Solar wasted watts/volts
I am curious what happens to the watts /volts when your system is fully charged and you have no demand? Were does the extra power go?
Forum Discussion
time2roll wrote:
Harvey51 wrote:
Have a link to this issue? I believe there is more to the story.
Anyone got an explanation for what Ontario Hydro does when it’s heavily subsidized solar panels produce too much power? They give it to their good neighbours in the northern states, and sometimes pay those power companies to take it. I suspect it is due to deals made by politicians that require the utility to buy all the solar power available at prices 5 to 10 times the cost of other power sources.
Toronto Sun storyAlmot wrote:
Though I don't see how this is related to perceived "problem" of excess power (that is not really a problem, as many have noted).
It's not a "problem" (the OP's concern), but it is an opportunitypianotuna wrote:
Some of the top of the line controllers do have voltage sense wires.
I would say that most top of the line controllers have voltage sense. Morningstar MPPT (at least, those 45-60A). Rogue 30A MPPT have it - or had, before going out of business, couldn't compete with $2/hr Chinese labor. For controllers 30A and higher this is a must to have.
Though I don't see how this is related to perceived "problem" of excess power (that is not really a problem, as many have noted). Voltage sense is to prevent voltage drop from affecting the voltage setpoints on battery terminals. Then controller brains would do their job, adjusting the absorption time and/or other parameters according to battery state of charge. Diversion doesn't have to be a part of this. One could use a diverted energy to heat the water, not big deal to me, it's not too cold and propane works well.mike-s wrote:
How does that circuit adjust to allow the batteries to reach absorption and equalization voltages and times so they're properly charged and maintained?
We have a relatively-fancy solar controller (Midnite Classic) that has a optional mode where it sets an auxiliary output signal once it reaches FLOAT stage. We have that control signal connected to a solid state relay which then turns the AC power to the water heater on or off.
Further, the controller will pulse width modulate that signal very rapidly, such that the on/off ratio is proportional to only the amount of "excess" solar input (if any), thereby maintaining a proper float voltage at the batteries.
Pretty slick, but the key is a smart enough solar controller that implements this kind of diversion mode.- mike-s,
The only measurement that can be taken is voltage. Some of the top of the line controllers do have voltage sense wires. If mine had that ability I would certainly use it. Rice wrote:
How does that circuit adjust to allow the batteries to reach absorption and equalization voltages and times so they're properly charged and maintained?
When batteries are in FLOAT mode, they need very little electricity to keep them floating. We divert that excess solar production via the use of a solid state relay that turns the water heater on and off depending on the battery voltage.starcraft69 wrote:
Ok forget the hot water part If i put a over size system in how does the system dissipate the extra power being generated?
I noticed you edited out your question about using the excess for hot water, but you shouldn't have. It can be done.
But first of all, the water heater has to be on the inverter circuit, and I believe that most RVs aren't wired that way. But we changed ours to the inverter circuit just so we could use it on solar.
(But I'll note that our inverter circuit is 30 amps, and when on shore power, it's very easy to go over that if you're using the microwave, water heater, and a hair dryer at the same time. That's probably why the water heater is usually not on the inverter circuit--that, plus most people would never run their water heater off their batteries, so it never needs to run through the inverter. So it's not hassle-free for us to have the water heater on the inverter circuit.)
When batteries are in FLOAT mode, they need very little electricity to keep them floating. We divert that excess solar production via the use of a solid state relay that turns the water heater on and off depending on the battery voltage. When the battery voltage is high enough, the water heater comes on. As soon as the water heater pulls down the battery voltage, it turns off. Over and over and over, dozens and maybe hundreds of times a second, without drawing anything from the batteries.
You can, of course, just turn on your water heater (if it runs through the inverter), but if it draws more than the sun is giving, the water heater will draw down your batteries. Plus you could forget that it's on. Our method automatically "turns off" when there's not enough sun to operate the water heater and keep the batteries fully charged.
However, we have 1,050 Watts of solar, compared to the 300-400 Watts you're looking at. On the one hand, using the "excess" solar is very satisfying, but on the other, having the water heater on the inverter circuit does require some thoughtfulness when using plug-in appliances that use a lot of electricity.
We'll often reach FLOAT state pretty early in the day, depending on where we are, and will have several hours of hot water generation, so it's worth it to us. If it were going to be much less than that, I'm not sure it would be worth the hassle--to me.
But it can be done.Harvey51 wrote:
Have a link to this issue? I believe there is more to the story.
Anyone got an explanation for what Ontario Hydro does when it’s heavily subsidized solar panels produce too much power? They give it to their good neighbours in the northern states, and sometimes pay those power companies to take it. I suspect it is due to deals made by politicians that require the utility to buy all the solar power available at prices 5 to 10 times the cost of other power sources.Harvey51 wrote:
Anyone got an explanation for what Ontario Hydro does when it’s heavily subsidized solar panels produce too much power? They give it to their good neighbours in the northern states, and sometimes pay those power companies to take it. I suspect it is due to deals made by politicians that require the utility to buy all the solar power available at prices 5 to 10 times the cost of other power sources. Electricity behaves logically but politics often doesn’t.
Pretty darn close for a guess. I forget the name of the act down here in the States but it basically states that anyone who wants to put generation on the grid cannot be denied from doing so. This, coupled with the tax credits/subsidies, winds up placing large surpluses of energy on the grid at times when wind blows and sun shines.
Because they are getting a tax credit, if you tell them to shut off their solar/wind, they tell you to stuff it, because they're getting paid $38/MWh for the energy they're producing, even though nobody needs it. So then they sell the energy for near-zero or even negative prices and still make money.
This places the burden on other generation facilities (mainly thermal) to "regulate" the grid, which is basically balancing load and supply. In return, they can purchase this surplus energy for a fraction of what it costs them to generate and save their customers money. An added benefit is that they don't have to burn coal/gas to do it which reduces emissions and also reduces chemical costs, etc.
We do this in our fleet on a daily basis. It all falls under the umbrella of what is called an "Energy Imbalance Market" or EIM. The more people you have participating, the more money there is to be "made". "Made" is in quotes because for a regulated utility, you don't "make" any money. You are really saving money, and these savings are passed back to the customer in the form of lower net power costs.
In a sense, it's win-win, unless you're the American taxpayer that's paying for the subsidies.- nice link red31
