Worked Examples
You’ve read the theory. You’ve seen the formulas. Now let’s run the whole design process twice — from the same starting point, down two different paths — and see where the numbers land.
The Starting Point
Same house, same goals, same solar resource. The only thing that changes is the equipment path.
- Location: Portland, Oregon
- Goal: Power essential circuits — fridge, freezer, furnace fan, lights, internet, a few outlets
- Daily load: ~8 kWh
- Peak simultaneous load: ~2,000W
- Available space: South-facing garage roof, room for 6-8 panels
Two paths forward: a consumer all-in-one unit, or a prosumer split-component system. Let’s see what each one actually delivers.
Example A: The Consumer Path
Inverter selection: You pick a consumer all-in-one rated at 3,000W continuous, 6,000W surge. MPPT specs: 2,400W max PV input, VOC 12-150VDC, 12A max input current. 120V output. Built-in transfer switch. Matching brand battery packs in 2-5 kWh units.
Panel selection: You’d like 6 x 400W panels = 2,400W nameplate, which matches the MPPT max. Sounds good so far.
String Math
Each panel: Voc 37.5V, Imp 12.8A.
With a 150V max input and 12A max current, the constraints hit fast:
- Three panels in series = 112.5V Voc — under the 150V cap, good
- But one string of 3 panels draws 12.8A — that’s already over the 12A limit
- Two parallel strings of 3 would double current to 25.6A — way over
You’d need the unit to have two separate MPPT inputs (some do), or you reduce your panel count.
Realistic Build
- Panels: 3-4 panels, ~1,200-1,600W of solar input
- Battery: Two 2 kWh brand-matched packs = 4 kWh total
- What it delivers: Good for overnight essentials in summer. Limited in winter. Limited daily offset overall. But it works, it’s simple, and you can be up and running in a weekend.
Cost Estimate
| Item | Cost |
|---|---|
| Inverter + 2 battery packs | $2,500-$3,500 |
| 4 panels | $400-$600 |
| Mounting, wire, BOS | $500-$800 |
| Total | $3,500-$5,000 |
Example B: The Prosumer Path
Inverter selection: An SRNE-based all-in-one rated at 5,000W continuous, 10,000W surge. MPPT specs: 5,500W max PV input, 120-500VDC range, 100A max input current. 120/240V split-phase output. CAN bus battery communication. Generator input.
Panel selection: 8 x 400W panels = 3,200W nameplate. Well within the 5,500W MPPT max — room to add more panels later.
String Math
Each panel: Voc 37.5V, Vmp 31.2V, Isc 13.9A. MPPT window: 120-500V.
One series string of 8 panels:
- Voc = 8 x 37.5V = 300V at STC. Cold-weather adjusted (worst case Portland): ~326V. Well under 500V max. ✓
- Vmp at hottest = 8 x 31.2V = 249.6V at STC. Hot-weather adjusted (hot roof): ~236V. Well above 120V minimum. ✓
- Current: 13.9A Isc. Well under 100A max. ✓
Single string of 8 panels works perfectly. One set of wires from roof to inverter. Clean and simple.
Battery
Two 5 kWh server rack batteries in parallel = 10 kWh total. At 85% usable depth of discharge, that’s 8.5 kWh of usable energy — enough for overnight essentials with solid margin. The rack has room for two more units when you’re ready to expand.
Wiring and BOS
PV wire from garage roof to inverter below (short run, ~15 feet — voltage drop is a non-issue). DC combiner with fuses. DC disconnect. 10-circuit manual transfer switch. AC disconnect. Grounding to rod. All labeled.
Cost Estimate
| Item | Cost |
|---|---|
| Inverter | $800-$1,200 |
| 8 panels | $600-$1,000 |
| 2 x 5 kWh batteries | $1,500-$2,000 |
| Transfer switch | $300-$400 |
| Wire, conduit, fuses, disconnects, mounting | $800-$1,200 |
| Total | $4,000-$6,000 |
What This Shows
Same house. Same goals. Two very different systems.
The consumer path gets you a working system faster with less complexity. You hit MPPT constraints that limit your array size and total capacity, but you’re up and running in a weekend.
The prosumer path takes more planning and more wiring work. But it delivers a larger, more capable, more expandable system for a similar or slightly higher total cost. The wider MPPT window means the string math just works, and the modular battery architecture means you can grow over time.
Neither is wrong. Know what you’re optimizing for, and go in with realistic expectations about what each path can deliver.
The Output Statement
By the time you finish your design, you should be able to write something like this:
That’s your system design. That’s your shopping list. That statement is the bridge between learning and building.
What’s Next
You’ve seen the full design process from start to finish. Now it’s time to source the equipment.
- Sourcing Equipment — Where to buy, what to look for, and how to avoid the junk
- 200W Starter System — The simplest build, step by step
- 3.2kW Permitted System — The prosumer build, step by step
- Back to Learn — Full topic index
DATA SOURCED FROM: Johnny Solarseed project documentation. Component specifications from manufacturer datasheets (Voc, Vmp, Isc ratings). Cost estimates based on 2025-2026 retail pricing for consumer and prosumer standalone solar equipment.