Friday, November 16, 2018
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What is solar water heating and how does it work?

This is a question that gets asked a lot.  This article will hopefully give you some basic information about solar water heating systems and what they can, and cannot do for you.

In a nutshell we use a very simple technology to heat the water in your home or business using the sun.  Solar water heating has been around for a very long time and does work very well in Canadian climates.  However how effective it is depends where you live in Canada, this article will give you a good head start on finding out what can be done to heat buildings with solar.

The technology is very well advanced, this is not a new "emerging technology".  There is no point thinking "Ill wait a while, the technology s going to get much better".  The Evacuated tube solar collectors we use are already about 94% efficient, that is they convert 94% of all the UV light (Sunlight) into heat which heats your water.  The other 6% or so is absorbed through the glass and other losses, its a small amount.

Note:  Solar PV (for making electricity from solar) is a totally different technology.  The efficiency of Solar PV is MUCH lower, about 15%, Most of the sunlight that falls on the solar PV panels is lost or wasted, only abour 15% is tuend into electricity.  This is why the payback is so poor for solar PV. 

Anyway, back to how solar water heating works, essentially the glass vacuum tubes collect the sunlight and heat water to very high temperatures.  Our collectors will reach a maximum of 270 degrees Celcius (about 500+ Degrees F), the temperature of the fluid flowing through the collector depends on how fast the solar pump runs.  This is why evacuated tube solar systems were chosen for 88% of the largest commercial solar systems in Canada during the ecoENERGY incentive program which ended in March 2011.

OK so what can you do with it?  

Domestic Solar Hot Water
In a residential home most of the time people just use it to heat their hot water for showers, washing and other domestic hot water uses.  The system will normally heat about 50% of the total annual hot water of the house.  Remember in summer the system will do more or less 100% of the summer hot water load, in winter the amount will be less.  As can be read in out client feed back section some customers are reporting a 66% drop in their natural gas bills.
Most people simply use the solar water heating for domestig hot water for the house for the following reasons.

1.  Smaller system needed - one  30 tube solar collectors will heat the water for 1 to 3 people in a home, and 2 x 30 tube solar collectors will heat the domestic hot water for 2 to 4 people in a home.  
2.  Roof space - most houses don't have a huge amount of south facing roof space which is needed to put the solar collectors on.  Normally 2 or 3 collectors is the most space people have room for.
3.  Space in the Mechanical Room - Most houses have small mechanical rooms.  All solar hot water systems need a tank to store hot water in.  Typically the size of the tank is limited by space in the mechanical room.  Tanks sizing is a big topic and will be covered in a future article.

So for most cases one or two 30 tube collectors will be enough for most normal sized homes if you would simply like to do domestic hot water only.

Solar Space heating.
This is the one topic with solar that causes the most confusion and the most questions.  A lot of people say "I want to heat my home / garage / shop, what will this cost?"
The answer we give is nearly always ".... get a cup of coffee, sit down, grab a pen and paper and I'll try to answer that its going to take a while....."  So finally this article will hopefully try to tell you the answer.....

Can it heat my home......yes, it just depends on a lot of factors, them main ones are below.

  • Where do you live?, i.e. How cold it is where you live?
  • Do you want to use Evacuated tube solar collectors or Flat Plate Solar Collectors?
  • How well insulated is your home?
  • Do you have forced air heating or infloor hydronic heating?
  • How big is your home?
  • How much money do you want to spend?
  • Commercial Space or Residential Solar Space?


Where do you live?
If you live in the Okanagan then it will be much easier, if you live in Calgary, Edmonton or Toronto then, the answer is still yes (possibly) but it is likely to be much more expensive.  Every city has a different climate, see the article on how climate affects solar collectors, If your winters are mild then it is much easier to use solar for space heating than if you want to heat you home in January in Alberta when it is -40 Deg C.

Evacuated Tube Collectors or Flat Plate Collectors?
In general, Evacuated Tube collectors can heat your home but dont even think about trying to heat a building with Flat Plate collectors unless you have a huge amount of money to spend and have a roof the size of the local WallMart Store.  Evacuated Tube collectors can product about 12 TIMES the heat in cold and cloudy conditions (see here) than flat plate collectors do.    Flat plate collectors produce lots of heat when it is warm outside, they don't do very well when the outside temperature is very cold which just happens to be when you need the most heat.  

