TalkBaja.com » Baja Mexico Forums » Off-Grid / Solar, Wind or Generator?

Here is a source for off-grid info for those interested.
On today’s edition of Off the Grid Radio, Solutions From Science founder Bill Heid and Brian Brawdy broadcast from a mobile unit powered exclusively by wind and solar power. Also, an endorsement of a mainstream TV show that will actually help you prepare for the challenges of ‘off grid’ living.
The one mainstream TV show to help you get off the grid – Episode 009 - Off The Grid News

I am glad there are more of these types of programs as there is way too much mis-information out there about life off-grid. I get people asking me if they can now disconnect from their local grid based power service provider once they hook up the three 15 watt solar panels they bought at Harbor Freight???

There is a lot of good info there also. Our neighbor raised holy h**l when our solar equipment went up, but was quickly informed by the powers that be here that it is the way of the future.Then the neighbor said of the solar hot water system, can't you get another color????

Looks like a good radio show. Since my satellite internet has limited bandwidth, I'll have to keep it bookmarked and listen when I have a slow internet use day.

People need education on just what solar can and can't do (unless you have an unlimited budget). My favorite question is: How many panels and batteries do you think it will take to run my air conditioning

Originally Posted by BigWooo

Looks like a good radio show. Since my satellite internet has limited bandwidth, I'll have to keep it bookmarked and listen when I have a slow internet use day.

People need education on just what solar can and can't do (unless you have an unlimited budget). My favorite question is: How many panels and batteries do you think it will take to run my air conditioning

Darned if I know, but do know someone who is a pro in that field if you are interested...

Actually one of my neighbors has AC on solar. He has 50-200 watt panels, 8-2500 watt inverters and some unbelievably sized battery system. Waaaaay out of my budget range.

Originally Posted by BigWooo

Actually one of my neighbors has AC on solar. He has 50-200 watt panels, 8-2500 watt inverters and some unbelievably sized battery system. Waaaaay out of my budget range.

YIKES, that's a HUGE set-up...

That's a 10kW system - probably around a $40K setup. I don't do well in heat which is why we chose to stay up here on the NW side of the peninsula...

Originally Posted by BigWooo

Actually one of my neighbors has AC on solar. He has 50-200 watt panels, 8-2500 watt inverters and some unbelievably sized battery system. Waaaaay out of my budget range.

I hope those are agm batteries, I can't even imagine servicing an FLA bank of the size that must be.
Larry

OMG, I hadn't thought of that. Can you imagine???

Off grid sounds great , up here where i bought my house just prior to my moving here it was off grid when i arriver we had power there was some good deals to be had for some used systems. Speaking of which I still have a Star Band Computer System I will give to someone if they need it.

J.P., we have Starband and I've been looking for spare parts in case something fails. Do you have the Nova system?

Originally Posted by rplarry

I hope those are agm batteries, I can't even imagine servicing an FLA bank of the size that must be.
Larry

They're not AGM's. Must be a lot of work.

Originally Posted by BigWooo

Actually one of my neighbors has AC on solar. He has 50-200 watt panels, 8-2500 watt inverters and some unbelievably sized battery system. Waaaaay out of my budget range.

I'm in the process of putting up an off-grid system and intend to run a single mini-split, 1 ton unit in the bedroom. I have a little over 5000 watts of panels, 7200 watts of inverter and 1300ah of batteries running at 48 volts. According to my calcs, I should be able to run the 1200w mini-split with this system. You really only need it to be cool at night to sleep comfortably. Anybody think I'm off base on this?? Just now installing, should know the answer in a few weeks.



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Originally Posted by ncampion

I'm in the process of putting up an off-grid system and intend to run a single mini-split, 1 ton unit in the bedroom. I have a little over 5000 watts of panels, 7200 watts of inverter and 1300ah of batteries running at 48 volts. According to my calcs, I should be able to run the 1200w mini-split with this system. You really only need it to be cool at night to sleep comfortably. Anybody think I'm off base on this?? Just now installing, should know the answer in a few weeks.

Are running any other heavy loads like an electric fridge, etc???

