Quick Answer
Preliminary solar design should answer one defined investment or development decision before detailed engineering. Control the evidence, compare site and capacity options, and reproduce the energy model. Map electrical, structural, civil, grid, authority, budget, schedule, and risk concepts. Identify required investigations. Accept a dated concept package with stated limitations, not construction or approval evidence.
Solar preliminary design services should support one defined concept decision before detailed engineering. The work compares options, exposes missing evidence, and states what must happen before greater money or schedule is committed.
Quick Answer
Preliminary solar design should answer one defined investment or development decision before detailed engineering. Control the evidence, compare site and capacity options, and reproduce the energy model. Map electrical, structural, civil, grid, authority, budget, schedule, and risk concepts. Identify required investigations. Accept a dated concept package with stated limitations, not construction or approval evidence.
Stage boundary
A preliminary design is a controlled concept. It is not a permit, interconnection approval, professional certification, final yield, final BOQ, procurement release, or construction package.
This guide explains how to procure and accept that concept package. It does not promise capacity, usable area, energy, loss, accuracy, cost, return, schedule, approval, or buildability.
Define the decision before the design
A preliminary design has value only when it supports a named decision. “See what fits” is too vague for a final scope.
Create a decision brief with these fields:
| Decision field | Required definition |
|---|---|
| Owner | Person or body authorized to decide |
| Decision date | Date when evidence must be usable |
| Project route | Rooftop, ground, canopy, floating, storage, captive, export, or other route |
| Current stage | Screen, opportunity, feasibility, concept, or another controlled stage |
| Objective | Question the package must answer |
| Alternatives | Options, including stop or defer |
| Threshold | Evidence-based condition for advancing |
| Spend at risk | Money exposed before the next gate |
| Schedule at risk | Dependencies affected by the decision |
| Unknown tolerance | Items allowed to remain unresolved |
| Stop condition | Finding that ends or redirects work |
| Advance condition | Evidence required to fund the next stage |
| Next gate | Survey, study, tender, detailed design, application, or other action |
Examples include selecting one roof zone, reserving land, choosing an architecture family, or funding a survey. Each needs different evidence.
Do not start with a preferred capacity and force the site to support it. Compare the stated objective with site, grid, safety, operation, and authority constraints.
Keep design stages separate
Document labels should show intended use and prohibited use.
| Stage | Suitable use | Excluded reliance |
|---|---|---|
| Screen | Reject obvious mismatches using bounded evidence | Site confirmation, yield commitment, approval |
| Opportunity | Define a possible project and information needs | Final layout, equipment, cost, schedule |
| Feasibility | Compare whether options deserve more investigation | Construction or professional reliance |
| Preliminary concept | Select or narrow options with controlled assumptions | Detailed design, permit, procurement, field work |
| Tender basis | Seek comparable proposals under defined requirements | Final coordination unless stated |
| Permit basis | Support a named submission after required development | Automatic authority acceptance |
| Interconnection basis | Support a named utility process | Grid-capacity or approval guarantee |
| Detailed design | Complete coordinated engineering for its defined issue | IFC use until checked and released |
| IFC | Controlled construction issue | Unrecorded field changes |
| Record or as-built | Preserve accepted or installed information | Proof of concealed conditions without verification |
Every artifact needs intended use, excluded use, date, revision, author, checker, approver, data cut-off, limitations, and next study.
Use the detailed engineering services guide after the concept gate. It covers design maturity and construction release.
Build a controlled input register
Preliminary work is assumption-led, but assumptions must remain visible. Start with one register rather than scattered emails and screenshots.
Record project identity, location, coordinates, parcel or roof, ownership, access, customer, load, utility, PCC, voltage, phase, export mode, capacity objective, route, schedule, and decision criteria.
Add site, environmental, equipment, and authority evidence as applicable.
| Evidence status | Meaning |
|---|---|
| Verified | Checked against an identified source for the intended use |
| Measured | Captured through a defined field method |
| Surveyed | Produced by a stated survey scope and responsible party |
| Authority issued | Issued by the named authority with date and status |
| Utility issued | Issued by the named utility for the stated purpose |
| Manufacturer issued | Exact product document with revision |
| Owner supplied | Provided by the owner without added verification |
| Estimated | Derived through a stated method |
| Modeled | Produced by a named model, version, inputs, and settings |
| Assumed | Used without verification under a stated limit |
| Conflicting | Sources disagree and require resolution |
| Stale | Age or change makes current use uncertain |
| Missing | Required evidence is unavailable |
| Superseded | Replaced by a controlled later source |
| Field verification required | Must be checked at the site before reliance |
Each record needs source, file or URL, date, revision, resolution, permitted use, limitation, affected decision, owner, open question, due date, and closure evidence.
