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Old 09-30-2017, 04:45 PM   #1
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Question New to this! Solar panels?? HELP

Hi all,

I own a 1999 20ft mid sized Bluebird I'm converting into my home.

I'm winging this entire project but what I'm the most confused about right now is the electricity...
I'd love to be able to go off-grid sometimes so I really want to do solar power but I have extremely limited knowledge about the subject so anything will help.

I will be needing to power a stove/oven, fridge, and a/c. Is this even possible to do solar powered? What's my alternative? Any price ranges? Truly anything will help..... Thank you so much in advance!!
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Old 09-30-2017, 06:32 PM   #2
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This would be a very good place to start.

In most RVs, the fridge is the biggest issue. Planning a solar system that could replace the energy use of the fridge would be a good place to start, and you could expand it later.

Solar will not run any but the smallest air conditioners without a multi-thousand dollar installation.

Electrical System Design | FarOutRide

You can also run a small generator for a few hours a day to give yourself much more flexibility.
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Old 09-30-2017, 06:36 PM   #3
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Recommend reading: https://handybobsolar.wordpress.com
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Old 10-22-2017, 06:49 AM   #4
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Ditto what Twigg said.
In addition let me add that you could purchase a "kill a watt" meter. You plug it into the wall and your appliances into it. I will tell you the immediate power consumption as well as the total over time (it has a running clock in it). If you are using it on your refrigerator I suggest you add an extension cord between it and the wall socket. It erases itself when unplugged and you can't see it when it's plugged in behind the fridge.
We found our new TV was only 35 watts when on. Our modem, wifi router, and Arlo security system is plugged into a battery back up from Staples and it only draws 35 watts. I can't remember what the little window ac uses, but it was a lot less than I though.
So I only suggest getting used to the energy you can reasonably afford to install before you commit to the various purchases you will have to make, or save up additional funds for the project.
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Old 10-22-2017, 09:08 AM   #5
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Quote:
Originally Posted by mckenziepollock View Post
Hi all,

I own a 1999 20ft mid sized Bluebird I'm converting into my home.

I'm winging this entire project but what I'm the most confused about right now is the electricity...
I'd love to be able to go off-grid sometimes so I really want to do solar power but I have extremely limited knowledge about the subject so anything will help.

I will be needing to power a stove/oven, fridge, and a/c. Is this even possible to do solar powered? What's my alternative? Any price ranges? Truly anything will help..... Thank you so much in advance!!
Good news is plenty of roof space for panels.

If you're thinking A/C boondocking you need a gennie, so then not as much solar needed.

Cooking and heating use propane.

An efficient little fridge isn't too bad, big house fridge forget it.

Come up with an energy budget AH per day and we can help with the many variables, it's not rocket science.
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Old 10-22-2017, 05:52 PM   #6
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I picked up the Kill-A-Watt that Trout suggested. It has been invaluable in getting an accurate gauge of how much power my devices really consume.

Regarding fridge size vs power consumption. I found that many of the fridge's ranging from 10-17 cubic feet have very similar power consumption. I put a Frigidare 10.8 in my 5er and am happy with the size and power consumption.
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Old 10-25-2017, 06:28 AM   #7
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Originally Posted by PNW_Steve View Post
I put a Frigidare 10.8 in my 5er and am happy with the size and power consumption.
That is a great size. Do you remember the amperage draw?

I like the look of Smeg, but not the price. or the name.

Screen Shot 2017-10-25 at 6.27.07 AM.png
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Old 10-25-2017, 01:12 PM   #8
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Originally Posted by Trout View Post
Ditto what Twigg said.
In addition let me add that you could purchase a "kill a watt" meter. You plug it into the wall and your appliances into it. I will tell you the immediate power consumption as well as the total over time (it has a running clock in it). If you are using it on your refrigerator I suggest you add an extension cord between it and the wall socket. It erases itself when unplugged and you can't see it when it's plugged in behind the fridge.
We found our new TV was only 35 watts when on. Our modem, wifi router, and Arlo security system is plugged into a battery back up from Staples and it only draws 35 watts. I can't remember what the little window ac uses, but it was a lot less than I though.
So I only suggest getting used to the energy you can reasonably afford to install before you commit to the various purchases you will have to make, or save up additional funds for the project.
Thank you for this. I've been looking for something like this for awhile now.
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Old 10-30-2017, 05:39 PM   #9
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I found this to be a very helpful list. Actual mileage may vary, but gives you a fair comparison between models and a ballpark idea of average energy consumption:
https://www.energystar.gov/most-effi...-refrigerators
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Old 10-30-2017, 06:47 PM   #10
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My basic strategy:

