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electrical:solar:nonessential [2019/06/23 08:39]
frater_secessus [how much surplus current is there?] |
electrical:solar:nonessential [2023/10/18 19:08] (current)
frater_secessus [when to run opportunity loads] |
| ====== opportunity loads ====== | ====== opportunity loads ====== |
| {{ :electrical:solar:discretionaryv5.png?direct&400|based on http://www.chargetek.com/basic-information.html}} | {{ :electrical:solar:discretionaryv5.png?direct&400|based on http://www.chargetek.com/basic-information.html}} |
| Solar power installations are generally [[electrical:solar:sizing|designed]] as if the load[s] will be steady around the clock. | Solar power installations are generally [[electrical:solar:sizing|designed]] as if the load[s] will be steady around the clock. This can lead new folk into buying [[opinion:frater_secessus:beginner_mistakes#too_much_battery|too much battery]]. |
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| In practice, actual loads may be heavier in the daytime (as when working with power tools) or at night (as when watching movies or running a forced-air furnace). | In practice, actual loads may be heavier in the daytime (as when working with power tools) or at night (as when watching movies or running a forced-air furnace). |
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| Due to the nature of battery charging there are better times and worse times to run non-essential loads. If done attentively (or automatically) **one can run electrical loads that do not affect the battery's | If loads are applied attentively (or automatically!) **one can run electrical loads that [[electrical:solar:offthepanel|do not affect]] the battery bank's |
| [[electrical:depth_of_discharge|State of Charge]]** at all. | [[electrical:depth_of_discharge|State of Charge]]** at all. Additionally, consuming loads at the right time can also increase the health and longevity of lead batteries.((by keeping them at 100% SoC more of the time)) |
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| This is especially true for Lead-Acid chemistries that do not take much current in [[electrical:12v:charging|Float or late Absorption stages]]. | |
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| ===== how much surplus current is there? ===== | ===== how much surplus current is there? ===== |
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| It is common for Lead-Acid batteries to consume C/100 or C/200 amps to Float, meaning that **during Float** you will have 99% or more of your panels' output available for loads.((normal + opportunity)) | It is common for Lead-Acid batteries to consume C/100 or C/200 amps to Float, meaning that **during Float** you will have **at least 99% your panels' output**((under present conditions)) **available for loads**.((normal + opportunity)) |
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| **During Absorption** the charge current is tapering down as the battery accepts less; the more it tapers down the more is available for loads.((agaom. normal + opportunity)) At the very beginning of Absorption ~0% of "bonus" output is available. At the very end of Absorption ~99% is available. Mid-way through Absorption((judging by current not time)) ~49% of the panels' output is available for loads. | **During Absorption** the charge current is tapering down as the battery accepts less; the more it tapers down the more is available for loads.((agaom. normal + opportunity)) At the very beginning of Absorption ~0% of "bonus" output is available. At the very end of Absorption 99%+ is available. Mid-way through Absorption((judging by current not time)) ~49% of the panels' output is available for loads. See the image at the top of the page for an example of how current demand drops in Absorption. |
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| There will generally be more "surplus" power available when using MPPT charge controllers v. PWM,((http://forum.solar-electric.com/discussion/comment/372165#Comment_372165))((http://forum.solar-electric.com/discussion/comment/250746#Comment_250746)) though the difference is less dramatic during periods one would run opportunity loads (see [[electrical:solar:nonessential#when_to_run_opportunity_loads|below]]). Siphoning off power can actually help PWM controllers run cooler by reducing the ON-OFF switching activity that generates heat. | There will generally be more "surplus" power available when using MPPT charge controllers v. PWM,((http://forum.solar-electric.com/discussion/comment/372165#Comment_372165))((http://forum.solar-electric.com/discussion/comment/250746#Comment_250746)) though the difference is less dramatic during periods one would run opportunity loads (see [[electrical:solar:nonessential#when_to_run_opportunity_loads|below]]). Siphoning off power can actually **help PWM controllers run cooler** by reducing the ON-OFF switching activity that generates heat. |
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| | [[electrical:solar:overpaneling|Overpaneled]] systems have even more excess power available. |
| ===== when to run opportunity loads ===== | ===== when to run opportunity loads ===== |
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| **The best time to run non-essential loads is when there is surplus current** over what battery charging needs. This means **during Float, or after current has started dropping off in Absorption**. | The optimal time to run loads is when there is **power available in excess of battery charging requirements**. When done at the right time, the loads are effectively run [[electrical:solar:offthepanel|off the panels]] rather than off the battery bank. This results in the bank having a higher state of charge both at sundown and morning. |
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| Opportunity loads should not be applied during [[electrical:12v:charging|Bulk stage]] since Bulk, by definition, means the battery is taking all the available current.((assuming no charging limit has been configured in the [[electrical:solar:charge_controller|charge controller]])) | With **lead** this means **during Float**, or **in late Absorption** when charge current acceptance has fallen enough that the system can run the loads //and still maintain the Absorption voltage setpoint//. |
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| | There is a little more wiggle room with [[electrical:12v:deep_cycle_battery#lithium_chemistries|LiFePO4]]; the loads can be run with no net negative effect on a Lithium system when |
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| | * the bank has reached the intended charge state; or |
| | * any time the bank can be //projected// to reach the intended charge state by sundown while carrying the extra loads. In effect, lithium allows you to "borrow" against future charging without penalty.. Exception: Lithium setups with PWM [[electrical:solar:charge_controller|solar charge controllers]] will make [[electrical:solar:pwm_tweaking|most power]] when bank voltage is highest. So waiting for Float or Absorption to run opportunity loads will mean the solar can make more Wh per day. |
