Need help choosing solar gear

[DeanS]

I'm looking at buyingg THIS

 

Total 680Watts

 

4x170W

80amp MPPT controller

 

 

Comments please?

 

If I want to perhaps upgrade in the future, would it be better to order 4 panels, each with a 20A MPPT controller (4 controllers) for the same price....(on Ebay..same company)

Edited April 25, 2013 by DeanS

[Psycloud]

Can't comment on the panels but the organisation do lots of festivals and run (as far as possible) their stage off-grid using a variety of sources. Have been in it often when the power's gone and they've needed to use a genny

 

Edit: I was almost interested in buying that setup myself but they are big panels and I havent really got room for 4 on the roof taking into account chimneys and vents.

Edited April 25, 2013 by Psycloud

[lexicon]

Too be honest looks pricy I would get a set of house 30v panels and a controller seperate

[Justme]

Just to put the cat in with the pigeons.

 

With the amount of energy you are using you would be better of with a battery bank of 24 or 48v.

[smileypete]

I'm looking at buyingg THIS

 

Total 680Watts

 

4x170W

80amp MPPT controller

 

 

Comments please?

Up to you, but I'd recommend starting with half that, 2 panels and 40A MPPT.

 

Keep the rest of the money in a savings account for a rainy day. You could buy an extra panel to give 3 panels and 40A MPPT if you really really must

 

cheers, Pete.

~smpt~

Edited April 25, 2013 by smileypete

[magnetman]

Just to put the cat in with the pigeons.

 

With the amount of energy you are using you would be better of with a battery bank of 24 or 48v.

Thats a good point. I was wondering about having a 12v domestic bank (already fitted) AND a 24v heavy duty bank for storage from solar, which would run a large inverter to run all mains loads and a 3stage charger which could be used to top up the domestic 12v low load bank when there was excess solar.

 

That way you stick with 12v pumps etc and have two battery banks to call on.

 

Or is that too complex

[DeanS]

Could someone advise me which is the better of these 2 options:

 

Option 1 - 680W panels with 2 x40Amp MPPT controllers - £660

 

Option 2 - 1020W panels with 2 x 60 PW controllers - £610 (I could upgrade the controllers in following years if needed)

 

 

I'm considering using solar to run the desktop PC as well.

[eightpot]

I bought one of these panels and a 20a tracer from Bimble a couple of weeks back for my boat. They look large on their own:

 

but when on the boat roof they don't look quite so unwieldy.

 

Prior to buying I did a little digging and found this: http://thegreenlivingforum.net/forum/viewtopic.php?f=22&t=107403

Basically, the panels had the wrong UV additive in the white backing behind the cells. Mike at bimble was very approachable so I'd suggest dropping him an email if you have any queries.

[Grace and Favour]

I bought one of these panels and a 20a tracer from Bimble a couple of weeks back for my boat. They look large on their own:

 

but when on the boat roof they don't look quite so unwieldy.

 

Prior to buying I did a little digging and found this: http://thegreenlivingforum.net/forum/viewtopic.php?f=22&t=107403

 

Basically, the panels had the wrong UV additive in the white backing behind the cells. Mike at bimble was very approachable so I'd suggest dropping him an email if you have any queries.

I hope that keeps your car battery fully charged, 8pot - - - - have you done a full power audit?

[George94]

Could someone advise me which is the better of these 2 options:

 

Option 1 - 680W panels with 2 x40Amp MPPT controllers - £660

 

Option 2 - 1020W panels with 2 x 60 PW controllers - £610 (I could upgrade the controllers in following years if needed)

 

 

I'm considering using solar to run the desktop PC as well.

 

Dean,

 

You have raised the right question here. It's very clear that MPPT is better than PWM. Just as it's very clear that a Rolls Royce is better than a Ford. So why doesn't everybody drive a Roller? Answer - cost.

 

I think it is highly likely that Option 2 will give you more usable amps over the year. I can't be certain, because it is impossible to find real comparison data anywhere, and because a lot depends on the weather.

 

BUT, advocates of MPPT controllers say they are UP TO 30% more efficient. (Note the "Up to"). So, looking at your choices, lets downgrade the wattage of the PWM package by 30%, and we get 1020*.7 = 714 watts, which is still more than 680, and at a saving of £70.00

 

Now in fact, we shouldn't use 30% when going the other way, we should use 23% (100% + 30% = 130%, and 100 is 23% less than 130). This gives a wattage of 785, not 714, which strengthens the case for PWM. BTW, 130% of 785 = 1020.

 

Of course, there are other considerations. You will pay more to mount the extra panels, and also you may not have room for them, You may be able to use the panels in series with MPPT, which means higher voltages and lower currents, and therefore smaller cables.

 

There's a lot to think about, but one thing is clear. MPPT offers benefits over PWM, but at a cost. Sometimes, as is probably the case here, the cost will outweigh the benefits (in financial terms, anyway). Those who blindly say that MPPT is always the best choice have never done the sums.

[boots]

Am I right in thinking that the difference between mppt and pwm is also down to the voltage of the panels? Seem to recall somewhere that (simplistically ) a pwm acts almost as a voltage regulator - just dumping excess voltage, so if you had a 40v panel at (say) 5A then with a pwm you would only ever get 5A where as a mppt is more of a power converter so you would get more amps at a lower voltage.

