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250W Photovoltaic Panel: Battery Capacity for 1kWh/24h Usage, MPPT Load & Gel Battery Options

RAINBOWBRIDGE 22752 21
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Can I draw 1 kWh per day from a battery charged by a 250 W photovoltaic panel, and what battery capacity should I choose?

Yes, but only under favorable conditions: a 12 V battery stores about 85 Ah for 1 kWh theoretically, but in practice you should choose at least 50% more capacity, and one reply suggests keeping the battery bank no larger than about 160 Ah so it can still recharge properly after deep discharge [#16490335] [#16490992] A 250 W panel can cover the daily energy demand on a sunny day, but it will be too weak in cloudy weather, when output may drop to about 30–100 W [#16490354] For year-round continuous operation and to guarantee 1 kWh per day in all conditions, the panel would need to be much larger, around 2 kW [#16492956]
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  • #1 16490312
    RAINBOWBRIDGE
    Level 14  
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    Hello. I would like to take 1Kwh / 24h from the battery at a 250W panel. Therefore, I wanted to ask those who know whether it is possible and what battery capacity to use. I have an mppt load driver. I'm looking for a gel battery now. greetings
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    #2 16490335
    Xantix
    Level 41  
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    RAINBOWBRIDGE wrote:
    what battery capacity to use

    1 kWh is stored in a 12 V battery with a capacity of about 85 Ah. Of course, this is the theoretical minimum. In practice, an amendment should be made to the finite efficiency of the battery, and also to the fact that the batteries should be discharged to zero because this significantly shortens their life. Therefore, I suggest taking a battery at least 50% larger.

    RAINBOWBRIDGE wrote:
    I would like to take 1Kwh / 24h from the battery at a 250W panel. Therefore, I wanted to ask those who know each other if it is possible

    It is possible - but not at all times and under all conditions.
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    #3 16490354
    vodiczka
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    From the battery side: 1kWh is otherwise 12V x 83.33Ah
    Panel side: 250W x 8h = 2 kWh
    Taking into account the efficiency of charging the battery, on a sunny day you will charge it calmly, but when it is cloudy, it will be a problem because depending on the degree of cloudiness, the panel will give away from 30 to 100W of power, which is too little to cover the daily energy demand.
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    #4 16490757
    3301
    Level 34  
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    On a sunny day, such a panel will charge the battery even 100Ah discharged to the acceptable level already before noon and if there is no additional load, the rest of the energy will be wasted. In order to optimally use the capacity and energy stored in the battery, it should be discharged with a current of 20h, which at 100Ah is 5A at a temperature of 20 degrees. batteries
  • #5 16490844
    Wr841nd
    Level 15  
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    What is the MPPT driver?
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    #6 16490992
    vodiczka
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    3301 wrote:
    On a sunny day, such a panel will charge the battery even 100Ah discharged to the acceptable level already before noon
    Please calculate. The author of the topic does not mention that his panel will follow the sun and that he will only use it between June 10th and July 5th when the days are the longest. I have the impression that my colleague, early afternoon was mistaken for morning. :)
    3301 wrote:
    in order to have a certain reserve it would be appropriate to have 2-3 such batteries
    In my opinion, no more than 160 Ah.
    If the batteries are deeply discharged, which may happen over a few consecutive cloudy days, batteries with a greater capacity may never fully recharge.
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    #7 16491334
    3301
    Level 34  
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    In my opinion, there is nothing wrong here, and my friend gave the calculations:
    vodiczka wrote:
    From the battery side: 1kWh is otherwise 12V x 83.33Ah
    Panel side: 250W x 8h = 2 kWh
    Taking into account the efficiency of charging the battery, on a sunny day you will charge it calmly, but when it is cloudy, it will be a problem because depending on the degree of cloudiness, the panel will give away from 30 to 100W of power, which is too little to cover the daily energy demand.

    Following the conversion, it would be 8kWh from 1kWp per day, which is real, although I obtained 6.8kWh max with 1kWp and also using my experience because I also use 16 batteries at 100Ah and 4.32 kWp on the roof which gives 270W / 1 battery 100Ah, so even a little less power on Ah than the author of the topic would have, after 12:00 on a sunny day, if I do not load more UPS than usual, some energy returns to the clouds.
    So if there are more of these Ah in stock, they will be less intensively discharged with the assumed consumption of 1kWh, which gives only advantages.
  • #8 16492461
    RAINBOWBRIDGE
    Level 14  
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    Wr841nd wrote:
    What is the MPPT driver?


