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76 /100 GO Medium complexity

SunVerdict — payback estimator for solar-storage sellers

Sizes the battery and proves the euro payback before a balcony-solar shop promises savings it can't back up.

CleanTech SaaS EU SMBCompliance-drivenAI-agentMultilingualSolar
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Evaluation Scores
76/100

GO

Overall Score

16
Problem
12
Demand
12
Build
11
Distrib.
11
Revenue
8
Time
6
Defense

SunVerdict — payback estimator for balcony-solar storage sellers

1. One-liner

Sizes the battery and proves the euro payback before a balcony-solar shop promises savings it can’t back up.

2. Trend signal — why now?

Germany crossed 1 million registered balcony solar systems in mid-2025 — double the year before — and the plug-in PV trade association estimates 4–5 million units already running across Europe, 1.5–4M in Germany alone once you count the unregistered ones. The thing that changed in the last 18 months: batteries. The share of balcony systems sold with storage jumped from ~20% in 2023 to ~40% in 2025 as per-kWh storage cost fell from €1,000 to €300–400.

That’s exactly where the trouble starts. Storage flips a clean 3–5-year payback into a “speculative” 5–8.5-year one that depends entirely on the buyer’s consumption pattern, panel orientation, and tariff. The German press and forums are full of it: a NotebookCheck-summarized study concludes storage “only pays off under favorable conditions”; a Finanztip/ComputerBase forum thread math-checks a €500–600 battery saving only “150–200 kWh ≈ €60/year → 8.5 years to recoup.” Installers, per a Reslink EPC guide, “size the battery on generic rules of thumb rather than the client’s actual consumption pattern,” guaranteeing a chunk of mismatched-expectation sales.

Meanwhile the inputs to do this properly all went free or cheap in the last year: EPEX SPOT moved to 15-minute pricing (Oct 2025), aWATTar’s market-data API is free with no auth, Tibber’s developer API now exposes quarter-hourly prices, and the brand inverter/battery clouds (Deye, Hoymiles, Marstek, Anker) expose generation/SoC data post-install. The data to prove payback exists; nobody has packaged it for the people doing the selling.

Provenance:

3. The opportunity

Balcony-solar storage is being sold on a payback promise the seller can’t substantiate. The existing tooling is split into two useless halves:

  • Consumer ROI calculators (VoltFlow, balconysolar.energy, the Anker/Deye marketing widgets) take three inputs — panel watts, sun hours, tariff — and spit out a flattering number that ignores shading, orientation (vertical railing mounting loses 15–25%; E/W loses 20–30%), the household’s actual load curve, and whether storage even helps. They exist to close a sale, not to be right.
  • Pro solar-design suites (PV*SOL, Reonic, OpusFlow, autarc, SurgePV) are built for rooftop EPCs doing full €10–25k installs with MaStR/KfW/EEG paperwork. They’re overkill, over-priced (€100–300+/mo, per-seat ERP), and none of them model a plug-in 800W + small-battery system against a dynamic tariff the way the balcony segment now needs.

The gap: a fast, dishonest-by-omission-proof tool that takes the buyer’s real consumption profile + address (for irradiance/shading) + tariff (flat or dynamic via the live EPEX/Tibber/aWATTar feed) and produces a defensible, branded payback report the shop hands the customer — and a recommended battery size so the seller stops guessing. Post-install, it ingests the brand cloud’s actuals and shows promised-vs-delivered, which kills the dispute before it becomes a return.

The disruption isn’t “a better calculator.” It’s moving the calculator from a sales-conversion toy to a liability shield + sizing brain for the seller. A focused team beats PVSOL here because PVSOL will never bother with €600 sales, and beats the consumer widgets because those are owned by hardware brands who want the optimistic number.

4. Target market

  • Primary customer: Small balcony-solar retailers and Fachbetriebe in Germany (then AT/NL/PL) — online shops (priwatt, Solakon-tier) and 1–10-person installer/electrician outfits that sell plug-in PV + storage. Not rooftop EPCs.
  • Why they buy (their words): “Customers come back angry that the savings are lower than I told them”; “I’m sizing batteries on a rule of thumb and it bites me”; “the manufacturer calculator makes me look like a liar when reality undershoots.” A payback report they can stand behind reduces returns, chargebacks, and bad reviews — and closes more deals because a credible number sells better than a suspiciously round one.
  • Rough TAM reasoning: BSW represents 1,000+ German solar companies; the plug-in segment specifically has spawned hundreds of dedicated online shops and thousands of small electrician outfits now attaching storage. Call it 3,000–6,000 sellers in DACH, more across the EU as EPBD transposition (deadline 29 May 2026) pushes plug-in PV in NL/PL/ES. Even 1,500 paying €79/mo is ~€1.4M ARR.
  • Why now for them: Storage attach rate doubled to 40% in two years, dynamic tariffs (Tibber 1M+ users) made payback math genuinely harder, and the first wave of “it didn’t pay off” complaints is landing in their inboxes and Trustpilot pages right now.

