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electrical:solar:gentle_intro [2019/09/24 15:55]
frater_secessus [daily power needs] |
electrical:solar:gentle_intro [2020/01/09 19:23]
frater_secessus [the easy answer] |
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| ===== limitations of solar ===== | ===== how solar power works ===== |
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| Solar is not a magic bullet; it is a compromise like anything else. | Solar power uses [[electrical:solar:panels|solar panels]] to convert sunlight into electricity. This power is usually stored in a [[electrical:12v:deep_cycle_battery|deep-cycle "house" battery]], which is seperate from the vehicle's starter battery. Electricity from the panels is fed to the battery by a [[electrical:solar:charge_controller|solar charge controller]], which keeps the battery [[electrical:12v:charging|optimally charged]] and powers any [[electrical:12v:loads|loads]] (things that consume power). |
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| **Solar has very high startup costs for the amount of power you get out of it.** It can cost several thousand dollars to get the same amount of reliable power one might might get from a residential (or campsite) outlet with a $20 extension cord. Over time, though, the power is "free". | |
| | ===== limitations of solar ===== |
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| | Solar is not a magic bullet; it is a compromise like anything else. **Solar has very high startup costs for the amount of power you get out of it.** It could cost several thousand dollars to get the same amount of reliable power one might might get from a residential (or campsite) outlet with a $20 extension cord. Over time, though, the power is "free". |
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| **[[electrical:solar:rationing|Minimizing power consumption]] is key** to happiness with a simple, affordable solar setup. It requires a change in mindset for most folks. Electrical power becomes a precious resource to be carefully consumed. The **path to frustration** (or at least considerable expense) involves [[hvac:solar|heating or cooling with electricity]] or trying to run household appliances in a van. | **[[electrical:solar:rationing|Minimizing power consumption]] is key** to happiness with a simple, affordable solar setup. It requires a change in mindset for most folks. Electrical power becomes a precious resource to be carefully consumed. The **path to frustration** (or at least considerable expense) involves [[hvac:solar|heating or cooling with electricity]] or trying to run household appliances in a van. |
| Given these limitations why do we do spend so much time and money on solar? Because having power off-grid, however expensive and limited, can make a //huge// difference in quality of life. Solar is silent, works for decades, and is always working when the sun is shining.((portable solar only produces when deployed)) | Given these limitations why do we do spend so much time and money on solar? Because having power off-grid, however expensive and limited, can make a //huge// difference in quality of life. Solar is silent, works for decades, and is always working when the sun is shining.((portable solar only produces when deployed)) |
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| ===== how solar power works ===== | ===== first things first: daily power requirements ===== |
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| | It's not fun but the first step in getting solar is to assess **daily power requirements**. It's like writing down all your monthly expenses when making a family budget. Unpleasant but necessary. |
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| | Power requirements are assessed as **daily** because solar power feeds the batteries((and [[electrical:12v:loads|loads]])) only in daylight. Then at night the 'dweller pulls power back out of the batteries. So a **minimal solar configuration** will meet your daytime needs then get you through the night without running out of power. No one but you knows how much power you will need daytime and nighttime. |
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| | ==== AC, DC, Amps, and Watts ==== |
| | The basic idea is to tally up all the [[electrical:12v:loads|loads]] you want to run daily, the time in hours each will run, and the amount of power (Watts) each will consume while running. |
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| | It is useful to calculate power use in Watts, because "watts are watts" no matter if it's a 12v load or a 120vac load.((inverter inefficiencies will be addressed later)) |
| | * AC (household) devices will usually give consumption in watts on a label. |
| | * DC devices may give watts, but more commonly show Amps on a label. From this we can derive watts: Amps from the label times voltage (12v) == watts |
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| | First things first: Bill needed some idea of [[electrical:solar:sizing#your_daily_power_needs|how much power he actually needed each day]]. |
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| | One way to figure it out is to [[electrical:solar:builds|see what configurations other people are running successfully in their own camper]] right now. The gamut runs from 100W to 1000W+, with 200W being the most common. |
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| | The details of Bill's logic and math has been [[electrical:solar:daily-gentle|moved to its own page]], but for now we will stipulate he came up with a daily requirement of **91Ah** of usable battery capacity for each 24hr period. On average he will consume that much power each day, and will have to replace that amount((and a little bit more due to charging inefficiencies)) from the sun. |
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| Solar power uses [[electrical:solar:panels|solar panels]] to convert sunlight into electricity. This power is usually stored in a [[electrical:12v:deep_cycle_battery|deep-cycle "house" battery]], which is seperate from the vehicle's starter battery. Electricity from the panels is fed to the battery by a [[electrical:solar:charge_controller|solar charge controller]], which keeps the battery [[electrical:12v:charging|optimally charged]] and powers any [[electrical:12v:loads|loads]] (things that consume power). | |
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| ===== the easy answer ===== | ===== the easy answer ===== |
