Photovoltaics: The Complete Guide
Solar power expansion is reaching new records. In 2025 alone, over 15 gigawatts of new PV capacity were installed in Germany – more than ever before. Solar module prices have dropped by over 50% since 2020, while electricity prices remain at high levels. This combination makes photovoltaics more attractive than ever.
At the same time, interest in intelligent combinations is growing: heat pumps, battery storage, and electric mobility can all be connected to a PV system. The combination with air-to-air heat pumps in particular offers a quick and cost-effective way to support existing heating systems.
This guide explains the fundamentals of photovoltaics, walks through the key components, covers economics and incentives, and shows how to optimally combine PV with heat pumps.
How Does Photovoltaics Work?
Photovoltaics converts sunlight directly into electrical power. The name combines the Greek "photos" (light) with "Volta" (after physicist Alessandro Volta, inventor of the battery).
The Photovoltaic Effect
In a solar cell, light particles (photons) strike a semiconductor material, usually silicon. This releases electrons from their bonds, allowing them to flow as electrical current. This process is called the photovoltaic effect.
The process works in three simplified steps:
- Light absorption: Photons enter the solar cell
- Charge separation: Electrons are released and separated from holes
- Current flow: Electrons flow through an external circuit
A single silicon cell produces about 0.5 to 0.7 volts. To achieve usable voltages, many cells are connected in series to form modules.
A detailed explanation of the physics can be found in the article From Photon to Volt: How Does a Solar Cell Work?.
Components of a PV System
A grid-connected photovoltaic system consists of several main components that must work together.
Solar Modules
The solar module is the heart of the system. Current modules are predominantly based on crystalline silicon and achieve efficiencies of 20 to 23%. Premium modules with TOPCon or heterojunction technology achieve over 22%.
Comparison of the most common module types:
| Module Type | Efficiency | Price | Characteristics |
|---|---|---|---|
| Monocrystalline PERC | 19–21% | Medium | Standard, good price-performance ratio |
| Monocrystalline TOPCon | 21–23% | Higher | Higher efficiency, better low-light performance |
| Polycrystalline | 16–18% | Low | Discontinued model, rarely installed |
| Thin-film | 10–13% | Low | Flexible, for special applications |
A standard module today has a power output of 400 to 450 watts with dimensions of approximately 1.7 × 1.1 meters.
Inverter
The inverter converts the direct current (DC) from the modules into grid-compliant alternating current (AC). Without it, solar power would not be usable in the household.
There are three inverter designs:
String inverters are the most common type. Multiple modules are connected in series (string) and connected to a central inverter. Advantage: inexpensive and efficient. Disadvantage: partial shading reduces the yield of the entire string.
Micro-inverters sit directly under each module. Each module operates independently; shading of one module does not affect the others. Advantage: optimal yield for complex roofs. Disadvantage: higher costs.
Hybrid inverters combine the inverter function with a battery charge controller. They enable direct integration of a battery storage system without additional components.
Details on the various inverter concepts are explained in the article AC/DC in PV: Inverters and Power Conversion.
Mounting System
The mounting system securely attaches the modules to the roof. For pitched roofs, roof hooks are anchored under the tiles, on which rails for the modules are mounted. Flat roofs receive elevated systems with tilt angles of 10 to 15 degrees.
Battery Storage (optional)
A battery storage system increases the self-consumption of solar power. Without storage, self-consumption is typically 25 to 35%; with storage, it rises to 50 to 70%. Current storage systems are almost exclusively based on lithium iron phosphate (LFP) technology and offer capacities of 5 to 15 kWh for single-family homes.
More on storage in the article Battery Storage: Energy for Later.
Sizing: The Right System Size
The optimal system size depends on several factors: electricity consumption, available roof area, and budget. A system that's too small doesn't exploit the potential; one that's too large takes longer to pay off.
Electricity Consumption as a Starting Point
Annual electricity consumption is the most important planning basis. An average 4-person household consumes 4,000 to 5,000 kWh per year. Households with electric cars or heat pumps are significantly higher.
