Photovoltaic Panels – What is it?

In this tutorial, you will learn the basics of PV system parts, load consumption analysis profiles, and how to join them into a functional system.

This will give you the basics of what is necessary to have in order to use power retained from the sun. For simplicity reasons, we will consider a basic setup with 1 panel.

In any case, you can use this section to know how to connect any PV system, it being for camping, off-the-grid, grid supply connection, household use, or industry application. The big difference between those applications are big electric loads, the number of panels, distances that power cables have to travel, specific electrical boards to accommodate inverters and mandatory protections, optional electric equipment, mechanical loads to consider in the roofs and subsequent structures, legislation to respect, bureaucracy to fulfill, grid contracts and geography. But all of the above is present and explained on our “PV systems” course coming, which tells more in detail about component dimensioning, calculations, number of panels to use, cost, and return on investment.

Let´s start!

Parts Required

Follows some parts to have in order to implement the full system. However, it was chosen just a kit with enough and minimum parts. Do not take into consideration the seller or the parts in this kit, it is just to give an idea and help to understand in the beginning.

Photovoltaic panel

Figure 1

What is a PV cell and panel?

A photovoltaic cell is the smallest part of a photovoltaic system. Through the photovoltaic effect, where an electrical voltage arises in a semiconductor material when it is exposed to the incidence of photons from the sun’s rays. This creates a movement of electrons through the cell and thus a current.

Figure 2

We get from a photovoltaic cell the Ipv + Vpv after the internal losses. Seems obvious, but if solar irradiation drop or if the ambient temperature raises above a certain level the Iph will also drop. Solar irradiation can drop caused by clouds, dust, object shade, or moister, so be sure to have it clean and free.

In the end, a PV panel is a set of PV cells. Therefore, a panel will be composed of a number of specific connection cells, with each other, power in a certain way,
it will be proportional to the number and type of internal connections.

Figure 3

There is also different type of cells, like polycrystalline, monocrystalline, and so on. Influencing the efficiency and performance in some conditions and final price.


It reduces the solar irradiance and sometimes can put one entire panel out of service. Most cheap panels are bad at dealing with shade, but others have their internal connection arranged in certain ways with bypass diodes to minimize the shade effect. Generally, the more bypass diodes a panel have the more expensive it gets, but if you assure that your surroundings are clean and shaded free the cheaper one will do the job.

Figure 4


PV panels have an optimal temperature of 25 Celsius. To characterize this there is a variable named Temperature coefficient which indicates how much the conversion efficiency drops with temperature increasing.

Figure 5

About the temperature, we can not do anything about it since we can not control the weather. Buying a very efficient panel is one solution however expensive. Have in mind that the same PV system in the Sahara Desert vs Germany will need more panels to reach the same power only due to higher temperatures.

Angle mount

Another way to maximize solar irradiation, depending on your geography, is to align the panel directly to the sun’s path and with the correct angle. To discover the best angle depending on your country/city you can use an online calculator like this: Angle calculator

If you do not have a mechanical system to move/orient them during the year, it will be better to place them in an average position good for all seasons. Below is an example of Lisbon, a angle of 40 will be good for most of the year.

Figure 6

Note: Mechanical sun tracking systems (Sunflower) can increase PV system output and efficiency by up to 30% but you must consider a bigger cost.

Remember, to be sure to meet all the criteria above in order to maximize the panel. Below we can see a typical output curve for one day.

Figure 7

The pic output happens at around 12 am, so we should take into account that this is the max power that can be subtracted from our electrical bill. Also, sun hours have a huge impact but in general PV power fluctuates a lot during the day.

Now knowing how it works and how to optimize it, let´s dive into panel arrangements. By grouping several panels in specific ways it can be achieved higher voltages or higher currents or both and minimize the effects of shade.

panels in Series

To wire solar panels in series, connect the positive terminal on the first panel to the negative terminal on the next, and so on. The resulting voltage will be the sum of all of the panel voltages in the series. However, the total current will be equal to the output current of a single panel. This can be made due to some voltage requirements from inverters.

Figure 8

panels in parallel

To wire solar panels in parallel, connect all of the positive terminals on each panel together and then do the same for the negative terminals. The resulting current will be the sum of all of the panel amps in the parallel array. However, the total voltage will be equal to the output voltage of a single panel. 

Figure 9

which is better

Solar panels in series are optimal in unshaded conditions. If shade covers a single panel of your series array, it will bring down the whole system’s power output.

Solar panels in parallel operate independently of one another and therefore are the best option for mixed-light conditions. If shade covers one or two of your panels, the remaining panels in the array will continue to generate power as expected.

Remember, wiring multiple solar panels in series or parallel doesn’t change the total output voltage. The choice will be influenced by shade or inverter specifications.

