An example of calculating solar panels for a home

Whether we confess to ourselves or not, this does not change the essence. Very often, when we begin to implement our serious, especially less serious plans, we neglect projects or calculations. This, as a rule, does not lead to the expected results, or the total time or material costs are not expected at all. Of course, everything must be considered. It is unlikely that anyone will disagree.

As for solar panels, the calculation of their power is simply necessary, since the slightest deviation in any direction leads to a change in material costs by an order of magnitude.

There is another indisputable benefit from the calculation procedure - a conscious, clear understanding of the operating procedure of the future solar power station is being formed. Only a person who has operated an autonomous power supply system in his house will fully understand what this means.

And this understanding comes down to one thing: how to save every Watt * hour of energy extracted. In a house whose power is supplied by an autonomous system, you will not see luminous lighting lamps without the need, as is often the case with traditional power supply.

In the process of using a solar power plant, such devices as motion sensors, timers for automatic lighting control, a photo relay for controlling outdoor lighting, etc. may appear in your home. This will go back to normal.

Do not be surprised that I devote so much time to this issue. It really should be known and understood. Someone will attribute the need to control each Watt * hour to shortcomings, I will not agree with him.

First, let's recall those who simply do not have other options for power supply. Secondly, when this robust economy suddenly became a drawback! You must admit that it would be wasteful to “swell” obviously more money into the power supply system only in order to waste energy uncontrollably.

The beginning of calculating a solar power plant is to calculate the total load of consumption of your home. There are many examples of such calculations in different interpretations, both with a descriptive part and online. In this case, it’s not worth inventing anything new. First, the goal is set, then ways to achieve it are sought. Also here: first, the needs are clarified, and then the technical and material possibilities of satisfying them are calculated.

Calculation of total consumption load

This is the first step in the calculation. It begins with the fact that you take a blank sheet of paper and on it make a list of all the instruments and devices that you assume will be used in the house. For starters, make this list without delving into its quantitative and qualitative composition. At the first stage of the calculation, if you did not have to do it, it is difficult to conclude whether it is advisable or not to leave this or that device in the list. We will add, delete or replace after, when the order of material costs will be clear.

In the meantime, write:

• Energy saving lamp

• TV

• Electric pump

• Iron

• A laptop

• Refrigerator

• Electric kettle

• Washer

• Microwave

• Vacuum cleaner

The next step is to find out the power consumption of each of the devices. This can be found out from the passports for the devices or look at the tags on the devices themselves, where their characteristics are indicated, including the power consumption. In an extreme case, if there are no passports and tags, you can find out the necessary information from sales managers in stores. And finally, you have the Internet at your fingertips, you can search for this data through search engines.

I put down approximate numbers, only to show the order of actions:

If you paid attention to the first two positions, then, as you can see, I divided the lamps with different power consumption. There is no need for small and rarely visited rooms to put the lamps the same as in living rooms. And since the next step will be to set the total operating time of these devices during the day, then there is no point in combining these lamps in one position.

We put down the number and total time of work per day:

The results in the last column should be explained. For example, if you do not use the vacuum cleaner every day, but once a week for 2 hours, then the total time per month will be 2 X 4 = 8 hours, i.e. per day 8 hours: 30 = 0.3 hours. Same thing with the pump. If you have to pump water, suppose twice a week and this process takes 2 hours, then 2 X 2 = 4 hours, 4 X 4 = 16 hours, 16: 30 = 0.6 hours. Of course, round up.

Now we can calculate how much each of the devices consumes electricity per day:

The final stage of daily consumption calculation is to add all the results of the last column. The result will be: 7919.8 W * hour per day.

Well then, let's get down to calculating solar panels. We have a daily consumption of 7919.8 W * hour, from which we will “push off”.

Selection of the DC voltage of the system

The choice of the magnitude of the voltage of the system is necessary, firstly, to select the devices of the system in terms of their consistency in voltage, inverter, battery charge controller, and secondly, the connection schemes of solar modules and batteries will depend on the magnitude of this voltage third, for further calculations of solar cells.

Typically, for autonomous power supply systems of a private residential building, either 12 V or 24 V is selected. Unless, of course, the power supply system is not too powerful and this, its power, does not force to resort to a voltage of 36 V or, say, 48 V, to reduce currents in chains, and therefore, be able to use a wire of a smaller cross section, i.e., cheaper.

In our case, I propose to adhere to the following logic: if you do not plan to increase the power supply system, but assume that it will be limited to 1000 W or 2000 W, then it is enough to stop at 12 V.

In the event that if you plan to increase it, in addition, operate it in the winter, it is more reasonable to build a 24-volt system. This will be reasonable because at a certain stage in the operation of the power supply system, you will most likely come to the inevitability of supplementing it with a wind generator. This is quite logical and gives the system undeniable advantages during operation all year round. We will talk more about this when we touch on the topic of wind generators.

