The Greening of St Barnabas Chapel of Ease

[StBarnabas]

Mike,
many thanks. The clearview is fine otherwise amd working very well though not quite as good as the Burley.

One of the classic effects of shading is that one can get multiple peaks on the power curve and the grid tie inverter can get stuck in a local maximum. This is very nicely illustrated in a SMA video. http://youtu.be/NBsCjESCcVE. The classic symptom is that when the shading gets less, the GTI suddenly jumps to the global maximum; there is a rapid increase in power and simultaneous drop in voltage.

There is good evidence that this is happening on the StBC array. At around 10:00 for example on the 6th November – and on other clear days we also get  this effect



We have about a dozen trees at StBC, but five of them (2 oaks and 3 ash) are the main culprits as they are to the east and SE of StBC. The problem is that I like trees and want to crown them in such a way that they don’t look stupid. Any thoughts and suggestions   as to how to trim them would be welcome.

Photos from  East moving towards south

[billt]

Have you worked out how much energy you're losing? Presumably the trees are only shading in the winter when the sun is low and only for an hour or so in the morning. If that's the case you won't gain much energy at all by reducing the trees, especially as most days are likely to be cloudy with low output and no shadow effect.

Looking at your power graph I'd say you're losing about half a unit on a sunny morning. If you have 10 sunny mornings a month that's 5 units. Not worth worrying about.

I'd leave the trees alone, unless they need attention because they're diseased. (The aesthetic benefit would grossly outweigh the small loss in energy, for me.)

[StBarnabas]

Hi Billit
sadly the effect is apparent all year around here is a plot from June. The trees are much higher than StBC and cause shading all year. I posted the Nov plot as it was a dawn to dusk clear day (not a common occurrence here in Northumberland)



The methodology to estimate shading is simply to time reverse the integrated PV plots around the centroid and look at the difference between the curves. This is not perfect but I think I am loosing about 10%

[wookey]

Buy some enecsys micro-inverters? And flog your nice platinum one to someone else?

[Baz]

Look like typical trees that have gone all spindly. Trouble is tree surgeons get trained to thin out trees while leaving lots 'up top' to ensure they have future work. You have to beat them over the head with their chainsaw to get them to thin properly as a gardner would thin a bush to expose a new leader lower down the branch. Then you have to go over it for the next few years to thinout the shoots that spring from the cut to avoid the pollarded look.

[KLD]

I'd leave the trees alone, unless they need attention because they're diseased. (The aesthetic benefit would grossly outweigh the small loss in energy, for me.)

I very much second what billt says: the trees contribute a lot to the special atmosphere of your place, don't sacrifice them to a few kWh extra pv generation.

Klaus

[StBarnabas]

Well the trees are safe for now. Largely due to inertia. I thought however I should warn of a recent possible fire at StBC. I have two sets of gauntlets one a fire resistant clorh provided by Burley and some leather ones from Clearview. Some weeks ago we were going to bed and there was a strong smell of burning which turned out to be the Burley gauntlet smouldering away. A bit poor I thought. Must have caught a spark when I was loading the fire and was happily smouldering away when I came down to investigate. This is now banned from use. The Clearview ones are leather and I have had no problems. I have recently upgraded my smoke alarms!



On a happier note I hit 6MWh of generation on my PV array last evening. Still about 1 year and a half before I get to 1GWh

[billi]

Leave the trees like they are,your place needs these ancient ones   and plant more energy trees  

[Stuart]

Hmmm...that is a good idea 

[StBarnabas]

Well it's been a while. Day job been very hectic recently.

Billi you will be pleased to hear that the trees are safe for another season, though much as I would like trackers sadly not a serious option for many reasons.
The "greening" this Easter has been the new StBC poly-tunnel, though sadly not finished due to bank holiday Monday  conditions. It is a12'x25' poly-tunnel from premier

Digging down 14" for anchor plates - 12x of these



plate on



Clipped down and the refilled. Supposed to prevent poly-tunnel flying...



Poly-tunnel site showing flying trampoline recovered on a few occasions from the next field. (poly-tunnel won't fare so well!)



Nearly finished poly-tunnel featuring Tassie (please throw this stick!) and Lucy (I used to like raw eggs you meanie!)



Lucy looking at our chicken run - mean daddy has put up bars so chickens can get out but poor puppy can't have her egg chaser every morning after breakfast!



Hens safe for now - plenty of eggs!


StB

[StBarnabas]

Some may be interested in the StBC shading simulation. This shows shading gradually leaving the StBC roof - the shaded insolation is 100W/m^2 and the unshaded insolation 1kW/m^2

Hopefully it will run OK


http://farm8.staticflickr.com/7246/6941110522_878e3188c7_o.gif

In my viewer one needs to click on the link but it works fine.

It is interesting to see how few cells need to be shaded before the panel gives almost no power and the sudden jump in the hill climb algorithm finding the local maximum.

[ericw]

Very impressive Sean.

[StBarnabas]

Hi Eric
Thank. There is quite a lot underneath the model with each of the 936 cells having a separate IV  curve which is a function of insolation and temperature, though the temperature has been kept constant at 25 degrees centigrade. THE IV curve is based on a twin diode model with series and shunt resistors. The main weakness is that the IV curve is scanned from the datasheet and there may be some artistic license. A better job could also  be done on the bypass diodes at present I am simply clamping the voltage at -0.6V when the diodes switch on.

I do have a spare panel and will try to get some realistic IV curves in the “near” future..