As people begin to consider solar, they frequently would prefer to NOT do the investigation necessary to determine how much capacity they need. To say “I have a 25 ft. Class C or a 38 ft. 5th wheel” does not provide a basis for determining \u00a0how much solar capacity you need. If you have an all electric, residential fridge with an ice maker & want to run your microwave, coffee maker, etc., your needs will be much different than someone who has a fridge they can and will run on propane and will make their coffee in an old style percolator on the stove. Therefore, there are no simple answers, no basic “rule of thumb”, to the question of “how much solar do I need”.<\/p>\n
Solar: Evaluation & Decisions<\/strong><\/p>\n STEP ONE:<\/strong> The first question you must ask is: “Why do I want solar?” \u00a0In my opinion, the only realistic reason to install solar is that you want to be able to camp for several days (or more) without any hook-ups (boondocking).\u00a0 Boondocking allows you to avoid campground fees, but<\/strong> even at $50 a night, it will take at 150 or so nights to pay for your solar installation.\u00a0 If you aren’t willing to spend $3,000 – $7,000, you will have to be VERY frugal with your electrical usage when off-the-grid. It “can” be done & some people do it; but you won’t use the TV or electrical appliances very much. (My DW would not be happy with that arrangement!)<\/p>\n “Solar use, and living “off-grid”, is a lifestyle decision.<\/strong> Adding an effective solar system to an RV will take months of living off-grid to pay back the costs of installing it.\u00a0 You will not likely recoup your investment when selling the rig.\u00a0 The best (and really only) reason to add solar is so you have the option of boondocking for long periods of time without hookups.\u00a0 If you do not enjoy doing this, then you should reflect on why you want to install a solar system.”\u00a0 \u00a0 \u00a0 \u00a0 [excerpts from Dan Mayer’s excellent website: http:\/\/jackdanmayer.com\/rv_electrical_and_solar.htm<\/a>]<\/p>\n STEP TWO:<\/strong> How much capacity do we need???<\/p>\n First, remember that your RV really has TWO electrical systems — a 12 volt system that already runs your lights, furnace fan, and similar items; and a 120 volt system (shore power) that runs the microwave, coffee pot, TV, etc. If your current battery is charged, you can easily tell which items are which by disconnecting your shore power cable (and turning off your inverter, if you have one) —\u00a0 anything that stays on is on the 12 volt system, anything that goes off is on the 120 volt system.<\/p>\n If you are going to have solar you have to do your own energy use review<\/strong>.\u00a0 As I said before, there are no reliable ‘rule of thumb’ guides.<\/p>\n — 12 volt usage: The best way to measure your 12 volt usage is to get and install a Trimetric Meter. It’s connectors are installed between your battery bank and your 12 volt load, and it records how much electricity you have used. Turn OFF your current battery charger and you can read how much you are currently using, or how much has been drained from your battery. If you go solar, you will want this meter anyhow, so this is not “wasted” money.<\/p>\n — 120 volt usage: The most reasonable way to calculate 120 volt usage is to identify what items you intend to use when on solar (microwave, yes; electric water heater, no; etc.) Purchase a “Kill-a-watt” meter for $15 or $20 at Home Depot or Lowes, and connect it to EACH and EVERY item that you plan to use when on solar — TV, microwave, computer, electric fan, sun lamp (just kidding), etc. Record their actual watts used and estimate how many hours you will use the item over the course of an average day.<\/p>\n Add up all the watts of power you expect to use on an average day.<\/p>\n (Watts of use) x (hours of use) = (daily watts)<\/p>\n Conversion of electricity from one voltage to another is not 100% efficient.\u00a0 Multiply the (daily watts) by a safety factor say 1.2 to be safe.<\/p>\n (Daily Watts) \/ 12 volts = The number of 12v Amp Hours you will need\u00a0 \u00a0(the typical RV batteries are rated in 12v Amp Hours or Ah).