Félix Perez: Renewable energy essentials

How the human convert water or sun light into energy to charge your phone? Félix Perez, PV engineer answers this and more questions about the essentials of renewable energy.

Laura Rodríguez
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Check our episode notes and the transcript for the episode on renewable energy essentials. Finally, here you have our refered links:

This is an automated translation of our original episode. If you want to check the original version, have a look at Los esenciales de las renovables (Spanish).

Who's Felix Perez?


Welcome to Ogami Station, a podcast created by RatedPower. As every month we bring you closer to the exciting world of renewable energies through interviews with relevant figures in the sector.

Good morning to all who’s listening. Truth is that we are very excited because after several months of hard work, we can finally present our first episode of Ogami Station. I'm Gabriel Cañadas and together with my colleague Laura Rodríguez we will have the pleasure and honor of presenting you this monthly podcast. How are you doing, Laura?


Very well, Gabi. How are you? How are you all? Very excited to be here today with our first podcast. I'll tell you a little bit, if you like. Ogami Station was born with the intention of bringing renewable energies to all Spanish speakers in a didactic, simple, but above all entertaining way. So we hope you like it. In addition, the idea of this podcast is that every month we will be visited by influential people in the industry with whom I will discuss more topics, more simple, such as today's introduction to renewable energy, but also on the evolution of new technologies and other current issues within the industry.

So Gabi, what are we going to talk about today?


For this first episode we have the exceptional presence of our colleague Félix Pérez Cicala. An industrial engineer by vocation, he decided to specialize in energy technologies and as soon as he graduated he jumped right into the world of renewables, researching the application of software for renewable engineering. After several years of experience, Félix decided to join the RatedPower project very, very early on. He has always led all kinds of projects within the company, both on the engineering side and on the software development side to make pvDesign, after all, become the leading software in the market.

With Felix today we are going to try to make a first approach to renewable energies to understand: where they come from; explain in a simple way whatsolar photovoltaic energy is in specific; and also its different applications. And finally, how does this technology work?

Without further ado, first of all, I would like to thank Felix for accepting our invitation. Thank you very much, Felix. How is everything going?


Well, thank you very much. I am delighted to be here and very happy to be able to share with you the experience of the first episode of Ogami Station.


Great, great.

So let's start at the beginning. We know that the first application of renewable sources was not exactly for electricity generation. As early as the 3rd century BC, there is evidence of the first water mill. It used the natural motive power of river water to grind different types of foodstuffs, tubers, seeds and grain to make flour. Later, throughout the Middle Ages, its use was extended and other types of applications arose, such as the water pump. It was also used to drive bellows or saws for different manual works.

But let's go specifically to what interests us. Tell us a little bit, Felix, when the first real hydroelectric projects arose.


Well, the first recorded project for electricity production was in England and it was for a very simple use.

It was to light a light bulb in a house. One imagines it in an English mansion, with a small light bulb and a warm light and powered by a hydraulic energy source. Then, the uses, let's say industrial, were at the end of the 19th century in the United States that began to build large companies for the production of electrical energy and the technology had a very good option. By 1920, 25% of U.S. electricity production was from hydropower. The worldwide expansion was from 1950 or so, and it has been growing quite steadily since then.

Logically, these are projects that take a long time to build as they are large dams, but many countries have built them in large quantities and there are countries that have a lot of hydraulic resources available, such as Sweden, which has a very high production with hydraulic energy.

History of renewable energy


Great, great. Let's see, tell us a little bit about how it works, in a basic way, how this technology works and how it generates electricity.


Well, hydropower takes advantage of the potential energy of water. It consists of accumulating a very large amount of water behind the dam and using a column of water, which is the height of the water, the jet is dropped through a conduit and passed through a turbine.

As it passes through the turbine it drives a spin on the turbine which in turn goes to a generator and the generator is the one that produces electricity. The larger the dam, the more water column is available to drive larger turbines, and the more water in volume, the more electricity can be produced for a longer period of time, to the extent that water is available.


Truth is that it is impressive and also, since we are talking about renewable energies in general, I would like to take the opportunity to also talk about wind power. Like hydropower, it had its first uses centuries ago. The windmill, for example, its first uses date back to the 16th century in Afghanistan to grind wheat or even extract water.

