Community composting method-7: Marigold composter for an efficient solar solution

Marigol solar composter from Prudent Eco Systems, Bengaluru.

Marigol solar composters designed by Prudent Eco Systems, Bengaluru.

With 300 sun-blessed days in a year, any solar solution makes absolute sense in India, doesn’t it? When it comes to community composting, how about a composter that relies only on sunlight to get things going?

Marigold solar composter is a brainchild of Bengaluru-based Ravindra Karnad, IIT-Kanpur, Prudent Eco Systems Private Limited. That said, Marigold doesn’t have all the bells-and-whistles of a solar product. It is not fitted with PV panels but gets its name mainly because it absorbs sunlight through its roof made of high-quality acrylic.

The design

When he got down to designing the product, Ravindra’s philosophy was simple: “Composting is a natural process. Let’s use the natural elements to power it.” Rightly so, Marigold sits pretty in the garden as the sun and the wind work around it 24×7 to convert wet waste into nutrient-rich compost.

The-3-bins-1Interestingly, the design, just as the philosophy behind it, has evolved organically. Ravindra loves composting and has tried out composting methods at home. For his own product, the thought of avoiding heavy carbon footprint by making it less energy- and water-intensive dominated all other concerns and limitations.

So, Marigold underwent a great deal of transformation in design. Initially, Ravindra used cement rings instead of a steel body for the container but soon realised how unwieldy it was due to its weight. It was difficult to lift or to be shifted to another spot. This prompted him to opt for steel and it seems to be working fine.

The steel-bodied container sits below the rain-proof acrylic roof and the gap in between is covered with a strong perforated steel plate which lets in enough air. This much of air and sunlight is sufficient to set up a bacterial bonfire. The roof is easy to lift and can be left open with the help of a hook. It has a latch to help you close it tight when the work is done to avoid rodents entering the pile. Right below the container, another plate collects leachate, if any. However, in the two sites I visited to do the case study, I didn’t see any leachate leak. That means no loss of nutrition.

Bad odour & rodent issues

There was no bad odour in either of the two sites I visited. As explained above, the perforated steel layer blocks the gap between the container and the roof to keep the rodents at bay.

The capacity

The composters come in four capacities: Small (38 litres), medium (100 litres), large (175 litres) and extra-large (300 litres).

Convenience & aesthetics

It is portable. The roof protects the container from rainfall and hence, it can be placed anywhere in your garden or terrace so long as there is enough sunlight to keep the composting happening. These composters can be lined up in one spot or perhaps, you could spread them all over the garden if you do not have the luxury of sufficient space in one spot. A Marigold cluster looks elegant in your garden and you will probably stop associating composting with everything that’s “dirty” and “ugly”. Put simply, it is high on aesthetics.

The process

All you need to do is add ½ a bucket of dry leaves or cocopeat or sawdust to one bucket of kitchen waste to absorb the extra moisture. Mix the entire pile thoroughly once a day. Remember, it’s all in how well you turn the pile to aerate the decomposing mass. For ease of use, the firm sells a rake, which is an expandable fork, so that workers do not have to bend while turning the pile.


When well aerated, the possibility of anaerobic conditions and the inevitable bad odour issues diminish. The procedure goes like this: A 100-unit community needs six extra-large composters of 300 litre capacity each. According to Ravindra’s observation, 1-1.2 litre is approximately equal to 500-600 grams of kitchen waste. Each composter will hold nearly two days of kitchen waste (approximately 100 kgs) and the suggested quantity of dry leaves or cocopeat. On the 12th day, you will fill up the sixth composter. On the 13th day, you can take out the semi-compost from the first composter and transfer it to jute bags that Prudent Eco Systems sells at just Rs 30 a piece. You can let the semi-compost stay in the bag for further breakdown for 20 days more before sieving and applying it to plants.