\u00a0\u00a0\u00a0All solar requirements need to be converted to 12 Volt Amp Hours; that is what your batteries store.<\/p>\n (While you are at it, also note the highest simultaneous<\/strong> wattage required by devices that will be used at the same time, ie, the coffee pot & microwave at the same time. This will help determine how big your power inverter must be — see STEP Four).\u00a0 Here is the results of our energy usage review:<\/p>\n 12 volt usage per day: 1000 watts Here is an Excel spreadsheet that I used to calculate usage\/demand: \u00a0Electrical Consumption Calculations<\/a><\/p>\n STEP THREE:<\/strong> How many batteries, and what kind??? All of your solar power is going to go to recharge the batteries, your batteries will be actually providing the electricity for your RV. Different batteries have different charge\/discharge limits. The most common type (because of cost) is lead-acid batteries (either flooded cell or AGM) — similar, but not identical to those starting your car. \u00a0Lead-acid batteries should not be discharged below 1\/2 of their rated capacity; therefore a battery rated for 100 amp hours should never have more than 50 amp hours drawn out of it before it is recharged. The further you discharge the battery, the shorter the battery’s life.\u00a0 Lithium (LiFePO4) batteries can reasonably be discharged down to 15% or less of their capacity, but they are more expensive.\u00a0 In either case,\u00a0 you never want to discharge a battery below the recommended threshold, and you should take that threshold into account on all of your calculations.<\/p>\n If you need 300 amp hours of 12 volt power to run your RV for a day, and you are using lead-acid batteries, you will need AT LEAST 600 amp hours of 12 volt storage capacity. If you think it might ever rain or be cloudy so that your solar system does not charge your batteries on those days, you need additional storage capacity to cover those “no solar” days. (2x ??, 3 x ???, that’s up to you!)<\/p>\n Lead-acid batteries are heavy!\u00a0 A standard for many RVers is the Trojan T-105 deep cycle battery.\u00a0 It is a battery designed to be drawn down to 50% State of Charge (SoC) again and again — unlike a car’s starting battery.\u00a0 These are 6 volt ‘golf cart’ batteries, so they must be installed in pairs.\u00a0 They are rated at a 20-hour rating of 225 Amp Hours, so two wired in series would provide 110 Ah of 12v power before reaching the 50% threshold.\u00a0 They weigh 62# each.\u00a0 So a bank that would provide a usable capacity of 440 Ah would require eight batteries for a total of almost 500#!!\u00a0 They cost about $160 each, so an 8 battery bank would cost about $1,300.\u00a0 The Trojan T-105 is a flooded cell battery requiring regular monitoring and maintenance.<\/p>\n Lithium batteries are much lighter and fewer are required — Battle Born is a common standard for RV lithium batteries.\u00a0 Their 100 Ah battery has an actual capacity of about 120 Ah with an automatic cut-off at 100 Ah used, so you can use the full rated capacity.\u00a0 \u00a0Each battery weighs 31# and four would support the same system that the 8 lead-acid batteries would, so your total weight would be about 125# and they would take up only half the space!\u00a0 However, those four batteries would cost $3,600 – $4,000.\u00a0 A final factor for consideration:\u00a0 properly cared for, the lithium batteries should last at least twice as long as the lead-acid batteries and includes a Battery Management System (BMS) and would require no maintenance.\u00a0 A relatively new entry into the RV lithium battery market is Ohmmu, a company that has been providing aftermarket lithium batteries to the electrical vehicle market.\u00a0 Here is a link to the batteries we just bought:\u00a0 150+ Ah Deep Cycle Lithium<\/a><\/p>\n STEP FOUR:<\/strong> How big of an inverter?? First, what IS an inverter & which kind? \u00a0An inverter\u00a0converts the 12 volt power from your batteries into 120 volt power that your TV & microwave can use. There are two kinds of inverters: MODIFIED sine-wave and PURE sine-wave. Pure sine-wave is just like what you get from the electric company, maybe better; Modified sine-wave attempts to approximate the plus & minus cycles of 120 volt power with steps (sometimes very crude steps). \u00a0Pure sine-wave will run your computer, TV, microwave, etc. just like you were connected to the electric company; sometimes, computers, TVs, microwaves do not work well on modified sine-wave, or they fail prematurely. Many people use modified sine-wave successfully, but I personally will only use a pure sine-wave inverter.