Load/flow controller

Figure 10

A solar charge controller manages the power going into the battery bank/Inverter from the solar array and from the batteries to the load. Like when there is an excess of power from the panels the controller charge the batteries or power the loads directly from the panels and at night drains the batteries to the load. However, if you do not have DC loads all the supply will be made by battery/inverter path.

Figure 11

Also, it ensures that the deep cycle batteries are not overcharged during the day and that the power doesn’t run backwards to the solar panels overnight and drain the batteries. Some charge controllers are available with additional capabilities, but managing the power is its primary job.


Batteries as part of our PV system can store excess solar energy instead of wasting it. If your panels are producing more electricity than you need, this energy can go back into charging your battery. When your solar panels aren’t producing electricity, you can draw from the stored energy when you need it. Without a battery bank, you won’t be able to store energy for later use, meaning that if you are off-grid you will have a black-out at down. The electricity is sent back to the grid or not used only when your battery is full or draws from the grid only when the battery is low.

Choosing the best battery for your solar panels involves many factors in your decision, including the capacity, power, efficiency, and costs depending on your needs.

Batteries are typically made of lead-acid or lithium-ion. When selecting the best battery for your solar system, it’s important to understand the difference between what is a deep cycle battery vs. flooded lead-acid, sealed lead-acid, and lithium batteries before making your selection.

For simplicity, let´s stick to Flooded lead-acid (FLA) batteries, since they are among the most common batteries used for off-grid solar setups, and are inexpensive and recyclable.

DC/AC Inverter

Figure 12

PV inverter is a type of power inverter which converts the DC output of PV panels AC Voltage that can be fed into a commercial electrical grid or be used locally by ordinary AC-powered equipment. Solar power inverters have special functions adapted for use with photovoltaic arrays.

Solar inverters may be classified into 4 types:

  • Stand-alone inverters, are used in isolated systems where the inverter draws its DC energy from batteries charged by photovoltaic arrays. Many stand-alone inverters also incorporate integral battery chargers to replenish the battery from an AC source, when available.
  • Grid-tie inverters, which match phase with a utility-supplied sine wave. They do not provide backup power during utility outages.
  • Battery backup inverters, are special inverters that are designed to draw energy from a battery, manage the battery charge via an onboard charger, and export excess energy to the utility grid.
  • Intelligent hybrid inverters, manage photovoltaic array, battery storage, and utility grid, which are all coupled directly to the unit. These modern all-in-one systems are usually highly versatile and can be used for grid-tie, stand-alone or backup applications but their primary function is self-consumption with the use of storage.

Remember that if you are off-grid you do not need an inverter capable of grid interaction but one capable of battery management. However, if you have access to the grid and no batteries capable of interacting with this the grid is a good option then you continue to be powered at night by the grid. Also very important, some inverters are capable of replacing the load/flow controllers since they can integrate generator, grid, and batteries all in one unit.

Figure 13

Load profile

But first, let’s talk about something that is a priority in this application and very important for electrical dimensioning and the number of panels. In order, to be precise let’s consider hypothetical and small load.


  • Small fridge
  • Alarm system
  • lights bulb

The fridge represents an intermittent load always connected like the alarm the light bulbs can be connected when the user desires. The type of load and the time it enters into operation is crucial for solar systems.

Let´s detail the load on this setup:

  • A fridge is working a great amount of time. On average with a power of 130 W and works several times during the day and depends on atmospheric conditions. Let´s consider it works 5 times a day so +- 6h. Equals 130Wx6h = 780 Wh per day.
Figure 14
  • An alarm system is always working with a constant power of 30W, then equals 30Wx24h = 720Wh
  • Lights bulbs only work when the user desires and in this case with 40W, then equals 40Wx6h = 240Wh

In total, our setup has 200W max, 30W constant, and 40W controlled by the user.

Figure 15

Remember that is a good practice to manage the loads and use them when the max production is happening, for example, 10-16h, but sometimes is difficult due to the load type, like light bulbs are only used at night. So in our case, we can not do much, since fridge consumption is unpredictable and the light bulb will not be turned on at daylight, we will only be able to power the fridge when on and alarm.

How to join them without batteries

Figure 16

Let’s start by looking at the figure above. It shows the way to connect all the parts of our simple solar system to the loads without considering batteries. If we use cheaper inverters, like Stand-alone inverters, we will need the load/flow controller even if we do not have DC loads or batteries.

The question that arises is “why should I have a PV system without storage?”. Well, price, weight and load management, and type can have a huge influence on this choice. Batteries cost a lot; sometimes loads do not need to function during the night, or priority loads only work during the day. That decision may come after analysis.

If we chose a Stand-alone inverter with no batteries it means that we will not have grid supplying when the sun is down, which is not ideal. So, from now on we decide to use a Grid-tie inverter.