These guidelines serve as orientation:
| Household Size | Electricity Consumption | Recommended PV Size |
|---|---|---|
| 1–2 persons | 2,000–3,000 kWh/a | 4–6 kWp |
| 3–4 persons | 3,500–5,000 kWh/a | 6–10 kWp |
| 5+ persons | 5,000–7,000 kWh/a | 8–12 kWp |
| With EV | +2,000–4,000 kWh/a | +2–4 kWp |
| With heat pump | +3,000–5,000 kWh/a | +3–5 kWp |
Roof Area and Orientation
Approximately 5 to 6 m² of roof area is required per kWp of system power. A roof with 40 m² of usable area provides space for a 7 to 8 kWp system.
Orientation significantly affects annual yield:
| Orientation | Tilt | Yield (relative) |
|---|---|---|
| South | 30–35° | 100% |
| Southeast/Southwest | 30–35° | 95% |
| East/West | 30–35° | 85% |
| Flat roof elevated | 10–15° | 90% |
East-west orientations are not necessarily worse: they generate power more evenly throughout the day, which can increase self-consumption.
Rule of Thumb for System Size
A proven rule of thumb: 1 kWp per 1,000 kWh annual consumption, but at least as large as the roof area allows. In Germany, 1 kWp produces about 900 to 1,100 kWh per year, depending on location and orientation.
Economics and Costs
A PV system is an investment that should pay for itself over its lifetime. Economics depend on investment costs, electricity yield, and electricity price trends.
Investment Costs 2026
Prices for turnkey PV systems continued to fall in 2025. For a typical rooftop system without storage, costs are:
| System Size | Cost (without storage) | Cost per kWp |
|---|---|---|
| 5 kWp | 7,000–9,000 € | 1,400–1,800 €/kWp |
| 10 kWp | 12,000–16,000 € | 1,200–1,600 €/kWp |
| 15 kWp | 16,000–22,000 € | 1,100–1,500 €/kWp |
Battery storage adds 500 to 800 € per kWh of capacity. A 10 kWh storage unit costs 5,000 to 8,000 €.
Operating Costs
The operating costs of a PV system are low:
- Maintenance: 100–200 €/year (cleaning, visual inspection)
- Insurance: 50–100 €/year
- Meter fee: 20–40 €/year
- Reserves for inverter replacement: ~50 €/year
A total of about 200 to 400 € per year; for a 10 kWp system, that's 2 to 4 cents per kWh generated.
Feed-in Tariff and Self-Consumption
Self-consumption is more economically attractive than feed-in. With a household electricity price of 35 cents/kWh and a feed-in tariff of 8 cents/kWh, each self-consumed kilowatt-hour saves 27 cents more than one fed into the grid.
Example calculation for a 10 kWp system with 10,000 kWh annual yield:
| Scenario | Self-Consumption | Feed-in | Savings/Revenue |
|---|---|---|---|
| Without storage (30%) | 3,000 kWh | 7,000 kWh | 1,050 € + 560 € = 1,610 €/a |
| With storage (60%) | 6,000 kWh | 4,000 kWh | 2,100 € + 320 € = 2,420 €/a |
Payback Period
The payback period indicates when the system has recouped its investment costs.
Example calculation (10 kWp without storage):
- Investment: 14,000 €
- Annual benefit: 1,610 €
- Payback: 14,000 € ÷ 1,610 €/a = 8.7 years
After payback, the system generates pure profit for the rest of its lifespan (another 15–20 years).
Incentives
Direct subsidies for PV systems have been largely discontinued. However, there are indirect benefits:
- 0% VAT on PV systems up to 30 kWp (since 2023)
- KfW loans for storage and e-mobility (Program 270)
- Regional incentive programs (federal states, municipalities)
- Tax simplification for small systems
The Dream Team: PV + Heat Pump
The combination of photovoltaics and heat pump is considered the royal road to climate-neutral heating. Both technologies complement each other excellently: the PV system supplies the electricity that the heat pump needs for operation.
Using Synergies
A heat pump significantly increases the self-consumption of the PV system. While a normal household only directly consumes 25–35% of solar power, a heat pump can increase this proportion to 40–50%. With intelligent control (SG Ready), the heat pump can preferentially operate when solar power is available.
