5,000 watts of solar panels on the roof of a van?

[Inverlyon]

I see that this section is for "small 12v systems". If this should be posted in a different section, please let me know.

The short version of this, is that I'd like to discuss a 5,000 watt PV system on the roof of a van.

The long version, is that I am considering ordering a new 1-ton dually 170" wheelbase extended tall roof Mercedes-Benz Sprinter van and converting it for full-time stealth van living for my wife and I, until we're too old to do it anymore. I plan to insulate the van well, but I'd like for us to be able to make generous use of a large air-conditioner, as well as running LED interior lights, water pump, and both laptops all day long, without relying on shore power, and we're not interested in running from hot weather to do it. I've looked into many methods of powering the electricals, to include a 3kw diesel generator mounted under the back of the van, super-quiet Honda generator hidden inside a sealed box in the back with external forced ventilation, a second alternator, and combinations of those paired with a more modest solar system, and all three major types of batteries typically used for these types of purposes (flooded, AGM, and lithium).
.

I have an extensive background in auto repair, to include having specialized in chassis electrical, among other things, so I'm fairly handy, and I'm not quite starting from zero knowledge. But there is even more stuff that I don't know, when it comes to something like this.

I'm sketching this out using 100-watt panels wired in a combination of series and parallel as needed. I'm reading that larger panels are less durable in mobile PV systems.

I'm designing a roof-mounted solar panel rack that would be the legal maximum width (102") for road use, running the full length of the roof, mounted just high enough to clear a low-profile 15,000 BTU rooftop air conditioner, and carrying 20 100-watt panels, for 2,000 watts.

On top of that, I'm designing a second solar panel rack of the same size, holding another 20 100-watt panels, for another 2,000 watts. The second rack would be mounted on slide-outs moved by a linear electric actuator, and would slide to the right, to serve as an awning.

And then finally, a third power slide-out solar panel rack mounted under the front half of the first rack, containing 10 100-watt panels, for another 1,000 watts, that would extend to the front bumper when deployed.

The combined weight of the solar panels alone, not counting the three racks, the two actuators, and a 100-pound air conditioner, is 825 pounds. For that reason, I would need to fabricate tubular steel "roll bar" type supporting structures inside the van, one at the rear, and one at the B-pillar, to support the weight of the entire solar system, before insulating and paneling the walls.

When it's all folded up when moving or when in stealth mode at night, it would be 102" wide, about 188" long, and add about 14.5" to the height of the van. The van would weigh about 6,000 pounds, and has a GVWR of about 10,000 pounds.

Of particular interest to me, is how much battery capacity would be appropriate for something like this.

Would I need three MPPT solar charge controllers, one for each rack?

So let's dive in...

[bcroe]

Your 5000W system would only approach a lesser part of that figure for a short part of the day, and would
be reduced by an angle considerably different from your latitude. Serious clouds could block all but 10% of
your output. Running an air conditioner of much size from batteries is pretty impractical, esp from the limited
ability of 12V and the weight of batteries for mobile. RVers have solved these problems with a generator and
some propane. Bruce Roe

[SunEagle]

Besides the limitation of getting maybe 50% output from that 5kw array you still have to worry about DOT certification that will allow you to drive a vehicle with that array attached to the roof. You might end up spending a lot more on the structure just to increase the rigidity of that array so it can be driven at highway speeds. Good Luck.

Oh Just a though. A 12volt battery system is usually limited to 1000 watts due to the maximum charge controller rated at 80 Amps. You would need 5 CC's at that rating which could be a cluster-f**k getting to work. Maybe look into a 48volt battery system that is then converted DC to DC to the lower voltage loads.

[J.P.M.]

You'll need an absolute minimum of something like ~ 270 ft^2 of panels for a 5kW system. As for extensions and add-ons, good luck in holding the vehicle on the ground or at least keeping from getting sea sick when you're inside and it's rocking in the wind. Good luck on getting that much space panel surface on a van roof.

I bet you'd have a better chance of meeting your needs if you reduced your required or design electrical load or, as Bruce notes, by using other means than PV to meet the load. What you want is probably considered unrealistic by most of those knowledgeable in such things.

[Sunking]

Dang you owe me a new monitor because I spewed my Dr Pepper all over the monitor when I read your post.

Never going to happen.

[Inverlyon]

Besides the limitation of getting maybe 50% output from that 5kw array you still have to worry about DOT certification that will allow you to drive a vehicle with that array attached to the roof. You might end up spending a lot more on the structure just to increase the rigidity of that array so it can be driven at highway speeds. Good Luck.

Oh Just a though. A 12volt battery system is usually limited to 1000 watts due to the maximum charge controller rated at 80 Amps. You would need 5 CC's at that rating which could be a cluster-f**k getting to work. Maybe look into a 48volt battery system that is then converted DC to DC to the lower voltage loads.

I appreciate your input.

