What 500w of solar will get you...

[KatTravels]

Hey y’all, my nephew and I are at the point in our build where we have to decide on the amount of solar power to use. We have a strict $1500 budget for solar, which I realize is tiny. I wanted to share our journey of solar on a budget in order to inspire others and hopefully get some tips along the way.

I’m going to be completely honest with you; we didn’t arrive at the number of solar panel watts we wanted in any sort of rational way. We read a bunch of articles about other people with solar panels and determined that 500 was a healthy mid range number, and since NEWPOWA was having a sale, we decided to just go for it and buy five 100w solar panels.

After we did that, we took a look at all of the items we were hoping to power in the bus and determined each item’s wattage, voltage, amperage, and watts per hour. This led us to the conclusion that we needed 1400 W of solar panels.

Unfortunately, that is out of reach for us financially, so we decided to stick with the 500 W of solar panels that we already have and try to make that work the best we can. We do have an advantage in that my nephew is extremely tech savvy and will actually be building our lithium ion batteries saving us quite a bit of money.

We have priced out all the components and it looks as though we will be able to build a 400 amp hour lithium ion battery for about $600.

That leaves us $400 for an inverter, charge controller and various cables/wires.

If anyone would like to share their solar power system setups, we’d love to hear from you!! How big is your system and what are you able to power off of it?

[dzl_]

Victron make great charge controllers, Epever is a more budget oriented brand that is worth considering if Victron is too pricey for you.


Regarding your battery bank, that sounds remarkably cheap, even for DIY. What cells are you using?


How did you arrive at the conclusion you would need 1400W solar to power everything you want to power, what are your biggest energy consumers?

[Ronnie]

I have 400 watts , and that powers my 4.7 cu ft fridge, all lights, water pump,vent fans, phone charging, and laptop . Sometimes use it to charge a scooter, or even boat batteries. That will run it down , so I want sunny days to recover. Overall I am pleased with the system. I used Renogy panels and their MPPT charge controller, with AGM batteries.

[Johnny Mullet]

I am running bare minimum at 200 watts of solar, 240 am hrs of battery, but my entire bust is wired for 12V except the fridge running off a power inverter. I can also recharge my bank with an isolator switch or generator if needed.

https://www.youtube.com/watch?v=IBbCVlLW9IM

[ermracing]

We have 520w on the roof and 920ah of FLA batteries at 12v. Right now we use the 110v inverter for a 12k mini split, standalone kitchen appliances, microwave and some LED lights. I also use it for recharging 18v tool batteries and various tools in the workshop like grinders and drills.

We also use the inverter for the block heater of the bus on cold winter mornings (-15f was the coldest so far). On that day we had to plug in the kerosene torpedo heater to help it get started.

Like Johnny Mullet we can use a generator to top up the batteries and will be connecting them to the bus alternator soon.

[Ronnie]

I forgot to mention we are 12volt for everything except the fridge, and use an inverter for that. 1000watt Zantrax.

For a/c we have a generator, and also use it for power tools. It is not set up to charge the batteries, but we do charge from the bus alternator while driving. Two weeks of boondocking is the longest without moving that we have done so far, and our solar has kept up.

[KatTravels]

Thanks for all the replies, Y'all!

Forgot to include a list of what we want to power with solar.

For AC (our biggest power drain by FAR) we will have a very efficient fridge, a portable induction stove, and a 3in1 coffee maker/toaster/griddle.

For DC, 2 laptops, 2 phones, 32ft of led light strips, water pump, 2 reading lights, 2 tiny bed fans, a maxxair fan, the inverter and the charge controller.

We used parked in paradise's online solar calculator to plug in our appliances' info and come up with that number of 1400w solar panel. It also told us that we needed a 1000ah lithium ion battery bank. Both of those sizes are wayyyyyy out of our price range, so we are trying to figure out how to get our power consumption down to a more reasonable level.

Ronny, what size battery bank are you using and is 400w sufficient to fully recharge it on a sunny day?

Ermracing, that's about the size of system we want too. Do you power a stove with that?

Johnny Mullet, I'm so jealous of how small a system you need! We are going to be living in this full time for several months (and I might live in it longer than that) so we want to make sure we are comfortable.

