Simple solar for full-time living

kbatson

New member
Hey everyone. I've been lurking around here for long enough and trying to do research in my conversion, but I think that an actual conversation with experienced Sprinter folks is the next step. There are just so many options, it's hard to know whether I'm going down the right path. I want to get this solar thing figured out so I can start getting on the road as soon as possible.

So, if you'll indulge me, this is where I'm at so far. My needs for power:
  • 12v Fridge (Novacool)
  • MacBook Pro laptop
  • External hard drive
  • Camera charger
  • Phone charger
  • Fan-Tastic Vent Fan
  • Water pump for sink
  • LED lights
  • Bunk heater (Espar diesel) for cold weather/locations

I want to have enough buffer both in wattage from solar panels as well as amp hours in my batteries that I'm not going to worry about running out if I have a few cloudy days.

Though I have more knowledgable friends who are available to help with the install, I am not at all knowledgeable about electricity, wiring, etc. so I thought I would use a kit as a starting point. For example, this 300W Renogy kit seems reasonable in price, power, though 3x 100W panels seems someone inefficient when the square footage of the roof of a van is limited.

I would hook it up to roughly 400ah worth of sealed batteries (recommendations welcome).

Does the Renogy kit seem reasonable as a starting point? I can always swap out components in the future, but I'd like to get off on the right foot.
 

d_bertko

Active member
kbatson,

Your electrical needs as described seem modest---I'd guess the 12v fridge will account for 2/3 of your daily ah's. No inverter at all?

Our bank size was similar and our loads were like yours with the addition of a small microwave and mag induction burner. No solar for the first decade and 90% of the ah's came from the alternator. We would use electricity freely on the road and conserve a little when we parked to drycamp. A 410 ah bank would safely last four days (to 50% SoC). The dc fridge accounted for about 2/3 of our daily ah use in camp. We generally like to mostly cook and heat water outside in camp but would still use the micro and induction a little most days.

One advantage to a largish 410 ah bank is that it accepted a kw-hr of charge very quickly---so even a short run for groceries would add a day's worth of camping energy back into the bank.

The second advantage of the large bank is that it powers our 2000w inverter readily. Could be too much inverter voltage drop on a smaller bank for a short large load.

The tenth anniversary of the original agm bank meant it had been through enough cycles to lose perhaps 20% of its original ah capacity by then. Solar panels had dropped in price from 2004's $10/w to close to 2015's $1/watt---so I installed 200w of solar to extend the bank's useful life for my needs.

The 200w of solar is enough to allow us to drycamp forever in a moderately sunny location. The bank is otherwise sufficient for several days at a time of shade/rain/snow.

If you have no large inverter loads like a micro or mag burner then you can trade roof solar size for bank size at the cost of what to do when the sun doesn't shine--ie shore power, alternator, conserve.

My Grape 100w solar panels were $250 for the pair in 2015 and I wired them in series to a $89 Victron mppt controller (nicely matched in size). I built an AL frame to attach them to my existing roof rack. I was snowbirding in AZ at the time---a Phoenix rv solar shop drilled my roof and wired it up for about $150. A good deal there. too. My inverter charger has a good display panel so I did not feel the need to buy a solar one.

I'd think the advice of others here to go with a single large panel makes some sense but not a deal breaker if it is modular like mine.

Your Renogy kit sounds typically more expensive than assembling your own parts. Phoenix is the Mecca of rv solar so I had the advantage of competence and competitive pricing there. My panels came from Costco and shipped UPS to me. Larger panels might be better picked up direct from a supplier?

My walk-on roof gets used for canoes and other storage uses. So more panels than I needed were undesirable. But one can spend ah's more freely if you don't need roof space for anything else.

My four Concorde Lifeline agms were the heaviest allowable by normal UPS. (Local prices were not competitive for the nearest three states!) Pricy but I'll sing their praises for bringing us through a 12 years of heavy use.

We are at a bad point where retail li-ions are not standardized and will surely drop in price the way solar panels did with volume and tech improvements. I'd guess a replacement li-ion bank will cost half of today's price in five years with better chemistry and standard charging systems. Perhaps agms for now if weight is not a concern.

