In article number 4 of the series, I want to talk about an important component, namely the solar controller, which essentially organizes the energy coming from the panel to put it into the batteries. Without a controller, if you hooked the solar panel directly to the battery it would work a little and then ... the battery would make popcorn.
There are two types of controllers: PWM and MPPT. The main difference between them is that PWM or Pulse Width Modulation is essentially a slightly smarter switch - it either draws current or doesn't draw current to the batteries, using pulses. Once the "switch" is "open", the battery will pull the panel voltage down and charge. This process stops when the PWM shuts down, hence the name pulse width modulation. And it keeps repeating the process until the battery is full, increasing the break intervals as the battery voltage increases. This type of controller needs a panel with a voltage close to that of the battery to do its job, which is quite important but also a notable limitation. I mean, for a 12 volt system, the panel needs to be up to 20 volts or so, which isn't great. Clear example: If you take a 100w panel at 20V and put it in a PWM controller, it will still drop to 13V. Mathematically, if we have 100W at 20V, it will result in 5 amp hours. But, because a PWM can't intervene in the voltage, we have 13v with 5 amp hours so the efficiency drops to 65%, come on 70% in the most optimistic scenario.
If we now look at the other variant, MPPT or Maximum Power Point Tracking, it works completely differently. If PWM connects and disconnects through a panel battery circuit, MPPT has two different circuits. This notably more advanced controller lowers panel voltage and behaves like a smart DC-DC Charger, especially in common 12v systems. Let's take the whole 100W panel example from earlier to see what happens. In the case of the MPPT, if you input 100W at 20V, so 5 amps, it will drop the voltage and produce almost the same 100W but at 13V so somewhere around 7 amps. I have made these approximations because in any such process there will naturally be some losses. Maybe 2 amps don't seem like a lot, but they are relevant as a percentage. And when you have 300-500-1000w of panels on your camper, the 30% difference in efficiency is more than relevant. Anyway, you don't get to put PWM on large systems, because it's not designed for that, you still go back to MPPT. But, as an idea, PWM is an old technology that doesn't really make sense anymore except for small and low-budget systems or slow loads over long periods of time (garden lights and the like).
I've tried to explain the difference simply, so as not to get too technical, although I still did a bit. The most relevant aspect is that MPPT has about 30% higher efficiency than pwm so, without a doubt, this is the controller we want to choose. But you have to be careful, because many cheap Chinese controllers say MPPT but ... usually they are not.
And MPPTs are of many kinds. Personally I use a Victron Smart Solar 100-30, that means it can operate at max 100V and 30Amps. Sure, each manufacturer will describe it differently or have different terminology for their models, but with Victron controllers the first number is maximum voltage and the second is maximum amperage. Smart means it has bluetooth and I can connect to it anytime to see the history, trends and what's happening in real time. Bonus, thanks to my setup, I can also see the information from the net with the help of Cerbo GX via VRM. I would say this is a simple and effective system. There are alternatives, such as those that draw power from both the solar and the alternator, from Epever, Renogy or C-Tek or Redarc. I admit, I like the idea, it seems like a clean, simple solution that works both as a solar controller and as a DC-DC from the car. But basically, they tend to make me wary of stuff that is all in one, because when it breaks, it breaks everything, obviously. And for safety, I chose to use a Victron Smart BMS CL100 to charge from the alternator and SmartSolar for the panel. That way, if one goes down for whatever reason, you're left with a possible power source. By no means am I saying they are bad, on the contrary C-Tek and Redarc are excellent manufacturers, especially on the overlanding side. But, I preferred to separate them for my peace of mind.
Another point to touch on here is installation and efficiency. Just like any other product, the controller has an output that can vary according to temperature. If the installation is done in an enclosed space, where there is no room to ventilate, you may be surprised to see either a low output or it stops. Also, not all MPPTs are built the same, hence the price differences. Some have yields of 98% up to temperatures of 40 degrees, others can be below 90% on their best days. It's an important point because the whole process that energy goes through from when it comes from the sun to when it reaches your iPhone jack involves some losses. And quality equipment ensures you the lowest losses. If we go back to PWM and think that from 70% efficiency we cut about 10% when it's hot, you better buy a dynamo and put in an hour of cardio, you get better results.
Besides the controller, you need cables, connectors, fuses and all sorts of things and I would like to talk briefly about them because they are important. First of all cables and connectors, because I remembered a discussion on a group of RVers where someone argued that the specific ones for solar are expensive. It may be, but dedicated cables have, besides another quality, increased UV resistance, which is a very important aspect. Normal cables can bake after two to three summers and the results can range from failure to short circuit or fire. So whatever you mount at home, do it with dedicated products. Also related to the cable there is an aspect of fitting that I have encountered more in the states and less in Europe. On many systems I've seen an automatic fuse placed on the route between the panel and the controller. The utility I see is to cut the power to the panel when you want to remove the batteries, as you basically have to remove the panel first and then the batteries. Otherwise, without a battery connected, you have a chance that the energy in the panel will make a popcorn controller. Whether you want to unplug the system to turn off the panel or protect against possible surge problems, a fuse here doesn't hurt. Maxim never uses it, but it doesn't hurt.
Well, looks like we've solved the mystery of the solar controllers. So, in this series, so far we've talked about how to build and size an offgrid camper system, what batteries exist and what we should buy, what solar panels and controllers to choose. I think it's worth talking a bit about the 12v-230v inverter because we found a lot of myths and misconceptions out there and it's good to know exactly what we're looking for when we spend our money on a product like this. Because 2000w from a no name inverter made in a pile in a village in China is not quite the same 2000w from a Renogy, Victron or MasterVolt.