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Guide to Using the Solar Calculator (PV System Calculation)

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:

1.2 Who Is This Calculator For?

The solar calculator is suitable for:

Note: Calculations are based on long-term averages and real weather data. Actual yields may vary by ±5-10% depending on the year.

1.3 Data Source: PVGis

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

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:

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:

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 sizeSelf-consumptionSelf-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 sizeSelf-consumptionSelf-sufficiency
5 kWh50-60%50-65%
10 kWh60-75%60-80%
15 kWh70-85%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

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:

Tip: If you have already performed a heating load calculation, you can import the location with one click and save yourself from re-entering it.

3.2 Tab 1: Location

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

Address Entry

Enter the complete address:

Automatic Data Retrieval

After entering the address, the following are automatically determined:

Fallback data: If PVGis is unavailable, the calculator uses DWD grid data (German Weather Service) as backup.

Manual Coordinate Entry

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

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:

Orientation:

Losses:

Multiple Surfaces

You can create any number of surfaces with different orientations:

Tip for East-West systems: Although the total yield is slightly lower than with pure south orientation, production is distributed more evenly throughout the day. This increases self-consumption without storage!

Duplicating a Surface

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

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:

ObstacleDescriptionTypical height
BuildingNeighboring buildings, chimneys5-15 m
Deciduous treeLoses leaves in winter8-20 m
ConiferYear-round shading10-25 m
HedgeLow shading1-3 m
ForestDistant forest edgevariable
ChimneyOn your own roof1-2 m above roof
Power poleSlim shading10-30 m
AntennaSmaller obstacles1-3 m
HillTerrain 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:

Calculating Shading Losses

Click on "Calculate shading" to determine annual losses:

Important for deciduous trees: In winter (without leaves) losses are lower, but solar yield is generally lower too. In summer (with leaves) losses can be significant, exactly when yield would be highest!

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:

Household Profile

Select a standard load profile:

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

Entering Annual Consumption

Adding Consumers

For precise calculation, you can record individual consumers:

ConsumerTypical consumptionLoad profile
Refrigerator150-300 kWh/yearConstant
Washing machine150-250 kWh/yearFlexible
Dishwasher200-300 kWh/yearFlexible
EV (8,000 km/year)1,500-2,000 kWh/yearEvenings/nights
Heat pump3,000-8,000 kWh/yearHeating season
Air conditioning200-500 kWh/yearSummer

Tip: Flexible consumers like washing machines or EVs can be scheduled during sunny hours to increase self-consumption!

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:

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

Economic note: Storage increases self-consumption and self-sufficiency but is often not yet economical. Payback period typically extends by 5-10 years. Check profitability in the results tab!

3.7 Tab 5: Finances

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

Investment Costs

Cost calculator: Clicking "Estimate costs" automatically calculates an estimate based on your system capacity (€1,200/kWp).

Electricity Prices

Analysis Period

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:

ShadingTypical yield loss
None0%
Chimney2-5%
Single tree5-15%
Neighboring building10-30%
Forest edge15-40%
Heavy shading30-60%

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:

4.4 Shading Analysis Results

After calculation, you receive:

Practical tip: Shading in winter is less critical than in summer, since solar yield is low anyway. Pay special attention to shading between March and October!

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:

MetricMeaningExample
Annual yield [kWh/year]Electricity your system produces5,500 kWh
Self-sufficiency rate [%]Share of your demand covered by PV65%
Annual savings [€/year]Saved electricity costs€850
CO₂ savings [kg/year]Avoided CO₂ emissions2,200 kg

Surface Overview

Table with all configured PV surfaces:

5.2 Tab 2: Finances

Year Selection

Select a year within the analysis period to see development.

Before/After Comparison

ParameterWithout PVWith PVChange
Electricity consumption4,500 kWh4,500 kWh-
Electricity generation0 kWh5,500 kWh+5,500 kWh
Grid purchase4,500 kWh1,800 kWh-2,700 kWh
Electricity costs€1,350€540-€810

Revenues

Cumulative View

5.3 Tab 3: Yield

Summary

Generation (dark blue area):

Consumption (light blue area):

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:

5.4 Tab 4: Surfaces

Detailed results per PV surface:

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

However: Bigger is often better! Since module prices have dropped, a larger system can be more economical - even if more electricity is fed in.

6.2 Orientation and Tilt

OrientationTiltYield vs. South-30°
South30-35°100% (optimum)
South45°98%
South15°95%
Southeast/Southwest30°95%
East/West30°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:

Module optimization:

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

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:

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:

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):

What happens during power outage?

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

How long do PV modules last?

Do I need a permit?

For PV systems on residential buildings:

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:

8.2 Sun Position Calculation

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

8.3 Standards and Norms

The solar calculator follows:

8.4 CO₂ Calculation

CO₂ savings are calculated with:

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

CO₂ factors:

8.5 Typical Module Specifications (2024)

ParameterTypical value
Power per module400-450 Wp
Efficiency20-22%
Area per module1.7-2.0 m²
Weight20-25 kg
Temperature coefficient-0.3 to -0.4 %/°C
Performance warranty25 years (80%)

9. Further Information

Official Sources

Funding Programs

Standards

To Calculator: Start Solar Calculator

Last updated: December 2025