You've got three quotes from solar installers sitting in your WhatsApp. One is Rp 28 million, one is Rp 41 million, and the third is a confusing per-kWp number with no total attached. All three say they'll cover your needs. You have no idea which one is right, or whether any of them are sizing the system correctly for your house.
This guide fixes that. We'll walk through the full solar panel calculator logic for Indonesian homes, step by step, using your PLN bill as the starting point and ending at a total investment number you can use to evaluate any quote you receive. The math isn't complicated. A spreadsheet or even a notepad is enough. And once you understand it, vendor proposals stop looking like black boxes.
TL;DR
- Your PLN bill tells you everything you need to start sizing. Divide monthly kWh by 30 for daily usage, then apply the formula: kWp = daily kWh / (PSH x 0.85). That single formula covers 80% of standard Indonesian home sizing cases.
- Peak Sun Hours (PSH) vary by city: Jakarta 4.5, Bali 4.7-5.0, Kupang 5.5, Medan 4.2-4.5. Use the right PSH for your location or you'll over-size for eastern Indonesia and under-size for Sumatra.
- Inverter brand tier by system size: Growatt for under 3 kWp, Luxpower SNA for 3-5 kWp, Deye SUN for 5 kWp and above. Don't buy an 8 kW inverter for a 2 kWp system.
- Battery chemistry for Indonesia: LiFePO4 only. Lead-acid degrades fast in tropical heat. Size battery to night load x autonomy days / 0.8 for DoD ceiling.
- Benchmarks: 1 kWp system Rp 15M, 3 kWp Rp 30-35M, 5 kWp Rp 45-55M, 8 kWp Rp 70-80M. Quotes below these ranges are missing line items.
- Payback for most Indonesian homes: 5-8 years. After that, 17-20 years of near-zero electricity cost. 25-year effective IRR beats bank deposits by 6-12 percentage points.
- SLO permit from PLN is required for any grid-connected system. Budget Rp 1-2M and 2-4 weeks. Your installer handles it, but budget for it upfront.
- This guide doesn't replace a site survey for systems above 10 kWp, multi-orientation roofs, or properties with significant shading. Use these numbers to validate vendor quotes, not to replace the professional assessment.
Why calculate yourself before talking to an installer
The solar industry in Indonesia is still maturing. The majority of installers are honest and competent, but the quoting process has a structural problem: a vendor who gets paid per kWp has a natural incentive to recommend a larger system than you need. This doesn't have to be deliberate dishonesty. When someone doesn't know your actual consumption, they default to conservative over-sizing "just to be safe."
The result is that many homeowners end up with a 5 kWp system when a 3 kWp system would have covered 90% of their usage at two-thirds of the cost. The extra 2 kWp sits on the roof generating electricity that your house can't fully absorb, and under Permen ESDM 2/2024, surplus export to the grid no longer earns credits. That money is simply gone.
Doing the sizing math yourself takes about 20 minutes. It gives you a defensible number to bring into every installer conversation. When a vendor quotes you a system that's 40% larger than your calculation suggests, you can ask a specific question: "My daily usage is 8 kWh and my PSH is 4.5. That implies 2.1 kWp. Why are you recommending 3.5 kWp?" Either they have a good technical reason (shading, future load growth, conservative PR factor), or they don't, and now you know.
That conversation also helps you compare quotes on equal footing. If one installer quotes 2.5 kWp and another quotes 4 kWp for the same house, they're not quoting the same product. Our interactive solar panel calculator runs this math for you automatically, but reading this guide first means you understand what the calculator is doing and why.
A quick note on what this guide covers: we're sizing for standard grid-connected or hybrid homes with PLN backup. Off-grid villas, commercial buildings, and systems above 10 kWp have additional complexity. More on that in the "When this guide doesn't apply" section near the end.
The 3 fundamental numbers you need to understand
Before we get into formulas, you need to be fluent in three terms. They're used consistently across every solar calculator, installer quote, and technical document you'll encounter.
kWh (kilowatt-hour) is a unit of energy. It's what PLN sells you and what your appliances consume. A 1,000-watt air conditioner running for one hour consumes 1 kWh. Your PLN bill shows how many kWh you used last month. This is the input to your sizing calculation.
kWp (kilowatt-peak) is the rated capacity of a solar panel or system at ideal conditions (1,000 W/m² irradiance, 25°C cell temperature). A 580 Wp Jinko Tiger Neo panel produces 580 watts at those lab conditions. Your 3 kWp system consists of panels adding up to 3,000 Wp total. kWp is what installers quote when they say "we'll install a 5 kWp system."
