# Help with solar panels/invertors



## 95038 (May 1, 2005)

Hi all,

Just acquired my first ever motorhome (picking it up on Fri).

The first things I'm thinking of adding are an invertor and solar panels.

The invertor's fairly simple - continuous load rating and type of sine wave. The thing I want to know about invertors is - do they actually have a plug socket on them? Or can you wire them into the sockets on your MH?

Solar panels need a bit more research I think.

A MAJOR consideration here is cost. What sort of cost are we looking at?

To start with, won't be running many electrical appliances over and above the lights and water pump (presume it's best to run the fridge off gas?).

However, later on, we'll be looking at adding a telly, satellite receiver and possibly other stuff such as playstation for the kids etc.....

Any recommendations on capacities etc?

Having read a couple of recent threads on both of these topics, there's clearly a lot of knowledge on this board about these things.

So.............all advice greatly appreciated!!!


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## 88724 (May 9, 2005)

Hi Lucky

Invertor choice is far from simple, yes they have a socket on them and some are OK to wire into the standard system.

Solar Cost, depends on how much power you want to generate (for how many days away from hook up) really unless there is no other way, solar is too expensive and not reliable enough.

Invertor Size for the items you want to run a Sterling 300w Quasi Sine wave, If you want to use another manufacturer bear in mind that their ratings are not as easy to decifer, one I had a look at the oher day the invertor was actually only 1/4 of the BOX figure ieit said 1600 watt invertor and was actually only 400w rated cont at 40 degree's !

How many days away from hook up?


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## DABurleigh (May 9, 2005)

Lucky Striker,

Solar panel output. If all you wish to do is to compensate for the drain of the alarm, etc., something small and cheap of 10W output is fine. Beyond that, I would go to at least 80W for use in the UK, say up to £400 or a little more depending on professional fitting, charge controller, etc. But even this will not power the TV for hours a day. As to technology, amorphous or crystalline, that is more tricky and strong feelings abound. I went crystalline, mainly due to the inferior life of amorphous.

Inverters. Yes, they do have a mains socket and they can also be integrated into your mains wiring, but in the general case it requires a lot of thought to handle hook-up power or not, alarm for inadvertent battery drain, battery charging, avoid batteries powering fridge on mains, etc. and not least earthing issues. I have this in my van, courtesy of a Victron Phoenix Multiplus integrated sine-wave inverter/charger. Short of this sort of integration, I'd be tempted to wire the inverter into a dedicated socket, perhaps near where your TV will be situated, though always turn the inverter off when not in use as they have a small standing current drain. A 300W modified-sinewave inverter should be enough for your anticipated use; if you can get away with 150W these tend not to have a fan, which can be obtrusive in quiet environments. A sine-wave can be needed for inductive loads, such as motors (electric fans, hairdryers, mains aircon) and certain lighting, and inductive toothbrush chargers.

Power absorption fridge off external mains, then gas, and finally 12V when motoring.

Dave


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## 88724 (May 9, 2005)

Hi Dave 

The inferior life of Amorphous????? Sounds like the sales patter of a crystaline salesman.

Amorphous Uni Solar is what NASA sends in to space it lasts longer, produces more power especially in slight shadow conditions, one bird splat loses nearly all output from a crystalline panel.

Quote

A sine-wave can be needed for inductive loads, such as motors (electric fans, hairdryers, mains aircon) and certain lighting, and inductive toothbrush chargers. 

