Solar Water Heater Sizing: 50-600L Guide for Importers

Two questions fill our inbox more than any other. The first is price. The second is size, and it usually arrives phrased like this: “What is your best-selling capacity?”

That question has no useful answer. The best-selling tank in Kenya is not the best-selling tank in Iraq, and a 200 L unit that flies off the shelf in one market sits in the warehouse in another. What we can do instead is walk you through how to size a system in about ten minutes, and what a wrong size costs you six months after the container lands.

Start with demand per person, not with the tank

The number you need first is not litres. It is litres per person per day. Sizing guides published by installers in our main markets generally land between 40 and 50 litres per person for ordinary shower use, and 60 to 75 litres where people use bathtubs or take long showers (EnergyBee, South Africa, 2026; Omega Boyler, Türkiye, 2026).

Multiply that by the number of users, then add a margin. The margin matters because the collector only has daylight hours to refill the tank, while hot water gets used in a rush, usually between 6 and 8 in the morning.

Who is using it	Daily demand per person	What to add on top
Family home, short showers	40-50 L	Nothing, if collectors face the sun well
Family home with bathtub	60-75 L	A larger tank, not just a bigger collector
Guest house or small hotel	50-70 L	Morning peak: several rooms draw at once
Worker hostel or dormitory	40-50 L	Timing, not volume. Baths happen in one block

Our capacity range runs from 50 L to 600 L. Above 600 L the practical answer is rarely one enormous tank. Two or three units piped together are easier to install on a roof, easier to service, and cheaper to replace when one day a single tank fails.

Three sizing mistakes that come back as complaints

We hear these three more often than any technical fault, and all three are decisions made at the quotation stage.

• Sizing on tank volume alone. A 200 L tank tells you nothing about how fast it recovers. If the collector is too small for that volume, the household gets lukewarm water every cloudy morning and blames the manufacturer, not the design.
• Ignoring the inlet water temperature. Cold mains water means more hot water per shower, because it takes more of the hot side to reach a comfortable temperature. Winter mornings in the Highveld or in northern Iraq are not the same job as a warm coastal town.
• One SKU for a whole market. Retail buyers want something that fits a small roof and a small budget. Project buyers want banked units and a proper recovery rate. Trying to serve both with one model means losing one of the two.

The part of sizing that lives in the container, not on the roof

The awkward part is this: capacity does not only change the tank. It changes how much glass you are shipping.

A larger tank needs more vacuum tubes, and tubes are the part that arrives broken when a container has been packed badly. So when you plan a product mix, the packing list per model matters as much as the price list per model. Ask for both, in writing, before you commit to quantities. If the packing sizes are not available, that is a signal about the supplier.

Getting the container plan right before production:

1. Send us the mix you want to stock, with quantities per capacity.
2. We return a loading plan: how many sets fit, how the pallets and cartons are stacked, and which surfaces get extra bracing.
3. You approve the plan before we start production. Changing a mix after the tanks are made is expensive for both sides.
4. Before loading, we photograph the braced load. Keep those photos. If a claim happens later, they are your evidence, and they cost nothing to take.

Mixed capacities in one container is completely normal for distributors, and we plan for it. What we do not recommend is adding an unplanned size at the last minute to fill leftover space. That is how the corners get crushed.

How much to order the first time

New importers tend to over-correct. They receive advice about a market, get excited, and commit to five capacities at once. Six months later the warehouse holds forty sets of the one size nobody asked for, and the cash to restock the fast mover is gone.

Our suggestion, from watching this go well and badly: start with two capacities – one gravity-fed unit for the entry market and one pressurized unit for customers with mains plumbing. Minimum order is one set, so use it. Take a sample of each, put them in front of real installers, and let the first sell-out tell you where the third capacity belongs.

Warehouse reality is part of sizing too. Tanks are bulky, they do not stack like cartons of fittings, and a slow-moving size costs you floor space every month it sits there. Ask us which capacities are commonly shipped together and how they are packed – it is usually the difference between a container that earns its freight and one that quietly eats your margin.

Nine questions to ask before you quote

Whether you are quoting a household or a 60-room hotel, these questions decide the specification. Ask them in this order and the model mostly picks itself.

• Who uses it, and how many at once? People count first, peak overlap second.
• How many litres per person? Short showers, long showers, or bathtubs.
• What is the inlet water temperature? Ask for a winter morning figure, not a summer average.
• Mains pressure or gravity feed? This is the one that decides pressurized versus non-pressurized, and it is the most common cause of a dissatisfied end user.
• How many outlets draw at the same time? Two bathrooms at 7 am is a different job from one.
• Roof type, available area, and access? Flat roof, pitched roof, or ground-mounted frames. A tank has to get up there.
• Any freeze risk? Inland plateaus and desert nights both drop further than buyers expect.
• Is there backup power or heating? What happens on the third cloudy day is part of the design.
• Who maintains it afterwards? Scale in hard water areas is normal, not a fault, and somebody has to plan for it.

What happens on our side before you get a quote

We will not size a system from a photo, and we would rather ask twice than ship the wrong tank. So the first reply to your inquiry is usually a few of the questions above, not a price.

Once the demand and the market are clear, we put together a mix across our range – for example a gravity-fed unit for the rural trade and a sealed unit for urban plumbing in the same order – and you can compare them against your own costs. If it helps you sell, we can prepare drawings for your own labelling and packaging, and send a sample unit before you commit to volume.

If you are at the stage where you are comparing suppliers rather than capacities, the material selection inside the tank is worth reading next: see our pressurized solar water tank page and the difference between a gravity-fed non-pressure solar water heater and a sealed integrative high pressure unit. The standard packaging page shows how our exports are packed for sea freight, and the full product range lists the eleven lines we manufacture in Shandong.

Usual ground rules, so you can plan: minimum order one set, production 18-25 working days, three-year warranty, and a reply within 12 hours. If you tell us the market and the daily demand, we will tell you which capacities actually make sense there – and which ones you can safely skip for the first order.