Focus on solar energy payback is wrong

Congratulations on your cover and articles relating to solar energy in the March 2002 issue. Although I disagree with a number of points in the editorial and Ross Tester's effort I am pleased to see the profile of appropriate technology raised.

Firstly and most importantly I will address the 'Payback' issue. Using your logic, I would not purchase any product unless its purchase price was 'repaid' by the product's operation or use during a set period of time. If I applied this same logic to buying a TV, boat, jet ski or caravan, for example, than I would most certainly never get my money back.

My payback occurred the day I purchased the system. I supported one of the few successful electronics industries left in Australia and all the people it employs. I supported a growing solar HW industry which exports the majority of its output and employs people in manufacturing, export and installation of their products.

I have a 6-module system generating about 2kWh/day in sunny weather. It provides lighting and ceiling fan operation most nights in a 4-bedroom brick veneer home using an Australian-made 1.6kW sinewave inverter, 24V regulator and 24V 215A.h battery bank. I also have a 305-litre Australian-made solar HWS saving about 8kWh/day.

Should the power fail, I can cook with gas, have a hot shower and watch a DVD until it comes back on. It will reduce my electricity bill every day the sun shines. Personal payback achieved.

The inset "Better Ways to Save Greenhouse Gases" was well meaning but only got it about half right. Buying a new car is OK if you can afford it and certainly avoid a 4WD if you don't need one. I support the points regarding new fridges, freezers, aircons and a solar HWS also. However, for a large number of people purchasing new goods of any type is not an option.

So what is cheap and easy and has a significant effect on energy consumption? The off switch is number one on my list. I found that by turning off small energy consumers such as TVs, VCRs, microwaves and plugpack-operated devices when not in use, I saved about 1.5kWh/day. Before my solar HWS arrived I fitted a 7-day timer to the electric unit and reduced its on-time to a few hours per day.

I also turned the thermostat down to 55°C. Around 2kWh/day can be saved easily this way. The saving of a few percentage points nationwide is a big number of kWh that never needs to be generated.

Brian Bartlett,
Rockhampton, Qld.

Fix for LCD in Parallel Port PIC Programmer I recently assembled the Parallel Port PIC Programmer from the March 2001 issue and it works well. However, I did encounter a problem with the Liquid Crystal Display Adapter which did not work. I dissected the code. It worked in the simulator software available from MICROCHIP.COM (free) but the hardware refused to cooperate. Focusing on the "LCDBUSY" subroutine in the program led to a detailed investigation of the LCD display response time to the instruction "MOVF LCD_DATA,W" in this subroutine. The PIC did not read this correctly but read some arbitrary data after executing this loop many (?) times. The trick I remembered was to re-read the peripheral several times if necessary. This fixes the problem and the program and hardware are working now. To summarise, if you have problems getting the LCD display project to work, find and change: MOVF LCD_DATA,W to MOVF LCD_DATA,W MOVF LCD_DATA,W in subroutine "LCDBUSY", then "rebuild" the program and write it to the PIC using the Programmer. Hopefully all will be well. Thanks for a great magazine and may you never run out of projects. Frank Winter, VK4BLF, via email.

USB LED lamp follow up

I was delighted to see a great writeup of my Itsy-Bitsy USB Lamp in the March 2002 issue of SILICON CHIP. The diagrams were, as always, quite magnificent. In fact several outside comments arrived along the lines of "it's good to see universities doing some simple, cheap, but clever real world projects that normal people can understand and need"! The ultimate compliment must however be from Jaycar, since I note they've already rustled it up as a kit. Yah!

An obvious enhancement (since adopted here) is to recognise that light will also be needed when the PC is switched off. In fact, this is often where it's REALLY needed - fiddly cable, jumper and connector setups normally occur when powered down. USB ports only supply 5V when the PC is on, of course.

What we've done here is to take a one-metre M-F USB cable, make a somewhat longer "Itsy Bitsy" with almost all this but use the otherwise wasted female part, along with some insulated crocodile clips/battery snaps and another dropping resistor (or 7805 3-terminal regulator) and connect to a normal 9V battery. Trials show that at least 10 hours bright light results - depending on the battery type but a 7805 allows a 12V SLA battery to be connected instead, giving days of bright lighting.

I've even experimented with a small rechargeable battery (ex-motherboard 3.6V nicad) in the itsy bitsy line, that would charge whenever the USB lamp is plugged in. Only about two hours light is available from this, however.

Stan Swan,
Massey University, NZ.