Originally Posted by ncampion

I'm in the process of putting up an off-grid system and intend to run a single mini-split, 1 ton unit in the bedroom. I have a little over 5000 watts of panels, 7200 watts of inverter and 1300ah of batteries running at 48 volts. According to my calcs, I should be able to run the 1200w mini-split with this system. You really only need it to be cool at night to sleep comfortably. Anybody think I'm off base on this?? Just now installing, should know the answer in a few weeks.



.

What does the mini split draw? Just guessing, and without doing the math, it looks like your array will be OK, but it looks like you'll be short on battery storage if you plan to run it much at night.

Like BG says, it depends a lot on what/if you're running other heavy loads

Originally Posted by BigWooo

What does the mini split draw? Just guessing, and without doing the math, it looks like your array will be OK, but it looks like you'll be short on battery storage if you plan to run it much at night.

Like BG says, it depends a lot on what/if you're running other heavy loads

He mentioned that the a/c unit is rated at 1200 watts. The 7200 watt inverter as well as the battery capacity should handle the initial surge of compressor startup. With normal cabling/inverter losses it will draw somewhere around 30 amps at 48v I figure. 10 hours = 300 amp hours, right? So that would draw you down about 25% in addition to any other loads and natural battery losses. The actual number may differ if his unit will be cycling a lot.

I agree with you Wooo - might be good to add some batteries. Maybe a few more panels at the same time so he doesn't get his charge current / battery bank ah ratio too far out of whack.

This is what I came up with, which is basically the same as BG, just a longer way to get to the same figure:

At 10 hours per day, your total power use per week for the A/C at 1200 watts per day is 84000 watts.

84000 x 1.2 (battery inefficiency coefficient) = 100800 watts per week

10800/48 (watts divided by battery voltage)=2100 amps power requirement per week

2100/7=300 amps per day use for the AC unit @ 10 hours/day

Since the batteries are most likely over 80 degrees, there wont be a battery temp loss coefficient. (cold batteries perform worse than warm batteries, to a point) A temp loss coefficient comes into play if the batteries are normally 70 degrees or less. ( If your batteries were at 70 degrees you wouldn't need to worry about air conditioning )

So...if you want to keep your battery bank limited to a maximum 25% discharge, you divide the battery storage by .25: 300/.25 (maximum discharge) = 1200 amps of batteries dedicated just for the A/C @ 10 hours/day to keep the discharge rate at 25%.

NCampion has 1300 Ah of battery storage. Using the above formula, the use of the A/C for 10 hours a day (300 amps) would account for 23% of the total battery storage. If you're willing to discharge down to 50%, you will have another +/- 1200 watts to play with per day for other use. I think it's cutting a bit close though. And as Gringo mentions, I have no idea what the surge is when it starts up which may be another factor.

Let's work the formula for 5 hours of A/C per day:

Your battery amp hours use drops to 150 amps
150/.25=600 amps of your battery bank would need to be dedicated to AC for a maximum discharge rate of 25%

Now applying that to your 1300 amp battery bank, running the AC for 5 hours would use about 12% of your total storage capacity. A little more doable depending on you other loads.

Now...if you want extra battery to account for a cloudy day or two, the battery storage increases even more.


For comparison: I don't have AC, just ceiling fans. I run an AC fridge, a separate AC box freezer, along with normal lighting, computer, water pumps, TV, ceiling fans etc. I've factored in three days of battery storage for cloudy days. My battery bank is 2968 amps. With that size battery bank, after three cloudy days, theoretically I should be at 50% of my battery capacity. More than 3 cloudy days and it's time to fire up the generator.

I've discovered that with high clouds the batteries charge pretty well. With the coastal low clouds and fog, just about all charging stops. I don't think you (Ncampion) have to worry about coastal low clouds and fog so backup storage is probably not as critical.

Ahem...

isn't the appropriate unit really amp/hours (kWh)...?

I understand the calcs and what you are saying in substance, but leaving that out in certain parts introduces some unnecessary noise into one's thinking, IMO.

Originally Posted by Marty Cortez

Ahem...

isn't the appropriate unit really amp/hours (kWh)...?

I understand the calcs and what you are saying in substance, but leaving that out in certain parts introduces some unnecessary noise into one's thinking, IMO.

I'm not an electrician, but I stayed at a Holiday Inn Express last night