diy solar

diy solar

Any Advice? Solar setup (24V tiny home)

smashmo

New Member
Joined
Mar 5, 2022
Messages
7
hello

Firstly thanks in advance for any advice that people may be able to offer.

I have a basic plan for a solar setup

REQUIREMENTS
1) run 6LED 12v lights
2) a small 12V compressor fridge (WEBASTO Cruise 130 Elegance - consumes about 418W/24h)
3) washing machine (day use only planned on 1hr short cycle) - https://www.johnlewis.com/bosch-ser...-machine-7kg-load-1400rpm-spin-white/p4917463
4) fiamma water pump (estimate 1hr/day total) - https://www.fiammastore.com/Fiamma-Aqua-Pumps-for-caravans-and-motorhomes/Fiamma-Aqua-8-pumps
5) use 2hr a day a 12v-->230V 3000W inverter to run a 2000W induction stove - https://www.campinggrej.dk/shop/carbest-sine-wave-85350p.html?CookieConsentChanged=1
7) charging mobiles


PLANNED SYSTEM
Location = Northern Spain = 3-4 daily sun hrs



2 x 450W JA SOLAR (144 cells, mono), 24V https://www.bricomart.es/pub/media/..._solar_mono_perc_hc_10940412_techsheetsup.pdf

---

2 x Victron 12/24V, MPPT 75/15 - https://www.victronenergy.com/uploa...MPPT-75-10,-75-15,-100-15,-100-20_48V-EN-.pdf

OR

1x 3600W inverter/charge controller
https://assets.leroymerlin.es/is/co...s/inv-car-ais-m-power-um-v4-3-6k-24v-120a.pdf (this system leaves space to grow as our power needs will increase over time - as we build more. BUT its way more $$ upfront. Eventually would love to charge a small electric car one day, not sure if this unit will do it tho)

---

2 x 260AH sealed 12V AGM ELEKSOL batteries (in spanish - https://www.bricomart.es/pub/media/...para_sellado_v_ah_c_10195822_techsheetsup.pdf)



CONFIG
Basically plan to hook each panel to a seperate MPPT then both to the 2 batteries that will be wired in parallel

OR

just hook panels and batteries direct into the inverter/charge controller unit (batteries as 24V in series)


QUESTIONS:

a) Am I on track or totally off on my panel sizing in relation to planned usage?

b) How about the battery sizing? As I will only use the washing machine during sunny hours I assume I may not need extra capacity for the battery? Is that correct? any comments welcome

c) for the victron MPPT option spec sheet says 'Nominal PV power' is 440W but the panels are 450W. Is this a problem? I ask cos I dont really understand what Nominal PV power is and how serious the number is. Having trouble finding 400W panels that are 24V in my area.

d) JA solar - looking online and not really finding many reviews on it. Youtube has a couple but mainly from stockists as I see. I am wondering if anyone has experience with them. In peoples experience do brands of panels make much difference?

e) any obvious cheaper ways to achieve the same setup?

Thank you
 
Its best to measure the W-Hr/day you are actually using, take the readings for about 3 days worth to get rough ideas then go from there.
Do you have something equivalent to Kill-A-Watt you can get in your country?
 
Its best to measure the W-Hr/day you are actually using, take the readings for about 3 days worth to get rough ideas then go from there.
Do you have something equivalent to Kill-A-Watt you can get in your country?
hi, thanks for the reply. the trouble is the fridge and inverter are not even purchased yet so i dont have any 'real' data on the usage. My guesses are based on manufacturer data but even then my knowledge of electricity isnt that good to calculate. My knowledge is limited to W= V * A!!! Im learning as im going but hoping to get it as close to right before buying all this expensive stuff
 
Victron will limit the PV input power if over-paneled, it would be unlikely to see 450w on a regular basis from each panel.

This is similar to my setup, only thing is you may want to oversize the battery bank incase you get a 2 or 3 rainy days in a row (unless you have access to a generator or mains power)

I just purchased a smartsolar 75/15 to play with and so far I'm liking it, that inverter charger looks like a good option too.
 
got it mate. i guess on a really sunny siummer day could also shade the panel a little also to ensure it doesnt give any issues to the mppt. they are expensive little things!



Victron will limit the PV input power if over-paneled, it would be unlikely to see 450w on a regular basis from each panel.

This is similar to my setup, only thing is you may want to oversize the battery bank incase you get a 2 or 3 rainy days in a row (unless you have access to a generator or mains power)

I just purchased a smartsolar 75/15 to play with and so far I'm liking it, that inverter charger looks like a good option too.
 
Assuming you will have a 24V battery then with those 2 450W solar panels you can put them in series with a single Victron 150/35 or put them in parallel with a single 100/30 or 100/50. With the 100/30 you can make use of about 800W. That's fine. You will rarely get 900W from the panels. A single 100/30 is about the same price as two 75/15 but you will save even more on the simpler wiring and setup. You will get better performance putting the two panels in series with the 150/35 but it will cost a little more for the bigger SCC.