Sizing for the Combination
When planning a PV system with a heat pump, the additional electricity demand of the heat pump should be considered:
| Heat Pump Capacity | Electricity Demand (at SPF 4) | Additional PV |
|---|---|---|
| 6 kW | ~2,500 kWh/a | +2.5 kWp |
| 8 kW | ~3,500 kWh/a | +3.5 kWp |
| 10 kW | ~4,500 kWh/a | +4.5 kWp |
A detailed treatment of the various heat pump types and their combination with PV is offered by the Heat Pump Guide.
Air-to-Air Heat Pumps: The Quick PV Addition
In addition to classic air-to-water heat pumps, air-to-air heat pumps are gaining importance – better known as split air conditioners. They offer a particularly attractive way to support existing heating systems and increase self-consumption of solar power.
What Makes Air-to-Air Heat Pumps Special?
Air-to-air heat pumps heat room air directly, without the detour through a water circuit. This makes them the ideal supplementary system for households with existing heating:
| Aspect | Air-to-Air HP | Air-to-Water HP |
|---|---|---|
| Installation | 1–2 days | 3–5 days |
| Investment (typical) | 2,500–5,000 € | 12,000–20,000 € |
| Intervention in heating system | None | Complete conversion |
| Heating and cooling | Yes | Only with additional equipment |
| Hot water preparation | No | Yes |
| Ideal role | Supplement | Main heating |
Application Scenarios
Old building with high flow temperature: In buildings whose radiators require 60–70°C flow, an air-to-water heat pump operates inefficiently. An air-to-air HP can selectively relieve rooms here: it takes over part of the heating load while the gas boiler provides base heat and hot water.
Attic with overheating problem: In summer, attic rooms often become unbearably hot. A split air conditioner solves this problem and efficiently heats the same room in winter. The solar power from the roof drives cooling practically cost-free.
Home office and study: Rooms that are only used part-time can be brought up to temperature quickly with an air-to-air HP – faster than any water-based heating system.
Bivalent Operation: Two Systems, One Goal
In bivalent operation, the air-to-air heat pump and existing heating work together. The distribution can occur in various ways:
Bivalent-parallel: Both systems run simultaneously. The air-to-air HP continuously relieves the main heating, especially at moderate temperatures when its efficiency is highest.
Bivalent-alternative: Above a certain outdoor temperature (bivalent point, e.g., 5°C) only the air-to-air HP runs; below that, the existing heating takes over.
Solar-controlled: The air-to-air HP runs preferentially when solar power is available. At night or when cloudy, the conventional heating kicks in.
Economics Example
Initial situation: Single-family home, 120 m², gas heating with 65°C flow, annual consumption 18,000 kWh gas (2,160 €/a at 0.12 €/kWh). The attic overheats in summer.
Measure: Installation of a split air conditioner with 3.5 kW heating capacity in the living/dining area and expansion of the PV system by 3 kWp.
Result after one year:
- Air-to-air HP takes over 30% of heating load
- Gas consumption drops to 12,600 kWh/a (−5,400 kWh)
- Gas cost savings: 648 €/a
- Electricity consumption air-to-air: 1,500 kWh (SCOP 3.5)
- Of which from PV: 900 kWh (free)
- Remaining grid electricity: 600 kWh × 0.35 € = 210 €/a
- Cooling in summer: Largely from PV surplus
- Annual savings: 648 € − 210 € = 438 €
- Additional comfort gain: Cooling in summer
With investment costs of 4,500 € for the split unit and 3,500 € for the PV expansion, this results in a payback period of about 18 years. If you factor in the comfort gain from cooling – comparable portable air conditioners consume three times as much electricity – the balance improves significantly.
Sizing: PV Size for Air-to-Air Operation
For the additional electricity demand of an air-to-air heat pump, the following PV expansion is recommended:
| Air-to-Air Capacity | Electricity Demand (SCOP 3.5) | PV Addition |
|---|---|---|
| 2.5 kW (single split) | ~700 kWh/a | +1–2 kWp |
| 3.5 kW (single split) | ~1,000 kWh/a | +2–3 kWp |
| 5.0 kW (multi-split) | ~1,500 kWh/a | +3–4 kWp |
The PV addition should be sized more generously if the cooling function will also be used intensively in summer. The good news: in summer, when cooling demand is highest, the PV system produces the most electricity.