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| For lead-acid batteries the loads are best applied in Float stage, or once past the beginning of Absorption. | |
| At the start of Absorption the controller still needs near-Bulk levels of current for charging. At the end it needs almost no current. **Halfway through Absorption about half of the system's peak power will be available for loads.** See the image at the top of the page for an example of how current demand drops in Absorption. | |
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| For [[electrical:12v:lifepo4_batteries_thread|LiFePO4]] set the LVD to Vfloat; there is no actual Absorption stage _per se_ in fractional-C charging. We use these setpoints only because our traditional lead-acid controllers work that way. | |
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| ===== timing opportunity loads ===== | ===== timing opportunity loads ===== |
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| | The trickiest part of running opportunity loads is running them at the right time so battery charging is not affected. |
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| | ==== manual model ==== |
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| You can start the loads **manually** (ie, start using the power when you have extra). This is error-prone but is free and requires no equipment (except your own memory). | You can start the loads **manually** (ie, start using the power when you have extra). This is error-prone but is free and requires no equipment (except your own memory). |
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| The most precise way to do it **automatically** is to use a charge controller which turns on the LOAD output only when the batteries are in Float stage. Charge controllers with this feature tend to be expensive. | ==== charge controller ==== |
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| | The most precise way to do it **automatically** is to use a charge controller that can act as a diversion controller. Charge controllers with this feature tend to be expensive, and tend to run in either solar **or** dump load mode. This may be preferable with lithium or other chemistries that do not require multistage charging. |
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| | Read the documentation and ask their techs questions before taking this $$$ approach. |
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| | Related: |
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| | * you can also build a Pi or similar that talks to the controller over its communication port/protocol and checks when the controller is in Float, and then triggers the diversion. |
| | * [[https://www.youtube.com/results?search_query=AC7391|some hobbyists are using AC7391 controllers]] to directly run dump loads w/out battery charging. Not necessarily a solution for vandwellers but may help our thinking. |
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| | ==== diversion controller ==== |
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| | The [[https://amzn.to/3f6Aogh|Victron BMV-700 battery monitor]] can act as a programmable relay controller((https://www.victronenergy.com/upload/documents/Manual-BMV-700-700H-702-712-EN-NL-FR-DE-ES-SE.pdf)), turning loads off/on at a given state of charge. |
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| ==== LVD only ==== | ==== LVD only ==== |
| ==== LVD + timer ==== | ==== LVD + timer ==== |
| {{ :electrical:solar:discretionaryTimer.png?400|}} | {{ :electrical:solar:discretionaryTimer.png?400|}} |
| A [[http://amzn.to/2pN3O9o|12v timer]] could give the system a chance to make some progress in Absorption before starting up opportunity loads. | A [[http://amzn.to/2pN3O9o|12v timer]] could give the system a chance to make some progress in Absorption before starting up opportunity loads. If mistimed or overly heavy loads applied, Absorption duration could be affected. |
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| In this approach the LVD is set just below Vfloat as above, but activation of the loads is delayed by some amount of time. Observation of the system during charging will suggest how long it normally takes takes charging amperage to drop off (ie, when the system has surplus current). | In this approach the LVD is set just below Vfloat as above, but activation of the loads is delayed by some amount of time. Observation of the system during charging will suggest how long it normally takes takes charging amperage to drop off (ie, when the system has surplus current). |
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| Suggested delay for conservative opportunity loading == the time from [passing Vlvr setpoint during Bulk] to [completed charging].((settling to Float)). This delay might be 2-3hours. | Suggested delay for conservative opportunity loading == the time from [passing Vlvr setpoint during Bulk] to [completed charging].((settling to Float)). This delay might be 2-5hours. |
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| This setup looks like: [LVD or controller LOAD output] --> timer --> relay --> load | This setup looks like: [LVD or controller LOAD output] --> timer --> relay --> load |
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| | ==== LVD + timer - eternal Absorption ==== |
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| | This setup avoids timer juggling/estimation and does not affect Absorption charging.The downside is the opportunity circuit engages much later. |
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| | - [[electrical:12v:eternal_absorption|set Vfloat to Vabs]] |
| | - observe how long Absorption actually takes to drop to [[electrical:solar:charge_controller_setpoints|endAmps]] on your system |
| | - set the LVD to just under Vabs, set the timer to the Absorption duration |
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| | Similar to the above, this setup looks like: [LVD or controller LOAD output] –> timer –> relay –> load |
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| ===== uses for opportunity loads ===== | ===== uses for opportunity loads ===== |
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| | For best results the opportunity load should be sized to the excess power. Otherwise the system could go into dump/recharge cycling. |
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| * heating water | * heating water |
| * [[hvac:dehumidifier|dehumidification]] | * [[hvac:dehumidifier|dehumidification]] |
| * [[electrical:12v:laptop|laptop]] and phone charging | * [[electrical:12v:laptop|laptop]] and phone charging |
| * rice cooker((http://www.cheaprvliving.com/forums/Thread-How-much-solar-do-I-need?pid=141508#pid141508)) | * [[food:cooking:excess_power|cooking with small appliances]] |
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