Prosumer regrets after 2 years — 5 lessons with numbers

Most solar mistakes don't show up immediately — they appear at 18-24 months post-installation, when you realise you sized for your life back then, not for the one you have now. Below are five regrets you hear from prosumers with two years of experience — each with the concrete situation, the loss in numbers, and what they'd do differently if they could redo it.

Source: conversations with installers who do maintenance + users who came back to expand their system. Not invented cases — patterns you see repeat.

1. "I bought too few panels"

Context: family of 4, 350 kWh/month in 2024. Calculator → 4 kWp recommendation. They put 4.5 kWp to be safe.

What happened at 2 years:

• Bought an electric car (extra 3,500 kWh/year)
• Replaced the gas furnace with a heat pump (extra 5,000 kWh/year)
• New consumption: ~16,000 kWh/year (was 4,200)
• 4.5 kWp produces ~5,600 kWh/year — covers 35% of the new consumption

Cost of "I'll just add 5 more kWp now": extension on existing roof = ~€7,000–9,000 for another 5 kWp + new inverter (the current one doesn't accept another 5 kWp). Plus a new DSO ATR, new connection contract, potentially a single-to-three-phase upgrade (another €1,500).

What they'd do differently: size with a 20-30% buffer over current consumption for foreseeable additions in the next 5 years. At purchase time, 7-8 kWp instead of 4.5 kWp would have cost ~€4,000 more, not €9,000 as a later extension. See the calculator which has inputs for EV + heat pump.

The lesson: at sizing time, ask yourself: will I buy an EV in 5 years? Will I switch to a heat pump? Will I add AC to an extra room? If the answer to any is "maybe", add them to the calculator before signing.

2. "I didn't add the battery when it was subsidised"

Context: 2024 prosumer, Casa Verde offered up to €6,000 extra subsidy for batteries on top of panels. The program required a separate or combined application, but many installers didn't communicate it clearly.

What happened:

• Took panels only in 2024, no battery (thought they could add anytime)
• Casa Verde 2025-2026 eliminated or dramatically reduced the battery subsidy
• Now a 10 kWh battery costs 35,000 RON in full (was ~€5,000 with subsidy, ~€7,000 without)

Cost of "I'll add the battery now": 35,000 RON cash. Per the payback calculator, the battery doesn't pay back financially on 1:1 net-metering. The investment goes into backup + autonomy, not ROI.

What they'd do differently: on the 2024 AFM application, they'd have included the battery — even if not a priority. The €6,000 subsidy made the initial install ~30% cheaper on the storage side. Adding it later without subsidy rarely pencils out.

The lesson: when an active battery subsidy program exists, it's your last chance to add storage cheaply. Even if you don't use it 100% in the first 12 months, the subsidised incremental cost is hard to beat.

3. "I picked the cheapest firm"

Context: quotes from 3 firms. Two premium (€12,000–14,000 for 6 kWp + battery), one "local with good price" (€9,500). The prosumer picked the cheap one.

What happened at 18 months:

• Inverter fault (fan noise, Wi-Fi comms error)
• The installer firm no longer answers the phone — site still up but no local staff
• RMA to manufacturer (Growatt): 3 months wait for the part; nearest authorised installer 250 km away
• Transport + labour for inverter swap: 2,500 RON from the prosumer's pocket (warranty covers the part, not the travel)

Real cost of the "savings" of €3,000 at purchase: 2,500 RON RMA + 3 months without production = ~700 RON lost injection. Net loss: ~3,200 RON added to the initial savings, plus significant stress.

What they'd do differently: verified the firm's local presence (real workshop, not just a website), Google Reviews history with resolved RMAs, official partnership with the inverter manufacturer (not just reseller). A firm 50 km away vs 250 km changes the warranty math.

The lesson: local presence + verifiable history > price 15-20% lower. See how to recognise a weak installer for concrete filtering signals.

4. "I signed the fixed buyback clause"

Context: in the supplier addendum, the prosumer had two options — 1:1 net-metering with carry-over and buyback at final tariff, or fixed buyback at 0.40 RON/kWh for 5 years "guaranteed". They picked fixed for predictability.

What happened:

• Supply tariff rose to 1.35 RON/kWh in 18 months (was 1.10 at signing)
• Buyback fixed at 0.40 RON/kWh — doesn't adjust with the tariff
• Annual surplus: 2,500 kWh × 0.40 = 1,000 RON
• With the 1:1 + final-tariff buyback option, they would have got: 2,500 × ~1.00 RON = 2,500 RON

Real annual loss: ~1,500 RON. Over a 5-year fixed contract: ~7,500 RON cumulative. Possibly more if tariffs keep rising.

What they'd do differently: checked competing offers from other suppliers (Hidroelectrica, Restart, Premier) for the prosumer clause. A few buy at your final tariff, not a fixed price. See prosumer contract for the 4 compensation models.

The lesson: "fixed" clauses in prosumer contracts feel safe but lock you out of inflation. 1:1 + buyback at your tariff tracks the market.

5. "I never thought about the EV at sizing"

Context: single-phase prosumer, 5 kWp in 2024, 32A single-phase service line (enough at the time). System 100% functional, net-metering active, no drama.

What happened:

• Bought an EV in 2026, wants 11 kW (three-phase) home charging
• Single-phase 32A service line can't support the charger → needs upgrade to three-phase
• Power upgrade: ~€1,500 (~7,500 RON) for the DSO work
• Inverter swap single-to-three-phase if they want full tabloul electric optimisation: another €1,500–2,500
• Total "I'd like an EV": 9,000–14,000 RON extra on top of the car itself

Real cost: at initial sizing, three-phase directly + three-phase inverter would have cost ~€500 extra. At 2 years, the conversion costs 5-10× more.

What they'd do differently: even if in 2024 they had no EV, think ahead at the service line — three-phase is the standard for anyone planning EV or heat pump in 5-7 years. See single-to-three-phase switch for details.

The lesson: the service-line decision (mono/three-phase) is a once-in-a-lifetime opportunity for the system. If there's a real chance of EV or heat pump in the next 5 years, pick three-phase from day one.

How to avoid all 5 regrets — pre-install checklist

1. List foreseeable additions in the next 5 years (EV, heat pump, extra AC, kids growing into gaming PCs). Add them to the calculator at sizing time.
2. If there's an active battery subsidy program (Casa Verde Plus, currently variable), include the battery in the application even if you don't think you need it now.
3. Verify the firm's local presence — workshop under 100 km, Google Reviews with resolved RMAs, official partnership with the inverter manufacturer.
4. Read the buyback clause carefully in the addendum. Compare 3-4 suppliers before signing. Prefer 1:1 + buyback at final tariff.
5. Three-phase service line if you're planning EV or heat pump in 5 years. The incremental install cost is a fraction of the later conversion cost.

For the math complement, see 5 prosumer mistakes — direct numbers on what you lose from oversizing, no-payback batteries, night-charging the EV. For concrete numbers on your system, the payback calculator. Request a quote from AFM-verified firms with your list of foreseeable additions in hand — the installer will adjust the sizing for what you've planned.