Dan
 

PaulDavis

Member
There's a big difference in the demand your laptop will create depending on how you plan to use it. Assuming you don't do CPU-intensive stuff (compiling software, continuous image processing or video editing), then it won't play much of a role in your energy needs. If you do, then it will use more than your fridge.

The fridge is generally the biggest load, and can be particularly problematic if you end up in the worst possible combination: hot, cloudy weather. We have 455 aH of storage using AGMs, so effectively 225 aH of usable storage, and the one time I've been really nervous was when we were stuck in New York state on summer for several days of high 80's to mid 90's weather with no direct sunlight. The fridge duty cycle was close to 100% and the batteries got down below 60% SOC for the first and only time.

We have 540W of panel capacity on the roof, and that is enough that from about mid-March until mid-October across the middle of the USA, we can more or less never use shore power (we do not recharge via the alternator).
 

bstory

New member
Keep in mind you need to balance the amount of power your panels will produce with the capacity of your batteries or you will never fully recharge them and they will fail prematurely.

If you have a big battery bank, as it sounds like you do, you may want more wattage than you are contemplating.
 

kbatson

New member
There's a big difference in the demand your laptop will create depending on how you plan to use it. Assuming you don't do CPU-intensive stuff (compiling software, continuous image processing or video editing), then it won't play much of a role in your energy needs. If you do, then it will use more than your fridge.
My guess is that my laptop needs are going to be more than the average user. I'm a photographer and a software developer. That's one of the reasons I'd rather go big and end up with more power than I need that be in a situation where I have too little.
 

kbatson

New member
Keep in mind you need to balance the amount of power your panels will produce with the capacity of your batteries or you will never fully recharge them and they will fail prematurely.

If you have a big battery bank, as it sounds like you do, you may want more wattage than you are contemplating.
You're basically saying that the bigger bank, the more wattage I need? Is there a basic rule of thumb for that sort of relationship, or is it highly dependent on power usage?
 

bstory

New member
The only way to do a close-to-accurate calculation would be to actually figure out how many amp hrs you will use per day and then figure out how many watts the solar panels will actually produce, on average.

For example, panels on van roofs are not at the ideal angle to produce full rated wattage, but it isn't worth doing panel racks that angle up because the van is always changing its orientation to the sun. Unless you could always park so the tilted panels faced south it wouldn't help much. Also, sometimes the panels will be partially shaded or on a dark cloudy day, not producing much power at all. So, when people size their solar panel array they usually assume they will get only 50-60% of the rated wattage in power to the batteries.

When you say 'roughly 400 amp hrs of sealed batteries' are you referring to AGMs? If so, you can safely bring these down to 50% every day prior to recharging. With conventional lead acid batteries you shouldn't do that very often. Every type of battery has its own charging needs so you should read the fine print on whatever you have or whatever you plan to buy. Also, you didn't say whether your setup would mean the alternator would also be charging your house batteries via an automatic charging relay. If so, you can rely on the charging you get from the engine via the alternator to charge up the batteries when needed. For example, if you use a lot of battery power for a day or two and the solar isn't keeping up enough to fully charge the batteries, you can always drive for awhile.

All this says you need to look at the whole 12 volt system: all ways you will be able to charge your house batteries, how many amp hrs you are likely to draw between charging opportunities, and then you can size the solar and battery bank. The only rule of thumb I've noticed (don't know if it is widely seen as useful or not) is that people's total solar wattage in situations sort of like yours is usually a higher number than the total amp hr capacity of the house batteries. For example, our uses are almost exactly like yours, but without the Espar heater and without the intensive laptop use. For us, 210 amp hrs of Lifeline AGM batteries and 270 watts of solar seems just right. Of course, we drive at least every couple of days when we camp. So we have a fail-safe in alternator charging to fall back on.

You don't need to worry about being super exact, just know about how much you will need for your average day of usage and then have a plan for what you will do if you need to use more. That said, something telling you the charge of your batteries is pretty important. We get that from our solar controller so don't have a separate battery monitor, but many people wouldn't consider traveling without a battery monitor.

