How Many Panels, Batteries, Charge Controller and Inverter Do I Need?

Electrical Technology

A Complete Guide About Solar Panel Installation. Step by Step Procedure with Calculation & Diagrams

Below is a DIY (do it yourself) complete note on Solar Panel design installation, calculation about No of solar panels, batteries rating / backup time, inverter/UPS rating, load and required power in Watts. with Circuit, wiring diagrams and solved examples. Anyone who follows the simple steps (DIY tutorial) below can install and connect solar panels in home for residential applications.

If you pick this article related to solar panel installation, You will be able to;

To calculate the no of solar panel (with rating)
To calculate the rating of Solar panel
To calculate the rating of batteries for Solar panel system
To calculate the back up time of batteries
To calculate the required and charging current for batteries
To calculate the charging time for batteries
To calculate the rating of charge controller
How much watt solar panel we need?
Connect Solar Panel in Series or Parallel?
How to select the proper solar panel for home
UPS / Inverter Rating for load requirement and much more…

Solar Panel Installation: Step by Step Procedure with calculation and examples

Before we start, its recommended to read the article about proper selection & different types of solar panels and photovoltaic panel for home & commercial use as well. To the point, lets know how to wire and install a solar panel system according to the proper calculation and load requirements.

Related Post: How to Design and Install a Solar PV System? Solved Example

Now lets begin,

Suppose, we are going to install a solar power system in our home for a total load of 800W where the required backup time of battery is 3 hours (You may use it your own as it is just for sample calculation)

Load = 800 Watts

Required Backup time for batteries = 3 Hours

What we need to know?

Inverter / UPS Rating =?
No of batteries for backup power =?
Backup Hours of batteries =?
Series or Parallel Connection of Batteries = ?
Charging Current for Batteries = ?
Charging Time for batteries = ?
Required No of Solar Panel =?
Series or Parallel Connection of Solar Panels = ?
Rating of Charge Controller = ?

Solution:

Table of Contents

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Inverter / UPS Rating:

Inverter / UPS rating should be greater than 25% of the total load (for the future load as well as taking losses in consideration)

800 x (25/100) = 200W

Our Load + 25% Extra Power = 800+200 = 1000 Watts

This is the rating of the UPS (Inverter) i.e. We need 1000W UPS / Inverter for solar panel installation according to our need (based on calculations)

Related Post: How to Determine the Suitable Size of Inverter for Home Appliances?

Required No. of Batteries

Now the required Back up Time of batteries in Hours = 3 Hours

Suppose we are going to install 100Ah, 12 V batteries,

12V x 100Ah = 1200 Wh

Now for one Battery (i.e. the Backup time of one battery)

1200 Wh / 800 W = 1.5 Hours

But our required Backup time is 3 Hours.

Therefore, 3/1.5 = 2 → i.e. we will have to connect two (2) batteries each of 100Ah, 12V.

Backup Hours of Batteries

If the number of batteries are given, and you want to know the Backup Time for these given batteries, then use this formula to calculate the backup hours of batteries.

1200 Wh x 2 Batteries = 2400 Wh

2400 Wh / 800 W = 3 hours.

In the first scenario, we will use 12V inverter system, therefore, we will have to connect two (2) batteries (each of 12V, 100 Ah) in Parallel. But a question raised below:

Related Post: What are the Blocking Diode and Bypass Diodes in a Solar Panel Junction Box?

Series or Parallel Connection for Batteries

Why Batteries in Parallel, not in Series?

Because this is a 12V inverter System, so if we connect these batteries in series instead of parallel, then the rating of batteries become V₁+ V₂ = 12V + 12V = 24V while the current rating would be same i.e.100Ah.

Good to Know: In Series Circuits, Current is same in each wire or section while voltage is different i.e. Voltage are additive e.g. V₁+V₂+V₃….Vn.

That’s why we will connect the batteries in parallel, because the Voltage of batteries (12 V) remains same, while its Ah (Ampere Hour) rating will be increased. i.e. the system would become = 12V and 100Ah +100Ah = 200Ah.

Good to Know: In parallel Connection, Voltage will be same in each wire or section, while current will be different i.e current is additive e.g. I₁+I₂+I₃…+In

We will now connect 2 batteries in parallel (each of 100Ah, 12V)

i.e. 2 12V, 100Ah batteries will be connected in Parallel

= 12V, 100Ah + 100Ah = 12V, 200 Ah (Parallel)

Good to Know: Power in watts is additive in any configuration of resistive circuit: P Total= P₁ + P₂ + P₃. . . P_n (Neglecting the 40% installation loss)

Related Post: Series, Parallel and Series-Parallel Connection of Batteries

Charging Current Needed for Batteries

Now the Required Charging Current for these two batteries.

