Short answer
Comparing solar quotes only by installed power and total amount is misleading. The brand and model of the panel and inverter, the assumptions behind the production estimate, the mounting structure material, cables and protection devices, who runs the permit process, and maintenance after installation should be written in every quote in the same detail. An item left out comes back later as extra cost or low production.
Why the same power, different results?
You have two quotes in front of you, and both say 10 kW. One is clearly cheaper than the other. The difference is most often in what is not written in the lines: a thinner mounting profile, a thinner cable cross-section, a missing protection device, or a permit process left to the customer. Even if the installed power is the same, these differences change the system's production, safety and maintenance cost over the years.
So lay the quotes out line by line in the same table. Ask the company about every item that is in one quote and not in the other. The ten points below will help you build this table.
Before you start comparing, make sure the companies are quoting for the same need. If you told one your monthly consumption and the other your roof dimensions, the two quotes answer different questions. Give every company the same last-year bills, roof or land information and what you expect from the system. The answers to questions such as whether it is grid-connected, battery-backed or will be expanded later should also be the same for everyone.
Equipment: panel and inverter
The first point is the brand and model of the panel. If the quote states only the power, that is not enough; ask for the panel's technical datasheet along with the model number. The datasheet contains the panel efficiency, the temperature coefficient and the manufacturer's statement on power loss over the years. The temperature coefficient matters in a Şanlıurfa summer, because a hot panel produces less.
The second point is the inverter. The model, the number of inputs and the ratio to installed power should be stated. Ask whether the inverter has the certificates needed for grid connection and whether it has an authorized service in the country. An inverter that is faulty and sits for months waiting for parts means the system produces nothing during that time.
The third point is the manufacturer's warranty terms for the equipment. Ask in writing who issues the warranty certificate, how long it lasts and what it covers. Look at the manufacturer's or importer's document instead of the company's verbal statement.
How was the production estimate calculated?
The fourth point is the annual production estimate. Quotes calculate this figure with software or a data source such as PVGIS. Annual production per kW is high for Şanlıurfa; the calculator on our site assumes about 1,600 kWh for it. If a quote gives a value clearly above this, ask what assumptions it was calculated with.
The production estimate depends on the following assumptions and the quote should state them clearly:
- Panel direction and tilt
- Value used for shading loss
- Dust and dirt loss
- Temperature loss
- Cable and inverter losses
- Panel aging over the years
Expert note: If there is a big difference between the production estimates of two quotes, ask the companies for the calculation report. If one of the loss items has been taken as zero, the figure is optimistic.
- Panel brand, model and technical datasheet
- Inverter model and authorized service
- Manufacturer warranty certificate
- Assumptions of the production estimate
- Mounting structure material and thickness
- Cable type and cross-section
- Protection devices and grounding
- Who runs the permit process
- Handover documents and maintenance scope
Mounting structure, cable and protection
The fifth point is the mounting structure. It should state whether the material is galvanized steel or aluminum, the profile thickness and whether the fastening bolts are stainless. For a land installation, the method of fixing to the ground should be stated, and for a roof installation, whether the roof will be drilled. Ask whether a wind and load calculation was made.
The sixth point is the cabling. On the DC side, UV-resistant cable made as solar cable is used. The cable cross-section is calculated according to distance; a thin cable on a long run means some energy is lost as heat every day. The brand and type of the connectors must be compatible with the panel.
The seventh point is the protection devices. On the DC and AC sides, fuses, surge protectors, residual current relays and grounding should appear separately in the quote. Ask whether the grounding will be measured and the measurement result handed over. The quote should also state that the panel board that holds the protection devices has a protection class suitable for outdoors and will be placed where it does not get sun. In a Şanlıurfa summer, a plastic board in the sun wears out the fuses and surge arresters inside faster than expected.
Permit process and documents
The eighth point is the permit and connection process. For grid-connected systems, an application to the distribution company, project approval and acceptance procedures are needed. Who will carry out these tasks and whether items such as application fees are included in the quote should be in writing. Also discuss in advance what happens if the connection opinion is negative.
The ninth point is the handover documents. When the installation is finished, you should be given the single-line diagram, the equipment list, serial numbers, the grounding measurement result and the user manual. These documents are useful years later when a fault occurs or an expansion is made.
After installation: monitoring and maintenance
The tenth point is what happens after installation. Whether a monitoring system is set up, in whose name the account will be opened and who the alerts will go to should be clear. If the account is opened in the company's name, you may have access problems later.
The scope and frequency of maintenance, and whether it is paid or free, should be written in the quote. Ask who will clean the panels, check the connections and inspect the inverter, and how often. Find out how to reach the company if something fails, and whether a response time for the service visit is committed to.
Finally, you may want to see the installations the company has done before. Talking to the owner of a system that is a few years old tells you more than a catalog does.
After you build the table
When you fill in the ten points for two quotes, most of the differences show up on their own. If one quote is clearly cheaper, the empty cells in the table usually show why. Ask the company to complete the missing items in writing, then compare the quotes again in that form.
Price is a fair yardstick only between two quotes with the same scope. In quotes with different scopes, a low figure can mean you pay for the missing item later.
Frequently asked
Why can the cheapest solar quote be risky?
A low figure often comes from items not written in the quote: a thin mounting structure, low cross-section cable, a missing protection device, or a permit process left to the customer. Do not decide without comparing quotes with the same scope.
Can I trust the production estimate?
An estimate is only as reliable as the assumptions used. Ask what values were used to calculate panel direction, tilt, shade, dust and temperature losses. If a loss item has been taken as zero, the estimate is optimistic.
Which documents should be requested in the quote?
The technical datasheet of the panel and inverter, the manufacturer's warranty certificate, a draft single-line diagram and a list of the documents to be handed over after installation should be requested. After installation, the grounding measurement result is also added to the handover documents.
Get a detailed, comparable quote
Desa Bilişim prepares a quote that lists every item of the system to be installed, with model and quantity, so you can put it side by side with the other quotes you have.
