Guide to Using the Solar Calculator (PV System Calculation)

Table of Contents

1. Introduction
2. Calculation Basics
3. Step-by-Step Guide
4. Shading Analysis
5. Understanding Results
6. Tips and Best Practices
7. Frequently Asked Questions
8. Background Information

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Introduction

1.1 What Does the Solar Calculator Calculate?

The Solar Calculator enables precise planning and economic calculation of photovoltaic systems based on current PVGis climate data (Photovoltaic Geographical Information System of the European Commission).

The calculator determines:

• Annual yield: Hourly and monthly electricity production based on real weather data
• Self-consumption: How much of the generated electricity you can use yourself
• Self-sufficiency rate: How independent you become from the grid
• Profitability: Payback period, annual savings and return
• CO₂ savings: Your contribution to climate protection

1.2 Who Is This Calculator For?

The solar calculator is suitable for:

• Homeowners: Planning a PV system for your home
• Builders: Sizing as part of new construction planning
• Energy consultants: Quick preliminary calculation for client advice
• Installers: Rough system planning and customer quotes

1.3 Data Source: PVGis

The calculator uses the PVGis database (Version 5.2) from the European Commission. It contains:

• Solar irradiation: Hourly global irradiation (GHI, DNI, DHI) for every location
• Typical Meteorological Year (TMY): Representative weather data from 2005-2020
• Horizon data: Consideration of terrain shading
• Europe-wide coverage: Precise data for Germany, Austria, Switzerland and all of Europe

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Calculation Basics

2.1 Basic Formula for PV Yield

The hourly electricity yield of a PV system is calculated as:

P = G × A × η × (1 - Losses)

Parameters:

• P = Electrical power [kW]
• G = Global irradiation on the tilted surface [kW/m²]
• A = Module area [m²]
• η = Module efficiency [-]
• Losses = System losses (cables, inverter, soiling) [-]

2.2 Specific Annual Yield

The specific annual yield indicates how much electricity is generated per installed capacity:

Yield [kWh/kWp] = Annual yield [kWh] / System capacity [kWp]

Typical values for Germany:

• Northern Germany: 850-950 kWh/kWp
• Central Germany: 900-1000 kWh/kWp
• Southern Germany: 950-1100 kWh/kWp
• Alpine region: 1000-1200 kWh/kWp

2.3 Self-Consumption and Self-Sufficiency

Self-consumption rate = Share of self-used solar power of total production:

Self-consumption [%] = Self-used energy / Generated energy × 100

Self-sufficiency rate = Share of electricity demand covered by solar power:

Self-sufficiency [%] = Self-used solar energy / Total consumption × 100

Typical values without battery storage:	System size	Self-consumption	Self-sufficiency
Small (3 kWp)	30-40%	25-35%
Medium (5 kWp)	25-35%	30-40%
Large (10 kWp)	20-30%	35-50%

With battery storage (5-10 kWh):	Battery size	Self-consumption	Self-sufficiency
5 kWh	50-60%	50-65%
10 kWh	60-75%	60-80%
15 kWh	70-85%	70-85%

2.4 Economic Calculation

The economic calculation follows VDI 2067 (Economic efficiency of building services):

Annual savings:

Savings [€/a] = Self-consumption × Electricity price + Feed-in × Tariff

Payback period:

Payback [a] = Investment costs / Annual savings

Return:

Return [%] = (Savings - Annual costs) / Investment × 100

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Step-by-Step Guide

3.1 Project Management

Creating a New Project

Click on "New Project" to start a new PV calculation. The calculator guides you through all required inputs.

Loading an Existing Project

You can load a saved project at any time using the project key:

1. Click on "Load Project"
2. Enter your 5-character project key
3. Click on "Load"

Importing a Project

A special feature is importing from other calculators:

• From heating load calculation: Transfers location data (address, coordinates)
• From heat pump calculation: Transfers location and can use consumption data

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3.2 Tab 1: Location

The first step is entering the location of your planned PV system.

