Learn how to calculate the correct solar water heater capacity for your home. Compare 100, 150, 200, 220 and 300 LPD models based on family size, bathrooms, bathing habits and hot-water usage.

How to Calculate Solar Water Heater Capacity in Litres

A solar water heater uses sunlight to heat water and store it in an insulated tank. The capacity of the system is normally mentioned in LPD, which means Litres Per Day.

For example:

• 100 LPD means approximately 100 litres of hot water can be supplied per day.
• 150 LPD means approximately 150 litres per day.
• 200 LPD means approximately 200 litres per day.

Selecting the correct capacity is important. A smaller system may not provide enough hot water, while an oversized system may cost more and require additional rooftop space.

This guide will help you calculate the right solar water heater capacity for your home, apartment, villa, hostel or commercial property.

What Does LPD Mean?

LPD stands for Litres Per Day.

It indicates the approximate quantity of hot water a solar water heater can produce and store under suitable sunlight conditions.

The actual hot-water output may vary depending on:

• Sunlight availability
• Weather conditions
• Water temperature
• Incoming cold-water temperature
• Installation direction
• Collector type
• Usage pattern
• Plumbing distance
• Tank insulation
• Hard-water scaling

LPD should therefore be treated as a practical capacity guide rather than a fixed daily guarantee.

Basic Solar Water Heater Calculation Formula

A simple calculation is:

Required capacity = Number of users × Hot water required per person

For bucket bathing, a practical estimate is:

25 to 35 litres per person per day

For shower bathing, a practical estimate is:

40 to 60 litres per person per day

Example 1: Bucket Bath

A family has four members.

4 people × 30 litres = 120 litres per day

A 150 LPD solar water heater would be a suitable choice.

Example 2: Shower Bath

A family has four members using showers.

4 people × 50 litres = 200 litres per day

A 200 LPD solar water heater would be more suitable.

Recommended Capacity Based on Family Size

Family size	Bucket bathing	Regular shower use	Recommended capacity
1–2 people	50–70 litres	80–120 litres	100 LPD
2–3 people	75–105 litres	120–180 litres	100–150 LPD
3–4 people	100–140 litres	160–240 litres	150–200 LPD
4–5 people	125–175 litres	200–300 litres	150–300 LPD
5–6 people	150–210 litres	240–360 litres	200–300 LPD
6–8 people	180–280 litres	300–480 litres	300–500 LPD

These figures are approximate. Choose a higher capacity when several people need hot water at the same time.

Quick Capacity Selection Guide

100 LPD Solar Water Heater

Suitable for:

• 2–3 people with bucket bathing
• 1–2 people with regular shower use
• One bathroom
• Small apartments
• Couples and small families

Common applications:

• Bathing
• Limited kitchen use
• Light daily hot-water requirement

150 LPD Solar Water Heater

Suitable for:

• 3–4 people with bucket bathing
• 2–3 people with shower use
• One or two bathrooms
• Medium-sized homes
• Small villas and apartments

This is a popular option for families with moderate hot-water consumption.

165 LPD Solar Water Heater

Suitable for:

• 4–5 people with controlled bucket usage
• 3–4 people with moderate shower use
• Homes requiring slightly more capacity than 150 LPD
• Two bathrooms with planned usage

A 165 LPD model provides an additional buffer without moving directly to a 200 LPD system.

200 LPD Solar Water Heater

Suitable for:

• 5–6 people with bucket bathing
• 4 people with regular shower use
• Two bathrooms
• Large families
• Villas, farmhouses and guest houses

It is also suitable when hot water is used for bathing, washing and kitchen cleaning.

220 LPD Solar Water Heater

Suitable for:

• 5–7 people
• Two or three bathrooms
• Families with mixed bucket and shower usage
• Homes requiring additional reserve capacity
• Light commercial applications

This capacity provides a useful buffer for heavy morning usage.

300 LPD Solar Water Heater

Suitable for:

• 7–10 people with controlled use
• 5–7 people with regular shower use
• Three or more bathrooms
• Large villas
• Guest houses
• Hostels
• Clinics
• Small lodges

Commercial users should calculate capacity based on actual daily hot-water demand rather than family size alone.

Step-by-Step Solar Water Heater Litre Calculation

Step 1: Count the Number of Daily Users

Include everyone who will regularly use hot water.

Example:

• Adults: 4
• Children: 2
• Total users: 6

Do not calculate based only on the number of bedrooms.

Step 2: Identify the Bathing Method

Bucket Bathing

Usually requires less hot water.

Estimated hot-water requirement:

25–35 litres per person

Shower Bathing

Usually consumes more water.