PSH (Peak Sun Hours) is the key variable that connects kWp capacity to actual kWh production. One PSH equals one hour of solar irradiance at 1,000 W/m². If your location gets 4.5 PSH per day, a 1 kWp system will produce approximately 4.5 kWh on an ideal clear day. In practice, system losses (heat, wiring, inverter efficiency) reduce that by about 15%, which is why the standard Performance Ratio (PR) factor of 0.85 appears in the sizing formula.
Indonesia's PSH varies significantly by geography. Regions closer to the equator with fewer cloudy months get more sun hours. Here's the regional breakdown based on Global Solar Atlas data:
| Region | Representative Cities | Daily Average PSH |
|---|---|---|
| West Java | Jakarta, Bandung, Bekasi, Bogor | 4.5 |
| Central Java | Semarang, Yogyakarta, Solo | 4.6 |
| East Java | Surabaya, Malang, Banyuwangi | 4.7 |
| Bali | Denpasar, Ubud, Canggu, Kuta | 4.7-5.0 |
| West Nusa Tenggara | Mataram, Sumbawa | 5.0-5.2 |
| East Nusa Tenggara | Kupang, Maumere, Labuan Bajo | 5.3-5.5 |
| Sumatra (north) | Medan, Padang, Pekanbaru | 4.2-4.5 |
| Sumatra (south) | Palembang, Bandar Lampung | 4.4-4.7 |
| Kalimantan | Pontianak, Banjarmasin, Balikpapan | 4.2-4.4 |
| Sulawesi (south) | Makassar, Kendari | 5.0-5.2 |
| Sulawesi (north) | Manado, Palu | 4.8-5.0 |
| Maluku and Papua | Sorong, Manokwari, Jayapura | 4.8-5.3 |
The eastern islands consistently get more sun than Java. A system sized for Jakarta in Kupang is 20% over-built. PSH accuracy matters.
Step 1: From PLN bill to daily kWh consumption
Your PLN bill or the PLN Mobile app shows monthly kWh consumption. Find it and write it down. This is the most important number in your sizing calculation, and it's the one number a vendor cannot calculate for you without access to your account.
Basic formula:
Daily kWh = Monthly kWh / 30
Example: if your bill shows 240 kWh/month, your daily usage is 8 kWh/day.
If you don't have the kWh figure and only have the rupiah amount, you can estimate backwards using PLN's 2026 tariff tiers:
| Connection (VA) | Category | Tariff (Rp/kWh) |
|---|---|---|
| 450 VA | Subsidized | Rp 415 |
| 900 VA | Subsidized | Rp 605 |
| 900 VA | Non-subsidized | Rp 1,352 |
| 1300 VA | Non-subsidized | Rp 1,444 |
| 2200 VA | Non-subsidized | Rp 1,444 |
| 3500-5500 VA | Non-subsidized | Rp 1,699 |
| Above 5500 VA | Non-subsidized | Rp 1,699 |
Divide your monthly bill amount by your applicable tariff to get approximate kWh. For a Rp 1,500,000 bill at 2200 VA: 1,500,000 / 1,444 = approximately 1,039 kWh/month = 34.6 kWh/day.
A few practical notes. Take the average of your last 3-6 months of bills if possible, because seasonal variation (more AC use in the dry season, water heater use in the cool season) can shift monthly usage by 15-25%. If you know you're adding a significant appliance (another AC unit, EV charger), factor that load into your planning number.
Also separate your load into daytime load and night load. Most solar panel sizing for hybrid systems asks this because your battery only needs to cover the night load. A house that uses 12 kWh/day total but only 4 kWh after sunset needs a much smaller battery than a house that shifts all heavy usage to the evening.
Step 2: Daily kWh to panel size (kWp)
With your daily kWh number in hand, one formula gets you to panel size:
kWp = daily kWh / (PSH x 0.85)
The 0.85 is the system Performance Ratio (PR), representing real-world efficiency losses from heat (panels run hotter than 25°C in Indonesian sun), wiring resistance, inverter conversion losses, and soiling. 0.85 is the industry-standard conservative estimate for Indonesia. Some installers use 0.80 for systems in very hot locations or with known shading; a few claim 0.90 for premium equipment. 0.85 is the right default.
