Solar Thermal · Manufacturing since 1997

Solar water heating systems, made by us — not bought in

Greentek manufactures its own flat plate collectors, absorber fins and storage tanks in Telangana, and engineers complete hot-water plants for hospitals, campuses, industry and homes — from a 100 LPD rooftop unit to a 2,00,000 LPD institutional system.

In short: Greentek India is one of India's top five manufacturers of solar flat plate collectors, producing collectors, absorber fins and pressure-rated tanks in-house at a rate equivalent to 2,00,000 litres per day of hot-water capacity every month. Systems are BIS-licensed to IS 12933 and installed across AIIMS hospitals, IITs, IIMs and medical colleges.

1997Manufacturing since
2,00,000LPD/month capacity
10.6 lakhLPD institutional installed
IS 12933BIS licensed
In-houseFins · collectors · tanks

Why buy from a manufacturer

What does "we manufacture our own collectors" actually change?

Most solar water heater suppliers in India assemble bought-in collectors. Greentek makes the absorber fin, the collector and the tank itself. That means the specification is ours to control, replacement parts exist a decade later, large institutional orders are not gated by a third party's queue, and a non-standard tank, pressure rating or heat exchanger can be built rather than substituted.
Control

Specification integrity

Copper absorber, selective coating, riser count and insulation are built to our own spec sheet — not to whatever the trader's supplier shipped that quarter.

Continuity

Spares in year 12

Institutional systems run 20+ years. Because the collector is ours, a replacement matches the original instead of forcing a full-array change.

Scale

Large orders absorbed

A 2,00,000 LPD hospital system is roughly one month of our collector output — schedulable, not a special import.

Engineering

Non-standard is normal

Pressurised tanks, SS 316 vessels, immersed heat exchangers and glycol loops are manufactured to the project, not selected from a catalogue.

Industrial & institutional — our core

Who runs Greentek solar hot water at scale?

Greentek has delivered more than 6,20,000 LPD of institutional solar water heating, with a further 4,40,000 LPD in execution, plus 3,00,000 LPD of heat-pump capacity. Installations include AIIMS hospitals at Guwahati, Bathinda, Bilaspur and Gorakhpur, IITs and IIMs, the Indian Institute of Science, and the Central Armed Forces Medical Institute.
Greentek's 20,000 LPD solar water heating plant for Flipkart — rows of flat plate collectors on a rooftop feeding two large horizontal stainless steel storage tanks.
20,000 LPD for Flipkart: rows of Greentek flat plate collectors feeding twin horizontal storage tanks. This is the architecture that scales — more banks, bigger vessels, pumped circulation.
InstitutionCapacityTechnologyStatus
Assam Cancer Care Foundation2,00,000 LPDSolar water heatingDelivered
Central Armed Forces Medical Institute1,00,000 LPDSolar water heatingDelivered
Deendayal Upadhyaya Hospital, New Delhi1,00,000 LPDHeat pumpDelivered
Indian Institute of Science, Bengaluru61,900 LPDSolar water heatingDelivered
AIIMS Gorakhpur60,000 LPDSolar water heatingDelivered
AIIMS Guwahati50,000 LPDSolar water heatingDelivered
AIIMS Bathinda50,000 LPDSolar water heatingDelivered
AIIMS Bilaspur, Himachal Pradesh50,000 LPDSolar water heatingDelivered
Lodha, Telangana36,000 LPDSolar water heatingDelivered
Dumka Medical College, Jharkhand25,000 LPDSolar + heat pumpDelivered
IIT Jammu1,20,000 LPDHeat pumpIn execution
Assam Cancer Care Foundation (phase 2)1,00,000 LPDSolar water heatingIn execution
Patna Medical College92,800 LPDSolar water heatingIn execution
IIM Jammu80,000 LPDHeat pumpIn execution
IIT Bhilai70,000 LPDSolar water heatingIn execution
L&T Constructions45,000 LPDSolar water heatingIn execution
Lodha, Mumbai (two systems)39,875 LPDSolar water heatingIn execution
IIM Sambalpur36,000 LPDSolar water heatingIn execution
IIT Jammu20,000 LPDSolar water heatingIn execution
IIM Amritsar · IIM Jammu · IIM Bodh Gaya40,000 LPDSolar water heatingIn execution

Capacities stated as litres per day (LPD) of hot water at design conditions.

