Temperature limits for solar pump controller

I was interested in the article about a pump controller for a solar hot water system by John Clarke which appeared in the March 2002 issue of SILICON CHIP. I don't know why anyone would want to build this unless he built his own system from scratch, because I would have thought commercially available systems would have their own controller built in. However, being a 'dabbler' from way back I can certainly appreciate why there would be an interest in this type of thing.

I thought you may like to hear of my own experience with a system similar to this. About 18 years ago, I bought a house (in country Queensland) which was already fitted with a solar hot water system manufactured by Rheem. Because this system had the storage tank situated in the laundry and the solar collectors up on the roof at a higher level, it had a built-in pump to circulate the water.

After I had moved into the house, in the dark and early hours one morning when I had risen to answer a call of nature, I noticed that the HWS circulating pump was running. (The pump motor was actually very quiet in its operation but in the dead of night it could just be heard). To me, this had to be nonsense and the HWS must be defective! After all, the Sun was around the other side of the globe somewhere, so how could this possibly be?

When I contacted the Rheem people to find out what may be happening, they asked me what the outside air temperature was at the time. At that stage, I could not answer the question but he informed me that if the outside air temperature fell below a certain figure (I think it was 4°C), the controller was designed to start the pump to circulate the water in the collectors to prevent them freezing.

The next night, I put a thermometer up on the roof and although the weather was not cold and the nights were a little cool, I was surprised to find that the roof temperature went down to 0°C and the circulating pump was running.

I found that, in operation, the HWS pump started when one of these conditions existed:

(1). The temperature difference between the roof panels and the storage tank exceeded a certain amount. (I don't remember the figure, but it was stamped on the pump controller itself. This was for the normal water heating operation);

(2). The roof panel temperature fell below 4°C (to prevent the collectors freezing up and subsequently being damaged);

(3). The storage tank temperature rose above a certain figure (I think it was 75°C and I think this was to limit the temperature reached by the water in the storage tank).

All in all, it shows that there are often a few more factors which have to considered by the designers of devices such as these than may at first be realised.

Alan Adam,
Bald Hills, Qld.

Environmental politics: does it add up? Firstly, I would like to state that I agree that solar power and in particular, solar panels, are still quite a distance from becoming mainstream and the sums don't always add up for a successful installation. However, I was concerned by Ross Tester's extreme bias against solar power and lack of research for his article "Solar Power for All" in the March 2002 issue. This was evident from statements such as "Why not make a solar panel which IS the roof cladding". Roof integrated solar tiles have been around for quite a while, along with solar panel skylights and windows. Check out the Australian publication ReNew by the Alternative Technology Association and their website at www.ata.org.au Perhaps in future you could do an article that explains the technology behind solar panels and even about the plants in Australia that produce them. One is gearing up near Canberra to build translucent solar panels based on a new technology where the solar panel cell is created using a titania (TiO2) substrate. Apparently a rise in temperature actually increases the efficiency of the panel slightly, unlike older technologies. See their website at www.sta.com.au You could also add purchasing "green" power to your "Better Ways To Save Greenhouse Gases List" - this has to be an obvious choice for making a difference, particularly with the recent deregulation and publicity about the power industry. Also I could not understand Leo Simpson's argument for being completely off the grid. Are our infrequent power outages enough to justify the much greater cost of such a system? There is the added downside of greater maintenance costs due to the required batteries. Wayne Bowers, via email.

Greenhouse effect is real

I would like to firstly commend you for the article on solar power in the March 2002 issue of SILICON CHIP. It gives a clear assessment of the current state of economics of domestic use of solar power. I also liked the inset panel on other ways to reduce energy usage.

However, Ross Tester is on less firm ground with his dismissal of the significance of the Greenhouse effect. He has confused two separate elements. The basic physics of radiative interaction between trace atmospheric gases such as carbon dioxide, methane, nitrous oxide and water vapour and the long-wave emission of energy to space is well established. The fact that these gases have absorption spectra in the long-wave part of the radiation spectrum gives them an important role in the Earth's energy balance.

This has been known for over 100 years. The so-called natural Greenhouse effect has kept global temperatures some 30°C warmer than without those gases.

Where most of the controversy arises is how the ocean/atmosphere system will respond when concentrations of some or all of those radiatively-active gases change over time. We know from ice cores in Antarctica that both global temperature, carbon dioxide and methane levels tend to vary in phase - that is, higher temperatures tend to coincide with higher levels of carbon dioxide and methane, and vice versa. This has happened over millennia with the cycle of ice ages and interglacial periods.

So climate change is entirely natural. It occurs on shorter time scales (decades and centuries) as well as on longer time scales. Knowing this background and the sensitivity of the global climate system to trace gases, it is reasonable to expect some impact if concentrations of these gases increase rapidly. They are being given a big nudge. We are conducting a global experiment with the atmosphere that cannot be stopped.

Ross Tester has mixed up the controversy of just how the atmosphere will respond to the changed composition with the underlying theory. Most of the arguments come from how well global climate models can firstly simulate current climate and secondly simulate future climate. They tend to get the big picture right but are less satisfactory at the details, such as regional effects and simulating rainfall.

Thanks also for the excellent article on remote sensing. It also has a good summary of issues relevant to climate change.

Ian Foster,
Research Officer,
Department of Agriculture,
South Perth, WA.

