The modules and inverter are usually specified first and separately. Everything else — the balance-of-system (BOS) — is the long tail of components that actually makes a solar project buildable, compliant and inspectable. For an EPC contractor, a missing or under-specified BOS item is what stalls a container or a commissioning date.
This is a working BOS components list for EPC projects: each category, what to specify, and how to consolidate it into one coordinated bill of materials rather than chasing parts from multiple suppliers.
What counts as balance-of-system
Balance-of-system is everything a PV installation needs except the modules and the inverter: the structure, the DC and AC electrical protection, the cabling and connectors, the combining and distribution, and the accessories that tie it together. It is typically a modest share of project cost but a large share of the line items — and therefore of the things that can go missing.
The BOS components list, by category
A complete EPC BOS BOM usually spans these categories. Each links to the matching product range and needs its own ratings in the RFQ.
- DC protection: DC isolators/disconnects, DC breakers (MCB/MCCB), gPV fuses, DC SPD
- Combiner boxes: string combiners with internal fusing, SPD and isolation
- PV cable: H1Z2Z2-K DC cable and grounding cable, sized by current and run length
- Connectors: MC4-compatible pairs, branch/Y, fuse and diode connectors
- AC protection: AC isolators, AC SPD, AC breakers and RCDs
- Distribution: AC combiner / distribution boards and enclosures
- Accessories: cable management, glands, labelling, grounding and earthing parts
What to specify for each item
Across every BOS category, the same handful of fields turn a vague list into a quote-ready BOM: the rating (voltage/current), the certification standard, the IP/enclosure for the environment, and the quantity. A BOS line without ratings is the single most common cause of incompatible quotes and inspection problems.
Sourcing the BOS as one coordinated BOM
The advantage of consolidating the BOS is fewer suppliers, one set of certificates, one shipment and no missing accessories. Rather than buying combiner boxes from one supplier, cable from another and protection from a third, an EPC can specify the whole BOS BOM once and have it sourced, QC'd and shipped together.
- One BOM with ratings, certificates and quantities per line
- Matched components across DC protection, combiner and cabling
- Pre-shipment QC and a single certificate pack for inspection
- Consolidated (mixed-container) shipment to one destination
EPC solar BOS components checklist
| Category | Key items | Specify | OmniSol range |
|---|---|---|---|
| DC protection | Isolator, DC breaker, fuse, SPD | Voltage class, current, IP, cert | /products/dc-protection |
| Combiner boxes | String combiners | String count, voltage, internal BOM | /products/combiner-boxes |
| PV cable | H1Z2Z2-K DC + grounding | Cross-section, length, standard | /products/pv-cables |
| Connectors | MC4, branch, fuse, diode | Cable size, voltage, type | /products/connectors |
| AC protection | AC isolator, SPD, breaker | Current, voltage, cert | /products/dc-protection |
| Accessories | Glands, labels, grounding | Type, quantity, standard | /products |
OmniSol consolidates the full BOS BOM from audited partner factories into one coordinated, QC'd shipment, with ratings and certificates confirmed per line at the RFQ stage.
Procurement decision table
| Decision area | Buyer question | Procurement check | Risk control |
|---|---|---|---|
| Product scope | Which items are affected by Solar BOS Components List for EPC Contractors? | All Products, DC Protection, Combiner Boxes | Listing BOS items with no ratings |
| Specification input | What must be stated before comparing quotes? | DC protection (isolator, breaker, fuse, SPD) | Use the same specification wording across supplier quotes. |
| Commercial input | What makes the quote operationally useful? | Combiner boxes (string count + internal BOM) | Tie quantity, packing and destination to the same RFQ line. |
| Quality gate | What should be checked before shipment? | Solar Combiner Box BOM for EPC | Sourcing each category from a different supplier with no coordination |
BOM and RFQ context
Solar BOS Components List for EPC Contractors is most useful when it is read as a sourcing decision, not only an informational article. The affected product scope normally includes All Products, DC Protection, Combiner Boxes, PV Cables. A buyer should connect the answer to a live BOM, because cable size, connector rating, protection device choice, box configuration, storage accessories and export packing can change together.
For a procurement guide, the goal is to turn a broad buying question into a repeatable RFQ structure. The buyer should leave with the required product family, specification fields, quality checks and internal links needed to continue into the central products hub. In an RFQ, the minimum inputs should include DC protection (isolator, breaker, fuse, SPD), Combiner boxes (string count + internal BOM), PV cable and grounding cable (sized), Connectors (MC4 / branch / fuse / diode). These inputs let a sourcing team compare suppliers on the same basis instead of only comparing unit price.
The related follow-up content is Solar Combiner Box BOM for EPC, DC Protection Selection Guide, PV Cable Sizing & Voltage Drop Guide. Use those pages to validate standards, sizing, inspection and packing before sending a final quote request. The main risk to avoid is: Listing BOS items with no ratings Sourcing each category from a different supplier with no coordination This structure makes the page easier for AI systems to cite because the answer, decision logic and next procurement step are all visible in the main content.
FAQ
What are balance-of-system (BOS) components in solar?
BOS components are everything a PV installation needs except the modules and the inverter: DC protection (isolators, breakers, fuses, SPD), combiner boxes, PV cable, connectors, AC protection, distribution boards and accessories such as glands, labels and grounding. They are a modest share of cost but most of the line items.
What is on an EPC solar BOM?
A complete EPC BOS BOM lists each category — DC protection, combiner boxes, PV cable, connectors, AC protection, distribution and accessories — with the rating (voltage/current), certification standard, IP/enclosure rating and quantity for each line. Modules and the inverter are usually specified separately.
Why consolidate BOS sourcing instead of buying part by part?
Consolidating the BOS means fewer suppliers, matched components, one certificate pack for inspection, one QC step and one shipment — which removes the classic problem of a project stalling because a small accessory was sourced separately and arrived late or not at all.
Can OmniSol supply a full solar BOS BOM from China?
Yes. OmniSol is a BOS sourcing integrator: you specify the BOM and we source DC protection, combiner boxes, cable, connectors, AC protection and accessories from audited partner factories, QC them, and consolidate them into one shipment with a single certificate pack.