And yes, I realize that I'm not going to actually get 5,000 watts of power out of a set-up like this. The air conditioner that we're currently looking at, requires about 2,000 watts of power to run, and everything else that we're doing, would be incidental to that. We'd be cooking and heating our water with gas.

What "DOT certification" would be required? The structure that I'm designing, would be strong and rigid enough to drive at highway speeds (when it's all stowed).

Five charge controllers in parallel would allow me to have 1,000 watts of panels feeding each one. What would be hard about getting that to work?

The top 2,000 watt array would be working at all times. When we park, we can slide out the front 1,000 watt array without increasing the vehicle's footprint. And when there is room, we can slide the side one out. We have a second vehicle, so even if we were parking in a parking lot, we'd be able to simply park her vehicle beside the van, and run out the 2,000 watt "awning" over it. And I'd like to explore wiring each longitudinal "string" of panels (in the bottom 2,000 watt array) in series and then paralleling those five strings, so that if we were not able to run the side slide all the way out, we'd at least be able to harness power from the panels that were exposed.

What kind of battery bank would be required for something like this? We're currently leaning in the direction of AGM batteries, because they can be recharged faster than flooded batteries, allowing us to take full advantage of those peak sun hours.

[Inverlyon]

Your 5000W system would only approach a lesser part of that figure for a short part of the day, and would
be reduced by an angle considerably different from your latitude. Serious clouds could block all but 10% of
your output. Running an air conditioner of much size from batteries is pretty impractical, esp from the limited
ability of 12V and the weight of batteries for mobile. RVers have solved these problems with a generator and
some propane. Bruce Roe

If it was cloudy, I probably wouldn't need to run the air conditioner, or at least I wouldn't have to run it much.

I'm interested in avoiding having to do oil changes on a generator once a week, as well as the noise and fumes. I'd like for our fresh water capacity to be the limiting factor in how long we can boondock- I don't want to be limited by how much propane, diesel, and/or gasoline we can carry.

[Inverlyon]

You'll need an absolute minimum of something like ~ 270 ft^2 of panels for a 5kW system. As for extensions and add-ons, good luck in holding the vehicle on the ground or at least keeping from getting sea sick when you're inside and it's rocking in the wind. Good luck on getting that much space panel surface on a van roof.

I bet you'd have a better chance of meeting your needs if you reduced your required or design electrical load or, as Bruce notes, by using other means than PV to meet the load. What you want is probably considered unrealistic by most of those knowledgeable in such things.

A little over 320 square feet, using fifty 100-watt monocrystalline panels.

We'd have everything pulled in if we were experiencing enough wind to rock the van. The Sprinter is also well-supported by the aftermarket, when it comes to larger anti-sway bars and other suspension upgrades. We'd be carrying a significant amount of batteries and fresh water, and we'd be carrying them as low in the van as we could get them.

[Inverlyon]

We'd obviously be carrying around an awful lot of shade with us, which in and of itself should reduce our need for air conditioning somewhat.

And although this would be a significant financial expenditure, we do intend to take advantage of whatever the current tax laws would allow us, and the ROI would be significantly higher than a residential PV setup, because we're not comparing PV to the local power company, we're comparing PV to buying, maintaining, and periodically replacing a portable generator. And even then, we're only comparing the part of the system upstream from the batteries, because no matter what we do, we're still gonna have to have batteries and at least one good-sized inverter.

[J.P.M.]

A little over 320 square feet, using fifty 100-watt monocrystalline panels.

We'd have everything pulled in if we were experiencing enough wind to rock the van. The Sprinter is also well-supported by the aftermarket, when it comes to larger anti-sway bars and other suspension upgrades. We'd be carrying a significant amount of batteries and fresh water, and we'd be carrying them as low in the van as we could get them.

Sounds like a great way to get into the great outdoors and away from the hustle/bustle of modern conveniences.

Have you done any load analysis/estimates and matched that to any array size ?

I'm out of this one thread.

[Inverlyon]

Have you done any load analysis/estimates and matched that to any array size ?

I'm not familiar with that terminology. What do you mean?

[Inverlyon]

We'd obviously be carrying around an awful lot of shade with us, which in and of itself should reduce our need for air conditioning somewhat.

And although this would be a significant financial expenditure, we do intend to take advantage of whatever the current tax laws would allow us, and the ROI would be significantly higher than a residential PV setup, because we're not comparing PV to the local power company, we're comparing PV to buying, maintaining, and periodically replacing a portable generator. And even then, we're only comparing the part of the system upstream from the batteries, because no matter what we do, we're still gonna have to have batteries and at least one good-sized inverter.

And instead of paying for a separate power awning, we'd be able to put that money towards the PV system, since the second rack would serve as a power awning also.

[SunEagle]

I appreciate your input.

And yes, I realize that I'm not going to actually get 5,000 watts of power out of a set-up like this. The air conditioner that we're currently looking at, requires about 2,000 watts of power to run, and everything else that we're doing, would be incidental to that. We'd be cooking and heating our water with gas.

