SolvSolar Global Solar Encyclopedia

Question 1

How to design solar layouts online?

Accepted Answer

Design a solar layout online by entering the site address, roof type and monthly electricity bill into a browser-based design engine — no CAD install needed. SolvSolar's 2D/3D array engine auto-places modules on flat roofs, metal sheds or ground mounts, locks the panel count to the bill of materials, and returns a shareable proposal in about 45 seconds.

Question 2

What is payback period calculation?

Accepted Answer

Payback period is turnkey system cost divided by annual electricity savings, giving the number of years until solar pays for itself. Annual savings equal system size in kW multiplied by effective yield in kWh/kWp after shade losses, multiplied by your electricity unit rate. Typical rooftop payback runs 3–6 years in high-tariff markets and 6–9 years elsewhere.

Question 3

Can I generate solar proposals on WhatsApp?

Accepted Answer

Yes — you can generate a complete solar proposal inside WhatsApp. SolvSolar runs native WhatsApp and Telegram bots: a homeowner sends their address and monthly bill, and the bot replies with a hosted proposal URL covering system size in kW, 25-year savings and a financing link. The whole exchange takes under a minute with no manual work from the installer.

Question 4

Is there free solar design software for installers?

Accepted Answer

Yes — SolvSolar charges $0 per seat, so solar design software is free to staff. You add unlimited team members at no cost and pay only for the kilowatts you actually design, drawn from a 100 kW free trial, then a monthly subscription quota, then a pay-per-kW wallet. There are no per-user licences to renew.

Question 5

Mono PERC vs TopCon — which is more efficient?

Accepted Answer

TopCon is more efficient than Mono PERC. Mono PERC modules typically deliver 20–21% cell efficiency, while TopCon (tunnel oxide passivated contact) reaches 22–23%, with a lower temperature coefficient and better low-light performance. TopCon costs slightly more per watt but yields more kWh per kWp over a 25-year life, and the gap widens in hot climates where PERC derates faster.

Question 6

How many panels do I need for a 5 kW system?

Accepted Answer

A 5 kW solar system needs about 10 panels of 540 Wp, or 13 panels of 400 Wp. The maths is simply 5,000 W divided by the module wattage, rounded up. Plan for roughly 350–400 sq ft of shade-free roof area, or more if the array is elevated on a structure with inter-row clearance.

Question 7

What is bifacial gain?

Accepted Answer

Bifacial gain is the extra energy a double-sided module produces from light reflected onto its rear face. It typically adds 5–15% to annual generation, depending on ground albedo, mounting height and tilt. Elevated or ballasted structures over white membrane, concrete or light sand see the highest gain; dark or heavily shaded ground sees almost none.

Question 8

How much roof area does 1 kW of solar need?

Accepted Answer

One kilowatt of rooftop solar needs about 65–80 sq ft (6–7.5 m²) of shade-free area. Elevated or ground-mount layouts need 100–120 sq ft per kW because inter-row spacing must avoid self-shading. Higher-efficiency modules of 550 Wp and above pull the requirement toward the lower end of each range.

Question 9

Difference between On-Grid, Off-Grid and Hybrid inverters?

Accepted Answer

On-grid inverters export surplus power to the utility and shut down when the grid fails; off-grid inverters run entirely on batteries and work without any grid connection; hybrid inverters do both. Hybrids export to the grid in normal operation and switch to a battery bank during outages, which costs more upfront but removes the need for diesel backup.

Question 10

String inverter or microinverter?

Accepted Answer

Choose a string inverter for uniform, unshaded roofs and microinverters for complex or partly shaded ones. String inverters cost less per watt and are simpler to service. Microinverters and DC optimisers perform panel-level MPPT, recovering more energy on multi-orientation roofs, and they simplify rapid-shutdown compliance in markets where that code applies.

Question 11

What DC/AC ratio should I design for?

Accepted Answer

Design for a DC/AC ratio of 1.1–1.3 in most rooftop systems. Oversizing the array relative to inverter capacity flattens the generation curve and raises annual yield, especially in cloudy or high-latitude sites. Above roughly 1.35, midday clipping losses start to outweigh the morning and evening gains, so the extra modules stop paying for themselves.

Question 12

Do I need a battery with rooftop solar?

Accepted Answer

No — a battery is optional and only worth it if you need outage backup, face poor export rates, or pay high time-of-use peak tariffs. Where net metering credits exports 1:1, a grid-tied system without storage gives the fastest payback. Batteries add cost per kWh of usable capacity and buy resilience rather than ROI.

Question 13

What is the solar payback time?

Accepted Answer

Rooftop solar typically pays back in 3–6 years in high-tariff, high-irradiance markets and 6–9 years in lower-irradiance ones. Commercial and industrial systems usually sit at the fast end because unit rates are higher and daytime load matches generation. Modules keep producing for 25 years or more, so most of the asset life is effectively free energy.

Question 14

How to calculate solar savings?