Hospitals & medical colleges

Round-the-clock hot water for wards, theatres, CSSD and laundry, where a boiler outage is a clinical problem. Solar carries the base load; heat pump or existing boiler covers the tail.

Campuses & hostels

Concentrated morning demand across hundreds of rooms. Sized on simultaneous-draw peaks rather than nominal occupancy, with buffer volume to flatten the load.

Industrial process heat

Pre-heating boiler feed water, dairy and food processing, textile dyeing, plating lines and CIP wash-downs — cutting fuel burn on the lowest-temperature end of the heat demand.

A 2,000 LPD Greentek solar water heating plant — evacuated tube collector banks connected by manifold headers, feeding a vertical stainless steel storage tank on a rooftop.
Evacuated tubes at institutional scale — a 2,000 LPD plant on manifold headers. Where the duty suits ETC rather than flat plate, the same engineering applies.

Zero-capex option

Can we get the fuel saving without the capital cost?

Yes. For industrial process heat and boiler feed water, Greentek will fund, install and operate the system and charge only for the useful thermal energy delivered. The plant integrates with your existing boiler rather than replacing it, so there is no change to your process and no capital on your balance sheet.
No capex

We own the asset

Greentek funds, installs, owns and maintains the plant. You approve the roof area and the tie-in point.

Metered

You pay for heat delivered

Billing is against useful thermal energy actually supplied — not installed capacity, not sunshine hours.

Non-disruptive

Your boiler stays

Solar pre-heats the feed; the existing boiler carries the rest and remains the guarantor of supply. Nothing about the process changes.

Best suited to continuous hot water or low-temperature process heat loads — dairies, food processing, textiles, plating, hotels, hospitals and laundries.

Selecting the technology

FPC, ETC, heat pipe or heat pump — which should you use?

Use flat plate collectors for commercial and industrial systems needing durability and hard water tolerance; evacuated tubes for cost-sensitive domestic use up to about 500 LPD; heat pipe collectors where outlet temperature must exceed 80 °C or ambient drops below 10 °C; and heat pumps where hot water is needed independent of sunshine, or to cover the non-solar hours of a large institutional load.

FPC and ETC do different jobs — they are not cheap and expensive versions of each other

The two collector types fail and perform in genuinely different ways. A flat plate collector is a sealed, glazed box built around a copper absorber; an evacuated tube collector is a row of double-walled glass tubes holding a vacuum. That difference in construction is what decides which one belongs on your roof.

Greentek flat plate collectors on a rooftop — glazed panels in aluminium frames feeding horizontal insulated storage tanks.
FPC · Flat Plate Collector

Built to survive

A selectively coated copper absorber, sealed under toughened glass in an insulated aluminium box.

The speciality is durability and pressure. One rigid glazed surface instead of dozens of individual glass tubes, copper waterways that tolerate descaling, and a body rated to hold pressure — which is what makes it the collector for systems that must still be working in twenty years.

Specialises in

  • Hard and borewell water. Copper risers can be descaled, and the collector can be run indirect so site water never touches it at all.
  • Hail, stones and impact. One toughened pane over a rigid frame — no individual tube to shatter and drain the array.
  • Pressurised supply. Rated to 3 kg/cm², so it feeds mains-pressure plumbing directly.
  • Institutional scale. Modular banks to 2,00,000 LPD, serviceable in place, with spares that still match a decade on.
  • India's climate. High ambient and strong direct radiation is exactly where the flat plate is at its most efficient.

Where it isn't the answer

  • Higher first cost per litre than ETC on a small domestic system.
  • Loses more to ambient in genuinely cold climates — heat pipe territory below 10 °C.
Absorber
Copper · 96% absorptivity
Working pressure
3 kg/cm²
Capacity range
100 – 2,00,000 LPD
Made by Greentek
Fin, collector & tank
Greentek integrated evacuated tube collector solar water heater — stainless steel tank above a bank of double-walled borosilicate glass tubes on a frame.
ETC · Evacuated Tube Collector

Built to lose nothing

Double-walled borosilicate tubes holding a vacuum below 5×10⁻³ Pa around a selectively coated inner wall.