    I have BlueSolar by Victron MPPT 100/15
  • #9 16492887
    vodiczka
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    From my no calculations compared to the assumptions (panel and battery), there was a large excess of power on sunny days and at the same time its shortage on cloudy days.
    The author of the topic did not specify whether the installation should operate all year round or only in summer or only on sunny days? He also did not say whether the demand for energy is from dusk to dawn or, for example, is 40% from morning to evening and 60% from evening to morning. Only when you have all the data you can perform calculations and select the panel power and battery capacity.
    3301 wrote:
    which gives 270W / 1 battery 100Ah, so even a little less power on Ah than the author of the topic would have
    The author of the topic has a 250W panel, i.e. he would have less power for a 100A battery and a friend suggested 2-3.
    3301 wrote:
    in order to have a certain reserve it would be appropriate to have 2-3 such batteries
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  • #10 16492930
    RAINBOWBRIDGE
    Level 14  
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    The installation is to be year-round, energy demand will be dimmed. I would like the battery to be charged in the morning and in the afternoon.
  • #11 16492956
    Xantix
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    As the whole year is supposed to work continuously, in order to ensure this 1 kWh in all conditions, the panel would have to be at least a dozen times larger than at present (I would aim at about 2 kW). IMHO, forget to ensure that this installation is operational all year round in reasonable money. In winter, it will be cheaper to charge the battery with electricity from the energy sector. :(
  • #12 16493256
    vodiczka
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    Xantix wrote:
    (I would aim for some 2 kW)
    In my opinion, 1kW should be enough, as long as the sequence of consecutive days with strong cloud cover is not too long.
    When it is overcast, the panel optimally set for winter conditions (in summer it will provide excess power without moving it) should produce a minimum of 0.8 kWh / day. The remaining 0.2 kWh can be obtained at the cost of gradual discharge of the batteries.
    https://www.youtube.com/watch?v=iNSP2bGXQgs
  • #13 16493339
    RAINBOWBRIDGE
    Level 14  
    Posts: 201
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    Thank you for the information. So with one 250W panel I will not do anything? I'm starting to regret buying it.
  • #14 16493367
    vodiczka
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    Unfortunately not.
    What was this set supposed to power? Where to work Is it possible to recharge the battery from the mains or not?
  • #15 16493456
    RAINBOWBRIDGE
    Level 14  
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    Initially, a laptop and LED lighting, there is a possibility of recharging, but I do not see any sense in recharging the battery from the network, you can also connect everything to the network and give it a rest with the panels :)
  • #16 16493627
    Xantix
    Level 41  
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    RAINBOWBRIDGE wrote:
    everything can be connected to the network as well and give yourself peace of mind with the panels

    You know, it can be even more cost-effective to use electricity from the energy sector - especially in winter ...
  • #17 16493794
    vodiczka
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    RAINBOWBRIDGE wrote:
    Initially, a laptop and LED lighting, there is a possibility of recharging, but I do not see any sense in recharging the battery from the network, you can also connect everything to the network and give it a rest with the panels :)
    Since you have already bought, you can use the set in the summer and personally observe the difference in work depending on the degree of cloudiness. Treat the installation as experimental. :|
    You will also find out (after a long time) that if you do not use some of the energy on a regular basis, it is not as good and it is better to use electricity from the network, unless you have access to partially used batteries for the proverbial one zloty.
  • #18 16493805
    Kwazor
    Level 33  
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    RAINBOWBRIDGE wrote:
    Initially, a laptop and LED lighting, there is a possibility of recharging, but I do not see any sense in recharging the battery from the network, you can also connect everything to the network and give it a rest with the panels :)


    You can do it easily.
    My configuration is up to 180W + 150Ah battery and I do not know what external charging is.

    Laps runs an average of 6 hours a day a day and does not feel even on 1 panel, i.e. 90W, would not charge my battery when I am not there.

    Only in winter there were some deeper discharges (about 30%) because the weather was not daily.
    The laptop uses an average of 31W and takes about 2.5-3.5Ah from the batteries per hour.
  • #19 16493871
    vodiczka
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    Kwazor wrote:
    ] You can do it easily.
    With a laptop, yes, especially when it works no longer than 8 hours a day, but we know nothing (power, working time) about LED lighting.
  • #20 16494686
    theo33
    Level 27  
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    Hello and welcome
    I have been observing topics related to photovoltaics for a long time, I also test the 180W 24V panel and the 108Ah battery connected via the inverter and I need advice what is wrong because after two days of charging the battery voltage is 13.2V at 3A current and nothing rises despite the fact that on the inverter input is 25V.
    The converter has an input range of 15-30V and an output of 13.8
  • #21 16495330
    3301
    Level 34  
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    As I wrote in another post, check the inverter and this panel.
  • #22 16710946
    romanha1
    Level 10  
    Posts: 20
    Rate: 7
    And is it not possible to use an inverter with a VOlta sinus pro 1000s controller?

