How to Choose the Right Solar System Size
How to choose the right solar system size: annual electricity use, roof area, shading, real energy yield, future loads and grid connection limits.
The material was checked against the cited sources. A site-specific decision still needs an engineering calculation.
Solar sizing is not a formula such as “house area × coefficient.”
A 250 m² home may use less electricity than a 120 m² home. Demand depends on appliances, heating, air conditioning, number of occupants, lifestyle, swimming pools, pumps, servers, electric vehicles and many other factors.
Building area alone is therefore not a reliable sizing method.
1. Collect annual electricity consumption
Start with 12 months of electricity bills.
Add the actual kWh consumption for the full year. This shows how much electricity the property used across all seasons and reveals seasonal patterns.
If hourly or daily data is available, it is even more useful because it shows when the load occurs.
2. Do not confuse power and energy
Solar system capacity is measured in kWp.
Energy produced over a period is measured in kWh.
Two systems with the same kWp capacity can generate different amounts of energy if one has good orientation and no shading while the other suffers from shade, temperature losses or a poor tilt angle.
That is why real performance cannot be estimated using kWp alone.
3. Consider real energy yield
The U.S. Department of Energy distinguishes module efficiency under laboratory conditions from energy yield — the amount of usable energy actually harvested by a system in real operation.
Energy yield is influenced by temperature, dirt and dust, shading, orientation, tilt, electrical losses and equipment characteristics.
This distinction matters in real system design. A module with excellent laboratory efficiency does not guarantee maximum annual energy if the system is poorly designed.
4. Check the roof
After estimating the required capacity, confirm whether the necessary modules can physically be installed.
Consider roof geometry, usable area, setbacks from edges, chimneys, roof hatches, rooftop equipment, shade, structural condition and safe service access.
If the roof is complex, it may be better to use another surface or several installation zones.
5. Analyse shading
Even partial shading can affect production.
The important questions are not simply “is there shade?” but what time it occurs, during which season, which modules are affected, how the strings are configured and what shading-management features the selected equipment provides.
Shading analysis should be part of design, not a surprise after installation.
6. Consider the permitted connection capacity
A solar installation interacts with the property's electrical connection.
The desired production level must therefore be considered together with the permitted connection capacity and applicable interconnection rules.
For autonomous generation in Armenia, installed capacity cannot exceed the maximum permitted capacity of the relevant connection point and is also subject to a statutory upper limit of 150 kW.
This becomes especially important for larger homes and commercial projects.
7. Add future loads
Before choosing the final system size, ask:
— will there be an electric vehicle? — is a heat pump planned? — will heating become electric? — will the property be expanded? — will new business equipment be installed? — will battery storage be added?
Future electricity demand can change the optimal system size.
8. What does “right-sized” mean?
The right system is not the largest system that can physically fit.
It is the system that reasonably matches:
electricity use + solar resource + roof + electrical connection + budget + future needs.
A preliminary calculator is useful, but the final decision should be based on the actual property.
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