Address Entry

Enter the complete address:

• Postal code
• City: Town or municipality
• Country: Germany (DE), Austria (AT), Switzerland (CH), France (FR), Italy (IT)

Automatic Data Retrieval

After entering the address, the following are automatically determined:

• GPS coordinates: Latitude and longitude
• Elevation above sea level: For precise sun position calculation
• PVGis climate data: Hourly irradiation values for the entire year

Manual Coordinate Entry

For special locations, you can also enter GPS coordinates directly:

• Latitude: e.g., 52.520 for Berlin
• Longitude: e.g., 13.405 for Berlin

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3.3 Tab 2: Surfaces (PV Modules)

In this tab, you define your PV surfaces (roof areas or ground-mounted modules).

Adding a New Surface

Click on "Add Surface" and enter:

Basic data:

• Name: Description of the surface (e.g., "South roof", "East flat roof")
• Power [kWp]: Total power of modules on this surface
• Number of modules: Number of individual solar modules
• Module power [Wp]: Power per module (typically 400-450 Wp)
• Area [m²]: Automatically calculated from number × module area

Orientation:

• Azimuth [°]: Compass direction of the surface
  • 0° = South (optimal for yield)
  • 90° = West
  • -90° = East
  • 180° = North
• Tilt [°]: Roof pitch
  • 0° = Flat (flat roof)
  • 30-35° = Optimal for Germany
  • 90° = Vertical (facade)

Losses:

• System losses [%]: Lump sum for cables, inverter, soiling
  • Standard: 14%
  • Optimized: 10-12%
  • Unfavorable: 16-20%

Multiple Surfaces

You can create any number of surfaces with different orientations:

• East-West system: One surface each with azimuth -90° and +90°
• Roof + facade: Combination of tilted surface and vertical surface
• Dormer + main roof: Different tilts

Duplicating a Surface

With "Duplicate" you can copy a surface and adjust only individual parameters - practical for symmetrical roofs.

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3.4 Shading Analysis (per Surface)

For each PV surface, you can perform a detailed shading analysis.

Opening the Shading Editor

Click on "Analyze shading" next to the respective surface.

Adding Obstacles

In the 2D editor (top view), you can draw various obstacles:

Obstacle	Description	Typical height
Building	Neighboring buildings, chimneys	5-15 m
Deciduous tree	Loses leaves in winter	8-20 m
Conifer	Year-round shading	10-25 m
Hedge	Low shading	1-3 m
Forest	Distant forest edge	variable
Chimney	On your own roof	1-2 m above roof
Power pole	Slim shading	10-30 m
Antenna	Smaller obstacles	1-3 m
Hill	Terrain elevation (horizon shading)	variable

Setting System Height

Enter the height of the PV system above ground (e.g., 7 m for a two-story house). This is important for correctly calculating shading angles.

Starting Sun Simulation

After drawing obstacles, you can start the sun simulation:

1. Select month: Dropdown for January to December
2. Start animation: Shows sun path in time-lapse
3. Select hour: Slider for each hour of the day

Displayed:

• Sun position: Visualization of sun angle
• Shadow cast: Which areas are shaded
• Hourly yield: How much power is produced at this hour
• Sunrise/sunset: Automatically calculated for the selected day

Calculating Shading Losses

Click on "Calculate shading" to determine annual losses:

• Monthly losses [%]: How much yield is lost per month
• Annual loss [%]: Total yield reduction
• Yield with shading [kWh]: Realistic annual yield

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3.5 Tab 3: Consumption

In this tab, you enter your electricity consumption to calculate self-consumption and self-sufficiency.

Selecting Building Type

Choose your building type:

• Single-family house: Typically 3,000-5,000 kWh/year
• Apartment: Typically 1,500-3,000 kWh/year

Household Profile

Select a standard load profile:

• Family with children: High daytime consumption
• Working professionals: Consumption mornings and evenings
• Home office: Even daytime consumption
• Retirees: High daytime consumption

The load profile determines when electricity is consumed - crucial for self-consumption!

