Battery choices for a 200W 12V system in winter

[antobag]

I am looking to buy a 12V 200W solar panel system for an off-grid hut in Wales, where I will be staying during the month of February. I require roughly 100 to 200 daily Watt-hours to power an LED light and a laptop on which I will be working. I know that the area I will be staying receives an average of about 1 hour of sunshine per day in February (this is a conservative figure).
Here is the solar panel that I will most likely be using: http://www.ebay.co.uk/itm/2-100Watt-...3D301459750815

I've used a few battery sizing calculators online and it seems that a 100Ah AGM battery will be enough to ensure that I do not drop below 50% charge. However, the batteries I have found on ebay (UK) have quite a range in prices:
http://www.ebay.co.uk/itm/12V-Xplore...-/171376568297 (Brand - Xplorer; Price - £89.99, roughly 140 USD)
http://www.ebay.co.uk/itm/100Ah-12V-...-/130982265055 (Brand - Ultra Max; Price - £114.99, roughly 175 USD)
http://www.ebay.co.uk/itm/100Ah-12V-...-/121122811935 (Brand - Photonic Universe; Price - £139.99, roughly 215 USD)

- As a complete newbie to solar power, it looks to me that there are no major differences between the cheaper and more expensive batteries. Should I just go for the cheapest battery? (If anyone has used any of these brands, I would love to hear your thoughts on them - although I realise that they may not be available in the US)

- Secondly, I've heard that in order to make the full use of MPPT charge controllers, the array voltage should be substantially higher than the battery voltage. Would any of these three batteries be okay for this?

- Finally, is it better to buy the most Ah that my budget will allow (ie. so the percentage of battery discharge is lower) or should I just stick to a 100Ah battery?

Apologies for all of the questions, I'm new to this and just want to be completely sure about it before I commit to a purchase. Any help would be much appreciated.

[mschulz]

I am looking to buy a 12V 200W solar panel system for an off-grid hut in Wales, where I will be staying during the month of February. I require roughly 100 to 200 daily Watt-hours to power an LED light and a laptop on which I will be working. I know that the area I will be staying receives an average of about 1 hour of sunshine per day in February (this is a conservative figure).
Here is the solar panel that I will most likely be using: http://www.ebay.co.uk/itm/2-100Watt-...3D301459750815

I've used a few battery sizing calculators online and it seems that a 100Ah AGM battery will be enough to ensure that I do not drop below 50% charge. However, the batteries I have found on ebay (UK) have quite a range in prices:
http://www.ebay.co.uk/itm/12V-Xplore...-/171376568297 (Brand - Xplorer; Price - £89.99, roughly 140 USD)
http://www.ebay.co.uk/itm/100Ah-12V-...-/130982265055 (Brand - Ultra Max; Price - £114.99, roughly 175 USD)
http://www.ebay.co.uk/itm/100Ah-12V-...-/121122811935 (Brand - Photonic Universe; Price - £139.99, roughly 215 USD)

- As a complete newbie to solar power, it looks to me that there are no major differences between the cheaper and more expensive batteries. Should I just go for the cheapest battery? (If anyone has used any of these brands, I would love to hear your thoughts on them - although I realise that they may not be available in the US)

- Secondly, I've heard that in order to make the full use of MPPT charge controllers, the array voltage should be substantially higher than the battery voltage. Would any of these three batteries be okay for this?

- Finally, is it better to buy the most Ah that my budget will allow (ie. so the percentage of battery discharge is lower) or should I just stick to a 100Ah battery?

Apologies for all of the questions, I'm new to this and just want to be completely sure about it before I commit to a purchase. Any help would be much appreciated.

First thing you need to tell us is how many watts each day you will be using.

Example:
With only 1 hour of sunlight per day, and running 200 watts, you only have 200 watts to work with. Figure our your watts needed each day, (LED light watts/hour * hours on) +(Lap Top watts/hour * hours plugged in) = total watts per day. That is what you want in solar at min. so if your led light is on for 5 hours each day and it draws 5 watts, 5*5=25 watts for the day. Lap top, draw of 60 watts and you have it plugged into power 10 hours each day, 600 watts. 600+25=626 watts per day.

Take 625watts/12volts = 52 AMPs. So you will use 52 amps per day. If you had your 200 watt solar panel on the roof for 1 hour of sun each day, you will get 200/12= 16.6 amps if you were 100% efficient which you will not. There for you will be deficit spending each day by 52-16= 36 AMps. So your 100AMP hour battery will be dead in 3 days even with your 200 watt solar panel.

Total watts used each day divided by total sun hours each day will equal your solar panel sizing for your 1 month. You will not be off grid long enough to worry about destroying your battery.

