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electrical:solar:sizing [2020/01/07 21:19] frater_secessus [Sizing a solar installation] |
electrical:solar:sizing [2022/01/02 14:52] frater_secessus [usable capacity in Amp-hours] |
Words of Wisdom: "I'd say 500 watts is the minimum for the [Pacific Northwest] in winter and you would be better off with [750 watts] if you can get it on the roof." akrvbob((http://www.cheaprvliving.com/forums/Thread-One-large-solar-panel-or-several-small-ones?pid=101801#pid101801)) | Words of Wisdom: "I'd say 500 watts is the minimum for the [Pacific Northwest] in winter and you would be better off with [750 watts] if you can get it on the roof." akrvbob((http://www.cheaprvliving.com/forums/Thread-One-large-solar-panel-or-several-small-ones?pid=101801#pid101801)) |
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====== Sizing a solar installation ====== | ====== Sizing a solar installation ====== |
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- worst case scenario [[electrical:12v:loads|loads]] (the max loads you will apply in any 24hr period((or at any given time, if you plan to run heavy loads))) | - worst case scenario [[electrical:12v:loads|loads]] (the max loads you will apply in any 24hr period((or at any given time, if you plan to run heavy loads))) |
- worst case scenario sunlight, usually December in your geographical area due to shortest daylight hours, but also affected by tree canopies, mountains, "urban canyons", or other forms of [[electrical:solar:electrical:solar:output#shadeelectrical:solar:output#shade|shading]] | - worst case scenario sunlight, usually December in your geographical area due to shortest daylight hours, but also affected by tree canopies, mountains, "urban canyons", or other forms of [[electrical:solar:shading|shading]] |
- days of reserve (ie with no solar charging) you want | - days of reserve (ie with no solar charging) you want |
- whether or not you have access to other forms of charging: [[electrical:shore_power|shore power]], [[electrical:12v:alternator|alternator]], [[electrical:generator|generator]] | - whether or not you have access to other forms of charging: [[electrical:shore_power|shore power]], [[electrical:12v:alternator|alternator]], [[electrical:generator|generator]] |
- the kind of [[electrical:12v:deep_cycle_battery|battery chemistry]] - some((lithium, for example)) charge more efficiently than others | - the kind of [[electrical:12v:deep_cycle_battery|battery chemistry]] - some((lithium, for example)) charge more efficiently than others |
- These factors will tell you size of the system needed. If the system you need will not physically fit on/in your vehicle, you will have to take [[electrical:solar:sizing#maxxed_system|a different approach]]. | - the kind of camping you do. Full-timers will need more robust systems. Weekenders can [[https://mouse.mousetrap.net/blog/2020/07/04/agm-for-weekenders/|"get by" then recharge batteries fully at home]]. |
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| These factors will dictate the system capactity you will need. If the system you need will not physically fit on/in your vehicle, you will have to take [[electrical:solar:sizing#maxxed_system|a different approach]]. |
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Before you dig in, consider that it is far **easier and cheaper to [[electrical:solar:rationing|use less power]]** than it is to make more power. | Before you dig in, consider that it is far **easier and cheaper to [[electrical:solar:rationing|use less power]]** than it is to make more power. |
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Power requirements are usually expressed in Amp-hours needed every day (Ah/day). There are two different kinds of loads 'dwellers usually run, [[electrical:shore_power|AC (110v)]] and [[[electrical:12v:intro|DC (12v)]]. | Power requirements are usually expressed in Amp-hours needed every day (Ah/day), although thinking in Watt-hours (Wh) might be simpler less complicated. |
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| There are two different kinds of loads 'dwellers usually run, [[electrical:shore_power|AC (110v)]] and [[electrical:12v:intro|DC (12v)]]. Appliances run off an inverter will incur additional efficiency penalties (see below). |
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==== how much power does stuff use? ==== | ==== how much power does stuff use? ==== |
* [[http://gpelectric.com/tools/GoPowerCalculator.htm?state=RvDiv|GoPower calculator]] | * [[http://gpelectric.com/tools/GoPowerCalculator.htm?state=RvDiv|GoPower calculator]] |
* [[http://www.rvsolarsystemsonline.com/wattage-calculator/|RVSSO calculator]] | * [[http://www.rvsolarsystemsonline.com/wattage-calculator/|RVSSO calculator]] |
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| Also see [[https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html#SA|the EU PVGIS modeler]]. |
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===== your reserve needs ===== | ===== your reserve needs ===== |
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| > ...one that really [effed] with me was running out of power or spending a few days in the dark cause the weather is bad. -- hellexual((https://www.reddit.com/r/vandwellers/comments/er4gf7/whered_you_get_your_van/ff1i66p/)) |
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Solar power is highly dependent on local conditions like weather, season, and latitude. One cannot assume getting a full charge every day in every condition. | Solar power is highly dependent on local conditions like weather, season, and latitude. One cannot assume getting a full charge every day in every condition. |
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To account for this decide how many reserve days of power you need if there is little [[https://www.wholesalesolar.com/solar-information/sun-hours-us-map|solar power available]]. You may need few in desert regions and many more in the Pacific Northwest. Long stretches of little solar charging may necessitate | To account for this decide how many reserve days of power((https://duckduckgo.com/?q=days+of+autonomy&t=ffab&ia=web)) you need if there is little [[https://www.wholesalesolar.com/solar-information/sun-hours-us-map|solar power available]]. You may need few in desert regions and many more in the Pacific Northwest. Long stretches of little solar charging may necessitate |