Worked example: Jakarta home, Rp 1.5M bill at 2200 VA
Step 1: Monthly kWh = 1,500,000 / 1,444 = 1,039 kWh/month Step 2: Daily kWh = 1,039 / 30 = 34.6 kWh/day Step 3: PSH for Jakarta = 4.5 Step 4: kWp = 34.6 / (4.5 x 0.85) = 34.6 / 3.825 = 9.05 kWp
That's a large system. For a more typical household with a Rp 450k bill at 1300 VA:
Monthly kWh = 450,000 / 1,444 = 312 kWh/month Daily kWh = 312 / 30 = 10.4 kWh/day kWp = 10.4 / (4.5 x 0.85) = 10.4 / 3.825 = 2.72 kWp, round up to 2.8 kWp
From kWp to module count
Modern residential panels are 540-580 Wp. The most common 2026 standard is 580 Wp (Jinko Tiger Neo, LONGi Hi-MO 6, JA Solar DeepBlue 4.0).
Module count = ceil(system kWp x 1000 / module Wp)
For 2.8 kWp using 580 Wp panels: ceil(2800 / 580) = ceil(4.83) = 5 panels = 2.9 kWp actual
Round up to the next whole panel. Don't round down, it under-builds the system.
How many square meters of roof do you need?
A 580 Wp panel is roughly 2.3 m² including mounting frame clearance. For a 3 kWp system (5-6 panels): 11-14 m² of clear unshaded south-facing roof. For a 5 kWp system (9 panels): 21-23 m². A standard Indonesian terrace house (type 36-72) typically has 12-25 m² of available south-facing roof, which constrains systems to 3-5 kWp regardless of load.
Try our interactive calculator to run your specific numbers with your city's PSH pre-loaded.
Step 3: Pick the right inverter (matched to panel size)
The inverter converts the DC electricity from your panels into AC electricity your house can use. Choosing the right inverter matters for two reasons: efficiency losses at low load (a 10 kW inverter running a 2 kWp array is inefficient and expensive) and reliability over the 8-12 year inverter lifespan.
Brand tier by system size
Juragan Listrik uses this three-tier rule, based on what installers across Indonesia stock and service reliably:
| System Size | Recommended Brand | Key Model | Why |
|---|---|---|---|
| Under 3 kWp | Growatt | MIN/SPF series | Efficient at small load, cheapest service network |
| 3-5 kWp | Luxpower | SNA series | Mid-range sweet spot, good hybrid features |
| 5 kWp and above | Deye | SUN series | Parallelable, modular expansion, strong warranty |
These are the tiers we validate against Tokopedia market pricing and installer feedback. Sungrow and Huawei perform excellently but are priced for larger commercial systems; they appear occasionally in premium residential installs but are usually overkill for under 10 kWp.
DC:AC ratio
The DC input from your panels should be 1.1-1.3x the inverter's AC output rating. This "oversizing" is standard industry practice: panels rarely hit peak rated output in real conditions, and a slightly undersized inverter runs at higher utilization efficiency.
For a 3 kWp panel array, the right inverter is 2.5-3 kW AC output. For a 5 kWp panel array, the right inverter is 4-5 kW AC output. For an 8 kWp panel array, the right inverter is 6-8 kW AC output.
If a vendor quotes you a 10 kW inverter for a 3 kWp panel array, ask why. The answer is sometimes legitimate (planning for future expansion), but often it's padding the quote.
For more detail on the Deye vs Growatt vs Luxpower comparison, see our inverter buyer's guide.
Step 4: Battery sizing (kWh, autonomy, chemistry)
Batteries are optional for grid-tied systems but essential if you want backup power during PLN outages or full 24-hour solar coverage. They're also the most expensive line item in a hybrid system, so sizing them correctly matters more than any other component.
Chemistry: LiFePO4 (LFP) is the only real choice for Indonesia
Indonesia's tropical climate is hard on batteries. Temperatures regularly hit 35-40°C, and extended heat above 35°C accelerates degradation in most battery chemistries. LiFePO4 (also called LFP, short for Lithium Iron Phosphate) is the exception: it maintains full cycle performance at up to 45°C and has intrinsic thermal stability that makes it safe in hot roof-mounted installations.
Avoid NMC (Nickel Manganese Cobalt) chemistry in hot Indonesian climates. NMC has higher energy density but thermal runaway risk rises significantly above 35°C. Avoid flooded lead-acid entirely for solar applications: it needs maintenance, off-gasses hydrogen, and loses 30-40% of its capacity in sustained heat.
Recommended LFP brands for Indonesia in 2026: HinaESS (well-distributed, competitive pricing), Pylontech (proven track record, modular stacking), BYD Battery-Box (premium, modular, BYD service network). See our LiFePO4 comparison guide for a detailed chemistry breakdown.
