Monday, October 3, 2011

Solar hot water...things you need to consider

I have now had three commercial companies come and provide me with quotes for a solar hot water system for my house and I feel that it would be easy to get caught up in the sales pitch that these "environmentally-friendly" companies give you. So, here are a few things that I learnt about solar hot water systems and some of the greenwash or sales pitches I have heard.

Things you need to consider:

  • Size of hot water storage tank (this will depend on the number of people using hot water in your household)
  • Whether you want a split system or not (this is whether you want the storage tank on your roof or not)
  • Where you can and/or want to accommodate the solar system on your roof
  • What type of boosting system (gas or electricity) you want for your system
  • What orientation your roof has (use a compass to find out) and whether it will appropriately accommodate a solar hot water system (see previous post on Solar Hot Water).
  • How large your house is in area and where the areas that use hot water are (this will help you position your storage tanks and/or solar collection "panels" on the roof and whether a solar hot water system will efficiently deliver hot water to those areas)
  • How much money you have to purchase a system
  • What rebates are available to you from the government (if this an important factor)
  • What your climate is like and whether is it appropriate to a solar hot system
  • Is there enough open solar access for a solar hot water system to be effective and efficient at your location
  • The amount of structural capability your roof has and whether it can accommodate a roof-mounted hot water storage tank
  • Whether you want to show the world you have a solar hot water system (this will determine whether you are happy to mount the collector panels to achieve best orientation, if needed, or have a flat panel system on your roof)
Now here are some things I have learnt about:

  • for maximum efficiency and to increase the likelihood that I can get hot water all year round, I should be positioning my solar hot water collector panels to the north. This is particularly important for those winter months when I want to catch as much of the sun's energy as possible, when the sun is positioned further into the northern hemisphere
  • on my house this means mounting the panels on a frame, these are constructed to position my panels in a northerly direction, my problem with my position is that these potentially collector panels will still be shaded in some parts of the year and thus, boosting from either mains electricity or a gas system will be required
  • insulation of pipes between the collector panels on the roof and the storage tank below (if you're opting for a split system) will ensure maximum hot water is collected in your tank and therefore you don't loose heat through the transfer process
  • the storage tank is either boosted (from electricity or gas) or water re-circulated into the "panels" when the water is lower than sixty degrees Celsius
  • in a split system the water is pumped onto the roof with a small motor in the storage tank
  • you may require more than two "panels" on your roof if you have a particularly large family or have a significant hot water use
  • most of the storage tanks seem to have what is called a sacrificial anode, which corrodes overtime and requires maintenance approximately every five years (depending on the quality of your water)
Here are some things that I am a little unsure about and either smell of greenwash or just outright competition between businesses (there may be legislative requirements but can't seem to figure it out yet):

  • one company offers a titanium based panel which means that you can orient them outside of the optimum orientation (north) and not loose efficiency....apparently the titanium has the capability of heating hotter than the standard components and therefore can orient outside the optimum north facing 
  • consideration of winds if you are mounting your system on racks. Obviously this is important in some locations, but the amount of winds and strength that we have at my place i think is unlikely to impact on the system, but you should definitely get this checked out
  • the size of your storage tank needs to be the next size up from your current storage tank. Apparently, this is because solar hot water can only be generated during the day and not consistently and therefore for continuously available hot water, whenever you want you need a larger storage capacity. To me you just need to train your family to use hot water when available and not demand hot water anytime. 
  • If you are mains electricity boosting your hot water storage tank, you're not suppose to have this on Tariff 33 (the overnight/off-peak tariff). I am unsure about this and will have to contact my energy provider to see if this is true. The company that told me this said it was legislation. If this is the case and you only use this for hot water, again this company told me that I should have the meter for this tariff disconnected because the energy company would still charge me a service fee for this meter even if I wasn't using it for hot water heating any more.
  • the life span of these systems seem to be about 10 years, but no one will put a firm number on it and there is often the statement that the technology has improved so they are likely to last longer than this magic number. Also from the information I received from the companies it seems as if it is the storage tank that will need replacing first and this is just as you would with a traditional hot water storage tank.

A useful Australian government publication is the "Your Home: Technical Manual", which has a section on hot water systems and provides a lot of facts that you need to consider when deciding what hot water system is appropriate for you and has great tips and facts associated with solar hot water.

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