Category: Solar Hot Water

Freezing A Solar Hot Water System

Before you look at buying a Solar Hot Water System think about the freezing risk.

It might not be a concern in many areas but in Victoria, Tasmania and the colder parts of other states freezing conditions can damage cheaper systems.

What is the Problem?

The more basic systems have the water from the mains flowing through the panels and on to the storage tank, a direct system.

With a prolonged period of temperatures below zero the water can freeze.

As the water freezes it expands stressing the panels and pipes causing leaks.

What is the Solution?

The problem is well understood and can be solved by specifying an indirect system.

These systems use a different liquid to transfer the heat from the panels to the water in the tank, which is kept separate from the water going to your taps

This liquid may be water with an antifreeze additive or even water kept at a lower pressure.

 

Thanks to Save H20 for alerting me to this issue

 

Will Your Roof Take Solar Panels?

Plenty of people are thinking about solar panels as they can save a lot of money.

But is your roof strong enough?

In the old days a house roof had a good factor of safety so they could take the additional weight of solar panels, or a solar hot water system easily.

These days it would seem some builders are cutting costs by using lighter trusses in the roof.

This means that the roof doesn’t have  the strength to take the weight of solar panels.

I have heard of new builders asking for $300, or more to upgrade the roof.

If you think you might want solar panels, and I suggest that it is a good idea, make sure you ask the builder if the roof is strong enough.

Solar Citizens

Do you want to be a Solar Citizen?

Do you know who the Solar Citizens are?

 

Well I only found out about them a couple of weeks ago.

Basically they are a nationwide group of people that support a more sustainable future.

Amongst other things they are campaigning for are ‘Better Feed In’ rates for people with Soalr PV panels on their roof . . . . they believe a fair rate for Feed In Tariffs is between $0.10 and $0.18 rather than the $0.05 to $0.08 you might be currently getting!

 

To find out more follow the link below

www.solarcitizens.org.au

Three Reasons Why Natural Gas Isn’t Better Than Electricity

With all the publicity about rising gas prices the gas networks must be feeling the heat. (AAAARGH what a shocking ‘Dad’ Joke)   

Why else would I find an article on my Facebook feed entitled ‘Three Reasons Why Natural Gas Is Better Than Electricity’   

Like a lot of advertising there is a fair bit of Bull Dust around so lets look at what they say, (with my comments in Italics afterwards)

1. It’s always there when you need it

Natural gas infrastructure allows distributors to deliver gas to customers on demand, without the supply and reliability issues associated with electricity. In fact, when it comes to reliability, Australia’s natural gas network experiences only one unplanned outage, on average every 40 years.

But when it happens it can be a big one!  After the Longford Gas Disaster in 1998 the Whole of Victoria had no gas for more than 2 weeks. Daily cold showers over that one period was worse than the total of around 50 hours (say 2 hours a year) of power cuts over the last 25 years!   We were just happy that we didn’t have gas cooking.

Also what about these articles on the upcoming   Gas Shortage   that forced Malcolm Turnbull to step in

 

2. It’s up to 40% cheaper than electricity to use

Natural gas has always been consistently affordable and is likely to continue to be so well into the future. Unlike electricity, where increased consumption drives your tariffs higher, generally the more gas appliances you install the more you can save. This is because in most cases, the cost per unit of gas decreases as consumption increases.
While gas appliances may cost a little more to install initially, running costs are generally lower. This means that using natural gas almost always works out cheaper in the long run.
For example, take one cook top and hot water system running in an average Australian household for one year:

  • Running on electricity, the cost would be $1,156 p.a. in South Australia and $1,235 p.a. in Victoria.
  • Running on natural gas, the cost would be $782 p.a. in South Australia and $725 p.a. in Victoria.

Installing a heat pump would save 50 – 60% of the electricity costs. That would bring electricity costs down to below gas.   A solar hot water system with electric boosting could save more . . . . and think of the savings if you could get rid of the gas standing charge!

