# How many photovoltaic modules do you need for your home?

If you think about installing solar panels in your house, you must think about many variables, one of them and very important is to know how many photovoltaic modules you need for your home. Then I will show you how to do it.

# How many photovoltaic modules do you need for your home?

The price of the photovoltaic installation is a priority for a potential investor. That is why we often hear the question “What is the cost of installing a photovoltaic installation for a single-family house?” Regardless of whether the customer wants to install a photovoltaic installation in a company building or in a home, the approximate price is decisive for him. Generally, before we start talking about the costs of photovoltaic energy, we must determine its power, the number of photovoltaic modules installed and their arrangement on the roof or possible floor structure to meet energy needs.

## How to calculate the power of a photovoltaic installation?

The basic parameter when selecting the power of a photovoltaic installation is the annual energy consumption of a potential inverter. Electricity consumption is determined by electricity bills. The base is the average annual energy consumption of a home or production plant. In general, the amount of energy consumed during the previous year is added or the electricity bills of the last six months or a quarter are taken into account.

Given the annual electricity consumption expressed in kWh, it is assumed that 1000 kWh is equivalent to 1 kWp of the photovoltaic installation. Thus, if the annual consumption in a single-family home is 4235 kWh of electricity, then a photovoltaic equipment with a capacity of at least 4.3 kWp is required. Taking into account that 20% of the surplus electricity generated must be transferred to a power company, the real demand should amount to approximately 5.2 kWp.

The choice of the final wattage depends on one more factor: the location and size of the roof. If the roof is well lit, located to the south or southeast or southwest, the designated wattage will perfectly suit the needs of our single family home.

However, if the roof is oriented east-west or its non-standard dimensions, the number of photovoltaic modules will have to be slightly increased. With the East-West configuration, the performance is 10% -15% lower compared to the optimal configuration. Therefore, there are times when the installation must be increased by 1 kWp. Consequently, the number of photovoltaic modules installed on the roof is increasing.

## How many solar panels do you need for your home?

The number of photovoltaic modules depends on two main aspects:

• Size of photovoltaic installations
• The dimensions of the roof itself.

The size of a photovoltaic installation is determined by its power. However, the number of modules that we will need to achieve this value depends largely on the size of the roof itself. However, before dealing with the specific number of PV modules, let’s look at the power of the PV cells and see how many solar modules per kW they can fit.

1. Polycrystalline panels have powers in the ranges of 270 Wp-290 Wp – taking into account that 1 kWp is equivalent to 1 kW of power, we can say that 3.5 polycrystalline modules per 1 kWp of installation.
2. Monocrystalline panels with power ranges from 300 Wp-360 Wp; here we have 3.3-2.7 modules per 1 kWp of photovoltaic installations.

So how many photovoltaic modules will be needed for a home where electricity consumption requires a 5 kWp installation?

1. If we use polycrystalline panels, we need about 18 photovoltaic modules.
2. When we decide on single crystals, we have to install between 14-16 PV modules.

At the same time, it should be taken into account that polycrystalline panels are modules of an older type, which translates into their lower efficiency and useful life. Monocrystalline cells are currently used, which have higher efficiencies and a useful life of more than 30 years.

The power of the photovoltaic modules that we install depends on the size of the roof and the needs of the client. Here, the area of ​​the roof on which the photovoltaic panels are to be mounted is generally measured. Once we know the dimensions of the roof (length and width), we design the module design template. However, to exactly fit the dimensions of the roof, we need to know the dimensional parameters of the modules themselves. Here it is so simple that the photovoltaic modules have more or less similar dimensions; sometimes this size may differ slightly, depending on the manufacturer and the power of the modules themselves  Classic 60-cell panels have values ​​of 99.2 ± 1 X 167 ± 1 cm.

Knowing the parameters of the roof and a single module, we can count how many modules can actually fit in it. If the area is small, we have to choose more powerful modules to save space. A small ceiling often determines the choice of modules from the very beginning. When our roof is large enough, we have more leeway and can present the customer with various options. This situation is the best possible, because we can present the investor with the most profitable variant of a photovoltaic installation.