Estimated hot-water requirement:

40–60 litres per person

Bathtub Use

A bathtub may require significantly more water and should be calculated separately.

A home with bathtub usage may require a larger system or a backup heating arrangement.

Step 3: Add Kitchen and Utility Usage

Hot water may also be used for:

• Washing vessels
• Cleaning greasy cookware
• Laundry
• Floor cleaning
• Salon or clinic activities
• Guest usage

Add approximately 10–30 litres per day for light kitchen and utility use, depending on the household.

Step 4: Consider Simultaneous Usage

A family may have enough total daily capacity but still face shortages when several bathrooms are used at the same time.

Choose a larger capacity when:

• Two or more people bathe simultaneously
• Multiple bathrooms are connected
• Everyone uses hot water during the morning
• Guests frequently stay at the property
• Shower use is high

Step 5: Add a Safety Margin

After calculating the basic requirement, add a reserve of around 10% to 20%.

Example

A family requires 160 litres per day.

Adding a 15% margin:

160 + 24 = 184 litres

Recommended selection:

200 LPD solar water heater

This reserve helps during winter, cloudy weather and higher-than-normal usage.

Detailed Calculation Examples

Example 1: Three-Member Family

Usage:

• Three people
• Bucket bathing
• Light kitchen usage

Calculation:

3 × 30 litres = 90 litres

Add 10 litres for kitchen use:

90 + 10 = 100 litres

Recommended capacity:

100 LPD

Example 2: Four-Member Family

Usage:

• Four people
• Mixed bucket and shower bathing
• One kitchen
• Two bathrooms

Calculation:

4 × 40 litres = 160 litres

Add approximately 15 litres for utility use:

160 + 15 = 175 litres

Recommended capacity:

200 LPD

Example 3: Six-Member Family

Usage:

• Six people
• Mostly bucket bathing
• Two bathrooms
• Moderate kitchen use

Calculation:

6 × 30 litres = 180 litres

Add 20 litres for kitchen use:

180 + 20 = 200 litres

Recommended capacity:

200 or 220 LPD

Choose 220 LPD when all members bathe during the same period.

Example 4: Six-Member Family with Showers

Calculation:

6 × 50 litres = 300 litres

Add utility usage:

300 + 20 = 320 litres

Recommended capacity:

300–400 LPD

A 200 LPD model may not be sufficient for this usage pattern.

How Many People Can Use Each Capacity?

Capacity	Approximate users	Suitable usage
100 LPD	2–3 people	Bucket bathing and light household use
110 LPD	2–3 people	Small family with slight extra reserve
150 LPD	3–4 people	Medium family and moderate usage
165 LPD	4–5 people	Controlled usage with additional reserve
200 LPD	5–6 people	Larger family and two bathrooms
220 LPD	5–7 people	Heavy family use and multiple bathrooms
300 LPD	7–10 people	Large families and light commercial use
500 LPD	12–18 people	Hostels, lodges and commercial applications

Actual suitability depends heavily on shower duration and water-flow rate.

Factors That Affect Solar Water Heater Performance

Sunlight Availability

Solar water heaters perform best when collectors receive direct sunlight for most of the day.

Avoid installation under:

• Trees
• Water tanks
• Nearby walls
• Tall buildings
• Rooftop structures that create shade

Installation Direction

The collector should be positioned to receive maximum sunlight throughout the day. The correct orientation and tilt should be decided by a trained installer based on the property location.

Climate and Season

Water may heat faster during hot summer days and more slowly during:

• Winter
• Rainy periods
• Cloudy weather
• Heavy fog

A slightly higher capacity or electrical backup may be useful in locations with prolonged cloudy weather.

Inlet Water Temperature

Cold groundwater requires more solar energy to reach the desired temperature. Homes in colder locations may need more capacity than homes in warmer regions.

Hard Water

Hard water can cause mineral deposits inside:

• Tubes
• Collectors
• Pipes
• Storage tanks

Choose a model suitable for the local water condition and follow the recommended descaling schedule.

Length of Hot-Water Pipeline

Long pipelines may cause heat loss before water reaches the bathroom.

Use:

• Proper pipe insulation
• Shorter plumbing routes
• Correct pipe diameter

This improves efficiency and reduces water wastage.

ETC vs FPC Solar Water Heater

ETC Solar Water Heater

ETC means Evacuated Tube Collector.

It uses glass vacuum tubes to absorb solar heat.

Advantages

• Good heating performance
• Generally economical
• Lightweight system
• Suitable for many residential applications
• Easy tube replacement

Considerations

• Glass tubes require careful handling
• Water quality should be checked
• Maintenance may be needed in hard-water areas

FPC Solar Water Heater

FPC means Flat Plate Collector.