3. It produces significantly less greenhouse gas emissions than electricity

Yes, natural gas is a fossil fuel, but it is also far more environmentally friendly than electricity. Its chemical structure is quite different to coal, meaning its emissions are much lower.
Here are some quantifiable examples of why natural gas is a better environmental choice:

  • In South Australia, a gas powered hot water system emits 67% less CO2 than an electric equivalent
  • In Victoria, a gas powered hot water system emits 83% less CO2 than an electric equivalent
  • The emissions from a natural gas powered hot water system is on par with those produced by a system using 50% renewable energy and 50% coal electricity mix.
  • Gas currently delivers 44% of Australia’s household energy, but only produces 13% of household greenhouse gas emissions
  • Gas has a higher yield rate* from extraction to delivery (90%) compared to electricity, making it far more efficient.

With either of the alternatives mentioned in my response to Point 2 above the CO2 for electricity drops dramatically.   I also have 3kw of solar panels on the roof of my 2 bedroom unit,  on current performance it looks like I will be generating more power than I consume* . . . . Net effect no CO2 generated.

Although gas does have a higher yield rate what they don’t say is gas appliances have a lower efficiency typically 70 – 90% compared to electricity. Even the most basic electricity heater is 100% efficient. Some heat pumps are better than 300% efficient (for every kw going into the unit it delivers 3kw of heat)

Conclusion

If you want good advice on hot water, cooking, and heating your property don’t rely on the gas networks (or the electricity networks) . . . . find some independent advice, like this blog.

 

* Between when my solar system was switched at the end of January 2017, and 15th May 2015, I have generated 510kwhrs more power than we have used. I know I won’t be generating as much for the next few colder months, but I did miss out on a peak generating month of January.

 

Solar Panel Alignment (Revised 2015)

The suns position in the sky varies throughout the year and over each day.

The ideal situation is when the sun is hitting the panels closest to a perfectly perpendicular angle (90°).

So in Australia, what angle and orientation are best?……….. Well when mounting solar panels there are two elements of the alignment that affect the final efficiency of the panels.

 

Orientation – the compass direction the panel faces

Ideally in the southern Hemisphere solar panels should be facing as close to true North as possible to reduce the impact that the Winter seasons have on efficiency. Once the angle is above 30 degrees from North the efficiency really starts to drop away.

 

Tilt – the angle from the horizontal

The tilt is the angle that the panels are facing up into the sky. On a flat roof, the tilt is 0°, whereas if the panels were on a wall, it would be 90°.

The best tilt angle for more even efficiency throughout the year is generally the same angle as the degree of latitude of the site. Best for if your only power supply is solar.

Flatter tilt angles increase the power generated during summer, but reduce the winter power generation. If you have a system connected to the grid then you can go 15 degrees flatter than the degree of latitude without losing annual efficiency. (It can even help if your roof doesn’t face directly North)

 

Alignment Efficiency Table

The  table below provides an indication of the approximate solar panel efficiency levels for Melbourne for various alignments.

Orientation

Tilt

15 degrees flatter

Angle of latitude

15 degrees steeper

North

100

100

94

30 from North

98

96

90

60 from North

93

89

82

90 from North

86

79

71

The following site will carry out calculations for sites around the world:

http://pvwatts.nrel.gov/version_5.php

2015 Update

I first wrote this post in 2012 but since then a fair bit has changed.

Off Grid

If you are going to be ‘Off Grid’ its still best to have panels at the optimum alignment.

Grid Connected

If you are still connected to the grid the ‘Feed In Tariffs’ are now that low that there are real advantage in a more westerly alignment.

This means you are generating more power in the late afternoon-evening when you are most likely to be home and using it.

As the cost of panels has gone down it can also be more economical to have a couple of extra panels; rather than pay for angled mounting brackets.

For more Green Ideas see Sustainability

For problems see Reasons For Low Output

 

Solar Electricity To Heat Water

Do you need a separate solar hot water system?

Could you just heat the water by electricity generated by your Photo Voltaic (PV) solar cells?

I have carried out a desktop exercise to help you review the options.

