solar water heater

How Solar Water Heaters Work: A Complete Buyers’ Guide

If you’re like most people, you can’t do without your hot water. 

It’s become part of your daily life and how you work. 

Though heating water on a daily basis piles up your electricity or gas bills, you need it — just like food.

Fortunately, there’s a solution.

A solar water heater can help you cut down on your water heating energy cost. Without giving up your daily hot water needs.

Solar water heaters are becoming popular for good reasons.

For example, according to Energy Star, solar water heaters can reduce your energy costs by 50%.

In this article, we’d take you through what a solar water heater is, and solar water heater working principles. Also, we’d explain how a solar water heater works — with images — and the benefits of solar water heaters.

That’s not all. 

We also share some of the challenges with solar water heaters, and the steps to install a solar water heater in your home or office. We also share the top solar water heaters in Nigeria that you can buy.

Let’s dive in.

What is a solar water heater?

Solar water heaters are heating systems powered by the sun. It is also called solar domestic hot water systems.

A solar water heater installed on a roof top

Source: energy.gov

Imagine your hot water supply from your water heater. Now, remove the electric supply and the heater, and replace them with the sun and a solar water heater. 

You’d get the full picture once you see how it works.

How solar water heaters work

A solar water heater uses the heat from the sun to heat water that is then distributed into your plumbing system.

Below is a simple diagram of the solar water heater and how it works. 

schematic diagram of a solar water heater with a solar collector, a water tank, and connecting pipes.

Source: funscience.in

In the simplest way, the solar water heater consists of the following:

  • Solar collector: A surface that absorbs heat from the sun and transfers the heat to the water. 
  • Storage tank: To store the water. Some have separate thanks for cold and hot water.
  • Connecting pipes: To move water to and fro the tank and solar collector.

Water circulates from a cold source into the solar collector. The collector heats the water and then the water flows into a storage tank or straight into your home.

Here’s a little more detail on how solar water heaters work.

Solar water heaters can work in two ways — direct or indirect heating.

In the direct heating system, water is moved into the collector. The collector transfers the heat from the sun directly to the water and the hot water is circulated directly into your home. This method works well in areas without serious cold weather conditions.

In the indirect heating system, a non-freezing fluid is circulated around the collector. The fluid is heated and moved to a heat exchanger — a set of tubes in a water tank — where the water is heated by the fluid. The hot water is then distributed into your home.

There are two types of solar water heaters that apply the direct and indirect heating methods.

Types of solar water heating systems

There are two types of solar water heaters — active and passive solar water heaters.

Here’s a breakdown of how they work and what makes them different.

Active solar water heater

Active solar water heaters add an electric pump to the system. 

The pump helps to move water or a non-freezing fluid from the collector into your plumbing system or a water storage tank.

Here’s the diagram of an active solar water heater circulating water directly from the collector.

Active solar water heater moving water from the collector straight to the home for use.

Source: energydepot.com

Here’s the diagram of an active solar water heater moving a non-freezing fluid from the collector to the heat exchanger.

active solar water heater moving a non-freezing fluid from the collector to the heat exchanger where water is heated and moved into the plumbing system.

Source: energy.gov

Active solar water heaters work in two ways. 

In the first method. The pump circulates water from your home — or office — into the collector and then distributes the heated water back into your home. 

Here’s how the second method works. The pump circulates a non-freezing fluid into the collector. The collector heats the fluid. The fluid moves into a heat exchanger in a tank. The fluid heats the water in the tank which circulates back into your home.

In both cases, a pump helps to move the water and non-freezing fluid through the system.

Active solar water heaters have some advantages over passive solar water heaters.  

Advantages of Active Solar Water Heaters?

Here are two pros of active solar water heaters.

  • Active solar water heaters are more reliable and efficient in cold areas: Because of the pump and the antifreeze fluid, you can use it all year round and during cold seasons.
  • Active solar water heaters are easy to install: Because of the pumps that move the water around, you can install active solar water heaters anywhere and not necessarily on your roof. This makes installing active solar water heaters convenient.

Disadvantages of Active Solar Water Heaters

Here are two cons of active solar water heaters:

  • Active solar water heaters are more expensive than passive solar heaters: The pumps and other components increase the cost of installing an active solar water heater.
  • Active solar water heaters are more expensive to maintain: The pump, heat exchangers, and other components increase the maintenance need of active solar water heaters.

Passive solar water heater

Passive solar water heaters do not have a pump.