- Figure out how many watts each thing you use draws (either by manufacturers rating, or preferably measure with a kill-a-watt)

- Add up the wattage of all the things you want to be able to run at the same time to figure out how big an inverter you need. Probably good to give yourself at least 20-30% margin. Be advised some loads draw extra current/watts at startup (particularly things with big motors like AC compressors, refrigerators). The inverter needs to be able to handle this extra under its surge rating, or you may need to size up your inverter. Note that you may be able to get rid of the biggest surges by looking for different appliances. For example a modern inverter based mini-split AC has very little surge, while an older window mount unit might have a lot.

- For each load multiply it's power in watts by the amount of time you think you'll use it each day to get energy consumption in kWh. Add that up for all loads, and you start to get an idea how many kWh of battery you need. You multiply battery Amp hours (Ah) by voltage (for example 12V) to get the watt hours of your battery. Divide Wh by 1000 to get kWh.

- Now it starts to get a little messy / painful. The inverter efficiency tells you how many AC kW (or kWh) you get for each DC (battery) kW or kWh. A 75% efficienct inverter will draw 1kW from the battery when putting out 0.75kW AC. Since you calculated AC kWh above, you need to divide that by inverter efficiency to get the corrected DC battery kWh required. So if you needed 1kWh AC, now you need 1.34kWh DC out of the battery. Inverters with 95%+ efficiency are available, but tend to be more expensive.

- To extend the life of your batteries you really don't want to use more than half their capacity before recharging. So that doubles the required capacity. Continuing the example above, we're up to 2.68kWh battery capacity to get 1 AC kWh.

- More bad news. The more current you draw from a lead acid battery the less it's effective capacity. Most batteries capacity is spec'd at a "20 hour" rate. In other words at the constant current / power output that will drain them in 20 hours, multiplied by 20 to get Ah. For an example a Trojan T105 is rated for 225Ah, divided by 20 hours that's rated at 11.25A. If you were to put two of these 6V batteries in series to make 12V you "should" have 2.7kWh of capacity which seems like it should be enough to provide 1 AC kWh in the example above. Assuming the example inverter from above is 1kW continuous, 75% efficiency, you could be drawing over 100 Amps (1000/12)/0.75. According to the data sheet, at 75A output the T105 battery capacity falls to about 144 Ah. At 100A lets say it's 120Ah. So if you routinely run close to max on your inverter, your effective battery capacity could be closer to 1.4kWh for each pair of T105s. So you may actually need a second pair to get 1 AC kW out without going below 50% charge. Good news, adding a second pair cuts the current out of each battery in half, so you get some effective capacity back too.

A small energy star residential refrigerator will probably consume most of that 1 AC kWh in a day, so you start to see what you're up against. Air conditioning will use considerably more. Electric stoves generally draw a few kW, so depending how long they are on can be a challenge as well.

- Once you are happy with how many kWh of battery you need, you can size your solar. Under good sunny summer conditions where your panels are in full sun all day you will generally get about 5 "peak sun" hours per day. In theory you would just take your expected DC energy usage above (1.34kWh from the example above to produce 1 AC kWh) and divide by 5 hours to get 268W of solar. In reality you'll do well to get about 70% of that actually out of the panels and into the battery, so say 382W (268/0.70) to account for panel and charging efficiency. In winter you might only get half as much, so you may want to double again if year rounding to 766W.

- If you don't want to have to fire up the generator every time you have a cloudy day, you will want to think about whether you want to increase the size of your battery to cover more than one day. To cover one very cloudy day you'd need to about double the size of the battery. to get the battery back up to full on the next sunny day you'd need to double the size of your solar.

Often this is an iterative process, and when you get to this point people go back and look for ways to use less power, find more efficient components (charger, inverter, batteries, etc), etc. Or just say screw it, and try something and see how it works ;)

Rob
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Old 10-30-2017, 09:53 PM   #11
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Front door freezer models as in above pic are energy hogs. Figure that into any useage calculations if your bus is going to be self-sufficient. It would perform better on strictly 115v shorepower as compared with other sources that may run it. The freezer compressor has to work extra hard on these models when all the cold air it made falls out on the floor when the door opens. And the cycle continues..

