#171596  by gerard
 Wed Mar 24, 2021 12:57 pm
Picking up on this earlier thread, we have decided to keep the satellite dish on the roof which limits the space we have for the replacement solar panels. Also have to deal with the shading of the awning when the sun is low. I have pretty much settled on the following option to replace the two bulky 150W panels which are exposed to the awning shading.

5 new 100W or 120 W panels. At 670 mm width I can have two pairs next to each other on the width of the roof (2x670mm=1340mm compared with the current 1520mm panels), with "enough" distance from the awning shading. In winter there will still be shading, but having seperate panels, the ones furthest away should still work well enough. The fifth panel could go in between the awning and the satellite dish, and will potentially get shading at times from either.

So two will be unshaded, three will be shaded somewhat in the morning by the awning, and one of those three may under certain circumstances possibly get some shade from the sat dish.

The question now is how to wire them up. All parallel? Or the three next to the awning in series, the two unshaded in series, and those then all in parallel?

Currently we have 6mm wiring installed. Five metres of this will be carrying the load of all panels. If we go five panels parallel, this may become a bottleneck. I am not so concerned about drop in voltage, as we will only be an issue when at maximum generation in summer at maximum Amps (when we do not need all the power), however is this a problem (overheating?). It would be nice if we don't have to renew all the wiring (big job). I realise I will have to upgrade the controller (from a 20A model to 40A).

Any comments and suggestions are much appreciated. The panels I am looking at have around Pmax 19V and 6 A.

Thanks,

Gerard
 #171598  by mattn
 Wed Mar 24, 2021 1:42 pm
Wire the panels in Parallel. That way a shaded panel does not reduce the output of a panel in full sun to nothing. If you install 600W total of panels at nominal 20V, you have 30Amps. A 30Amp your not going to burn up 6mm cable, which is good for 40-50AMPs (Jaycar claim their 6mm is 70Amp rated).

You are correct not to worry about wiring voltage drop. Your voltage drop will be around 1V, purists will say less than ideal, but pragmatically if you cost engineer it, solar costs around $1 a Watt, 6mm cable costs about $15/meter (pair), for the same cost, thin wires and more solar gets more power to the battery despite the wire losses. In the days when solar was $20 a Watt, fat copper was the way to go, but much less so today. Keep in mind in low light, the MPPT controller is sending solar output direct to the battery, so the voltage drop in the wire means nothing.
 #171601  by scubadoo
 Wed Mar 24, 2021 3:15 pm
I fully agree with mattn.

Parallel all panels, use the existing wiring and connect to a quality MPPT solar controller.

Prudent parking orientation can often reduce shading. Our satellite dish is mounted towards the rear left hand side of the roof. Facing the truck somewhere between NW and NE minimises shading and heat inside for most of the year.
 #171603  by Neddy
 Wed Mar 24, 2021 4:08 pm
All good suggestions (on this page) Gerard. There is one other option that you might like to consider, though. Go to a "two controller" setup. Keep your existing 20A controller and buy another 20A controller rather than moving to a single 40A controller. This would give you the most effective minimisation of shading losses, provide useful redundancy and would also be the cheapest option. It does mean that you would have to run another couple of cables from rooftop to controller and I appreciate that this might well be enough to put you off this idea, but it's what I would do if I were in your situation.
 #171606  by gerard
 Wed Mar 24, 2021 4:44 pm
Hi Neddy,
Thanks for your reply, always value your input. I am out of my depth here, but how would the two controllers be more effective than one 40A controller? Key question, as summers are no problem, but winters with a Nespresso (x 8 cups a day), downloaded Netflix movie viewing and recharging ebikes pushes the envelope in winter. You are getting away with one 100 Ah battery if I understand right? We have 2x95Ah, and eventually will go Lithium. But as long as these 2x95Ah do the job we may as well stick with them. They are now 5 years old.

Gerard
 #171607  by Neddy
 Wed Mar 24, 2021 6:29 pm
The most efficient way to minimise shading losses is to have a separate controller for each panel. Say you have 5 panels paralleled to the same controller, shaded panels will pull down the "average" voltage that the MPPT controller will run the array at, with the result that some panels will be running at less than their optimum voltage while others (the shaded ones) will be running at more than their optimum voltage. With separate controllers, each and every panel can be run at its ideal voltage. For you, with two controllers the highest output overall would be achieved by running your potentially shaded panels on one controller and your unshaded panels on the other.

To decide on suitable House battery capacity, you need to consider your Average overnight battery drawdown along with what you consider to be an acceptable discharge level. For me, those figures are 30 Amphours and 30%, so a 100Ah AGM battery is more than adequate. The trick is to fit enough solar power to ensure that your battery is always fully charged by the end of the following day.
 #171617  by gerard
 Thu Mar 25, 2021 8:51 am
Thanks for your reply and help Neddy. I will consider that option.

Our Nespresso (1400W) and charging the ebike batteries means we use quite a bit more than you do. And there are some quite heavy loads, the Nespresso will draw something like 120 A. After five years I have not seen the two 95Ah degrade noticeably, but obviously we are pushing it in winter under cloudy conditions when both Ebike batteries need charging and when we are not driving. One such day is OK, the second day is really demanding for the batteries.
Increasing solar input from 300 to 480Wp will help, but once the current batteries eventually start degrading or failing we will be looking at 200Ah Lithium.

Gerard
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