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Residential solar power systems - how to heat water in your home using alternative solar energy

Updated on October 20, 2011

Introduction

Recent improvements in the design of solar hot water technology has made it a much more interesting and affordable option for those who want to reduce both their heating bills, hot water bills and carbon footprint.

It is no longer necessary to live in the Caribbean or in Africa to install an economic solar hot water system.

For example, throughout the UK, with modern solar hot water systems it is economical and cheaper over a number of years to use a solar hot water heater than a conventional one powered by electricity or by gas.

This article explains how solar energy can be used to heat water in your home, and sets out the main types of residential solar power systems available.

It also provides diagrams and videos for those main types of system, and a guide to working out whether it is worh it financially to install solar powered water heaters.


Average solar irradiance across the world, show in watts per square metre per 24 hours
Average solar irradiance across the world, show in watts per square metre per 24 hours

How residential solar power systems work to heat water in your home

A solar hot water installation in a residential building usually consists of solar panels to collect the sun’s energy, and a system to move the heat from the solar collector to a tank where it can be used.

Solar panels are usually put on the roof of a building because that enables the most energy to be collected by the panels.

A solar thermal collector which collects the sunlight in order the heat the water is a much more simple type of technology than panels which collect sunlight in order to generate electricity.

Many solar hot water systems in most of the world will need a back-up energy source, particular in winter when sunlight is uncommon and the days are short.

Solar hot water systems use both direct and defused sunlight, so the sunlight doesn’t need to be shining directly on your collector at all times in order to heat your water.


Different types of solar power water heaters

There are two main types of solar hot water residential systems.

The first is a compact or passive system, and is simpler to install and more basic in design (and therefore cheaper) but is less efficient in collecting the sun's energy and does not cope well with cold weather.

The second is an active system, which is more expensive, more complicated, but more efficient and better able to cope with freezing conditions

Solar Power Your Home For Dummies
Solar Power Your Home For Dummies

A fantastic guide to using solar power in your home, economically and easily.

 

Passive solar powered water heaters

In a passive system, there is no external energy input such as electricity to pump water around.

The first type of passive system is an integral collector. In this type the water tank is both the storage place for hot water and the place that collects the sunlight to heat it.

It is in effect a large water tank on the roof of a house where the water inside it is heated by sunshine.

They are not particularly suitable in climates without good and constant sunshine or in places where it can get cold. They are simpler and cheaper to run than other systems, but are less efficient.

In a Thermosyphon, the water tank is installed higher than the collector for the solar energy. Warm water rises after being heated, and cold water sinks back into the collecting panels.

Again, this is not a great system unless you live in a very hot place and there are risks if the temperature drops below freezing.

In addition, if it gets really cold at night even if not freezing, the process can go into reverse and water flows from the tank into the solar panels.

It is again, a cheap and reliable solution so long as you live in a reliably sunshiny place.

Active solar powered water heating systems

Active systems pump and control the hot water, and do generally use electricity to do so.

This slightly reduces energy saving and carbon footprint saving, but the systems are generally far more efficient and better able to cope with cold weather.

In active systems, the tank is inside the building and water is pumped from the solar energy collection panels to the tank as it heats up.

Many of these systems are a closed loop, which means that they use a heat exchange.

This means that the solar panel system and the fluid in it is sealed, and the water in the tank is not heated directly by the sunshine but the heat is transferred from the fluid heated by the sun into the water in the tank.

This has advantages, as antifreeze can be put in the closed loop, and there is less of a risk of limescale and other gunk building up in the closed loop system as the fluid is not continuously replaced.

How to tell how efficient a particular solar energy water heater is

Solar Energy Factor (SEF) is defined as the amount of energy released by a system divided by the energy put into the system to run it, electricity or gas.

The higher the number the more energy efficient the system is, and energy factors of at least 2 or 3 should be looked for.

There are also Solar Fraction (SF) ratings. The Solar Fraction is the proportion of the total conventional hot water heating load (delivered energy in tanks standby losses).

The higher the Solar Fraction the greater the solar energy contribution to your water heating, and the less other energy is needed in back-up water heaters.

