Battery/Panel requirements for electric fence charger

Re: Battery/Panel requirements for electric fence charger

at least you know what your loads are to be and that's a good start. for the el fence 1/2a x 24hrs is 12ah and if 4 days autonomy (backup) that's 48ah and is 52% soc (state of charge) and you don't want this under 50%. normally 3 days autonomy is what is recommended, but 100ah is a common capacity for a battery. for 3 days it would be a 36ah load and for 50% soc this means no less than 72ah battery capacity.
the 20w pv they cite is coming up short as you should minimally be able to feed 5% to the battery and up to about 13%. for a 100ah battery this is 5a and equates roughly to about a 90w-100w pv. this seems allot for the loads you normally see, but the loads are 24/7. if you get even as low as 3hrs of full sun (which is low for summer, but may be high for winter) a day that we are talking about 15ah from a 5a pv. with loads at 12ah a day this is a 3ah margin so it's about right. if you expect more cloudy/rainy days per week or are needing more for winter then use a pv that is rated higher as added insurance.

as to adding the chest freezer we are in a different realm as it will need far more power and the added losses introduced from inverter efficiency. the 5a at 110vac is about 550w and must store 8hrs worth of that power for 4400wh. for 12v battery power this is at 367ah and to prevent going below 50% soc this is now doubled to 734ah minimally. now it may be advisable to go to maybe a 24v or even 48v inverter and battery system to keep current levels in wires down which helps reduce losses and wire sizing. without going below 50% soc this is 367ah battery capacity for 24v and 184ah at 48v respectively. charging losses can be 20% with fla type batteries and about 10% with agm types, but you guessed it agms cost more. you may want agms anyway as they do not normally vent hydrogen which is explosive when it concentrates. i'll assume the added 10% for agm style batteries and go with a 24v battery system for a total capacity of 404ah minimally.
now for charging the battery bank you already know it will be at least a 5% rate normally recommended and this is 20.2a. now i will assume this to be getting roughly 20hrs of full sun over the 7 day period (may be a high estimate depending on where you are) which is a perfect match for the 5% as that is based on a 20hr rate anyway. the result is 20.2a of current from a 24v pv (vmp at least 34v) as a minimum. you will of course only need half of the 20hr rate because the other half of the batteries you did not use in making sure one does not kill the batteries. this now cuts in half that pv requirement to 10.1a and is now a 2.5% rate of charge. now there are other losses that can occur and you could add another 10-20% to the charge rate to help overcome them which puts it at roughly 11a-12a from pv. the real problem is 2.5% is a low charge rate and for long-term charging as you propose here it should not be below a 3% charge rate which that turns out to be about 11a making an 11a-12a 24v pv system viable.
the inverter should be a sine wave type and to insure proper compressor starting you may need at least a 1500w rating and most likely a 2000w rating. the guys can kick this around more.

in general, you will not find batteries that give the exacting requirement that is calculated and when batteries age you could lose a bit of capacity so upping to the next commercially available capacity area is warranted. after that make sure the pvs will supply the power needed, not only by the loads, but also to properly charge the battery.
also i would recommend an mppt controller with battery temperature sensor for the freezer. the fence can be a simpler pwm, but if you would like an mppt would work also and as always i recommend the use of a bts.
do make sure the pvs can be aimed south at the proper angle or you may need even more pv capacity.

i hope i covered it all and didn't goof, but in general there are many variables to this stuff so there isn't a hard and fast formula. you can get a good idea from my train of thought in explaining this to you, or at least i hope i explained it well enough.

Re: Battery/Panel requirements for electric fence charger

Consider a propane fridge/freezer. If you are only going to open it rarely, added insulation on the cabinet will make it use very little propane. I think that Sunfrost makes a freezer, as does dometic. You could also take a propane fridge and turn down the t-stat so the whole case freezes.

We use a small Dometic as a freezer (freezes to ~0f) for those times when we are going to be ice bound for a month or so.

Tony

PS I also think that Norcold makes a 12 vdc compressor RV fridge that only draws ~2 amps @ 12 vdc if memory serves.

Re: Battery/Panel requirements for electric fence charger

A honda EU 1000 right out side a normally insulated building virtually cannot be heard inside. 100' away it can't be heard either.

2 chained together are a bit louder, but not as loud as an EU 2000.

Tony,

PS. It really is amazing how quiet and fuel efficient they are!

Re: Battery/Panel requirements for electric fence charger

you're right marc, but i thought i'd throw in an option for him to possibly save some $ on the batteries. we also assume he has room for that much battery power and that may not be the case either.

Re: Battery/Panel requirements for electric fence charger

Could not resist this blast from the past; "PV's are expensive."

Cariboocoot wrote: »

If you want quiet power you don't necessarily need the generator: just the inverter and batteries plus a good charger. Transport the batteries & inverter with the freezer (how easy is it to move that? ) and re-charge from grid power at home. PV's are expensive.

Re: Battery/Panel requirements for electric fence charger

If batteries and inverters had come down like PVs have, counter arguments might be mounted. Problem with the arguments is the 1001 possible pitfalls eagerly awaiting the solar enthusiast.