Solar Geysers / Water Heating Systems – Part 2

In part 2 we look at environmental and climate considerations to help choose the right combination of solar water heating systems and collectors.

In the previous post, we got to grips with the terminology and different categories of solar water heating systems, along with their pros and cons. In this post I’ll be focusing more on specific solar geysers available in South Africa, and what to consider in terms of environment, climate and cost.

Climate Considerations

  • How many sunny days a month / a year does your area experience on average?
  • How many overcast / rainy days a year?
  • What’s your area’s UV index throughout the year?
  • Does your area experience frost or freezing temperatures? What about hail?
  • Does your area experience strong, gusting winds?

You can look up your area’s weather statistics on sites like Climate Data and World Weather Online. Suurbraak is in the Overberg region of Western Cape. Temperatures can drop to below 5 degrees celcius and the surrounding mountains can get snow. So our system will need to be tolerant to frost and freezing temperatures. Like most of the Western Cape, we experience a lot of wind, so we’ll need to take that into consideration in terms of placement and fixtures. We get a lot of rainy days and cloud cover, with a UV index of minimum 3 and maximum 7. The system we choose would ideally have good performance on overcast days and a wider angle to get the most hours of sunlight.

Environmental Considerations

  • Will you be using municipal water, pumped water or gravity fed water?
  • Is your water supply harsh (full of minerals and / or impurities) or very good?
  • What distance will the water need to travel from water storage tank to tap/s?
  • Where will you install your system? If on your roof, what angle is it at and in what direction?
Image from Photovotaic Solar Panels

Since our property is off the grid, we don’t get potable water from the municipality. We do get ‘irrigation water’, which is water pumped up from the river when available. Unfortunately the river water is contaminated with chemicals from farms further upstream, and is not considered potable. We’ll either need to filter this water before feeding it into our water storage tank, or invest in rain harvesting tanks – which would require its own filtration and pump.

Quick Overview of Systems:

DIRECT:

  • Suits high solar radiation areas
  • Suits medium to good quality water
  • Bad for frost-prone areas
  • Shorter lifespan
  • Reliable & efficient
  • High maintenance
  • Cheaper

ACTIVE:

  • More effective in cold climates
  • More expensive
  • More maintenance
  • Need additional equipment / power

INDIRECT:

  • Suits low solar radiation areas
  • Suits hard water areas
  • Suits frost-prone areas
  • Good insulation (retains heat longer)
  • Longer lifespan
  • Low maintenance
  • More expensive

PASSIVE:

  • Can fail in cold climates
  • Cheaper
  • Less maintenance
  • Lighter & greener option (no additional equipment / power needed)
  • Doesn’t suit all situations (distance to taps & angle of roof)
Image from WBDG

We’ll have to go with an indirect system – our water carries a lot of minerals and impurities, and Suurbraak can experience freezing temperatures. Indirect systems perform better under cloudy conditions, so that’s another win.

I’m leaning towards a passive system at the moment, just out of preference. However, we may need a back up water heating system in this case. The jury is still out on this one 😉

In terms of collectors, Evacuated Tube collectors appeal to me most, since they handle cold weather and high winds very well, they have a wide angle for more hours of sunlight, they work well in overcast conditions, and individual tubes can be replaced rather than having to replace the entire system.

So we’re leaning towards an Indirect, Passive system using Evacuated Tube collectors. Let’s look at pricing options here in SA:

Prices & Options

This is a pretty good deal from Solar Advice if we are willing to consider an ‘all in one’ or ‘closed couple’:

  • 18 tube collector
  • 150L low pressure tank
  • 5 year warranty
  • Stand for pitched roof
  • Feeder Tank

Price: 6,500
(excludes valves, thermostat, shipping & installation)

The price difference is enormous when you look at a solar geyser with the evacuated tubes collector separately. Sustainable have a full kit available for a 150l tank – bearing in mind this package comes with a pump and no feeder tank (note the image is not of this kit, but looks similar):

  • 150L indirect solar geyser
  • 15 Tube Collector
  • 12V Pump Kit
  • Solar Probe 22mm Brass Pocket kit
  • Valve Pack
  • 2 x 22mm Ball Valves

Price: R21,000
(excludes feeder tank, shipping & installation)

So What Have We Learned, Kids?

Overall, I feel a bit discouraged by my foray into the world of solar water heating. They’re not super cost effective, they can require a lot of maintenance or complete replacement, and you’ll most likely need a back up for winter days of freezing cold, overcast, rainy weather.

I’d love to hear from you if you’ve had a positive experience with using a solar water heater, what your set up is like and in what environment. Am I being too easily discouraged? Let me know!

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