If you have a 24V battery then you would want a 24V 3000W inverter for your induction stove, not a 12V 3000W inverter.

If you do want a 12V system for a 12V inverter then you need much bigger (more expensive) charge controllers. 900W at 12V is 75A of charge current. You need either a single 150/70 to put the panels in series or two 100/30 - one for each panel. But that won't make full use of wattage.

The 3600W solar inverter/charger is what many would call an all-in-one since it is an inverter, charger, transfer switch, and solar charge controller.
 
i guess on a really sunny siummer day could also shade the panel a little also to ensure it doesnt give any issues to the mppt. they are expensive little things!
that's not really necessary as the mppt will only draw what it needs to keep the system happy
 
Assuming you will have a 24V battery then with those 2 450W solar panels you can put them in series with a single Victron 150/35 or put them in parallel with a single 100/30 or 100/50. With the 100/30 you can make use of about 800W. That's fine. You will rarely get 900W from the panels. A single 100/30 is about the same price as two 75/15 but you will save even more on the simpler wiring and setup. You will get better performance putting the two panels in series with the 150/35 but it will cost a little more for the bigger SCC.

If you have a 24V battery then you would want a 24V 3000W inverter for your induction stove, not a 12V 3000W inverter.

If you do want a 12V system for a 12V inverter then you need much bigger (more expensive) charge controllers. 900W at 12V is 75A of charge current. You need either a single 150/70 to put the panels in series or two 100/30 - one for each panel. But that won't make full use of wattage.

The 3600W solar inverter/charger is what many would call an all-in-one since it is an inverter, charger, transfer switch, and solar charge controller.
firstly thanks for the reply.

hmmm, now im a bit confused. lets see if I can understand it.

This is the bit that confused me
If you do want a 12V system for a 12V inverter then you need much bigger (more expensive) charge controllers. 900W at 12V is 75A of charge current. You need either a single 150/70 to put the panels in series or two 100/30 - one for each panel. But that won't make full use of wattage.

cos as I see the 75/15 will do the job for each 24V panel, unless I have made an error.

My plan was to have 1 x 450W (24v) panel running into 1 x victron 75/15 MPPT and then connected to 2 x 12V batteries in parallel (12V system, 12V inverter etc). I would then do the same with the other panel. I am doing this for a bit of redundancy in case a solar charger fails I can still get power from the other one.

As i understand from my reading and @pollenface the SCC will take a 24V panel and convert it down to a 12V battery system without any issues as long as you dont go over the maximum PV voltage and the maximum battery charge current. For the victron 75/15 that is 75v max PV voltage and 15Amps max current charge - https://www.screencast.com/t/sd2FdehjV2A3

When I go to the spec sheet of the JA solar 450W 24V panel I see these 2 numbers https://www.screencast.com/t/I2NwSmDq that are below 75 and 15 respectively.

Then when I further check the spec sheet of the panels I see that the 24V nominal power and the Max Short circuit current are both below the max rated of the SCC. https://www.screencast.com/t/Tcog4uMdzeVE

As newbie Im wondering if I have messed something up or just not understood your meaning correctly.
 
cos as I see the 75/15 will do the job for each 24V panel, unless I have made an error.
You are referring to a 450W panel on a 12V battery. 450W / 12V = 37.5A of charge current. A Victron 75/15 only supports up to 15A of charge current. 15A at 12V is 180W. Even using a 100/30 per 450W panel limits what you get since 30A x 12V = 360W. Though when the battery is full that will be closer to 400W. So using two 100/30 SCC with your two 450W panels means that you can only use at most 800W of the 900W available.

Remember, the whole concept of a panel being a "12V" panel or a "24V" panel is marketing nonsense. When using an MPPT solar charge controller, that label has no meaning of any kind. Only pay attention to the panel watts and actual voltage (Voc and Vmpp) and current (Isc and Imp).

As i understand from my reading and @pollenface the SCC will take a 24V panel and convert it down to a 12V battery system without any issues as long as you dont go over the maximum PV voltage and the maximum battery charge current. For the victron 75/15 that is 75v max PV voltage and 15Amps max current charge
Again, it's not a 24V panel. The Voc is nearly 50V and the Vmpp is over 41V. The MPPT SCC will take the incoming panel wattage (whatever that is at the moment given the current solar conditions) and it will convert that power into the battery charge voltage and associated current (battery charge current = panel incoming wattage / battery charge voltage). That charge current may also adjusted down as needed based on the current state of the battery.

You are correct about what the 75/15 means except to be clear, the 15 is 15A of max battery charge current.

When I go to the spec sheet of the JA solar 450W 24V panel I see these 2 numbers https://www.screencast.com/t/I2NwSmDq that are below 75 and 15 respectively.
You have circled the Vmpp and the Impp. When looking at the max PV input voltage of a SCC, that is based on the Voc of a panel, not the Vmpp. But the Voc is still well below 75V, even in the coldest of temperatures. But the 15A of charge current provided by the Victron 75/15 has nothing to do with any of the panel specs. It is the largest amount of charge current that it can put out. You can calculate your needed charge current by taking the input wattage divided by the battery charge voltage. For your panel the max input wattage is 450W. For your battery setup the max charge voltage will be somewhere around 13V. This means your needed charge current is 450W / 13V = 35A. So you need a SCC that can provide close to 35A. This is why the 15A 75/15 is far too small for your 450W panel.