Instead, they rely on conventional current — the ability of hot water to move to the top and cold water to move down. As well as gravity to circulate water around the system.

Passive solar water heater moving water directly from the collector to the storage tank and into your home.

Source: energy.gov

Here’s how it works.

A water tank placed above the collector supplies water into the collector. The collector heats up the water — using energy from the sun. The water flows either into your home — when a tap or faucet is opened — or into a storage tank. To achieve this the collector and the tank must be at a height — on your roof for example. This enables gravity to push the water through the system and into your home.

Because passive solar water heaters do not have anti-freeze fluids, they can not be used in cold seasons. This is because, without the anti-freeze fluid that moves heat from the collector to the heat exchanger in the storage tank, water will free in cold seasons and will not be able to hold heat for long.

Advantages of Passive Solar Water Heaters

Here are three pros of installing a passive solar water heater:

  • Passive solar water heaters are less expensive: Passive solar water heaters are far less expensive than active water heaters. This is because they do not need more than a collector and a tank.
  • Passive solar water heaters are easy to maintain: You do not have much to maintain in a passive water heater
  • Passive solar water heaters are may last longer: Passive water heaters can last longer than active solar water heaters. This is because of the simplicity of the design and the low maintenance need.

Disadvantages of a Passive Solar Water Heater

Here are two cons of installing a passive solar water heater:

  • Passive solar water heaters are not reliable: Because they can not operate in cold seasons.
  • Passive solar water heaters are harder to install: This is because passive solar water heaters are bigger than active solar water heaters. Also, they need to be placed at a height.

What do you stand to gain from installing a solar water heater?

Benefits of solar water heater

By now you already know some of the benefits you stand to enjoy from installing a solar water heater. But here are six more benefits including the very obvious one.

  • Savings in energy cost: Once you install a solar water heater, you may not need to do any repairs or maintenance for years. This means you enjoy a continuous flow of hot water in your home all year round, without the high energy bill that usually comes with it.
  • Become a superhero: Installing a solar water heater means you’re contributing to the movement to rid the county of pollution from fossil fuels, reduce the earth’s carbon footprint, purify and make the planet safer.
  • Long-term investment: Once you install a solar water heater in your home, you’re set for the next 10 to 20 years. Most solar panel brands promise up to 20 years of high-efficiency use and hot water supply.
  • More efficient than just solar panels: It is more efficient to heat your water directly from the sun than first converting it to electricity using solar panels and then using the electricity to heat up your water. They also take less space than solar panels.

Solar water heaters are not all cake and roses. There are some challenges with using solar water heaters.

Challenges and disadvantages of solar water heaters

Here are three cons of using solar water heaters over traditional electric or gas-powered water heaters.

  • Need for rooftop space or elevation: In places where you do not have such a space or your roof is weak, installing a solar panel may be a problem.
  • Need sunlight: Solar collectors need sufficient sunlight to heat the water or the non-freezing fluid. In locations with low sunlight, or during rainy seasons, solar water heaters may not be effective.
  • Works only during the day: Solar water heaters only work during the day. This means if you use a direct heating system, you may not have hot water to use at night.

But these challenges can easily be overcome by having a backup traditional heating system, using active solar water heaters instead of passive heaters, and using a well-insulated storage tank — so that heat can not escape.

Frequently asked questions about solar water heaters

We dedicate the next section to answering frequently asked questions about solar water heaters. You can also speak with a solar contractor for questions pertaining to your specific needs.

Is a solar water heater worth it?

The straight answer is YES.

Here’s is why:

  • It is an initial investment that saves you thousands in energy costs for years.
  • It generally requires minimal maintenance.
  • It uses a free energy source which is the sun.
  • It is environmentally friendly, no carbon, no waste no noise.

So if you have the budget and stay in locations that receive sufficient sunlight, you should consider installing a solar water heater.

For example, in Nigeria, installing a solar water heater during the dry seasons of November/December to April can provide you a continuous supply of hot water. Without huge electricity bills or the expenses of fuelling your generator set.

How much for a solar water heater?

What is the price of a solar water heater?

It all depends on the brand you buy, the size you want, and your hot water consumption rate.  But expect to pay from 200,000 Naira and above — a few thousand rands and cedis — to get one set up for you.

In any case, know that you’d spend more in installing a solar water heater than you would spend in installing a traditional electric or gas-powered water heater. 

But here’s the catch. The long —terms savings in electrical or gas heating costs will pay for it many times over.