How well insulated is your home?
However, a very well insulated home in Alberta might be easier to heat than a old leaky house in the Okanagan or a home in Vancouver.
As a guide, in Alberta, you will need about 1 x 30 tube solar collector for every 100 square feet of home but this number will vary greatly (up and down) depending on how well insulated your home is built.
So just to give you an idea a 2000 sq foot home will need about 20 of our 30 tube collectors.    Remember this will depend on how well insulated the house is.   If you are in a normal 2x6 inch framed home with standard insulation this number might increase to 30 collectors required.  However if you have a very well insulated home (R2000 or better) you might only need 12 or 13  x 30 tube collectors to heat the home.  You will also need sufficient tank storage space for a water tank to hold about 80 gallons PER 30 tube collector.
As you can see there is a huge difference in the size of the system depending on how the house is built.  The best option is to make sure the home you build is very well insulated in the first place, it then makes heating your home much easier, especially if you want solar to help the heating.
If you are heating a shop or workspace then it is likely you will need much fewer collectors as you are not likely to be heating it to the same temperatures as your home.

Remember that if you do add solar space heating to your home, the solar will supplement your existing heating system, it can get costly to try and replace your heating system entirely and is usually not practical, unless you live in a milder climate.  For example if it is -30 Deg C around the end of December, the sun is at its lowest point in the sky so you will get the least sunshine falling on  the solar collectors.  This means in effect you have about 6 or 7 hours of sunshine to try and heat the house for 24hours a day, its not really going to work unless you built the home with this in mind.

Do you have forced air heating or infloor hydronic heating?
Most homes and a lot of commercial buildings in Canada use forced air heating.  This probably the least efficient method of heating a building every designed by man.  Its noisy, in efficient, dusty and ridiculously complicated to install.  It was invented back in the day when the oil and gas were insanely cheap and plentiful so no one really cared how well they worked as you just feed it more gas.  Air is a very poor conductor of heat, hence it needs to be heated to very high temperatures to warm your house.

In-floor hydronic heating runs at much lower temperatures, as it warms the floor you walk on, the warm floor warms your feet then the heat rises up past your body.  It keeps you feeling much warmer than blasting forced air around your building.  As the inflow heating uses much lower temperatures of water it is much better suited to solar water heating applications.

How much money do you want to spend?
This is important because if you own an older house that is not very well insulated, you would be better off spending moeny on upgrading the insulation in the house, such as sealing any leaks, or putting  more insulation in the roof space. Also if your roof area is like most peoples homes, you will only have enough space for 2 or 3 x 30 tube collectors anyway, which is more than enough to do your domestic hot water  but not enough for space heating.  However if you live on an acerage then you can mount the collectors on the ground and the roof space is not an issue.
The payback on a solar system varies enormously depening on if you are putting the system in yourself or having it proffessionally installed, also depening on what fuel you use to heat your home with.

How much you spend on the system will also depend on how you heat your home now.  If you live in Alberta then the natural gas prices are so low right now that it is almost free anyway and the costs to heat your home with solar will be very hard to justify.  However in BC and Ontario a lot of businesses still heat the buildings with electricity which not are charged peak rates during the day.  Also in Nova Scotia heating fuel costs have been rising about 10% per year and the milder climate makes heating your home with solar much easier and much more cost effectibve.

Commercial Solar Space Heating
Heating commercial building is definitely a viable project, much more so than for residential buildings.  Commercial buildings tend to have much larger roof areas where the collectors can be placed and often have some form of in-floor heating.  They tend not to be heated to the same temperature your house will be and at night it often deosnt matter if the building is little cooler.  The solar equipment also has very generouse tax benefits which enable businesses to write down the capital cost of the equipment much faster then other heating systems.

Here are a few articles that relate to solar space heating that you might find interesting
This article describes a home that tied the solar collectors direclty into the infloor heating without using a water tank for storage.  This house was in a warmer climate but it was a nice simple system that has been running for 20 years. See page 26.  Click here for solar space heating

This article describes a families DIY approach to solar heating their home.  One point to remember is in this article they mention Victoria, it is Victoria in Australia! however it is a good article.

For more information please visit the Solar School Section of the website.
For details of equipment for your solar water heating project please visit the storefront.

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