Electrical – Can 12V 130 Watts/7A Solar Panel power 500 Watts inverter

invertersolar cell

I had an inverter of 500 Watts that I use with my car batteries and recently purchased two 130w/7A solar panels that is yet to arrive. Is it a good practice to use the two panels directly to the 500 Watts inverter without batteries or do I purchase extra two panels of 130w/7A?

Best Answer

What you use depends on your application and finances.
As you are using a 500 Watt inverter you could use up to about 500 Watts of solar power directly if it as available and the load required that much power.

Panels are specified in full midday sun with the panel at 25 degrees C. In practice when they get hot they give less power out and less when the sun is off angle. How much you get in a day depends where you live but as a guide you typically get 2 to 4 hours equivalent full sun in winter and 4 to 6+ in summer. More in Kabul. Less in Copenhagen. I'll tend to work with full panel wattage below and this will need to be scaled down depending on circumstances and location.

Your 130 Watt panels will never give 130 Watts if connected to a 12V battery with a diode or simple NON-MPPT controller. Maximum will be maybe 90 Watts each. See below.

You say the panels are 12V, 130 W, 7A.
130W / 7A =~ 17.6 V which is typical for a panel intended to charge nominally 12V lead acid batteries. If you connect a 12V car battery inverter directly to a 12V input inverter then if the inverter drew 7 Amps at 12V the input power would be about 12V x 7A = 84W. If the battery voltage was 13V (see below) then at 7A the power = 13V x 7A = 91W.

If you operate a 130W, 7A panel at it's optimum load voltage it will deliver 130 Watts in full sun (by definition). However, if you connect the panel to a 12V car battery and then connect the pait to a 12V input inverter the voltage will be clamped to ABOUT 13V by the battery. So if the panel delivers 7A it will provide 7A x 13V = 91W into the inverter and NOT 130 Watts.

IF the inverter is able to tolerate 18V or more input - say 24V absolute maximum, then if the panel delivers 7A to the inverter WITHOUT the battery connected then Vin to the inverter can be as high as 17.8\7V and 130 Watts.

What the above means is that by connecting panels + battery + inverter together in a simple manner you limit maximum panel output to about 90 Watts in full sun and not 130 Watts. So 2 panels = 180 Watts (not 260) and 4 panels gives 360 Watts (and not 520).

So, 4 panels at 12V in full sun will not quite exceed your inverter capability if a 12V battery is connected.

One way of getting more power from a panel is to use an MPPT (Maximum Power Point Tracking) controller which better matches the battery to the panel. In full sun an MPPT controller may get 110- 120 Watts from a 130 Watt panel.

MPPT controllers tend to be costly. Whether you are better off buying more panels or buying an MPPT controller depends on circumstances and local costs but nowadays more panels is usually a cheaper $/Watt approach.

So - a panel will give up to about 70 to 80 Watts in full sun when hot. It will give substantially less in lower light parts of the day. If you look up the SSH (sunshine hours) for your location on GAISMA you can work out the total Watt hours per day that you will typically get in a given month.

Bagdad data. SSH = Sunshine Hours = kW/m^2/day = 1st data line.
X = October = 3.96 SSH/day average.

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Watt hours ~= Gaisma_SSH x 80 Watts per panel

eg in [Baghdad in Octobet[http://www.gaisma.com/en/location/bagdad.html] chart 4 shows 3.96 = 4 ssh per day so one panel will give about
80W x 4 = 320 Watt hours into a battery or into a battery connected inverter without MPPT. Dirty panels, shadowing and lack of all day sun will reduce that.

You need to balance that level of energy per panel and provide as load and finance allows.