.

For its right sizing, I need to look at the Imp (current at the maximum power) of the solar panel.

The Imp of a 150-watt solar panel is 8.35 Ampere.

I will take 1.25 times of Imp, to get the sizing of my solar charge controller.

It is in Ampere = 1.25 x 8.35 Ampere

= 10.4 Ampere.

I need to place a 10.4 Ampere rating solar charge controller in between the solar panel and the battery.

Okay,

coming back to the battery sizing.

This will run my electrical appliances in the night.

Therefore, I need to size the battery which can store 525 watt-hr energy.

We have understood above that the 150-watt solar panel is producing 18 volts.

And the current flows from the higher potential to the lower potential.

Therefore, I should look for a battery that is at lower potential with respect the solar panel.

So that my 150-watt solar panel can charge it efficiently.

We see batteries come in 12 volts, 24 volts and so on.

Therefore, I should select 12 volts battery.

The battery capacity comes in Ampere-hour.

In this case, my battery size would be:

Usable energy produced from the solar panel/Battery voltage

= 525 watt-hr/12 volts

= 44 amp-hr

This means I can withdraw 44 amp of current in 1 hour or 22 amp current in 2 hours or 4.4 amp current in 10 hours.

Understanding the DOD of the battery

But

Withdrawing the whole current will leave the battery empty.

And doing this affects the duty cycle and the useful life of the battery.

Therefore, I need to keep some current in it to keep it working effectively.

How much charge you should leave in the battery is decided by its depth of discharge (DOD).

A battery with 80% DOD means you can safely withdraw 80% of the charge and keep 20% in the battery.

So that it works fine.

Similarly, a battery with 50% DOD means you should withdraw 50% of the total charge and keep another half in the battery.

I am taking a battery with a DOD of 80%.

In that case, my new battery capacity would be:

Useable energy from the solar panel/Battery voltage x DOD

= 525 watt-hr/12 volts x 0.8

= 55 watt-hr

It means 80% of 55 amp-hrs, 44 Amp-hr should be used and 11 Amp-hr should be left in the battery.

The efficiency of the Inverter

This charge is stored in the battery in the form of chemical energy.

When you extract energy from the battery.

The chemical energy gets converted into Direct Current.

But most of our electrical appliances run on AC.

The inverter converts DC to AC.

And in doing this conversion, some of the energy is lost.

The amount of loss depends on the efficiency of the inverter.

Assuming my inverter is 95% efficient (It will lose 5% energy in this conversion).

This means I will get 5% less energy for running my electrical appliances.

To compensate for this loss, I need to increase my battery size by another 5%.

Therefore, the right battery size would be:

Useable energy from the solar panel/Battery voltage x DOD x inverter efficiency

= 525 watt-hr/12 volts x 80% x 95%

= 58 watt -hr.

Finally, I should go to the market and look for 12 volts/58-amp hr battery.

My 150-watt solar panel can charge this battery in a day.

Finally, What can I run with a 150-watt solar panel?

Now my system is ready.

I can run my electrical appliances in the daytime with solar panels.

At night with a battery (charged by the solar panel in the daytime).

Let me write down some of the common electrical appliances and their power rating.

Fan: 75 watts
TV: 100 watts
LED: 15 watts
Laptop: 40 watts

The 150-watt solar panel is producing 525 Watt-hr in Delhi/NCR.

With this energy,

I can run my fan for 525 watt-hr/75 watts = for 7 hours
TV for over 5 hours
10 LEDs of 15 watts each for 3.5 hours
My laptop for 13 hours

I can run 1 fan, 1 TV, 1 laptop, and 1 LED for 2.3 hours.

You can make combinations that suit your energy requirements.

Do want to know the PSH in your region?

Check out my solar feasibility spreadsheet.

I’ll see you with another interesting post next time.

Yash 🙂