Battery sizing formula
The key variable is your night load: how many kWh you use after the sun goes down, from roughly 6 PM to 6 AM. For most Indonesian homes, this is 30-50% of total daily usage.
battery_kWh_needed = night_kWh x autonomy_days / 0.8
The 0.8 represents LFP's 80% Depth of Discharge (DoD) ceiling. LFP is rated for 80% DoD at full cycle count. Going deeper shortens battery life disproportionately. Keep your calculations at 80% DoD.
Autonomy days by use case:
| Use Case | Autonomy Days | Notes |
|---|---|---|
| Hybrid with PLN backup | 1 day | PLN covers extended outages |
| Hybrid emergency backup | 2-3 days | Covers typical PLN outages (1-8 hrs) |
| Full off-grid | 3+ days | No PLN connection or reliance |
For most urban and suburban Indonesian homeowners, 1 day of autonomy is the right call. PLN in Java-Bali is reliable enough that 24-hour outages are rare, and sizing for 3-day off-grid capability adds 3x the battery cost for protection you'll rarely need.
Worked example: 2200 VA home, 8 kWh night load, hybrid with PLN backup
battery_kWh_needed = 8 x 1 / 0.8 = 10 kWh
HinaESS standard unit is 5.12 kWh. You need ceil(10 / 5.12) = 2 units = 10.24 kWh actual capacity. Close enough.
Pylontech US5000 is 4.8 kWh per unit. You need ceil(10 / 4.8) = 3 units = 14.4 kWh. This gives you more headroom for cloudy days.
Battery systems are modular: buy what you need now and expand later. Most good hybrid inverters support adding battery units post-installation.
Step 5: Coverage percentage (full backup, 50% hybrid, daytime only)
Not every homeowner needs 100% solar coverage. Your budget and your priorities determine the right coverage mode. Here are the three common configurations for a 2200 VA Jakarta home paying Rp 1.5M/month:
Mode 1: Daytime-only (grid-tied, no battery)
Your panels cover daytime load from 7 AM to 5 PM. PLN covers everything at night. No battery cost. System size: sized to cover daytime load only, typically 1.5-2 kWp for a standard home. Under Permen ESDM 2/2024, surplus daytime generation exports to PLN at a compensation rate but doesn't generate credits you can draw back. Best for: homeowners who shift heavy loads (washing machine, dishwasher) to daytime, have minimal evening usage, and want the cheapest entry point.
| Metric | Value |
|---|---|
| System size | 1.5-2 kWp |
| Battery | None |
| Estimated capex | Rp 18-25M |
| Monthly saving | Rp 400-600k |
| Payback | 4-6 years |
Mode 2: Hybrid 50% coverage
Solar covers approximately half your total daily load through a combination of daytime direct use and stored battery power for early evening. PLN covers the rest. System size: 2-3 kWp with a 5-7 kWh battery bank. This is the most common configuration we see for 2200 VA homes.
| Metric | Value |
|---|---|
| System size | 2.5-3 kWp |
| Battery | 5-7 kWh LFP |
| Estimated capex | Rp 35-45M |
| Monthly saving | Rp 700-900k |
| Payback | 5-7 years |
Mode 3: Full backup (100% coverage)
Solar plus battery covers the full 24-hour load with PLN as emergency backup only. System size: sized to full daily kWh with 1 day battery autonomy. Higher capex, but near-zero PLN bills and full blackout protection.
| Metric | Value |
|---|---|
| System size | 3.5-4 kWp |
| Battery | 10-14 kWh LFP |
| Estimated capex | Rp 55-70M |
| Monthly saving | Rp 1.2-1.4M |
| Payback | 6-8 years |
For a detailed comparison of grid-tied vs hybrid vs off-grid configurations, see our system type guide.
Step 6: Capex breakdown (equipment, install, SLO)
Now you can build the full investment number. Here's how a complete system price breaks down into its actual components.
Panel cost
Tier-1 residential panels (Jinko, LONGi, Canadian Solar, JA Solar) cost approximately Rp 3-3.5M per kWp landed in Indonesia as of 2026 Q2. That's equipment only. At 3 kWp, budget Rp 9-10.5M for panels.
