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Old 14-12-2019, 07:47   #16
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Re: Dump loads for Renewables.

It strikes me that you are expecting quite a bit from a "smart" device to achieve your goals.

The problem of excess energy seems simple at first, but Mother Nature throws quite a few curves at us. For example, a nice day in the Bahamas with solar panels out:
1. From sunup until the batteries enter "float", we route all energy into charging (plus whatever loads (refrigerator, lights, instruments,radio, etc.) we have on all the time. We don't really care about the actual rate of charge since it's all going one place.
2. The batteries are now at "float", hence "full" (not really, but close). We presumably can divert "excess" energy to "over and above" tasks such as heating or making water..

3. The difficulty now is in switching on those loads without negatively impacting the state-of-charge of our battery. If we simply switch in a large load (like that 300w water heater), it will draw down the battery rather quickly every time a cloud drifts by. Switching a resistive load on & off quickly (using say, FET switches to get around the relay contact wear problem) based on maintaining "float" voltage could work, but this approach won't work for a watermaker. If the passing cloud is large & dark enough, the voltage may drop enough to convince our solar regulator it needs to go back to "absorption" or even "bulk" depending on how far the system voltage drops. Any "extra load" switching device needs to understand this and react properly by removing these loads.
Loads that are more complex (like a watermaker) that cannot be turned on & off at will complicate matters even more.

4. As the sun sets in the West, the "extra load" device needs to shut down properly so the last few solar rays go into the batteries and standing loads.


Complicating factors:

a. Weather changes (i.e., a bank of dark clouds) approaches - you really should shut down all the extras before it arrives to ensure you are at full charge.
b. Changing seasons means that initial, peak and ending charge times will change.
c. Changing locations (you sail to the Chesapeake or Maine) means the expectations for sunlight (and the hourly availability of charge) will change.



I suspect someone could probably build such a smart device, given enough sensors to drive it - or you could substitute a human into the loop and switch in loads as your superior "smarts" allow - for example, in the tropics with expectations of several hours of good charge available, you energize the watermaker for a couple of hours. Upon spotting an approaching front, you shut it down.


Food for thought


Hartley
S/V Atsa
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Old 14-12-2019, 08:15   #17
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Re: Dump loads for Renewables.

You may be overtinking this. The dump load on a wind generator is not needed electrally it is to stp the device overpspeeding and damaging the blades if there is no load. In effect it is an electrial brake. Other power sources simply shut down output. The charge controller shoukd protect the batteries.
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Old 15-12-2019, 13:35   #18
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Re: Dump loads for Renewables.

Quote:
Originally Posted by Hartleyg View Post
It strikes me that you are expecting quite a bit from a "smart" device to achieve your goals.

The problem of excess energy seems simple at first, but Mother Nature throws quite a few curves at us. For example, a nice day in the Bahamas with solar panels out:
1. From sunup until the batteries enter "float", we route all energy into charging (plus whatever loads (refrigerator, lights, instruments,radio, etc.) we have on all the time. We don't really care about the actual rate of charge since it's all going one place.
2. The batteries are now at "float", hence "full" (not really, but close). We presumably can divert "excess" energy to "over and above" tasks such as heating or making water..

3. The difficulty now is in switching on those loads without negatively impacting the state-of-charge of our battery. If we simply switch in a large load (like that 300w water heater), it will draw down the battery rather quickly every time a cloud drifts by. Switching a resistive load on & off quickly (using say, FET switches to get around the relay contact wear problem) based on maintaining "float" voltage could work, but this approach won't work for a watermaker. If the passing cloud is large & dark enough, the voltage may drop enough to convince our solar regulator it needs to go back to "absorption" or even "bulk" depending on how far the system voltage drops. Any "extra load" switching device needs to understand this and react properly by removing these loads.
Loads that are more complex (like a watermaker) that cannot be turned on & off at will complicate matters even more.

4. As the sun sets in the West, the "extra load" device needs to shut down properly so the last few solar rays go into the batteries and standing loads.


Complicating factors:

a. Weather changes (i.e., a bank of dark clouds) approaches - you really should shut down all the extras before it arrives to ensure you are at full charge.
b. Changing seasons means that initial, peak and ending charge times will change.
c. Changing locations (you sail to the Chesapeake or Maine) means the expectations for sunlight (and the hourly availability of charge) will change.



I suspect someone could probably build such a smart device, given enough sensors to drive it - or you could substitute a human into the loop and switch in loads as your superior "smarts" allow - for example, in the tropics with expectations of several hours of good charge available, you energize the watermaker for a couple of hours. Upon spotting an approaching front, you shut it down.


Food for thought


Hartley
S/V Atsa
Well usually there is the signal of the charge controller for the dump loads of the wind gen
&
With this battery monitor from Victron it will also not depend on clouds. There is a signal for high and low energizing for a relay according to state of charge. Often this function is used to auto start and stop the GEN to prevent over discharging of batteries but this signal can used for many applications. There is an inverted relay mode and there is even a timer. So there are plenty of options. So let´s say once the battery is full then all solar goes to the water heater while the consumers stay online till the state of charge of the battery has dropped to a certain voltage set point and after that the solar goes fully back into the batteries.
With this monitor You also get programable set points for an alarm. I would use that as first defense to protect the battery from overcharging. Second and further defense when default of battery monitor and with closer set points is when the BMS detects a dangerous state of charge and shuts the batteries down. To prevent short cycles the timer of the Victron can be used.
Since You should already have a battery monitor anyway this function is very simple. reliable and also cheap.
Now also the controller of the wind gen should never go in mode of dump load unless the water heater has too low watts. Well, use a dual water heater on the same socket and actuated by a manual switch in parallel. Now You have storm mode with higher capacity load. The wind gen should not go in mode dump load.
Let´s asume the water is hot. Well, switch on the dehumidifier that will draw from the battery and with the high consumption the battery goes down to Your set point and then also the solar panels come back online to prevent getting lower and shuts down the humidifier to allow the battery coming back to Your high set point. If You have a Victron inverter there is an auxillary AC output and there are also relay set points.
If the battery goes beyond the set points of the monitor the BMS will come online to protect the battery from over charge/discharge and shut the battery down. As You can see the essential parts of the process are already there.
Basic process should also work when the engine is charging with the alternator. Only now everything goes much faster as the water heater draws also heat from the engine cooling system.

Of course a little fine tuning and playing with the set points has still to be done by MK1

Read at page 23-25 > 4.2.2 Relay settings

https://www.victronenergy.com./uploa...S-SE-PT-IT.pdf

Yeah, those Victron monitors are small and nothing flashy but they are awesome
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