Dzl, thanks for the suggestions! I will definitely look into those. Sam is going to use used Samsung 18650 battery cells to build our battery. They have 95% capacity left. We would love to have new, but at 4x the cost, I just can't afford it.

[ermracing]

We have a propane camp stove/oven. Can't say we've really stressed tested the system, but I feel comfortable with it. We might add one or two panels in the future, plenty of room on the roof.

[JDOnTheGo]

Originally Posted by KatTravels

For AC (our biggest power drain by FAR) we will have a very efficient fridge, a portable induction stove, and a 3in1 coffee maker/toaster/griddle.

For DC, 2 laptops, 2 phones, 32ft of led light strips, water pump, 2 reading lights, 2 tiny bed fans, a maxxair fan, the inverter and the charge controller.

Please publish your energy budget for review. Your numbers sound high.

My energy budget is here. I am a large energy consumer and I live on what is listed in my signature.

[Ronnie]

Originally Posted by KatTravels

Thanks for all the replies, Y'all!

Forgot to include a list of what we want to power with solar.

For AC (our biggest power drain by FAR) we will have a very efficient fridge, a portable induction stove, and a 3in1 coffee maker/toaster/griddle.

For DC, 2 laptops, 2 phones, 32ft of led light strips, water pump, 2 reading lights, 2 tiny bed fans, a maxxair fan, the inverter and the charge controller.

We used parked in paradise's online solar calculator to plug in our appliances' info and come up with that number of 1400w solar panel. It also told us that we needed a 1000ah lithium ion battery bank. Both of those sizes are wayyyyyy out of our price range, so we are trying to figure out how to get our power consumption down to a more reasonable level.

Ronny, what size battery bank are you using and is 400w sufficient to fully recharge it on a sunny day?

Ermracing, that's about the size of system we want too. Do you power a stove with that?

Johnny Mullet, I'm so jealous of how small a system you need! We are going to be living in this full time for several months (and I might live in it longer than that) so we want to make sure we are comfortable.

Dzl, thanks for the suggestions! I will definitely look into those. Sam is going to use used Samsung 18650 battery cells to build our battery. They have 95% capacity left. We would love to have new, but at 4x the cost, I just can't afford it.

My battery bank is a bit small at 220 ah. But it does what I need well. Yes a sunny day will recharge it.

Your stove is a big consumer of electric, using a propane stove will go a long way to saving electric. We do have propane for cooking, heating, and hot water. If you really want an electric stove, maybe use a propane camp stove just for now till you can upgrade the solar system to handle the electric stove.

[KatTravels]

Hey JDonthego,

Yea, I'm not sure why that website gave me such a high numbers, so Sam and I manually went over everything today with a good old pencil and paper and came up with VASTLY different numbers.

We found that our total watt hours/day (except for inverter and charge controller) will be around 3100 WH. Based on that, we will need a battery capacity of 260 amp hours. We are going to build a 12V 300 AH lithium ion battery bank just to give ourselves a little wiggle room. I'll post a pic of our calculations in just a minute.

Thanks for adding the link to your own calculations! That was very helpful!

[KatTravels]

Here is a pic of our calculations

[Ronnie]

On your fridge it looks like you have it on for 24hours. Typical duty cycle is about 30% depending on how much the door is opened and temp inside the bus. So although it is on all the time it is not actually running all the time.

[KatTravels]

Hey Ronnie,

We took the yearly kilowatt usage divided by 365 to get the watt hours for the fridge since we couldn’t find the wattage or amperage. I knew that fridges cycled, but I was hoping that the way we calculated watt hours would account for the cycling. Is there a better way to do this? Thanks!!

[PNW_Steve]

I put 300 watts on the roof of my trailer. I used the Renogy Rover MPPT charge controller, a Xantrex PSW inverter and two GC-2 batteries in series.

I have a residential fridge in my trailer. If it wasn't for that, 300 watts would handle all of our needs except for the big draw items that call for generator run time. We fire up the generator every morning to run the coffee maker, microwave, hair dryer and curling iron. Then shut the generator down.

My cost, excluding miscellaneous hardware and consumables, was around $750. I didn't get the best buy on the batteries. They were $129 each. You can get a comparable batteries for less than $100.

[Native]

Originally Posted by KatTravels

Hey JDonthego,

Yea, I'm not sure why that website gave me such a high numbers, so Sam and I manually went over everything today with a good old pencil and paper and came up with VASTLY different numbers.

