System 2: Permitted Standalone (3.2kW)
What you’ll build
A permitted, inspected, signed-off 3.2kW standalone solar installation. Eight 400W panels in a single series string, an off-grid inverter/charger, a 5kWh LiFePO4 battery, and a single 120V duplex outlet. Not connected to the grid. Not connected to your house. Standalone — on your shed, garage, or workshop.
This is the minimum viable code-compliant standalone installation. One permit, two inspections, signed off, done. No reason for anyone to come back.
If System 1 was your learning platform, this is the real thing. Permits, AC output, full code compliance, grounding, labeling — and enough capacity to run actual loads. Power tools, a mini-fridge, phone and laptop charging, LED lights, battery chargers. A system that does real work and is legally bulletproof.
What you can power
Daily generation in Oregon: roughly 9.6 to 12.8 kWh per day (3,200W x 3-4 peak sun hours x 0.80 system derate). That’s real energy.
Through your single 120V outlet, you can run:
- Power tools — circular saw, drill, router, grinder (one at a time, mind the surge)
- Mini-fridge — keeps drinks and lunch cold in the shop, runs 24/7 off the battery
- Phone and laptop charging — indefinitely
- LED lighting — wire shop lights off the AC outlet
- Battery chargers — tool batteries, e-bike, whatever you need
- Small space heater — with caveats: a 1,500W heater will drain the battery in about 3 hours overnight and consume most of your daily generation. It works, but it’s a trade-off.
One outlet is intentional. It’s the minimum endpoint for a complete, inspectable circuit: generation, storage, conversion, disconnection, utilization. The inspector sees a finished system. You can add more outlets or a subpanel later under the same permit — but one outlet is the “done, signed off, never come back” minimum.
The permit process
This is bureaucratic, not adversarial. The inspector wants you to pass. Here’s how.
Who can do this
You — the homeowner. You must be both the owner and occupant of the property. The property cannot be intended for sale, lease, or rent in the near future. You perform the work yourself.
Where to go
Your local Authority Having Jurisdiction (AHJ). In Portland, that’s the Bureau of Development Services (BDS) at https://www.portland.gov/bds. Residential electrical permits can be applied for online or in person.
What to bring
- Completed electrical permit application
- Basic site plan showing structure location on property
- Simple line diagram (panels -> DC disconnect -> inverter -> battery -> AC disconnect -> outlet)
- Equipment spec sheets showing UL listings (panel, inverter, battery)
- You sign the permit as the homeowner
What it costs
A few hundred dollars for a residential electrical permit. Contact your local building department for the current fee schedule.
The 180-day clock
Per OAR 918-309-0000, the permit expires if work is not started within 180 days of issuance, or if work is suspended for 180 days after starting. Each passed inspection resets the clock.
Inspections
Two inspections, in order:
- Rough-in: Wiring installed but not concealed. The inspector checks conductor routing, sizing, box fill, grounding path, and general workmanship.
- Final: Everything installed, connected, and complete. The inspector checks disconnects, labeling, grounding, listed equipment, overcurrent protection — the whole system against code.
Have the permit on site, equipment spec sheets available, and your line diagram posted.
System design
Panels and string configuration
8x 400W monocrystalline panels, series wired (single string).
Typical specs per panel (varies by manufacturer):
| Spec | Value |
|---|---|
| Open-circuit voltage (Voc) | ~41V |
| Short-circuit current (Isc) | ~13A |
| Maximum power voltage (Vmp) | ~34V |
| Maximum power current (Imp) | ~11.8A |
String electrical characteristics (8 panels in series):
| Spec | Calculation | Result |
|---|---|---|
| String Voc | 8 x 41V | 328V DC |
| Temperature-corrected max Voc (-15°C) | 328V x 1.14 | 374V DC |
| String Vmp | 8 x 34V | 272V DC |
| String Isc | Same as single panel | 13A |
Listing requirement: UL 61730 (current standard) or UL 1703 (legacy). Every panel from a reputable manufacturer meets this — Canadian Solar, REC, QCells, LONGi, JA Solar, Trina. It’s printed on the panel label.
Why 400W panels: They’re the sweet spot — good output, manageable size (6.8’ x 3.4’, about 50 lbs), widely available, and well-priced. Lower wattage means more panels, more connections, more mounting hardware. Higher wattage means physically larger and harder to handle on a roof with two people.
