8 Best Small-Cap Data Center Infrastructure Stocks — September 2026

Data center infrastructure demand has not cooled in 2026 — it has changed shape. The four largest hyperscalers (Amazon, Microsoft, Alphabet, Meta) have guided combined 2026 capital expenditure to more than $700 billion, with Meta alone lifting its full-year range to $125–145 billion. But the binding constraint has moved from chips to electrons. Lawrence Berkeley National Laboratory's report for the DOE put data centers at 4.4% of U.S. electricity use in 2023 and projected 6.7–12% by 2028. "Accredited capacity" — power a grid operator will actually count toward a large load — now gates a new campus, which is why on-site generation and gas-driven chillers are being bought as bridge solutions rather than science projects.

The small-cap layer (market cap under $2B) is where that shift shows up first: these companies are the sub-suppliers, not the landlords, carrying both the operating leverage and execution risk of that position. This is the September 2026 update to our June 2026 data center infrastructure list, re-scored on our September 6 snapshot. Three things changed. We added a power-supply block — Hallador Energy (HNRG) and FuelCell Energy (FCEL) — and a cooling specialist, Tecogen (TGEN). We dropped LYTS and MPTI, whose data center exposure we judged too indirect. The five returning names — PPIH, PLPC, LMB, OCC, RFIL — carry refreshed scores and a dense September earnings calendar: Perma-Pipe and Optical Cable report on September 9, RF Industries on September 14.

---

Why the Small-Cap Data Center Setup Is Different This Cycle

1. The bottleneck is accredited power, not silicon. LBNL's June 2026 "Queued Up" edition counted more than 2,060 GW of generation and storage waiting in U.S. interconnection queues at the end of 2025, with natural gas the only major resource class growing (253 GW active, up 86% year over year). A campus that brings its own megawatts — or frees up the ones it has — jumps the line. Hence the three additions: Hallador owns an Indiana generating station with a data center project breaking ground next door and a gas plant nearing FID this month; FuelCell Energy holds a Capacity Reservation Agreement for an on-site fuel cell project in Texas; Tecogen's gas-driven chillers free grid capacity for compute.

2. Rack density has turned cooling and piping into a capacity constraint. AI racks have pushed liquid and district cooling loops from niche to standard, dragging piping, leak detection and mechanical contracting along with them. Order books show it: Perma-Pipe's backlog rose to $136.5 million at April 30 from $121.6 million three months earlier, helped by newly awarded AI data center projects, and Limbach blamed its Q2 2026 gross-margin squeeze on "competition for skilled labor and materials associated with construction activity in data center markets."

3. Connectivity orders are visible in backlogs, not just narratives. Optical Cable's backlog climbed to $13.3 million at April 30 from $7.3 million at October 31, 2025; RF Industries booked $26.3 million in its April quarter and lifted backlog to $20 million; Preformed Line Products posted a record $212.7 million quarter, its U.S. business up 32% on energy demand. These are small numbers against hyperscaler capex, which is the point: a rounding error in a hyperscaler budget would be a record year for a $0.12B cable maker.

The honest bear case: sub-suppliers sit at the wrong end of the whip. Hyperscaler capex plans are guidance, not contracts; one quarter of discipline at one buyer would ripple through every backlog on this list. Two of the eight names carry SPECULATIVE grades — negative Rule of 40, heavy dilution — and in both cases shareholders, not customers, are still financing the data center pivot. And the September earnings cluster cuts both ways: three of these companies print within a week, before the next score snapshot.

The Names

PPIH — Perma-Pipe International Holdings

Score: 70.6 (SOLID) | Market cap: $0.22B | Revenue YoY: +33.2% | Rule of 40: 47.1 | Cash runway: net cash

Perma-Pipe makes pre-insulated piping and leak-detection systems for district energy, oil and gas, and — increasingly — the chilled-water loops connecting data halls to central cooling plants. Second-quarter bookings topped $67 million, and in March 2026 the board ended its strategic review by staying independent and committing to a new U.S. Northeast facility for AI data center customers.

The 70.6 score rests on full-year revenue growth of +33% and a net-cash balance sheet; it does not show that Q1 fiscal 2026 growth slowed to +7.5% and net income fell to $1.8 million from $5.0 million as the new Ohio and Qatar plants ramped. Upcoming catalyst: Q2 fiscal 2026 results on September 9, 2026 — the first quarter in which data center awards should show up as revenue, not backlog. If awards convert more slowly than ramp-up costs accrue, the growth the score rewards will not repeat. → See full PPIH score card

HNRG — Hallador Energy Company

Score: 69.7 (SOLID) | Market cap: $0.77B | Revenue YoY: +16.2% | Rule of 40: 28.6 | Cash runway: net cash

Hallador's value sits in the 1 GW Merom plant in Indiana. In May 2026 it signed a 12-year capacity agreement as part of roughly $1.1 billion of new contracted revenue, lifting the forward sales book to about $2.4 billion on a segment basis (about $1.8 billion consolidated) with commitments through 2040. Next: Turtle Creek, a 460 MW gas plant budgeted below $800 million, FID targeted this month.