The speciality is insulation. A vacuum cannot carry heat by convection, so once the tube has captured energy very little of it escapes back to the air — which is why ETC outperforms flat plate on cold mornings, in winter and under cloud.

Specialises in

  • Cool mornings and winter. The vacuum jacket means output holds up when ambient is low and a flat plate is bleeding heat.
  • Cloudy and diffuse light. The cylindrical tubes accept radiation across a wide angle, so they keep working when the sun is not direct.
  • Cost per litre. The most hot water per rupee on a domestic system — which is why it dominates the 100–500 LPD market.
  • Higher outlet temperature for a given collector area; stagnation above 200 °C.
  • Modular repair. A tube is a consumable — replaced individually rather than as a panel.

Where it isn't the answer

  • Hard water scales the inside of the tubes and is very difficult to clean out.
  • Glass breaks — hail, stones, site traffic.
  • Standard integrated systems are non-pressurised.
Tube
Borosilicate 3.3
Absorptance
> 92% · emittance < 8%
Capacity range
100 – 500 LPD integrated
Heat loss
< 0.8 W/m²
The short version: if your water is hard, your roof takes hail, or the system has to run for twenty years under an institution's maintenance regime — flat plate. If you are heating a house on soft water in a cool or cloudy place and cost per litre is what matters — evacuated tube. Greentek manufactures the flat plate collector end to end and supplies both, so the recommendation is not steered by what happens to be in stock.
TechnologyBest suited toTypical rangeKey strengthWatch-outs
Flat Plate Collector (FPC)Commercial, industrial, institutional100 LPD – 2,00,000 LPDRobust in hail and hard water; pressurisable; long service life; serviceable in placeHigher first cost per litre than ETC
Evacuated Tube Collector (ETC)Domestic and small commercial100 – 500 LPD (integrated)Lowest cost per litre; good in diffuse lightGlass tubes are breakable; scaling in hard water
Heat pipe collectorCold climates, high-temperature process heatUp to 1,00,000 LPDWorks below 10 °C ambient; delivers above 80 °C; one failed tube does not drain the arrayHigher cost; over-specified for simple bathing loads
Heat pump24×7 institutional demand, low roof area10,000 – 1,20,000 LPDSun-independent; small footprint; pairs with solar to cover night and monsoonConsumes electricity; needs airflow and acoustic planning

Large institutional systems are frequently hybrid: solar as base load, heat pump for continuity. Both are supplied and integrated by Greentek under one contract.

Greentek evacuated tube collector array with a central manifold, ground-mounted on a frame at an installation site.
Manifold-type ETC array. Above the integrated domestic format, evacuated tubes are built as modular banks feeding separate central storage — the same architecture as a flat plate array.

Engineering capability

How a large Greentek system is actually built

Above roughly 5,000 LPD, a solar water heating system stops being a product and becomes a plant — pumped circulation, freeze and stagnation protection, heat exchange and controls. This is the part most suppliers subcontract.

Schematic of a Greentek forced-circulation indirect solar water heating plant: collector array, glycol primary loop with pump and differential temperature controller, storage tank with immersed heat exchanger, heat pump or boiler backup, and hot water distribution.
A typical institutional plant. The glycol primary loop is closed, so hard or saline site water never enters the collectors — the single biggest determinant of service life on borewell-fed sites.
Hydraulics

Forced circulation

Pumped collector loops with balanced arrays, air venting and expansion control, sized to the real simultaneous draw rather than nominal occupancy.

Isolation

Indirect glycol loops

Glycol on the collector side keeps hard or corrosive site water out of the collectors and protects against freezing at altitude and in the north.

Heat transfer

Immersed SS 316 exchangers

Ladder-type heat exchangers built into the storage vessel — used on projects such as the ESIC 400-bed hospital at Visakhapatnam.

Controls

DTC panels

Differential temperature control starts circulation only on useful gain, with pump sequencing, backup interlock and fault indication.