Diesels may be more economical than cars Ross Tester's recommendation, in the March 2002 article on solar power, about getting rid or your "full-size 4WD" to save fuel compared to say, a Ford Falcon, cannot go unchallenged. I own one of each and my Nissan Patrol Turbo Diesel truck beats my Falcon by a long margin around town. My Falcon can easily use as much as 18l/100km on short runs, which is what I do most of the time. The Patrol will never use more than 14 and mostly about 12.5l/100km under the same conditions! On the freeway, the Falcon will use less than the truck but not a lot less. Horst Leykam, via email.

Solar panels have a long energy payback

I read with interest your editorial and article on solar power in the March 2002 issue with reference to solar power. I'm a little disappointed that you didn't have anything to say about a very important environmental aspect of photovoltaic cells, that is the energy payback period.

Solar panels require quite a lot energy to manufacture as the wafers of silicon have to be heated to a very high temperature as part of the "diffusion" process. So solar panels are not environmentally friendly until they have given back all that energy that went into manufacturing them! Actual payback period figures of 8-10 years seem to be generally accepted.

Solar panel manufacturers don't seem to want this aspect to be widely known but it puts a whole new slant on the solar energy debate. I presume that the 8-10 year payback period is based on full usage, so having a solar panel to just keep your boat battery topped up would not be "green" at all because you would probably never get back all the energy that went into making the panel in the first place!

Ray Chapman,
via email.

Comment: to a large extent, the long payback period is reflected in the high price of solar panels. In other words, if solar panels were much cheaper to make, they would have a shorter payback period, both in financial and environmental terms.

Web link for Historical Radio Society In the April 2002 issue of SILICON CHIP, Ray Creighton supplied you with the URL for the Historical Radio Society of Australia Inc. Unfortunately, he supplied the old address; The current address is www.hrsa.asn.au Warwick Woods, President, Historical Radio Society of Australia Inc.

Distributed power generation has merit

While I agree with your economic analysis on home installation of solar cells within the city, the basic idea of generating power on a distributed basis has real merit as it potentially reduces infrastructure expense.

Also the widespread use of local power generation might help reduce urban heating. Maybe business should be encouraged to install systems. Or maybe just shopping malls to reduce lighting costs, as their usage is fairly well in sync with daylight hours.

Paul Maynard,
via email.

Comment: distributed power generation makes a lot of sense. However business will not install any of these systems unless the payback period is realistic; five years or less.

Limitations of negative feedback

Keith Anderson (Mailbag, March 2002 issue) went to some length to extol the virtues of large amounts of negative feedback as employed in audio power amplifiers. I feel that some of his comments are misleading if taken at face value, however. Keith cites P. J. Baxandall, then follows this with some paraphrasing, leading to the conclusion that "a little bit of feedback makes things worse, not better."

He then tells us that "It is really dumb to do gross, brutal things like using class-A to reduce feedback", and that "it is necessary but difficult to use lots of it".

For Keith to discard such inherently linear systems such as Linsley Hood's 10-15W class-A design (Wireless World, April 1969) with these platitudes seems to me in itself "really dumb". Numerous authors (Baxandall, Bailey, Blomley, Hood and others) have gone to great lengths over the years to explain just exactly why negative feedback is not the panacea that Keith seems to imagine.

Class-B amplifiers have the operating point of each output device set at the lower extreme of its transfer characteristic. Most commercial designs still use bipolar (quasi) complementary symmetry output stages, and in these the mutual conductance varies wildly as an audio signal drives each output half (upper and lower) in and out of conduction. In other words, the open-loop gain varies significantly near the crossover point.

This is precisely why negative feedback is less than completely effective with such designs. At the crossover point, the open-loop gain falls and so does the amount (and the effectiveness) of the overall negative feedback.

To compound the problem further, most people only run their amplifiers at output levels of around a watt or less for general listening. This results in their audio signals being very close to this highly non-linear crossover point for most of the time and the resulting distortion level will be much higher than the manufacturer's quoted figure for (near) full output.

Such "bumpy and localised" non-linearities also produce quite high-order harmonics, (9th, 11th and higher) and as such, are far more apparent to the human ear.

When the distortion is predominantly low-order harmonic, such as that produced by (eg) class-A designs, the same amount of distortion which causes audible "edginess" in class-B designs no longer sounds like distortion at all. Rather, it tends to make instruments and voices sound slightly "different" tonally, since the ear now has a much harder job picking the generated harmonics as separate, distinct signals. Class-A operation happens to be a very effective solution to these problems. Inefficient, maybe. But "really dumb, gross and brutal", as Keith suggests? Most certainly not!

Tony Sanderson, VK3AML,
Surrey Hills, Vic.