<\/p>\n So, how big? You need to evaluate the power requirements of the most power hungery 120 volt items you might use SIMULTANEOUSLY. If you must run the coffee pot, microwave, and toaster all at the same time, you are going to need a BIG inverter. If you can let one finish before you start the next one, your requirements will not be so large. Look at your 120 volt usage chart you created in step two and decide how much will be used at the same time — then add a safety factor … Murphy does tag along, even in our RVs.<\/p>\n STEP FIVE:<\/strong> How much solar and what kind of a solar charger?? You now know how much 12 volt electricity you expect to use in amp hours. \u00a0Now, how much sun do you expect to have where you will typically be using your solar? \u00a0Will you be tilting your panels to maximize your solar harvest? I didn’t want to have to climb up on the roof to tilt the panels, and also make sure I parked with a good orientation to the sun, therefore I permanently mounted my panels flat on the roof and figured I would get about 70% efficiency for 6 – 8 hours each day and would get “some” sun every day in the U.S. Southwest. My estimated usage would be 300 amp hours or less, so I went with 4 panels at 260 watts each totaling 1040 watts at full capacity and about 60 amps per hour at 70% efficiency or 360 amp hours over a six hour charging day. \u00a0(If I get better solar harvest than this, that’s great.) ( *** See Below)<\/p>\n Your charger must be determined by the solar panels you purchase. If you use higher capacity panels (as I did) then they will be sending power down as 24, 30, 36 or even higher voltages which will reduce line loss (see STEP SIX). Your charging unit must be able to accept this higher voltage and send the appropriate charging output for your batteries (an MMPT unit). It also must be able to utilize the power coming from the solar panels for charging your batteries — it does no good to have the equivalent of 100 amps of 12 volt coming down from your panels if your charger can only send 30 amps of 12 volt power to the batteries each hour.<\/p>\n STEP SIX:<\/strong> \u00a0 Wires and other “stuff”. \u00a0As power is transmitted through our electrical wires resistance steals part of the power. \u00a0The longer the wire run, the greater the power loss. \u00a0So, how do the power companies transmit power over hundreds of miles? \u00a0Higher voltage! \u00a0The higher the voltage, the less the loss in a given size of wire. \u00a0You will have less power loss when running 8 gauge wire than when running 12 gauge (the smaller the number, the bigger the wire — don’t ask me why!) \u00a0You will also have less loss running 60 Volt power than running 12 volt power.<\/p>\n So, make long runs using higher voltage if possible. \u00a0Use the largest practical wire for any particular run and calculate your voltage drop — attempting to keep the drop to less than 0.5%. \u00a0Here is a calculator that I like: \u00a0Calculator.net<\/a> or you can search for “voltage drop calculator” to find one you like.<\/p>\n You will want to make most\/all of your connections to a “buss bar”, a high capacity electrical conductor that you can bolt all of your cables onto. \u00a0Of course, you will want to put fuses or circuit breakers on each segment of your new electrical system, you don’t want an “oops” to destroy the whole system!<\/p>\n STEP SEVEN:<\/strong> \u00a0Preparing to install. \u00a0I strongly recommend that you plan out your entire solar installation before you start buying components. \u00a0With a well thought out plan you can buy items piecemeal and not end up wasting money by buying the wrong items.<\/p>\n I recommend that you start with the Trimetric Battery Meter, then the batteries, then other items.