Photovoltaic solar panel installation

It is the ability of one or more consumers to generate, manage and consume energy in the same location or remotely, whether with or without energy accumulation. Each kWh produced and self-consumed is 1 kWh less that we must buy from the electricity company with its corresponding savings on the electricity bill.

Solar panels generate direct current that is received by the inverter, which transforms it into the alternating current that we consume at home.

We inject the generated solar energy (in most cases) directly into the main electrical panel of the house, so that if at a given time we are generating 3 kWh and consume 4 kWh, then the first 3 kWh of consumption will come from the solar panels we will buy the kWh that remains to complete consumption from the electricity company.

And also the other way around, if at a given hour we are generating 3 kWh, and we are only consuming 2 kWh, then the entire consumption will come from the solar panels and the excess solar kWh will be sent to the grid.

For this kWh that we send to the grid, the electricity company will apply a discount to our electricity bill (compensation).

In those self-consumption facilities with less than 100 kW of power and that are connected to the internal network of any of the consumers associated with the generation facility, the electricity company will value the surpluses (leftovers) that we send to the distribution network in accordance which is called simplified compensation mechanism.

Of the energy produced by the photovoltaic installation, the energy that cannot be self-consumed at the moment (solar surplus) will go to the electrical grid and the bidirectional meter of the marketing company will count hourly the total energy sent (exported) into the distribution grid.

Each electricity marketing company values the kWh sent to the network at a different price, adding their value during the month.

At the end of the month, when we receive the invoice, we will see a discount line with the total economic value of the kWh sent to the grid.

The electricity bill can never be negative, and therefore if the installation has many surpluses, a part of these may not be able to be valued and may be lost.

It is important to keep in mind that the value they give us for the surplus is always lower than the value we pay for the electricity consumed, and therefore we will always have maximum profitability and lower payback with installations with little surplus.

However, if we try to make an installation without surpluses, the resulting installation may be very small, and therefore the savings in absolute value will also be lower.

Therefore, the most appropriate thing is always to achieve an optimal balance between profitability (small installation with little surplus) and savings (larger installation with more surplus) that satisfies the client's needs, each client is different.

If we install a battery we reach the maximum value for each kWh generated, since we value all the kWh generated at the price we buy electricity at home. To achieve this maximum value, it is necessary to invest in the battery, which generally represents an extra cost of between 60% and 70% compared to the installation without a battery. This extra cost can be significantly reduced with the grants and subsidies currently available, which are especially focused on storage systems.

On the contrary, if we do not install the battery, the surpluses that would go to the battery will be sent to the electrical grid and will be compensated/valued at a lower price than if we had saved them. The advantage of not installing the battery is that you save that 60% - 70% extra cost.

If we think about buying a battery in economic terms, the amortization of the installation may be longer, but in any case the economic factor is not always decisive, since there are many people who buy batteries from us because they want to achieve maximum autonomy with respect to the electricity company.

Furthermore, we must not forget that as more solar systems are installed, the price of electricity during the day will fall and at night it will be more expensive, and therefore it will be more profitable to install batteries.

Yes it is possible, but not really wise. If you want to disconnect, you will have to size the installation to guarantee at least 3 days of autonomy, which means making the installation bigger and installing batteries large enough to store energy for 3 days.

In addition, you will need to install a backup generator in case, for example, we go through a week of bad weather in winter without being able to charge the batteries.

Obviously this is much more expensive than setting up a grid-tied self-consumption installation.

In addition, having an off-grid installation means always keeping an eye on consumption and battery charge, which goes against comfort: you can't just come home and switch on the heating or air conditioning whenever you feel like it, or disconnect without a second thought.

This is a very common question asked by anyone considering installing solar panels at home, and the answer is yes, except in exceptional cases. Most photovoltaic panels on the market today are manufactured to comply with a specific standard for high-impact resistance on the glass.

They use tempered glass, thermally processed to achieve greater resistance than conventional glass. They must pass hail impact tests (Hail test) that, according to the IEC 61215 standard, require them to withstand impacts from hailstones of different diameters and at different speeds.