The 69.7 score does not reflect Q2 2026, when a 60-day planned outage at Merom Unit 1 plus unplanned downtime at Unit 2 produced a net loss of $15.2 million. The 2025 agreement with a data center developer was terminated by the counterparty in May 2025; today's exposure is adjacency plus capacity contracts, not a hyperscaler PPA. With $29.0 million of cash against $45.0 million of bank debt and $84.2 million of liquidity at June 30, funding Turtle Creek makes more equity issuance (already +9.7% dilution over 12 months) the likeliest path. → See full HNRG score card

PLPC — Preformed Line Products Company

Score: 68.9 (SOLID) | Market cap: $1.90B | Revenue YoY: +12.7% | Rule of 40: 21.0 | Cash runway: net cash

Preformed Line Products makes the ties, connectors and splice closures that hold transmission, distribution and communications networks together. It is the least direct name here: PLP reports no data center segment, but utility capex to interconnect large loads runs through its T&D catalog. Q2 2026 was a record: net sales up 25% year over year and 21% sequentially, diluted EPS of $4.49 (+75%), gross margin of 34.3%.

The 68.9 score captures +12.7% trailing growth and net cash but lags the Q2 acceleration; insider ownership near 49% is a two-sided feature — strong alignment, but roughly half the shares are not in public hands. PLP gives no guidance; the next data point is Q3 2026. The risk is rotation: if T&D budgets tilt toward transformers and switchgear rather than line hardware, or communications closures slip back into their 2024–2025 downturn, the record quarter becomes a peak, not a base. → See full PLPC score card

LMB — Limbach Holdings, Inc.

Score: 67.3 (SOLID) | Market cap: $0.58B | Revenue YoY: +24.7% | Rule of 40: 32.6 | Cash runway: net cash

Limbach is a mechanical, electrical and plumbing contractor rebuilt around owner-direct relationships (ODR) with building owners rather than subcontracting to general contractors. In Q2 2026 revenue rose 21.9% to $173.5 million with ODR at 74.0% of the total, and on August 4, 2026 it closed the $30.0 million acquisition of CYMCOR, a data center program manager expected to add about $12 million of revenue in 2027.

The 67.3 score rewards +24.7% trailing growth and net cash; it does not yet capture the Q2 margin hit, when gross margin fell to 21.5% from 28.0%, prompting management to raise 2026 revenue guidance to $760–790 million while cutting adjusted EBITDA guidance to $78–84 million. Catalyst: the Q3 print, which needs to show CYMCOR-led data center work at ODR-type margins; if gross margin does not recover toward the high-20s, Limbach gets re-rated as a contractor, not a services company. → See full LMB score card

OCC — Optical Cable Corporation

Score: 61.9 (SOLID) | Market cap: $0.12B | Revenue YoY: +9.5% | Rule of 40: 8.9 | Cash runway: net cash

Optical Cable makes fiber-optic and copper cabling and connectivity for enterprise, data center and harsh-environment ("severe duty") applications. Q2 fiscal 2026 (ended April 30) was an inflection: net sales rose 26.6% year over year to $22.2 million and 35.2% sequentially.

The 61.9 score is held back by a modest +9.5% trailing growth figure and a Rule of 40 below 10 — lagging indicators for a company whose latest quarter grew almost three times as fast — while net cash and 40.6% insider ownership provide the floor. Upcoming catalyst: Q3 fiscal 2026 results on September 9, 2026, showing whether the backlog surge converted into sales. The risk: one quarter of slower enterprise ordering can flip OCC back to losses, and its data center exposure is a share of sales, not a dedicated product line, so it competes with far larger cable makers for hyperscale volumes. → See full OCC score card

RFIL — RF Industries, Ltd.

Score: 66.1 (SOLID) | Market cap: $0.11B | Revenue YoY: +24.3% | Rule of 40: 26.5 | Cash runway: net cash

RF Industries builds interconnect products — connectors, direct-attach copper (DAC) cables and custom cabling — for wireless carriers, and is steering that catalog toward data center and AI infrastructure customers. Q2 fiscal 2026 (ended April 30) showed the mix shift working: net sales of $20.7 million (+9%) and gross margin up 360 basis points to 35.1%.