Why single string: Eight 400W panels in series produce a voltage window (272V-374V) that fits cleanly into a prosumer inverter’s MPPT range. One string means one set of wires from roof to inverter. Simple, reliable, fewer failure points.
Inverter selection
You need an off-grid inverter/charger — a single unit that accepts high-voltage DC from the panels, charges the battery, and outputs 120V AC.
Critical specs:
| Requirement | Spec |
|---|---|
| MPPT voltage window | Must accept 272V-374V DC range |
| AC output | 120V single-phase |
| Continuous power | 3,000-3,500W to match array |
| Listing | UL 1741 — non-negotiable for inspection |
Representative brands: EG4 6000XP, Victron MultiPlus/Quattro, Sol-Ark, Growatt SPF series. These are starting points — verify UL 1741 listing on the specific model before purchasing.
Mount the inverter inside the structure with adequate ventilation and clearance per manufacturer specs. Bond the enclosure to the equipment grounding system.
Battery
5kWh LiFePO4 (48V 100Ah server rack battery).
| Requirement | Spec |
|---|---|
| Chemistry | LiFePO4 (Lithium Iron Phosphate) |
| Capacity | 5kWh (48V x 100Ah) |
| Listing | UL 9540, UL 9540A, or UL 1973 |
| Communication | CAN bus or RS485 — verify compatibility with your inverter |
Why LiFePO4: No hydrogen gas (minimal ventilation requirements), built-in BMS for cell balancing and protection, 3,000-6,000+ cycle life, thermally stable chemistry. It’s the safest lithium chemistry available.
Why 5kWh: Meaningful overnight capacity for lights and small loads, single-unit simplicity, expandable later by adding another rack battery in parallel. Starting with enough to be useful, with room to grow.
Representative products: SOK 48V 100Ah (UL 1973), EG4 LL series (UL listed), Victron Lithium Smart (UL listed). Verify listing status and inverter communication compatibility before purchasing.
Installation requirements: DC disconnect or breaker between battery and inverter. DC-rated fuse or breaker on the battery circuit. Battery accessible for inspection and maintenance. Labeled with voltage and chemistry. For LiFePO4, standard shed ventilation is adequate — no special ventilation system required. Secure against tipping.
Grounding and bonding
This is the section most DIY systems get wrong. Every metallic component that could become energized during a fault needs a low-impedance path to ground.
Equipment grounding:
- Install a listed PV grounding lug (UL 2703) on every panel frame — products like WEEB, IronRidge, Burndy, or Ilsco. These have serrated contact surfaces that bite through the anodized coating on aluminum frames. Cost: $2-5 each.
- Run a continuous bare or green copper Equipment Grounding Conductor (EGC) from lug to lug, daisy-chaining through every panel.
- Continue the EGC to the inverter grounding terminal and then to the grounding electrode.
- EGC sizing: 10 AWG copper minimum (NEC 690.45 / Table 250.122). Larger (8 AWG, 6 AWG) is fine and provides margin.
- Bond all metallic enclosures: inverter, battery rack, junction boxes, conduit, disconnect enclosures.
Grounding electrode system:
- Drive two ground rods (8 ft copper-clad steel), at least 6 feet apart.
- Connect with 6 AWG bare copper Grounding Electrode Conductor (GEC) using listed acorn clamps at each rod.
- Protect the GEC from physical damage where exposed (route it in conduit or where it won’t be hit or snagged).
- This is a standalone system — no bond back to the house grounding electrode system. The shed has its own ground rods and its own GEC.
Bill of materials
Full component list with specs, approximate cost, and listing requirements.
