Peer Review - Club hut solar lighting

[aidan.f]

I have volunteered to upgrade the solar lighting system for this hut in Southern Scotland:
https://www.cyclinguk.org/group/page/memorial-hut-albert-watson

It is used by a variety of community groups and scouts plus myself and a friends.
Having spent some time designing a replacement system I'm pretty sure I have something that will provide 16 hours lighting and three iPhone charges*.
for all but six weeks of the year, when hopefully it will be occupied by sensible people who can turn lights off!

*I did this by scaling the winter output of my home array

My choice of charge controller is EP Solar MPPT 1206N: USP's  are: simple intuitive LED display of battery level and charge with one load on/off button.

There is an RS485  interface for PC commissioning  and performance data download,
yes, I have tested the software on my lapdog...


Battery would be a 100 Ah Gel rated  for  500 Cycles@50%  ..worst case  discharge is 500 Wh

Solar panel
https://callidus.shop/products/solar-panel-115w-12v-mono-1015x668x30mm-series-4a?_pos=1&_sid=cde404452&_ss=r
https://callidus.shop/products/solar-panel-175w-12v-mono-1485x668x30mm-series-4a?_pos=1&_sid=130fa8c7a&_ss=r
The panel would be on the Southern gable end of the hut. It is not pictured in my first link, but is  a mirror image of the Northern side.
For simple installation the new panel would be vertical or maybe if we can engineer it, 60 degrees for winter efficiency.
As the panel location is likely to be sub-optimal and a 175 W panel only a few  ££'s more than a 115W i'm inclined to 'bigger is better'

The charge controller is maximum panel rating is a bit vague, headline figure is 130W.
Quotes below are from the manual:
https://www.sunstore.co.uk/wp-content/uploads/2021/01/XTRA-SMS-EL-V1.3-min.pdf

WARNING:  When the  power of PV  module  is greater than the rated
charging power, and the maximum open-circuit voltage of PV array is more
than 60V(XTRA**06N)/100V(XTRA**10N)/150V(XTRA**15N) (at the
lowest environmental temperature), the controller may be damaged.
According to “Peak Sun Hours diagram”, if the power of PV array exceeds the rated
charging  power  of  controller,  then  the  charging  time  as  per  the  rated  power  will  be
prolonged, so that more energy can be obtained for charging the battery. However, in
the practical application, the maximum power of PV array shall be not greater than 1.5
x the rated charging power of controller. If the maximum power of PV array exceeds
the rated charging power of controller too much, it will not only cause the waste of PV
modules, but also increase the open-circuit voltage of PV array due to the influence of
environmental  temperature,  which  may  make  the  probability  of  damage  to  the
controller rise. Therefore, it is very important to configure the system reasonably. For
the recommended maximum power of PV array for this controller, please refer to the
table below:

Model Rated Charge
Current  |  Rated Charge Power | Max. PV Array Power
10A        |  130W/12V                  | 195W/12V

What do you think the chance of cooking the controller is at midday in June?
In writing this I realise we could  actually put a sun-shade over it angled for summer only ..
Any other general design comments please?

[grams]

If you’re only using a single panel the output voltage will never be above about 21V, so the chance of cooking the controller is zero I’d say. It should just switch off or cycle on and off.

How much of the capacity of the battery are you expecting to use?

[aidan.f]

Regarding battery. Not more than 50%  capacity and that will only be if the scouts are there...all lights on all the time.
We managed all last weekend onna 7ah temporary battery.

I have just had a  re-read -of the converter manual. I think what is lost in translation is...
"you can use a panel up to 1.5 x nominal rating just so as long as you don't try to charge a bat flattery at midday in June"
The converter is rated at 10 Amps ~120 Watts.

What also is interesting is that 2 x series panels are recommended as 'best' match to the  controller
- so I'm going to use 2 x 55 Watt or 2 x 80 Watt (all the  panels are 36 cell)

[SoreTween]

Initial impression is it seems under powered.  The panels are 36 cell with VOC=23.7, the manual for the controller says it really needs 2 in series which still gives a string VOC less than 60V and only a smidge over the warm day 46V VOC.
But 2x 175W is way over the 1.5x array to charger ratio.  You'd be better off with 2x 90 watt or 1x 215 watt (72 cell) panel.
https://callidus.shop/products/solar-panel-90w-12v-mono-780x668-30mm-series-4a
https://callidus.shop/products/solar-panel-215w-24v-mono-1580x808x35mm-series-4a
Don't forget to factor in 90% power at 10 years old & 80% at 25 years.  The panels degrade but the charger will not so it's life gets easier over time.

Higher array voltage means lower current, you'll be nowhere near the 10A hard limit even at max output.  You'll need to verify the controller can take 24v (nominal) input and charge at 12V but it ought to, the main job of a controller is to regulate varying input voltage (up to VOCmax) to steady charge voltage & current.  The fact that the nomenclature allows for a 1106 but that doesn't exist tends to reinforce that view.

You are looking at 6.6 hours of direct (i.e. perpendicular) sunlight to charge the battery from 50%.  In reality it will need longer.
If you only need 7Ah I'd be looking for a smaller LiFePO4 battery, they should be good for 2000 cycles or more at your planned 50% DoD.  Lithium also has better self discharge characteristics.  But I guess you arrived at 100Ah off your 50Wh max load?  Is that over egging the omelette?  Lithium at that capacity is super spendy.  (I'm encouraging you to take a critical look at your requirement spec here, you know it - I don't)

[fimm]

The (mountaineering) club I'm a member of has a hut near Inverness that has had solar panels on the roof for about 10 years now. We've never had an over supply of power that I know of. We did recently put a mini wind turbine on the roof to help in the winter.
If you like, PM me and I'll give you some contact details - I know we had a lot of help from owners of other huts when we did our system.
I don't have the knowledge to comment myself.