So no rule of thumb can substitute for doing the calculations - especially if you are not sure how much power your Macbook Pro will need for your uses. I'd start by researching that - either online or some electrical measuring device. Maybe Paul can give you some pointers as his uses are computer intensive also. I recommend a book on calculating basic 12 volt power draws in a 24 hr period - $6-18.00 from Amazon (used is fine):https://www.amazon.com/Managing-12-Volts-Troubleshoot-Electrical/dp/0964738627

This book provides clear information on the basics of each part of the system - aimed at boat owners but almost entirely transferable to campers.

I'm sure other Espar owners on this forum can give you data on how much electrical power theirs use.

Good luck!
 

kbatson

New member
Thanks for your input guys. This forum is incredible for detailed feedback. I'll check out that book. I'll look into the details more, but I think at least 300W will be a good idea for me to pursue. The problem I am seeing now is that the higher wattage panels are considerably larger than the 100W panels. For example, this LG 300W panel is 65"x45" and this Renogy 100W panel is 40"x20". It looks like a lot of the higher wattage panels aren't actually getting any higher wattage for the size, they're just bigger. Does that seem to be the case everywhere, or are there some smaller higher wattage panels also?
 

bstory

New member
No, you are right, there is a clear relationship between wattage and size. However, if it helps to have 3 smaller panels, in terms of usage of your roof space, consider the Kyocera panels. They have been best sellers in the marine world for years because the workmanship is so good and they hold up so well in tough environments. We have two 135 watt panels on our van and they have been great for 7 years.

They are not monocrystalline, but get between 15-16% efficiency despite that.

You could get 3 of their 150 watt panels and have 450 watts of theoretical capacity for your 400 amp hr battery bank. https://www.solar-electric.com/kyocera-kd150gx-lfu-150-watt-solar-panel.html

The very best panels for efficiency are Sunpower and Panasonic with ratings over 20% but Sunpower doesn't sell retail and the Panasonic ones are the 64" x 39" size you didn't think would work for you?
 

kbatson

New member
Thanks. Does anyone have any experience with Grape panels? It seems that a lot of people doing conversions use them. They have a 180 watt mono panel for less than the Kyocera. Almost the exact same size.
 

HarryN

Well-known member
You might want to consider to have 2 methods of charging your battery pack.

As an example, just 1 hour of driving and using a 40 amp battery to battery charger, pulling power off the alternator, will provide a substantial power boost to the pack, especially during the bulk charge stage. It is hard to beat solar panels for a cost effective way to do the final charging stage(s).

Every battery technology has it's strengths and limitations and if you want them to last, it is important to operate them in the way that specific brand and type are designed.
 

kbatson

New member
When it comes to batteries, I'm looking at AGM batteries. I don't want to worry about off-gassing as I will have them mounted inside the cabin. I am deciding between these two options at this point: Lifeline GPL-8DL with 255Ahr capacity and Odyssey PC1800 with 215Ahr capacity. I like the idea of the Odyssey because of it's narrow shape, it should take up less floor space. I've seen a lot of people using Lifeline, does anyone have any experience with Odyssey?
 

PaulDavis

Member
I se 4 Grape Solar 160W panels on our van. Nothing to report: they just work.

Re: batteries. If you're tech-minded, at some point the behaviour of AGMs is going to bug you. More precisely, the behaviour of smart charge controllers, which will (correctly) avoid dumping huge currents into your AGMs if they are close to 100% SoC. The result is that you can have oodles of available power but still close out the day with batteries at < 100% SoC. The only way to fix this is to switch to Lithium. Whether this is worth the massive increase in cost is a personal choice.
 

kbatson

New member
Thanks everyone. I decided to go with 2x 180W Grape panels and 2 Odyssey AGM batteries. I'm sure you're right about the AGMs, Paul, however they still seem like the best balance of power, safety and price at this time. When I'm up for a replacement in a few years, hopefully the LPF batteries will have come down in price. I'm looking forward to it.
 

HarryN

Well-known member
Thanks everyone. I decided to go with 2x 180W Grape panels and 2 Odyssey AGM batteries. I'm sure you're right about the AGMs, Paul, however they still seem like the best balance of power, safety and price at this time. When I'm up for a replacement in a few years, hopefully the LPF batteries will have come down in price. I'm looking forward to it.
There is a lot of consumer level optimism that someday, they will be able to purchase very inexpensive, mobile grade, LiFe packs that just drop into their van application and it will work through the 4 seasons we have just like the car batteries we are used to.

