Define basis before cost.

1. 1

   Define the system

   State the technology, purpose, and operating requirement. Fix the units and measurement boundary before counting equipment: DC nameplate, AC inverter capacity, and the export rating at the point of interconnection describe different things.

   Project description · Single-line diagram · Owner requirements · Rating basis
2. 2

   Set the scope boundary

   Identify what is included, who furnishes the major equipment, and where responsibility transfers. Receiving, storage, installation, testing, and utility work need an owner even when the equipment itself is owner-furnished.

   Responsibility matrix · Supply boundary · Contract structure · Utility scope
3. 3

   Translate into quantities

   Connect the system basis to equipment counts, assemblies, cable routes, foundations, and terminations. Keep the drawing, revision, and quantity basis with the takeoff so changes can be reconciled.

   Site layout · Equipment schedules · Cable routes · Referenced takeoff
4. 4

   Account for conditions

   Consider soils, access, working height, weather, outage windows, sequencing, labor availability, and commissioning. A quantity alone does not explain the effort needed to install it.

   Geotechnical report · Survey · Schedule · Logistics · Labor basis
5. 5

   Review the uncertainty

   Separate confirmed information from assumptions and open decisions. Identify allowances, evaluate risk, reconcile the scope against benchmarks, and document what could materially move the result.

   Basis of estimate · Assumptions and exclusions · Risk register · Benchmarks

Class follows the maturity of the required project definition deliverables. Accuracy also depends on technology, market conditions, data quality, and risk. It needs its own assessment; a class number does not promise a fixed percentage range.

Framework: AACE’s guide to estimate classification. Apply the relevant industry guidance; process-industry accuracy ranges are not universal solar or storage guarantees.

Power, Energy, and the Measurement Boundary

A 100 MW system delivering for four hours represents 400 MWh at the stated boundary. That is not automatically 400 MWh of battery DC nameplate. Usable depth of discharge, conversion losses, auxiliary loads, and the required operating life affect the equipment needed to meet the delivery requirement.

Overbuild or Augmentation

Initial overbuild installs extra energy capacity on day one. Augmentation adds capacity later as the original equipment degrades. Compare both on the same delivery requirement, while accounting for space, electrical provisions, installation access, and equipment compatibility.

DC Block & Enclosures

Cells, racks, battery management, enclosures, and the DC rating basis. Supplier scope and delivery terms need to be explicit.

PCS & MV Transformers

Bidirectional conversion equipment, step-up transformers, block size, equipment counts, and associated connections.

Civil & Electrical BOS

Foundations, grading, access, MV collection, grounding, auxiliary power, and communications.

Fire & Life Safety

Detection, mitigation, separation, and emergency planning based on the selected equipment, adopted codes, and authority requirements.

Controls & Commissioning

EMS, SCADA, metering, utility telemetry, integration, performance testing, and turnover.

Lifecycle Scope

Degradation assumptions, augmentation or overbuild strategy, O&M, and the responsibilities retained by the owner.

Safety reference: NFPA 855. Confirm the adopted edition and project-specific requirements.

Two Ratings, Different Quantity Drivers

Modules and their individual wattage establish the DC array size. The DC/AC ratio relates that size to inverter capacity. Installed capacity then follows the selected equipment’s discrete block sizes; it does not necessarily equal the project’s permitted export rating.

Piles & Geotechnical Conditions

Embedment, refusal, pre-drilling, corrosion protection, and verification of the assumed installation method.

Tracker or Fixed Tilt

Structure count, row spacing, slope tolerance, motor wiring, and control architecture.

DC Collection

Harnesses, combiners, homeruns, or trunk systems. The architecture changes both material and installation effort.

Inverters & MV Collection

Inverter blocks, MV skids, feeder count, conductor selection, trench length, splices, and terminations.

Civil & Site Work

Grading, roads, fencing, stormwater, laydown, and restoration, coordinated with electrical routes.

Supply & Construction Boundary

Who furnishes modules and equipment, and who receives, stores, distributes, installs, and replaces damaged material.

MV Collection

Feeders from the plant blocks to the substation: circuits, conductor size, routes, splices, testing, and terminations.

Project Substation

Main power transformer, breakers, protection and relaying, station service, metering, grounding, and SCADA.

Gen-Tie

Voltage, distance, structure type, terrain, crossings, right-of-way, and underground transitions where required.

POI Facilities

Switching, protection, telemetry, and metering at the point of interconnection. Identify who designs, builds, owns, and funds each element.

Network Upgrades

Off-site system work identified by the utility or regional studies. Keep these costs distinct from the project’s own facilities.

Schedule & Energization

Study milestones, agreements, equipment delivery, outages, acceptance testing, and utility energization windows.

Pricing Date & Escalation

Separate current quotes from historical rates. Relate procurement and installation dates to the assumed escalation basis.

Trade & Origin

Track the origin, delivery terms, and commercial exposure of major components. Confirm applicable duties when pricing.

Incentives & Requirements

Keep tax assumptions and any domestic-content, labor, or eligibility conditions explicit. Verify current requirements for the project.

Labor & Productivity

Wage classes, crew composition, installation rates, union or open-shop conditions, travel, per diem, access, and available workforce.

Indirects & Execution

Mobilization, supervision, temporary facilities, laydown, rental equipment, safety, commissioning support, and schedule duration.

Allowances & Contingency

Identify known but incompletely defined scope separately from the risk allowance. Explain the basis for each rather than hiding both in a unit rate.

Make proposals comparable before ranking them

Level bids to a common scope and work breakdown. Reconcile quantities, exclusions, equipment supply, schedule, testing, taxes, and commercial terms. The lowest submitted total may carry costs that are sitting elsewhere in the project budget.

Power Distribution

Service equipment, transformers, switchgear, feeders, branch circuits, protection, grounding, and terminations.

Lighting & Controls

Fixtures, switching, control systems, emergency operation, supports, commissioning, and integration with existing systems.

Low Voltage & Communications

Structured cabling, fiber, DAS, fire alarm, and security scope, including pathways, devices, testing, and system interfaces.

Existing Facilities

Survey, demolition, temporary service, working clearances, shutdowns, phasing, restoration, and turnover in an occupied or energized environment.

Behind-the-meter storage and distributed generation add operating objectives to the construction basis: peak demand, backup requirements, available service capacity, and the boundary between owner and utility equipment.

EV charging: price the make-ready scope

The charger is one package. Service capacity, transformers, switchgear, trenching, conduit, communications, accessibility, and restoration can materially change the installation. Confirm the utility’s service requirements and delivery schedule early.

Microgrids: define the operating modes

Generation, storage, and loads must work in the intended grid-connected and islanded modes. The scope may include a microgrid controller, additional protection, transfer or isolation equipment, resynchronization, and integration with existing distribution.

These are estimating considerations for adjacent systems, rather than a claim of completed project experience in every application.

Further background: U.S. Department of Energy — solar-plus-storage fundamentals.