That said, we are increasingly experiencing more extreme weather events, which means it cannot be guaranteed that if hail falls that is larger or faster than usual, the panels will not break. One example was the historic hailstorm on the afternoon of 30 August 2022 in the Baix Empordà (Catalonia), with hailstones of up to 10 cm in diameter.

In this sense, there are premium solutions such as SunPower Performance panels, certified to withstand hail impacts of up to 45 mm in diameter — well above the standard market benchmark of 25 mm.

The most advisable option is to insure the solar installation beyond your home insurance, protecting it against these extreme wind and/or hail events.

In cases of this type of disaster, insurance often will not cover the damage either if the Government declares a catastrophic zone; in that case, the Insurance Compensation Consortium (Consorcio de Compensación de Seguros) will take charge. However, for this to happen, you must have an active insurance policy.

A solar installation currently has a proven lifespan of more than 25 years. Consider that a solar installation has no moving mechanical parts subject to wear, nor circulating fluids that cause overpressure as happens with solar thermal energy. Therefore, if the installation has been well designed, it is very reasonable to expect a useful life of more than 25 years.

Modules gradually degrade over time and lose production capacity; however, manufacturers offer a minimum production warranty of 80% at 25 years — that is, they guarantee that after 25 years, the solar panels will produce at least 80% of what they produced on the first day.

In addition, panels have a product warranty of at least 12 years against manufacturing defects. Premium solutions are also available, such as SunPower Performance panels, which offer a triple 30-year warranty (product, power output and service).

Current inverters have a useful life of more than 15 years, and the inverters we offer come with a 10-year warranty.

Battery: the most common batteries in solar installations are lithium iron phosphate (LiFePO4) and usually have a 10-year warranty and a useful life of more than 6,000 cycles (16 years).

The mounting structures we offer generally have a 10-year warranty.

In addition, as an installation company, we offer a 5-year installation warranty, far beyond the 2 years legally required that most installation companies offer.

Facing modules to the north will always be the last option, but if it is not possible to face them south because we do not have space, or because we need more power to cover consumption and we do not have east-west options either, then we will face the panels north without any problem.

It should be noted that panels facing north in Catalonia produce approximately 10% less than modules facing south in Germany.

In any case, at SolarTradex we design every residential installation making the most of the orientation and surface available on your roof.

At SolarTradex it is a very bad option, for the following reasons:

Aesthetics. We need to make PV sexy, and seeing a house with raised panels on a sloping tile roof is just the opposite. There are aesthetically refined options such as SunPower Performance panels with a full-black finish.

It is dangerous: we are experiencing more and more extreme weather conditions, and placing elevated panels on a sloping roof only increases the wind load and plays with fire, so that the installation flies away on the day you least expect it.

The Urban Planning Law does not allow it, since the urban planning of the municipality where they are installed would have to be modified. Installation on the roof of buildings and other auxiliary constructions, including car park pergolas, is only permitted when the installations do not exceed one meter in height from the flat roof or, in the case of a sloping roof, when the collectors or panels are located attached in parallel.

If we want to maximise solar generation, today it is much more profitable and safe to install a couple more solar panels in a coplanar arrangement facing east or west, since the price of solar panels has dropped very significantly and the cost of the structure will also be cheaper.

Permanent shading, even if it only affects part of a panel, has a fairly significant impact on the production of the solar array.

Solar panels are connected in strings, in the same way that within a single panel the different solar cells are also connected in 3 or 4 strings that join at the top of the panel (currently some panels have the connection point in the central part).

These strings can be imagined as pipes through which water flows. If a shadow affects only one cell, water will not circulate through any of the cells connected in that string within the panel.

And if that panel has 4 strings, then only 75% of the water will reach the top of the panel, and this panel will only pass 75% of the water to the next panel connected in the string. As a result, only 75% of the water will reach the end of the string — all because of a single shaded cell.

