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electrical:solar:sizing [2020/01/07 21:07]
frater_secessus |
electrical:solar:sizing [2023/08/31 19:54] (current)
princess_fluffypants [Voltage] |
| 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 ====== |
| Sizing **residential off-grid solar configurations** is relatively easy: calculate power needs in the worst case scenario (December in a particular geographical area)((https://web.archive.org/web/20110906013732/http://www.solarpowerforum.net/forumVB/solar-energy/1793-basic-off-grid-solar-design.html)) and pay for it. | Sizing **residential off-grid solar configurations** is relatively easy: calculate power needs in the worst case scenario (December in a particular geographical area)((https://web.archive.org/web/20110906013732/http://www.solarpowerforum.net/forumVB/solar-energy/1793-basic-off-grid-solar-design.html)) and pay for it. |
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| Sizing **off-grid solar configurations for campers** has many more variables: | Campervan solar configurations have a more variables: |
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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 | - 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]] |
| - 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 [[electrical:12v:deep_cycle_battery|battery chemistry]] - some((lithium, for example)) charge more efficiently than others |
| | - 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? ==== |
| ==== calculators ==== | ==== calculators ==== |
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| | * Unbound Solar [[https://unboundsolar.com/solar-information/offgrid-calculator|offgrid calculator]] |
| | * AltE [[https://www.altestore.com/store/calculators/off_grid_calculator/|offgrid calculator]] |
| * [[https://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html|BatteryStuff 12v load calculator]] | * [[https://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html|BatteryStuff 12v load calculator]] |
| * [[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]]. |
| 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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| ==== voltage ==== | |
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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 ==== |
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| Most camper solar installs run at [[electrical:12v:electrical_notation|nominal]] [[electrical:12v:intro|12v]]. Because of this most accessories are 12v. | Most camper solar installs run at [[electrical:12v:electrical_notation|nominal]] [[electrical:12v:intro|12v]]. Because of this most accessories are 12v. |
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| | Some installations utilize 24v electrical systems. This is common in boats, and occasionally some very large commercial RVs. The common theme of an advantage to 24v is that you're using half the amperage to transfer the same amount of power, which can result in cheaper components |
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| You may want to consider running a 24v system if: | You may want to consider running a 24v system if: |
| * your panels are rated at 600w or higher - Ohm's law tells us that 600w / 12v = 50A but 600w / 24v = 25A. A 24v system can use a much smaller/cheaper charge controller and small/cheaper wiring to handle the same amount of power. | * You have a //lot// of solar, like 600w or more. |
| * the run from panels to charge controller is lengthy | * Ohm's law tells us that 600w / 12v = 50A but 600w / 24v = 25A. Therefor, you can use much smaller (and cheaper) wiring to connect your solar panels to the charge controllor |
| * you will be using inverters heavily - inversion from 24vdc to 110vac is more efficient than inversion from 12vdc. | * You will be using inverters heavily |
| | * Inversion from 24vdc to 110vac is more efficient than inversion from 12vdc. |
| | * You have large, power-hungry appliances that can run natively off of 24v |
| | * Some [[food:refrigeration|DC refrigerators]] and induction cooktops can run off of both 12v or 24v, and are slightly more efficient when running off of 24v. |
| | * [[hvac:solar_ac|Off-grid Air Conditioning]] can be slightly more efficient with 24v native systems, and will allow smaller wires to be used. |
| | * You have a lot of long, large cable runs |
| | * 24v doesn't have as much voltage drop as 12v over a similar distance, and can use smaller/cheaper cables. |
| | * A 24v system can use a much smaller/cheaper charge controller |
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| There are downsides to 24v, however. There are fewer 24v accessories, and you cannot use a chassis ground as it is already grounded to the coach's 12v system. | There are downsides to 24v, however. There are fewer 24v accessories, and you cannot use a chassis ground as it is already grounded to the coach's 12v system. It can also make alternator charging difficult, as [[https://www.amazon.com/Hyuduo-Converter-Voltage-Regulator-Stabilizer/dp/B07NM52VV5|DC-DC boost converters]] get quite expensive when they are sized to handle the required loads. |
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| ===== 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 daily power requirements and battery bank capacity. A common **rule of thumb for matching panels to battery bank** is that //at a minimum// there should be 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 ===== |