Solar Water Heaters

There are now hundreds of thousands of solar hot water heaters installed around Australia so the technology is well understood.

One of the main reasons for their choice is they are fairly simple.

Also they are very efficient, as around 60% of the sunlight that falls on the panel is converted to usable heat.

This efficiency has meant that the panel size can be kept relatively small.

 

Direct Heating with PV Panels

Efficiency of Solar Photo Voltaic (PV) is much lower than solar hot water at around 20%.

To provide comparable direct heating using PV panels and an immersion type heater will need an area of panels larger compared with a solar hot water heater.

How Many Panels Will Be Needed

The equation for calculating the power to heat water is:

kW hours = litres  x temperature rise in degrees centigrade / 853

Assuming the incoming water will be around 16ºC you are going to need to raise the temperature to around 60ºC

for 200 litres of water the equation becomes:

kw hours = 200  x  44 /853  =  10.3 kwhr.

1,000 watts of panel on average generates around 3.5 kw hours per day .

So to provide hot water by PV panels you will need around 3,000 watts, a considerable area, and expense.

 

Using A Heat Pump With PV Panels

One way of reducing the area of PV panels needed for water heating is to install a heat pump.

The most common hot water heat pump systems extract heat from the air.

Efficiency of heat pumps does vary between winter and summer  but an overall Coefficient Of Performance (COP) is typically around 3.

That is for every 1 kW of electricity 3kW of heat are produced. (300% efficiency)

West Facing Solar Hot Water System?

If you are committed to sustainability then space on the North facing roof is at premium.

One option may be to look at putting the solar hot water system on a West facing roof.

This will mean you can maximise the space for north facing Photo Voltaic (PV) solar panels.

Although the solar hot water system will not be quite as efficient there are a couple of reasons why it is a worthwhile option.

    • If you check the solar alignment post you will see that its possible to get around 80% of the maximum efficiency compared with a North Facing system.
    • For most families the time when you will be using most hot water is the evening and early morning. The West facing system will have less time to lose heat before use than the North facing system.

I’m not saying West facing is best but it can be a good compromise.

 

For more Green Ideas see Sustainability

 

Solar Hot Water

With the current emphasis on building efficiency solar hot water systems are pretty much a standard option if not automatically included.

These systems incorporate either gas or electricity boosting for cloudy days.

Here are a few thoughts on the options for solar hot water:

Split System or Tank On Roof

  • Systems with Tanks on the roof are the most efficient . They don’t need a circulation pump to circulate the hot water to the storage tank and don’t have long pipe runs that lose part of the heat you have collected. If this is the way you decide to go make sure your roof has been designed to take the load.
  • Split systems are easier to service when they go wrong as everything other than the panels is at ground level. Many people also prefer the look as they don’t like the large tank on the roof for aesthetic reasons.

Flat plate or Evacuated Tube Panel

  • Evacuated tube systems are more effective. Also from comments on forums I hear 2mm evacuated tubes are stronger than flat plate collectors in the case of large hail, and are less likely to be hit square-on, due to their shape. Just make sure you aren’t getting cheap quality thinner walled tubes.
  • Modern good quality evacuated tube and flat plate systems should be essentially maintenance-free. Just make sure of the quality, it can cost $300-$400 in labour to replace a defective panel even if the actual panel is replaced under warranty.

Insulation

Some of the early Solar water systems only insulated the hot water coming from the system. This is poor practice as once the system starts running the water from the storage tank back to the panels warms up. If this cools in the pipes to the panels you will be loosing efficiency. Make sure you have all pipes insulated.

Boosting Systems

  • I think Gas Boosting is probably the best way to go even if you have the higher priced bottle gas rather than mains gas. This is because gas systems only boost the water when you want it rather than electricity where you are heating the whole tank up even if you are only using 10% of the contents.
  • If you `go for electricity its best go for an off peak boosting, but only switch it on if the forecast is for cloudy weather.

 

See why a West Roof Mounting may be worth thinking about

For more  information on choosing systems for your new house see  ‘Selection / Pre-Start Guide’

 

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