Array
| Item | Specs | Approx. Cost |
|---|---|---|
| 400W Monocrystalline Panel x8 | Voc ~41V, Isc ~13A, UL 61730 | $800-1,200 |
| Z-Bracket Panel Mounts (for 8 panels) | Universal roof mount | $60-120 |
| PV Grounding Lugs x8 | UL 2703, serrated contact | $16-40 |
DC Wiring
| Item | Specs | Approx. Cost |
|---|---|---|
| 10 AWG PV Wire (red, 100ft) | USE-2, UV-rated, 600V | $30-50 |
| 10 AWG PV Wire (black, 100ft) | USE-2, UV-rated, 600V | $30-50 |
| 600V DC Disconnect Switch (30A) | NEMA 3R, DC-rated | $40-80 |
| EMT Conduit (3/4”, 10ft sticks x2+) | Exterior runs | $15-30 |
Inverter
| Item | Specs | Approx. Cost |
|---|---|---|
| EG4 6000XP Off-Grid Inverter | 6,000W, MPPT 120-500V DC, UL 1741, 120V output | $1,200-1,800 |
Battery
| Item | Specs | Approx. Cost |
|---|---|---|
| SOK 48V 100Ah LiFePO4 Battery | 5.12kWh, UL 1973, CAN bus | $1,500-2,500 |
| DC Battery Fuse/Breaker | DC-rated, sized per battery specs | $20-40 |
AC Wiring
| Item | Specs | Approx. Cost |
|---|---|---|
| 12 AWG NM-B (25ft) | AC branch circuit, 20A rated | $15-25 |
| 120V AC Disconnect/Breaker (20A) | Standard AC disconnect | $15-30 |
| 20A GFCI Duplex Outlet (NEMA 5-20R) | NEC 210.8(A) compliant | $15-25 |
| Electrical Boxes + Cover Plates | Listed | $10-20 |
Grounding
| Item | Specs | Approx. Cost |
|---|---|---|
| 6 AWG Bare Copper Wire (25ft) | GEC | $25-40 |
| 10 AWG Green/Bare Copper Wire (50ft) | EGC | $20-35 |
| Ground Rods (8ft copper-clad, x2) | 6ft apart | $20-30 |
| Ground Rod Clamps (acorn, x2) | Listed | $8-15 |
Labels
| Item | Specs | Approx. Cost |
|---|---|---|
| PV Warning Labels (set) | Pre-made, UV-resistant | $15-30 |
| Label Maker | Brother P-Touch or similar | $30-50 |
Total estimate: $3,900-6,100
Buying advice: Order all 8 panels together — shipping is the expensive part, and you want matched panels from the same batch. Confirm UL listings on everything before ordering, especially the inverter and battery. Stick with known brands for the inverter and battery — this isn’t where you save money with off-brand equipment. Buy extra wire and fuses — a spare $20 in wire beats a second trip to the hardware store mid-build.
Wiring topology
Here’s the full connection map from panels to outlet:
Panels (8x series) -> PV Wire (10 AWG) -> DC Disconnect (600V, 30A) -> Inverter MPPT Input -> Battery OCPD -> Battery -> Inverter AC Output -> AC Disconnect (120V, 20A) -> GFCI Outlet (NEMA 5-20R)
Conductor sizing
| Run | Wire | Gauge | Notes |
|---|---|---|---|
| DC source (panels to inverter) | PV Wire / USE-2 | 10 AWG min | UV-rated, 600V, exterior |
| Interior DC runs | THWN-2 in conduit | 10 AWG min | Transition at junction box |
| AC branch (inverter to outlet) | NM-B (Romex) | 12 AWG | 20A circuit, interior |
| Battery to inverter | Per manufacturer specs | Per specs | Short run, heavy gauge |
| EGC (equipment grounding) | Bare/green copper | 10 AWG min | Continuous through all panels |
| GEC (to ground rods) | Bare copper | 6 AWG | Protected from damage |
Wire types
- Exterior (roof to equipment): PV Wire or USE-2 — UV-resistant, weather-resistant, 600V rated. This is the only acceptable wire for outdoor solar runs.
- Exterior conduit: EMT for exposed runs on the structure exterior.
- Interior DC: Transition to THWN-2 in conduit at a listed junction box where conductors enter the building.
- Interior AC: NM-B (Romex), stapled per NEC (within 12” of each box, every 4.5’ along the run).
GFCI protection
The outlet must have GFCI protection — NEC 210.8(A) requires it for receptacles in garages and accessory buildings. Use a GFCI receptacle or protect the circuit with a GFCI breaker. This is a common inspection failure point, and it costs $15.
Labeling
Labeling is where DIY systems most commonly fail inspection. It’s easy, it’s cheap, it’s required. A label maker and a set of pre-made PV labels cost under $50 total.