Entering Annual Consumption

• Total consumption [kWh/year]: From last electricity bill or estimate
• Enter individual consumers: For more precise calculation

Adding Consumers

For precise calculation, you can record individual consumers:

Consumer	Typical consumption	Load profile
Refrigerator	150-300 kWh/year	Constant
Washing machine	150-250 kWh/year	Flexible
Dishwasher	200-300 kWh/year	Flexible
EV (8,000 km/year)	1,500-2,000 kWh/year	Evenings/nights
Heat pump	3,000-8,000 kWh/year	Heating season
Air conditioning	200-500 kWh/year	Summer

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3.6 Tab 4: Storage (Battery)

Here you configure an optional battery storage.

Activating Storage

Check the box "Use battery storage" to include storage in the calculation.

Choosing Capacity

Quick-select buttons:

• 5 kWh: For small systems (3-5 kWp)
• 10 kWh: Standard for single-family homes (5-8 kWp)
• 15 kWh: For larger systems or EV
• 20 kWh: Maximum independence

Manual entry: 1-100 kWh

Recommendation:

Optimal capacity ≈ 70% of daily consumption [kWh]

At 4,000 kWh/year → 4,000 ÷ 365 × 0.7 ≈ 7.7 kWh

Storage Parameters

• Efficiency [%]: Typically 90-95% (charge/discharge losses)
• Charging power [kW]: Maximum charge rate (typically C/2, so 5 kW for 10 kWh)
• Discharging power [kW]: Maximum discharge rate

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3.7 Tab 5: Finances

In this tab, you enter economic parameters for the profitability calculation.

Investment Costs

• System costs [€]: Total costs for modules, inverter, installation
  • Guideline: €1,200-1,500/kWp (small system) to €900-1,100/kWp (large system)
• Storage costs [€]: If storage is enabled
  • Guideline: €500-800/kWh capacity
• Annual costs [€/year]: Maintenance, insurance, meter fees
  • Guideline: €100-300/year

Electricity Prices

• Electricity price [ct/kWh]: Your current electricity purchase price
  • 2024: Typically 30-40 ct/kWh in Germany
• Feed-in tariff [ct/kWh]: Compensation for grid feed-in
  • 2024 (systems up to 10 kWp): 8.1 ct/kWh
  • 2024 (systems 10-40 kWp): 7.0 ct/kWh
• Electricity price increase [%/year]: Expected annual increase
  • Historical: 3-5%/year
  • Conservative: 2-3%/year

Analysis Period

• Analysis period [years]: Typically 20-25 years (module warranty)
• Degradation [%/year]: Annual module performance reduction
  • Standard: 0.5%/year (still ~90% performance after 20 years)

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Shading Analysis

4.1 Overview

Shading analysis is one of the most important features of the solar calculator. Even small shading can significantly reduce yield:

Shading	Typical yield loss
None	0%
Chimney	2-5%
Single tree	5-15%
Neighboring building	10-30%
Forest edge	15-40%
Heavy shading	30-60%

4.2 2D Top-View Editor

The top-view editor shows your PV surface from above. Here you can:

1. Place obstacles: Click on the desired obstacle and place it with a click
2. Adjust size: Drag corners to change size
3. Move position: Drag the obstacle to the correct position
4. Set height: Enter height in meters
5. Delete: With delete key or trash icon

4.3 Sun Simulation

The sun simulation shows shadow casting throughout the day:

1. Select a month (e.g., June for summer maximum, December for winter minimum)
2. Start the animation or select a specific time
3. Observe which areas of the PV surface are shaded
4. Yield is displayed in real-time

Special days:

• June 21 (Summer solstice): Highest sun position, longest day
• December 21 (Winter solstice): Lowest sun position, shortest day
• March/September 21 (Equinox): Medium sun position

4.4 Shading Analysis Results

After calculation, you receive:

• Annual yield without shading [kWh]
• Annual yield with shading [kWh]
• Yield loss [%]
• Monthly breakdown: Which months are most affected?