Never silently reuse a neighbouring project, old bill, generic loss stack, public screenshot, unverified GIS layer, or representative equipment file.
An assumption can support comparison when both options use it consistently. It should not become a fact through repeated use.
Treat public data as discovery evidence
Public imagery, GIS, weather layers, online calculators, and provider models can speed screening. Their outputs remain bounded by source and method.
The Global Solar Atlas methodology describes modeled solar, temperature, and PV power layers. Those layers do not establish surveyed site conditions or legal rights.
The USGS 3DEP accuracy guidance shows how resolution and accuracy vary by product and source. It is a US example, not a universal site tolerance.
USGS also publishes known dataset issues. This supports checking metadata and corrections. It does not prove an error at a specific site.
For every public layer, record:
- acquisition and publication date
- horizontal and vertical basis
- spatial and temporal resolution
- coverage gaps
- processing method
- known limitations or issues
- conflict with other evidence
- permitted decision use
- required survey or field check
A satellite image cannot confirm roof condition. A GIS boundary cannot replace legal or surveyed evidence. A utility map cannot prove available capacity.
Model the site and constraints
Start by matching address, coordinates, parcel, building, and utility context. Resolve identity conflicts before drawing options.
Map boundary, usable zones, rights, access, easements, setbacks, fire routes, drainage, flood, slope, aspect, obstructions, shading, vegetation, and security.
For roofs, include roof build-up, condition, remaining life, waterproofing, structure records, access, fall protection, drainage, and equipment zones.
For land, include topography, geotechnical evidence, hydrology, roads, crossings, vegetation, environmental constraints, construction laydown, and future access.
Record wind, snow, seismic, heat, dust, salt, corrosion, chemicals, pollution, and hazardous-area evidence where relevant.
Do not calculate “usable area” without defining exclusions and evidence. Keep gross boundary, screened area, provisional exclusion, and concept layout area separate.
The land feasibility study guide covers land due diligence. The rooftop design services guide covers measured roof and coordination stages.
Develop comparable project-route options
Preliminary design should compare viable routes, not only module count. Define which routes belong in the decision.
Possible routes include residential, multifamily, commercial, industrial, rooftop, ground mount, canopy, floating, storage, generator, EV, captive, open access, behind-meter, export, zero-export, and utility-scale.
Each route needs a controlled option card:
| Option field | Required content |
|---|---|
| Identity | Option name, drawing, revision, and decision status |
| Site use | Zones, exclusions, access, routes, drainage, security, expansion |
| Capacity | Module count, DC rating, AC rating, ratio, storage power and energy where relevant |
| Architecture | Candidate topology, voltage, phase, inverter grouping, PCC, operating mode |
| Geometry | Orientation, tilt, height, spacing, setbacks, clearances |
| Equipment | Exact candidate models or representative envelopes |
| Evidence | Inputs, models, calculations, assumptions, and conflicts |
| Discipline effects | Electrical, structural, civil, grid, fire, environmental, operations |
| Commercial effects | Quantity, budget-category, schedule, service, and replacement effects |
| Risk | Studies, veto gates, unresolved questions, and next action |
Candidate options can compare string and central architectures, or fixed tilt and tracker. They can also compare attached and ballasted roofs, or storage coupling methods. Compare only relevant options.
Do not declare one architecture universally better. Site, grid, equipment, operation, service, and contract evidence control the decision.
The ground-mount design guide provides deeper spacing and land-use context.
Keep capacity tied to evidence
State capacity in module count, DC rating, inverter AC rating, and DC-to-AC ratio. Define the module and inverter basis.
For representative equipment, use a bounded envelope. Record dimensions, ratings, weight, voltage, current, temperature limits, clearances, and interfaces used by the concept.
Do not present representative equipment as selected equipment. Later product changes can affect geometry, stringing, structure, protection, and yield.
Capacity options should preserve access, fire routes, drainage, electrical routes, equipment clearances, maintenance, cleaning, replacement, and future work.
