Need help with solar setup!!

[John Frum]

80 watts * 24 hours = 1920 watt hours

Lets say you get 5 hours of sunlight per day
1920 watt hours / 5 hours = 384 watts

1x 400 watt panel
1x 200 amp hour 12 volt battery

legend {
    {} { functional block }
    nnn|NNN| { fused busbar position where nnn is the wire size in AWG and NNN is the fuse rating in amps }
    nnn|UUU| { un-fused busbar position where nnn is the wire size in AWG }
    <-> { bi-directional current flow }
    -> { uni-directional current flow }
    <- { uni-directional current flow }
    @ { back reference }
}
main {
    * 12 volt system
    * floating
    positive_busbar {
        008|UUU|<->50_amp_fuse<->battery.positive
        008|050|<-solar_charge_controller.out.positive
        014|015|->80_watt_load.positive
    }
    negative_busbar {
        008|UUU|<->battery.negative
        008|UUU|->solar_charge_controller.out.negative
        014|UUU|<-80_watt_load.negative
    }
}
solar_charge_controller {
    in {
        positive<-dpst_breaker<-400_watt_panel.positive
        negative->dpst_breaker->400_watt_panel.negative
    }
    out {
        positive@
        negative@
    }
}

 

[SunnySoCal]

So 80 Watts x 24 hours is just under 2 kWh. How many days does it need to run if you have no sun? I'm going to do the math for three sunless day and thus you will need to have storage of about 6 kWh. That means a pretty expensive battery. It seems LiFePo4 (lithium) has come down in price enough that over the life cycle of the battery is should cost 1/2 or less of what a flooded lead acid deep cycle battery (think Trojan, for instance). For one day without sun you'd need 12V @200ah, two days @400ah, and 3 days @600ah. Note that the nominal lowest price I've seen is about $300 per 200ah...so about $1200 if you need 3 days. If you have a modicum of mechanical skills you'd be able to buy the individual cells and make yourself for about 1/2 to 2/3 the cost. Here's a pretty good vid on a-z of making a battery:

Is it something that can run on a modified sine wave inverter vs a more expensive pure sine wave (PSW) inverter? I'm going to assume PSW as at this power level they're pretty inexpensive. Put "300 W pure sine wave inverter" into amazon (for instance), put $50 minimum and 4 or more star ratings. Yes, more power than you need but this is on the low end for inverters. Assume you can now get a decent, well-reviewed one for $100.

You will need a solar charge controller. Don't know your latitude so can only guess your sun hours per day (winter being the lowest) so you'll need to do that homework (google "insolation by latitude and longitude"...insolation is the incident energy for any given day and lat/long). But I will assume a minimum of 5 hours/day and thus for one day you'll need to produce 2 kWh, 2 days (without sun) or 4 kWh, and 6 kWh. 5 hundred watt panels will produce ~80 W per panel (with an MPPT controller, maybe ~70 with a PWM controller). So assuming MPPT, 80W x 5 panels x 5 hours would generate 2000 Wh or 2 kWh. To double you'd need 10 100 W panels, or 5 200W panels, etc.


As for cost of system...
Sine Wave inverter: $100
MPPT controller (depends on amperage) but figure ~$200
Battery (as stated above) N x $300 (N-number of sunless days)
Panels ~ $0.8-1.00 per Watt
Misc (wires, fuses, etc): $200


Not an inexpensive proposition to fire up your 80 W device! I see that someone else beat me to this post so will take a gander at that one...

 

[MisterSandals]

So 80 Watts x 24 hours is just under 2 kWh. How many days does it need to run if you have no sun?

80 watts * 24 hours = 1920 watt hours

That runs for 25h on 2kWh.

You have to add 2kWh of battery for every day of autonomy. And then you need more solar to charge back up those batteries, either in a single day or whatever you choose.

 

[Mikeanthony100]

So 80 Watts x 24 hours is just under 2 kWh. How many days does it need to run if you have no sun? I'm going to do the math for three sunless day and thus you will need to have storage of about 6 kWh. That means a pretty expensive battery. It seems LiFePo4 (lithium) has come down in price enough that over the life cycle of the battery is should cost 1/2 or less of what a flooded lead acid deep cycle battery (think Trojan, for instance). For one day without sun you'd need 12V @200ah, two days @400ah, and 3 days @600ah. Note that the nominal lowest price I've seen is about $300 per 200ah...so about $1200 if you need 3 days. If you have a modicum of mechanical skills you'd be able to buy the individual cells and make yourself for about 1/2 to 2/3 the cost. Here's a pretty good vid on a-z of making a battery:

Is it something that can run on a modified sine wave inverter vs a more expensive pure sine wave (PSW) inverter? I'm going to assume PSW as at this power level they're pretty inexpensive. Put "300 W pure sine wave inverter" into amazon (for instance), put $50 minimum and 4 or more star ratings. Yes, more power than you need but this is on the low end for inverters. Assume you can now get a decent, well-reviewed one for $100.

You will need a solar charge controller. Don't know your latitude so can only guess your sun hours per day (winter being the lowest) so you'll need to do that homework (google "insolation by latitude and longitude"...insolation is the incident energy for any given day and lat/long). But I will assume a minimum of 5 hours/day and thus for one day you'll need to produce 2 kWh, 2 days (without sun) or 4 kWh, and 6 kWh. 5 hundred watt panels will produce ~80 W per panel (with an MPPT controller, maybe ~70 with a PWM controller). So assuming MPPT, 80W x 5 panels x 5 hours would generate 2000 Wh or 2 kWh. To double you'd need 10 100 W panels, or 5 200W panels, etc.


As for cost of system...
Sine Wave inverter: $100
MPPT controller (depends on amperage) but figure ~$200
Battery (as stated above) N x $300 (N-number of sunless days)
Panels ~ $0.8-1.00 per Watt
Misc (wires, fuses, etc): $200


Not an inexpensive proposition to fire up your 80 W device! I see that someone else beat me to this post so will take a gander at that one...

You are amazing my friend!!! You brought up very good points!! I would need it to be able to last 3 days and I never thought about that to much!! The latitude is 26.20772
And longitude -98.18126
I wish I knew more about what you where talking about, but unfortunately I am barely learning.

 

[Bud Martin]

So that 80W device runs on 12VDC or runs on 120VAC? That will make a lot of difference on the power consumption from battery, if you need 80W 120VAC on the output side of the inverter, then the DC side of the battery will be close to 100W due to conversion loss that you need to factor in.

 

[John Frum]

I missed the inverter part.
Here is a good one https://samlexamerica.com/products/150-watt-pure-sine-wave-inverter-pst-150-12/

We will have to factor the ac to dc conversion overhead.

80 watts / .85 conversion factor = 94.117647059 dc watts
94.117647059 dc watts * 24 hours = 2258.823529412 watt hours
2258.823529412 watt hours / 5 hours sunlight = 451.764705882 watts
2258.823529412 watt hours * 3 days of autonomy = 6776.470588235 watt hours