A complete guide for Home Solar Power System

Welcome to this page!
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You are here, it shows your interest towards solar power.

I have designed a complete guide about residential solar power system that will ignite interest in you and I’m sure that you are going to install a system after understanding this guide.

What is Solar energy?

The light and heat we receive from Sun are called solar energy.
The Sun is providing this energy for the last 4.6 billion years and is capable of producing this energy for another 4-5 billion years.

Hence, it is a renewable source of energy.

Sun provides us energy in the form of packets called photons.

This energy is used by all the living beings for their survival.

Even all the energy sources like fossil fuels, wind energy, hydro energy that we use in our daily lives are derived from the solar energy.
"The sunlight falling on the earth in 1 hour is sufficient to fulfill the energy need of the entire world for a year"

Why Solar energy?

The extensive use of fossil fuels like coal and petroleum for the last 200 hundred have created a big damage to our planet.
  • The pollution level has increased far beyond the maximum limit, leading to many health-related serious problems.
  • The emission of green house gases has resulted in global warming and the melting of the glaciers.
  • What is Greenhouse effect?
Therefore, we will be needing an alternate energy source that fulfills our energy demands and solar power system fits in this category because of the following benefits:

  1. Pollution free hence environment friendly
  2. Low maintenance cost
  3. Reduced electricity bill
  4. Source of energy is free which is sun
  5. Can be installed in any terrain
  6. Technological development
  7. Hedge against rising electricity prices
​The renewable energy or to be more precise the solar energy is gaining popularity because of its long-term benefits over fossil fuels.

How electricity is produced?

Before explaining the process of how electricity is produced, let me first tell you what is electricity?
"Electricity is the flow of electrons from one place to another"
An atom consists of electrons, protons and neutrons.
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The protons (positively charged) and neutrons (no charge) are enclosed inside the nucleus while the negatively charged electrons are revolving around it.
Atom model
Source: www.goodfreephotos.com
I would suggest you to read the following posts, explaining everything about how electricity is produced from the solar energy?

How to harness solar energy?

One can harness solar energy through various techniques like solar thermal technology, passive heating and solar photo-voltaic technology.

But we will restrict our discussion to solar photo-voltaic technology.

In this technology when sunlight falls on semi-conductor material, like silicon, it gets converted into electric current that run the electrical appliances.

The silicon cells are connected together through soldering wires on frame, making a solar panel.

The photo-voltaic cells are made from different semi-conductor materials but the silicon based solar PV cells are more in practice.

There are different kind of silicon solar cells like
  1. Mono-crystalline silicon
  2. Poly-crystalline silicon
  3. Amorphous silicon
that are used in making solar cells.

The efficiency of the solar cells depends on the type of silicon is used in making it.

The mono-crystalline solar cells have the highest efficiency amongst the three.

What is home solar power system?

The set of equipment when connected in certain pattern is capable of converting sunlight into electricity, running the household electrical appliances like fans, bulbs, washing machine, fridge etc is called the Residential Solar System.

The basic system consists of following equipment:
  1. Solar Panels
  2. Charge controller
  3. Battery
  4. Inverter

All these devices are connected with wires in a certain pattern to complete the system.
The solar panels are generally installed at the rooftop of the houses to capture the maximum sunlight.

Let me tell you the functioning of this system.

1. The solar panels that are made up of silicon cells absorb the sunlight and convert it into direct current.
2. This direct current has two paths after passing through the solar charge controller (It regulates the charging of battery and prevents the back flow of the current to the panels): one connecting to the battery and another leading to the inverter.3. When direct current enters the battery, it gets converted into chemical energy and stored inside the battery. This process is charging the battery. When the direct current passes through the inverter, it gets converted into alternating current and run our electrical appliances. The household electrical appliances are designed to run on alternating current.

These components work together and produce alternating current to run the household appliances.

The different types of system

There are 3 different types of system
  1. Grid tied system
  2. Grid tied with battery backup
  3. Off-grid solar power system
In grid tied system the household appliances are connected to both solar power system and grid supply. The homeowners home-owners have the option to get electric supply from either source.

This type of configuration creates a balance between supply and demand.

For example, in a clear sunny day, your system may produce excess electric than your home appliances are consuming. In that case, the homeowners can feed and sell the excess electricity to the grid through Net Metering and get paid for it. During bad weather conditions, your system may be producing less current than required by the appliances. In that case, homeowners can withdraw power from the grid. The addition of the batteries can help the home owners to get the smooth supply even during power outage or the grid failure.

