Solar for 500 Units a Month: 4 kW or 5 kW?

Short answer: 500 units a month is 6,000 units a year, which needs about 3.6–4.3 kW of on-grid solar depending on the city. Most families pick 4 kW if their use is steady or 5 kW if it is growing (new AC, EV). Both get the same ₹78,000 central subsidy because the subsidy is capped at 3 kW (check current notification). Budget about 350–500 sq ft of shadow-free roof.

Step 1: confirm your real yearly use

Bills of 500 units are often seasonal. A home might use 650 units in May and 350 in December. Add 12 months of bills and divide by 12. If your average is 420, you need a smaller system than if it is 550.

Step 2: divide by your city's yield

Global Solar Atlas long-term yields with a 5% rooftop derate (Sunlectric Studio data, Oct 2026).

4 kW or 5 kW?

Price ranges are from the installed-cost range we track for residential systems in 2026 (about ₹50,000–65,000 per kW at this size). Get itemised quotes.

Choose 4 kW if your use is stable, your state pays little for surplus units, and roof space is tight.

Choose 5 kW if you plan an electric car, more ACs or an induction kitchen, or if your state pays a reasonable rate for surplus (for example Rajasthan's net-billing option at ₹3.65 per unit, check current notification).

Why 500-unit homes save the most

At 500 units you are in the top slabs of most tariffs, so every unit solar replaces is an expensive unit.

• Maharashtra (MSEDCL): units from 301 to 500 cost ₹15.03 energy + ₹1.60 wheeling + 16% duty, roughly ₹19 per unit (FY 2026-27, verify on your bill).
• Andhra Pradesh: the 226–400 slab is ₹8.75 and above 400 is ₹9.75.
• Kerala: above 250 units a month the tariff is non-telescopic, so all units are charged at a higher rate. Solar that keeps your net use under 250 can save a surprising amount.
• Telangana: above 200 units the slab set jumps to ₹5.10–10.00.

That is why 500-unit homes often see paybacks of three to five years even after paying for good structure and earthing. Model yours:

Single-phase or three-phase?

Many 500-unit homes have three-phase supply because of multiple ACs.

• Up to 10 kW, CEA connectivity rules allow single-phase or three-phase connection; above 10 kW it must be three-phase.
• Many DISCOMs cap a single-phase inverter on a three-phase connection at about 5 kW to avoid phase imbalance (MSEDCL practice; check your DISCOM).
• A three-phase inverter costs more, but spreads export evenly and often has two MPPTs, useful when modules face two directions.

Roof layout tips for 4–5 kW

• One direction is best. South-facing at 10–20° tilt is ideal in most of India. East-west splits lose some output but can fit awkward roofs; use a two-MPPT inverter.
• Watch the water tank. At 9 am and 3 pm in December, shadows are long. In central India a tank 1.5 m tall can throw a shadow roughly 2.5–3.5 m long at 9 am in December, and longer further north.
• Elevated structure. In Maharashtra and Karnataka, raising the front legs about 1 m keeps the terrace usable and makes cleaning easier.

Do you need a battery at 500 units?

Usually not for savings. Under net metering, the grid is your free "battery". A battery makes sense if you face frequent long outages or if your DISCOM has a strong time-of-day tariff that charges more in the evening. See do I need a solar battery.

Before you sign

• Ask for the module make, wattage and DCR certificate (needed for subsidy).
• Ask for the inverter make, model and whether it is on the DISCOM's approved list.
• Ask how the structure is anchored and what wind speed it is designed for.
• Ask who handles net metering and the PM Surya Ghar portal steps.

Our installer checklist has the full list. If your use is lower, see solar for 300 units.

What the bill looks like after solar

With net metering, expect the energy part of the bill to fall to near zero in sunny months, rise a little in July and August, and settle at the end of the period. The fixed charge stays every month.

Talk to Sunlectric

WhatsApp your last 12 bills (or just the latest one) to +91 89567 89307 (wa.me/918956789307) and our Solar Desk will tell you whether 4 or 5 kW fits your use and roof. We stock modules, single- and three-phase inverters, structure and BOS at our Pune hub and can connect you with an installer who buys from us.

Sources

• PM Surya Ghar CFA cap ₹78,000 at 3 kW: pmsuryaghar.gov.in; PIB guidelines, Aug 2024 (accessed Oct 2026)
• MSEDCL tariff FY 2026-27: MSEDCL tariff page (secondary-source rates, verify)
• APERC retail tariff FY 2026-27 press note: APERC
• KSEB tariff 2025–27: KSEB revision circular
• Rajasthan net-billing rate ₹3.65: SolarQuarter, 4 Nov 2025
• City yields: Global Solar Atlas, fetched 19 Oct 2026