You should be looking for 0.5 to 0.75 solar factor when choosing a heater.

Back-up systems for solar powered water heaters

If you buy a residential solar power system for heating water, you must be prepared for times when there will not be enough sunshine to heat the water properly.

It is generally the case that they either use your existing home system as back-up for when the weather is not suitable, or include an immersion switch on the solar tank, or have a type of combination boiler which heats hot water on demand when the water heated by solar energy is too cool.

Map of solar electricity potential in Europe © European Communities, 1995-2007; (Reproduction is permitted provided the source is acknowledged)
Map of solar electricity potential in Europe © European Communities, 1995-2007; (Reproduction is permitted provided the source is acknowledged)

Working out whether it is economical to use solar energy

In many western countries, there are significant tax breaks and incentives for installing green types of energy.

When considering the cost of installing a residential solar energy system, you should check out and include in your calculations any tax you can reclaim or subsidies which are applied by local or national government.

In order to work out how much of your hot water can be generated in your specific house, taking into account where the panels could be located, you will need to get a quote of the estimated energy which could be generated from a particular system on your house per year.

Obviously these estimates can’t be exact, as it depends on the sunshine. Solar energy providers in the UK tend to give a range of plus or minus 20%.

This will give you an idea of whether it’s economically worthwhile to do it.


Comments

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    • poetryman6969 profile image

      poetryman6969 3 years ago

      When I lived in New Mexico, the air was so dry that you could cool a dwelling by what was called "swamp coolers". They cool the air by evaporation. I never looked into it when I was there but I imagine that all over the southwest that solar water heating could be a good way to go.

    • alanlsg profile image

      Alan Bowman 6 years ago from The World

      Your hub was so prescient when you look around you now and have voted it up useful interesting and awesome.

      Keep spreading the message.

      Kind regards

      Alan

    • SallyTX profile image

      Sally Branche 7 years ago from Only In Texas!

      I sure wish we had more solar water heaters here in the US! Voted up and useful! :)

    • LondonGirl profile image
      Author

      LondonGirl 8 years ago from London

      Couldn't agree more with you.

    • DIYSolarEnergy profile image

      DIYSolarEnergy 8 years ago from USA

      Great hub on solar water heating...it's time to stop relying sooo much on fossil fuels and take advantage of a natural resource.

    • LondonGirl profile image
      Author

      LondonGirl 9 years ago from London

      Not exactly lazy, there's a fair amount of stuff about at the moment!

    • Uninvited Writer profile image

      Susan Keeping 9 years ago from Kitchener, Ontario

      Excellent hub. I'm a bit late reading through the hubs...been a little busy :)

    • LondonGirl profile image
      Author

      LondonGirl 9 years ago from London

      It would indeed - my next solar hub, to be found here, gives the details of generating electricity at home using solar power:

      https://hubpages.com/technology/Residential-solar-...

    • JamaGenee profile image

      Joanna McKenna 9 years ago from Central Oklahoma

      I'd think it'd be feasible to have additional solar panels to generate the electricity to run the pump for the active solar water heating system. ???

    • LondonGirl profile image
      Author

      LondonGirl 9 years ago from London

      Hi Brian - even in the UK, not top of anyone's list for constant sunshine, these are becoming economical.

      NMS - I agree, it's an important source of green energy.

    • nms profile image

      nms 9 years ago from Cochin

      save earth..promote solar enery source

    • BrianS profile image

      Brian Stephens 9 years ago from Castelnaudary, France

      Very useful information and something I really need to look into, energy costs using fossil fuels are rising exponentially so apart from the fact they are not considered environmentally friendly they really are expensive. This has to mean that the break even point of installation costs versus operational savings must be coming down with respect to time.

    • LondonGirl profile image
      Author

      LondonGirl 9 years ago from London

      Sounds like a great place for solar energy, then! This hub is only on hot water - other uses of solar energy coming soon.

    • Teresa McGurk profile image

      Sheila 9 years ago from The Other Bangor

      I'm bookmarking this one to come back to. I have got to get solar panels for my house -- it's kinda criminal that I don't already have them. The sun shines here all day every day 355 days of the year.

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