The off-grid solar power systems are completely cut-off from the grid supply. Therefore, the power back in the form of the solar batteries is the must.
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Which type of system suits you depends on the amount of sunlight, grid supply and your energy needs.

Do it Yourself: Solar

Many adventurous homeowners are designing the complete solar power system by themselves.

Because Do-it-Yourself has major financial benefits. Thus making solar more lucrative and financially rewarding.

DIY Solar has the following 3 components:
  1. Sizing and designing the system
  2. Purchasing the components
  3. Installation
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We'll discuss the first 2 parts and leave the third one for your local solar installer.

Actually, solar installation requires electrical and mechanical instruments, training and experience. There are chances of electrical hazard while connecting and testing the equipment. Therefore, it is better to leave this part to the local installer as he is better equipped and experienced.

Advantages of DIY Solar

When you design the complete system yourself, you are in full control of the project.
  1. You know your energy needs clearly and there is no scope left for any mismatch between your energy demand and electricity produced by the solar power system.
  2. You know the specifications of each component clearly
  3. When you size and design the system yourself, you are in position to buy each component used in making it. 
  4. You can get multiple quotes from the companies and can negotiate for the best price.
  5. There is always a scope to save around 15% of the total cost when you are designing, sizing and purchasing the equipment yourself.
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Let us move on and start designing and sizing the home solar power system

Step 1: Know your energy needs

The first step is to know your energy needs.

To know this, first find the load that you want to run on solar power
"Load is the amount of power of your electrical appliances"
  1. Select the appliances that you want to run on solar
  2. Write the power rating of each appliance
  3. Add them all

For example, I want to run 2 LEDs of 20 watts each and 2 fans of 100 watts each on solar power.

In that case my load would be equal to (20 + 20 + 100 + 100) watts = 240 watts

Energy need:
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Next, I say that I run these appliances for an average of 6 hours in a day.
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Then my energy need would be 240 watts x 6 hours = 1440 watt-hours

Step 2: Know the Peak sun hours in your region

It is very important to know the amount of sunlight in your region.

If the sunlight is good then even small system will produce enough current to meet your demands.

While the same is not true with the poor sunlight.
"The total amount of sunlight falling on the surface of the earth over a 1 square meter area in a day is termed as solar insolation" ​
It is expressed in Watts/m²/day

On a clear sunny day at noon, the intensity of sunlight is 1000 watts/m².

1000 watts/m² of sunlight for 1 hour is called 1 peak sun hour.

When you add sunlight, falling every hour on 1 m² area, from sunrise to sunset and then divide the result by 1000 watts/m² or 1 peak sun hour, you get total peak sun hours in your region.

I would suggest you to read "What is the concept of solar insolation?" before going to the next step.

Step 3: Size your panels

​The current produced by the panels passes through different equipment and undergo many conversions before reaching to your fans and lights and running them.

In this process, the some of the current is lost as heat and other losses.

If I'm going to highlight them then there would be many like:
So, in order to run your fans with right speed and bulbs can glow properly, the panels must produce some extra current than required by the appliances so that even some of it gets lost, the remaining current would sufficient to meet the demand.

I can write the above statement in the following form:
  • Current produced by the panels – losses = current reaches to the household appliances
 Or
  • Energy produced by the panels – losses = Energy required by the appliances
 
Or
  • Energy produced by the panels = Energy required by the appliances + losses

Read: How to size the panels of your solar power system?
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​So, we take a multiplying factor and multiply this by the energy demand. And when you divide the result by the peak sun hours, you get the size of the panels in watts.

For example, the energy demand is 1440 watt-hours and the multiplying factor is 1.3. The energy produced by the panels would be 1440 x 1.3 = 1872 watt-hours.

Assuming further, the peak sun hours is 5.

Then the size of the panels would be 1872/5 = 374.4 watts (calculated)

You can either purchase one 375 watts panel or can buy two panels of 190 watts each.

The general rule of thumb is look for panels whose power ratings are nearest to the calculated one.

​Step 4: Configuring the panels

In this step you are going to connect the panels in a certain pattern (series, parallel or a combination of both) that will give you desired output in terms of voltage and current.

Step 5: Size the Inverter

The solar panels are able to convert the solar energy into d.c. electrical energy. 

But most of the electrical appliances like ceiling fan, fridge, cooler, LEDs etc run on the a.c. current. 

Therefore, you need a device that could convert the d.c. current from the solar panels into a.c. current and then fed to the electrical devices .

This work was done by the device named the Inverter.

It converts the d.c. current into the a.c. current. 

Most people use size of the panels and multiply it by 1.3 as an expansion margin to size the inverters.

