Please help me with my solar woes

Mika loves caravaning · Newbie

Please help me with my solar woes

Jaahn · Guru

Hi Mika smile ,

That's a very detailed analysis of your needs. Great you understand what you have and want too ! I will give a quick reply and come back when I have some time to consider your questions and possibly others may also give their input.

However to avoid confusion could i suggest you look at your power units and perhaps edit them so others are not confused and give incorrect answers. Tricky this solar electricity and the units confuse The power of the panels and the items using it is in WATTS and that is a flow of power{like the tap water running out}. When you use them for a certain time, in hours, it then becomes WATT HOURS. That then becomes a quantity of power {like a bucket of water}. The batteries hold a quantity of power in AMP HOURS too at their voltage eg 12V.

Your calculations look good but the units need to be sorted to get it straight in the mind biggrin

Good luck Jaahn

PS a quick answer is that more panels always solves power problems, the more the better smile

-- Edited by Jaahn on Tuesday 13th of February 2018 12:23:01 PM

Jaahn · Guru

Hi Mika smile

Here are some answers to your post !

Hi everyone. Im having a few issues with my solar system and am hoping to get some advice. I have a 22 Roadstar offroad with a Waeco fridge (70w per hour), a television (24w per hour), led lights, and water pump.

I have two 123w solar panels in parallel with an mppt controller (now broken and needing to be replaced). My daily consumption is (70wx24hr fridge)+(24wx4hr TV)+100w (lights approx) and 100w (waterpump approx) x 1.2 (20% margin of error)=2371watts per day. By my calculations my solar panels produce, at peak effectiveness, 1722 watts (123w x 2 x 7hrs (peak solar hours in Adelaide summer) however there can be up to a 30% loss due to hot solar panels so that places my solar output at 1205.4 watts (1722-516.6). My questions are:
Your Estimates; Power use 2371 Whrs. power production 1205 Whrs

Am I right in thinking that solar panels in parallel are more effective than in series for small systems? YES on a VAN I understand that series is more likely to work with an MPPT controller when the panels are not working at peak effectiveness due to heat/light NOT correct. but the whole series will fail if one section of panel is in shade YES CORRECT while panels in parallel will produce higher direct amperage though will require a heavier cable to the controller. Yes but the cables are easy and cheap to do.
Am I right in thinking I need 600 watts of solar on the roof to maintain my batteries? (600watts x 7 hrs with a 30% leeway = 2940 watts) YES at least.
Would it be better to buy two 300 watt 32 v solar panels? Ive been looking on ebay atthese I do not favour flexible panels. Too expensive for the advantage IMHO See comments about the panel voltage also these are 42V
Or would it be better to buy 3 of these 200 watt 12v also on ebay? Possibly ok, standard panels are the best value. But more smaller ones are a better idea.
What MPPT controller would be best? Ive been looking at this thinking I need the extra amperage since my panels will be producing up to 50Amp. I also like that it logs performance day by day over a year. It is not the right controller for you It is for a 48 V battery system. Look for a 12V system with a high allowed voltage panel input. EG 50V 0r 75 V or more! Then at the amp rating.
Has anyone got any general suggestions or advice that I might have missed? another missive

I might let you digest that and see if there are other inputs too. What is you battery voltage and capacity. Do you want to use your existing panels 2 x 123W also. What is their MPV ratings on the back label.

Jaahn

-- Edited by Jaahn on Tuesday 13th of February 2018 02:51:54 PM

T1 Terry · Guru

Just a few mud map calculations that might help. Solar panels put out 70% of their advertised capacity as a general rule, multiply the max power amps by the battery voltage and that is what you can expect ...... if the panels are perfectly angled to the sun. Flat mounted on a van you can expect maybe 50% on average. Next, 5 peak sun hrs in summer , maybe 5.5 peak sun hrs in the nth of Australia, but 4.5 hrs in Adelaide summer and 2.5 hrs in Adelaide winter. We are in Mannum and it was a bit of a shock how much solar we lost compared to when we were in Lake Illawarra NSW.

