Solar panel advice

[Grey Owl]

Hi everyone,

 

Just now starting to look for solar panels, just to top up the batterys.

we have a flat roof and victron invertor . The connections are already in place and waiting on good advice.

We are living in southern Ireland..

cheers m :

[Smelly]

We kept a "want it now" on ebay until we found a dcent price... Took about 3 weeks. As it turned out the vendor wanted to fill a container that he bringing over so stuck some decent sized panels in amongst the caravan sized ones and was selling them at a lower markup.

[Justme]

How many watts do you want?

What voltage system do you have?

Will you use a MPPT controller?

Is this on a boat or house (IE will you want ridgid or flexible panels)?

Are you risk adverse? (IE would you do a personal import but then if they have a problem its basicaly tough)

 

For rigid panels the best price I can get in the uk inc del is £2.72 per watt on 400 watts

 

Justme

[PaddingtonBear]

Be very careful, solar panel are very overrated , the mostly DONT do what it says on the tin.

[Justme]

Be very careful, solar panel are very overrated , the mostly DONT do what it says on the tin.

 

 

I would counter that & say that most people under size the array they use as they cant / dont want to pay for the system the actually need. They buy a piddling little 20watt jobby & expect it to power the QE2.

 

Its very easy to check the specs of a panel & know with a good degree of accuracy how much power you will get in an average year IF installed correctly.

 

 

Justme

[Smelly]

I would counter that & say that most people under size the array they use as they cant / dont want to pay for the system the actually need. They buy a piddling little 20watt jobby & expect it to power the QE2.

 

Justme

 

Or you buy what you an afford and live with the results. It is always an improvement on burning dinosaurs, it;s just a question of how much you love the dinosaurs you're burning.

[larrysanders]

ok here's the million dollar question then... ? we've got a weekend boat (with an outboard so this doesn't always do much for for the batteries) i need to top up three leisure batteries in a bank during the week. we power a small lcd tv, a fridge part of the time, lights... and battery power to kick start a gas water heater.

 

would a 20 or 35 or 50 watt solar panel do anything, or do i need to think much bigger?

[WotEver]

ok here's the million dollar question then... ? we've got a weekend boat (with an outboard so this doesn't always do much for for the batteries) i need to top up three leisure batteries in a bank during the week. we power a small lcd tv, a fridge part of the time, lights... and battery power to kick start a gas water heater.

 

would a 20 or 35 or 50 watt solar panel do anything, or do i need to think much bigger?

 

You need to do a Power Audit.

 

Theo wrote a spreadsheet and Gibbo's hosting it here, if you like to do things the pee-cee way.

 

Regards,

Tony

[larrysanders]

thanks for that... however i'm trying to work it out, but still no clearer...

[WotEver]

thanks for that... however i'm trying to work it out, but still no clearer...

 

Hi Larry,

 

Search around this forum or elsewhere on the web for threads about Power Auditing - they abound

 

You could do a lot worse than starting here:

 

http://www.tb-training.co.uk

http://www.smartgauge.co.uk

 

 

Basically, what you're trying to do is to accurately list the power consumed by all of your electrical equipment in an average (cruising) day. For example, you'll need to know the power consumption of your fridge, guestimate its duty cycle (50% or less if it's fairly modern; way worse if it's older) and thereby calculate how many watts it's going to remove from your batteries in this 'average day'. You have to do this for every piece of electrical equipment on the boat. Everything after the fridge is easier because their consumption is generally constant.

 

Once you know how much power you're drawing in a cruising day you know how much power you need to be putting back into the batteries. It's a little more complex than that, but I'm just trying to give you a broad overview.

 

If you're only drawing a tiny amount of power then sure, you only need a tiny array - but there's no point in guessing, you have to do the boring maths.

 

HTH

 

Regards,

Tone

[Chris Pink]

ok here's the million dollar question then... ? we've got a weekend boat (with an outboard so this doesn't always do much for for the batteries) i need to top up three leisure batteries in a bank during the week. we power a small lcd tv, a fridge part of the time, lights... and battery power to kick start a gas water heater.

 

would a 20 or 35 or 50 watt solar panel do anything, or do i need to think much bigger?

 

Because of the long time during the week I would suggest one of the 50-65 Watt panels around, they are quite an economical size in terms of cost-per-watt.. I have one that more or less runs my boat this time of year but although I don't use the laptop for a couple of days the batteries usually end up fully charged. You may not get 100% in the winter but then you would waste a lot of energy (= money spent on panels) in the summer.

 

An energy audit is never a bad idea but unfortunately solar power generation is such a non-linear thing that you will struggle to end up with meaningful results. if you are trying to be definitive then you have to choose a time of year (equinox for example) and accept that half the time you will generate too much and half the time not enough.

 

For your use i would start with 50-65 Watts and see how you get on.

Edited June 18, 2009 by Chris Pink

[Justme]

Ok I am going to make some assumptions

 

1, 3 x 110amp batts

2, you discharge them to 50% soc over the 2 day weekend & also use all the power produced by the panel for those two days.

 

We now know we need to "make" 165 ah over the 5 days.

 

3, assuming equal weather thats 33ah per day

4, assuming summer only & 6 hours of full sun per day thats 5.5 ah/day or 77watts (at 14v charging volts)

 

Now there are a few things wrong with that

 

1, I have not added on the % for charging losses

2, you wont get 5 sunny days in a row

3, you might use more or less power than that

 

But its a start.

 

I would go for a bit more than Chris Pink has suggested say 80-120watts to start with. But without knowing the amount of power you use its a guess.

 

Oh & dont forget a charge controller. If you can use a MPPT one. Not sure how much diff it will make on a small panel but on a bigger one its worth the cost.

 

Justme

Edited June 18, 2009 by Justme

[larrysanders]

many thanks for that... i was looking at a 40w panel kit on ebay... but i now going to splash out on a bit bigger one. but that's really helpful indeed!!