 

Or is this totally wrong?

[Chris Pink]

No. Although Mr 94 seems to ignore this.

[eightpot]

I hope that keeps your car battery fully charged, 8pot - - - - have you done a full power audit?

Yeah, it's got a Cléon 1108cc engine which is okay-ish. I do have a 1.3l TS engine out of a challenge cup car which would make it somewhat of an amusing Q-car...

[Chris Pink]

And not particularly simplistic, pretty spot on. The case where it doesn't make a difference is where the panels are fairly well matched to the batteries. There used to be (may still be) panels with VOC around 17V where there's not much difference.

[DeanS]

I do understand that MPPT controllers are far superior, but could I start with 1020Watts with PW controllers now, and upgrade them to MPPT as time allows? As I see it, that would still give me more charging for lower cost (compared to 680+MPPT now). I could even consider putting in a 7th battery.

[blodger]

To be honest I would go for neither but if the two choices were all that were available then I would go for for the 1000+ & mpw.

 

Perhaps locality of self & panels dictates what is available.

 

Personally, I would EBay panels at not much more than 0.50/watt, as you are widebeam I would probably go above the 100watt and 12v nominal I have gone for so as I can still hop scotch along the roof.

 

I am biased against MPPT as I bought one that proved not to be and another that does not seem to work despite its cost and, the upto 30% better is only in ideal condtions which do not prevail much on the cut and fitting flat on roofs.

 

I would get a decent ampage and float voltage MPW and start with 2/3 panels an d gradually grow the system as the advantage shows and stop when the return diminishe

Edited April 26, 2013 by blodger

[DeanS]

My roof is approx 2.5m across so I'd have 0.5m on each side of these panels to walk along, which is more than I had on my narrowboat which had the panel all the way across. I have space for 3 panels near the stern, and 3 near the bow, leaving space round the centre rope. If I dont spend the money on solar now, other things will come along and I may never have the opportunity again, so it's a case of buying something that will do the job, and walk away.

 

I think I'm going to go for the 1020W option for now.

[George94]

No. Although Mr 94 seems to ignore this.

 

A characteristically helpful post from Mr Pink.

 

Would you accept that if an MPPT controller cost £10,000 it would not make economic sense in this scenario? If so, then what we are talking about is the price point at which an MPPT controller WOULD make economic sense.

 

Now it may well be of course that there are other considerations which I have failed to take account of, and if so, feel free to point them out.

 

We all agree that MPPT controllers are better. However, when panels are this cheap, the economic argument seems to favour PWM.

[matty40s]

.....but MPPT do not cost £10k. You can get a 60A brand new model e-tracer for less than £300 if you do some sifting.

The sums for all those extra panels include thicker cable, many more brackets - and associated many more holes in boat roof!!.

 

Some of us do do the sums, and also use solar on a daily basis all year round.

[bizzard]

The sun is shrinking.

[smileypete]

Just noticed that Navitron are doing domestic sized solar panels for about 65p/watt delivered:

 

http://www.navitron.org.uk/product.php?proID=140

http://www.navitron.org.uk/product_detail.php?proID=471&catID=140

 

Also got just a few Sharp ones at that price. Suprisingly it looks to be cheaper for new panels delivered than any sellers on Ebay at the moment, might be ideal for those who prefer new panels with a guarantee and not second hand ones, or can't wait for the good ship Bimble Solar

 

cheers, Pete.

~smpt~

Edited April 26, 2013 by smileypete

[Christianonthecut]

These look well priced, have made an offer myself...

 

http://www.ebay.co.uk/itm/190830222228?ssPageName=STRK:MEBOFFX:IT&_trksid=p3984.m1432.l2649#ht_215wt_1255

[Psycloud]

I think I'm going to go for the 1020W option for now.

 

I will be watching your progress before taking the plunge. We don't really need them right now (shoreline) but they might be useful if we go off in the summer. I might just get 2 though as couldn't fit 4.

[George94]

.....but MPPT do not cost £10k. You can get a 60A brand new model e-tracer for less than £300 if you do some sifting.

The sums for all those extra panels include thicker cable, many more brackets - and associated many more holes in boat roof!!.

 

Some of us do do the sums, and also use solar on a daily basis all year round.

 

The sums are changing as panel prices come down.

 

So given your experience, please do the sums for Dean's scenario, and tell us which controller makes sense.

 

If you say MPPT, then you will be claiming much more for the efficiency of MPPT than the people who sell the things. Which is a little unusual, to say the least.

 

Just because MPPT worked for you, at the prices you paid, doesn't mean it will necessarily work for Dean.

[smileypete]

The sums are changing as panel prices come down.

 

So given your experience, please do the sums for Dean's scenario, and tell us which controller makes sense.

 

If you say MPPT, then you will be claiming much more for the efficiency of MPPT than the people who sell the things. Which is a little unusual, to say the least.

 

Just because MPPT worked for you, at the prices you paid, doesn't mean it will necessarily work for Dean.

 

Fair enough then, please post a link to a PWM controller that has a reasonably long absorption charge time, say around 2 hours or more.

 

cheers, Pete.

~smpt~

Edited April 26, 2013 by smileypete