We install a lot of solar and design custom lithium battery systems for off grid and RVs including houseboats and in general PWM controllers work best on systems smaller than 3kW. The cabling needs to be heavier and is more expensive, but compared to the cost between a PWM controller that works well with other charging systems and an MPPT controller that works well with other charging systems, you can buy a few panels as well and still be in front.

T1 Terry

Mika loves caravaning · Newbie

Thanks a lot guys. Youâve been really helpful. The ratings of the solar panels are: Pmax123w, Voc 21.78v, Isc 7.99A, Vpmax 17.21v, Ipmax 7.15A, max sys voltage 600v, max series fuse 15A. I have two 120Ah batteries.

daffyfrancis · Senior Member

Hi,

I would think your fridge should use less than 70Wx24hr = 1680W (140AH) - ie: should cycle on & off under thermostat - perhaps you could advise the Waeco Model for the gurus on here to give you their estimation of its 24hr useage.

David

Jaahn · Guru

Hi Mika smile

Terry gave some good ideas to consider !

A couple of comments on solar panels from my experience. Big standard panels may not be best in mobile use and risk cracking the glass front panel. So smaller ones are better for that and also for the problem of shading which occures on a van or MH. A small shaded area on a panel can reduce the output down to nil, so if you have many panels it is better for random shade which you get camping as the sun travels over the sky. biggrin Best solar is on that treeless plane, worst camping spot furious

You should look further on ebay but these look alright to match up with your existing panels. https://www.ebay.com.au/itm/12V-Solar-Panel-150W-Monocrystalline-Caravan-Boat-Camping-Battery-Power-Charge/332515586409?epid=22012787390&hash=item4d6b793169:g:3YEAAOSwlxRaelE~

4 of them will be 600W nominal plus your 246W of existing panels.WOW 846 Watts nominal for only $490.20 delivered (with the special discount). Look for the VMP (Max Power Voltage) of around 17-18Volts to match the other ones, close enough.

AS said already perhaps the gain from a MPPT regulator/controller may not be worth the extra cost. Buy a quality PWM one instead. I use a MPPT reg but I also have a PWM that I use too for other things. While it is true that series panels into a MPPT reg can get some power under bad conditions when the lower voltage from the same parallel panels is not enough to charge, in practice the power available is very low anyway and the losses may use it up. The MPPT advantage comes with different configurations but is not as great as some claim.

My suggestion is to measure your roof and the vents, A/C, pipes, etc, positions and draw a sketch. Then see where the panels will fit on there and what way they need to be positioned. Then you can look for suitable shaped panels of suitable size if the space is tight. If the VMP is approximately the same you do not have to match them exactly in other ways including the watts. They will work together OK.

If you want to travel a lot then do not forget the tug has a powerful charger on the motor. Modern vehicles need more hardware to work OK so consider that as you go.

Jaahn

-- Edited by Jaahn on Tuesday 13th of February 2018 10:55:47 PM

T1 Terry · Guru

Just an example of small panels compared to larger panels

720w to replace the 240w there originally.jpg

These are 60w panels and we fitted 720w where 240w fitted originally

180w mounted between the sat dish and air con.jpg

In this spot we were able to fit 180w where no other panel would fit because the space is only 440mm wide.

-- Edited by T1 Terry on Thursday 15th of February 2018 03:34:34 PM

swamp · Senior Member

HI
power audit
Fridge 100% duty cycle 70w =divide x 12 = 6 amps at 100% per hr
say 66% or 2/3 duty +4amps per hr
4amps x 24 = 100ah

lights 4hrs at 100watts 32 AH

pump 1 hr =8ah

Fridge needs higher margin during very hot weather 80-100% run time

Fridge 100ah
light 32ah
pump 8ah
margin for fridge 30ah

Total 170Ah
THIS DOES NOT ALLOW FOR RAINY DAYS

double this is battery size 340ah [ USABLE CAPACITY IS 50 %]
Add safety Margin of choice 400ah battery 200ah usable

200watter production is 48ah in 24hr

300watt production is 72 ah in 24hr

The above production is 5.5 PSH only, with 20% loss caused by panel not chasing sun ,wire loss , controller loss. Does not include gain by MPPT function .