Wind power compares to solar I thought the article on Solar Power in the March 2002 issue of SILICON CHIP by Ross Tester very well balanced and an accurate assessment of the situation. Yes, the "greenhouse effect" is far from proven. We should stop talking about "greenhouse gases" and refer to CO2 or whatever gas is of interest, by name. Of course, if we are to conserve fossil fuel, we should be concerned about CO2 emissions. Ross did not mention small wind generators for use next to a home. We live on a windy hill and the notion of capturing some of that wind energy is appealing. A rule of thumb says the average wind speed needs to be about 6m/s to make a wind generator worth-while. I have done calculations for a small wind generator which just feeds a heater and nothing else; the simplest possible system. Assuming the 6m/s average applies for the whole year, thus assuming heating is needed all year, which it isn't, the payback time on the purchase of the generator, compared with heating by furnace oil and no subsidy, is of the same order as Ross's figures. John Waller, Connecticut, USA.

Solar power is a worthwhile investment

I read with some annoyance the article on "Solar Power for All: Does it Add up?". I was particularly concerned by the section entitled "Payback period".

Think of it as an investment and tell me this doesn't make sense: Let's assume the person does have $11,000 to invest. If your return on investment is $800 per annum that's 7.2% tax free! Because you are not selling the electricity, just subtracting it from what you buy in the first place, the government has not worked out how to tax us on the earnings.

Investing $11,000 in a term deposit at 3.5% returns $385 per annum. If you are in the top tax bracket, take away 47% tax from that and you end up with $204; net return is 1.8% after tax. I give you one guess where I would put my money!

And let's face it, if you move house unbolt the system and take it with you because it is not going to add $11,000 of value to the house.

Alan Barrow,
Aspendale, Vic.

Comment: comparing "Plug'n'Power" to bank interest does make it seem more favourable except that you can always go to the bank and get your $11000 back. But we take your point: that a 7.2% notional return is actually equivalent to almost 15% before tax, when the top tax rate and Medicare levy is taken into account. The only problem is, how does a $20,000 solar system save $800 in a year? On our figures, the best saving you could expect would be less than $200 per year, not per quarter.

Solar power has a cost disadvantage

Ross's article about the solar power will put the cat amongst the solar panels! Seems it will be awhile yet before the price of solar comes down enough and the price of hydrocarbons goes up enough for there to be a direct economical benefit.

People will no doubt argue that Ross hasn't taken environmental costs/savings into account but neither will many people take it into account when they are deciding to make a purchase. The "Better ways to save greenhouse gases" (and costs) was very good!

G. Nolan,
via email.

Interest cost should be taken into account I read Ross Tester's article entitled "Solar Power for All: Does it Add Up?" in March 2002 with interest. Unfortunately, his financial analysis is nowhere near the standard of his technical analysis. He makes the common mistake of comparing the capital cost of one setup (solar power) with the current or running cost of another setup (paying electricity bills). This is like comparing apples with lemons! Talk of a payback period is irrelevant - especially if it ignores inflation and interest rates. Ross states that "If your current electricity bill is, say, $200 per quarter then $11,000 is equivalent to 55 quarters". This is invalid because that $11,000 investment results in an asset being acquired. What he should be comparing is the cost of servicing the $11,000 investment against electricity bills. Current mortgage rates are about 1.5% to 2% per quarter. So the cost of setting up $11,000 worth of solar equipment comes to around $165 to $220 per quarter - roughly equivalent to the cost of buying electricity from the authorities. Therefore, you have two ways of paying for your electricity: you can give it to the electricity generating authorities and help to burn more coal or you can give it to your banker and enjoy "green" electricity. Another way of looking at this is that if you have $11,000 to invest then one option is to invest in solar power. The $200 or so that you save in electricity bills each quarter represents tax-free interest on your investment. Of course this is an idealised assessment in that it does not take into account depreciation, maintenance costs or inflation. When we analyse Pacific Solar's "Members Pack" using Ross's figures then we get a significant difference in costs. The $6000 investment has a life of 25 years (this takes account of depreciation). If we assume that the real interest rate (the difference between the mortgage rate and inflation) is 5%, then the annual cost of the investment is $425 - significantly more than the $64 that the 640kWh would cost each year if you got it from the authorities. Of course, maintenance needs to be added on top of this. No figures are given for maintenance of a solar power system but I guess that a preventative maintenance program would cost $20 to $50 per year. Incidentally, I notice that Ross suggests that gas or solar hot water systems might be a better way to save greenhouse gases. It might be better to crunch a few numbers before you make this conclusion Ross! G. Schoenmakers, via email.

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