Maximum module count can create a weaker operating option. Score decision needs rather than density alone.
Make the preliminary energy model reproducible
An energy estimate needs a model register. Record software, version, settings, weather source, weather vintage, geometry, timestep, horizon method, shading method, equipment, and operating mode.
Include applicable assumptions for irradiance, temperature, albedo, soiling, snow, availability, mismatch, DC wiring, AC wiring, conversion, clipping, curtailment, export, degradation, and downtime.
The NREL PVWatts Version 8 page explains its current model basis and limitations. It supports a preliminary estimate, not site or engineering proof.
The PVWatts API documentation describes a simplified grid-connected estimate. API access does not change the limits of inputs or model purpose.
The European Commission PVGIS manual documents its weather, horizon, and PV inputs. Tool output still depends on selected data and assumptions.
Report only decision-relevant results
Annual energy, specific yield, performance ratio, monthly profile, clipping, export, or self-consumption may support the decision. Include only outputs justified by the input quality.
Separate modeled output from measured production, contractual guarantee, lender case, independent opinion, final energy assessment, and prediction interval.
Do not promise savings, payback, return, or generation. Those require additional commercial and operating evidence.
Use the PVsyst simulation services guide for model-file and reproducibility procurement.
Run decision-changing sensitivities
Select sensitivities that can reverse the choice. Examples can include weather dataset, usable area, shading, soiling, outage, export limit, clipping, equipment, and availability.
Show one changed input at a time where practical. Explain interactions when variables cannot be separated.
For each sensitivity, record base value, test value, source, reason, affected output, and decision effect.
Do not create a generic loss percentage. Build a project-specific preliminary stack and state unresolved items.
Define the preliminary electrical and grid concept
Map candidate DC and AC topology, string and MPPT envelope, inverter grouping, cable routes, protection families, grounding, bonding, lightning, metering, transformer, switchgear, and PCC.
For storage or generators, define preliminary operating modes, transfer boundaries, controls, protection, communications, and safety questions.
For export control, identify the measurement point, control concept, failure state, communications, and utility evidence needed.
Keep preliminary lines and ratings distinct from final sizing and coordination. Protection and equipment settings need detailed study and approval.
Grid concepts must use current connection evidence. Do not infer available capacity from a nearby line or substation.
List applications, studies, deposits, upgrades, metering, protection, communications, agreements, and decisions that remain open.
The engineering services for developers guide covers grid and owner-engineering stage gates.
Define structural and civil concepts
For rooftops, record the candidate structural system, load path, attachment or ballast concept, waterproofing boundary, drainage, corrosion environment, and required assessment.
Do not call a roof suitable without the required evidence and professional review. A visible roof condition is not a structural calculation.
For ground projects, map table or tracker geometry, candidate foundation, grading, drainage, erosion, roads, fencing, trenches, crossings, pads, water, and construction logistics.
Keep cut, fill, foundation, and drainage quantities preliminary. Tie each quantity to source resolution, measurement rule, and investigation status.
List boundary, topographic, geotechnical, hydrology, structural, environmental, fire, hazardous-area, corrosion, and field investigations before the next gate.
Use the structural engineering services guide for professional structural scope.
Build an approval and study roadmap
Preliminary design should map the path without claiming approval.
Consider legal, land, title, lease, roof rights, planning, zoning, building, electrical, fire, environmental, aviation, and heritage routes. Add water, drainage, road, crossing, utility, interconnection, metering, export, professional, inspection, testing, and commissioning routes.
For each route, record:
- responsible authority or party
- current evidence source and date
- required input
- dependency
- submission or study
- fee category
- review and comment step
- decision and validity
- conditions or inspections
- closure evidence
- next action
The US DOE permitting page separates local permit, inspection, and utility connection. It does not define another project’s authority route.
Do not publish a universal code, threshold, fee, licence, review clock, or approval path. Obtain current evidence for the exact site and date.
The solar permit drawings guide covers later permit-stage documentation.
Produce concept quantities, not a final BOQ
Tie every quantity to an option, drawing, assumption, measurement rule, contingency class, exclusion, and maturity.
Possible quantities include modules, inverter capacity, table or roof zones, structure lengths, cable-route lengths, trench lengths, road areas, equipment pads, fencing, and major devices.
Label allowances and unknowns. A concept quantity is not a purchase list or construction quantity.