Required labels
At the DC disconnect:
- “SOLAR PV SYSTEM DISCONNECT”
- Maximum DC voltage: 374V DC
- Maximum DC current: 13A
At the AC disconnect:
- “SOLAR PV AC DISCONNECT”
- Rated voltage: 120V AC
On conduits/raceways carrying PV circuits:
- “SOLAR PV CIRCUIT” or “PHOTOVOLTAIC POWER SOURCE”
- At every accessible point, junction box, and where conduit enters the building
At the inverter:
- Manufacturer’s listing label visible and intact
At the battery/ESS:
- “ENERGY STORAGE SYSTEM”
- Voltage (48V DC)
- Battery chemistry: “LITHIUM IRON PHOSPHATE — LiFePO4”
Power source directory (NEC 710.10):
- At the main disconnect location, a permanent plaque identifying:
- Type of power source: Solar PV
- Location of each disconnect
- Operating voltage
Warning labels at accessible energized points:
- “WARNING: ELECTRIC SHOCK HAZARD — DO NOT TOUCH TERMINALS. TERMINALS ON BOTH LINE AND LOAD SIDES MAY BE ENERGIZED IN THE OPEN POSITION.”
- At the array: “WARNING: SOLAR PV — ENERGIZED IN DAYLIGHT”
Labels must be durable, weather-resistant (exterior), UV-resistant, and legible. Per NEC 110.21(B), labels must be suitable for the environment.
Step-by-step build
Fifteen steps, in order. Take your time. Getting this right on the first pass is the whole point.
1. Prep workspace. Clear the equipment location inside the structure. Have your line diagram printed and posted on the wall. Lay out all materials and tools. Verify you have everything on the BOM before starting.
2. Pull permit. Submit your application, site plan, line diagram, and equipment spec sheets. Pay the fee. Get the permit number. Post the permit on site.
3. Mount panels (two-person job). Carry panels up, position on roof, bolt down with Z-brackets or your chosen mounting system. Panels are about 50 lbs each and awkward in the wind. Late afternoon or overcast days are easier on you and produce less voltage while you work. Verify layout matches your site plan.
4. Install grounding lugs on every panel frame. One UL 2703 grounding lug per panel, with serrated contact surface biting through the anodized coating. This is your equipment grounding connection point.
5. Run PV wire from array to equipment location. Pull 10 AWG PV wire (red and black) through EMT conduit from the panel array to where the inverter will live. Leave service loops at both ends — extra slack so you can comfortably make connections.
6. Drive ground rods. Two 8-foot copper-clad steel rods, at least 6 feet apart. Drive them vertically (or at an angle if you hit rock, maintaining 8 feet of earth contact). Connect with 6 AWG bare copper GEC using listed acorn clamps.
7. Install inverter and battery. Mount the inverter on the wall. Set up the battery rack. Position everything with ventilation, access for maintenance, and room to work.
8. Install DC disconnect. Mount the 600V DC-rated disconnect between the array wire endpoint and the inverter. This is the switch that isolates solar voltage from everything downstream.
9. Wire DC side (leave disconnect OFF). Connect PV wire from panel string to DC disconnect input. Connect DC disconnect output to inverter MPPT input. Run the EGC from the panel grounding lugs through the daisy chain, to the inverter ground terminal, and on to the ground rods.
10. Wire battery (don’t connect yet). Install the battery OCPD (DC-rated fuse or breaker). Run cables from battery OCPD to inverter battery input terminals. Do not close the battery breaker yet.
11. Wire AC side. Inverter AC output -> AC disconnect (20A) -> 12 AWG NM-B -> GFCI outlet (NEMA 5-20R). Staple NM-B per code. Install the outlet in a proper box with cover plate.
12. Install all labels. Every label listed in the Labeling section above. Do this now, before the inspector comes. A label maker and 30 minutes is all it takes.
13. Call for rough-in inspection. Have the permit posted, spec sheets available, and line diagram visible. The inspector checks conductor routing, sizing, grounding path, box fill, and workmanship.
14. After rough-in passes: energize and test. Close the battery breaker first. Verify the inverter sees the battery (state of charge displays, communication status shows connected). Then turn ON the DC disconnect. Check the voltage reading at the inverter’s MPPT input — it should match your expected string voltage. Check AC output voltage at the outlet with a multimeter. Verify GFCI trips and resets.
15. Call for final inspection. The inspector checks the complete system: disconnects operational, all labels in place, all grounding continuous, all equipment listed, overcurrent protection correct, GFCI functional, outlet properly wired. After final passes — you’re done.