In the end, it is similar to the water mill that my colleague Gabi could be talking about before. I also wanted to ask you Felix, a little more about more modern uses of wind energy, which although it dates back centuries ago, now we can classify it as one of the most powerful renewable energies.


Well, the first use for electric energy production was also at the end of the 19th century, in Scotland. The use was for charging batteries. It was to charge accumulators. They made a mill - it has nothing to do with what is used today - but it was for charging batteries. Then the technology development is interesting because during the transition between the 19th and 20th century, it had a pretty good option for pumping water for pumping operations on farms and in industries.

It was a pretty good use because it is a very localized use. You set up a windmill on a farm, you drive a water pump. These may be places where electricity was not available in any other way, but with wind power it could be harnessed. Then the technology had that use for many years. Technologically, until the 1970s, there was no significant development again. In the 1970s, with the oil crisis in the United States, a lot of money began to be invested in the development of this technology.

NASA was even given grants to develop projects. And that was when windmills, as we know them today, began to be designed and produced. Between 1980 and 2000, the first windmills with one megawatt of power began to be manufactured. From the year 2000 onwards, when the technology had the explosion in installation capacity that brought us to where we are today. It is one of the most widely used technologies.

That was from the year 2000 and then it has had a very good growth, very stable over time. And well, compared to photovoltaic, which boomed a little later, wind power has been in a situation in which it is a very high option for almost 20 years.

History of solar photovoltaics


Very interesting, indeed.

It is curious how these energies have evolved. Well, imagine a windmill on a river centuries ago, to the large companies that we can find today in any country in the world. But well, let's continue with something you like, Felix. Let's get right into photovoltaics. I am going to make a small introduction. I ask you to please correct me in case I make a mistake.

Back in 1839, a Frenchman, Beckerell, just 19 years old, experimentally demonstrated the photovoltaic effect. This effect consists in generating electricity from a material that is illuminated. Logically, not all materials produce the same. The effect is mainly observed in metals or other conductive materials. A few years later, in 1883, Charles Fritz built the first photovoltaic cell, which was basically selenium with a thin layer of gold around it. This device had a very low efficiency of 1%.

But hey, it was something. It wasn't until 1905. This is a rather curious fact. When this effect was explained theoretically by Einstein and also for this explanation, Einstein won the Nobel Prize -which everybody thinks he won for the theory of relativity, but it was not-. It was for this effect. We still had to wait until 1954 for Bell Laboratories, the famous Adam Bell, inventor of the telephone, to manufacture the first real practical photovoltaic cell.

So much for a bit of history as a way of introduction. But please, Felix, we know you know much more about this, enlighten us and tell us a little about the first practical uses of this technology.


It's interesting that you mention the first practical cell in 1954, because the first, let's say applied use of the technology was 1958, it was used to power a satellite (Vanguard-1). It was the fourth satellite to go into orbit and the second launched by the United States.

And I thought it was interesting to talk about the use in satellites because today it is fully accepted and common, but I guess it was not very obvious at that time. The first satellites were battery-powered -Sputnik I was battery-powered. There is another source that uses a form of nuclear energy to power satellites. Using the radioactive decay of plutonium. But solar technology is the most common form. All satellites in orbit today use solar power.

The space station has the most power of what's in orbit right now on Earth, and that use came from 1958 and the laboratory conditions that were used at that time.


And already after that, we can go to the commercial applications on Earth, that we know today. We can start with some remote, off-grid communities. Then we can go to other commercial and residential applications. And from there, to the renewable boom we are experiencing now.

What is the origin of this boom? We can summarize it in two factors. First, social awareness. And secondly, economic viability. If we start by talking about social awareness, then we can say that the boom in renewable energies is not only about social awareness, but also about economic viability. If we start talking for social awareness. This started with the active fight against climate change with recurring sustainability issues, such as resource scarcity, environmental pollution, nuclear disasters, etc. And from this arose, for example, the first breakthrough at the political level, which is the famous Kyoto Protocol of years ago, and the subsequent Paris Agreement, which is the one currently in force.