Step 6: Size your battery

The size of the battery depends on:
  • Load
  • Backup in days
  • Depth of discharge of the battery
  • Efficiency of the battery
The battery size in Ampere-hour can be calculated as 
  • (Load x No. of days of backup)/ (DOD x Efficiency x Battery voltage)
The battery voltage is same as system voltage from the panels.

Step 7: Size the solar charge controller

A solar charge controller is required in almost all solar systems which require the battery backup.

The solar charge controller is an electronic device when placed between the solar panels and the battery regulates the voltage coming from the solar panels to the battery.

It protects the battery from being overcharged. The solar charge controller monitors the voltage of the battery and when the battery voltage reaches to the certain level it opens the circuit and the charging of the battery from the panels get stopped. 

You can size the charge controller as follows:

Divide the size of the panels by the voltage of the battery or the nominal voltage of the system. Take a multiplier of 1.3 to add extra cushion to it.
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Step 8: Size the wire

The size of the wire is very important; an undervalued wire may result in excessive heating and can burn out while an over-sized wire may cost more. 

Therefore, it is very important to choose the right size of the wire. 

Whenever energy flows through wire, it offers some kind of resistance. The resistance offered by the wire is directly proportional to its length and inversely proportional to its area, or I can write in a mathematical equation like this: 
  •  Resistance α Length/Area 
Or
  • R = ρ L/A 
Where ρ is the resistivity of the wire, generally copper wires are used

The size or the thickness of the wire is directly proportional to the current produced by the panels.

For example, if your panels are producing more currents, you need thick wires on the other hand when your panels are producing less current then you need thin wires.

Step 9: Determine the angle and orientation of the panels

Now, in order to receive the optimum energy from the sun, my solar panels should be tilted and oriented in the right direction, otherwise the solar system will not operate effectively and efficiently.

The position of the earth with respect to the sun keeps on changing due the rotation around its own axis and the revolution around the sun.

The orientation & the tilt depend on the two factors:
  • Hemisphere (Northern hemisphere or the Southern Hemisphere)
  • Coordinates latitude

If you live in the Northern Hemisphere like India, then you should keep your solar panels facing in the south direction.

If you live in the Southern Hemisphere like Australia, then you should keep your solar panels facing in the North direction.The tilt (the angle from the earth’s surface) that you should keep your solar panels is based on your latitude value as follows:
  • If latitude > 25°, then tilt = 0.76 x latitude + 3.1
  • If the latitude < 25° then tilt = 0.87 x latitude

Step 10: Calculate the roof area

Your solar panels should be placed on the roof where there is no shade of tree or other building as it obstructs the sun light and reduce the efficiency of the solar module.

Therefore, it is very important to calculate the shade free area.

Your sizing will go waste if you do not have the adequate shade free area on your roof. 

The calculation of the shade free requires the following steps:
  • Calculate the area of the one panel
  • Multiply it by the number of the panels used to design the system
  • Multiply the result by 1.3 to accommodate the gap between the

Home solar feasibility

You know home solar power system requires a good amount of investment.
"An investment is an asset which is purchased with an expectation of getting income in future"
If the income or the return is more than what you expect then it a good investment otherwise you do not consider that project.
 
Same holds true for home solar power system.
 
If your system gives you good return then it is a profitable investment otherwise not.
 
You too can know the technical and financial feasibility of the system even before installation.
 
The feasibility of the home solar power system depends on the following factors:

​Average Peak Sun Hours

By now, we all know that average peak sun hours play very important role in finding the feasibility of the system.

A region with poor sunlight requires more panels than required by the region with good sunlight to produce the same amount of current.

People living at or around equator have an advantage of good peak sun hours throughout the year.They can have enough current with fewer panels that can meet their energy needs.

Therefore, the cost of the system is comparatively less in sunny areas than that in regions with poor sunlight as fewer panels can produce enough current to meet the energy needs.  

Let me explain you with the help of an example:
You can see the average peak sun hours of
  • Berlin (Germany): 3.01
  • New Delhi (India): 5.51 and
  • Colombo (Sri Lanka): 5.75

Colombo is the sunniest amongst the three and Berlin receives the least sunlight amongst the three.
For example, 3 friends living in each of the location have same energy needs.
Then the friend living in Berlin will have the costliest solar power system while the friend from Colombo will be paying the least amount to meet the same energy needs.

Cost of the home solar

First was the case of cost difference on the basis of Peak sun hours due different locations.

You can also see the cost difference even if the location is the same.

