# Where does the extra solar energy go?

Registered Users Posts: 10
Hello all !!
There is always a mismatch between the capacity of solar panels installed and the loads which are in use. Even after considering the losses and efficiencies of all the components, the load is still less than the installed capacity.
What happens to the excess energy being generated from solar? Surely the output from panels will not decrease right?
A grid-tie inverter is not being used here.

• Solar Expert Posts: 1,913 ✭✭
Re: Where does the extra solar energy go?

The output does decrease. The extra energy is simply not generated. This is very convenient compare to wind, which requires a dump load to dissipate all the unwanted energy.
• Solar Expert Posts: 2,382 ✭✭✭✭
Re: Where does the extra solar energy go?

Unless your grid tie and then the meter spins backwards and you get a net metering credit from the utility in some form.
• Registered Users Posts: 10
Re: Where does the extra solar energy go?

I do not understand.... how can the extra energy not be generated?
• Solar Expert Posts: 173 ✭✭✭
Re: Where does the extra solar energy go?

I think the explanation lies in something called "Potential"

The panels have a "Potential" capability, but unless there is a load (somewhere for the current to flow and do work), they are not actually producing their "potential"

A battery has a 600ah Potential. but unless you connect it and let that current flow, it is only potential. It doesn't "go" anywhere.

That doesn't necessarily preclude "Wear" however.
If you leave those panels sitting in the sun long enough even without using their potential, they will still eventually go bad.
• Solar Expert Posts: 3,123 ✭✭✭✭
Re: Where does the extra solar energy go?
I do not understand.... how can the extra energy not be generated?

A solar panel will deliver an output ranging from maximum voltage and no current (Voc, I = 0) to its maximum for a given amount of light (Vmp, Imp). In between, the output of the panel will depend on what load is put on it.
If no current is being drawn, the panel simply stops converting photons to electrical energy (the Voc voltage keeps electrons from being moved to a different energy level by the light) and that incoming sunlight ends up as heat instead. This will not do any harm to the panel, since 80% of the light is going to heat already.
SMA SB 3000, old BP panels.
Re: Where does the extra solar energy go?

Kind of like a gasoline pump--It has the potential to put 10,000 gallons of fuel in your tank. But you turn off the flow when your 15 gallon fuel tank is full.

You can turn off the current from a solar array without causing problems.

With horizontal axis wind turbines (and many hydro-turbines), they need to be loaded by an electrical load (battery bank, resistance heaters, dead short, etc.) to keep the turbine from "over speeding" and self destructing from excessive RPM... So that is an example of a power source where you cannot simply turn off the current when the battery is full.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Banned Posts: 1,807 ✭✭
Re: Where does the extra solar energy go?
BB. wrote: »
With horizontal axis wind turbines (and many hydro-turbines), they need to be loaded by an electrical load (battery bank, resistance heaters, dead short, etc.) to keep the turbine from "over speeding" and self destructing from excessive RPM... So that is an example of a power source where you cannot simply turn off the current when the battery is full.

A wind turbine is pretty much like any other driven generator when the power isn't needed - you can shut it down, either automatically or manually.
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Chris
• Solar Expert Posts: 963 ✭✭
Re: Where does the extra solar energy go?

Chris
Can you only shut a portion of a turbine down and still get a portion of the charging abilitie.
Don't divertion loads sort of pulse allowing some charging to go on but controlling the battery voltage. I ask cause I don't know.

gww
• Banned Posts: 1,807 ✭✭
Re: Where does the extra solar energy go?
gww1 wrote: »
Chris
Can you only shut a portion of a turbine down and still get a portion of the charging abilitie.

Not totally on-topic with where the extra solar power goes. But absolutely. You can stall the airfoils by making the rotor run at a lower TSR (Tip Speed Ratio) and vary the power output any way you like, just like with the throttle of an engine. This can be done by feathering the blades, or furling it. Many folks think of turbines in quite simplistic terms, based on the cheaply built pinwheel turbines built by the Chinese and the former SWWP that use "dump loads" to control battery voltage.

Furling turbines are a completely different ballgame, and are totally controllable for power output.

As an example, this is a photo of one of my 375 turbines running manually furled to regulate how much power it produces - notice the direction of the wind vane on the anemometer vs the direction of the rotor shaft and tail position. This method of controlling wind turbines has been used for over 100 years on Aermotor water pumping windmills - just pull the furling cable and set the power output to whatever you like.

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Chris
• Solar Expert Posts: 963 ✭✭
Re: Where does the extra solar energy go?

Chris
I had read in a different thread that you were getting away from the clipper and going to something that just shut down your turbines. When bill was comparing solar just not producing except what the load needed even in bright sun, and pointed out that wind was different, I was thinking of battery load. I am not saying he was saying that, it is just what my mind said it ment to me.

I see your point about lots of sun and no load and lots of wind and no load. I guess the differance with a generator and wind turbine is with the generator you can just not give it enough gas to destroy it and that makes it more simular to solar.

Solar seems to have a simple solution to controlling exess sun. Exess wind seems to be harder to get mynute control. The things you mention are all do-able but are much harder to do. I think your useful divertion loads like hot water heat are more valuble then just turning it off. Wind turbine controls seem to be more expensive or you have to keep a better eye on it.

I would love a way to controll a wind turbine as easily as solar is done, just incase I am not home and my hot water heater can take no more or my inverter breaks. With my knowlade level, that means a redundant divertion load or auto shut off.

Is your shutting off your turbines automated and based on voltage or end amps?

Thanks
gww
• Banned Posts: 1,807 ✭✭
Re: Where does the extra solar energy go?
gww1 wrote: »
Is your shutting off your turbines automated and based on voltage or end amps?

Well, solar doesn't automatically control itself either. You need a controller or the panels will boil your batteries dry. The Classic controller controls a wind turbine identically to the way it controls solar - it unloads the power source to regulate the battery voltage. However, with a wind turbine we use a voltage clipper so that when it's unloaded it doesn't exceed maximum operating rpm. The clipper applies a load to the turbine.

Alternatively, with both wind and solar, you can have the Classic turn on AUX loads like water heating and keep the power source busy and at full output. Other controllers do this as well - most not as good as the MidNite Classic.

The shutdown of my turbines is automatic and is done by the Classic. It leaves them running until Float mode is reached, then shuts them down. When the voltage of the bank drops to Float MPPT range (between rebulk and Float voltage) it starts them back up.
--
Chris
• Solar Expert Posts: 963 ✭✭
Re: Where does the extra solar energy go?

Chris
I had thought you burnt out a bunch of clippers and weren't using them but was instead just shutting them down. That may just show I don't pay as much attention as I would like to.

I don't want to put you to work but if you feel like it I would love to see you post a topic that explains how you inigrate your turbine shutdown through the classic.

Thanks
gww