However, although social conditioning was and still is the beginning of the renewable revolution, the real reason for the massive deployment of renewables, and especially solar energy, is economic viability. This is mainly due to falling prices. In just ten years, module prices have fallen by 80%. And that is where we can talk about this boom, especially in our specialty, which is solar energy.

Solar energy sectors breakdown


It's very interesting, of course.


So if you agree, what we are going to do now is to start talking a little bit about the difference between the different sectors of solar energy, such as residential, commercial and utility scale.


Great, so I'll start if you want. On the residential side, these are the projects that you can have in your house or the panels that you can install inside your house. They are self-consumption projects so that the houses themselves, because the energy they consume is produced by solar energy. Or even this currently with marketers that let you sell that surplus production if you do not consume it internally in your home, you can inject it back into the network and thus lower your electricity bill even more.

These facilities are usually very small installations that are installed on the roofs of houses and usually have a size of between 10-20 plates and between 3 and 10 kilowatts.

Then we would move on to commercial or industrial installations. These are larger installations. They would also be for self-consumption, but for companies or factories. And they would also be installed on the roofs of companies, buildings or factories.

These are, therefore, economically more viable because of the economies of scale that they have at the end. And that is the reason for the financing that these companies have, because they are expensive projects and, well, the size of these installations would be around 100 to 1,000 panels and between 50 and 200 kilowatts.

Although it is true that in recent years, there are larger companies that have already begun to install projects not only on the roofs of their companies, but also in parking lots, on the roofs of parking lots or even on empty land next to their companies. They can be projects that can even reach up to megawatts of capacity. To get into what we are interested in. Let's see if Felix can tell us a little more about projects of this scale.


The commercial and utility scale, which is the market we are referring to now, has fundamental differences with respect to residential and commercial. First of all, in purpose. The residential or commercial market arises from the need to achieve savings on the electricity bill. Fundamentally, to reduce electricity costs. Logically, depending on the location, the country, the supplier, depending on how much you were paying for electricity, it will be a very significant saving -or not so much-.

But in what is utility scale, the purpose is to sell electricity, to produce electricity on a large scale and commercialize that electricity in a national electricity market in order to make a profit. So that implies some differences in the size of the installation.

On the one hand, to give you an idea, when we are talking about utility scale, we are talking about at least one megawatt of power. Before, as Gabi said, a house, a few tens of panels can be 3 or 6 kilowatts. A commercial installation can be hundreds of kilowatts, but in utility scale, it is at least one megawatt. And that's a minimum.

Globally, the average size of a utility-scale project is around 80 megawatts and they can scale up much higher. They can go up to 100, 200, 500 megawatts. There are even mega-projects, worldwide, that can have one gigawatt or even two gigawatts. And they are being built today. It's interesting to think in terms of number of houses. It's a way to visualize a little bit how much electricity that is.

A project of hundreds of megawatts is going to be thousands, tens of thousands, of houses. So let's say they can produce electricity for a very large area. And in terms of solar panels, which is also another way to visualize how much equipment is actually being put in. We are talking about hundreds of thousands of panels and these are installations that occupy a very large area of land. We are talking about hundreds of hectares, if not thousands of hectares of land occupied to make the photovoltaic plant.


Of course, how big! I would like to take this opportunity to point out the difference between systems connected to the grid - to the national energy grid. They can thus dump the surpluses generated that have not been consumed. But also off-grid systems, which are those we have talked about before in remote communities in large countries, such as Australia, some African countries or even islands.

How a solar photovoltaic plant works?


Now Felix, what we would like to understand is how a solar PV power plant works. How does it work, what are the parts of it, how does it work?


The most important element of the plant is the photovoltaic module, photovoltaic plate or solar plate. It is called by many names. Basically it consists of a device that when exposed to sunlight, produces electrical energy. It produces direct current between the electrodes and generally each plate has a power of 300-400 watts, which is relatively little. So that's what is supposed to be good for achieving the powers that we were talking about hundreds of megawatts.

Now, if you do the division, you will soon reach the number of hundreds of thousands of plates. If we want to get there, we have to put a very large number of solar panels.

