- Review and Compare Quotations

Checklist - Best Buy Photovoltaic System

How to review and compare quotations for a photovoltaic system?

Find here a checklist with top questions you should check before you buy and what to compare when receiving any quotations from solar installers. Also, what to check after the installation is done and you do the acceptance procedure.

Find further about the technical background in our PV guideline and FAQ section.

Checklist Bes Buy Photovoltaics


I. Before Buying
The Size and Output of your System


 System Size

Maximum Power

The size of the system is given in "KWp".
KWp stands for Kilowatt Peak  

Is the calculated system size correct? Are you able to fit more modules on your roof?

Any shadows on your roof? Is it considered in the proposal?
Find more in our PV guideline


 Annual output of your PV System

The output is given in "KWh" per year.
KWh stands for Kilowatt hours.

Is the calculation correct and realistic?

Some installers tend to make a too optimistic calculation for the energy produced by your PV array and the profit of the proposed solar system looks better on paper than it will be in reality. So check carefully if the given data are realistic.
Find more in our PV guideline


 Any Feed-in Tariff or incentives in your country?

Feed-in tariff laws which supports photovoltaic are in place in in more than 50 countries worldwide!

Feed-in tariffs available in UK, Germany, Spain, Malta,  Italy, Australia, Czech Republic, South Africa, India, Netherlands and many more countries.
You typically can expect between 30 and 50 US Cents per kilowatt hour for surplus electricity fed into the grid which gives you an excellent yield return!

Is the calculated profit realistic?

This is related to I-b above. If the forcasted annual energy produced by the PV array is already too optimistic, your profit will it be, too. So check the data careful and also check your local Feed-in-Tariff.
Find Feed-in Tariff for Australia, Germany, UK, Canada in step 5 of our guideline
More information worldwide feed-in tariffs in Wikipedia:

II. Before Buying
The Components of your Photovoltaic System


 Photovoltaic Modules

- Manufacture, brand name, model
- Warranty

Characteristics, Data Sheet:
- Type (Mono, Polycristalline, Thin Film)
- Maximum Power
- Stability
- Module Dimensions


Get either modules made in Europe, Japan or USA. 

Chinese products are okay as well and cheaper. However, it is recommended to buy one of the Chinese top brands as Yingli, Trina, Solarfun or Suntech.

- Workmanship Warranty: 2 yrs / 5 yrs / 10 yrs
- Linear Performance Guarantee: typical 90% for 10 yrs / 80% for 20 or 25 yrs
Maximum Power (Pmax) and Power Tolerance:
- Most modules range from 180W - 240W, depending on type
- Standard for power tolerance today is +/- 3%, +/- 5% should not be accepted. Sometimes you find plus tolerances only.
- Maximum Load (from Data Sheet)
- Frame: In regions without snow a 35mm frame is the best choice. With snow a 40mm or even 45mm can be recommendable.
Module Dimensions:
- Is the module dimension suitable for your roof? Sometimes you are able to fit more modules on your roof just by choosing a module with other dimensions.
-  IEC-61215 and IEC/EN 61730 certificate.
All data should be listed in the data sheet



Solar Power

- Manufacture
- Brand name
- Model



- Inverter Efficiency
- Voltage operation range
- MPP trackers

Well known inverter brands are i.e. SMA, Fronius, Sputnik, Danfoss, Diehl.

Some important technical features:

Voltage operation range:
The higher the voltage operation range, the more flexibility in configuration of the modules.
MPP trackers:
MPP stands for "Maximum Power Point". If shadows on your roof occurs or you have a complicated roof situation it is important to have an own MPP tracker for each string. Choose a so called "multi string inverter".
Inverter Efficiency:
Important: Check not the maximum efficiency only, but compare the European degree of efficiency. The European efficiency reflects more realistic conditions.


III. Before Buying
The Price


What is included in your quotation?

Do you get a key turn system?

What is included, what excluded in the proposal?

Make sure everything is transparent without any hidden cost.
The proposal should at least include:

A listing of all components:
- Modules
- Solar inverter
- Mounting system
- Electrical wiring
- Connection to the grid
Name of manufacture or brand and model for all components to be able to compare the quotations
Start and end of installation work
Condition of Payment.
Your return on investment calculation
Investment vs. Annual income. Find more in our guideline: Step 5 - Return on Investment


IV. After Installation
Acceptance Procedure

Final check after installation
 Make sure to get a report at the end with all essential technical information

Get a list with all technical specification including
- The string connection
- S/N numbers of the modules

Also ask the installer for the so called "Flash Report". Every module is factory flash tested (at standard test conditions, STC) to determine the peak rated power output. The result is documented in the flash report.


b/ Some possible issues after installation Make a final check together with your installation company, note all defects and not make the final payment before the defect is fixed

Visual Appearance

- A good installer takes care about the visual appearance and makes sure that the panels align in the row but also in plane


Electrical cables should be fixed with UV resistant binders at the mounting system. If they are not fixed wind loads can let them rub the roof surface and damage the cable after some years


Mechanical tensions on panels:
The panels must be free of any tensions. Make sure there is a gap between the rows of modules that they are able to extend a hot tempearture. Also that the panels are not bended after installation because of unsuitable roof hooks.




Inverter - check the minimum distance:
Solar inverter are sometimes mounted too close to the floor below, the ceiling above or the distance between each inverter is too small


Technical Issues:












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