Cabin Solar - How To -

[Chris]

I love the idea of not paying for Electricity, and being an Electronics Engineer thought I would build my own system.

The whole Solar thing is made out to be complicated but its easy !!

Many Cars now have these Low Power Led's as Headlights/Back Lights etc
You can Leave them on all night in a car and it would not have even touched the Battery.
Found as strips or units they are usually 1W or 3W but in groups are very bright - So Bright that they blow away anything that is a normal standard 12V Car Bulb.

Being so Bright even in Daylight and using such a small amount of Power from the Battery over x amount of hours, Solar Lighting Systems can now
be made from a few pieces of Hardware, for not allot of cash.
- But calculations are critical -

Remember that what Power you take out - must be returned to the Battery.
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How to calculate a Complete Single Light System for a Cabin

1. Add up the hours that the light will be on for to get the Total of Energy Consumed.
2. From that you can Calculate everything you need IE: Solar Panel / Battery / Regulator
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My Calculations
1 Zone
1 x LED FLOOD @ 15W (could be 5 single 3W LED units)
on for (SEE CHART) hours per night
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-Watt/Hour Winter Chart- - Only ever use 12 volt LED light -
1 Zone - 15W on when required daily average use -- 4pm until 10pm - 6 hours x 15 Watts = 90wh
Total usage per night in Winter = 90wh/d
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-Load and Battery -

Cabin Lights Consumption = 90Wh
90 watt-hours divided by 12 volts = 7.5 amphours taken from system in 1 night

Because we can only use half the energy in a lead acid battery without harming the battery,
the minimum battery size is 7.5 amps x 2 = 15 amp hours.

I want my system to be reliable if we have four consecutive days of cloudy weather,
4 days of autonomy x 15 Amps = 60 amp hours for the battery. = 60 + amp hour battery
(Required Battery Bank = 1 x 60 Ah minimum - True Deep Cycle

cost so far = 15 for LED light + 50 Battery = 65 quid
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-Charging Battery from Panel-
This installation is in a location that gets 4 hours of full sun per day.
Check the charts for this depending on the month in the Season.
To recharge the battery for one day of use we need 15 amps in 5 hours = 15 / 5 = 3 Amps every hour from a 12 volt solar panel array.
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-Solar Panel -
Most load calculations include a discount factor for the inefficiency of recharging the battery.
20% is typical. 3 A / 0.8 = 3.75 Amps.

A single 70W solar array that has an Impp (amps maximum power point) of 3.9A would be suitable
Based on (Model - CS6D - 70P / Manufacturer - Canadian Solar Inc.)
cost of PV Array = 80 quid
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-Charge Controller Rating in AMPS-
The 70W solar array has a short circuit amp rating (Isc) of 4.21A 4.21A x 1.25 = 5.3A
use a 5.3A or larger charge controller with this array to charge the battery.

Cheap example - 10A Unit
For best efficiency to charge use an MPPT Type = 30 quid
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-Solar Panel specification-
CS6D - 70P..... manufactured by Canadian Solar
Related power
70W
Open circuit voltage Voc(V)
22.1V
Short-circuit current Isc(A)
4.21A
Optimum operation voltage Vmp(V)
17.8V
Optimum operation current Imp(A)
3.93A

etc ... Caution -12V Batteries can Cause Fire if not Fused or Stored Correctly-
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That's it - and if you like, just double up on the panels and Battery to create a system with double the lights.

Just remember that 12V systems are limited to Cable distance.
So 1 x 15W Flood would have a .75mm Diameter no longer than 6 meters.
Just spider it all out to get around that or double up on the cable diameter to double the distance.

Store the Battery in a dry/ventilated place where no hands can touch Terminals.

Be aware of Fire Hazards as Car Batteries can be bad boys if ignored !!

If you get no Sun then drag out the jump leads and charge your system off a motor for a few hours ...

[Skean Dhude]

Need to play about with these and set a few up.