| * [[http://amzn.to/2ztSSoO|200W kit]] + a [[electrical:12v:deep_cycle_battery#chain_store_batteries|wally world learner battery]] is about $450 at late 2017 prices. This is about $1.75 per solar watt produced((actually going out of the controller into the battery)) and would cost **~$750 over 5 years**, including expected battery replacement. | * [[http://amzn.to/2ztSSoO|200W kit]] + a [[electrical:12v:deep_cycle_battery#chain_store_batteries|wally world learner battery]] is about $450 at late 2017 prices. This is about $1.75 per solar watt produced((actually going out of the controller into the battery)) and would cost **~$750 over 5 years**, including expected battery replacement. |
| * 200W kit + 2 x [[electrical:12v:deep_cycle_battery#v_golf_cart_batteries|6v golf cart battery]] bank is about $550 at late 2017 prices. This is about $1.75 per solar watt, and would cost **~$550 over 5 years**. Flooded lead acid golf cart batteries are the most tolerant of beginner mistakes, and will take the most abuse. | * 200W kit + 2 x [[electrical:12v:deep_cycle_battery#v_golf_cart_batteries|6v golf cart battery]] bank is about $550 at late 2017 prices. This is about $1.75 per solar watt, and would cost **~$550 over 5 years**. Flooded lead acid golf cart batteries are the most tolerant of beginner mistakes, and will take the most abuse. |
| * [[http://amzn.to/2zrtTR5|200W kit w/MPPT controller]] + 2 x 6v golf cart batteries is about $675 at late 2017 prices. This is about $2.37 per solar watt, and would cost $675 over 5 years.((using a locally sourced 24v panel with the MPPT controller would bring the cost down to $1.25/solar watt)) | * [[http://amzn.to/2zrtTR5|200W kit w/MPPT controller]] + 2 x 6v golf cart batteries is about $675 at late 2017 prices. This is about $2.37 per solar watt, and would cost **$675 over 5 years**.((using a locally sourced 24v panel with the MPPT controller would bring the cost down to $1.25/solar watt)) |
| * 200W kit w/MPPT controller + [[electrical:12v:deep_cycle_battery#agm|AGM battery]] bank is about $875 at late 2017 prices. This is about $2.37 per solar watt, and would cost **$965 over 5 years**~. Note: AGM batteries are not particularly well suited for solar-only charging.((http://www.cheaprvliving.com/forums/Thread-How-much-of-an-issue-is-battery-off-gassing?pid=144704#pid144704)) | * 200W kit w/MPPT controller + [[electrical:12v:deep_cycle_battery#agm|AGM battery]] bank is about $875 at late 2017 prices. This is about $2.37 per solar watt, and would cost **$965 over 5 years**~. Note: AGM batteries are not particularly well suited for solar-only charging.((http://www.cheaprvliving.com/forums/Thread-How-much-of-an-issue-is-battery-off-gassing?pid=144704#pid144704)) |
| | * * 200W kit((no MPPT required)) + drop-in lithium bank is about $1350 at late 2017 prices. This is about $1.75 per solar watt, and would cost **$1350 over 5 years**. //But// with proper treatment LiFePO4 batteries can last up to 10 years, **bringing the 5 year cost down to $675**. |
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| 200W is not a magic number, but it is the most common size of solar install for vandwellers and [[camping:dispersed|boondockers]]. It is probably more than what's needed for the basics and has enough power to add in a [[food:refrigeration#compressor_refrigeration|12v compressor refrigerator]] if desired.((assuming good conditions like the desert southwest)) | 200W is not a magic number, but it is the most common size of solar install for vandwellers and [[camping:dispersed|boondockers]]. It is probably more than what's needed for the basics and has enough power to add in a [[food:refrigeration#compressor_refrigeration|12v compressor refrigerator]] if desired.((assuming good conditions like the desert southwest)) |
| Solar setups require a //battery bank// of some kind, even during the daytime.((this is to help the controller stay stable)) In simple installs the bank is one or two batteries.((not including your vehicle's starter battery)) The battery also stores excess power. At night or any other time your demand is higher than your solar is pumping out, you will be pulling power from the battery. | Solar setups require a //battery bank// of some kind, even during the daytime.((this is to help the controller stay stable)) In simple installs the bank is one or two batteries.((not including your vehicle's starter battery)) The battery also stores excess power. At night or any other time your demand is higher than your solar is pumping out, you will be pulling power from the battery. |
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| For reasons related to the chemistry of [[electrical:12v:deep_cycle_battery|deep cycle batteries]], it takes twice the amount of battery bank Ah rating to deliver the daily Ah requirement: | For reasons related to the chemistry of lead-acid [[electrical:12v:deep_cycle_battery|deep cycle batteries]], it takes twice the amount of battery bank Ah rating to deliver the daily Ah requirement: |
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| | **total**| 91| | | **total**| 91| |
| * staying at a RV park with hookups on bad days | * staying at a RV park with hookups on bad days |
| * buying a [[electrical:generator|generator]] | * buying a [[electrical:generator|generator]] |
| * investing in lithium or other exotic batteries | * investing in [[electrical:12v:deep_cycle_battery#lithium_chemistries|lithium]] or other exotic batteries |
| * [[electrical:12v:alt_and_solar|adding alternator charging]] to the mix | * [[electrical:12v:alt_and_solar|adding alternator charging]] to the mix |
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| A common rule of thumb for solar-only charging is that one needs one watt of solar for every Ah of rated battery capacity. 2:1 is recommended for winter or other challeging conditions, and 3x is even better for off-grid folks.((1:1 is usually sufficient if solar charging is [[electrical:12v:alt_and_solar|augmented with alternator or other sources]]. 2:1 might still be required in areas lihe the Pacific Northwest.)) | A common rule of thumb for solar-only charging is that one needs one watt of solar for every Ah of rated battery capacity. 2:1 is recommended for winter or other challeging conditions, and 3x is even better for off-grid folks.((1:1 is usually sufficient if solar charging is [[electrical:12v:alt_and_solar|augmented with alternator or other sources]]. 2:1 might still be required in areas lihe the Pacific Northwest.)) |
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| So about 200w of solar is a good fit for Bill's 200Ah golf cart bank if he stays in a sunny area like the desert southwest. | So about 200w of solar is a good fit for Bill's 200Ah golf cart bank if he stays in a sunny area like the desert southwest. In the Pacific NW he'd be better off with something like 600w. |
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| | **Ratio W:Ah**| **Panel watts**| | | **Ratio W:Ah**| **Panel watts**| |