Do solar water heaters work at night?

Short answer? No.

This is because solar water heaters use the heat of the sun directly to heat up the water and at night the collector does not receive any sun rays.

How long does solar water heated water last?

Short answer: It depends on the insulation of your collector and your water tank storage.

If your collectors are well insulated against heat loss by conduction — that is through contact surface — and radiation — that is from the surface of the water—,  then the water can remain hot for a long time — even for days. But certainly not forever.

How do I choose a solar water heater?

Before choosing a solar water heater for your home or business you need to consider the following:

Your budget

How much you have to spend will determine the brand and size you buy. It will also determine if you’d go for the passive or active type of solar water heaters.

Your hot water needs

For a family with children and the elderly, your hot water needs may be more than that of a single person.

To meet your needs you may have to purchase an active solar water heating system with big storage tanks. 

The same goes for schools, offices, and other businesses. The size of the users will determine the size of solar collectors you’d install if you’d buy an active or passive solar water heater, and the size of storage tank you’d need. If your hot water needs are minimal, a passive solar water system mounted on your roof may do.

The sunlight supply in your area

The supply of sunlight per day and the distribution of sunlight throughout the year will determine the size of collectors you’d need if you’d buy the passive or active solar water heaters, and the size and quality of storage tank you’d buy. 

If you receive sufficient sunlight and your water needs are not much, you may only need to purchase a passive solar water heating system. This can also work if your hot water needs are high but to ensure availability all day long, an active solar water heating system may serve you better. 

On the other hand, if the sunlight is not much, then definitely go for an active solar water heating system, with well-insulated storage tanks.

Putting all this together and talking with a solar contractor will help you determine the solar water heater brand to go for and the capacity that will serve you the best.

Do solar water heaters work in rainy seasons?

No.

The reason is simple. Solar water heaters heat water using the heat from the sun. So when it rains or is cloudy there is no heat to be transferred to the water.

How often should i maintain a solar water heating system?

It depends on a number of factors.

It depends on the type and brand of solar water heater you purchase. 

For example, passive solar water heaters require little to no repairs or maintenance for at least 3-5 years of use. An active solar water heaters system may require some replacement of electrical components after about 10years. 

The bottom line is once in a while, you may need to replace some components infrequently. But in all the maintenance requirement is very low.

How hot can a solar water heater get?

It all depends on the supply of sunlight and how long it is supplied.

But generally, solar water heaters can heat water up to 85 degrees centigrade. 

Can I drink solar-heated water?

While the water that goes into the heating elements may be clean, it is advisable not to drink water that is heated by a solar heating system directly. 

Here’s why.

The materials used in the collector, the pipes, and the tank can introduce some chemical elements into the water which if consumed directly or used to cook can harm the body.

Can I combine a solar water heater with my electric heater?

Yes.

It is advisable to have standby electric or gas water heaters to augment your solar water heaters. This helps to ensure the continuous flow of hot water in case of low sunlight or during extremely cold seasons.

Is a solar water heater for me?

Yes. If hot water is a part of your daily life.

If you consistently use hot water in your home or business, then a solar water heater can help you save thousands yearly on your electricity and energy bills. 

If on the other hand you only occasionally use hot water, installing a solar water heater may not be the best financial decision even though it will save you heating costs.

How to install a solar water heater in your home

Start by analyzing how much hot water you use daily. Then calculate how much you spend on heating water monthly to see the significant savings you’d gain from installing a solar water heating system.

After that, consider your environment to see if you have room to install a solar water heating system on your roof or a landed space. If you do, your next step will be to speak with a solar contractor to determine the best solar water heater for you.

Which solar water heater is best?

Before you choose any solar water heater, consider the following:

  • Your budget
  • How many litres per day (LPD) of hot water do you need
  • The  sunlight supply in your area
  • How much do you stand to save in cost from the brand? 

Here are four hand-picked solar water heaters you can choose from.

  • Duda Solar 200L Active Split System (active)
  • Sunbank 40 Gallon Solar Water Heater (passive)
  • Clean Republic Heat Streamer (passive)
  • Northern Lights Group SWH-1 Solar Hot Water Heating Package (active)

Wrap-up

Installing a solar water heater for your home or business can be expensive, but you’d smile every other month when you pay 50% less of your normal energy bill.

We hope this guide was able to get you started. You can always speak with a solar contractor to get a quote for your specific need.

If you found this guide useful, you may also like our guide on solar power generators.

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