You've spent two weeks researching, collected three quotes, and chosen an installer. It feels like the hard part is done. But this is exactly the point where many Indonesian homeowners make their most costly solar panel installation mistakes, not from ignorance but from skipping steps that seemed optional at the time.
The five mistakes below follow a consistent pattern: underperforming systems, warranty disputes that go nowhere, and owners who are frustrated not because the technology failed but because the process had gaps. Read this before you sign anything.
TL;DR
- Get a physical roof survey before agreeing to any design. Orientation, shading, and roof frame condition all determine real output, and assumptions are expensive.
- Over-speccing doesn't protect your investment. There's no net metering credit in Indonesia under Permen ESDM 2/2024, so surplus production goes nowhere.
- Inverter capacity should match or slightly exceed your panel kWp. An undersized inverter cuts output on your most productive days.
- SLO (the PLN operating permit) must appear in your contract. Without it, your grid-tied system isn't legally parallel to the PLN network.
- Workmanship warranty (2-5 years) and product warranty are separate documents from separate parties. Both must be written, not verbal.
Mistake #1: No roof survey before accepting a quote
What happens: Many homeowners agree to a quoted system size before anyone has physically been on their roof. The installer estimates based on a photo or a description like "south-facing tile roof, planning 4 panels," and that's enough to produce a number. But that number carries large assumptions.
The consequence: Wrong assumptions about orientation, tilt, or shading can put real output 20-30% below what the proposal promises. A concrete example: a tall tree to the west that casts shadow from 2 PM onward cuts 1-1.5 productive hours per day, which adds up to thousands of kilowatt-hours per year. If the roof uses old ceramic tiles and the timber frame condition was never inspected, neither the installer nor you know if the structure can hold the panel weight and mounting hardware.
How to avoid it: Require a physical site visit before agreeing to any system design. Professional installers do this for free. During the survey they should measure the usable roof area (after edge setbacks and obstacles like skylights or vents), inspect the frame, check orientation with a compass, and document shading points at different times of day. If an installer is willing to submit a proposal without visiting the site, that's worth taking seriously before proceeding.
Mistake #2: Over-speccing the system based on marketing advice
What happens: "Install a bigger system now, you'll be covered when PLN tariffs go up." This sounds reasonable until you understand one critical regulatory detail: Indonesia's current regulations offer no value for surplus production.
The consequence: Under Permen ESDM 2/2024, there's no net metering for residential solar systems. If your panels produce more than your home needs during the day, the surplus doesn't earn PLN credits, doesn't roll forward to next month's bill, and doesn't do anything. A 6 kWp system for a home that actually needs 3 kWp generates large surpluses every sunny day, and every bit of that surplus is wasted. You paid Rp 15-18 million per kWp for capacity that has no destination.
How to avoid it: Calculate your actual daily needs based on 3-6 months of PLN bills. A Rp 600k-700k monthly bill at a standard residential tariff suggests you're using roughly 15-18 kWh per day, which translates to 3-4 kWp in Java (PSH 4.5-4.7). Right-sizing isn't about being as conservative or as ambitious as possible. It's about matching your actual consumption with a small buffer.
Calculate the right size for your home →
Mistake #3: Inverter becomes the bottleneck
What happens: This is the opposite of mistake #2, and it occurs most often when a budget is being squeezed. The panels are tier-1, but the inverter is chosen at a capacity too small relative to total panel kWp.
The consequence: The inverter processes all DC output from the panels into usable AC power. If the inverter's rated capacity is smaller than the panels' peak output, it clamps production at its ceiling. A 6 kWp array with a 4 kW inverter on a clear day only processes 4 kW, wasting 25-30% of potential during the most productive hours (10 AM to 2 PM). Over a full year in Java, this can amount to 700-1,000 kWh of lost production, roughly Rp 1-1.5 million in value.