Power & water consumption

If you decide to go ahead without a shredder as is the case at Sobha Lotus in Brookefield, then you could put zero under the power consumption column. As far water, you may have to sprinkle some in case the heat builds up inside and the substrate begins to dry up. Placing a wet jute cloth can help minimise water evaporation. Otherwise, Marigold is quite water-efficient.

No accelerators

At all the demo sites and also at Sobha Lotus, Brookefield, where this system has been installed, Marigold composters have been working without the help of any accelerators. The compost is being used for the garden.

The customers seemed to be fine with the idea of running the show without being dependent on private players to source accelerators. “The customers were fine with the process as accelerators have to be sourced continuously.”

Open to procedural modifications

I visited Admiralty Manor apartment in Indiranagar when the composting had entered its 12th day and by then, the pile was beginning get that pleasing smell. The substrate was chunky mainly because it wasn’t shredded. No leachate leak. No bad smell.

In my view, avoiding accelerators can get tricky especially with large and extra-large composters. Turning a wet pile isn’t that easy and if you fail to aerate the entire mass uniformly, anaerobic conditions may set in and begin to smell bad. Things can go haywire during labour crisis.

Says Ravindra: “We are planning to fix a stirrer in the centre to help turn the pile easily. This will work well especially with larger composters but it is still in designing stages. But the expandable fork is working quite well in all the sites where we have sold the composters. No complaints.”

Secondly, although the material taken out after 12-15 days did smell like compost, because of its chunky appearance, the unsieved output didn’t give that typical compost experience. Ravindra is open to suggesting accelerators to speed up the process and bring down the quantity of reject compost (which is nothing but the semi-composted substance that you get after sieving). When handling huge quantities of kitchen waste in a large community, you wouldn’t want to deal with piles of semi-done compost. Storage can be a problem, too.

But if you are comfortable with Ravindra’s concept, then Marigold composters will demand nothing more than a labourer to turn the piles without fail. Later, if you can make space for jute bags to store the semi-done compost, you will certainly find Marigold one of the easiest as far as the process goes.

The Prudent Eco Systems Team: (L to R) Vaishali Kerekatte, Latha & Ravindra Karnad. These Marigold composters installed here were from the first batch with a cement container. Now you get steel-bodied Marigold which are more efficient, portable and elegant.

The Prudent Eco Systems Team: (L to R) Vaishali Kerekatte-Koppikar, Latha Thiruganam and Ravindra Karnad. These Marigold composters installed here were from the first batch with a cement container. Now you get steel-bodied Marigold which are more efficient, portable and elegant.

The cost

The number of bins and the size of each bin are determined by the number of houses in the community. This solution fits right from one home to 200 homes. Due to manufacturing economics, the cost per house would drop as the number of houses in the community increases. Here is an example for a mid-size apartment complex with 100 houses.

Number of houses: 100.

Size of each bin: 300 litres with a footprint of approximately 44” x 44” (1.1 mt x 1.1 mt).

Number of bins needed: 6 (Each bin takes in waste for two consecutive days and six bins would allow composting for a 12-day composting period.)

Typical cost of such a system: Rs 1,44,000 (Rs 24,000 per bin) giving a per-house, one-time cost of Rs 1,440. This does not include VAT or freight or other levies.

Labour needed: One person for approximately two hours of works per day.

Operational cost: Apart from labour cost, the recurring cost of cocopeat/sawdust and accelerators if you decide choose to add.

Contact details: Prudent Eco Systems Pvt Ltd, No 59/5, 1st Floor, 6th Main, 17th Cross, Malleswaram, Bangalore-560 055. Contact person: Latha (9886003355); Email:

5 thoughts on “Community composting method-7: Marigold composter for an efficient solar solution

  1. I would like to buy a home composter for a family of 3 adults and two children.
    I run an organisation called Senior citizen enrichment program for the past 14 years in indiranagar. Is it possible to come demostrate the product or give a presentation. We meet every Wednesday in the evening. Myname is Venkataramanan tel. No. 9845041963.
    Email id


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