I was bemused to read the article in the August 2007 issue "How to Cut Your Greenhouse Emissions Part 2"; bemused because my experience with solar hot water is so different.

I happen to live just inside the tropics in the light green-shaded area in the map on page 10, the 75-80% zone. Two years ago I had a solar hot-water system installed at home when the aged electric system gave up the ghost. I opted for a marginally larger capacity model than the minimum recommended, as the additional cost was less than 10% at the time.

I also opted to move from off-peak electricity, with its minimum monthly charge, to standard tariff (costs more per kWh but no minimum charge) and only switch on the booster when needed. There’s no reticulated gas supply here, so gas boosted wasn’t an option.

Having now lived with solar hot water for two years, I can report on how often I’ve had to switch on the electric booster. The answer is once during winter in 2006 for two hours, and twice during winter 2007 for four hours total. We had only one lukewarm shower experience during those two years due to my not turning the booster on early enough.

The only behavioural modification for the household, post solar, was evening rather than morning showers. Cold water washing was already the norm. Do I recommend solar hot water to friends and neighbours? Of course! And No, I don’t work in the plumbing or solar hot water industries.

It has been a while coming but like all good things, it was worth the wait. Since my letter in the February 2007 issue on the major speedo error in my Toyota Yaris, Toyota has recently fitted it with a new instrument panel.

I recently spent 1.5 hours checking the new speedo at the same location as the original test. Several runs were made on the near perfectly straight 8km section of road. Speeds tested were 60km/h, 80km/h and 100km/h.

The test regime was to drive for about one kilometre at the steady indicated speed on the speedo, before taking a photograph of the GPS, for each speed range tested. The reason for this was to allow the GPS to stabilise for an accurate reading. The odometer was also checked over a 10km distance, as measured by the GPS.

The results were as follows:

(1) 60km/h indicated; GPS reading 57.4km/h

(2) 80km/h indicated; GPS reading 76.7km/h

(3) 100km/h indicated; GPS reading 97.0km/h

(4) Odo 10km indicated; GPS reading 9.91km

This test revealed a fixed error margin of indicated speed versus actual road speed, over all speed ranges tested. The average speed difference was slightly less than 3km/h.

It would appear that the replacement instrument panel has had a total redesign, which possibly incorporates intelligent microprocessor handling of sensor inputs relative to displayed speed, over the tested speed range.

The original instrument panel had a fixed error percentage over its tested speed range, meaning the faster the vehicle speed, the worse the error between actual road speed and indicated speed.

Both instrument panels were tested for odometer accuracy and found to be within 1% difference between indicated and the GPS over a 10km distance. The results of this test have proven that the new instrument panel has far greater accuracy than the original.

The small fixed speed reading difference between indicated and actual speeds is very acceptable and should take into account any small mechanical or tyre variations over the service life of the vehicle, and still be compliant with the relevant Australian Design Rules.