How much extra solar is enough?

eftimios · Newbie

How much extra solar is enough?

Peter_n_Margaret · Guru

It is your power consumption that determines how much solar you require, not how many batteries you have.
Many sellers exaggerate the output of their panels and you will never get 13.3A from 160W anyway.
Fit as much solar as you can. You can't have too much.
And fit a quality solar controller to get the best from the panels and to take best care of the batteries.
Cheers,
Peter

Whenarewethere · Guru

As said above.

The panels will only work as maximum capacity if square to the sun. Often wiring is under size so you loose a bit there. Depending on the quality of the controller there are more losses. In hot weather the controller will throttle down. If the controller is not near the batteries more losses.

Depending on your load you maybe ok with 160 watts. Also if you move frequently enough based on your load the car can charge the batteries to get you through to the next camp site.

You need to look at the whole package!

Terryt · Veteran Member

And don't forget the rate of charge slows as the batteries fill

Jaahn · Guru

eftimios wrote:
We bought a small off-road camper (golf x-265). i got the manufacturer to add a second gel battery so now have 210 amp hours. The van has 160 watts of panel on the top. If my understanding of solar is correct, i can generate 160/12 = 13.3 amps per hour. I also got them to install a second anderson plug to allow me to connect more solar panels.
so the question now is, is there a limit to how much power i can generate to the batteries? Obviously, the larger the wattage, the less time it will take to charge the batteries to capacity. I'm thinking that 200 to 250 watts would be sufficient. A 250 watt setup would add 250/12=20 amps per hour approximately.
Are these calculations reasonable and appropriate?

___________________________________________________________________________________________________________________________________________

Hi eftimios smile

Welcome ! There have been some good comments so far. I will not add to them but just expand on your calculations and assumptions. A normal 160W panel will put out about 9 Amps. What the F**K !! Yes panel ratings are a con, we know ! AND you will be lucky to ever see that much due to the reasons given above. So get as much as you can on the roof and supplement it with portable too. There is no limit if you are setup correctly. And during low sun conditions you might still get some effective charging biggrin

So then get a good controller/regulator (MPPT also) and that will ensure the solar will never be too much, as it will control that and the batteries last well too. You must have one that has at least three function battery charging. Best to get one with some readouts of what is going on too. The cheap ones usually supplied are often not so good.

The electricity units are a mystery to most people and many here also. The flow of electricity from a panel is in Amps. When it gets stored in a battery there is a time of charging to add to that and the stored electricity is then measured in AmpHours. EG a 210 Amp Hour battery (AHrs) Or a fridge uses 5 Amps for 4 Hours which uses 20 AHrs. Volts always seems easier to understand. aww But the output of batteries and solar panels is not fixed and both the V and the A varies for a lot of reasons, the sun is only the main one. A 12V battery might max at say 14.4V charging but go down to 11.5V under load. hmm

Get another panel the same and that will be 320W total but only ~20Amps. A bit more if you use MPPT reg.

Jaahn

-- Edited by Jaahn on Tuesday 14th of April 2020 03:10:22 PM

-- Edited by Jaahn on Tuesday 14th of April 2020 03:33:01 PM

swamp · Senior Member

Hi
Remember OP u can only use what u can recharge

160 watts produces around 38ah in 24 hr period

2 batteries total 210Ah = Usable capacity is 105Ah

So u have capacity but no way to recharge =system not performing to FULL potential

200watt produces 48ah in 24hr period

####OP requires 400watts to be able to use system to full potential

---------------------------------------
Other benefits are
-if u donot use full allowance of AH105 recharge will be done in 2-4 hrs . This allows for cloudy weather as the time needed is only small.

_______________
Calculation
Peak Sun Hours avg 5.5hrs per day in summer spring autumn in ozzy
PSH is sun at 100% effective
Sun outside of this 99% & less and Mppt function are considered bonus as they are unreliable to measure
Less 20% inefficiencies due to wiring ,panel angle ,controller type etc etc
eg 200w at 5.5 hrs =48AH + bonus sun + bonus Mppt

Remember as battery get past bulk stage and into absorption mode amperage gradually declines . This extends charge time . Just another variable to try and figure in .

-- Edited by swamp on Tuesday 14th of April 2020 10:47:11 PM

Whenarewethere · Guru

Not only can you do a lot of things to make power input more efficient. You can do a lot of things to reduce consumption.

https://thegreynomads.activeboard.com/t65059593/extra-fridge-insulation-wattage-test/

stoney123 · Senior Member

You can get 350 watt panels now, might be time to upgrade. I have 2 X 200 watt panels and I will upgrade in a year. I chew power.........

Ram Man · Veteran Member

Reading with interest on your solar power quest:

Having just done the exercise myself, you haven't indicated your power usage (Load) and that's where you need to start.

Load will be in amps, used by all the stuff you'll run when boondocking eg: lights, TV, Fridge unless gas, shower fans all the 12 volt stuff, say the Load is 9.2amp x 12 volts =110.4 watts

Your going to run this Load for 4 hrs before bed: 110.4 watts x 4 hrs =441.6 Watt Hours

Depending on your location you'll need 3 days of power taking into account cloud cover and rain so, 441.6 x 3=1324.3 Watt hrs is how much Battery your needing @ night.

Batteries 12 x 210 =2520 Amp hrs divide x 2 = 1260 amp hrs is Watt you have to use 50%, so your about 120 Amp hrs short in the Battery area but not too worry because you still have calculate the solar panel.

Solar Panel: 1324 Whrs divide 5 hrs (This is daylight in Australian in winter) =264.8 Watts is needed to charge your batteries Easy!