Build budget categories without inventing prices:
| Budget group | Concept boundary |
|---|---|
| Development and rights | Land, roof, legal, access, agreements |
| Surveys and studies | Boundary, topographic, structural, geotechnical, hydrology, environment |
| Engineering and authority | Design stages, professional work, applications, reviews |
| Utility and grid | Studies, deposits, upgrades, metering, connection |
| Equipment | Modules, inverters, storage, structures, electrical, controls |
| Construction | Civil, structural, electrical, logistics, safety, testing |
| Commercial | Tax, finance, insurance, contingency, escalation |
| Operations and exit | O&M, communications, replacements, decommissioning, restoration |
Use dated project-specific evidence when amounts are needed. Do not turn a concept into a universal cost, savings, or return forecast.
Build schedule logic, not a duration promise
Map dependencies among decisions, surveys, studies, authorities, utilities, professional work, procurement, design, construction, testing, and handover.
For each activity, state prerequisite, responsible party, evidence, review, decision, hold, successor, and uncertainty.
A preliminary bar chart can show logic. It cannot prove approval, equipment availability, field productivity, or completion date.
Test schedule effects from survey delay, grid study, authority comment, equipment change, access, weather, and design rework.
Do not publish a universal delivery or project schedule. Define the provider clock and external dependencies in the contract.
Use risk gates before option scoring
A weighted average should not hide a fatal constraint. Establish veto gates before scoring.
Possible gates include legal access, safe concept, credible grid route, usable evidence, acceptable environmental risk, viable construction access, and defined next-stage work.
Maintain a risk register:
| Risk field | Required record |
|---|---|
| Cause and event | What could create the problem |
| Consequence | Safety, technical, authority, cost, schedule, or operating effect |
| Option | Concepts affected |
| Evidence | Source and date supporting the assessment |
| Likelihood and severity basis | Defined scale and rationale |
| Owner | Person responsible for response |
| Response | Avoid, investigate, reduce, transfer, or accept |
| Trigger | Event requiring action or reassessment |
| Residual risk | Exposure after planned response |
| Due date and gate effect | Timing and advance condition |
After gates, score evidence-backed criteria with documented weights. Mark missing evidence unresolved.
Run weight sensitivity. A preferred option should not depend on hidden scoring choices.
The recommendation should explain why an option advances, stops, or needs investigation. It should not claim certainty beyond the evidence.
Specify the deliverable and file package
A complete preliminary package can include:
- direct answer and decision brief
- input, assumption, and conflict registers
- data-room index
- site and constraint plan
- option layouts and capacity table
- preliminary energy model and sensitivities
- topology and PCC concept
- major-equipment assumptions
- electrical, structural, civil, and grid concept notes
- approval roadmap and investigation plan
- concept quantities and budget basis
- schedule logic
- risk register and option matrix
- recommendation and unresolved questions
- next-stage brief
Every file needs version, units, coordinate basis, dependencies, libraries, settings, permissions, ownership, retention, and issue status.
Editable files should be delivered only when contracted. Define formats, software versions, weather files, equipment files, scripts, macros, exports, naming, and licences.
Test provider evidence and reproducibility
Ask for a matched sample from the same project family and decision stage. Require its source set, assumptions, revision history, checker record, and use boundary.
A polished image without its inputs cannot prove reproducibility. A successful project outcome cannot prove which concept assumption caused it.
For recurring work, run a paid representative pilot. Use controlled inputs and measurable acceptance.
Trace important numbers, layouts, risks, and recommendations to sources, models, assumptions, limitations, owners, and next actions.
Run a clean-workstation reopen test. A qualified person should recreate key outputs using only the delivered package and documented dependencies.
Test missing libraries, broken references, unavailable equipment files, unit conversion, coordinate systems, and weather data. Record defects and closure.
Include security, confidentiality, access, subcontractors, retention, export, deletion, archive, and exit in the contract.
The design outsourcing guide covers recurring capacity and provider-exit controls.
Evaluate Heaven Designs under identical gates
Disclosure: SurgePV and Heaven Designs have a commercial relationship. Heaven Designs is therefore a related-party candidate in this guide.
The Heaven Designs 3D pre-design page contains first-party service statements. They do not independently prove model accuracy, project performance, approval, or outcome.