  • Horizontal cylindrical tanks with manhole
  • 4 kg/cm² rated vessels
  • PUF-insulated storage
  • SS 316 construction
  • Boiler / heat-pump interlock
  • Modular collector banks for large capacity

Homes & housing

What size solar water heater does a home need?

Size on hot water actually drawn, not on family size alone: roughly 100 LPD serves two to three people for bathing at 60 °C. A typical Indian household of four uses a 200 LPD system; villas with multiple bathrooms or a bathtub move to 300–500 LPD. Where water is hard or hail is a risk, choose FPC over ETC.
SegmentCapacities manufacturedTypical configuration
Domestic100 · 125 · 150 · 200 · 250 · 300 LPDThermosiphon — N, P or HE variant
Large residential & small institutional400 · 500 · 750 · 1,000 LPDThermosiphon, 60 °C or 80 °C delivery
Institutional & industrial2,000 LPD to 1,00,000 LPDForced circulation, engineered per site

Three system types — and your water decides, not your budget

Type N

Non-pressurised

For gravity-fed installations where the overhead tank supplies head. The standard, lowest-cost configuration.

Type P

Pressurised

Where hot water must arrive at mains pressure — multi-storey homes, hotels, anywhere a pressure pump feeds the plumbing.

Type HE

Heat exchanger

Where the supply is hard or saline. Site water never enters the collectors; heat crosses through an exchanger instead. The right choice on most borewell-fed sites.

Storage is SS 304, TIG welded, PUF insulated and fitted with a sacrificial anode; delivery temperature is 60 °C to 80 °C depending on configuration. Greentek supplies domestic systems through a dealer and channel-partner network built up since 1997. Apartment projects and gated communities are handled as central plants rather than many individual roof units, which lowers cost per litre and takes the maintenance burden off residents.

Trade, OEM & channel supply

Can we buy collectors and fins rather than complete systems?

Yes. Greentek supplies bare flat plate collectors, absorber fins and storage tanks to other manufacturers, EPC contractors and dealers. Absorber fin output runs to 20,000 fins per month — nine fins make one 125 LPD collector — and collector and tank production is equivalent to 2,00,000 LPD of hot water capacity per month.
Component

Absorber fins

Copper absorber fins with selective coating, supplied loose to collector manufacturers. 20,000/month capacity.

Component

Bare collectors

Complete FPC units to Greentek specification, or built to a customer's drawing for OEM branding.

Component

Tanks & vessels

SS 304 TIG-welded and PUF-insulated storage as standard; SS 316 and vessels with immersed heat exchangers to order.

Backward integration into fins is unusual in the Indian market — most collector manufacturers buy the absorber in. It is the reason Greentek can hold cost and specification on large orders, and the reason other manufacturers buy from us. See how we manufacture.

Approvals & quality

Is Greentek approved for government and institutional tenders?

Greentek holds a BIS licence to IS 12933 — the Indian Standard for solar flat plate collectors — and is registered with the MNRE, NEDCAP (Telangana's renewable energy agency), NSIC and as an SSI unit, under ISO 9001:2015 and ISO 14001:2015 management systems. These are the registrations institutional and CPWD-route tenders normally require.
  • BIS — IS 12933
  • MNRE registered
  • NEDCAP registered
  • NSIC registered
  • SSI registered
  • ISO 9001:2015
  • ISO 14001:2015

Certificates available on request for tender submission.

Working with us

How does a solar water heating project run?

  1. Load assessment

    Actual hot water demand, draw profile, water quality and available roof or ground area — not a rule-of-thumb per head.

  2. Design & offer

    Technology selection, array and storage sizing, hydraulic scheme, backup integration, and expected fuel or electricity displaced.

  3. Manufacture & install

    Collectors, fins and tanks built in our own plant; supply, installation, testing and commissioning under one contract.

  4. Service life

    AMC, descaling, glycol replacement, pump and controller service, and spares that still match the original array a decade on.

Questions buyers ask

Solar water heating — frequently asked questions

Tell us your hot water load. We'll size it.

Send your daily requirement, usage pattern and location — we'll return a sized scheme, the technology we'd recommend and what it displaces in fuel or electricity.

Request a system designSee how we manufacture