John
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Old 10-30-2017, 10:11 PM   #12
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Originally Posted by BlackJohn View Post
Front door freezer models as in above pic are energy hogs. Figure that into any useage calculations if your bus is going to be self-sufficient. It would perform better on strictly 115v shorepower as compared with other sources that may run it. The freezer compressor has to work extra hard on these models when all the cold air it made falls out on the floor when the door opens. And the cycle continues..

John
The door of a freezer isn't opened very often.

The fact is that 11-12 cuft fridge/freezers consume very little power these days, and vastly less than absorption fridges designed for RVs.
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Old 10-30-2017, 10:32 PM   #13
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Front door is only a tiny bit less efficient than chest style, all else being equal.
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Old 10-31-2017, 12:32 PM   #14
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Originally Posted by miscrms View Post
My basic strategy:

- Figure out how many watts each thing you use draws (either by manufacturers rating, or preferably measure with a kill-a-watt)

- Add up the wattage of all the things you want to be able to run at the same time to figure out how big an inverter you need. Probably good to give yourself at least 20-30% margin. Be advised some loads draw extra current/watts at startup (particularly things with big motors like AC compressors, refrigerators). The inverter needs to be able to handle this extra under its surge rating, or you may need to size up your inverter. Note that you may be able to get rid of the biggest surges by looking for different appliances. For example a modern inverter based mini-split AC has very little surge, while an older window mount unit might have a lot.

- For each load multiply it's power in watts by the amount of time you think you'll use it each day to get energy consumption in kWh. Add that up for all loads, and you start to get an idea how many kWh of battery you need. You multiply battery Amp hours (Ah) by voltage (for example 12V) to get the watt hours of your battery. Divide Wh by 1000 to get kWh.

- Now it starts to get a little messy / painful. The inverter efficiency tells you how many AC kW (or kWh) you get for each DC (battery) kW or kWh. A 75% efficienct inverter will draw 1kW from the battery when putting out 0.75kW AC. Since you calculated AC kWh above, you need to divide that by inverter efficiency to get the corrected DC battery kWh required. So if you needed 1kWh AC, now you need 1.34kWh DC out of the battery. Inverters with 95%+ efficiency are available, but tend to be more expensive.

- To extend the life of your batteries you really don't want to use more than half their capacity before recharging. So that doubles the required capacity. Continuing the example above, we're up to 2.68kWh battery capacity to get 1 AC kWh.

- More bad news. The more current you draw from a lead acid battery the less it's effective capacity. Most batteries capacity is spec'd at a "20 hour" rate. In other words at the constant current / power output that will drain them in 20 hours, multiplied by 20 to get Ah. For an example a Trojan T105 is rated for 225Ah, divided by 20 hours that's rated at 11.25A. If you were to put two of these 6V batteries in series to make 12V you "should" have 2.7kWh of capacity which seems like it should be enough to provide 1 AC kWh in the example above. Assuming the example inverter from above is 1kW continuous, 75% efficiency, you could be drawing over 100 Amps (1000/12)/0.75. According to the data sheet, at 75A output the T105 battery capacity falls to about 144 Ah. At 100A lets say it's 120Ah. So if you routinely run close to max on your inverter, your effective battery capacity could be closer to 1.4kWh for each pair of T105s. So you may actually need a second pair to get 1 AC kW out without going below 50% charge. Good news, adding a second pair cuts the current out of each battery in half, so you get some effective capacity back too.

A small energy star residential refrigerator will probably consume most of that 1 AC kWh in a day, so you start to see what you're up against. Air conditioning will use considerably more. Electric stoves generally draw a few kW, so depending how long they are on can be a challenge as well.

- Once you are happy with how many kWh of battery you need, you can size your solar. Under good sunny summer conditions where your panels are in full sun all day you will generally get about 5 "peak sun" hours per day. In theory you would just take your expected DC energy usage above (1.34kWh from the example above to produce 1 AC kWh) and divide by 5 hours to get 268W of solar. In reality you'll do well to get about 70% of that actually out of the panels and into the battery, so say 382W (268/0.70) to account for panel and charging efficiency. In winter you might only get half as much, so you may want to double again if year rounding to 766W.

- If you don't want to have to fire up the generator every time you have a cloudy day, you will want to think about whether you want to increase the size of your battery to cover more than one day. To cover one very cloudy day you'd need to about double the size of the battery. to get the battery back up to full on the next sunny day you'd need to double the size of your solar.