In short, every shadow matters and it is worth minimising them even when they seem small or only affect part of a single panel. There are panels with specific designs that minimise this issue, such as SunPower Performance panels, which use cells cut to a third and parallel circuits to reduce the impact of shading to a minimum.

There are other storage systems to store surpluses. We have surplus diverters, which when they detect that solar generation is lower than consumption, they divert the surplus to an electrical resistance located inside a hot water tank, so that the water is preheated coming from the street before reaching the boiler/water heater and thus the thermal jump necessary to heat it is reduced.

Batteries store energy in the form of chemical energy and DHW accumulators in the form of thermal energy.

Another solution for those who have an electric car and a possible charging point is to install an electric vehicle charger (EVC) that allows them to take advantage of solar surpluses.

Virtual batteries are a mechanism whereby the electricity retailer manages the solar surpluses you send to the grid and applies an economic compensation on your subsequent bills, sometimes allowing you to assign the surplus to different supply points.

At first they seem an attractive idea, since they allow you to take advantage of surplus kWh without investing in a physical battery.

However, today most retailers have introduced significant limits: compensated amounts cannot exceed the cost of the energy billed (there is never a credit balance in cash), and the price at which they value the surplus is progressively decreasing due to solar oversupply during daytime hours (the "duck curve" phenomenon).

In addition, the current framework (RDL 7/2026) and the active grants and subsidies (IRPF, CAE, FACTOR 2026 in the Balearic Islands) are especially boosting systems with physical batteries, which provide real autonomy and maximum valorisation of the surpluses.

Therefore, virtual batteries are a useful short-term solution, but in the medium-long term, the future of energy storage will lie with physical batteries.

It makes sense if you are clear that you will consume more in the future, but we should remember that adding 4 more panels later will always have a significantly higher cost than installing them now.

Bear in mind that the electrification of the home (heat pumps, electric car, induction hob) will increase your electricity consumption in the coming years, so sizing the inverter correctly from the outset is a profitable long-term decision.

In photovoltaics, as in real life, size is not the most important thing…

What really makes a difference is efficiency, which is the ratio between the panel's power output and its surface area (W/m²). A panel with higher power output and larger size can be less efficient than a smaller one if its W/m² ratio is higher.

The more efficient the panel, the more kWp you can install in a given surface area — something especially important on roofs with limited space.

The panels we work with at SolarTradex are positioned in the high-efficiency segment of the market, which ensures making the most of every square meter of your roof.

And if you are looking for the maximum efficiency available, there are premium solutions such as SunPower Performance panels, with efficiency above 22.5% and a triple 30-year warranty (product, power output and service).

Installing microinverters can be a very good option if you have significant shading on your installation.

Working with microinverters means that shadows on some panels do not affect the rest; however, if you do not have shading, you will pay a premium for the installation and it will perform just as well as without microinverters.

If you install microinverters and one of them fails, you will not lose all of the production as would happen if you worked with a single central inverter; but, on the other hand, you will have a much higher chance of a microinverter failure than if you worked with a single central inverter.

Furthermore, if a microinverter fails, you will need to climb onto the roof to repair it and dismantle the corresponding panel, so the repair or replacement cost will be much higher.

An alternative to microinverters for managing shading are SunPower Performance panels, which use cells cut to a third and parallel circuits to minimise the impact of shading without the need to install microinverters.

The VAT law allows a 10% VAT rate to be applied to renovation and repair works.

A photovoltaic solar installation can be considered a renovation or repair work if, and only if, all of the following conditions are met:

• The recipient of the work is someone who uses the home for private use, or a residential owners' community.
• The recipient cannot act as a business or professional.
• The construction of the home was completed at least two years earlier.
• The cost of the materials purchased by the installer does not exceed 40% of the total cost of the works.

For this reason, we always request a signed statement from our clients in order to apply this 10% rate.

This 10% VAT rate is compatible with other tax advantages and active grants such as the IRPF deductions, the CAE system and other current grant programmes.

Lastly, we can also apply the 10% VAT rate to self-promoters (private individuals who build or renovate their own home).