<\/p>\n ***\u00a0 How Much Solar Yield Should I Expect ***<\/strong><\/p>\n With the same solar setup, you will get much different results if you are in Portland, Oregon, in December, as compared to Phoenix, Arizona, in the summer (although I would never chose to stay in Phoenix in the summer! 120 degrees!)\u00a0 I found a great web site that helps you set “reasonable” expectations on how much solar power you should expect to yield from a particular setup & location:<\/p>\n https:\/\/www.renewables.ninja\/<\/a><\/p>\n You can put in your info: location, wattage of panels, tilt, etc. It will generate a graph of the “capacity factor” (comparing actual vs. rated output capacity x 24 hrs\/day<\/strong>). So, if you are in Quartzsite with 1000 W of solar panels in February, the factor is about 15% — so you can reasonably expect to generate 3600 Watts (1000 watts x 24 hours x 0.15 = 3,600 watts) over the course of a day, or about 300 Ah of 12 volt power per day.<\/p>\n You can also download the underlying data to a spreadsheet to look at any day or time period you want. Their data takes into account normal weather, so “typical” cloudiness is factored in.<\/p>\n I also recommend the following web sites, see below.<\/p>\n OUR SOLAR INSTALLATION:<\/strong><\/p>\n After much review of recommendations from various forum sources, especially from<\/p>\n We decided to go with four larger 60 cell panels rated at 265 watts and a nominal voltage of 30 volts, in two pairs of serial connections with a net output of 8.8 Amps at 60 volts.\u00a0 This allows greater Solar Capacity with fewer panels, and the higher voltage reduces the voltage drop problem associated with transmitting DC power.<\/p>\n This configuration will \u201cmax out\u201d the capability of the Morningstar Tristar TS-MPPT-60 Solar Charge Controller.\u00a0 To add more panels, we will need to get another Tristar plus a HUB-1 Meter Hub to combine the two Tristar units.\u00a0 Hopefully, we can be a little conservation minded and avoid that.\u00a0 \u00a0Our original setup used wet-cell lead acid batteries.\u00a0 After over 5 years of constant use, we have now switched to lithium (more on that later).\u00a0 I had contemplated going with a 6 battery bank, but that left very little safety factor.\u00a0 So we expanded to a 8 battery bank to push our usable capacity up to 450 Amp Hours.\u00a0 Since the 6 hours of effective solar time is probably rather conservative, we could very likely be generating at least 450 Ah of power with this setup, especially in the American Southwest.\u00a0 However, remember that your battery charger reduces its output as the batteries approach full charge.<\/p>\n There are many from the Escapees Forum who provided great help, insights, and recommendations.\u00a0 To all of you, Thanks!\u00a0 For those who said \u201cPlan it out in detail ahead of time\u201d, you are SO RIGHT!\u00a0 When I connected everything & threw the switch \u2013 it worked!<\/p>\n Calculating Demand<\/strong><\/p>\n There is not a book that I am aware of that accurately tells the power usage of most items. \u00a0My best recommendation is to buy a “KillAWatt” meter (about $25 at most home improvement centers) and test\/check all of you 110 requirements.\u00a0 Here are the numbers I used in my calculations.\u00a0 I have included items we do not use (but others may) when on solar power:<\/p>\n
\n120 volt usage per day: 2000 watts
\nTotal estimated usage:\u00a0 3000 watts per day
\nPlus safety factor: 3000 x 1.2 = 3600 watts per day
\n12v Amp Hours = 3600 \/ 12 = 300 Ah<\/p>\n\n
![\"DSC_4048-Medium\"](\"http:\/\/yourpcgeek.com\/blog\/wp-content\/uploads\/2015\/07\/DSC_4048-Medium-300x201.jpg\")
<\/a>![\"\"](\"http:\/\/yourpcgeek.com\/blog\/wp-content\/uploads\/2020\/10\/20201029_142239-Large-300x225.jpg\")
![\"\"](\"http:\/\/yourpcgeek.com\/blog\/wp-content\/uploads\/2020\/10\/20201029_142304-Large-300x225.jpg\")
<\/p>\n![\"DSC_4051-Medium\"](\"http:\/\/yourpcgeek.com\/blog\/wp-content\/uploads\/2015\/07\/DSC_4051-Medium-300x201.jpg\")
<\/a> ![\"DSC_4049-Medium-e1433097270807\"](\"http:\/\/yourpcgeek.com\/blog\/wp-content\/uploads\/2015\/07\/DSC_4049-Medium-e1433097270807-201x300.jpg\")
<\/a><\/p>\n