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Ejm
Member
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# Posted: 3 Oct 2014 03:58pm
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Hello All,
I am looking for a starter setup for my small cabin. I mainly want to run a freezer box year round so I do not have to haul up food. When we want to go there for the weekend. It looks like the freezer box would use 700 watt hours per day.
Please let me know, if you could help me out by picking a kit that I could continue to upgrade each year.
Thanks,
EJ
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bldginsp
Member
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# Posted: 3 Oct 2014 05:41pm - Edited by: bldginsp
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Upgrading a given solar system can present problems if you don't plan for it. It's easy to add more elec panels, but by doing so you will be either increasing voltage or amperage or both, which means that your charge controller will have to be able to accept the change. Adding new batteries to a bank of used batteries doesn't work well, because the new total bank of batteries operates only as well as the weakest of them all, the used ones. Again, added batteries creates the problem of the capacity of the old charge controller. Then, with the inverter, it doesn't work well at the outset to get an inverter much bigger than you use at the moment, because inverters use power themselves just by running, so a larger one is wasting more power.
So, when you 'upgrade' the system you may have to replace charger, batteries and inverter to accommodate the increase in panels, which is really buying a new system except for a few original panels.
I think the best thing to do is design the smallest system you can for your present needs (plus a degree of extra) and plan to keep it until the batteries die, then redesign the system.
But I'm not as experienced with this as others on this site, they may have other info for you.
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groingo
Member
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# Posted: 3 Oct 2014 07:43pm - Edited by: groingo
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To take the guesswork out use a killawatt power meter and plug it into your appliance for 24 hours which will tell you exactly how much juice you are using in kwh in a day and from there it is relatively simple....include everything you plan to use, this will give a solid starting point and take much of the guesswork out which can get pricey.
A good place to get a general idea is here: http://www.renogy-store.com/Solar-System-Sizing-s/1865.htm
This is for GENERAL INFORMATION but you will want to do your own verifications... .but it is helpful.
I got my system from Renogy and have been very pleased with the results.
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ILFE
Member
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# Posted: 4 Oct 2014 07:48pm
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Ejm,
One of the first things I learned, when sizing my (second) system was, do not go by what is on the labels of appliances. I use the 10% charging method, as demonstrated below.
As groingo said, use a power meter to determine actual usage. But, for your example, let's go with 700 watt hours. (How large is this thing? Are you certain it only uses 700 watt hours per day?)
700 watt hours / 12 (nominal system voltage) = 58.33 AH
Since you do not want to deplete your battery bank less than 50%, you have to (at least) double that figure.
So, 120AH X .10 (10%, a good charge rate) would roughly be 12 amps.
To get a 10% charge rate, you would calculate it this way:
120 (amp hours) X 14.4 (charge rate for a 12vdc system) / .80 (solar module efficiency) X .10 (charge rate) = 216 watts array. 225 watts would probably be the next closest panel size.
So, from this we have determined your bare minimum needs for a 10% charge rate:
Panels: 225 watts
Controller: PWM 15 amp
Battery: 120 AH deep cycle
Please Note: This calculation does not take into account days of autonomy (days of cloud cover / rain causing little to no charging of your battery). You would have to determine that by your weather patterns where your cabin is located.
Also, while some members here may say you can "get by" on less than that, providing power for something that is going to store your food, is not something to skimp on. Just my 2 cents on the matter.
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