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Understanding Results

After entering all parameters, click "Calculate". Results are presented in four tabs.

5.1 Tab 1: Overview

Key Metric Cards

Four large cards show the most important results:

Metric	Meaning	Example
Annual yield [kWh/year]	Electricity your system produces	5,500 kWh
Self-sufficiency rate [%]	Share of your demand covered by PV	65%
Annual savings [€/year]	Saved electricity costs	€850
CO₂ savings [kg/year]	Avoided CO₂ emissions	2,200 kg

Surface Overview

Table with all configured PV surfaces:

• Surface (name)
• Generated electricity [kWh]
• Power [kWp]
• Area [m²]
• Number of modules
• Tilt [°]
• Orientation (azimuth)

5.2 Tab 2: Finances

Year Selection

Select a year within the analysis period to see development.

Before/After Comparison

Parameter	Without PV	With PV	Change
Electricity consumption	4,500 kWh	4,500 kWh	-
Electricity generation	0 kWh	5,500 kWh	+5,500 kWh
Grid purchase	4,500 kWh	1,800 kWh	-2,700 kWh
Electricity costs	€1,350	€540	-€810

Revenues

• Feed-in tariff [€/year]: Income for excess electricity
• Self-consumption value [€/year]: Savings from self-used electricity
• Storage contribution [€/year]: Additional value from storage

Cumulative View

• Investment costs: One-time acquisition
• Cumulative savings: Sum of all savings up to selected year
• Payback point: When has the system paid for itself?

5.3 Tab 3: Yield

Summary

Generation (dark blue area):

• Total generated energy [kWh]
• Fed into grid [kWh]
• Self-consumed [kWh]

Consumption (light blue area):

• Total electricity consumption [kWh]
• Purchased from grid [kWh]
• From solar power [kWh]

Charts

Three pie charts visualize:

1. Use of generation: Self-consumption vs. feed-in
2. Generation vs. consumption: Balance between production and demand
3. Self-sufficiency rate: How independent are you?

Monthly Breakdown

Bar chart with:

• Monthly yield [kWh]
• Monthly consumption [kWh]
• Surplus/deficit per month

5.4 Tab 4: Surfaces

Detailed results per PV surface:

• Hourly generation: Typical daily profile
• Monthly yield: Seasonal distribution
• Shading impact: If shading analysis was performed
• Specific yield [kWh/kWp]: Efficiency of the surface

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Tips and Best Practices

6.1 Optimal System Size

Rule of thumb for single-family homes:

System size [kWp] ≈ Electricity consumption [kWh] / 1,000

At 4,500 kWh consumption → approx. 4.5 kWp

6.2 Orientation and Tilt

Orientation	Tilt	Yield vs. South-30°
South	30-35°	100% (optimum)
South	45°	98%
South	15°	95%
Southeast/Southwest	30°	95%
East/West	30°	85%
East+West (50% each)	30°	90%

Flat roof: Mounting at 10-15° is often optimal (self-cleaning, no snow problem)

6.3 Maximizing Self-Consumption

1. Schedule consumers during sunny hours:

   • Run washing machine, dishwasher during the day
   • Use timers or smart home

2. Large consumers:

   • EV: Charge during the day when sun is shining
   • Heat pump: Increased hot water production at noon

3. Size storage sensibly:

   • Not too large (cost-effective: 1 kWh storage per 1 kWp system)
   • Not too small (otherwise little effect)

6.4 Avoiding Shading

Check before installation:

• ✅ Will trees grow into the line of sight in the next 20 years?
• ✅ Are new buildings planned in the neighborhood?
• ✅ Can antennas, satellite dishes be relocated?
• ✅ Can the chimney be optimized?