Then, another aspect they have is that the conversion efficiency is relatively low. That means that if a panel receives approximately 1,000 watts per square meter of solar energy, that is, 1,000 watts of energy per square meter of exposed surface. The conversion ratio is 15%.

We are talking about a 300-watt panel and that is usually two square meters of panel. So if 2,000 watts of solar energy goes in and 300 watts of electrical energy comes out, it is relatively little. Another aspect to mention is that solar energy production is not constant. It's not constantly at full power. Say, at that 1,000 watts per square meter it would be like what you would have at noon on a summer day.

Under more normal conditions, there will be half or two-thirds. It is important to understand that the electrical output of the PV module is proportional to the light it receives and is almost directly proportional. If it receives half of the radiation, it will produce more or less half of what it would produce in nominal conditions.

The next point to understand is that earlier we talked about the differences between residential and commercial and utility scale. In residential and commercial, the panels are mounted on rooftops. But now in utility scale we are talking about them being mounted on the ground. We have large areas, hundreds of hectares, on which the plant is installed. For that we use mounting structures.

The mounting structure is a metallic structure, basically, on which the modules are placed. There are two types, which are the fixed structure and the tracker. The fixed structure is the cheapest, simplest type to manufacture.

It is fundamentally a structure that separates the module from the ground, which is logically important to avoid problems of humidity, vegetation, etc. And also, what is done is that the module is tilted to take advantage of more solar energy. It is tilted in the direction in which the ground is going to be present most of the year.

Then, the trackers are kind of an evolution of that system. They are single-axis trackers because they only have one axis of rotation and the operation of the tracker that tracks the sun as it moves from east to west on the horizon.

So in the morning the trackers would be facing east and in the afternoon they would be facing west. At noon they would be practically horizontal, because the axis of rotation is oriented on the north south axis. So, that is why the turning axis oriented north-south in the morning faces east, in the afternoon faces west. At noon, they will be practically horizontal.

The difference with a fixed structure is the cost - a little bit higher, logically - because now we have moving parts in the system. But because they track the sun, they allow the solar panel to capture more radiation, more sunlight. So, by capturing more radiation, it produces more. So each module is better utilized and the plant produces more per module installed.

Well, these two elements constitute a little of what one sees in the photo of a photovoltaic plant. You see on a surface, a very large area, with modules that have a blue color and you can see them. One also senses the presence of a structure on which they are mounted. They are not, let's say, just lying on the ground.

But then there is a whole additional system, because well, let's say we want to sell electricity to the grid. Then we will have to connect that whole series of modules to the grid somehow.

There is a system that is not visible to the naked eye, which is the electrical system. What constitutes the electrical connections from the module, which is the smallest element, all the way to the grid, which is the destination of the production.

The first element to mention is the inverter. The inverter is a very important piece of equipment because the modules, as I said before, produce energy, DC direct current energy.

The fundamental issue is that the power grid is in alternating current, it is in AC current. You have to make a conversion from direct current at the output of the module to alternating current to get there. That is done in the inverter. 

The inverter is an equipment that converts from continuous alternating current and that one characteristic defines it, that it has a very high efficiency. As of today, an efficiency of around 98 or 99%. All this to put it in context, thinking before in the photovoltaic module, we say that it has a conversion difference of between 15 or 20% an inverter and 98%. That's about right.

There are also quite a large number in the plant. There can be 100, 200, 500 inverters, depending on the type of inverter. There are smaller inverters with which you are going to have a much higher number. Fundamentally the function is to convert from direct current to alternating current.

Then the inverters are physically located in the plant, in a building that is the power station, which will also have dozens of power stations in a plant.

The power station has the function of being the physical location of the inverter, but it also has another equipment which is a medium voltage transformer. The problem is that the alternating current that comes out of the inverter does not come out at sufficient voltage to transport it efficiently. So what is done is to raise the voltage of the inverter using the transformer and thus achieve better transmission efficiency to the cables.

Basically, the idea is to achieve better transmission efficiency to reduce losses and reduce the size of the cables needed to size the electrical system.

The last step of the system is the electrical substation.


Very well explained. Truth is that it is a pleasure to hear from you. Where I do have doubts is: how do you then connect this mega solar plant to the grid?