[Bjm]

Hi,
Just won a 60w solar panal.85ah leisure battery, regulator,and a 120 watt inverter on ebay, I will be playing around with these next weekend, so i will let you know how it goes.

[Straight Shooter]

great stuff good post

[Skvez]

Unfortunately you have made the very common blunder of assuming that you will get 70W out of a 70W solar panel.
Solar panels are rated under ideal circumstances. Ideal being equatorial sunlight, which we *never* get in the UK even on our brightest cloudless summer day.
A sunny cloudless day in winter in the UK (which lets be honest are pretty uncommon) will get you a lot less than 70W exactly how much less depends a bit on the technology of the solar panel.

On the tests I did back in 2011 I was getting about 12Wh *per day* from a 100W panel in December. Your calculations assume 280Wh from a 70W panel (or over 33 times more power than I measured in a real world environment)

People complain that I say Solar doesn't work, I don't, solar is great but you need to have realistic expectations of what it will provide, especially in Northern Climates in Winter when performance is very poor compared to ideal.

[Chris]

(16 October 2012, 18:29)Skvez Wrote: Unfortunately you have made the very common blunder of assuming that you will get 70W out of a 70W solar panel.
Solar panels are rated under ideal circumstances. Ideal being equatorial sunlight, which we *never* get in the UK even on our brightest cloudless summer day.
A sunny cloudless day in winter in the UK (which lets be honest are pretty uncommon) will get you a lot less than 70W exactly how much less depends a bit on the technology of the solar panel.

On the tests I did back in 2011 I was getting about 12Wh *per day* from a 100W panel in December. Your calculations assume 280Wh from a 70W panel (or over 33 times more power than I measured in a real world environment)

People complain that I say Solar doesn't work, I don't, solar is great but you need to have realistic expectations of what it will provide, especially in Northern Climates in Winter when performance is very poor compared to ideal.

Thanks - now listen - Electronics scares people to the point where they will shy from Maths and even thinking about simple projects.
You do not have to worry yourself or even others about the Real world loss scenarios, as this clouds the the topic...
With Sunlight the odds are : - !!!!.
The point is realisation that you can create Voltage, even if it means jumping a car engine with cables to charge your system / using a wind Turbine, using a ceiling fan converted to a water turbine
In a survival scenario you will use whatever you can get and not give a plonk about Loss - You may not even have a meter to check -
- By the way - When you cook chips . . do you make sure the temperature of your chips are at an exact temperature so you can eat them ... Of course not . . .that is my point

[Skvez]

I didn't mention "losses".

The OP tried to size their system properly, they worked out what their desired load was and worked backwards to see how big the solar panel and battery needed to be.
Unfortunately they made a number of errors and incorrect assumptions in that calculation which resulted in them believing that a 70W solar panel would suffice when in fact is was woefully undersized for what they needed.

A 70W solar panel feeding a battery is a great first solar system (And all preppers should seriously consider something similar) but expecting to run 15W of LED lights for 4 hours a day (in winter) is not realistic.

Sure there are other ways to charge the battery but the OP believed (and was sharing the belief) that a single 70W panel could do this.

To take your cooking chip analogy, if someone posted that they could cook a meal of chips on a single match (and it wasn't self evident that they'd made a miscalculation somewhere) would you leave the post uncorrected?
When it comes to solar people can't see that a "match-sized" solar panel can't cook a "meal of LED lights".

[bigpaul]

so you will have electricity when all around you is in darkness?? i forsee a visit from the local chav scavenger patrol!!

[Skean Dhude]

Guys,

I've deleted a few posts that were not adding to the thread, except for some entertainment.

This seems a very popular subject for confusion. If someone points something out to you then there is no need to get defensive. We all have something that we don't fully understand and this subject seems to be one of those. Would you rather you found out after an event that you had an issue with a lack of power.

[Chris]

So has anybody built much here in the Uk, and what did you discover.
If you were pushed into a situation of no Electricity which is very possible, how would you cope? pro's n Con's