[antobag]

Sorry, I think I was a bit vague in my previous post (I just said I require roughly 100 to 200 watts of power a day). It'll most likely be around 140-170 watts used a day - I won't be using my laptop all day (only about 4 to 5 hours or so), and it only uses about 30 watts on average. My LED light uses 4 watts an hour and will be used for under 5 hours a day (and if necessary, I can work by candlelight!) Would all three of the batteries I listed be okay for my needs? Please let me know if I ought to give any more information about my requirements, etc.

[inetdog]

The thread will be a lot clearer if you are able to use standard terminology.
30 watts is a unit of power, the rate at which you are using energy.
If you consume at a rate of 30 watts for 4 hours, you have used a total energy for that period of 120 watt-hours.
Sometimes it is hard to tell what is meant if you leave the "hours" out of watt-hours and amp-hours.

The inverter watts tell you how fast it can deliver energy, the battery watt-hours tell you how long the inverter can keep that up.
Watt-hours divided by volts gives you amp-hours.
Watts divide by volts gives you amps.

[antobag]

inetdog, thanks a lot for the clarification! The difference between watts and watt-hours was admittedly causing a bit of confusion for me.

So I estimate I will be using energy at a rate of 34 watts (Laptop - 30 watts; LED - 4 watts) for 5 hours daily, which means that each day I will have used a total energy of 170 watt-hours.

[inetdog]

inetdog, thanks a lot for the clarification! The difference between watts and watt-hours was admittedly causing a bit of confusion for me.

So I estimate I will be using energy at a rate of 34 watts (Laptop - 30 watts; LED - 4 watts) for 5 hours daily, which means that each day I will have used a total energy of 170 watt-hours.

Great. At a nominal 12V, that would be about 14 amp-hours (AH). By the rule of thumb of only discharging 20% each day, that means that you would need about a 70AH battery. But the battery requirements would be lower if a large part of your power use (computer maybe) happens during the day while the panels are producing.

And for winter in UK, you would need about a 100W panel if the weather is clear and you are just fighting low sun angle. Much more if it is regularly cloudy.

[antobag]

Great. At a nominal 12V, that would be about 14 amp-hours (AH). By the rule of thumb of only discharging 20% each day, that means that you would need about a 70AH battery. But the battery requirements would be lower if a large part of your power use (computer maybe) happens during the day while the panels are producing.

And for winter in UK, you would need about a 100W panel if the weather is clear and you are just fighting low sun angle. Much more if it is regularly cloudy.

Perfect, that's really helpful. So my 200W (2 x 100W) panels alongside any of the 100Ah batteries should be more than enough to suit my needs.

I think I'll go for the 100Ah Xplorer battery at £89.99 as I can't seem to see any advantages of paying more for the other batteries I've listed. I know that Varta (a reputable brand) makes a 95Ah battery for £189.99 (http://www.alpha-batteries.co.uk/agm...e-agm-battery/), but I'm not sure if the extra £100 would be justified.

Many thanks once again.

[mschulz]

Perfect, that's really helpful. So my 200W (2 x 100W) panels alongside any of the 100Ah batteries should be more than enough to suit my needs.

I think I'll go for the 100Ah Xplorer battery at £89.99 as I can't seem to see any advantages of paying more for the other batteries I've listed. I know that Varta (a reputable brand) makes a 95Ah battery for £189.99 (http://www.alpha-batteries.co.uk/agm...e-agm-battery/), but I'm not sure if the extra £100 would be justified.

Many thanks once again.

With that low of draw your 100 amp battery will treat you well. If you can, mount your panels so you can turn them throughout the day to be pointed directly into the sun, it might give you 2 hours of good sun vs the 1. That would be big.

[antobag]

Thanks for the knowledge everyone, it's much appreciated.

[inetdog]

With that low of draw your 100 amp battery will treat you well. If you can, mount your panels so you can turn them throughout the day to be pointed directly into the sun, it might give you 2 hours of good sun vs the 1. That would be big.

A mechanized tracker would probably not be worth the effort, but the classic "Armstrong" rotator system makes sense if you are at/near the yurt during the day.

[antobag]

A mechanized tracker would probably not be worth the effort, but the classic "Armstrong" rotator system makes sense if you are at/near the yurt during the day.

Haha ah yes, I've been using an Armstrong system on other applications for years! Glad to hear it can be put to use on solar power.

[mschulz]

Haha ah yes, I've been using an Armstrong system on other applications for years! Glad to hear it can be put to use on solar power.

I put mine on a pole and manually twist it into the sun every two hours. At Night I turn it back to the East to be ready when the sun comes up. Granted this is a 45 Watt panel.