Your going to bump this up to 300 Watts at least and here's why, the solar panel specifications are at STC @ 25C facing the sun with no shadow and sitting on the grass isn't facing Sun a angle of 45 is close enough or place a can on a cardboard the same size as (1) solar cell and if no shadow your sweet. But your not going to do this they'll be on the roof and so your only get a % of their capabilities.

I have gone to 400 Watt Panels yet to be install but testing (1) panel showed 23.58 Volts @ 20C facing the sun no shading or 45 angle, Amps calculated to about 15.00 was being generated.

Solar panels work best at colder temperatures, NOT hot and must be ventilated raise of the mounting surface.

Another traveller mentioned MPPT Solar Controller you should be buying one of these forget PWM there ok but you have a Motorhome and wanting to get as much power as possible from the Solar array is your goal or should be. MPPT Controllers have faster startup or processing of the Panels input so they'll grab extra Amps a PWM controller is much slower but fine if your adjusting your Panels throughout the day, even if you are a MPPT will still win.

If you have a microwave it will use roughly about 13.7 amps over a day but that's a whole bunch more calculations, so if you use it for 4 minutes at night you should be fine.

Don't mismatch your solar array with different Wattage panels, be certain to check the spec's main 1's Voc and STC and size going on your available roof area

How much is enough all comes down to how much you can store and how much are you going to use?

Regs

Jeff

Jaahn · Guru

Just a comment about big solar panels. A lot of people find that several smaller panels might work out better than one big one. Why you ask more complication ??

Firstly there is the FACT that the panel is a big sheet of glass that is not designed to be bouncing around on the road, but fixed stationary on a roof. blankstare The bigger it is the more likely it is to be damaged by rough roads, rocks and tree branches.

Secondly if there is any shading of the panel, from branches or masts or even vents or AC units on the roof the affected panel will loose most of its output, out of proportion to the shading. One big panel may easily get down to 25%. So having several panels means you can drop one panel and the others may keep going full output OK. aww

It means a bit more wiring but that is a one off and if you damage a panel it is not catastrophic either and you can just keep going. Check that the panels all have diodes to work in parallel. You can fit those easily.

Jaahn

PS I find it is easier to work only in Volts and Amps and Hours. Working calculations in Watts just confuses me and other people(because either of the inputs for watts may change). My comment. disbelief

-- Edited by Jaahn on Tuesday 28th of April 2020 03:23:55 PM

Whenarewethere · Guru

I agree.

Personally I would go for redundancy. Murphy's Law that you are in the middle of nowhere & you can't run your fridge.

As small as my system is there is plenty of redundancy. Also in the thread are some examples of how much reduction in power a small shadow can do.

https://thegreynomads.activeboard.com/t65231112/custom-6x20-watts-solar-setup-with-mppt/

Delta18 · Guru

Whenarewethere wrote:
I agree.
Personally I would go for redundancy. Murphy's Law that you are in the middle of nowhere & you can't run your fridge.
As small as my system is there is plenty of redundancy. Also in the thread are some examples of how much reduction in power a small shadow can do.
https://thegreynomads.activeboard.com/t65231112/custom-6x20-watts-solar-setup-with-mppt/

Exactly why I have 21 x 60w panels on the roof of our Silverline.

blissonwheels · Senior Member

Gooday,
Seems as though you have already bought your batteries, if you can afford it I would suggest if you can sell those batteries without too much loss you go for 2 Good Quality 12 V Lithium Batteries, you will not only save a lot of weight but have a massively improved usage.

The old phrase-: "Do it Once Do it Right".
Cheers, Bliss on Wheels.

Peter_n_Margaret · Guru

blissonwheels wrote:
Gooday,
Seems as though you have already bought your batteries, if you can afford it I would suggest if you can sell those batteries without too much loss you go for 2 Good Quality 12 V Lithium Batteries, you will not only save a lot of weight but have a massively improved usage.

The old phrase-: "Do it Once Do it Right".
Cheers, Bliss on Wheels.

Goodness.....You do not need lithium batteries to run a fridge.

We are much higher power users than most and are ALWAYS off grid. I recently replaced 400Ah of 9 year old AGMs with more of the same for $1,000 total.

AGMs can do anything that lithiums can do. They are just batteries. So unless weight is critical (and it is for some) AGMs will be fine.

Lithiums seem to have become a fashion thing. These options should be evaluated on technical and financial grounds, not emotional ones.

Cheers,

Peter

Whenarewethere · Guru

My issue was space, I could tuck 4 batteries around the car. The 4 batteries also provide over 1000 amps for jump starting or 360 amps for 5 minutes (my car needs 238 amps to start).

100ah of lead or lithium is a 100ah. Ok, it is recommended not to discharge a lead acid battery as far as lithium but if it happens a handful of times a year it doesn't matter. Most days the battery will be discharged far less so it's swings & roundabouts.

In my situation the battery is primarily for a fridge at typically 12 - 15ah per 24 hours. Camera & torches have back up batteries of their own which can be charged while driving. The phone is in aeroplane mode or off.

Weight saving would have behen nice!

-- Edited by Whenarewethere on Wednesday 29th of April 2020 08:05:02 PM

Reed · Senior Member

Weight is critical and LFP is so much lighter. We have about 9 kW-hrs of LFP which weigh about 250 lbs (98 kg). Equivalent lead-acid would weigh twice as much and occupy at least twice volume. 200 kg is a lot of stress on frame. The only negative to LFP besides cost is the problem with charging below 0 C. This is probably not a major problem in Australia but it is in most of USA. Most aficionados of solar would probably say there is no such thing as to much solar. A contributor to US caravan forum, RV2, has just finished installing 2400 W on his vehicle (ran out of real estate on roof). He can run A/C all day.