Size Your Air-to-Air HP Now
With our Air-to-Air Calculator, you can calculate the optimal unit size, expected electricity consumption, and economics in conjunction with your existing heating.
→ To the Air-to-Air Calculator
Advantages and Disadvantages of Photovoltaics
Photovoltaics offers numerous advantages but also has limitations. A realistic assessment helps with the decision.
The advantages are obvious: solar power is practically free after installation and makes you more independent of rising electricity prices. The technology is mature, low-maintenance, and has a lifespan of 25 to 30 years. Government regulations such as VAT exemption and guaranteed feed-in tariffs provide planning security. Additionally, a PV system significantly improves the household's COâ‚‚ balance.
Some disadvantages offset the advantages: electricity generation fluctuates with time of day and weather. Without storage, production fails precisely when evening consumption is highest. Investment costs are considerable, even if they pay off in the long run. Also, not every roof is suitable – shading, orientation, and load-bearing capacity set limits.
Frequently Asked Questions
Is photovoltaics still worth it in 2026?
Yes, conditions are favorable. Module prices are historically low while electricity prices remain high. VAT exemption makes systems even more attractive. With payback of 8 to 12 years and a system lifespan of 25 to 30 years, there remains a significant economic advantage.
How large should my PV system be?
As a rule of thumb: 1 kWp per 1,000 kWh annual electricity consumption. If roof space permits, more is fine – marginal costs per additional kWp decrease with system size. If you're planning to acquire a heat pump or electric car, the system should be sized larger from the start.
Do I need a battery storage system?
Storage increases self-consumption from a typical 30% to 50–70% and provides greater independence from the power grid. Economically, however, it pays off more slowly than the PV system itself. Storage makes sense primarily when the household consumes a lot of electricity in the evening or when backup power capability is desired.
Can I combine PV with my old heating system?
A PV system can be combined with any heating system. Particularly sensible is the addition of an air-to-air heat pump (split air conditioner). It uses solar power for heating and cooling without requiring replacement of the existing heating. In summer, PV surplus can be used directly for cooling.
Conclusion
Key takeaway: Photovoltaics has become the most economical form of electricity generation for private households. With investment costs of 1,200 to 1,600 euros per kWp and rising electricity prices, a system pays for itself in 8 to 12 years. Combining with heat pumps increases self-consumption and profitability. Air-to-air heat pumps are particularly interesting as a quick and cost-effective supplement to existing heating systems – they use solar power for heating in winter and cooling in summer.
The decision for a PV system should be well prepared. Professional planning considers roof condition, consumption profile, and future developments such as e-mobility or heat pump deployment. With the right components and appropriate sizing, photovoltaics becomes the foundation of a sustainable energy supply.
Photovoltaics Article Series
- Photovoltaics: The Complete Guide – You are here
- From Photon to Volt: How Does a Solar Cell Work? – Understanding the basics
- Structure of a PV System – From module to system
- AC/DC in PV: Inverters and Power Conversion – DC to AC
- Power Electronics: Inverters and DC-DC Converters – Technical details
- The All-Rounder: Hybrid Inverters – PV, storage, and grid
- AC or DC? System Topologies for Solar Systems – System architectures
Further Reading
Heat Pumps: Heat Pump: The Complete Guide · Heat Pump Types and PV · Key Figures: COP, SPF, SCOP
Battery Storage: Battery Technology Basics · Lithium vs. Lead · Battery Storage Market Analysis
Balcony Power Plants: Balcony Power Plants: Introduction · Installation and Setup
Sources
- Fraunhofer ISE: Current Facts on Photovoltaics in Germany
- Federal Network Agency: EEG Remuneration Rates
- BSW Solar: German Solar Industry Association
- BAFA: Federal Office for Economic Affairs and Export Control – Funding
- KfW: Renewable Energies – Standard (Program 270)
- VDI 4650: Calculation of the annual performance factor of heat pump systems
- DIN EN 14825: Air conditioners and heat pumps – Testing and rating
Calculate Your PV Yield Now
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