(Charging current should be 1/10 of batteries Ah)

200Ah x (1/10) = 20A

Related Post: How to Calculate the Battery Charging Time & Battery Charging Current – Example

Charging Time Required for Battery

Here is the formula of Charging Time of a Lead acid battery.
Charging Time of battery = Battery Ah / Charging Current
T = Ah / A

For example, for a single 12V, 100Ah battery, The charging time would be:

T = Ah / A = 100Ah / 10A = 10 Hrs (Ideal Case)

due to some losses, (it has been noted that 40% of losses occurred during the battery charging), this way, we take 10-12 A charging current instead of 10 A, this way, the charging time required for a 12V, 100Ah battery would be:

100Ah x ( 40/100 ) = 40 (100Ah x 40% of losses)

the battery rating would be 100Ah + 40 Ah = 140 Ah (100Ah + losses)

Now the required charging current for the battery would be:

140Ah / 12A = 11.6 Hours.

Required No. of Solar Panels (Series or Parallel) ?

Now the required No of Solar Panels we need for the above system as below.

Scenario 1: DC Load is Not Connected = Only Battery Charging

We know the famous power formula (DC)

P = VI ………… (Power = Voltage x Current)

Putting the values of batteries and charging current.

P = 12V x 20 A

P = 240 Watts

these are the required wattage of solar panel (only for battery charging, and then battery will supply power to the load i.e. direct load is not connected to the solar panels)

Now

240W/60W = 4 Nos of Solar panels

Therefore, we will connect 4 Solar Panels (each of 60W,12V,5A) in parallel.

The above calculations and system was only for battery charging (and then battery will supply power to the desired Load) to AC electrical appliances, which will get power through inverter and DC loads via Charge controller (via charged batteries)

Scenario 2: DC Load is Connected as well as Battery Charging

Now suppose there is a 10A directly connected load to the panels through inverter (or may be DC load via Charge Controller). During the sunshine, the solar panel provide 10A to the directly connected load + 20A to the battery charging i.e. solar panels charge the battery as well as provide 10A to the the load as well.

In this case, the total required current (20 A for Batteries Charging and 10 A for directly connected load)

In this case above, total required current in Amperes,

20A + 10 A = 30A

Now, I = 30 A, then required Power

P = V x I = 12V x 30A = 360 Watts

I.e. we need 360 W system for the above explained system (This is for both Direct Load and Batteries Charging)

Now, the number of solar panels we need

360/60W = 6 Nos of Solar Panels

Therefore, we will Connect 6 Nos of Solar panels in parallel (each of 60W, 12V,5A)

Click image to enlarge

Solar Panel Installation with Battery for charging and DC Load — fig: Circuit Diagram for the above Calculation for Solar Panel Installation (Solar Panels only for battery charging + Direct connected load).

Rating of Charge Controller

As we have calculated above that the charging current for 200Ah battery is 20-22 Amperes (22A For Battery Charging+10A for direct DC Load), therefore we can use a charge controller about 30-32 Amp.

Note: The above calculation is based on ideal case, so it is recommended to always choose a solar panel some bigger then we need, because, there are some losses occurs during battery charging via solar panel as well as the sunshine is not always in ideal mood.

Related Post: How to Calculate the Right Size of Solar Charge Controller?

How Many Watts of Solar Panels Do We Need?

We have shown a very simple method in the previous post to find that How much Watts solar panel we need for our home electrical appliances? depends on the sunshine time and the load in watts we need to power up an electrical appliance. In case if you need to run an appliance only on solar power without battery backup power, you may need to refer to the previous article which shows how to determine the number of required solar panels to run an appliance during the day without batteries.

Related Posts: Basic Components Needed for Solar Panel System Installation

Which Solar Panel Should We Select?

First of all, there are two main types of solar panel e.g. N-Type and P-Type photovoltaic cells. The N-Type solar panel is suitable in terms of efficiency and long-life span while P-Type is recommended to reduce the initial cost.

Among lots of brands and material of solar panels like c-Si, String Ribon, Thin Film Solar Cells (TFSC) or (TFPV), Amorphous silicon (a-Si or a-Si:H),Cadmium Telluride (CdTe) Solar Cells, Copper Indium Gallium Selenide (CIGS/ CIS) Solar Cells, BIPV: Building Integrated Photovoltaic Panels, Hybrid Solar Cells and PV Panels, We have discussed in a very details post “different types of solar panels with advantages/advantages, cost, and applications” This way, you will be able to determine the best type of solar panel for home use.