Sunday, May 12, 2013 at 08:34
An 80W panel will give a maximum of 80W (given the specified light intensity). The panel will also have a maximum current, which no regulator can increase. One supplier of LED
camp lighting states in every advert that their MPPT regulator can increase the output of a 120W panel to 180W, but that is an outright lie (which is a shame, because their LED lights are quite good!).
The panel you have is probably specified as 80W at 18V, which is 4.44A. The short circuit current will be listed somewhere in the specs of the panel, as will the open circuit current and voltage and the maximum power voltage and current. The short circuit current (which will be only slightly above the 4.44A calculated above, perhaps around 4.6A) is the maximum current the panel will produce, or allow to pass through it, under any circumstances. Other than in a short circuit you will never see that current!
The problem that an MPPT regulator attempts to address is that if that panel is connected to a partially depleted battery, lets say 11V, it's voltage will be dragged down to 11V. Now 4.44A at 11V is 48W. So under full sun that panel will only be producing 48W when connected to that battery. When the battery is fully charged, lets say 13.5V, the panel will be able to produce 13.5x4.44=59W, but of course the battery is now fully charged so that power isn't needed (unless there are other loads that are using the power).
So the 80W panel will never produce anywhere near 80W when it's voltage is dragged down to batery levels.
An MPPT regulator will allow the panel to operate at it's "best" voltage, whilst reducing still providing the battery with the voltage that it needs to charge correctly. So 4.44A at 18V = 80W, given enough light!
Of course the other point is that no matter what regulator is used the panel can only produce 80W under "test" lighting levels. That is normally 25C and 1000W/m^2 of light, and this rarely occurs! Solar panel output reduces with increasing temperature, and 1000W/m^2 normally only happens for an hour or so at midday in the middle of summer, when the temperatures are far higher than 25C.
The MPPT regulator will, of course, still work under lower light conditions or higher temperatures, but if there is only enough light to produce 40W at 18V, then you will only get 40W! But then without MPPT you will get even less.
So:
1/ MPPT is good, but with only one small panel you have to decide if it's worth the cost.
2/ An 80W panel can only produce 4.4A, so a 6amp regulator is sufficient. Unless you plan to add panels later (which is also more involved than it might first sound!).
3/ A cheap MPPT regulator will not be true MPPT, it will simply lock the panel voltage at 18V. That's better than nothing but will not give the optimum result under all conditions.
4/ A "real" MPPT regulator is definitely not worth the price for an array rated in watts (rather than kW!!)
5/ For an 80W panel and the gains to be had, spending "named brand" money is of questionable worth. These days with panels costing <$1/W (unless you pay the outrageous prices the camping shops still charge!) it might be better to buy more panels. A folding 120W array can be had for about $160, and with your existing regulator it will produce 76W in to an 11.5V battery (given enough light).......A fixed 180W panel (roof top mounting on a caravan) will cost about $200. Perhaps new panels are a better way to go?
6/ Camping shops have no idea about solar panels. Most internet experts have no idea about solar panels. Many companys selling solar panels to campers lie, or don't know about solar panels. If anybody tells you that MPPT will increase the panels output above its specified level, run away vary fast!
7/ People with no understanding buy products from retailers with no understanding (or questional morals!) and then are either disappointed with the results or simply never know their system is not great.
Maximum is maximum. All we can do is to try to recover the losses and get as close to maximum as possible under any given set of conditions.
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