End quote

Only one of those needs a sine wave and thats the inductive toothbrush. sounds like sales patter again, many of the invertor manufacturers before OTHER than Sterling were insisting I needed a Sine wave invertor, all just to bump up their sales (either that or they just dont know their products)


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## DABurleigh (May 9, 2005)

George,

It was the review of solar panels in the July 2004 issue of Practical Motorhome that made me look into life at the time. Unfortunately I no longer have the article and the website only has an extract:
http://www.practicalmotorhome.com/product/jul04.html
The article was certainly pro-amorphous for UK use, but I decided crystalline 
Here is another typical reference:
http://www.ecocentre.org.uk/solar-electricity.html
"Amorphous cells are made by spraying the silicon directly onto glass or ceramic in layers. these types of cells are the cheapest to produce but contain impurities, so the overall conversion of light to electricity is low (~5%). They also have a much shorter life span than others and are usually guaranteed for 6 years. Recent developments in this field are constantly improving performance."
And another:
http://www.pvresources.com/en/technologies.php
"The most important tasks in the future are utilisation of less pure silicon and increasing efficiency (monocrystalline solar cells) and increasing efficiency and life-time (amorphous solar cells)."

As to sine-wave, I did say "can be needed", not "always needed". As a example a deskfan I used in southern France to get some air movement in the van (even with windows open!) hummed like crazy on a couple of modified-sinewave inverters, but it was fine on mains and when tested subsequently off a sine-wave inverter. Drove me as nuts as the stifling heat with it turned off .....

Conversely, some inductive toothbrush chargers work OK with modified-sinewave inverters.

Dave
PS Oh, yes, and I thought the "bird splat" issue was more how the cells are connected, rather than the underlying technology, though certainly amorphous' (lesser maximum) output rolls off less in cloudy conditions.


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## 88724 (May 9, 2005)

Hi Dave

Were do we begin

Yes they are larger for same output, but according that eco site they would have to be 3 X as large for same output, which is NOT true. they are at worst 50% bigger but according to the first serious site you linked too they would need to be 3X bigger ( The motorhome mags are only good for a laugh when it come to electrics heres a quote about a 64 watt panel from the link you supplied, "Two hours of light per day will quench a 128W/hour daily power demand" how many people are sucked in by the crap these people publish)

Amorphous is not the Cheapest ??? But maintains its output in Hot weather (were the others lose power on hot days !) bird splat or shadowing is poor on all types except Amorphous.

Uni Solar is used by NASA, these people use the best regardless of cost. If the life was low would they be using for long term space probes ?

Uni solar are not that much dearer. Actually just checked and average same price now.

They are bigger, but work better, the claimed life there bugs me, if NASA use for space probes they are not likely to use something that as an earlier failure rate especially as it bigger, that just doesnt add up.

On the toothbrush thing the only way to find out is to test, ie by new one test if it fails, taking it backs down to your conciense.

Birdsplat, one case, bloke could not figure what was wrong with his solar set up nice bright day and hardly any output. clean off bird splat and power back up.

With the fan, hard to say but were the Invertors Cheapo? The Nikkia (Maplins) ones I have tried all heat up Power supplies and increase hum on certain items, only if you have your ear close not generally intrusive and yet the Sterling as always been better in this regard.

Or maybe it was the control electrics in the fan?
Its hard to say on individual cases.

When I went to Sterling I was enquiring about a big PURE sine wave invertor (as all the invertor people I had enquired of before that insisted that was what I needed) Charles Sterling asked what I wanted to power and then proceeded to sell me a Quasi Sine wave Invertor and Guaranteed that if it didnt he would upgrade to full sine wave at trade cost (bear in mind that the pure sine wave is over twice as dear) I never got the Upgrade and think about this Charles lowered his sale by more than half. ALL the other companies tried to sell the more expensive but not needed Sine wave invertors.


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## DABurleigh (May 9, 2005)

I think it prudent if one decides to buy amorphous that one checks the guarantee and perhaps with the manufacturer for the data that shows how the maximum output drops off with time, that's all. The curves I saw showed a significant drop-off after as short as 3 years. No doubt these were not Uni-Solar, who "pre-soak" their panels to reduce drop-off, which itself invites comparison with the competition over maximum output per unit area.