So, so that you do not have to change the once installed devices, it is better to immediately select the 24 V option, then a wind generator with a 24 V output will fit into your existing system without any difficulties.

So. Suppose we stop at a 24 V power supply system variant. I make this choice in our example to show a more clear-cut calculation example. You do what you think is necessary based on your data, of course, taking into account the above.

Determination of the required amount of energy per day

To determine the required amount of energy per day, we need to calculate the daily consumption value calculated by us - 7919.8 W * hour, divided by the system voltage we selected - 24 V. The result of this division will be 330 A * hour.

But we must not forget that the inverter itself consumes part of the energy for its own needs. So we must provide for the energy reserve for him. Based on this, we multiply the result by 330 A * hours by a factor of 1.2 and get 396 A * hours.

Thus, we calculated the daily amount of energy needed to provide power to our consumers. And she was 396 A * hour.

What you should not forget when choosing solar modules

Undoubtedly, the electrical characteristics of PV modules are of paramount importance. Power, voltage, current. But one cannot but pay attention to such parameters as dimensions, design, weight, etc.

Let’s list in order the characteristics and parameters of these devices and simultaneously note how one or another value of these indicators can affect further operation.

Voltage

We begin, of course, with stress. The choice of the battery charge controller, the choice of battery voltage and, accordingly, the circuit of their connection will depend on the choice of voltage.

There is no dogma in this choice, you can choose any voltage. But! The most important thing is that it be standardized. Otherwise, you will encounter the difficulty of selecting equipment such as a charge controller, inverter, and batteries. Even based on a standardized line of voltages, it makes sense to look at which voltages all the necessary devices are available. This is usually 12 volts, 24 volts, 48 ​​volts.

Here you need to make a small remark. You paid attention to the fact that the magnitude of the voltage, and they are usually given by two for the photovoltaic module (maximum power voltage and open circuit voltage), differs from the standard upward. This is necessary in order to ensure a full charge of the batteries. This margin is intended to compensate for losses in the system and takes into account the operation of the module in real conditions when solar insolation is not equal to 1000 W / sq. m, the temperature does not correspond to 25 degrees Celsius.

We stopped at 12, 24, 48 Volts. It no longer makes sense to choose other quantities for the reason that it will be more difficult to find, if necessary, a device with a different voltage. Why deliberately create difficulties for yourself.

It should also be taken into account that some modules are designed for non-standard voltages and are designed to work with network inverters. For this reason, they cannot interest us.

In general, the main principle of building any system should be - whenever possible, to avoid the use of unique devices. Units and devices should be standard and as affordable as possible. Only in this case will you ensure the continued availability of your system.

Power and current

Of course, you gain the total power from those modules whose voltage corresponds to the previously selected for the system. I think that they should not be reminded that they should be with the same characteristics.

By connecting them either in parallel if the voltage of each of them is equal to the selected one, or in series, in the case when the voltage of each of them is less than the selected one. Well, in series and parallel, to provide the total power while ensuring the selected system voltage. Who missed the article “The scheme of connecting solar panels”I recommend reading.

Once you have decided on the number of modules and the circuit of their connection, you can make a choice of the charge controller based on the resulting current, because the voltage of the system is already selected.

Dimensions and weight

Remembering such a truth that each additional electrical connection in the system increases the probability of failure (breakdown), we understand that a single module corresponding to the required power and voltage would be an ideal option for us. Neither extra connections to you, nor extra wires to you.

But we understand that this is impossible. And by and large it is not necessary. It is not necessary if only because in this case we are depriving our system of flexibility, and maintainability will also suffer. I'm not talking about weight, which will play an important role during installation.

It will be much more difficult to build up the system, change the voltage of the system, if this is suddenly needed. Repair the module, after all. Again, high windage. This also should not be discounted, because you will mount the modules on a surface open to all winds.

Nevertheless, not forgetting the truth mentioned, we must pay attention to the dimensions of the modules from the point of view of installation (not every size will allow installation without lifting mechanisms), laying on the roof (no shading throughout the daylight hours).

On the other hand, too small to grind with dimensions - will cost more.

Design

The design also plays an important role both in terms of operational characteristics and from a financial point of view. Frameless modules, for example, will cost less, but it is only possible to use them if you have the opportunity to perform installation in such a way as to ensure their normal operation without frames.

Or you have the opportunity to make your own frame and it will cost you less. The issue of sealing the module should only be taken into account, since contact with the oxidation of moisture and moisture occurs. This significantly reduces their service life.

Things like glass. They are different and the price also depends on this. Conventional glass leads to losses of up to 15% due to reflection. Glasses that can withstand shock loads may be superfluous, but it makes sense to consider glasses with a high degree of transparency.

Continuation of the article:Choosing an inverter and calculating the battery for a home solar power station

Boris Tsupilo