Inverter cost
| Inverter Tier | Model | Approximate Price |
|---|---|---|
| Growatt 2 kW | MIN 2000TL-X | Rp 5-7M |
| Growatt 3 kW | MIN 3000TL-XH | Rp 7-9M |
| Luxpower 3 kW | SNA 3000 | Rp 9-12M |
| Luxpower 5 kW | SNA 5000 | Rp 12-16M |
| Deye 5 kW | SUN-5K-SG04LP1 | Rp 14-18M |
| Deye 8 kW | SUN-8K-SG04LP3 | Rp 20-26M |
Battery cost (LFP)
Budget Rp 4-5M per kWh for HinaESS or Pylontech class LFP. A 10 kWh bank costs Rp 40-50M for equipment.
Installation labor
Rp 2-4M fixed mobilization + Rp 1-2M per kWp for installation. A 3 kWp system: Rp 5-10M labor total.
Balance of system
Mounting rails, MC4 connectors, DC cabling, AC breakers, monitoring meter: Rp 3-6M depending on roof type and cable runs.
SLO (PLN permit)
Required for all grid-connected systems. Budget Rp 1-2M and 2-4 weeks. Without SLO, your system is not legally commissioned and you're operating without PLN's knowledge. A qualified installer handles the SLO application; do not skip this.
System benchmark table
| System Size | Panel kWp | Battery | Inverter | Total Benchmark |
|---|---|---|---|---|
| 1300 VA, minimal | 1-1.5 kWp | None | Growatt 1.5 kW | Rp 15-20M |
| 2200 VA, hybrid 50% | 2.5-3 kWp | 5 kWh LFP | Luxpower 3 kW | Rp 35-45M |
| 3500 VA, full backup | 5-5.5 kWp | 10 kWh LFP | Deye 5 kW | Rp 55-65M |
| 5500 VA, full backup | 8-9 kWp | 15-20 kWh LFP | Deye 8 kW | Rp 80-100M |
These are equipment-plus-install benchmarks. They include SLO budget. They exclude 11% VAT (PPN), which some installers add on top.
For a more detailed breakdown of installation costs, particularly for Bali, see our installation cost guide.
Step 7: Payback period and 25-year cumulative ROI
A solar investment decision should never be evaluated on payback period alone. Payback tells you when you recover your initial capital. It says nothing about the 17-20 years of near-zero electricity costs that follow.
Simple payback formula:
Payback years = total capex / annual savings (year 1)
Annual savings year 1 = monthly savings x 12. Monthly savings = monthly PLN bill x coverage percentage.
For a Rp 35M system covering 70% of a Rp 1.5M/month bill: Annual savings year 1 = (1,500,000 x 0.7) x 12 = Rp 12.6M/year Simple payback = 35,000,000 / 12,600,000 = 2.78 years
Wait, that looks too fast. The reason is that 70% coverage doesn't mean 70% bill reduction: you still pay PLN for the remaining 30% plus the fixed connection charge (biaya beban). Adjust:
Actual monthly saving = bill reduction = Rp 1M/month (realistic for 70% coverage) Annual savings = Rp 12M/year Payback = 35,000,000 / 12,000,000 = 2.9 years
That's optimistic. A realistic 2200 VA household with Rp 35M system in hybrid full-backup mode sees:
- Month 1 savings: Rp 900k-1.1M
- Simple payback: 3-4 years at today's tariff
- Payback with 5% annual PLN escalation: 2.5-3.5 years (savings grow, capex is fixed)
PLN tariff escalation matters enormously
PLN non-subsidized tariffs have increased an average of 4-5% per year over the past decade. Your system cost is fixed on day one. But your savings grow by 4-5% per year as PLN rates rise. Over 25 years at 5% annual escalation:
Year 1 saving: Rp 12M Year 10 saving: Rp 12M x (1.05)^9 = Rp 18.6M Year 25 saving: Rp 12M x (1.05)^24 = Rp 38.6M Cumulative 25-year saving (sum of escalating annual savings): approximately Rp 570-650M
Net of capex Rp 35M and maintenance costs (panel cleaning, one inverter replacement at year 10 for Rp 10-15M): cumulative net return is Rp 500-600M.
Comparing to a bank deposit
Rp 35M in a fixed deposit at 5.5% annual interest (typical 2026 Indonesian bank rate) grows to approximately Rp 130M in 25 years.
A solar system starting at the same Rp 35M delivers Rp 500-600M cumulative savings over 25 years. That's an effective IRR of 12-18% depending on PLN escalation scenario.
The full ROI framework is in our dedicated solar ROI article for Indonesian homes.
Sample sizing by VA tier (1300 / 2200 / 3500 / 5500)
These are complete worked examples you can use as reference points for your own situation.