We found that our total watt hours/day (except for inverter and charge controller) will be around 3100 WH. Based on that, we will need a battery capacity of 260 amp hours. We are going to build a 12V 300 AH lithium ion battery bank just to give ourselves a little wiggle room. I'll post a pic of our calculations in just a minute.

Thanks for adding the link to your own calculations! That was very helpful!

To power 3100 Watt-Hours a day, your solar panels would have to output their maximum for 6 hour every day. Most all panels do not run at maximum, even at good insolation exposure. There is also losses within the system to contend with.


The main thing I want to stress this that you may find your system is enough for your needs because your needs may not actually require all of your budget. However, if you actually use your calculated energy budget's worth of energy every day, you may need a secondary source to recharge the batteries. In addition, the battery bank you specified will handle about one day without sunshine. This also indicates you may want to consider a secondary source of power.


I am not saying your system will not work. I do think it is well thought out. I just want you to go into it with your eyes open knowing what you might face in the future.


I do wish you well with it ... sounds well planned.

[Ronnie]

Originally Posted by KatTravels

Hey Ronnie,

We took the yearly kilowatt usage divided by 365 to get the watt hours for the fridge since we couldn’t find the wattage or amperage. I knew that fridges cycled, but I was hoping that the way we calculated watt hours would account for the cycling. Is there a better way to do this? Thanks!!

If you took the manufactures yearly kilowatt figures then that would take into account time not running, as well as normal usage. Your figure just looked high to me. However a full size fridge could use that much. Mine uses just over 300 watts a day measured with a "kill a watt" meter. However it is a small dorm room fridge.

[Johnny Mullet]

Having a simple system like mine makes it very comfortable, but conserving power is key. The inverter is for the fridge only. Brewing coffee in the morning with a regular coffee maker kills my batteries, so now we make "cowboy coffee" with a perculator on the propane stove. It's the best coffee ever! We don't use a microwave at home and sure not using one in the bus. All our cooking is done with propane.

I have a portable A/C unit, but it's only used on shore power or generator. Other than that we have no need for AC devices in the bus and I can run 12v stuff all day and night without issue.

[kazetsukai]

Conservation is a part of any scale system, really. Batteries are too expensive to "set it and forget it". All mobile energy is, really, and will be so for quite some time. Even gasoline, which still stores quite a bit more energy for the weight than current battery technology- has us all keeping an eye on the fuel gauge from time to time.


Solar on any scale is an engineering marvel.



The guys with the small solar are very likely examples of how to save money on energy costs in even the short term- they can do with solar cheaper than what one could do with a generator even before fuel costs. Imagine what it would cost to run your lights or charge your laptops with a genny...

[dzl_]

Kat,
'days of autonomy' is something you should consider in your planning and design. I.e. if the sun don't shine, how many days or hours can your system sustain itself. How important this is depends on the specifics of your situation (how predictably sunny is it, do you have a generator, will you be near shorepower, fulltime or weekend trip), and how you calculate this will depend somewhat on your situation too. The simplest way is to take the Watt-hours consumed per day and multiply it by the number of days of autonomy you want to design for, but this is a rough calculation. In the real world, you would change your power consumption habits when your batteries are getting low, so you could adjust your calculations based on that.


One other point, if your heart isn't 100% set on an induction cooktop it might be worth reconsidering this. There isn't necessarily anything wrong with it and it is doable, but its a big power consumer (and remember anything going through the inverter should have another 15-20% tacked on to account for inverter inefficiency), and in my opinion propane makes much more sense unless you have a hefty solar array and battery bank, or plan to use your cooktop sparingly. If you have a strong preference for electric cooking, its doable, but I put induction cooking in the same category as electric heating and air conditioning (albeit on a much lower level) doable but to some degree you will have to design your system around it, and might incur substantial additional costs. An induction cooktop will use more energy in 10-20 minutes than an efficient DC fridge will use in 24 hrs. Add in the cost of morning coffee and some toast, and you have yourself a very energy-expensive breakfast.


That said, I do love seeing these all-electric builds that manage everything off solar and battery power, I love the idea of the self sufficiency and everything being powered by clean green energy, but the cost of this is often much higher than selectively using propane where it makes sense.