    If it is true what the manufacturer says, if there is no electricity, it will switch to the mains current and charge the battery, unless the straightener does not work as specified by the manufacturer.

    Can anyone comment on this voltage regulator with an inverter
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Topic summary

✨ The discussion revolves around the feasibility of using a 250W photovoltaic panel to supply 1kWh of energy over 24 hours, focusing on the required battery capacity and the use of an MPPT load driver. Participants suggest that a 12V battery with a capacity of at least 85Ah is theoretically needed, but recommend a larger capacity (around 160Ah to 100Ah) to account for efficiency losses and potential cloudy days. The panel can generate up to 2kWh on sunny days, but performance drops significantly in overcast conditions. The installation is intended for year-round use, which may necessitate a larger panel (around 2kW) to ensure consistent energy supply. Concerns are raised about the practicality of relying solely on solar energy during winter months, with suggestions to consider grid electricity as a backup. The author expresses regret over the purchase of the panel, questioning its adequacy for their needs.
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FAQ

TL;DR: A 12 V 85 Ah battery stores ≈1 kWh [Elektroda, Xantix, post #16490335]; "It is possible – but not at all times" [Elektroda, Xantix, post #16490335] With one fixed 250 W panel you’ll hit 1 kWh/day only in summer yet miss the mark in winter.

Why it matters: Correct sizing avoids dead batteries and wasted solar capacity.

Quick Facts

• 1 kWh load ≈ 12 V × 83–85 Ah [Elektroda, vodiczka, post #16490354] • 250 W panel outputs 30–250 W; 30–100 W under cloud [Elektroda, vodiczka, post #16490354] • Average winter insolation at 50° N: 1.2 kWh/m²/day vs 5 kWh in June [PVGIS, 2023] • Victron BlueSolar 100/15: 100 V Voc, 15 A charge, 98 % peak efficiency [Victron Datasheet] • Lead-acid life drops sharply below 50 % depth-of-discharge [Battery University, 2023]

How big should my battery be to draw 1 kWh every 24 h?

At 12 V you need 85 Ah for 1 kWh, but limit discharge to 50 %. Choose at least 130 Ah to double cycle life and provide reserve [Elektroda, Xantix, post #16490335]

Can a single 250 W panel supply 1 kWh per day all year?

No. Summer output can exceed 1.5 kWh, yet winter yield drops to ≈0.3 kWh at 50° N, leaving a 70 % shortfall [PVGIS, 2023].

How many panels ensure 1 kWh/day in winter?

Sizing for the worst month requires about 1 kW of modules; some users recommend 2 kW for multi-day autonomy [Elektroda, Xantix, post #16492956]

What Victron BlueSolar 100/15 settings suit gel batteries?

Select GEL preset: bulk 14.1 V, absorption 14.1 V, float 13.8 V, and enable temperature compensation (-4 mV/°C/cell) [Victron Datasheet].

Is a gel battery better than AGM or LiFePO₄ here?

Gel resists deep discharge but charges slowly. AGM is cheaper yet less cycle-robust. LiFePO₄ offers 2,000+ cycles at 80 % DoD but costs 3–4× more [Battery University, 2023].

What wiring and fuses do I need for a 15 A charge circuit?

Use 4 mm² copper (≤2 % voltage drop over 3 m) and a 20 A MC4 fuse or breaker on the battery lead “Electrical Guide”.

What if several cloudy days deeply discharge the battery?

Edge-case: "Batteries with greater capacity may never fully recharge" if overcast persists [Elektroda, vodiczka, post #16490992] Depths beyond 80 % can halve gel battery life [Battery University, 2023].

How do I estimate PV and battery size? (3-step method)

  1. Calculate daily load in Wh. 2. Divide by worst-month sun-hours to get panel watts. 3. Multiply load by days of autonomy and divide by system voltage → Ah. Adjust for 80 % efficiencies.

Can an inverter/charger like Volt Sinus Pro 1000S help?

Yes. It auto-switches to grid when PV is low and recharges batteries at up to 20 A, keeping loads alive [Manufacturer Specs].

Is grid power cheaper than oversizing solar for winter?

At €0.20/kWh, buying 90 winter kWh costs €18/month. Adding 1 kW PV plus batteries exceeds €1,000, a 4-year payback at best—longer if modules underperform “EU Energy Prices 2023”. "You know, it can be even more cost-effective" [Elektroda, Xantix, post #16493627]
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