5. Product sketch (MVP)

  • 3-minute payback report: enter address, panel/inverter/battery spec, and a rough consumption profile (or upload a utility CSV / pick an archetype) → branded PDF with honest year-by-year payback, self-consumption %, and a confidence range.
  • Battery sizing recommendation: “for this load curve, 2kWh pays back in 6.1y, 5kWh in 9.4y — don’t oversell the 5.” Stops rule-of-thumb mistakes.
  • Dynamic-tariff mode: pull live EPEX/Tibber/aWATTar prices and model charge/discharge arbitrage value on top of self-consumption — the differentiator no consumer calculator does.
  • Shading & orientation haircut: address-based irradiance + a guided “vertical railing / E-facing / partial shade” picker that applies the real 15–30% losses instead of hiding them.
  • Promised-vs-delivered tracking: connect the buyer’s Deye/Hoymiles/Marstek cloud after install; auto-flag if reality drifts >X% from the promise so the shop fixes it before the customer rages.
  • White-label embed: the calculator as a widget on the shop’s product page that captures the lead and pre-fills the report.
  • Multilingual: DE first, then NL/PL/EN.

6. AI angle — what’s load-bearing

Two places AI does real work, not decoration:

  1. Consumption-profile inference. Most balcony buyers have no idea what their hourly load looks like and won’t upload a clean CSV. AI takes sparse inputs (household size, home-office yes/no, EV/heat-pump, a photo of a monthly bill) and infers a plausible 15-minute load curve — the single biggest driver of whether storage pays. Without this the report is garbage-in-garbage-out, which is exactly why the incumbent calculators are wrong.
  2. Plain-language report generation + dispute triage. Turning a simulation into a customer-readable, jurisdiction-aware narrative (“here’s why 2kWh not 5kWh,” “here’s the realistic range”) in DE/NL/PL, and post-install, explaining why delivered undershot promised (shading? tariff moved? undersized?) so the seller has an answer.

Remove the AI and you’re back to a dumb three-field calculator — which already exists and is the problem. The load-curve inference is the moat-y part.

7. Localization angle

This is localization-as-the-whole-game. The product is worthless without country-specific irradiance, the local dynamic-tariff feeds (EPEX/Tibber/aWATTar for DE/AT, ENTSO-E elsewhere), local flat-tariff norms (~€0.28–0.40/kWh DE), MaStR registration context, and German/Dutch/Polish report language. A generic global ROI calculator is precisely the incumbent we’re beating. €79/mo works for a German micro-retailer; the play expands country-by-country as EPBD transposition pushes plug-in PV across the EU.

8. Business model — path to $1M–$5M ARR

  • Pricing: €49/mo solo (capped reports), €99/mo shop (unlimited reports + white-label widget + sizing), €199/mo multi-location. Usage-light, seat-light — these are tiny businesses.
  • ACV: ~€1,000–1,200 blended.
  • Math to €1M ARR: ~900 shops × €95/mo × 12 ≈ €1.03M. Against a 3,000–6,000 seller DACH base, that’s 15–30% penetration of one region — achievable.
  • Math to €5M ARR: ~3,500 sellers across DACH+NL+PL+ES, or layer a per-report transaction tier and a hardware-brand co-marketing/referral revenue line (brands want credible payback numbers attached to their batteries — but we stay brand-neutral to keep trust).
  • Expansion path: seats → unlimited white-label → post-install monitoring add-on (recurring per active system) → lead-gen marketplace where the embedded calculators feed qualified buyers back to shops.

9. Go-to-market wedge — first 100 customers

  • Scrape the sellers, hit them direct. The German plug-in PV shops and storage-attaching electricians are enumerable: marketplace seller lists, the Bundesverband Steckersolar member directory, Google Maps “Balkonkraftwerk + Speicher” by city, and the comment sections of the big DE solar forums (Finanztip, ComputerBase, PV-Forum). Build a list of ~1,500, send a personalized email with a pre-generated payback report for a system they actually sell showing how the honest number differs from their current widget. Expect 4–6% to book a demo.
  • Ride the complaint threads. Reply (founder, not bot) to “Speicher lohnt sich nicht” forum/Reddit threads with a genuinely useful honest calc — converts both the angry buyer’s seller and lurking sellers.
  • Intersolar Europe + regional installer trade days. The segment physically gathers there; one booth/sidebar demo of “size it right, prove it, defend it” lands a dozen shops at once.
  • Hardware-brand back door. Deye/Hoymiles/Anker distributors want their resellers to stop overselling and getting returns — co-market the tool to their German reseller networks (we stay neutral on brand choice).

10. Build complexity — justification

Medium. The web app, report generator, and tariff-API integrations (aWATTar free, Tibber, EPEX, ENTSO-E) are off-the-shelf. The two non-trivial pieces are (a) a credible irradiance+shading+self-consumption simulation engine — buildable on open PV models (PVGIS data, pvlib-style methods) without a research breakthrough — and (b) the brand-cloud connectors for post-install actuals, which are fiddly but documented. AI load-curve inference is an API + prompt + a modest validation dataset. A 2–3 person team ships a credible v1 in 3–4 months; the report quality is the work, not the plumbing.