Often this is an iterative process, and when you get to this point people go back and look for ways to use less power, find more efficient components (charger, inverter, batteries, etc), etc. Or just say screw it, and try something and see how it works ;)

Rob
Well said!
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Old 09-14-2018, 01:22 PM   #15
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Thumbs up Priceless Knowledge!

Quote:
Originally Posted by miscrms View Post
My basic strategy:

- Figure out how many watts each thing you use draws (either by manufacturers rating, or preferably measure with a kill-a-watt)

- Add up the wattage of all the things you want to be able to run at the same time to figure out how big an inverter you need. Probably good to give yourself at least 20-30% margin. Be advised some loads draw extra current/watts at startup (particularly things with big motors like AC compressors, refrigerators). The inverter needs to be able to handle this extra under its surge rating, or you may need to size up your inverter. Note that you may be able to get rid of the biggest surges by looking for different appliances. For example a modern inverter based mini-split AC has very little surge, while an older window mount unit might have a lot.

- For each load multiply it's power in watts by the amount of time you think you'll use it each day to get energy consumption in kWh. Add that up for all loads, and you start to get an idea how many kWh of battery you need. You multiply battery Amp hours (Ah) by voltage (for example 12V) to get the watt hours of your battery. Divide Wh by 1000 to get kWh.

- Now it starts to get a little messy / painful. The inverter efficiency tells you how many AC kW (or kWh) you get for each DC (battery) kW or kWh. A 75% efficienct inverter will draw 1kW from the battery when putting out 0.75kW AC. Since you calculated AC kWh above, you need to divide that by inverter efficiency to get the corrected DC battery kWh required. So if you needed 1kWh AC, now you need 1.34kWh DC out of the battery. Inverters with 95%+ efficiency are available, but tend to be more expensive.

- To extend the life of your batteries you really don't want to use more than half their capacity before recharging. So that doubles the required capacity. Continuing the example above, we're up to 2.68kWh battery capacity to get 1 AC kWh.

- More bad news. The more current you draw from a lead acid battery the less it's effective capacity. Most batteries capacity is spec'd at a "20 hour" rate. In other words at the constant current / power output that will drain them in 20 hours, multiplied by 20 to get Ah. For an example a Trojan T105 is rated for 225Ah, divided by 20 hours that's rated at 11.25A. If you were to put two of these 6V batteries in series to make 12V you "should" have 2.7kWh of capacity which seems like it should be enough to provide 1 AC kWh in the example above. Assuming the example inverter from above is 1kW continuous, 75% efficiency, you could be drawing over 100 Amps (1000/12)/0.75. According to the data sheet, at 75A output the T105 battery capacity falls to about 144 Ah. At 100A lets say it's 120Ah. So if you routinely run close to max on your inverter, your effective battery capacity could be closer to 1.4kWh for each pair of T105s. So you may actually need a second pair to get 1 AC kW out without going below 50% charge. Good news, adding a second pair cuts the current out of each battery in half, so you get some effective capacity back too.

A small energy star residential refrigerator will probably consume most of that 1 AC kWh in a day, so you start to see what you're up against. Air conditioning will use considerably more. Electric stoves generally draw a few kW, so depending how long they are on can be a challenge as well.

- Once you are happy with how many kWh of battery you need, you can size your solar. Under good sunny summer conditions where your panels are in full sun all day you will generally get about 5 "peak sun" hours per day. In theory you would just take your expected DC energy usage above (1.34kWh from the example above to produce 1 AC kWh) and divide by 5 hours to get 268W of solar. In reality you'll do well to get about 70% of that actually out of the panels and into the battery, so say 382W (268/0.70) to account for panel and charging efficiency. In winter you might only get half as much, so you may want to double again if year rounding to 766W.

- If you don't want to have to fire up the generator every time you have a cloudy day, you will want to think about whether you want to increase the size of your battery to cover more than one day. To cover one very cloudy day you'd need to about double the size of the battery. to get the battery back up to full on the next sunny day you'd need to double the size of your solar.

Often this is an iterative process, and when you get to this point people go back and look for ways to use less power, find more efficient components (charger, inverter, batteries, etc), etc. Or just say screw it, and try something and see how it works ;)

Rob
This was priceless knowledge for me. Been doing a lot of research on this very topic and it can be confusing for most. Thanks for the great advise.
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Old 09-14-2018, 10:24 PM   #16
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That is a great size. Do you remember the amperage draw?

I like the look of Smeg, but not the price. or the name.

Attachment 16899
I think I read something about Dometic buying them, has anybody heard something similar?
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