Hi Ga Rick You have several different tracked solar arrays on site. Can you please advise if the net power output and cumulative Kw-hours take account of electrical energy used by the tracking system. Thank you
All of the trackers at the Solar Centre, whether AC or DC powered, are powered from the array side of the meters so the power/energy data provided on the website is a true net figure, i.e. yes, the net power output and cumulative kWh readings take account of electrical energy used by the tracking system.
Yes, you are correct, the ADES tracker is currently in a fixed position. Please see the Notes on the Data page where we have advised - "This tracker has not functioned since initial installation and is currently in a fixed position facing near north. The tracker is in the process of being fixed by the supplier." http://www.dkasolarcentre.com.au/forum/viewforum.php?f=11
The trackers operate by continually monitoring light intensity, and processing this information to drive the arrays’ motorised supports. At sunrise, light hitting the sensor at the rear of the control units will trigger movement back towards the east. On a completely overcast day, the panel surface adjusts to horizontal. The control and drive systems use less than one watt of DC power from the array's output. Tracking is expected to increase this array's output by 35%. The long term performance of these tracking arrays can be compared to that of the fixed Trina monocrystalline array to see the gain contributed by the trackers at different times of the year.
Last edited by Ga Rick Lee on Tue 04 Jan, 2011 10:47 am, edited 1 time in total.
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Dear sir, I am a structural engineer who has have been working on the design of support frames for solar panel installations in the Townsville area (Qld). Documentation shows that the greatest ‘Total yearly energy output’ is achieve (from a fixed installation) by placing the panels facing north at a pitch equal to the latitude of the array (in the southern hemisphere). But how much benefit can be gained from having a two position (manually changed) array without having to go to the expanse of installing tracking systems?
I believe such a system might have benefits when used on remote, manned power systems such as cattle stations where the array owners/operators (normally independent, mechanically minded people) can manually adjust the arrays and thus the cost of purchasing tracking systems can be put into additional panels or batteries for the system. Alternatively, additional power can be generated in winter for warming and summer for cooling then would have been available for the same cost of a fixed installation.
During both the summer and winter solstice, the suns track through the sky is relatively stable, changing by only 0.5 degrees over 10 days each side of the solstice. This means that for 20 days at the summer solstice the noon sun is within 0.5 degrees. Meanwhile, on the March and September equinoxes, the sun position is changing nearly 1 degree each day.
What benefit would be achieved by placing the array on a tilting frame that allows the panels to be orientated at one angle for the summer and a second angle for winter? These angles could be biased towards the summer and winter noon’s as (in the summer) an additional 1 degree tilt flatter would benefit 20 days (10 each side of the summer solstice) by 1 degree while only disadvantaging 2 days (1 day after September equinox and 1 day before March equinox) by 1 degree.
Testing of this configuration should be compared to fixed, single and double axis tracking systems. I noticed on your very informative web site that the Kyocera hydraulic tracing arrays have been fixed due to issues with the tracking system. Could these panels be used to test the above system? They are the same age and type of panels being used on both fixed and tracking arrays which would give a good indication as to what benefit the above system would have with respect to the offset between the upfront costs and maintenance on a tracking array compared to the lower maintenance and better reliability of a system that only needs to be manually changed twice a year on or about the equinoxes.
I have worked out that angels of 15.4 degrees above and below the latitude of a fixed system angle (or 8.1 degrees from the summer and winter solstice angle) would provide the best weighted average of days verses angle from the normal of the panel. I have also attached a sketch of a simple support frame that would allow testing of the above configuration.
What are your thoughts? What is the possibility of having this idea tested at your research center?
Hi Andrew, great post and some good lateral thinking.
I have done a CRUDE calculation (for Alice Springs, latitude 24S and 1kW of panels) on the effectiveness of your strategy of having 2 positions for the tilt of the array: Summer and Winter. My calculations do NOT account for any losses from panels to final output, cloud, nor take into account the effect of "elevation dimming", where the sun is dimmed as it nears the horizon. This last effect will slightly decrease the Winter output relative to Summer but may well be negligible. The other neglected components might be expected to equally affect all months, unless Alice Springs has some months grossly more cloudy than others.
I have calculated the daily outputs on the 23rd of each month, and assumed this value applies for every day of the month for simplicity (first plot). I then calculated the total output for "Summer", being October to March inclusive, and "Winter" which was April to September inclusive. On my included second plot, these are the "Summer" and "Winter" lines.
The "Sum/2" line gives an indication of the annual output, halved so it plots nicely against the other lines and allows an expanded y-axis scale.
The point labelled "2 Pos'n" is the half-sum of the Summer value for a tilt of 0 deg (max Summer output) and the Winter value for a tilt of 44 deg (max Winter output).
The point to note is that by invoking a 2-position strategy, the total annual output has increased from 2660kWh to 2870kWh, an increase of 210kWh, or 8%.
The same exercise can be performed with a 3-position arrangement, choosing the best tilt for each "season". As a trial, set: "Summer" at -4 deg (yes: 4 deg South!) for Nov to Feb, "Autumn" at 24 deg for Mar and Apr, "Winter" at 48 deg for May to Aug, and "Spring" at 24 deg for Sept and Oct. Note that the Sun stays near the extremes for much longer than it does near the equinoxes, hence 4-month "Summer" and "Winter" and only 2-month "Autumn" and "Spring". This strategy leads to an annual output of 2895kWh.
Further small gains may be made by adjusting the dates the tilts are changed, but again, the gains will be small. The first plot suggests a better selection of the changeover dates for the 3-position strategy than chosen above. Choosing "seasons" as suggested for the off-grid discussion below, the annual output becomes 2911kWh. Now the gain from a single fixed tilt is 251kWh, or 9.4%. I am not sure that the additional gain of 41kWh from a 2-position strategy to 3-position is justified.
Perhaps a more important effect, if one is off-grid, is that this sort of strategy (particularly 3 position) can lead to a much higher minimum output month-by-month, and so less shortage of power in the "worst" month. Have a look at the first plot again, which gives average daily outputs for each month, with tilts of 0, 24 and 44 deg. If one sets the tilt at 24 deg for the whole year, the output varies between 7 and 7.6kWh/day. The obvious strategy is to choose the tilt for each month with the highest output: 0 deg for "Summer" now being Oct to Feb, 24 deg for the equinoxes Mar and Sep, and 44 deg for "Winter": Apr to Aug. Under this strategy, outputs vary from 7.6 to 8.5kWh/day, so the "worst" month is higher than for the fixed arrangement. Slight improvements are obtained by setting -4 deg for "Summer" and 48 deg for "Winter".
This discussion is quite complicated. While the calculations are crude, I believe the results to still be meaningful. This work suggests gains of near 10% in total annual output are achievable by having a multi-position tilt arrangement, manually changed a few times per year. Most of the increase in total annual output is obtained by moving to a 2-position strategy, while 3-position is a better choice if one is off-grid and wants the best outcome for the "worst" months in the year while also increasing the total annual output. c*p
Daily average outputs against month for 3 tilts at Alice Springs
I had thought about expanding the adjustments to 3 positions (and I agree that the Autumn and Spring positions would be in place for shorter periods then the Summer and Winter ones) but thought that if manual adjustment was going to be used, real work users might get tied of changing the arrays too often and just leave them in one spot (probably the worst one).
I see you point about increasing the monthly minimum though and the possible smaller battery bank with the three position design.
I note there are two hydrolic arrays, maybe one can be adjusted as a two position array and one as a 3 position array for testing purposes over the next 12 months?