[grams]

Higher array voltage means lower current, you'll be nowhere near the 10A hard limit even at max output.

On an MPPT charger the limit is usually on the output, so with a 12 V battery and a 13-14V charge at 10A you get 130-140 watts as the maximum throughput. It’s not clear to me what happens if you exceed this on the input. I’d expect it to either shut off or PWM allowing the solar voltage to float upwards, which is why they warn you about exceeding the input voltage.

Tbh the 2021 solution to all this is this kind of thing which integrates battery, solar controller and USB/mains output. Very thievable though.

[aidan.f]

Loads of  good  advice  whilst  I was  away  reading the manual and posting  this...

I have just had a  re-read -of the converter manual. I think what is lost in translation is...
"you can use a panel up to 1.5 x nominal rating just so as long as you don't try to charge a bat flattery at midday in June"
The converter is rated at 10 Amps ~120 Watts.

What also is interesting is that 2 x series panels are recommended as 'best' match to the controller
- so I'm going to use 2 x 55 Watt or 2 x 80 Watt (all the panels are 36 cell)

The  500 Wh in a weekend is worst case, all lights left on for 16 hours 6 x 3 Watts,
Two of  those  lights in the kitchen/lobby  can go on a  PIR which will be  a bonus as you have your hands  full when walking in..

You are looking at 6.6 hours of direct (i.e. perpendicular) sunlight to charge the battery from 50%.  In reality it will need longer.

seven days to recharge.. probably more in winter - unlikely to be occupied every  weekend
I am in any case planning to build and test at home before deployment

[LittleWheelsandBig]

I can't comment with regards to the electrics but solar panels get dirty, even with frequent rain, so efficiency is usually a little lower than theoretical. Regular cleaning is normal with solar farms.

[Socks]

If you need an unskilled labourer, happy to help if I'm available when the installation takes place.

[salar55]

No overhead cables nearby? The old Glasgow CTC hut was renovated years ago and we managed to have a 240v supply run in. Wired up lights and power, much safer than the gas lighting and making sure that the gas bottles were full  Wonder if it's still being used regularly?

[canny colin]

I did suggest Using some jump leads or  a kite and some copper wire , as the overhead electric cable  runs very close to the hut .
It might be worth contacting the money grabbing bustards . Sorry  Scottish power of Spain and seeing if they will help out a charity with a supply . I can easy pull a trench & Supply ducting / tape .

[salar55]

I did suggest Using some jump leads or  a kite and some copper wire , as the overhead electric cable  runs very close to the hut .
It might be worth contacting the money grabbing bustards . Sorry  Scottish power of Spain and seeing if they will help out a charity with a supply . I can easy pull a trench & Supply ducting / tape .

That might be a bad idea, overhead lines are usually more than 240v, transformer then 240 or 415 v to meter.

[Kim]

If it's just a few lights, and you don't have any labour costs, the standing charge for an electricity supply makes this sort of solution seem likely to pay for itself.

If they'd charge you for the costs of installing a supply at a location that doesn't have one, it rapidly becomes a no-brainer.

[grams]

When we took over management of our flats I briefly considered whether we could run the hallway lights off solar for exactly that reason.

More trouble than it's worth to actually make happen, mind.

[aidan.f]

Bah! Bat Flattery.. homeopathic amounts of charge retention after only 21 months of use..
It (was) a 100 Ah SLA lesiure battery - should have been adequate for a few watts of LEDS.
Problem is far more use than predicted, with limited solar. I suspect  that the battery has been at low levels of charge for long periods. Not a good recipe for SLA life.

Hut management have agreed to replacement. I am now looking at LiFePO₄
Four Eve 230 Ah B grade cells + BMS £360.  (we have a secure battery box, so don't need a 'package')
https://www.fogstar.co.uk/collections/lifepo4/products/eve-lifepo4-230ah-prismatic-cell-grade-b
To contrast: premium brand 110Ah GEL (Victron) £255
What could be the gotchas?
I know about not charging <5^oC (Both the BMS and existing charge controller will manage this). Unfortunately the battery is external, so bright winter days won't supply charge. Have looked at heaters but >50 Watts from winter solar is a non-starter.

[Tod28]

Bring your battery indoors - no risk of off gassing from LiFePO4.  I have installed 4x 304Ah EVE's in the MH.  Set the BMS to 5C for not charging and 8C to restart. More of a risk of attempted cold charging in the MH through the split charge relay.  Solar panel is plug in demountable so not operating over winter when the MH is not in use.

[Tod28]

As you know LiFePO4 is happy with partial spasmodic charge/discharge during winter whereas the LA of any kind is killed.

[aidan.f]

Have ordered the batteries,

Bring your battery indoors - no risk of off gassing from LiFePO4.  I have installed 4x 304Ah EVE's in the MH.  Set the BMS to 5C for not charging and 8C to restart. More of a risk of attempted cold charging in the MH through the split charge relay.  Solar panel is plug in demountable so not operating over winter when the MH is not in use.

Most of the time it's no warmer indoors..going to live with the charger temperature limiting.

[quixoticgeek]

Possibly relevant and of interest

https://youtu.be/f-mWmhh7i0U

J