Accepted Answer

Calculate annual solar savings as system size in kW multiplied by effective annual yield in kWh/kWp, multiplied by your electricity unit rate. Subtract any fixed charges that stay on the bill regardless of consumption. Project the figure across 25 years using a 2–5% annual tariff escalation and a 0.5% yearly panel degradation rate for a realistic lifetime number.

Question 15

What subsidies are available for rooftop solar?

Accepted Answer

Rooftop solar subsidies vary by country: India's PM Surya Ghar scheme pays up to ₹78,000 in central assistance for a 3 kW residential system, and the United States offers a 30% federal Investment Tax Credit. Many EU states, the UK, Australia and the UAE run feed-in tariffs, VAT relief or rebates. Commercial systems are usually excluded from residential schemes.

Question 16

Is solar worth it for commercial buildings?

Accepted Answer

Yes — solar is usually worth it for commercial buildings, with typical payback of 3–4 years. Commercial tariffs are higher than residential ones, daytime occupancy matches the solar generation curve almost exactly, and accelerated depreciation plus tax credits shorten payback further. After that the system delivers 20-plus years of near-free daytime electricity.

Question 17

What is the standard degradation rate of solar panels?

Accepted Answer

Solar panels degrade roughly 0.4–0.55% per year after an initial 1–2% drop in the first year. That means a Tier-1 module still delivers about 87–92% of its rated output at year 25, which is what a linear performance warranty guarantees. TopCon and heterojunction cells sit at the slower end; older polycrystalline modules degrade faster.

Question 18

How long does a rooftop solar installation take?

Accepted Answer

Physical installation of a 3–10 kW residential rooftop system takes 1–3 days. The longer wait is paperwork: utility interconnection, net-metering approval and inspection typically add 2–8 weeks depending on the DISCOM or utility. Commercial projects above 100 kW usually run 4–10 weeks on site plus the same approval cycle.

Question 19

What warranties should a solar proposal include?

Accepted Answer

A solar proposal should list module, inverter, structure and workmanship warranties separately. Expect 12–15 years product and 25–30 years linear performance warranty on modules, 5–12 years on inverters (often extendable), 10 years on mounting structures, and 1–5 years of installer workmanship cover. Anything vaguer than that is a red flag worth challenging before signing.

Question 20

How much maintenance does solar need?

Accepted Answer

Solar needs very little maintenance — mainly panel cleaning and an annual electrical inspection. Clean every 1–3 months in dusty regions and less often in rainy climates; skipping it can cost 3–8% of annual yield to soiling. Budget 0.5–1% of system value per year for O&M, and rely on remote monitoring alerts to catch faults early.

Question 21

What does a turnkey solar EPC scope actually include?

Accepted Answer

A turnkey solar EPC scope covers everything from survey to handover: site survey, structural and electrical design, supply of modules, inverters, mounting structure, cables, protection devices and earthing, plus civil work, installation, testing and commissioning. It also includes net-meter liaison with the utility and an O&M handover pack. Anything excluded should be listed explicitly in the contract.

Question 22

How long does a rooftop EPC project take end to end?

Accepted Answer

A 5–10 kW residential rooftop EPC project takes 7–15 working days on site, and 100 kW-plus commercial projects run 4–10 weeks. Net-metering approval adds another 2–8 weeks depending on the utility, and that approval, not construction, is usually the critical path. Budget six to ten weeks end to end for a typical home installation.

Question 23

What structural checks are needed before mounting on a roof?

Accepted Answer

Before mounting, verify that the slab or purlins carry the dead load plus wind uplift, that waterproofing is intact, that parapets or water tanks will not shade the array, and that there is safe access for cleaning. Elevated structures additionally need a certified wind-load calculation against the local basic wind speed for the site.

Question 24

Who is responsible for liaisoning and net-meter approval?

Accepted Answer

In most turnkey contracts the EPC contractor handles liaisoning: filing the utility application, coordinating the inspection and installing the bi-directional meter. Confirm this is written into the scope of work so approval delays are not later billed as extras. The consumer still supplies identity, ownership and electricity-bill documents.

Question 25

LFP or lead-acid for solar storage?

Accepted Answer

LFP (LiFePO4) is the better choice for almost all solar storage today. It delivers 4,000–6,000 cycles at 80–90% depth of discharge, needs no maintenance and lasts 10–15 years. Lead-acid is cheaper upfront but gives only 500–1,200 cycles at 50% DoD, so its lifetime cost per usable kWh normally ends up higher.

Question 26

How do I size a battery for backup?

Accepted Answer

Size a backup battery by listing the loads you must keep alive, multiplying by the hours of autonomy you need, then dividing by usable depth of discharge and inverter efficiency. For example, a 3 kW critical load for 4 hours is 12 kWh, which on LFP at 90% DoD and 95% inverter efficiency needs roughly a 14 kWh bank.

Question 27

Does adding a battery improve payback?

Accepted Answer

Usually no — a battery rarely improves payback on its own. Storage pays back where tariffs are time-of-use, export credits are well below the retail rate, or expensive diesel backup is being displaced. Under 1:1 net metering, a battery mainly buys resilience during outages rather than financial return, and it lengthens overall payback.