Example 1: 1300 VA, Rp 600k/month, 50% hybrid mode, Jakarta
Monthly kWh = 600,000 / 1,444 = 415 kWh/month Daily kWh = 415 / 30 = 13.8 kWh/day 50% coverage target = 6.9 kWh/day from solar kWp needed = 6.9 / (4.5 x 0.85) = 6.9 / 3.825 = 1.8 kWp, round to 2 kWp Panels: 4 x 580 Wp Jinko Tiger Neo = 2.32 kWp Night load covered by battery: 3 kWh Battery: ceil(3 / 5.12) = 1 HinaESS 5.12 kWh unit Inverter: Growatt 2 kW
Total estimated capex: Rp 22-28M (equipment + install + SLO, no VAT)
Example 2: 2200 VA, Rp 1.5M/month, full backup, Jakarta
Monthly kWh = 1,039 kWh/month Daily kWh = 34.6 kWh/day (this is high for a 2200 VA connection; verify your actual kWh on the bill)
More typical 2200 VA home: 200-300 kWh/month (Rp 290-435k at 1,444/kWh) Using Rp 1.5M which implies ~1,039 kWh: likely a larger villa or house with multiple AC units.
kWp needed = 34.6 / (4.5 x 0.85) = 9.1 kWp (above the 5500 VA sizing example, so re-run with 2200 VA realistic scenario)
Realistic 2200 VA home at Rp 600k: ~415 kWh/month, 13.8 kWh/day kWp = 13.8 / (4.5 x 0.85) = 3.6 kWp, round to 3.7 kWp Panels: 7 x 580 Wp = 4.06 kWp Night load: 5 kWh, 1 day autonomy Battery: ceil(5 / 0.8) = 6.25 kWh; 2 x Pylontech US5000 (4.8 kWh each) = 9.6 kWh Inverter: Luxpower SNA 3 kW
Total estimated capex: Rp 42-50M (full backup mode with 9.6 kWh battery, no VAT)
Example 3: 3500 VA, Rp 2.5M/month, full backup, Jakarta
Monthly kWh = 2,500,000 / 1,699 = 1,471 kWh/month Daily kWh = 49 kWh/day (large family home with full AC) kWp = 49 / (4.5 x 0.85) = 12.8 kWp (note: this approaches commercial sizing, see "When this guide doesn't apply")
More typical 3500 VA home: 500-700 kWh/month (Rp 850k-1.2M) Using 600 kWh/month = 20 kWh/day kWp = 20 / (4.5 x 0.85) = 5.2 kWp, round to 5.5 kWp Panels: 10 x 580 Wp = 5.8 kWp Night load: 7 kWh, 1 day autonomy Battery: ceil(7 / 0.8) = 8.75 kWh; 2 x HinaESS 5.12 kWh = 10.24 kWh Inverter: Deye 6 kW SUN-6K
Total estimated capex: Rp 60-72M (no VAT)
Example 4: 5500 VA, Rp 4M/month, full backup, Jakarta
Monthly kWh = 4,000,000 / 1,699 = 2,354 kWh/month Daily kWh = 78.5 kWh/day (this is a large commercial-residential property; professional design required)
Typical 5500 VA residential: 800-1,200 kWh/month Using 1,000 kWh/month = 33 kWh/day kWp = 33 / (4.5 x 0.85) = 8.6 kWp, round to 9 kWp Panels: 16 x 580 Wp = 9.28 kWp Night load: 12 kWh, 1 day autonomy Battery: ceil(12 / 0.8) = 15 kWh; 3 x HinaESS 5.12 kWh = 15.36 kWh Inverter: Deye 8 kW SUN-8K (parallel-capable if expansion needed)
Total estimated capex: Rp 85-105M (no VAT)
Practical note on large systems
At 5500 VA with a genuine Rp 4M monthly bill, your daily usage is at the boundary between residential and commercial design. Above 10 kWp, a professional load analysis and site survey become non-optional. The formulas here still give you a validation number, but the design complexity increases.