Solar power can be cost effective I have a number of comments on the article on solar power in the March 2002 issue. Mr Tester makes statements about greenhouse emissions and global climatic change based more on opinion than much scientific research. The debate about greenhouse modelling will be ongoing for years and is beyond the scope of this letter but references to the "Leipzig Declaration" are trivial. At best the declaration is controversial and many regard it largely as propaganda promoted by energy producing companies and countries. It is worth looking at www.naturalscience.com/ns/letters/ns_let08.html for a more comprehensive perspective. Mr Tester correctly notes that few installations would be net energy producers but this is rarely the intention - domestic grid interactive systems are designed to reduce electrical consumption. The fact that energy is available only during daylight is of little consequence, besides which daytime peak loads are responsible for load shedding (blackouts) by power companies. Battery storage is necessary in rural areas where the grid connection is not available but would be too costly and require ongoing maintenance for most users. The grid can be considered as a "battery" delivering power when solar is not available and is an elegant and practical solution to energy "storage". Sydney's annual 1500kWh/kW of solar energy would be based on an average of four peak sun hours (PSH) per day delivered by PV panel (1000W x 4PSH x 365 days = 1.46MHh). As the panel is supplying this energy, its inefficiencies including installation parameters are already factored in - 95% derating is not relevant. Computer modelling for a 1kW PV panel at Sydney's latitude returns figures of around 1.5-1.7MWh per annum which is in keeping with the stated claims. PV panels are between 10-14% efficient in converting total solar insolation to electrical energy and are limited to the solar radiation spectrum as much as cell design. A theoretical maximum of around 25% applies. The term "payback period" is nonsensical. If we apply it to other electrical appliances, the period is infinite yet we purchase any number of these without too much thought to efficiency. Payback periods are not true representations of the application - it is investment and must be considered as such. Consider the $11,000 (after rebates) system installed as described in Mr Tester article. The after-rebate cost would be typical for a 1.5kW system generating about 2.2MWh per annum. Based on our electricity costs of 15.5c/kWh (I am not certain where Mr Tester buys electricity at 9.8c), the annual return would be about $330, or about a 3% return on investment, tax-free. The figures for appliances quoted in reference to the 450W system are dubious. Our actual figures are as shown in Table 1 below. The 450W system delivers 675kWh annually (0.450 x 1500kWh). If equipment is used efficiently, and with appropriate lighting, the claims by Pacific Solar are reasonable. Note that three of these appliances are phantom loads and could add up to another 500Wh per day (182kWh/annum) - a good argument for turning them off at the wall, at least overnight. Without a comprehensive energy audit and site assessment, we never recommend a PV or any other renewable energy system, but sized correctly and with energy efficient appliances, good building design and proper financial practices rather than guesswork, they can be cost effective and environmentally sustainable. Roland Denholm, Powercom Solutions, North Ringwood, Vic. Comment: the current Energy Australia electricity rate for domestic consumers (Sydney) is 10.318 cents/kWh. Regardless of whether you regard payback period as relevant or not, a 2% or 3% after-tax return on investment is poor.

Washing circuit boards does work

I had to smile at the Serviceman's story in the March 2002 issue, where he took soap and water to the innards of a television set. Every serviceman knows that water and electronics means disaster but confession is good for the soul and so back in the 1980s I used to throw populated circuit boards into a tub of warm soapy water and scrub them with a small scrubbing brush! I never once had a failure.

The boards that got washed were computer keyboards that had been "christened" by the customer at smoko times by coffee, lemonade, creamcakes, etc. In those days, the keyboards were expensive and it was worthwhile spending the time to remove and put back 80-odd big chunky keys which strangely enough, never seemed to suffer any damage themselves from liquid ingress.

It was no good simply squirting the board with those products that servicemen know and love so well. The gunk just stayed there, taunting you! Coffee and lemonade spillage only came off with water and the soap and scrubbing ensured that none was left to continue electrical leakage between board tracks or IC pins.

The board also had to be totally immersed in the warm soapy water and moved back and forth to ensure that all the stuff was washed out from the tiny gaps between the silicon chips and the board where the brush couldn't reach. Then the process was repeated in fresh water to rinse off the soap.

Finally, (because it was only fresh water which is an insulator), the board got a good blasting under the water tap, just to be sure.

I used two methods of drying the boards. The old formulations of contact cleaner in a spray can touted as "leaving no residue" were ideal for blasting water out from under the chips. The stuff might have damaged the ozone layer back then but it had an enormous affinity for water, evaporated rapidly and left those narrow places where water could stay trapped bone dry.

The whole board was then placed somewhere static-safe where it would stay at a hot-but-touchable temperature (blazing sun, central heating, bench lamps, etc) for several hours after it was observed to be totally dry. Such was the low-level "scientific" approach to the drying process!

I did not coat the boards with a protectant advisedly. It was about that time that AWA issued a service bulletin to its agents that the specific product CRC 2-26 should NOT be sprayed on circuit boards to "protect" them from the environment.

I hasten to say that CRC 2-26 is an excellent product and one of its strong selling points is that it can soak in to every tiny nook and cranny and keep moisture out. But it was so good at its job 25 years ago that AWA warned in the 1970s that any electrolytic capacitor coated with CRC 2-26 was likely to suffer premature failure. The assumption was that the product was leaching inside the electrolytic via the legs and somehow ruining the chemical action so fundamental to these capacitors. I wonder if the situation is the same these days?

I can't leave without letting Rodney Champness know that he shouldn't try to "protect" any vintage selenium plate rectifiers he might find with CRC 2-26. It wrecks the forward-reverse resistance ratio over a matter of weeks or months and they stop being rectifiers.

Stan Hood,
Christchurch, NZ.