Fullscreen HTML5Med Res (??MB)HTML4

How To Cut Yo Greenhouse Em More environmental surprises – how solar water heating can be worse than gas, about fake “green electricity” and are carbon offset schemes the answer? I n last month’s article, I said that solar water heating was an excellent idea. I lied! Well, maybe not completely but I have to tell you a longer story. Seventeen years ago I connected solar water heating panels to our electrically heated off-peak hot water service. It’s still working – that’s the good news. The not-so-good news? Before the installation we used 4300kWh per annum for water heating, since then 2800kWh. This is a reduction of 35%. Why is it so modest? Competition! The big problem is that the solar and the electric booster compete with each other. If it is a cloudy day, then overnight, electricity heats the water. If the following day is sunny, the solar has not much to do. The temptation of course is to turn off the electric heater altogether and go 100% solar. This often works quite well for a while a time in the summer months. Then the inevitable happens – you run out – and you are the bad guy – the greenie! Here is a graph of my home electricity use for domestic water heating. Obviously 1989 was the year we installed the solar panels. What about the years 1986 – 1996? Why was it always climbing? The answer: Teenagers! We had two boys. By 1997 they had started to behave more responsibly. By about 2003 they had both moved out, as you can see from the graph. In fact you can almost read the history of the family through the hot water service! Solar water heating: does it really save money? The map below shows the proportion of solar contribution you can expect across Australia. As you can see, you need to live in Cairns, Brisbane, Perth or Darwin to get more than 75% from solar. That last bit boosted by electricity is the unfortunate part. Let’s consider water heating from the greenhouse gas perspective. One kWh of electricity produced by burning brown coal (as we do in Victoria) produces 1.3kg of carbon dioxide. So our solar panels were reducing our CO2 from 5.6 to 3.7 tonnes per year. That’s moderately good. However, what if we had just opted for a normal natural gas water heater? The answer to that can be obtained from 10  Silicon Chip siliconchip.com.au our missions Part II by Peter Seligman, PhD the Rheem hot water manual. Rheem manufactures both electric and gas heaters and the answer is that we would have used 62MJ/day, equivalent to 6300kWh per annum, more than with the pre-solar electric tank but the carbon dioxide emissions would have been only 1.4 tonnes per annum – less than half of the solar system. Preheat your water with solar and save! I was not planning to take out my solar system and simply replace it with a gas one. There is a much better way. That is, to use the existing solar as a pre-heater for one of the new generation instantaneous type systems. This is no greenie “Heath Robinson” idea, at least four major manufacturers of hot water systems now offer it. It offers the best of both worlds – a solar system that can do its best without interference from a booster and a gas heater to do the rest. Even better, the instantaneous system does not have heat losses associated with having a flue. I was horrified to discover that a conventional gas storage heater uses 25MJ/day just keeping the water hot without any being used. To supply 150 litres per day it uses 62MJ/day. When the unit is sitting there doing nothing while you are away on holidays, three equivalent 100W light globes of heat are going up the flue, all day every day. It’s a pretty good reason for turning it off when you go away! The electric storage tank, having no flue, has much lower losses, one 100W light globe, on 24 hours a day. That’s equivalent to four Melbourne-Sydney trips a year! The gas instantaneous boosted solar system wins handsomely over the others. To summarise: kWh per year 4300 Tonnes of CO2 per year 5.6 Solar with off-peak electric 2800 3.7 Gas storage heater 6300 1.4 Solar with instantaneous gas boost 3000 0.7 Type of water heater Off-peak electric Don’t even think about taking out gas to put in solar! siliconchip.com.au You might ask: why didn’t I do this years ago? Water heating by using electricity is obviously a silly idea – I must have known that. Well I did. But there were several other thoughts. One was that using gas is using a limited resource, whereas there is so much coal that we will never be able to use it all. The other thought was that coal fired power stations cannot be rapidly turned off and on. That’s why the power companies sell off-peak electricity very cheaply. The thought that I had was that the coal burnt overnight will be burnt anyway, whether we use the electricity or not. That’s why they were selling it for a third of the normal price. This was my thinking. So ideally, if you remove yourself from the off-peak load, it would be good to remove yourself from the peak load too. We’ll get on to that shortly. Heat pumps? I have mentioned the advantage of gas to boost solar but I realise that not everyone has this option. A good alternative, although expensive, is the heat-pump water heater. Examples can be checked on www.enviro-friendly.com/ quantum-heat-pump-water-heater.shtml and www.rheem. com.au/domestic product.asp?model=551310 Heat pumps work by pumping heat from the surroundings into the water, in the same way as a reverse-cycle airAugust 2007  11 conditioner can pump heat into the house. Heat pumps can provide about three times as much heating as a resistive heating element. The