[[electrical:solar:rationing|rationing solar power]]. | [[electrical:solar:rationing|rationing solar power]]. |
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Reserve days of power is also known as //days of autonomy//.((https://duckduckgo.com/?q=days+of+autonomy&t=ffab&ia=web)) | |
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It is safest and simplest for solar newbies to assume a day of poor solar harvest = zero solar harvest. In actuality zero harvest is highly unlikely; more experienced or risk-tolerant RVers can run with [[electrical:solar:slim reserve|less reserve or no reserve at all]]. | It is safest and simplest for solar newbies to assume a day of poor solar harvest = zero solar harvest. In actuality zero harvest is highly unlikely; more experienced or risk-tolerant RVers can run with [[electrical:solar:slim reserve|less reserve or no reserve at all]]. |
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A rule of thumb is flooded lead acid batteries in offgrid scenarios should be charged between C/10 and C/8. For a 200AH bank this would be 20A-25A. Charging at lesser rates may result in not getting fully charged each day. Charging at greater rates may result in increased outgassing and the need for a lengthier Absorption stage. | A rule of thumb is flooded lead acid batteries in offgrid scenarios should be charged between C/10 and C/8. For a 200AH bank this would be 20A-25A. Charging at lesser rates may result in not getting fully charged each day. Charging at greater rates may result in increased outgassing and the need for a lengthier Absorption stage. |
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| === reserve === |
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| | **total**| 91| |
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| | Minimum battery bank((except lithium))| 182| |
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| and that's just to get through a 24hr period **with good sun**. If you want to get through a day (or more) of terrible solar yield (rain, snow, fog) it requires even more battery capacity (//reserve//), money, and cargo capacity. These numbers are both very rough but will illustrate the pattern: |
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| | | **Rated Ah**| **cost (flooded)**| **cost (AGM)**| **weight in lbs**| |
| | **Minimum battery bank((except lithium)) |
| 0 days of reserve**| 182| $182.00| $364.00| 91| |
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| | **1 day of reserve**| 364| $364.00| $728.00| 182| |
| | **2 days of reserve**| 546| $546.00| $1,092.00| 273| |
| | **3 days of reserve**| 728| $728.00| $1,456.00| 364| |
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| ==== charging efficiency ==== |
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| Lead batteries take something like ~13% more amps to charge from 50% DoD than were consumed. So if you need to replace 50A it will take ~56.5A the next day to replace it. //While// you are running your normal loads. |
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| Lithium batteries have very high charging efficiency, so 50A consumed will take ~50A to recharge. |
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==== voltage ==== | ==== voltage ==== |
===== solar panel array ===== | ===== solar panel array ===== |
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Pick a solar panel array output on battery bank capacity. A common **rule of thumb for matching panels to battery bank** is that there should be 1-2 panel watts per amp-hour of nominal bank capacity. | Pick a solar panel array output on battery bank capacity. A common **rule of thumb for matching panels to battery bank** is that there should be **at least** 1 panel watt per amp-hour of nominal bank capacity. |
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> "...the person draining their batteries to the 50% range regularly would do much better with a 2 watts to 1Ah ratio, or even 3 to 1." -- SternWake((http://www.cheaprvliving.com/forums/Thread-How-much-solar-do-I-need?pid=278438#pid278438)) | > "...the person draining their batteries to the 50% range regularly would do much better with a 2 watts to 1Ah ratio, or even 3 to 1." -- SternWake((http://www.cheaprvliving.com/forums/Thread-How-much-solar-do-I-need?pid=278438#pid278438)) |
* deep cycling with [[electrical:solar:sizing#augmenting_solar|augmented charging]] in the morning | * deep cycling with [[electrical:solar:sizing#augmenting_solar|augmented charging]] in the morning |
* **2:1** - deep cycling and charging from solar only | * **2:1** - deep cycling and charging from solar only |
* **3:1** - deep cycling and charging from solar only in areas with low insolation like the Pacific Northwest (PNW) | * **3:1** - deep cycling and charging from solar only in [[opinion:frater_secessus:panelsizesforinsolation|areas with low insolation]] like the Pacific Northwest (PNW) |
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A **crude rule of thumb for panel output per day** is a horizontally mounted panel on a sunny day will generate Ah (amp hours) roughly equal to Rated Wattage / 3.((http://www.cruisersforum.com/forums/f14/current-strategies-in-solar-power-42602.html#post473854)) \\ | A **crude rule of thumb for panel output per day** is a horizontally mounted panel on a sunny day will generate Ah (amp hours) roughly equal to Rated Wattage / 3.((http://www.cruisersforum.com/forums/f14/current-strategies-in-solar-power-42602.html#post473854)) \\ |
There are two general rules: | There are two general rules: |
- voltage from panels must not exceed controller voltage, ever. | - voltage from panels must not exceed controller voltage, ever. |
- controller rating should be the panels' output plus a safety margin, unless you are [[electrical:solar:overpaneling|overpaneling]] on purpose. | - controller rating should be the panels' output plus a safety margin, unless you are [[electrical:solar:overpaneling|overpaneling]] an [[electrical:solar:charge_controller#mppt|MPPT controller]] on purpose. |
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===== augmenting solar ===== | ===== augmenting solar ===== |