One of the frustrations I found was that it was impossible to get at the underlying data or tests that could truly compare annual output per unit area or £ for different suppliers' products for horizontal mounting in an open environment in the UK, let alone in various types of partial shade. It makes a purchase a bit of a crap-shoot, particularly if one is reluctant to do the necessary research.

One of the modified wave inverters that made the fan hum like mad was a Maplin (mine); the other a Sterling "can" one (borrowed).

Dave


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## 88724 (May 9, 2005)

Hi Dave

Uni Solar is the one I alway's point too, I think solar in general is not usually the answer to peoples power probs, so I have no reason backing any particular brand or type.

NASA putting them into space tells me they have a far better life expectancy, than the guarantee's suggest. If they are putting them on Space Station and probes tells me NASA think they are going to last. Their budget is bigger than we can muster !

The drop off on amorphous is down to the rated capacity, ie when new a 75 w panel can be chucking 90w out but this settles back to the rating.

You can throw an awful lot of money into solar panels and still not get the results you want, it takes a lot of planning and research to get it right.

That line from Practical motorhome sums up why most people have not got a clue to say that a 64w Panel will in 

"Two hours of light per day will quench a 128W/hour daily power demand"

Shows they do not have a clue and now many readers believing that dross will be under the wrong impression too.

Panel rating

1. the panel could be set at 21v when this is bought down to useful voltage, you lose wattage in conversion

2. Next the above is on Angled panel to collect direct rays, it also assumes Perfect sunshine

3. generally its done in a lab which means the panel temparature is lower

Typically you will only get 70% of panels (normal panel) rating in real world if you angle the panel and can be lower in hot conditions

Just for comparison an Uni Solar Amorphous gives out 84 % of its rating under same conditions and maybe even higher under hot conditions

Under shadow there is no comparison the Uni solar is way better.

With the fan it was probably the electronics in the fan. On the Air Cooler unit I have (the Swamp cooler air-con) it runs as quiet under either really needed it last year in Belgium!!


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## 95038 (May 1, 2005)

WOW!! This is great! You guys have just taught me in 5 minutes what it would probably have taken 12 months to find out - and saved me a load of cash as well!

Our MH will be used for a variety of different things:

1. Weekends away on proper sites with hook up.

2. Weekends away at motor racing tracks with no hook up.

3. The odd weekend where there will be no external power at all.

I think I'll leave the solar panels for now - seems they're not all they're cracked up to be - especially if you get it wrong!

As for the inverter - what's the calculation to figure out how long your batteries will last?

And what's the calculation to find out what capacity you need? (I know George, you suggested a 300W unit)

Presumably, if your leisure batteries go flat and you REALLY need power, you just run the engine for a while?

George - where do you get these Sterling inverters from? and how much ££££££ ??!


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## Anonymous (Nov 10, 2000)

Hi Lucky Striker. All the information about just about anything is available online on the Internet. It just takes time to find it. These Forums are to help people like yourself that perhaps have not got the time to do the research. However, there are always opposing arguments to other's recommendations. I have been using Solar Power for over 4 years and Inverters for the same amount of time. I would say on the whole they are well worth the outlay if you are an heavy user of electricity off-site. If you are only an occasional user, then don't bother. An inverter is a must of course if you wish to use normal TV's etc. 300W should cover most uses.


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## 88724 (May 9, 2005)

Hi Lucky

For weekends off power and with the kind of usage you have indicated I would reccomend 

2-3 batteries and a good charger (Sterling 10 A International which also act as a power supply when on site) , NO split charge whatsoever (loses charge when you are driving along)

300 W Sterling invertor

If you are using 100w at 12v (nominal) that will be around 9 amps (the TV and DVD togethor will not usually use that much, with TV and PS 2 it occassionally uses more.

At the rate you could watch DVD's for 15 Hrs over the weekend and still run everything else happily and not drain the batteries (3) below 50% 

TV alone? over 30 hours (and I am being conservative here)


Trouble with solar is that when you are likely to need power ie stuck in the van due to poor weather thats when its producing next to nothing when its bright sunshine why would you be sat in the van all the while?

