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electrical:solar:nonessential [2019/10/01 13:05] frater_secessus [when to run opportunity loads] |
electrical:solar:nonessential [2020/07/08 11:13] frater_secessus [timing 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 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**. For [[electrical:12v:deep_cycle_battery#lithium_chemistries|LiFePO4]] there is excess power any time after the bank has reached the intended charge state. |
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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]])) | 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]])) |
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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:deep_cycle_battery#lithium_chemistries|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 ===== |
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. | 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. |
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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. |
==== LVD only ==== | ==== LVD only ==== |
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