One thing that may help is to play with Victron's MPPT calculator:


Use the "Custom Module" radio button and enter the specs for your panels. Try various combinations of panels such as 1S1P (one panel), 2S1P (two panels in series), and 1S2P (two panels in parallel) and see what Victron recommends.
 
right, i see. Damn back to school for me!! Im slowly getting the hang of things as I see. Thanks for the explanations. that helps alot and using the straight out calculations rather than the marketing of the panel does make sense. ok.

I now get when people start talking about the costs of the MPPT's. I was checking prices just now and they go up in price significantly. that inverter charge controller is starting to look more appealing. lots of $$ tho!!

Ill review anyway. thanks again for your time. I appreciate it as you have saved me some costly mistakes by the looks of things
 
My plan was to have 1 x 450W (24v) panel running into 1 x victron 75/15 MPPT and then connected to 2 x 12V batteries in parallel (12V system, 12V inverter etc). I would then do the same with the other panel. I am doing this for a bit of redundancy in case a solar charger fails I can still get power from the other one.

If you plan to use 1x 450w panel per 1x victron 75/15 you MUST connect your batteries in series for 24V as the victron 75/15 will only support a max PV size of 220w in a 12v system.

For more information see here
 
If you plan to use 1x 450w panel per 1x victron 75/15 you MUST connect your batteries in series for 24V as the victron 75/15 will only support a max PV size of 220w in a 12v system.

For more information see here
ok. noted. so based on what im hearing above from you and rmaddy, it seems i am best to store in 24V and then convert down to 12V using a 24V-->12V converter. That part is becoming clearer now.

questions
a) assuming I store in 24V and need to convert to 12V for the lights, fridge etc, how can I size the Amps needed on the converter. is it just the total max W that i plan to use at any one point divided by 12V??

b) is it more efficient to run a 24V inverter directly off the battery or convert to 12v and then run a 12V inverter? Im guessing that direct off the battery would be simpler and allow a cheaper 24V-->12V converter (say 30A or 40A)?

c) Also it seems according to the above calculations from @rmaddy i might be a little over the max charge current. Assuming then I wire the batteries in series, 450W/24V = 18.75A which is over the rated 15A for the victron 75/15.

So I guess my question is, if you are unlikely to actually ever get 450W out of the panel, is going a few amps over ok or running a decent risk?


Otherwise 100/20 is what it looks like to be safe. 70 euro more per unit but in the long run will be worth it im sure - especially with these energy prices!! In spain we ahve had a 40% increase in 6 months! :) total joy!
 
a) basically correct. Add up all of your 12V loads to get the max watts. Divide by 12V for the minimum amps needed by the converter.

b) definitely use a 24V inverter on a 24V battery. You do not want to make any attempt to run an inverter off of a DC-DC converter.

c) see post 6 where I show the best solutions for charge controller(s) on a 24V setup. It’s ok if the charge controller’s charge current value is slightly less than what your panels could ideally provide. The most important metric is that the Voc of the panel arrangement, adjusted for the coldest temperatures you will see, is less than the controller’s max PV input voltage.
 
c) see post 6 where I show the best solutions for charge controller(s) on a 24V setup. It’s ok if the charge controller’s charge current value is slightly less than what your panels could ideally provide. The most important metric is that the Voc of the panel arrangement, adjusted for the coldest temperatures you will see, is less than the controller’s max PV input voltage.
Once again thanks for the comments. Appreciate it very much.

Ah yes, the main thing here is that I was thinking to hook up one panel with one charge controller. Main reason was that I read that MPPT's can fail and in the world we are going into with supply chain shortages I thought to spend the extra and get a seperate second MPPT.

So to be clear what it seems like Im looking at (after everyones helpful advice) is:

2 x 450W JA SOLAR (144 cells, mono), https://www.bricomart.es/pub/media/..._solar_mono_perc_hc_10940412_techsheetsup.pdf

2 x Victron 12/24V, MPPT 100/20 - https://www.victronenergy.com/uploa...-MPPT-75-10,-75-15,-100-15,-100-20_48V-EN.pdf

2 x 260AH sealed 12V AGM ELEKSOL batteries (in spanish - https://www.bricomart.es/pub/media/...para_sellado_v_ah_c_10195822_techsheetsup.pdf)

1 x 24V inverter

1 x 24v-->12V converter




SETUP

Tried my hand at drawing it. See attached!
Ok, i didnt draw it but I edited one by whiting out and adding parts :)
 

Attachments

  • 2022-03-09_18-27-23.png
    2022-03-09_18-27-23.png
    406.4 KB · Views: 4
Back
Top