Dont get me wrong solar can have its uses and depending on what people want to do I have said it can be part of the answer in certain circumstances


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## 95038 (May 1, 2005)

OK thanks again guys!

Just had another thought - we'll probably need to run a microwave in the van - young baby - easier to heat up milk etc etc.

I'm being incredibly ignorant here, but is there anything to stop us using our household microwave, as long as the inverter/leisure batteries are up to it?

Presume we'd need a higher rated inverter than 300W?

Cheers,

Rob


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## 88724 (May 9, 2005)

Mains Microwave through invertor 

Modern 240v Microwaves are getting more efficient (most are anyway) so for 700w cooking power they require about 50% more input ampage so a 700w microwave would need 1050w of power in.

1050w thru an invertor would cost about 10% extra to allow for invertor efficiency so thats 1155w so the ampage required would be in the order of 96 amps. Microwaves tend not to run at 100% efficiency on quasi invertors so allowing for this we get 630 cooking watts costing 96 A

So an Invertor fed mains microwave gives roughly 6.56 watts per Amp

Direct 12v microwave 

12v microwaves have not advanced as much efficiency wise, a 450 watt Samsung uses 750w, 750w at 12v = 62.5 Amps

So a 12v Microwave gives 7.2 watts per Amp

Overall a 12v microwave is only slightly more efficient. 

Other Factors 

Price a 240v Microwave can be had for as little as £25, with a brand and good guarantee £40. A 12v version costs up to 10 times more than the average entry level mains version

Size Mains microwaves tend to be 25% bigger capacity

Speed mains will cook quicker (having 630w, against the 450w of the 12v version)

Battery bank size , to maximise the life of your battery bank no current draw should exceed 10% of the amp hour rating of the battery bank, so for a 12v the battery bank "officially" should be greater than 650 ah, for the mains version 1,000 ah is the "reccomended" size. 

Another effect of this is that taking say 5 amps per 100 ah battery bank is the 20 Hour rate which allows 5 amps to be withdrawn for 20 hours before flattening battery completely at 10A draw the battery will not last 10 hours as expected. This is just to show that the amp hour draw will cost you more amp hours than the consumption suggests, this would apply to either microwave.


In practice most take the performance "hit" in terms of longivety and actual ah usage.

In the end its all down to what is important to you, cost £, performance (cooking), efficiency (watts per amp used), actual amps used, size of cooking area and ease of replacement out in the cuds (will always be easier to replace a mains microwave)


Ah Comparison figures for a 5 minute warm (not allowing for battery bank size)

12v 5 mins @ 62.5 amps = 5.21 Ah

240v 3.57 mins @ 96.25 amps = 5.73 Ah (the mains will cook quicker 630w against 450w)

You are now talking about a 1600w invertor (£350 ? probably less) Definately 3 battery minimum, little bit less TV no probs at all.


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## 95038 (May 1, 2005)

Yikes! Looks like we might have to do without the microwave!!

Does this look like a good deal? ANd more to the point - will it do what I want it to? (excluding microwave)

http://www.cybermarket.co.uk/ishop/923/shopscr3422.html

Or would this be better?

http://www.cybermarket.co.uk/ishop/923/shopscr3429.html

The Sterling ones are more expensive for sure, but as you say, the rating/loading info is more honest.


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## 88724 (May 9, 2005)

Hi Lucky

My last posts shows that its easily possible to run one, the actual drain is only around 5.6 amp hours for 5 Mins, whats babies bottle 30 secs? whats that 1/2 an amp hour

The Big Sterling should cost you less than £340 , the microwaves arew £25 NOW !

LOOKED AT THAT WAY THOUGH even if you used consistantly for every bottle baby ever as it would be too expensive.

350w direct from sterling would cost you less than that site too.


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