# The Naked Scientists Forum

### Author Topic: Solar Energy HELP!  (Read 3622 times)

#### Curve

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• Posts: 2
##### Solar Energy HELP!
« on: 02/07/2006 21:53:41 »
Hi there Im new to this site and Im wondering if any1 could help me, I have to design a solar installation to provide 133.45Amps per day to charge 12v batteries which will then go through an inverter to supply household circuits, the house is in scotland, glasgow area. I cant find anything on how to calculate the PV array size required and how many to supply the amount of current with the average irradiance levels in scotland, can any1 help me?[:I]

#### neilep

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##### Re: Solar Energy HELP!
« Reply #1 on: 02/07/2006 23:06:09 »
Hi Lee,

welcome to the forum.

Please grace us with some patience as sometimes answers take a little while to come....but hang on in there.

Men are the same as women, just inside out !

#### Curve

• First timers
• Posts: 2
##### Re: Solar Energy HELP!
« Reply #2 on: 03/07/2006 17:03:32 »
Thanks neil, Just worried becuase its a project i have to do and Im really struggling trying to find out how to calculate the solar panel size Required with the amount energy the sun supplies in scotland.

#### Soul Surfer

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• keep banging the rocks together
##### Re: Solar Energy HELP!
« Reply #3 on: 03/07/2006 18:18:34 »
133.45 (so precise!) amps x 12v  is around 1.7 Kw

This tallies with the figures given by the "21st cenury smallholder" which suggests that  a 2kw peak system will manage to supply about half the domestic power for an average household

This will cost about  £12,000 - £14.000  and take up just about the whole of the roof space.

Still interested?  there are cheaper and probably better ways of doing it.

Learn, create, test and tell
evolution rules in all things
God says so!

#### another_someone

• Guest
##### Re: Solar Energy HELP!
« Reply #4 on: 03/07/2006 19:16:46 »
It does seem a very specific requirement, for which I can well understand that the amount of raw data available would be somewhat limited.

I suppose the starting point is how many hours of daylight does Glasgow have during the winter months?  How strong is that daylight?

The other question has to be how much storage capacity will the batteries have?  If the batteries can store 5 days worth of energy, then you can afford to average the sunlight over 5 days, and judge that a few good days in that 5 day period will overcome one or two bad days.  Ofcourse, if you can store 12 months worth of energy, then it all becomes easy – but that would be ludicrously impractical.  On the other hand, if you can only store 24 hours of energy in the batteries, then you will have to ask how much light you will get on the worst possible day, assuming it is the shortest day in winter, with 100% thick cloud cover, and heavy precipitation (snow or rain).

I know this doesn't answer your question as such.  I am not really capable of answering your question.  Maybe someone else might have more specific and relevant information; but without knowing over how long a period one needs to average the sunlight (i.e. how much charge can your batteries store), I don't think anyone can really say what is the worst case scenario that you reasonably need to allow for (although there can never be an absolute worst case, since it can always be envisioned that some freak condition may yet be even more disadvantageous than even the worst that you had thought of).

Also, you have to ofcourse take into account the differences between different types of solar panel, and the balance between cost and efficiency.  Is the exercise a 'cost no object' project, or are you looking at real life trade-offs?

George
« Last Edit: 03/07/2006 19:33:29 by another_someone »

#### neilep

• Withdrawnmist
• Naked Science Forum GOD!
• Posts: 20602
• Thanked: 8 times
##### Re: Solar Energy HELP!
« Reply #5 on: 02/07/2006 23:06:09 »
Hi Lee,

welcome to the forum.

Please grace us with some patience as sometimes answers take a little while to come....but hang on in there.

Men are the same as women, just inside out !

#### Curve

• First timers
• Posts: 2
##### Re: Solar Energy HELP!
« Reply #6 on: 03/07/2006 17:03:32 »
Thanks neil, Just worried becuase its a project i have to do and Im really struggling trying to find out how to calculate the solar panel size Required with the amount energy the sun supplies in scotland.

#### Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
##### Re: Solar Energy HELP!
« Reply #7 on: 03/07/2006 18:18:34 »
133.45 (so precise!) amps x 12v  is around 1.7 Kw

This tallies with the figures given by the "21st cenury smallholder" which suggests that  a 2kw peak system will manage to supply about half the domestic power for an average household

This will cost about  £12,000 - £14.000  and take up just about the whole of the roof space.

Still interested?  there are cheaper and probably better ways of doing it.

Learn, create, test and tell
evolution rules in all things
God says so!

#### another_someone

• Guest
##### Re: Solar Energy HELP!
« Reply #8 on: 03/07/2006 19:16:46 »
It does seem a very specific requirement, for which I can well understand that the amount of raw data available would be somewhat limited.

I suppose the starting point is how many hours of daylight does Glasgow have during the winter months?  How strong is that daylight?

The other question has to be how much storage capacity will the batteries have?  If the batteries can store 5 days worth of energy, then you can afford to average the sunlight over 5 days, and judge that a few good days in that 5 day period will overcome one or two bad days.  Ofcourse, if you can store 12 months worth of energy, then it all becomes easy – but that would be ludicrously impractical.  On the other hand, if you can only store 24 hours of energy in the batteries, then you will have to ask how much light you will get on the worst possible day, assuming it is the shortest day in winter, with 100% thick cloud cover, and heavy precipitation (snow or rain).

I know this doesn't answer your question as such.  I am not really capable of answering your question.  Maybe someone else might have more specific and relevant information; but without knowing over how long a period one needs to average the sunlight (i.e. how much charge can your batteries store), I don't think anyone can really say what is the worst case scenario that you reasonably need to allow for (although there can never be an absolute worst case, since it can always be envisioned that some freak condition may yet be even more disadvantageous than even the worst that you had thought of).

Also, you have to ofcourse take into account the differences between different types of solar panel, and the balance between cost and efficiency.  Is the exercise a 'cost no object' project, or are you looking at real life trade-offs?

George
« Last Edit: 03/07/2006 19:33:29 by another_someone »

#### The Naked Scientists Forum

##### Re: Solar Energy HELP!
« Reply #8 on: 03/07/2006 19:16:46 »