11. Gating checklist

GatePass?Note
Legal in target market✅Decision-support tool; no regulated advice, no approval needed.
Ethical — no harm / dark patterns✅The entire pitch is anti dark-pattern — honest numbers vs. inflated ones.
Market exists (evidence above)✅1.5–4M DE systems, 40% storage attach, documented payback disputes.
1–5 person team can build this✅2–3 people, 3–4 months.
Launchable with <$50K / ₹40L✅APIs are free/cheap; cost is dev time.

12. Feasibility score

AxisWeightScoreNotes
Problem intensity2016/20Real money + reputation pain for sellers (returns, bad reviews), felt on every storage sale. Not daily-hair-on-fire, but recurring and costly.
Demand evidence1512/15Strong demand signals (forum disputes, “speculative payback” press, rule-of-thumb sizing) but the seller’s willingness-to-pay for this specific tool is inferred, not yet observed.
Build feasibility1512/15Mostly off-the-shelf; the simulation engine + brand connectors are the honest 3–4-month work.
Distribution clarity1511/15Sellers are enumerable and reachable direct; conversion math is plausible but unproven.
Revenue mechanics1511/15Pricing fits micro-wallets, path to €1M is 15–30% of one region; €5M needs multi-country + add-ons.
Time to first revenue108/10Direct outbound to an enumerable list + a tool that closes their sales = paid pilots within 6–8 weeks.
Defensibility106/10Load-curve inference + accumulating promised-vs-delivered data + neutral-broker trust compound; but a determined incumbent (autarc/Reonic) could add a balcony module. Speed + niche focus is the moat.
Total10076/100

13. Qualitative modifiers

Founder-fit tags

technical-heavy (PV simulation + integrations) · domain-expertise-required (German solar/tariff/storage economics — get a solar-savvy co-founder or advisor).

Key assumptions to validate (3–5)

  1. Assumption: Balcony-solar sellers will pay €79–99/mo for a payback/sizing tool to reduce returns and close more deals. How to test: 30 direct seller interviews + a pre-sell of paid pilots at €49/mo before building the full engine.
  2. Assumption: An honest, consumption-aware payback number increases conversion (sellers don’t just want the inflated number). How to test: A/B the SunVerdict report vs. the shop’s current widget on real product pages of 3–5 pilot shops; measure close rate.
  3. Assumption: AI load-curve inference from sparse inputs is accurate enough that delivered tracks promised within tolerance. How to test: Backtest inferred curves against 50 real smart-meter datasets; require median error under target before launch.
  4. Assumption: Brand-cloud connectors (Deye/Hoymiles/Marstek) are stable enough to power post-install tracking. How to test: Build two connectors first; monitor uptime/data quality for a month.

Risk flags

  1. Platform dependency: Tariff feeds (Tibber/aWATTar) and brand clouds can change/restrict APIs. Mitigate by leaning on the free/open feeds (aWATTar, ENTSO-E, EPEX) and treating brand connectors as a nice-to-have, not core.
  2. Incumbent encroachment: autarc/Reonic/OpusFlow could ship a lightweight balcony module. The defense is being the neutral, seller-defense-first tool the brands and EPC-suites won’t be — and owning the niche before they care.
  3. Market timing / policy: If a government subsidy or a brand bundles “guaranteed sizing” for free, the standalone value erodes. Watch DE storage-subsidy moves and brand calculator quality.
  4. Thin per-customer revenue: These are micro-businesses; churn and price sensitivity are real. Needs volume + low-touch onboarding to work.

14. Structured verdict

Score:                  76/100
Verdict:                GO
Confidence:             Medium
Best-fit builder:       Technical founder + German solar/storage domain advisor
Time to revenue:        6–8 weeks to first paid pilots
Capital to launch:      €15–40K (mostly 3–4 months of build time)
Top 3 assumptions to validate first:
  1. Sellers pay €79–99/mo to cut returns & close deals — 30 interviews + paid-pilot pre-sell
  2. Honest payback report raises conversion vs. inflated widget — A/B on 3–5 pilot shops' product pages
  3. AI load-curve inference is accurate within tolerance — backtest vs. 50 real smart-meter datasets
Kill criteria:
  - Abandon if <10% of 50 cold-contacted sellers show concrete interest (book a demo)
  - Abandon if the A/B shows the honest report does NOT beat the inflated widget on close rate
  - Abandon if a hardware brand or PV*SOL/autarc ships an equivalent free balcony payback+sizing tool before v1

15. Next step — 1-week validation sprint

  • Day 1–2: Build the seller list — scrape Bundesverband Steckersolar directory, Google Maps “Balkonkraftwerk Speicher” across 10 DE cities, marketplace seller lists → ~300 named shops with email.
  • Day 3–4: Hand-build 5 real payback reports for systems specific shops actually sell (using open PV models + live aWATTar prices), showing honest vs. their current widget number. Send personalized to 80 sellers + DM 10 forum complainants’ sellers.
  • Day 5: Decide. Go if ≥8 sellers reply with interest and ≥3 agree to a paid pilot at €49/mo; no-go if replies are polite-indifferent (<10%) — meaning sellers prefer the inflated number to the honest one, which would be fatal.

Falsifiable outcome: paid-pilot commitments, not “they liked it.”

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