Well, the last step in this process of transmitting the electrical energy from the module to the grid is the substation. In this case, there are not a large number of substations. There is one substation per plant, fortunately.

The substation consists of two elements, mainly one is a high voltage transformer and the others are disconnectors or circuit breakers. The high voltage transformer raises the voltage one more step. If you remember before in the power station we had gone to medium voltage.

Well now we are going to go to high voltage. High voltage is what is called the voltage of the power grid, of the country's power grid. Logically, in each country it is different, even for grid connection points it will be different. And the fundamental reason is that in the power grid, since we are talking about transmitting electricity, tens or even hundreds of kilometers from one point to another, with a high voltage line -like the ones you see on the road-. To transmit electricity on that scale requires very high voltage.

The transformer that is in the substation, what it does is to raise the voltage another step higher to reach the grid voltage. And once you are at the same attention as the grids, when you can already dump energy to the grid and sell.

From there it is said that it is the end of the photovoltaic plant. Once you are connected to the grid you are already selling energy and you are already part of the system.

The other element that I was talking about before, the selectors are elements in charge of disconnecting the plant from the grid. Because the plant cannot always produce, nor do you want it to be connected all the time. Sometimes for maintenance or whatever, it has to be disconnected and that is done from the substation. It is literally a switch or electrical switch. It is disconnected from the grid so that they are isolated from each other.

Pros and cons of solar energy


Great. If you guys want to continue a little bit talking about the advantages or the disadvantages of solar. So, I want to start, because I think the easiest thing that comes to our minds is that solar energy is a clean, ecological energy, especially if we compare it with other traditional energies.

And it is also renewable. And what does this mean? It means that it uses a free and natural source of energy such as the sun, which is also abundant. We are not going to run out of it. I wanted to mention those two. I don't know if you want to continue with any extra.


Utility scale PV has a couple of advantages that are very relevant when compared to other energy sources. One that comes to mind is modularity. Earlier we were talking about these plants having capacities of tens or hundreds of megawatts. The plant can be configured to have almost any power value and that is not possible in other sources. When we talk about, for example, coal-fired thermal plants or nuclear power, for example, they are gigawatt by gigawatt groups.

So you can have a nuclear power plant of 1, 2, 3, 3, 4? gigawatts. But you can't once make 770 megawatts unless you make a reactor of just that power and dimensions all of that power. Photovoltaics, however, as fundamentally you can put more or less modules or plates; the inverters, the electrical system. Also, you can increase inverters and power stations and they are much smaller intervals or steps than in other sources.

So, fundamentally, if you want to build a larger photovoltaic plant, you can put more panels and more inverters and occupy more land. And as more land becomes available, the plant grows. This very linear way of scaling is very different from other sources.

Then, another aspect of photovoltaic that I find interesting is that compared to other types of energy sources, it has relatively simple engineering, especially if we compare it with traditional sources, thermal plants, and nuclear. If we compare it with hydropower, which requires the construction of large dams, it is not even possible in all places. Obviously there have to be certain conditions for a dam to be built.

That simplicity of photovoltaic -that it has no moving parts, that it scales very easily-. We also think from the point of view of maintenance. If I have a problem in one part of the plant, I can shut down that part of the plant only. I can shut down those inverters, that power station without having to shut down the rest of the plant.

If you compare it to a nuclear reactor, one gigawatt. If I have a problem with the reactor, then I have to shut down the whole module.


You have a problem, of course.


And that's without going into the level of problem that can be caused by that. Which can be very big, as we all know.

These advantages in terms of simplicity make it have operation and maintenance costs that are low compared to other types of sources. For example wind, which has a mobile generator, can have much higher maintenance costs than photovoltaic.

Thinking about wind power, for example, to perform maintenance on wind generators, operators have to climb to the top of the nacelle, which can be dozens of meters above the ground. It is not that it is difficult, but that it can be even dangerous for the operators.


Of course. Speaking of inconveniences as well. We are not going to say that everything in photovoltaics is great, although much is, but it also has its small drawbacks. As Felix has commented, the issue of efficiency. Photovoltaic is not very efficient. Also because of the occupation of the land it occupies, because of all the space it takes up.