It uses a flat, insulated collector panel with metal tubes.

Advantages

• Strong and durable construction
• Suitable for pressurised systems when designed accordingly
• Long service life
• Good choice for villas and commercial properties
• No exposed glass vacuum tubes

Considerations

• Usually costs more than ETC
• Heavier structure
• Requires proper installation
• Rooftop load should be checked

Pressurised vs Non-Pressurised System

Non-Pressurised Solar Water Heater

Suitable for:

• Normal gravity water supply
• Overhead tank installations
• Standard residential use

The cold-water tank should normally be installed above the solar water heater to provide sufficient flow.

Pressurised Solar Water Heater

Suitable for:

• Pressure pumps
• High-rise villas
• Rain showers
• Multiple bathrooms
• Premium plumbing systems

Do not connect a standard non-pressurised solar heater directly to a high-pressure pump unless the manufacturer confirms compatibility.

Rooftop Space Requirement

The required space depends on:

• Capacity
• Collector type
• Number of tubes
• Tank size
• Installation angle
• Service access

The roof should be:

• Structurally strong
• Flat or properly supported
• Free from shade
• Accessible for maintenance
• Close to the hot-water pipeline

Keep sufficient space around the unit for servicing and cleaning.

Solar Water Heater Maintenance Tips

To maintain efficient performance:

• Clean dust from tubes or collectors regularly.
• Inspect the plumbing for leakage.
• Check the supporting stand for rust or damage.
• Clean the storage tank as recommended.
• Remove mineral scale in hard-water areas.
• Inspect insulation on hot-water pipes.
• Ensure the collector is not shaded.
• Arrange professional servicing periodically.
• Replace damaged tubes immediately.
• Check safety valves in pressurised systems.

Common Mistakes to Avoid

Choosing Only by Family Size

Two families with the same number of members may have very different water usage.

Always consider:

• Shower or bucket use
• Number of bathrooms
• Bath duration
• Guest usage
• Kitchen requirements

Buying a Very Small Capacity

A small system may save money initially but can lead to daily hot-water shortages.

Ignoring Water Pressure

Check whether the model supports your pressure pump or rain-shower system.

Installing in a Shaded Area

Even a high-capacity unit will perform poorly without sufficient sunlight.

Ignoring Hard-Water Conditions

Select the correct tank and collector type based on local water quality.

Frequently Asked Questions

Is 100 LPD enough for four people?

It may be enough only when usage is very controlled and bucket bathing is limited. For comfortable use by four people, 150 LPD is generally safer.

Is 150 LPD enough for five people?

It may be sufficient for controlled bucket bathing. For regular shower usage or two bathrooms, consider 200 LPD.

Is 200 LPD enough for six people?

It is generally suitable for six people using buckets or moderate hot-water quantities. For regular showers, choose a higher capacity.

Can solar-heated water be used in the kitchen?

Yes. It can be used for washing utensils and cleaning, subject to proper plumbing.

Will the system work during rainy weather?

Heating performance reduces during continuous cloudy or rainy conditions. Some models include or support an electrical backup heater.

Does a higher LPD mean hotter water?

No. LPD indicates water quantity, not necessarily temperature. Water temperature depends on sunlight, collector efficiency, season and system design.

Can a solar water heater work with a pressure pump?

Only if the model is designed for pressurised operation. Confirm the pressure rating before installation.

Simple Buying Recommendation

Choose:

• 100 LPD for 2–3 people
• 150 LPD for 3–4 people
• 200 LPD for 5–6 people
• 220 LPD for 5–7 people with heavier use
• 300 LPD for 7–10 people or multiple bathrooms

Move to the next higher capacity when your family uses showers, has multiple bathrooms or requires hot water simultaneously.

Why Buy a Solar Water Heater?

A properly selected solar water heater can offer:

• Reduced electricity consumption
• Lower monthly power bills
• Renewable energy usage
• Daily hot-water convenience
• Long service life
• Low running cost
• Reduced dependence on electric geysers
• Environment-friendly water heating

Conclusion

The correct solar water heater capacity should be selected based on more than family size. Consider how many people use hot water, whether they use buckets or showers, the number of bathrooms, kitchen requirements, water pressure and seasonal conditions.

A practical calculation is:

Number of users × hot-water requirement per person + utility usage + safety margin

For most homes, choosing the next higher available capacity provides better comfort and prevents hot-water shortages.

At LG Shopnest, customers can compare solar water heaters from brands such as Lalith Solar, Supreme Solar, V-Guard and Sudarshan Solar. Select the capacity according to your home, usage pattern, water condition and installation requirements.