200watt per 100-120ah is ideal

SOLAR SIZING
SIze to average winter and summer [not including Tazzy]
5.5 Hrs is Peak Sun Hours [sun at 100%]
sun out side psh is unreliable

600watt system 33amp + mppt function = 44 amp
3x 120 ah would be a good starting point
Projecta 50amp mppt./dc/dc charger

need more accurate consumption by fridge but in reality 2 batteries [240ah ] most likely will not give u enough cloudy day margin

-- Edited by swamp on Tuesday 20th of February 2018 05:17:11 PM

T1 Terry · Guru

swamp wrote:
HI
power audit
Fridge 100% duty cycle 70w =divide x 12 = 6 amps at 100% per hr
say 66% or 2/3 duty +4amps per hr
4amps x 24 = 100ah

lights 4hrs at 100watts 32 AH

pump 1 hr =8ah

Fridge needs higher margin during very hot weather 80-100% run time

Fridge 100ah
light 32ah
pump 8ah
margin for fridge 30ah

Total 170Ah
THIS DOES NOT ALLOW FOR RAINY DAYS

double this is battery size 340ah [ USABLE CAPACITY IS 50 %]
Add safety Margin of choice 400ah battery 200ah usable

200watter production is 48ah in 24hr
300watt production is 72 ah in 24hr
The above production is 5.5 PSH only, with 20% loss caused by panel not chasing sun ,wire loss , controller loss. Does not include gain by MPPT function .

200watt per 100-120ah is ideal

SOLAR SIZING
SIze to average winter and summer [not including Tazzy]
5.5 Hrs is Peak Sun Hours [sun at 100%]
sun out side psh is unreliable

600watt system 33amp + mppt function = 44 amp
3x 120 ah would be a good starting point
Projecta 50amp mppt./dc/dc charger

need more accurate consumption by fridge but in reality 2 batteries [240ah ] most likely will not give u enough cloudy day margin

-- Edited by swamp on Tuesday 20th of February 2018 05:17:11 PM

Using the same figures although I'm not in full agreement with a few of them, the 600w of solar will barely keep up with demand and does not bring into account the fact lead acid batteries of any type will not recharge to 100% SOC at the full charging rate put forward in the calculations.

The same scenario using lithium (LYP) cells for the battery, a quality PWM controller, a 240vac dedicated inverter to power the equivalent household inverter style fridge would out perform the lead acid set up.

For the same cost or less than the lead acid battery cost and solar requirements using a 12v compressor fridge, a lithium battery and control system with a household 240vac inverter fridge and dedicated inverter could be installed with a far better long term out come. Use the money saved for more solar and the system should be able to stand up to 3 days of rain without an issue, much longer if power minimisation was employed while it was raining.

The lead acid batteries will reach the end of their useable capacity equalling system requirements well before the LYP cell battery. Generally it was accepted at a minimum of 2 sets of lead acid batteries per LYP cell set, but we are now seeing the LYP cells still going strong into the period a 3rd set would have been required. If the money saved from the first battery refresh was put towards more solar then the system would be able to handle any weather event that didn't separate the solar from the dwelling, life could be expected to carry on as normal as far as electricity requirements were concerned. Whether it makes sense to spend the extra $$ when initially installing the system is only something the purchaser can decide, or even starting with a smaller set up and upgrading as the $$ become available or the need exceeds the need to spend the $$ on something else, a problem that never seems to change no matter what choices we make :lol:

T1 Terry

Edited to add a few bits to make it easier to understand, and fix my usual crappy typing

-- Edited by T1 Terry on Wednesday 21st of February 2018 01:01:19 PM

-- Edited by T1 Terry on Wednesday 21st of February 2018 01:02:44 PM

Jaahn · Guru

Mika loves caravaning wrote:
Thanks a lot guys. You have been really helpful.

_________________________________________________________________________________________

Hi Kika smile

We forum junkies love people to come back and give some feedback on our replies. biggrin

Often we try to give good answers and discuss the questions but then never hear from the questioner again, so we are

Jaahn