The cable from the panels arrives, through a hole in the door frame, at the charge controller. This takes the power from the panels which is 100 volts peak and converts it to a suitable voltage to charge the battery bank. The charge controller ensures that the batteries are neither over nor under charged and that in use they are never deeply discharged. This type of controller uses a technique called Maximum Power Point Tracking (MPPT). We should do something detailed on this technology as they can improve the energy harvest from a given array, by up to 30%.
Here is the proof of the pudding - 14 amps flowing into the batteries. This was at 12volts so I was getting nearly 170 watts. When the batteries are full the output from the panels switches over to a grid tie inverter where it helps with the base load of the house. When the batteries need a charge the panels switch back to the charge controller. The other 12 panels are going to be connected to a 700Watt (peak) GTI. All of this will need to be tweaked (at least) as I learn but since most of the wiring is a lash-up, the occasional re-wire will do no harm.
This switching from charge to grid tie ..Done by controller?? Now I need a simple answer to a stupid question.... The GTinverter uses the energy in your bat bank before demanding from the mains... Or does it start reversing your meter units..
caveman was suggesting a piece of electronics which monitors the current / charge flowing to the batts. when this drops off, i.e., the batts are charged, a changeover relay is thrown which switches the pv output to the gti. so yes, it would be some sort of controller which does the switching, based on the battery current draw.
background on when a meter will go back and when it will not:
net import scenario: the gti, when fed with power by a genny or pv, pushes power to the mains circuit of your house. mains appliances in use in the house effectively draw from the gti as a power source , and, if they need any more power the power is drawn from the utility firm's source and the net import from the grid is recorded on the utility meter.
so if the gti is delivering 200w and your oven is using 300w then only 100w is drawn through the utility firms meter.
net export scenarios (but not net export over a whole billing period): if the gti produces more power than is being used in the house, then it feeds the utility grid. if you are registered as a microgenerator with your utility firm, you will have a generation meter to keep track of what you put in. if not, and you have an old style 'spinning disc' type meter, you will most likely wind the meter back when you are producing an excess, thereby getting some unofficial 'credit' for your net output, in the sense that you will get charged less per billing period to the value of the excess that you produced! if you have a modern digital utility meter and the utility firm knows nothing about your gti, then you'll simply not get any credit for the excess power you generate, but you will still save on your household load. in this last scenario the utility firm gets free energy to the value of the excess you produce.
net exporter for a whole billing period, spinny disk meter: if you produce so much that your meter now registers less than it did at the start of the billing period, the utility firm will think you have been up to funny business, when in reality you have not and you've simply been a net generator. may require some explaining.
caveman's proposal is a hybrid of 'off grid' and grid'. i do not believe he was proposing using battery power to feed back into the mains (though that is also possible). i think the batts are for running lights and the off-grid low load side of the house. charge your batts first, and when they are fully charged, any excess pv power is fed into the mains in the house via the gti.
The idea is to keep the panels busy. During the summer months the batteries will not be discharged very much at all so by mid morning they could be fully re-charged. There is little point running 16x50watt panels as a trickle charger so my plan is to switch them to GTI duty until the battery bank needs a top up. As Cye pointed out there is a box of electronics controlling this. There are 2 ways (at least) to control the switch between battery charging and GTI. The first is to monitor the battery voltage to establish when the battery bank is on a 'float' charge. (13.8 volts for a 12 volt system) The second method involves measuring the current flowing to the battery bank and switching over when it falls below a preset level. I prefer the second for a number of reasons. The current can be measured at the DC meter so I do not need to add anything to the circuit. This current reading connection can also be used to keep a track on the current used from the bank to the extent that it should be easy to work out when the bank could take a charge and roughly what size of charge. This would allow the system to take enough panels back to charge the bank and to leave the rest to GTI. In the winter all 16 panels will be fed to the charger in an effort to bring the batteries back to a respectable level in time for each long dark evening. A small system like this would really be worth tracking in our climate. I could easily see a 30% increase in output. Perhaps even the 40% Dermot mentioned. I hope this makes sense. Fire away with the questions if there are any. c