Sample sizing by city (same load, different PSH)
To show how much location matters, here's the same home (200 kWh/month, 6.7 kWh/day) sized across four Indonesian cities:
| City | Daily kWh | PSH | kWp Needed | Panel Count (580 Wp) | Relative Cost |
|---|---|---|---|---|---|
| Jakarta | 6.7 | 4.5 | 1.74 kWp | 3 panels (1.74 kWp) | Baseline |
| Bandung | 6.7 | 4.6 | 1.71 kWp | 3 panels (1.74 kWp) | ~Same |
| Bali (Denpasar) | 6.7 | 4.8 | 1.64 kWp | 3 panels (1.74 kWp) | ~Same |
| Kupang (NTT) | 6.7 | 5.5 | 1.43 kWp | 3 panels (1.74 kWp) | ~Same |
At this system size (3 panels), the PSH difference doesn't change the module count. The minimum order is 3 panels regardless. But look at annual production:
| City | System kWp | Annual Production (kWh) | Annual Savings Difference |
|---|---|---|---|
| Jakarta | 1.74 | 2,870 | Baseline |
| Bali | 1.74 | 2,979 | +109 kWh/year = +Rp 158k/year |
| Kupang | 1.74 | 3,327 | +457 kWh/year = +Rp 660k/year |
Over 25 years, Kupang produces 11,425 kWh more from the identical panel array. At a 2026 tariff of Rp 1,444/kWh with 5% annual escalation, that's a Rp 65M cumulative difference for the same upfront investment. Location matters.
For a larger 5 kWp system, the PSH difference is magnified: Kupang vs Jakarta produces roughly 1,315 kWh more per year, worth approximately Rp 2M in year-1 savings. The Kupang system pays back faster even though the upfront cost is identical.
5 most common sizing mistakes
These are the errors we see repeatedly when reviewing installer quotes or when homeowners come to us after a first install that underperforms.
Mistake 1: Accepting vendor sizing without checking it against your actual bill
The most common issue. A vendor quotes you a system "for your house size" without asking for your PLN bill or kWh consumption. The result is a system sized for an average house, not your house. If you have an EV charger, multiple ACs, or run a home business, an average estimate will under-build. If you're retired and rarely home, it will over-build.
Fix: before accepting any quote, verify the vendor has your actual monthly kWh number and has used it in their calculation.
Mistake 2: Forgetting SLO in the budget
Many first-time buyers see a panel-plus-inverter price from an online store and assume that's the whole cost. SLO certification, installation labor, balance of system (mounting, cabling, breakers), and the inverter itself are all separate line items. Getting surprised by Rp 8-15M in costs after accepting a "too good to be true" panel price is a real and common experience.
Fix: always ask for a fully scoped written quote that explicitly lists: panels, inverter, battery (if applicable), mounting hardware, cabling, installation labor, SLO filing fee, and commissioning.
Mistake 3: Under-speccing the inverter versus panel array
Buying a 2 kW inverter for a 4 kWp panel array, or a 10 kW inverter for a 1.5 kWp system. Both cause problems: the under-spec inverter clips production at peak hours, the over-spec inverter runs at low utilization and degrades faster. The DC:AC ratio should be 1.1-1.3.
Fix: the inverter AC output should be 75-90% of panel kWp.
Mistake 4: Battery bank sized for total daily usage instead of night usage
Night load is typically 30-50% of daily load. If you size battery to cover your full daily kWh, you're paying for 2-3x the battery you need. The battery only needs to cover what you use from sunset to sunrise, and in a hybrid system, PLN handles extended outages.
Fix: measure your actual evening-to-morning consumption using a smart meter app or PLN meter reading. Size battery to that number, not total daily.
Mistake 5: Ignoring shading from trees or neighboring structures
A single tree branch shading one panel in an otherwise unshaded array can drop total system output by 20-40% due to string-effect in series-connected panels. This is particularly relevant in Bali, where large frangipani, coconut, and bamboo can create partial shade that moves across the roof during the day.
Fix: before finalizing the roof layout, do a solar pathfinder analysis or use a shading app (SolarEdge Designer, Solargis, or even Google's sunroof tool where available). If there's partial shading, discuss microinverters or optimizers with your installer.
When this guide doesn't apply
This guide works for a specific profile: standard Indonesian home with PLN grid connection, predominantly south-facing roof with no significant shading, system size between 1 and 10 kWp. If your situation departs from that profile, the formulas give you a starting point but not a complete answer.
Non-standard heavy loads
Water pumps, welding machines, CNC equipment, and other high-inrush or high-continuous-draw appliances need separate load analysis. A 2.2 kW water pump starting 6 times per day has a very different impact on battery sizing than the same 2.2 kW spread across lighting and small appliances. If you have significant non-residential loads in your home, tell your installer upfront and ask for a load audit before sizing.
Multi-orientation or heavily shaded roofs
If your main roof faces west or north (uncommon but it happens in older neighborhoods where house orientation wasn't optimized for solar), or if large neighboring buildings shade your roof for 2-4 hours per day, the simple formula with standard PSH will over-estimate production. You need a site-specific irradiance analysis or at minimum a shading hour estimate.