Inspection checklist
Self-audit before calling the inspector. Every item the inspector will check:
Documentation
- Permit posted on site
- Equipment spec sheets available for all major components
- Line diagram of the system available
- Panel listing (UL 61730 / UL 1703) visible on panel label
- Inverter listing (UL 1741) visible on unit
- Battery listing (UL 9540 / UL 1973) visible on unit or spec sheet
Array
- Panels securely mounted
- Equipment grounding lug at each panel — listed, biting through anodization
- Equipment grounding conductor continuous through all panels
- MC4 connections seated and locked (tug-test every one)
- PV wire / USE-2 used for exterior runs
- Conductors secured and protected from physical damage
Disconnects
- DC disconnect installed, accessible, properly rated (600V DC, 30A)
- AC disconnect installed, accessible, properly rated (120V, 20A)
- Both disconnects operational (open/close)
Wiring
- Conductor sizing correct (10 AWG min DC, 12 AWG for 20A AC branch)
- Proper wire types (PV wire exterior, NM-B interior, THWN-2 in conduit)
- All connections in listed boxes or enclosures — no open splices
- Conduit fill within limits
- NM-B stapled properly (within 12” of boxes, every 4.5’)
Grounding
- EGC continuous from array through all components to grounding electrode
- Ground rod(s) driven 8 feet, listed clamp connection
- GEC properly sized (6 AWG minimum)
- GEC protected from physical damage where exposed
- Inverter enclosure bonded
- All metallic enclosures bonded
Overcurrent Protection
- DC fuse or breaker for source circuit
- Battery circuit overcurrent protection installed
- AC branch circuit breaker matches wire gauge (20A for 12 AWG)
Outlet
- GFCI protection (GFCI receptacle or GFCI breaker)
- Proper box, cover plate, and mounting
- Correct wiring (hot, neutral, ground)
Labels
- DC disconnect labeled with voltage and current
- AC disconnect labeled
- PV circuit conduits/raceways labeled
- Battery/ESS labeled with voltage and chemistry
- Power source directory posted
- Warning labels at accessible energized points
Safety
- Panels are always live in daylight. There’s no off switch on a solar panel. Cover them with opaque material while working on connections. Treat all panel-side wiring as energized during the day.
- Fuse and protect every circuit. DC source, battery, AC branch — each junction has overcurrent protection for a reason. Oversized protection doesn’t protect. Use the right ratings.
- Listed, certified components only. UL markings are not optional. They’re the inspector’s first check and your insurance policy’s requirement. If it doesn’t have a listing mark, don’t install it.
- Torque all connections to spec. Battery terminals, wire lugs, grounding connections — use a torque wrench or torque screwdriver. Loose connections create resistance, resistance creates heat, heat creates fire. Too tight cracks terminals. Tighten to spec.
- UV-rated wire for exterior runs. Regular Romex degrades in sunlight. PV wire and USE-2 are designed for decades of outdoor exposure. Don’t substitute.
- Mount inverter and battery indoors with ventilation. Protected from weather, accessible for maintenance, with adequate airflow per manufacturer specs.
- If anything feels wrong, stop. Unexpected readings, unusual heat, smells, sparks — disconnect and figure it out. The Johnny Solarseed consult page exists for exactly this.
What’s next
You have a permitted, inspected, signed-off system. Legal, safe, yours.
This is a foundation, not a ceiling. Everything from here is iteration, not starting over:
- More battery: Add another 48V 100Ah rack battery in parallel. Double your overnight capacity without changing anything else.
- More outlets or a subpanel: Run additional branch circuits from the inverter’s AC output. Same permit framework, more utilization points.
- Ground mount expansion: If you run out of roof space, a ground-mounted array expansion is straightforward — same wiring principles, different mounting.
If you haven’t built System 1 yet and this feels like a lot, start there. It’s an afternoon project that teaches you every core concept. The 200W safe harbor is the best way to learn before committing to a permitted build.
If you want to understand the components in more depth: batteries, inverters, string design, wiring and safety.
DATA SOURCED FROM: Oregon Revised Statutes (ORS 479.540, 479.560), Oregon Administrative Rules (OAR 918-309-0000), Oregon Residential Specialty Code (ORSC R105.2), NEC 2023 (Articles 210.8, 250, 480, 690, 706, 710), Oregon Solar Installation Specialty Code (2010), NEC 690.12 Exception No. 2 (rapid shutdown exemption), NEC 690.7 Table 690.7(A) (temperature correction), NEC 690.8 (circuit sizing), NEC 690.45 / Table 250.122 (EGC sizing), NEC 250.53 (grounding electrodes), manufacturer published specifications (component data, listing certifications)