Use the sample request route to request a matched project-family sample. Require inputs, history, assumptions, and decision context.
Use its contact route for a project-specific proposal. Treat the response as vendor evidence.
Do not rank Heaven Designs. Apply the same decision, input, constraint, option, model, discipline, approval, risk, sample, pilot, security, contract, archive, and exit gates.
SurgePV is separate design and proposal software. It is not the preliminary-design provider, surveyor, engineer, authority, utility, professional reviewer, or source of verified site evidence.
Keep adjacent work separate
This page owns the decision-grade concept before detailed engineering. Use focused guides for later or adjacent work:
- solar detailed engineering services for mature coordinated design
- PVsyst simulation services for reproducible model procurement
- solar land feasibility study for land due diligence
- rooftop design services for roof-stage deliverables
- solar structural engineering for professional structural work
- engineering for developers for development stage gates
- design outsourcing company for recurring operating models
- post-design services for RFIs and changes
- solar design company for provider selection
- permit drawings for authority submission content
Accept the solar preliminary design services package
Acceptance should trace each important output to controlled evidence. Check source, date, revision, model, assumption, limitation, owner, and next action.
Confirm that the package answers the decision brief. Record whether the option advances, stops, defers, or needs investigation.
Mark every artifact with its intended and excluded use. Preliminary files should not be released for construction or approval reliance.
Accept open questions only when the decision brief permits them. Assign each open item to a study, owner, due date, and next gate.
The next-stage brief should preserve selected concepts without freezing unverified assumptions. Detailed teams need the option history and rejected alternatives too.
Archive inputs, files, settings, review records, decisions, and exports. Test retrieval before closing the engagement.
Frequently asked questions
What are solar preliminary design services?
They develop controlled concept options for a defined decision before detailed engineering. The package can compare site use, capacity, layout, architecture, energy, grid, discipline, budget, schedule, authority, and risk concepts. It records evidence limits, investigations, stop conditions, advance gates, and the next-stage brief.
Can preliminary solar design be used for construction?
No. Preliminary drawings, quantities, topology, equipment, calculations, and routes are not construction instructions. They require the stated surveys, studies, coordination, professional review, authority process, detailed engineering, checking, approval, and controlled construction release before field reliance.
What inputs should a preliminary solar design use?
Use controlled project identity, ownership, access, load, bill, tariff, utility, PCC, survey, roof or land, structure, weather, environment, equipment, authority, schedule, budget, and decision evidence. Classify every input by source, date, revision, resolution, status, permitted use, limitation, owner, and closure action.
Are satellite images and GIS data enough for preliminary design?
They can support discovery and screening when their source, date, resolution, basis, and limitations are recorded. They do not prove legal boundaries, surveyed geometry, roof condition, structure, drainage, shading, utility capacity, access, authority acceptance, or buildability. Define field verification before the next gate.
How should preliminary solar capacity options be compared?
Compare module count, DC and AC capacity, ratio, geometry, architecture, PCC, export mode, access, safety, structure, and drainage. Add electrical routes, construction, operation, maintenance, replacement, expansion, studies, risk, budget categories, and schedule logic. Use evidence-backed veto gates before weighted scoring.
How accurate is a preliminary solar energy model?
No universal accuracy applies. Results depend on weather, geometry, horizon, shading, equipment, operating mode, loss assumptions, software, settings, and unresolved site conditions. Preserve the model and inputs, disclose limitations, test decision-changing sensitivities, and refine the estimate after stronger evidence becomes available.
Does preliminary design confirm grid connection or permit approval?
No. It can map the current authority and utility route, required inputs, studies, applications, fees, dependencies, decisions, validity, and next actions. It cannot establish available grid capacity, professional acceptance, permit issuance, interconnection approval, inspection, or commissioning outcome without the responsible process.
How should buyers test a preliminary design provider?
Review a matched sample with its input and revision history, then run a paid representative pilot. Trace important outputs to sources, assumptions, models, and calculations. Test option comparison, sensitivity, checking, files, security, response, archive, and a clean-workstation reopen before recurring work.
Is Heaven Designs ranked as the best preliminary design provider?
No. SurgePV and Heaven Designs have a commercial relationship. Heaven Designs is a related-party candidate, and its statements are first-party evidence. Apply the same decision, input, option, model, discipline, sample, pilot, security, contract, acceptance, archive, and exit gates to every provider.