The industry standard: inverter capacity should be between 100-130% of total panel kWp (DC:AC ratio of 0.77-1.0). For 3 kWp of panels, a 3 kW inverter is right. For 5 kWp, a 4 kW inverter is the absolute floor if budget is constrained. Below that, you are systematically discarding system potential.
How to avoid it: Check this ratio in every quote you receive. Ask the installer to explain why they chose that inverter size. If the answer is "that's what comes in the package" without a technical explanation, push further. For reference, common brands used by experienced Indonesian installers: Growatt for systems under 3 kW, Luxpower for 3-5 kW, Deye for 5 kW and above.
Mistake #4: SLO gets ignored until the very end
What happens: SLO (Sertifikat Laik Operasi, or Operating Certificate) is the official PLN document that authorizes your grid-tied system to run in parallel with the PLN network. Many homeowners only discover this exists after the system is already installed and about to be switched on, sometimes after it has been running for months without the certificate.
The consequence: Without SLO, your on-grid system is technically operating but not legally authorized. If there's an inspection, an insurance claim involving the system, or a grid-connection dispute, the absence of SLO becomes a problem. More practically, the PLN process takes 2-4 weeks depending on your area. If this isn't built into the project timeline from day one, it delays your legal commissioning and can create awkward grey-area operation in the interim.
How to avoid it: Before signing any contract, confirm in writing whether SLO is included in the package, who handles the application (your installer, not you), and what the estimated timeline is. Experienced installers manage SLO as part of the package because they know the required technical documents and have working relationships with PLN in their service areas. If an installer says the SLO is your responsibility to obtain independently, get clarity on why before proceeding.
Mistake #5: Skipping workmanship warranty or relying on verbal promises
What happens: "We guarantee everything for 5 years" gets said during the sales presentation. You feel reassured. The contract gets signed. The contract document turns out not to specify this guarantee explicitly, or it does but with no details about what it covers, how long it lasts, or how to claim.
The consequence: Eighteen months after installation, there's a water stain on the ceiling that turns out to trace back to a drilling point from the panel mounting. You call the installer. Without a written workmanship warranty with clear scope, "that's outside our responsibility" is a very real response, and you have no written basis to dispute it.
There's a distinction worth understanding: workmanship warranty is the installer's responsibility for the quality of their physical work (mounting, cabling, waterproofing at drilling points, connections). Product warranty is the manufacturer's responsibility for component performance (panels, inverter, batteries). Two different things from two different parties. Both need to be in writing, not just one.
How to avoid it: Ask for two separate written sections in your contract: one covering workmanship warranty (minimum 2 years, ideally 3-5 years) and one covering product warranty per component. The workmanship section must specify duration, scope (at minimum: drilling and waterproofing, mounting hardware, wiring connections), a valid contact method for claims, and a site-visit response time. If the installer objects to any of this, factor that into your decision.
| Component | Reasonable warranty duration | From whom |
|---|---|---|
| Workmanship (installation quality) | 2-5 years | Installer |
| Solar panels (linear output) | 25 years | Manufacturer |
| Inverter | 5 years standard, 10 years extended | Manufacturer |
| LFP battery | 5-10 years or 6,000 cycles | Manufacturer |
When this doesn't apply
If you already have an installer you can verify through direct references, such as a neighbor whose system has been running cleanly for 3+ years, you can simplify this process. "Simplify" doesn't mean skipping everything. You still want written specifications, SLO in the contract, and a written workmanship warranty. What you save is the time you'd otherwise spend independently verifying the installer's track record.
If your budget is tight enough that every installer you contact is quoting below Rp 12 million per kWp with unspecified components, it's worth pausing rather than proceeding with a system that's likely to have issues within 2-3 years. The right system at the right time beats the cheapest system at the wrong one.
Frequently asked questions
A physical roof survey determines usable area after edge setbacks, roof frame load capacity, panel orientation, tilt angle, and shading from neighboring trees or structures. Without a survey, the installer is quoting based on assumptions. Wrong assumptions about shading alone can cut real-world output 20-30% below what the proposal promises. Reputable installers do this for free as part of the process.
