Supercharged Panels Explained

Technical Guidance - Solar Panels

 

How do you upgrade your solar panels to “Supercharged Solar Panels”?

Solar cells are great technology. Unfortunately, they are not matched very well to batteries. Most solar panels are built to put out from 16 to 36 volts. The problem is that a nominal 12 volt battery is in range of 10.5 to 12.7 volts, depending on state of charge.

Under charge, most batteries want from around 13.2 to 14.4 volts to fully charge - quite a bit different than what most panels are designed to put out.

OK, so we have a 120 watt solar panel. Catch is that it is rated at 120 watts at a particular voltage and current. Typically 7.1 amps at 16.9 volts - 7.1 amps times 16.9 volts = 120 watts.

So what happens when you hook up this 120 watt panel to your battery? Unfortunately, what happens is not 120 watts.

Where did my Watts go?

Your panel puts out 7.1 amps. Your battery is setting at 12 volts under charge: 7.1 amps times 12 volts = 85 watts. You lost 35 watts - but you paid for 120.

That 35 watts is not going anywhere, it just is not being produced because there is a poor match between the panel and the battery. With a very low battery, say 10.5 volts, it's even worse - you could be losing as much as 35% (10.5 volts x 7.1 amps = 75 watts. You lost 45 watts.

One solution you might think of - why not just make panels so that they put out 14 volts or so to match the 12V battery?

The panel example is rated at 120 watts at full sunlight at a particular temperature (STC - or standard test conditions). If the temperature of the solar panel is high, you don't get 17 volts.
At the temperatures we have seen under test at Kimberley in Australia, you might get under 15 volts. If you started with a 15 volt panel (like some of the so-called "self regulating" panels), you are in trouble, as you won't have enough voltage to put a charge into the battery. (Our experience in very high ambient temperatures is operating the solar panels without a controller can be close to optimum power output )

Solar panels have to have enough leeway built in to perform under the worst of conditions. How can their output be optimised?

We upgrade our solar panels to “Supercharged Solar Panels” by adding a Maximum Power Point Tracking solar (MPPT) Controller.

First, this is NOT Panel tracking - this is where the panels are on a mount that follows the sun.

Maximum Power Point Tracking - this is electronic tracking, and has nothing to do with moving the panels. Instead, the controller looks at the output of the panels, and compares it to the battery voltage. It then figures out what is the best power that the panel can put out to charge the battery. It takes this and converts it to best voltage to get maximum AMPS into the battery. (Remember, it is Amps into the battery that counts). Our Supercharge MPPT is around 92-97% efficient in the conversion. You typically get a 20 to 45% power gain in winter and 10-15% in summer. Actual gain can vary widely depending weather, temperature, battery state of charge, and other factors.

How Maximum Power Point Tracking works:

Assume your battery is low, at around 11.5 volts. In the example we started with above, a MPPT controller takes that 16.9 volts at 7.1 amps and converts it, so that what the battery gets is no longer 7.1 amps at 16.9 volts, but 9.6 amps at about 12.5 volts. Now you still have almost 120 watts, and everyone is happy.

Ideally, for 100% power conversion you would get around 10 amps at 11.5 volts, but you have to feed the battery a higher voltage to force the amps in. And this is a simplified explanation - in actual fact the output of the MPPT charge controller might vary continually to adjust for getting the maximum amps into the battery.

MPPT's are most effective under these conditions:

• Low battery charge - the lower the state of charge in your battery, the more current a MPPT puts into them – this is THE time when the extra power is needed the most.
• Cloudy, hazy days, or when the ambient temperature is low - when the extra power is needed the most. Solar panels work better at cold temperatures, but without a MPPT you are losing most of that. - the time when sun hours are low and you need the power to recharge batteries the most.

Can you add a Maximum Power Point Tracking solar controller to any existing solar panel?

Eco-camper is not selling individual MPPT controllers at this stage as there is a shortage of supply.

For solar panel suitcases, the controller has to be configured so that the battery power is switched to the MPPT controller BEFORE the solar panel is connected. If not it wont function correctly. As a result it would be difficult to have the controller mounted at the back or near the solar panel. Eco-camper has the controller in a separate bag as close to the batteries as possible.

 

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