Question 28

What is round-trip efficiency and why does it matter?

Accepted Answer

Round-trip efficiency is the share of energy put into a battery that comes back out again. LFP systems achieve 90–95%; lead-acid manages only 75–85%. It matters because every lost percentage point must be replaced by a larger array or a bigger bank, so low efficiency quietly inflates both system cost and roof area.

Question 29

How does the Indian rooftop subsidy work today?

Accepted Answer

Indian residential consumers apply on the national rooftop portal, choose an empanelled vendor, and receive the central financial assistance directly in their bank account after inspection and net-meter installation. The subsidy is capped by system size, with roughly ₹78,000 available at 3 kW. Commercial and industrial systems are not eligible under the residential scheme.

Question 30

What accelerated depreciation is available to businesses?

Accepted Answer

Indian commercial and industrial owners can claim accelerated depreciation on a solar asset, writing off a large share of its cost in the early years and cutting taxable income. That tax shield often shortens effective payback to around three years. Rates change with finance legislation, so confirm the current percentage with your auditor before putting it in a proposal.

Question 31

What is the US federal investment tax credit?

Accepted Answer

The US federal Investment Tax Credit lets taxpayers claim a percentage — 30% under current rules — of the installed cost of a qualifying solar system against their federal tax liability. It stacks with state rebates, utility incentives and net-metering benefits. Eligibility criteria and the percentage change with legislation, so verify the current position before quoting it.

Question 32

Should subsidies be shown inside the proposal price?

Accepted Answer

No — show subsidies as a separate line, not folded into the headline price. Quote the gross turnkey cost first, then each incentive, then a net effective price. Regulators and finance partners distrust proposals where the subsidy is silently netted off, and lenders need the gross figure to size a loan correctly.

Question 33

What is the difference between net metering, gross metering and net billing?

Accepted Answer

Net metering credits exported units 1:1 against consumption, gross metering sells all generation to the utility at a fixed feed-in tariff, and net billing pays for surplus exports at a rate below the retail tariff. Under net billing and gross metering, self-consumption during daylight hours matters far more to the economics than raw system size.

Question 34

Is there a sanctioned-load cap on rooftop capacity?

Accepted Answer

Yes — most Indian DISCOMs cap rooftop solar capacity at the consumer's sanctioned load, and many also cap total penetration on a distribution transformer or feeder. Always size the system against the sanctioned load printed on the electricity bill, not the connected load, or the application will be rejected at technical feasibility stage.

Question 35

What documents does a DISCOM application need?

Accepted Answer

A DISCOM rooftop application typically needs the latest electricity bill, consumer identity proof, roof ownership documents or an NOC, a single-line diagram, module and inverter datasheets with test certificates, an earthing layout and the empanelled vendor declaration. Requirements vary slightly by state, so check the local utility's current checklist before filing.

Question 36

What grid protection is mandatory?

Accepted Answer

Grid-tied solar must include anti-islanding protection, over- and under-voltage and frequency trip settings, DC and AC surge protection, an AC isolator the utility can access, and earthing to the applicable national standard. Anti-islanding is the non-negotiable one: it stops the inverter energising a dead line and endangering utility crews during an outage.

Question 37

How long is net-meter approval valid?

Accepted Answer

Technical feasibility approval for net metering typically lapses after 3–6 months if the system is not commissioned, and the application must then be refiled from scratch. Build that window into project timelines and avoid filing before equipment procurement is confirmed, since a lapsed approval can push a project back by several weeks.

Question 38

What is a realistic performance ratio?

Accepted Answer

A realistic performance ratio for a well-designed rooftop system is 0.75–0.82 after temperature, soiling, mismatch, cable and inverter losses. Treat anything above 0.85 in a proposal as optimistic marketing rather than an engineering estimate. Ratios below 0.70 usually point to heavy shading, poor ventilation behind modules, or undersized cabling.

Question 39

How much does soiling cost per year?

Accepted Answer

Soiling costs 3–8% of annual yield at dusty urban and industrial sites if panels are never cleaned, and can exceed that near construction or cement works. Fortnightly dry cleaning during dry seasons and monthly wet cleaning otherwise typically holds the loss under 2%. Rain-washed coastal and hill sites need far less intervention.

Question 40

What should an O&M contract cover?

Accepted Answer

A solar O&M contract should cover scheduled cleaning, thermal inspection of joints and combiner boxes, inverter firmware updates and fault handling, string IV curve checks, and monthly generation reporting against a guaranteed performance ratio. It should also state a maximum response time for downtime, since an unpriced response clause is where most O&M disputes begin.

Question 41

How do I detect underperformance early?

Accepted Answer

Detect underperformance by comparing actual specific yield in kWh/kWp/day against the design irradiance baseline every week. A sustained gap of 10% or more usually means new shading, heavy soiling, a failed or disconnected string, or a derated inverter. Monthly-only checks let a dead string run unnoticed and quietly cost a full season of generation.

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