The 10 most common solar install mistakes (and how to avoid them)

We've seen the same mistakes repeat for years. Here are the 10 most expensive ones — and how to dodge them before signing any quote.

1. Undersizing to 'start small'

The most expensive error: installing 2 kW thinking 'I'll expand later'. When you want to add more, the racking, inverter and permits won't support it. Size for your next-10-year consumption now (include possible EV).

2. Ignoring seasonal shading

The installer surveys a sunny June day. But the neighbour's tree grows, casts winter shadow on your whole array, and nobody simulated it. Demand a year-round shading study with software (PVsyst, HelioScope, Aurora).

3. Picking the cheapest inverter

You save $700 today and 7 years later there's no service network. The inverter is the failure point. Pick a brand with local service + 10-15 year warranty.

4. Poorly sized battery

Buying 5 kWh because 'it's the bestseller' when your night use is 8 kWh. You cycle it to 100% daily and kill it in 5 years instead of 15. Calculate on your real use, not catalog.

5. Trusting the sales rep with sizing

The rep earns commission. The bigger the kit, the more they earn. Verify every number with an external calculator. Numbers don't add up → don't sign.

6. Ignoring service phase (split vs three-phase)

In commercial three-phase services or 240/120 V split-phase US homes, the wrong inverter topology causes uneven export. Make sure the inverter matches your service.

7. Undersized wiring

10 AWG when 8 AWG was required. Voltage drop, heat, fire risk. Demand a voltage-drop calc (<1.5%) on the technical quote.

8. No dedicated grounding

Inverter and racking must each be grounded properly. Without ground: your install is a lightning magnet and warranties void.

9. Incomplete permitting

Installed but no net metering active: you're giving the utility free energy. Verify your interconnection agreement is signed and the new meter is installed before final acceptance.

10. No monitoring

Without monitoring you don't know if a panel fails. Seen systems with one dead panel for 2 years because nobody checked. Set inverter alerts from day 1.

Dive deeper into how to pick an inverter, what battery do I need and permits to install solar panels.