In the end, in a plot of land we would say that in about two hectares of land -which is a lot of land-, there would be room for about one megawatt of solar power. But for example, if we compare it with another renewable energy such as wind power, for example, a single wind turbine that would be this giant windmill, which may have a diameter of 200 meters, there are even modern windmills or modern wind turbines that are capable of generating up to 12 megawatts of power in a much smaller area of land.

Another drawback of photovoltaics is intermittency. What does this mean? What it means is that a solar panel can ultimately only generate power if the sun is shining on it. At night it is not able to produce. It produces zero energy. This is a problem because at night we also consume energy. So the solar plants would not be useful for the night consumption of the population.

Then, on the other hand, there is also unpredictability. This also happens to wind power, for example. If there are suddenly clouds and the sky is covered, that plate will produce much less than expected. Just as with wind, if it doesn't blow at a certain moment, it won't be able to produce electricity at that moment. These are the drawbacks -that there is some way to solve-. But that's not what we're dealing with now.


Well, yes, referring to the problems of intermittency and unpredictability of renewable sources, it is a problem that all renewable sources have today -the main ones, hydro, wind and photovoltaic-, each one in a different way.

With hydro we have the problem that there is no water in times of drought, because you don't have that source. Which, depending on the energy mix of each country, is a very big problem. In the case of wind power, it can produce for several days and there is a strong wind, but it can also have moments in which there is no wind for several days and the atmospheric conditions are very calm and they do not occur.

In the case of photovoltaic. We have the problem that it only produces during the day. Then it already presents difficulties. And on top of that, the intermittency due to the passage of clouds, which produces peaks in production, generally downward peaks.

One technology that can help solve these problems of all renewable sources are batteries or storage. The idea is to use a large battery plant to accumulate electrical energy during times when there is more availability of renewable energies.

For example, in the case of photovoltaic, during the radiation peaks of the day at midday, it may be that there is a surplus of energy because the plant was producing more and that surplus is dumped into the battery system. The idea is to discharge the batteries during the night and sell the energy during those hours.

We must also understand that this has a very strong economic component from the point of view that it is possible to sell that electricity during the night, which is a time when the price may be different and may be more favorable than during the central hours of the day in which energy availability is called.

These battery systems can be used for both photovoltaic and wind power. Because it is like a buffer, a system of inertia that allows to accumulate energy in the moments in which there is availability and then discharge it little by little. And that energy is just as renewable as if it had been produced at the moment, because the source is the same, but it allows energy to be discharged at other times.

Above all, this solves the problem of the manageability of these sources. We cannot decide when the sun rises or when the wind blows.

Yes, with traditional energy sources we can turn a plant on and off, and this is done, in fact, to manage production and match supply to demand. But we cannot do that with renewables.

Battery systems solve this fundamental problem, which is that they allow you to manage when you produce with renewables.

We expect that as the years go by, today they are, let's say, marginally economical in certain very specific locations, but they are not yet economically viable, such as photovoltaic or wind. The expectation is that as the years go by and the cost goes down, they will reach that point and start to be installed and to achieve that manageability.


And politically, they are realizing that. And there is a lot of investment in that direction, of course.


Great, great. Batteries is a topic that could certainly take a whole episode of Ogami Station.


We'll have to think about it.



Yes, of course, for the future.

This is the end of our first episode!. Thank you very much for joining us today, Felix. Truth is that we have loved this time we have spent with you and I think we have all learned a lot. For those of you who are listening to us, we also hope that you have learned something new about the world of renewables.

If you would like us to cover a specific topic in the future, you can always leave your questions or your comments on iVoox and you can also leave your reviews on the podcast and we will follow them carefully for future topics.

It would also help us a lot if you subscribe to Ogami Station from your favorite podcasting platform, since we are on all of them and you rate us positively. That way we can also have more visibility and we can reach more people and spread the message of renewables, which I think is important. As you say, Laura, there is social awareness, but I think there is a long way to go.

You can see the episode notes and all the links that we've discussed at ratedpower.com/podcast and I think that's all. Thank you all very much.


Goodbye! And have a nice day.



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