advantages are that you don’t need a north facing roof, and you don’t need a gas supply. The bigger picture So far I have concentrated on water heating, because water heating takes about half of the energy used in a household. However, now let’s look at a bigger picture, the normal electricity load for lights, fridge etc. For us, that’s about 2700kWh/year, which translates into 3.5 tonnes of CO2/year for electricity generated from coal. Before our change to low energy lamps, it was about 4000kWh/year – 5.2 tonnes. From that down to 3.5 tonnes was a big improvement but what’s the next step? Eliminate the 3.5 tonnes! That could be in done in two ways. We could either spend $18,000 on a grid-connected solar photovoltaic system or for about $150 per year, buy electricity from a renewable source. For a very obvious reason, we chose the second option. A word of warning about “green” or “renewable” electricity: you almost certainly have been approached by an electricity company offering “100% renewable” for no extra cost. Don’t believe a word of it! If you have already signed up for this, check your electricity bill. It will tell you how much CO2 has been emitted. My first “100% renewable” bill, reproduced below, said “Total greenhouse emissions for this bill: 1.08 tonnes. Total greenhouse savings for this bill 0.15 tonnes”. Huh? Run all that past me again? How one can describe that as 100% renewable source is a mystery and pure deception. In fact of the 40-odd companies/products, there are only three which really provide 100% renewable. The rest are far less. Origin (Solar and Wind) and TRUenergy (Windpower) do. AGL do, but watch it! Unless you are being quoted about 5 cents extra over the standard rate, you can be sure you are not getting that 100%. The old maxim applies – if it sounds too good to be true – it usually is. And if you do sign up – look at your bill! Space heating In southern Australia you need space heating, if you don’t want to be the bad guy who goes around telling everybody to put on sweaters instead of heating the house. Our house in Melbourne is heated by gas. Space heating, as you can imagine is one of the big energy users and also a big CO2 producer. In the pre-green “business as usual” scenario for us it looked like this: As you can see, the central heating accounted for about a quarter of the CO2 production of our house. Before we went to gas-boosted solar, our gas consumption was due to heating and cooking. Cooking, (we have a gas top only and an electric oven – as many people do) accounted for a very small proportion of our total CO2 production. My wife cooks a lot – for a lot of people. But heating is the big gas user. We were using, on average, 55,000MJ (Megajoules) per annum. Gas is sold in MJ whereas electricity in kWh (kilowatt-hours). This graph shows how, between 1992 and 1998, our gas consumption inexorably rose, despite numerous heating service calls. The abrupt drop was when we installed the new heating system. By the way, in 1987 we extended the house so our gas consumption is now about what it was before the extension. 12  Silicon Chip siliconchip.com.au They are both units of energy. You can convert MJ to kWh by dividing by 3.6. Let’s not dwell on it (see the box). To convert MJ to tonnes of CO2 produced divide MJ by 16,000. Our central heating was producing (55,000/16,000) 3.4 tonnes of CO2 a year. It was an older type with a pilot light. I had already taken the measure of turning off the pilot light during the summer. That was using more gas than the cook-top! I decided, rather than wait until our 10-year-old unit actually conked out, to replace it with a 5-star unit with electronic ignition. At the same time we added some insulation to the ceiling, The combined effect (and I can’t tell you how much is due to what) was that we are now using about 39,000MJ per year, a saving of 1 tonne of CO2 per year. So looking at more comprehensive picture, on our domestic level, our CO2 reducing journey is now like this: After taking out the silliness of electric water heating, The author’s solar hot water heater doesn’t compete with the instantaneous gas heater – it assists it by pre-heating the water going into it, thus using less energy. This system has helped to reduce CO2 emissions from more than 14 tonnes per annum down to just three. The hot water component of that three tonnes is significantly less than one tonne. Inset at top left is the gas heater’s rating plate showing the output rating: 42kW – that’s 420 lightglobes! central heating accounts for the majority of our CO2 production but at least the overall result is quite satisfying. We are producing about a quarter of the CO2 that we out started with. You will, of course, be saying “what did all this cost?” Well it wasn’t cheap but it was only a fraction of the price of a four wheel drive – and will last a lot longer! And here’s another way of looking at it: if you drive a normal-sized car instead of a large 4WD, it will decrease your CO2 production by about 2 tonnes a year (from about 6 to 4 tonnes). For a fraction of that cost, you could potentially reduce it by 11 tonnes (from 14 to 3 tonnes per annum). What are your priorities? SC NEXT MONTH: In the third and final part of this series, Peter Seligman takes a look at the economics – both in dollars and CO2 – of electric vehicles. How do they stack up against the green lobby’s bete noir, the gas-guzzling automobile? And what of carbon trading schemes? Is there a better way to generate sustainable electricity? Stay tuned: and prepare to be surprised! siliconchip.com.au August 2007  13