How much energy from my solar panels?

[Bessy765]

Hi all in France been overcast most of the day my system shows 1.2 kw from 700 watts of panels am I correct in assuming that is 100 amps, or have I lost the plot?

 

[LostInSpace]

What plot?

 

[barryd]

Yep 100 amps according to this calculator.

Watts To Amps Calculator | Electrical Safety First

You can calculate Amps using the relationship between Amps, Volts and Watts. To calculate Watts to Amps, simply use our free calculator.

www.electricalsafetyfirst.org.uk

 

[LostInSpace]

my system shows 1.2 kw from 700 watts of panels

If you can get 1.2 kw from any solar panels, they are not on a motorhome.

 

[barryd]

If you can get 1.2 kw from any solar panels, they are not on a motorhome.

I assume Bessy meant harvested over a day.

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[Bessy765]

Yes that’s correct, gain today

 

[TheMobileWanderer]

Hi all in France been overcast most of the day my system shows 1.2 kw from 700 watts of panels am I correct in assuming that is 100 amps, or have I lost the plot?

Yep. 1200W / 12V = 100Ah.
W = V * A

 

[IRHP]

.

 

[CAB96]

It's kWh, or kilo-watt hours, which is the total amount you have harvested during the day.

1.2 kWh (1200 Watt-hours).


W or kW (Watts or kilo-Watts) is the power that the panels can give at any one time. Your panels are 700W, so 700 watts at maximum efficiency at any one point in time.


If you mean 100A as in battery capacity, again it is 100Ah, (Amp-hours). This is how the capacity of 12 volt leisure batteries are described.

So yes, 1.2 kWh (total energy harvested) divided by 12 volts (because you are storing it in a 12v battery) =100Ah (100 Amp-hours) of battery capacity.

The actual current flowing through the solar controller and into the battery at any one time will be nothing like that, it will be in the single figures or 10s of amps.

 

[Millcourt]

I think many folk have an unrealistic expectation as to how much power they will get from their solar panels.

Power being measured in watts (i.e. amps x volts) would suggest that a 120 watt solar panel feeding into a 12-volt system would produce a current flow of 10 amps in “ideal” conditions. These conditions would seem to be bright, directly overhead sun, a spotlessly clean panel, no area of shading, together with a partially charged battery and/or appliances in use able to absorb a current flow of 10 amps. Maybe in laboratory conditions with a new panel this might happen. In a real application (e.g. in a motorhome), various factors will likely reduce this. For example, cable resistance, losses with the solar regulator, but possibly mostly because in the “ideal” circumstances described above the solar panel will become hot and this will reduce the efficiency and thus the current output.

A few years ago, an electrician installing solar panels advised me that dividing the panel rated watts by 17 rather than 12 gives a more realistic expectation of the peak current you are ever likely to see in a 12-volt system. My own experience suggests that this is a reliable indication of what to expect.

I am curious to learn if other folk have found that dividing by 17 rather than 12 is a good guide to their actual experience.

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[Lenny HB]

A few years ago, an electrician installing solar panels advised me that dividing the panel rated watts by 17 rather than 12 gives a more realistic expectation of the peak current you are ever likely to see in a 12-volt system. My own experience suggests that

That will give you the current coming from the panels, with a godd MPPT controller the current going into the batteries will be quite a bit higher as the voltage will be between 13 to 14v when charging.

The sun has just come out I'm getting 14 amps at 17.5v from my panels and 18 amps into my batteries at 13.5v.

 

[Millcourt]

That will give you the current coming from the panels, with a godd MPPT controller the current going into the batteries will be quite a bit higher as the voltage will be between 13 to 14v when charging.

The sun has just come out I'm getting 14 amps at 17.5v from my panels and 18 amps into my batteries at 13.5v.

Thanks Lenny. I am aware that the PV voltage may well be more than 12v and the potential gains of using MPPT, but I was just trying to keep the maths simple with using, as my example, a 120 watt Panel in “ideal” circumstances yielding 10 amps at 12 volts, and suggesting this was a power yield which is an unrealistic possibility in a real-life situation.

If I recall correctly, you have two 175 watt solar panels on your new MoHo i.e. a total of 350 watts. At 12v if you are getting 100% of the stated output power actually being harvested, you theoretically will have a current flow of a little over 29 amps. If instead of dividing the panel wattage by 12 you divided by 17 (the yardstick which had been mentioned to me), the current would be around 20 amps. Allowing for a little inefficiency in the MPPT regulator etc, this is not far from the 18 amps you mentioned you were getting when the sun was out (perhaps not directly overhead for maximum yield). This does suggest that what I was told about dividing by 17 rather than 12 may be a good guide as to what to expect.

 

[Raul]

I never see the point in complicating things by calculating the Ah in and out. As the voltage sags under draw and rises when charging you are never gonna get the same Ah at 12v compared to a Ah at 14v. It's a massive difference over 100Ah flow.
Stick to true power W and Wh for energy, thats the end product you are using anyways.

 

[Bessy765]

When it’s full it’s full, when it’s empty it’s empty. Never the two should meet (well hopefully)

 

[Peter Beeston]

Here in Cheshire it was a glorious sunny day, and I got 2.4kWh from 520 watts of solar. Today it's raining. Time to go home.

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[funflair]

Here in Cheshire it was a glorious sunny day, and I got 2.4kWh from 520 watts of solar. Today it's raining. Time to go home.

That's a good yield from 520 watts and the answer the OP's question I think it is all down to the sun and clouds, I have seen slightly over our rated panel wattage but this is usually spring and early summer when the sky is clear as later into summer there always seems to be a haze even on a bright day, so yes 100% is possible but rare.

 

[Raul]

I had 3.33kwh few days ago, and most days 2.5-3kwh as just replenishing what we use.
Thats 600Wp flat on the roof, around the Peloponnese coast. With peak power exceeding 610w at midd day, if there is a breeze.