I have been wrong many times, but I am fairly involved in this industry and I have some real doubts about this expectation. These large price drops have already happened and (I believe that) we are largely past achieving these economy of scale inflections. Added features and some modest price reduction - yes. Big price inflections - maybe not.

It is actually possible that the price might rise like home solar installations are about to, due to some costly additional fire code related add-ons that are being required now. Have you gone to HD or Lowes lately and seen the price of the new NEC code breakers vs the traditional ones? Try 2 - 3X increase rather than price declines.

Every single item related to the various Li and LiFe type batteries, BMS, power management, charging, protection, etc is already being built in very high volumes using chip scale technology, automatic assembly and low cost manufacturing methods.

The way to buy a "better than I can afford car" is to buy a used one. I think that this will also be the way that the price sensitive LiFe battery pack market will become fulfilled.
 
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Midwestdrifter

Engineer In Residence
The type of large volume inexpensive LiFe packs you are talking about will likely not be on the near horizon.

However, several manufacturers have made big gains in Lithium cobalt longevity. Tesla especially has been working hard to make this happen. I would expect 2k+ cycle lithium cobalt packs to be available in the next 5 years. This chemistry is widely used in portable electronics, so the volume is there, it is mostly a packaging and BMS issue at this point. As the cost of the cells drops, we can likely expect more consumer level options. The main reason you see lithium Iron phosphate batteries used is due to their higher stability (though they have lower energy density). When packaged properly with a goood BMS lithium cobalt are safe in a mobile application though.

Currently, unless you have lots of cash to burn, or are building your own pack, LiFe batteries are not mainstream.
 
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ranchworld

'06 158 2500 Passenger
What size AGM's did you go with?

Thanks.



Thanks everyone. I decided to go with 2x 180W Grape panels and 2 Odyssey AGM batteries. I'm sure you're right about the AGMs, Paul, however they still seem like the best balance of power, safety and price at this time. When I'm up for a replacement in a few years, hopefully the LPF batteries will have come down in price. I'm looking forward to it.
 

HarryN

Well-known member
The type of large volume inexpensive LiFe packs you are talking about will likely not be on the near horizon.

However, several manufacturers have made big gains in Lithium cobalt longevity. Tesla especially has been working hard to make this happen. I would expect 2k+ cycle lithium cobalt packs to be available in the next 5 years. This chemistry is widely used in portable electronics, so the volume is there, it is mostly a packaging and BMS issue at this point. As the cost of the cells drops, we can likely expect more consumer level options. The main reason you see lithium Iron phosphate batteries used is due to their higher stability (though they have lower energy density). When packaged properly with a goood BMS lithium cobalt are safe in a mobile application though.

Currently, unless you have lots of cash to burn, or are building your own pack, LiFe batteries are not mainstream.
For large packs, like in an EV, LiCo will definitely play a major role.

Boeing's experience with LiCo frightened away a lot of suppliers, because unlike an commercial aircraft or EV pack, RV users expect to be able to do self - repairs. Boeing's setup works mostly because of intensive maintenance inspections on every landing, not because they did it correctly.

It would be too high of business risk for anyone to bring out a 4 - 10 kW-hr (usable) LiCo pack to the RV or marine market, so those are dominated by LiFe. I could not find anyone who would insure a small business working with LiCo, but did with LiFe.

It isn't that difficult to find 3K cycle capable LiFe packs today and the supplier I use is starting to be pretty confident in 4K cycles at 80% DOD when used at C/2.

Battery packs under 4 kW-hr (usable) are almost too small to be economically served by Li based setups and probably should just stay with 8D AGMs or similar. People might think they want it, but it is like trying to build a 1 passenger car at 1/4 the price of a 4 passenger sedan.
 
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Thumbs

New member
We are considering purchase of a 144" wheel base sprinter. We want to add a roof top air conditioner and fantastic fan. We would also like to add as much solar as the roof capacity allows. I am looking for advice on the brand, size, and placement of the panels. From what I have seen some panels are mounted with individual brackets; others attach to a roof rack. Given the desire for the a/c and the fan is the rack possible- desirable.

Thanks
 

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