E-News Issue #26
Summer Greetings! Another month and I'll be wishing you a Merry Christmas - time flies! To our Queensland customers, please note we are now on daylight saving time. The cows over here don't need to see first light at 4.30 am!!
Last newsletter I mentioned we had some 12V - 10W halogens. A few asked me what was new about that?! We meant to say that we had some 24V - 10W bulbs in. We also expect to finally receive some 24V - 20W dichroics this month. It has been a long wait..
Fridges - 230V
A friend at Tenterfield NSW has been monitoring a standard 230V Whirlpool 3621 frost free fridge running off his SA21 inverter for a few months now. The Star label suggests 1.3kWh even though his house is closed during the day and is rather hot. In reality, he has measured it at an average 0.8 kWh/day which was measured on the AC side. When we tested a fridge on an SA21 inverter a couple of years ago we found the efficiency to be about 80%. With solar panel subsidies and prices being slowly forced downwards, there may be an increasing argument in favour of efficient 230V fridges (4 - 5 star) versus the more expensive 12/24V units. Any comments or feedback from you is always appreciated.
Need a Price?
Our price list is not in a format that can be sent easily by email. If you give me your postal address, I'd be pleased to mail you one. If you urgently require a price, let me know the item(s) and I'll email you back their individual prices.
Someone recently asked me about the efficiency of trackers. So for this month's larger article, I've extracted a page out of our Energy from Nature book on the topic written by Peter Pedals.
IS TRACKING COST EFFECTIVE?
Whether tracking is really worth the expense depends on a number of factors:
- the cost of the tracker
- the extra installation cost (concrete, etc.)
- the extra energy gained by tracking
It is not enough to say that the panel(s) may put out twice as much power under given circumstances. It is the accumulated amp-hours (amps times hours) over the course of the day that determines your daily gain.
The gain is not consistent throughout the year. The greatest gain is usually in summer when the hours between sunrise and sunset are the longest and the sun sweeps its greatest arc across the sky. If this potential for an increased gain in summer also coincides with a wet season or consistently overcast weather then the actual gain may be very little or nothing at all.
In fact, you will find that the horizontal (flat mounting) panels would frequently exhibit better performance patterns than the panels on fixed frames tilted to the north. This is because on mildly overcast days the sunlight is scattered and the best results on such days are often when the solar panels are facing straight up and getting maximum benefit of the diffused light rather than attempting to pick up the direct sunlight.
The gain is also dependent on latitude. At increased latitudes the sun's arc across the sky in summer is also increased but in winter it is decreased. The following table shows the daylight hours (between sunrise and sunset).
Solar energy usually has its greatest strength in the middle of the day and often the greatest cloud cover is in the mornings and evenings.. The energy from the sun has to penetrate through the greatest depth of atmosphere at the horizon.
Your immediate environment and your geographic location may play a major role in the hours of direct sunlight (without shading) that your panels may receive. Nearby mountains, hills, trees, tall buildings etc may considerably reduce the number of hours of direct sunshine that your panels receive. Shadow throwing objects tend to have their greatest effect on a solar panel site when the sun is lowest in the sky. Even the smallest amount of shading reduces panel output significantly.
After having determined how much gain you could expect in mid summer and mid winter you may find that you get the most benefit when you least need it. An automatic solar tracking system usually costs more than a 75W solar panel. Unless your loads are predominantly summer loads (e.g. fridge, freezer, space cooling, pumping) and you already have at least 8 solar panels, you may be better off with another solar panel. An extra solar panel gives greater benefit in mid winter when there is the greatest demand for night time lighting and entertainment.. If you need more power in winter for lighting and entertainment because of the shorter daylight hours then an extra solar panel may be money better spent than having a tracking device.
Seasonal Adjustments? The seasonal variations in the sun's angle are 23°15' added to latitude at the winter solstice (either 21 or 22 June in the southern hemisphere) and 23°15' subtracted from latitude at the summer solstice (either 21 or 22 December).. A simple system where you manually change the angle a few times per year would not involve much cost or effort but also gives you less gain than an automatic solar tracker.
Cheers from Dave and all the RPC crew.
Dave Lambert (Director)
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- Issue #87 - 29/07/2005
- Issue #86 - 04/07/2005
- Issue #85 - 03/06/2005
- Issue #84 - 05/05/2005
- Issue #83 - 01/04/2005
- Issue #82 - 03/03/2005
- Issue #81 - 23/02/2005
- Issue #80 - 02/02/2005
- Issue #79 - 05/01/2005