Remote off-grid villas and properties
For properties without PLN connection (remote Bali hillside, eastern island, jungle clearings), the sizing math changes significantly. Autonomy days extend to 3-5 days. Panel sizing goes up to compensate for worst-week solar radiation in the rainiest month (not annual average PSH). Generator backup sizing enters the equation. This guide's formulas will under-build an off-grid system by 30-50% if applied directly.
Systems above 10 kWp
Above 10 kWp, you're entering semi-commercial sizing territory. PLN's SLO process has additional steps, three-phase power may be required, string design becomes more complex, and the financial model should include a proper cash-flow discounting analysis rather than simple payback. Hire a certified PV designer for anything above 10 kWp.
For all of these edge cases, use this guide's numbers as a sanity check on the professional quote you receive, not as a substitute for it. And if you're still figuring out how to evaluate and choose between installers, see our guide to picking a solar installer in Indonesia.
How to use the Juragan Listrik calculator
The step-by-step math in this guide is what our solar panel calculator for Indonesia runs automatically. Here's how to use it most effectively:
- Enter your monthly PLN bill in rupiah. The calculator converts to kWh using the correct tariff tier for your VA connection.
- Select your city. PSH is pre-loaded from Global Solar Atlas data for 385 Indonesian cities.
- Choose your coverage mode: daytime-only, hybrid 50%, or full backup.
- The calculator outputs: system kWp, panel count, inverter recommendation, battery size (if applicable), total capex benchmark, and estimated payback.
The calculator result gives you a complete spec to bring into installer conversations. When a vendor's quote differs from the calculator output by more than 20%, ask them to justify the difference. That conversation is worth having before you sign anything.
If you want to discuss your specific situation, you're also welcome to reach out via WhatsApp. We review residential sizing questions at no charge.
Putting it all together: a complete sizing checklist
Before you accept any solar quote, run through this checklist:
Information you need from your PLN bill:
- Monthly kWh consumption (not just the rupiah amount)
- VA connection tier (1300/2200/3500/5500)
- Last 3-6 months of bills to identify seasonal variation
Calculations to run:
- Daily kWh = monthly kWh / 30
- kWp = daily kWh / (PSH x 0.85) using the PSH for your city
- Module count = ceil(kWp x 1000 / 580)
- Battery kWh = night load x autonomy days / 0.8
- Verify inverter DC:AC ratio = panel kWp / inverter kW = 1.1-1.3
Quote line items to verify:
- Panels (brand, Wp, quantity)
- Inverter (brand, kW, model)
- Battery (brand, kWh, chemistry)
- Mounting hardware
- DC and AC cabling
- Installation labor
- SLO filing fee
- Commissioning and handover
Red flags:
- Total quote below Rp 15M per kWp (something is missing)
- No mention of SLO
- Inverter significantly over-sized versus panel array
- No site survey before quote finalization
- No written warranty terms for installation workmanship
Green flags:
- Vendor asks for your PLN kWh number, not just your bill amount
- Quote includes all line items with unit prices
- Inverter brand matches the three-tier rule for your system size
- Vendor mentions SLO process and timeline upfront
- Written 1-year installation workmanship warranty separate from product warranties
Conclusion
A solar panel system for your Indonesian home is a 25-year financial decision. The difference between a well-sized system and a poorly-sized one isn't just money: a 40% over-sized system means 40% of your capital earns near-zero return for its entire life, while a 20% under-sized system leaves you disappointed with coverage and PLN savings.
The math in this guide is not complicated. Your PLN bill gives you the starting point. Your city's PSH gives you the solar resource. The formula kWp = daily kWh / (PSH x 0.85) gives you the system size. Everything else is verification: does the inverter match the panels, does the battery cover the night load, does the total price land within the benchmark ranges?
Run your numbers in the calculator now. Bring the output to your next installer conversation. Ask the right questions. The market in Indonesia has good installers at fair prices, and those installers will have no problem explaining every line item in their quote. The ones who can't, you've already identified.
If you have questions about your specific situation, reach out on WhatsApp and we'll take a look at your numbers.
Frequently asked questions
kWp stands for kilowatt-peak, the rated power output of a panel under ideal laboratory conditions (1000 W/m² irradiance, 25°C cell temperature). It's the standard unit for comparing system sizes. A 3 kWp system in Jakarta produces roughly 12-13 kWh per day in practice, because real sun hours, temperature losses, and wiring losses reduce what you get versus the nameplate figure.