The 66.1 score reflects +24.3% trailing growth and net cash; the caveat the metrics line does not surface is a debt-to-equity ratio near 76%. Upcoming catalyst: Q3 fiscal 2026 results on September 14, 2026 — the first print where data center cabling orders should be large enough to call out. The risk: wireless-carrier spending is still the core of revenue, so a carrier capex pause would swamp the data center growth, and with meaningful debt, two weak quarters would reopen the discount of its loss-making 2023–2024 stretch. → See full RFIL score card

TGEN — Tecogen Inc.

Score: 53.9 (SPECULATIVE) | Market cap: $0.09B | Revenue YoY: +19.7% | Rule of 40: -6.6 | Cash runway: 15 months

Speculative: Tecogen builds natural-gas combined heat and power units and engine-driven chillers, the latter repositioned as power-sparing data center cooling — the compressor runs on gas rather than grid electricity, freeing grid capacity for compute. Proof so far: $3.3 million of purchase orders, including a Vertiv order for a permanent 1 MW chiller deployment at a Vertiv facility, and 12 demonstrations for operators running more than 8 GW of data center capacity.

The 53.9 score is honest: Q2 2026 revenue was $5.75 million, net loss $2.15 million, 18% 12-month dilution. It is here because Vertiv is installing the product, not for the score. Losing about $2 million a quarter, it must raise equity before a large data center order lands; if demonstrations do not convert into multi-MW orders within two or three quarters, it reverts to a legacy CHP business. Catalyst: the first hyperscale or colocation order. → See full TGEN score card

FCEL — FuelCell Energy, Inc.

Score: 49.1 (SPECULATIVE) | Market cap: $1.14B | Revenue YoY: +41.0% | Rule of 40: -35.6 | Cash runway: 27 months

Speculative — lowest score on the list. FuelCell Energy makes carbonate fuel cell power plants and has pivoted to on-site data center power, producing a Capacity Reservation Agreement with a major operator for a 75 MW Texas project, with a 30 MW "Phase 0" due in fiscal Q4 2026. Committed backlog was $1.296 billion at July 31, 2026, plus $2.35 billion of awarded capacity tied to Fit Energy's option on up to 350 MW.

The 49.1 score is the correct warning label: fiscal Q3 2026 revenue fell 29% to $33.0 million, net loss was $45.3 million, gross margin is negative, and 12-month dilution is 169% after a string of raises, among them a $225 million July 2026 offering. Against that, $737.3 million of cash gives it runway. A Texas delay, or another equity raise before the Fit Energy option is exercised, would confirm the bear case. Catalyst: Phase 0 delivery and disclosure of the Texas counterparty. → See full FCEL score card

---

How to Think About Position Sizing

Eight names, three distinct trades. The inside-the-fence executors — PPIH, LMB, OCC, RFIL — are small, net cash, and growing on real data center orders, but their quarters are lumpy by construction. Treat the September releases as the first true test of whether backlog converts at acceptable margins. The grid-hardware compounder — PLPC — is the largest, most insider-owned and least direct name here; utility-capex exposure makes it the steadiest of the group. The power block — HNRG, FCEL, TGEN — holds the theme's binding constraint and splits again: Hallador is a SOLID-graded power generator with a real capacity book and bank debt, plus a September FID to watch, while FuelCell Energy and Tecogen are SPECULATIVE by grade and by construction, with stories that hinge on the next purchase order. Hold those two at option-sized weights or not at all.

What the mix does not diversify: hyperscaler capex itself. All eight are, directly or one step removed, downstream of the same four budgets; a capex pause would hit contractor backlogs, cable orders and power-developer counterparties at once. For dispatchable-power exposure not tied to one campus, our September 2026 nuclear and SMR list covers fuel-cycle and reactor names on the same electricity-scarcity thesis.

How We Scored

Our model rates every US small-cap stock across eight fundamentals: revenue growth, gross margin, cash runway, debt/equity, P/S ratio, Rule of 40, insider ownership, and 12-month dilution. Sector-adjusted where appropriate, refreshed regularly — this list uses the September 6 snapshot across our 2,200+ stock universe. See methodology and track record or browse all small-cap Industrials stocks.

Related Coverage

• 7 Best Small-Cap Data Center Infrastructure Stocks — June 2026
• 7 Best Small-Cap Nuclear & SMR Stocks — September 2026
• 6 Best Small-Cap Gold Stocks — September 2026
• 8 Best Small-Cap Biotech Stocks — September 2026

Data as of September 6, 2026. Updated monthly. Past performance does not guarantee future results. Not investment advice.