Enough is enough? Nah!
Can you get too much solar power? Spend too much time on Pensacola Beach and you’ll think so, and have a red face to remind you. But, no, I am talking about photovoltaic power. In the case of grid tie, it has gotten to the point in some places that they are having to add battery storage systems to balance things out. The lack of battery saw the advent of the “duck curve” in utility power production. Look it up.
On your OWN independent power system, can you have too much? In phase two of the Solar Shed project, I had gobs of power on a sunny day, but not having enough battery and reaping only 10% of rated power on a cloudy day (we have them a week at a time in winter) made me wish for more power. Phase 3 gave me LOTS more power as the shed went from 32′ to 80′ of solar roof. Now, I am finding some interesting conditions to which I must adapt.
In addition to more power, now around 10kw rated, there is more battery storage and more on the way as I get to the detail work. The flooded lead-acid batteries are fine, now 3 days into a cloudy spell, though next year’s Phase 4 should keep them really topped.
What about sunny days? If the day starts out clear, I see what I saw on my solar boat expedition, the batteries start charging at the crack of dawn and ease into a full charge without any stress on the system. (When not on the boat I make a point of sleeping too late to see what my system is doing at dawn.) What happens, though, if the batteries are low and the day starts out cloudy and suddenly the clouds part to reveal full, noontime sun? OH CRAP! Think about that for a moment. 10kw at 48 volts amounts to 200 amps of charge current into my 635 amp battery. That comes to a C3 charge. Batteries love a C20 charge, or a rate of about 1/20th of the A/H rating of the battery. They are ok with C10, but they will use a little more water. But C3??? Bubble bubble, toil and trouble, to misquoteThe Bard. If you have sealed AGM batteries, they will soon die a horrible death at that rate.
My system has big knife switches I can pull to disable strings of panels in sunny weather, but that hardly seems a good way of doing things. You really want this to all be automatic. So far, the only issues I have had is when the batteries are topped and then the sun abruptly comes out. My inverter blinks the power off and back on! Why? Well, the charge controllers, which are set fairly close to the overvoltage trip on the SunKing 5548 inverter, take an instant to react to the increase solar power and the inverter trips. So, what to do?
The inverter is very adjustable, but everything is working the way it is set up and it really isn’t it’s fault, so I will leave it alone. BTW, you can’t buy a SunKing 5548…I built it out of the ruins of my lightning-killed previous inverter and some driver hardware I found. (Note that the Sun Electronics kits include the lightning protector that I NOW use.) The next place to look would be the charge controllers. I have 4 and three different models. I don’t recommend having a bunch of mismatched hardware, but I ended up with leftovers from evaluating hardware for my Solar Yacht project. As I noted in a previous blog, each has a different personality and each is adjustable. The two least active, get satisfied early in the day and shut down. They are not a problem. The twins are very active and are where the trouble originates. I dug through my literature stack and found the manual and went through the setups, dropping the maximum on one and dropping it some more on the other. I’ll know if this did the trick sometime in May, when the sun comes out again. I will just tweak them until the maximum charge current is at a rational level under full sun.
Are there other remedies? Glad you asked! Yes, there is a gadget called a Diversion Load Controller. I think these were first used with wind generators because you can’t just disconnect a windgen in a stiff breeze or it might fly apart. It used to be that the cost of solar guaranteed that no one would have too much solar power, but that has changed. You can use the DLC to dump power into a giant resistor, but that is wasteful. A better plan is to find a 12, 24 or 48 volt water heater element, as appropriate, and dump the excess power into your water heater. It just screws in. Everybody likes a free hot shower, right? That won’t do in my situation because, first of all, the Solar Shed is 200′ from my house and, second, my water heater is wood-fired.
The way I will use the DLC, if needed, is to pull in a relay that disconnects some of the PV strings.So, can you have too much solar power? I’ll let you know next year when Phase 4 brings another 5KW online, because, so far, I am reveling in what I have and adding more loads.
By: Neal Collier