Module optimization:

• Power optimizers: Reduce losses with partial shading
• Module arrangement: Avoid critical areas
• Separate strings: Separate shaded and unshaded modules

6.5 Improving Profitability

1. Get multiple quotes: Prices vary widely
2. Check funding programs: KfW, regional subsidies
3. Plan wallbox together: EV drastically increases self-consumption
4. Plan maintenance: Budget €100-200/year

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Frequently Asked Questions (FAQ)

How accurate are the yield calculations?

Calculations are based on PVGis data with a typical deviation of ±5-10% compared to actual yields. Factors such as:

• Year-specific weather conditions
• Actual shading
• Module aging
• Snow load

can lead to deviations.

Can I combine multiple roof surfaces?

Yes! You can create any number of surfaces with different orientations. The calculator automatically sums the yields.

Is a battery storage worthwhile?

That depends on several factors:

• Electricity price: The higher, the more worthwhile the storage
• Self-consumption potential: Without storage typically 25-35%, with storage 50-75%
• Storage costs: Currently €500-800/kWh

Calculation: The finance tab shows profitability with and without storage.

How often do modules need cleaning?

In Germany, rain is usually sufficient for cleaning. With heavy soiling (agriculture, bird droppings):

• Cleaning every 1-2 years recommended
• Cost: €2-3/m² module area

What happens during power outage?

Standard PV systems automatically shut off during power outage (feed-in protection). For backup power you need:

• Hybrid inverter with backup function
• Battery storage of sufficient size
• Separate backup outlet

How long do PV modules last?

• Lifespan: 25-30 years (often longer)
• Warranty: Typically 25 years with 80% performance guarantee
• Degradation: Approx. 0.5% performance loss per year

Do I need a permit?

For PV systems on residential buildings:

• Usually permit-free: Systems on roofs under 10 kWp
• Registration required: With grid operator and market master data register
• Heritage protection: May require permit

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Background Information

8.1 PVGis Database

The Photovoltaic Geographical Information System (PVGis) is operated by the Joint Research Centre (JRC) of the European Commission. It contains:

• Satellite data: CM SAF (Climate Monitoring Satellite Application Facility)
• Radiation data: 2005-2020 for TMY (Typical Meteorological Year)
• Resolution: ~2.5 km grid spacing
• Accuracy: ±5% for global radiation

8.2 Sun Position Calculation

Sun position is calculated using the NREL SPA algorithm (Solar Position Algorithm):

• Azimuth: Horizontal sun position (0° = South)
• Elevation: Height above horizon
• Sunrise/sunset: Exactly calculated for each day
• Accuracy: ±0.0003° for years -2000 to 6000

8.3 Standards and Norms

The solar calculator follows:

• PVGis: European solar radiation database
• VDI 2067: Economic efficiency of building services
• DIN EN IEC 61724: Photovoltaic system monitoring
• IEC 61853: PV module performance measurement
• EEG 2023: Renewable Energy Sources Act (feed-in tariff)

8.4 CO₂ Calculation

CO₂ savings are calculated with:

CO₂ savings [kg] = Electricity generation [kWh] × CO₂ factor [g/kWh] / 1000

CO₂ factors:

• German electricity mix 2023: 380 g/kWh
• PV electricity (including manufacturing): 30-50 g/kWh
• Net savings: Approx. 330-350 g/kWh

8.5 Typical Module Specifications (2024)

Parameter	Typical value
Power per module	400-450 Wp
Efficiency	20-22%
Area per module	1.7-2.0 m²
Weight	20-25 kg
Temperature coefficient	-0.3 to -0.4 %/°C
Performance warranty	25 years (80%)

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9. Further Information

Official Sources

• PVGis Online Tool - Official EU database
• Market Master Data Register - Register your system
• Federal Network Agency - Current feed-in tariffs

Funding Programs

• KfW Funding - Loans and grants
• State funding programs - Depending on federal state

Standards

• VDI 2067: Economic efficiency of building services
• DIN EN IEC 61724: Photovoltaic system monitoring

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To Calculator: Start Solar Calculator

Last updated: December 2025