## Installation less or greater than the energy demand of the house?

The photovoltaic installation is designed according to the electricity demand of the home. The main parameter is the customer’s energy consumption. Large photovoltaic installations do not make sense, since they generate unnecessarily higher investment costs. Looking at the cost of the photovoltaic installation, for each additional 1 kWp, we have to pay up to 5,000. up to PLN 6,000  more for a photovoltaic system. That’s a lot of money.

If the inverter intends to increase power consumption over time by installing additional energy consuming devices, it is recommended to install a larger inverter. Thanks to this, in the future you will be able to buy additional panels and connect them to the existing installation. It is enough for you to communicate this fact to the corresponding photovoltaic service, which is responsible for the installation of the photovoltaic system.

## What determines the amount of electricity generated by photovoltaic panels?

Solar panels generate electricity when exposed to light. Therefore, how much light reaches the surface of the modules, they will generate as much electricity. The efficiency of the installation depends on the insolation. According to data from the Polish Institute of Meteorology and Water Management, the average insolation is in the range of about 950 W / m2 to 1200 W / m2. This is a pretty good result, considering that our western neighbors have lower returns by as much as 10%. Therefore, from 1 kWp of a photovoltaic installation, we can obtain 900 KWh – 1200 KWh of electricity per year. On average, 1 kWp corresponds to 1000 kWh per year.

## What can you save on building a photovoltaic system for your home?

When talking to a sales representative about potential PV cost reductions, you can generally hear that time is the factor that will reward us for any investment in our PV system and that energy consumption costs are increasing year over year. It may not be comforting for everyone. All the more so since the long-term rate of return may not satisfy everyone. Subsidies and allowances may not be enough for all investors, and they all want to pay as little as possible to get the best bottom line. So what can we save on?

• By choosing cheaper devices, we don’t have to immediately buy panels and a “top shelf” solar inverter. Mid-range panels will last at least 25 years, and mid-range inverters now have 10-year warranties. We do not recommend choosing the cheapest and untested devices. Here we can really lose because there is a possibility that we will buy a device (solar inverter) that breaks down after 2-3 years. Replacing the inverter costs between 5,000 and 8,000 PLN.
• Let’s also watch out for suspiciously cheap solar panels – they can be used as cells. In this case, let’s ask about your warranty, new devices generally have a 25-year performance warranty and a 12-year product warranty.
• You are looking for an assembly team on your own, a photovoltaic company that offers us a photovoltaic installation, usually also carries out the assembly. If the cost of assembly seems too high, we can look for photovoltaic installers on our own. However, the risk of problems after installation is high. Today, many people who have mastered electrical problems consider themselves PV installers and service technicians. Often times, these self-proclaimed experts have no idea how to handle PV modules during system installation. They often contribute to damage to the panels already in the assembly stage, which affects their efficiency. Additionally, poorly or incorrectly made cable connections on the AC / DC side can have far worse effects than loss of module performance due to damage. Remember that the photovoltaic installation is active.

## Why is photovoltaic for the home profitable?

How much does photovoltaic cost and is it profitable? This question is asked by everyone who thinks of setting up a photovoltaic installation of this type. Individual investors wonder more often about its profitability. Worth it?

Year after year, photovoltaic installations are more and more profitable for the home. This is because:

1. Individual recipients can be prosumers. A prosumer is a producer of electricity from renewable sources who uses it for his own needs and transfers the surplus to the electricity grid. It does not need to have a battery to store electricity because it has an energy accumulator for the operator. This situation is favorable because in the spring and summer months it transfers the surplus energy produced to the grid and collects it in the autumn and winter months.
2. Photovoltaic installations are becoming so popular that their prices are falling. In recent years, there has been record interest in photovoltaics, both among potential customers and among people installing electrical systems professionally. Speak for itself.
3. Energy prices increase every year, which translates into higher costs, individual consumers pay more, but so do production plants and farmers. If photovoltaic installations used farms and production facilities, services and products for households, mainly food, would be much cheaper.
4. The photovoltaic installation has a very wide range of applications. Thanks to it we can, among others,  not only have free electricity, but also free heating, using electric heating devices.