A quote is a promise about a roof. Every re-quote, return visit and argument about scaffold traces back to something that was not known when the price was written.
Getting the roof right is seven stages, the same in every firm and every country. Each has one principle and one way firms break it.
1. The desktop look: decide whether to survey before anyone drives out
Before a survey is booked, somebody spends ten minutes with aerial imagery and the address: which planes face the useful way and how big they are, the pitch roughly, what is on the roof already (chimneys, windows, vents, an aerial), and how many panels would fit, to the nearest few. The answer is not a design. It is a yes or a no to the survey, with a first panel count the surveyor can test on site.
The mistake: surveying from the enquiry form. The customer said "big roof, south-facing", nobody looked, and the surveyor finds a hipped roof split four ways that cannot carry the system the customer was told about.
2. The survey is structured capture, not notes
A survey has four parts, and each has a reader: the roof for the designer and the roofer, the electrics for the electrician and the grid paperwork, the site and access for the scaffolder and the crew, and the customer's kit (where the battery, inverter and charger will go, and what was promised) for the person writing the quote. Each part is a fixed list of questions answered in the house, with a photograph where one settles it. A finished survey is one every reader can work from without ringing the surveyor. A blank line is not a detail to pick up later. It is a reason the quote cannot go yet, because whatever fills it will change the price.
The mistake: "tiles, fuse box looks fine, battery under the stairs" on a pad, written up in the van. Each phrase becomes a phone call three weeks later, and one becomes a re-quote. The survey checklist sets out every line, with the reason it is there.
3. Design on the real roof, not a rectangle
A design starts from the roof planes as they are, with the pitch and bearing of each. Onto each plane go the obstacles, and a margin inside every edge for the fixings and the wind. What is left is the usable area, and the panels are laid in it row by row. Then the sun goes over it. Not the sun at the hour of the survey, but at noon on the shortest day, in the spring and autumn months that carry the year, and at midsummer, to see which rows the chimney and the tree reach and when. A row that catches a shadow in March belongs on its own string or on optimisers, decided in the layout, not on the day.
The mistake: the desktop panel count surviving unchanged into the quote. Fourteen fitted the rectangle. Twelve fit the roof once the vent, the edge margin and the hip are drawn. The customer was sold fourteen. Where the sun will be explains how the sun is placed for any day and hour, and which shadows matter.
4. The generation estimate: know where the number came from
Every annual kWh figure is built from four inputs: the array's rated power, its pitch and bearing, the sunlight the location gets over a year, and a shading allowance. Tools differ in how each input is sourced. One uses a published table of irradiance by region, a lookup for pitch and bearing and a standard shading band. Another uses measured sunlight for the specific roof from aerial data. A third models a clear sky from the astronomy and scales it to the local climate. Two tools giving two numbers for one roof is not a fault in either. It is two methods, and the firm's job is to know which one it quotes from, say so on the quote, and use the same one every time.
The mistake: a number typed from whichever tool was open, and nobody able to say a year later how it was worked out when the customer rings with their first bill. The clear-sky maths is worked through in where the sun will be.
5. Check the design before it is priced
A design that looks right on the roof can still be wrong at the inverter, so three checks sit between the layout and the price. The electrical check: does each string's voltage stay inside the inverter's window on the coldest morning and the hottest afternoon, does its current suit the tracker, and will the cable run carry it without too much drop. The kit check: is the battery one the inverter talks to, is the charger suited to the supply phase. And the approval: somebody other than the designer checks the whole thing against the survey and signs it off or sends it back with a reason, the last moment a mistake costs a conversation rather than a return visit.
The mistake: pricing straight from the layout. The strings were never sized, the inverter was the one in the van, and the electrician found the fault on the roof. How many panels can a string take walks through the four string checks with a worked example.
6. The design feeds everything after it
The design is the source of record for three things. The quote: every line comes from the design's quantities, so the panel count, inverter, battery, mounting and cable lengths on the price match the roof. The job pack: the layout drawing, the string plan, the kit list and the cable routes, so what is fitted is what was priced. And the paperwork: the system size, the module and inverter models and the panel count that the grid notification and the certification scheme ask for. Any one of the three typed by hand will drift from the other two.
The mistake: the quote built from a kit list in a spreadsheet, the design changed after the quote went out, and the crew turning up with the quote's inverter and the design's panel count. The order is design, check, price, every time.
7. One job record, from the survey to the quote
The survey, the roof model, the design, its approval and the quote are one job, on one record, where the next person reads the last person's work rather than asking for it. The approver's reason for sending a design back is on the record, not in a message deleted with the thread. A firm that keeps the survey on a phone, the design in one tool and the quote in another retypes every figure at least twice, and the retyping is where the quote goes wrong.
The mistake: the survey photographed to the designer, the design exported to the office, the office typing the panel count into the quote. Three hand-offs, three chances to lose the vent, the loft hatch and the promise about the garage.
Installa does the survey and the design for you
- Stop deciding from the enquiry form. Look at a roof from the sidebar, with any address, before a customer exists, and see the planes and a first panel count in minutes. Link the roof to a customer or an enquiry when you are ready.
- Stop filling in the sheet from memory. The survey form holds the roof, the electrics, the site and access and the customer's kit as fields, from the roof covering and supply phase to the MPAN, loft access, cable lengths, scaffold and the proposed battery, inverter and charger locations. Choose the battery location and the form says there and then whether the applicable siting standard rules it out, allows it with conditions, or prefers it.
- Stop drawing a rectangle. The designer builds the roof planes from Google's building data, and where that is wrong or missing you draw a plane by hand. Panels are laid on the real planes and each is checked against the edge margin and the obstacles as you place it. Measure anything on the model, undo and redo any change, and the design saves itself as you work.
- Stop guessing the sun and typing the yield. The sun is placed from the site's own latitude and longitude with sliders for the day and the hour, a heat map shows a year of sunlight on every surface from Google's annual flux data, and the design's annual estimate follows the applicable certification scheme's method for the roof's pitch and bearing, with a shading factor derived from the measured sunlight where the data exists.
- Stop finding the string fault on the roof. The electrical check validates string voltage and current and whether the battery, inverter and charger work together. Submit the design for approval and the approver signs it off, asks for a revision or rejects it, with a reason that stays on the job.
- Stop retyping the kit list. Price the design and the quote is built from its components at the design's quantities, with prices from your own price list, and the survey, the roof model, the design and the quote all sit on the same job.
Look before you survey, capture rather than note, design on the real roof, know your yield method, check before you price, and let the design feed the quote. That is the whole routine, and it is what the 3D designer is built to run. See how 3D solar design in Installa works, or try the sun path simulator on a roof you know.