Our loads are 200 W max so the inverter needs to deliver that to the load, however, the inverter has losses and those must be supported by the panels. Considering the efficiency of a cheap 300W inverter, that is 92%, the panel should deliver at least 220W.

Figure 17

Why are we choosing an inverter to match the max load if the load is not always on at the same time? that is more or less correct, but imagine the fridge turning on at the same time as the user turns on a light bulb. We would not have all the power available and aiming for a bit more power is always a good practice.

As we saw above, PV panels have low efficiency and power drops with temperature, shading, and cable losses, so we have to aim the total power of the PV panel to at least 250W. This output can be divided into 2 panels or just 1. But remember that the inverters have input DC voltage rates to be respected (22-60Vdc). Let´s choose 1 big one of 270W (TP270M). We match the requirements for our inverter at “STC-Standard test conditions” and we can expect a drop on power but always be close to the 220W needed.

Figure 18

Then the results of this combination will be something like the following figure, assuming that the inverter is giving 200W at every condition:

Figure 19

As we see the light bulbs have no effect since they work at night (worst case scenario all night), but we can see significant drops represented by the green arrows. Around midday all the power consumption from the fridge plus the alarm are supplied by the panels, so is always a good practice to use loads during this time of the day. Also, we see some blue areas touching the 170W which happens when the fridge is not working and is seen as excess energy. For this type of load, there is a possibility of storage since there is excess energy or adding more loads to use the excess power when the fridge is not working.

In conclusion, with this setup, we will save money by not consuming and not paying for this energy from the grid, plus it is cheaper because it has no batteries.

We can save up to (being generous):

  • On alarm 30wx8h = 240Wh
  • On 2h +1h in start/end of the day 130x4h = 520Wh
  • Total = 760Wh/day
  • Excess energy +- 800Wh/day

The load controller must accept the power and max voltage of our panels and if you have DC loads you can connect them directly to it. In addition, the controller must be programmed and configurated for the presence of only the inverter.

Joining with batteries

Figure 20

If we are planning to go off-grid a little error makes little difference for a grid-tie system, in the case of an off-grid,d it means the lights go out! It needs to produce as much energy as is being used, with a battery bank to get you through the nights. You can only get this right if you know how much energy is needed.

Now let´s analyze the possibility of installing storage on our setup. Have in mind that the excess power will be the only one responsible to charge the batteries. Taking that into account we have almost 800Wh/day of excess.

Aiming for one day of autonomy and a State-Of-Charge (SOC) of 20% which very low and risky, but in practice, this works out to more than 1 day of storage, since on overcast days solar panels produce more power, and lead-acid batteries can go all down to 20% SOC without doing damage.  There will still be times in deep winter when the batteries sized will fall short, so a grid or generator is generally still needed to bridge those gaps.

We have an energy need of 1.7kWh/day (780+720+240). To get to the total energy needed in battery storage we need to:

Bat size (kWh) = Daily energy (kWh) x Autonomy / (1 – SOC) <=> Bat size (kWh) = 1.7 x 1/(1-0.2) = 2,125 kWh

The result is the amount of energy our battery bank needs to hold when fully charged. Let´s assume a 24 Volt battery bank output since it is also an accepted rate by our inverter:

Amp-hours = 1000 x Energy storage (kWh) / Battery Voltage (Volt) <=> Amp-hours = 1000 x 2.125/ 24 = 89Ah at 24 Volt

So we need a bank of 2,125 kWh/89Ah at 24V. This can be achieved by connecting in series 4 batteries of 6V/2 batteries of 12V of 90Ah each or parallel of 2 batteries of 12V 45Ah each and so on…

Now we just have to calculate the money we save by not paying the energy to the grid vs the cost of the batteries. But if we are aiming for an off-grid system the return on investment is not important but yes the energy available at the desired time.

Looking to one random manufacturer Power Sonic we can see we have already one unit capable of matching the capacity we want however at 12V, so 2 in series are required:

Figure 21

The load controller must accept the power and max voltage of our panels and if you have DC loads you can connect them directly to it. In addition, the controller must be programmed and configurated for the presence of batteries and an inverter.


Have in mind:

  • Seasons were not considered in this tutorial for example deep winter.
  • You can double the panel to fight the winter or use a typical winter day and repeat the calculation. Summer will always represent an excess of power if you dimension your system with winter as a priority
  • This tutorial gives you the basics to understand a PV system and the respective load analysis. There is a lot more about it.
  • Load profile and analysis is the first thing to do when dimensioning a PV system
  • Consider the amount of light on your location to find the exact number of Area/PV panels needed and what pic power can be achieved.
  • Choosing the inverter and conversion losses. Generally, inverter max power is equal to the power of all the equipment that can be connected at the same time.
  • Defining if it is a completely off-grid system or half supplied by the grid
  • Annalise the battery bank capacity and price or if your system is meant to be full off-grid



May the force be with you. Towards the Future !!!

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