For example, 2 persons A and B installed home solar power system of same size and same configuration. But still A's total cost were found to be around 15%-18% less than that of B's.

This cost difference could be due number of reasons:
  1. Maybe 'B' could have purchased the equipment at the higher rate or could not have negotiated well.
  2. The solar installer might have charged higher installation rates from 'B'
  3. 'A' might have sized and designed the system himself. Thereby he got do away with these charges.
  4. 'A' could have purchased the equipment himself by getting multiple quotes. Hence he was successful in reducing  the cost of the system. 
You can see that when you learn to size and design the system by yourself. You have full control over the project and you are in good position to negotiate and cut the undesired expenses.

The more reasonable is the cost of system, better is the financial feasibility of the project.

Units generated by the system 

You see the home solar power system is not going to give you money every month.

You have to convert the units generated by it into equivalent amount of monetary value.

For example, you have installed a home solar power system at your rooftop and your household appliances are consuming 6 units daily.

You are not paying any bill for it because the source of electricity that is Sunlight is available at free of cost.

You would be consuming those 6 units from the grid if there would have been no solar power system at your rooftop.

It means by consuming 6 units from home solar you have saved 6 grid units.

Or

I can say that the monetary value of 6 solar units = monetary value of 6 grid units.

Or
  • Monetary value of 1 solar unit = Monetary value of 1 grid unit

In simple words when your home solar system is producing more solar units, you are saving more money that really means you are getting better returns from your solar power system.

​Cost of capital

People invest in project with some minimum value in their minds that they get out of it.

Going back to the school days, we use to hire the bicycles for an hour by paying Rs.10 in advance.

But we never use to give back the bicycles to the 'cycle uncle' in 1 hour. It was always 25-20 minutes extra. He was so nice that he never overcharged.

In the above example, rupees 10 was my investment and 1 hour ride was my minimum reward.

Anything less than this wasn't accepted to me.

Your cost of capital is something like this.
"It is the minimum rate of return that you expect from an investment"
If the project doesn't give this minimum return, it is rejected.

It may be possible that the same project is feasible for one but is not acceptable to other.

Let me clear you with an example, one home solar system is giving 8% annual return.

A and B are 2 friends.

A’s expectation is 6% per year while B’s is expecting 10% annual return from the system.

The same system is feasible for A but no for B because his expectation is more.

Maybe he has borrowed money from somewhere at higher rate while A had his own money invested in the project.

​That is why his expectation was low as compared to that of B’s.

Grid escalation rate

The system that you have installed is going to provide smooth electricity for at least 25 years.

Moreover, the grid price is not going to be the same every year.

If I’m not wrong, these are going to escalate with time.


If grid’s rates are going to escalate more, it means you will be paying more to the grid and if you install the solar power system then it means you are going to save more with time.
Therefore, high escalation rates of grid electricity are going to improve the feasibility of the solar power system.
Grid electricity is very costly in Germany and is escalating at an average annual rate of 3.85%.

In the year 2017, the grid price was 29.16 Euro cents per unit of electricity consumed or kWh

(Source: STROMVERGLEICH)
  • If Germans are going to use grid electricity for next 25 years then they will pay 75 Euro cents for every unit consumed in the 25th year.
  • But if they would be using solar then they would be saving 75 Euro cents for every 1 unit generated by home solar power system
In simple words when the grid electricity rate is high and is escalating every year, it makes solar more attractive.

Solar panel degradation rate

You know the performance of the panel degrades with time. It means that it is not going to generate the same number of units in future which it is producing now.

Obviously, they will reduce will time.
"Degradation is reduction in the output of the solar panel with time"
The degradation in the performance of the panel is caused by multiple factors which can be broadly classified as:
  • Reversible degradation
  • Irreversible degradation

When your panel degrades, it affects the financial feasibility of the system.

​Annual maintenance cost of the system

Just like your car, the solar power system do requires maintenance on regular basis like:
  • cleaning of the panels
  • filling water in the battery 
  • checking the connections
  • repair if anything gets out of order

All the above activities require money that increases the overall cost of the system and reduces the overall return offered by it.

All the above factors affect the financial feasibility of the home solar power system some positively while others negatively.

Let me tabulate these factors:

​Calculating the feasibility of the system

The feasibility of the home solar can be found through:
  • Internal rate of return (IRR) [Project is feasible when IRR > Cost of capital]
  • Net present value (NPV) [Project is feasible when NPV > 0]
  • Payback period (Time required to recover the cost of the system)

All the above methods have unique style of calculating the feasibility of the project.

But each one of them take same inputs like: