Solar panel tests

[Nickhlx]

I don't think we're talking about an "extra" panel being put in. We're talking about the same number of panels being wired up in different ways (that's what I thought anyway). If we have two panels in parallel at 12 volts and rewire them in series to get 24 volts then the voltage will double and the current will halve.

 

The voltage and current on the battery side of the MPPT controller will remain the same in both cases.

 

Gibbo

 

OK - for some reason I took it as an extra one but it confirms I am singing off the same song sheet anyway..

 

Nick

[Gibbo]

OK - for some reason I took it as an extra one but it confirms I am singing off the same song sheet anyway..

 

Nick

 

Or at least the other side of the same page

 

Gibbo

[Berty]

Yes wire them in series you can then either get less losses or use smaller cables for the same losses.

 

Why the FX80 when you only have 400w of panel when the cheaper "60" would have done just as well?

 

The 80 will go to 1000-1200w on a 12v battery bank (more on 24 & 48v ones).

 

Justme

 

The cheaper one was only about £60 cheaper, ie. about 10% of the price.

 

Based on the string sizing tool on the outback website (http://www.outbackpower.com/resources/string_sizing_tool/) the FX80 has plenty of spare capacity for adding additional panels, whereas the FX60 would be maxed out at three panels.

 

In practice, I admit I will probably only ever add one more panel, as size contraints become a major factor. On the other hand, should the technology take a sudden leap forward and provide panels with double the power density, the FX80 will still cope.

 

Paying the extra 10% seemed worthwhile to me.

 

I think the panels in series would have an open circuit voltage of 67V. Is this the value I would use for voltage drop calculations? Would 10mm^2 cable be suitable? (The cable run is approximately 8 to 10m, there and back.)

 

Cheers,

Berty

 

What input voltage will the FX60 and 80 go up to?

 

Gibbo

The specs say 150V (open circuit).

 

Just thinking about it, does volt drop even matter? Does it actually translate to lost power - ie. through cable heating? Or, can I assume that as long as the voltage to the controller is above 15V, I'll be able to charge my 12V batteries without problems.

 

Obviously I'm trying to minimise the losses in the system, but I'm probably going to have to route the cables (in conduit) between the T&G and insulation on the roof so space is definitely limited.

 

Cheers,

Berty

 

I don't think we're talking about an "extra" panel being put in. We're talking about the same number of panels being wired up in different ways (that's what I thought anyway).

 

Gibbo

 

That is indeed what I was talking about!

 

Just done the calculation based on the data in the tables here: http://www.csedistributors.co.uk/cable/voltage-drop.htm of 4.4mV per amp per meter, for 10mm^2 cable, for a 10m run, at 410W (=6.2A @67V) gives a voltage drop of just under 0.3V. That's only 0.4% which seems like it would be fine!

 

Unless I got my sums wrong

 

Cheers,

Berty

Edited May 26, 2009 by Berty

[Gibbo]

The specs say 150V (open circuit).

 

Just thinking about it, does volt drop even matter?

 

Yes.

 

Does it actually translate to lost power - ie. through cable heating?

 

Yes

 

Or, can I assume that as long as the voltage to the controller is above 15V, I'll be able to charge my 12V batteries without problems.

 

It will still work. But with less power because more of it will have been wasted heating the wires up.

 

That is indeed what I was talking about!

 

But that's not what your post said. You said you had two panels to wire up. Not that you already had one installed and you were adding another one. Two different things.

 

Just done the calculation based on the data in the tables here: http://www.csedistributors.co.uk/cable/voltage-drop.htm of 4.4mV per amp per meter, for 10mm^2 cable, for a 10m run, at 410W (=6.2A @67V) gives a voltage drop of just under 0.3V. That's only 0.4% which seems like it would be fine!

 

Unless I got my sums wrong

 

Your sums aren't wrong. The loses in those tables though are lifted from the IEE regs which gives them at 70 deg C. They only really reach that temp in conduit indoors at full load. Yours will probably be cooler than that because you're nowhere near maximum load for the cable so the losses will be lower.

 

The open circuit voltage isn't the voltage they will be running at so the current will be higher. The losses are still reasonable though (in fact they're very low).

 

Gibbo

[Justme]

Yep a max working V of 145 & a max before smoke of 150v & you can still charge a 12v bank.

 

They do say that the internal losses are higher if you do that but not hugely.

 

The max volts should be the OCV plus the allowance for the lowest temp you will ever see as thats when the array will give its highest power (sunny cold winters days) even if only for a short time.

 

Yes 10% extra for the better one is money well spent.

 

Justme

[Berty]

But that's not what your post said. You said you had two panels to wire up. Not that you already had one installed and you were adding another one. Two different things.

 

Sorry, I must not have been clear in my quoting.

 

I am indeed talking about how to wire up two new panels for the first time - in series or in parallel.

 

Cheers,

Berty

[Gibbo]

Sorry, I must not have been clear in my quoting.

 

I am indeed talking about how to wire up two new panels for the first time - in series or in parallel.

 

Then everything is honky dory.

 

Gibbo

[Tom6]

Surely the optimum angle for solar panels is the same as the angle required for the gnomen of a sundial? So in northern England the 'height' the panels 'should' be propped up at 'needs' to be more than in southern england? Presumably there's a point at which it might be better to have panels along the side of the boat rather than flat on the roof? Hopefully this would be opposite the towpath and effectively 'stealth' the panels a bit, just hope they don't slip in by accident! Could sundial technology be used to calculate the ideal height angle?

 

Regarding getting the panels to face the sun presumably this could be done by clockwork rather than by electronics? If you have an analogue watch and point the 12 position towards true north (a compass should help here) then doesn't the sun bisect both angles between the hour hand and 12 o'clock?

 

I'm curious if there's any comparisons with diesel generators, such as the 'suitcase' types. How long would a diesel (or other) generator have to run each day to charge a standard set of batteries? How much the fuel would cost (at todays prices). Given those standarisations then how many years do each last, i've heard solar panels might last 20years before needing replacing? Once longevity of devices have been factored in then does the total cost of running a generator for a full year (including an appropriate fraction of purchase price) compare well with the relative cost of running solar panels?

 

I would guess that panels are better added in parallel rather than in series. Being in series adds voltages together whereas parallel is more about getting more current out of them. Kirchoff's Laws would probably give a more precisely mathematical answer but i tend to think of electricity as water flowing down a slope - Voltage is the height the 'water' started from, current (amps) is how fast the water flows. Unfortunately since V=IR i guess that a bigger load is comparable to having a steeper slope and smaller load like having a shallow slope? I would guess that adding panels in series would make the internal resistance of each panel more of a factor, using more power before it even got out of the panels? Hmm, my 'simplification' really doesn't help here i think

 

Would thicker wires (or more wires in parallel with each other) reduce the resistance of the wires and hence less heat would be generated in the wires? Could the heat be useful for drying clothes or sundry heating. Hmmm, wet clothes and lots of electrikery presumably go together shockingly well

 

One day we were crunching through the ice coming in to moor and some fool on the towpath nodded at our bags of coal and said "Got enough coal?", i said i hoped so and he said "A boat back there had solar panels ..." I've never heard anyone say " ... " before. I looked around at the snow and ice and looked back at him wearing big heavy coat and probably thermals and wondered how to explain that machines and things are unlikely to be even 100% efficient, let alone more than that! Luckily the skipper yelled at me to get a move on with the ropes Using these types of solar panels to generate a bit of electrikery is good but i wondered if attempts have been made to get hot/warm water from non-electrical solar panels on narrowboats? My guess would be that it means a larger 'hot' water tank and that most people use a combination boiler instead because of the space required.

 

Also wondering if other volunteers are needed for the client involved? My dad's boat is on the Oxford, if that would help provide broader data. Lol, it must be unusual to have 'broad' and 'The Oxford' in the same sentence? Murphy's Law suggests that 1 narrowboat will be permanently under a big dark raincloud this summer, hopefully Gibbo isn't on The Oxford heheheheh. Similar terms sounds good btw

 

Good luck and regards from

Tom

Edited May 31, 2009 by Tom6

[Justme]

Surely the optimum angle for solar panels is the same as the angle required for the gnomen of a sundial? So in northern England the 'height' the panels 'should' be propped up at 'needs' to be more than in southern england? Presumably there's a point at which it might be better to have panels along the side of the boat rather than flat on the roof? Hopefully this would be opposite the towpath and effectively 'stealth' the panels a bit, just hope they don't slip in by accident! Could sundial technology be used to calculate the ideal height angle?

 

Rega

 

 

Its easier than that. The angle is roughly equal to the Latitude of where you are for winter. As you can be quite far out with minimal losses you can average the summer / winter setting & split the diff. Dep on usage you could max the winter or summer on a fixed system or have two settings.

 

How is the test coming along Gibbo?

 

June & July have been good for me but Aug has been terrible so far with all this rain & cloud cover.

 

 

Justme