What "DOT certification" would be required? The structure that I'm designing, would be strong and rigid enough to drive at highway speeds (when it's all stowed).

I planned to use whatever combination of series and parallel wiring of the three arrays is required, to keep the current output down to something that the charge controllers could handle. But now that you mention it, five charge controllers in parallel would allow me to have 1,000 watts of panels feeding each one.

The top 2,000 watt array would be working at all times. When we park, we can slide out the front 1,000 watt array without increasing the vehicle's footprint. And when there is room, we can slide the side one out. We have a second vehicle, so even if we were parking in a parking lot, we'd be able to simply park her vehicle beside the van, and run out the 2,000 watt "awning" over it. And I'd like to explore wiring each longitudinal "string" of panels (in the bottom 2,000 watt array) in series and then paralleling those five strings, so that if we were not able to run the side slide all the way out, we'd at least be able to harness power from the panels that were exposed.

What kind of battery bank would be required for something like this? We're currently leaning in the direction of AGM batteries, because they can be recharged faster than flooded batteries, allowing us to take full advantage of those peak sun hours.

DOT certification will vary depending on which US State you are traveling through. Some jurisdictions may require structural design that certifies a "modification" to your vehicle to drive at highway speeds. Then again if you drive on secondary roads they probably won't care but your vehicle insurance company may balk at any claim should you file one since you have modified your vehicle without the proper design.

AGM batteries are very expensive. The size of the bank is determined by the number of daily watt hours you want to use. A typical FLA bank should be sized so that it gets a charge rate between C/8 and C/12 where C = Bank Ah. So a quick calculation for a 1000 watt array for a 12volt battery bank would be 800Ah. (1000w / 12v = 83 amps. Using C/10 rate that calculates to 10h * 83A = 830Ah). Now multiple that by 5 for a 5kw system. That is a very big and heavy battery bank not to mention costly.

Of course your 5kw array won't be able to generate full nameplate amps so you could reduce the Ah size by X % depending on how much true production you get out of it. If you put in too small of a battery bank you can fry them. Too large and they will never get recharged properly and die an early death.

This all seems like way to much for me to worry about when a 5000 watt geny will do everything I want for a fraction of the price even with the need to maintain it.

Oh did I mention you still need to use a generator to charge your batteries periodically because the solar panels may not do the trick due to weather and lack of sunlight. So you have to purchase a generator anyway so why not just go that route instead of building a giant solar / battery system.

[J.P.M.]

I'm not familiar with that terminology. What do you mean?

Usually, a design for an application begins by defining the goals of the excercize. In the case of designing a PV system, the types of electrical loads, as well as their size and duration and when they are likely to be incurred are determined or estimated. That helps in system sizing, and choosing other design parameters. For off grid, one of those other sets of design parameters is battery sizing and other parameters associated with any energy storage.

One of several things that estimating likely system loads in the manner described above or similar methods helps with, but does not guarantee, is avoiding system over or under sizing.

Sometimes estimating loads also points out other ways of accomplishing a task. In this case, if the goal is to meet an electrical load, ways may be found to reduce that load and so increase options for meeting that load as well as allowing the load to be met with less expenditure of resources, or make a design actually workable and doable.

[Inverlyon]

DOT certification will vary depending on which US State you are traveling through. Some jurisdictions may require structural design that certifies a "modification" to your vehicle to drive at highway speeds. Then again if you drive on secondary roads they probably won't care but your vehicle insurance company may balk at any claim should you file one since you have modified your vehicle without the proper design.

I've had some formal training in Title 49 FCR. I know an awful lot of cops, and I have absolutely zero concerns about running afoul of the "roof rack police" in a private motor home with a GVWR of just under 10,000 pounds.

AGM batteries are very expensive. The size of the bank is determined by the number of daily watt hours you want to use. A typical FLA bank should be sized so that it gets a charge rate between C/8 and C/12 where C = Bank Ah. So a quick calculation for a 1000 watt array for a 12volt battery bank would be 800Ah. (1000w / 12v = 83 amps. Using C/10 rate that calculates to 10h * 83A = 830Ah). Now multiple that by 5 for a 5kw system. That is a very big and heavy battery bank not to mention costly.

Of course your 5kw array won't be able to generate full nameplate amps so you could reduce the Ah size by X % depending on how much true production you get out of it. If you put in too small of a battery bank you can fry them. Too large and they will never get recharged properly and die an early death.

This all seems like way to much for me to worry about when a 5000 watt geny will do everything I want for a fraction of the price even with the need to maintain it.

Oh did I mention you still need to use a generator to charge your batteries periodically because the solar panels may not do the trick due to weather and lack of sunlight. So you have to purchase a generator anyway so why not just go that route instead of building a giant solar / battery system.

I appreciate your help with the math.

So you're talking about roughly 4,000 amp-hours of batteries for a 5,000 watt solar system. If I'm doing the math right, it would take twenty L16 6-volt batteries to do roughly that, which would weigh over 2,000 pounds and cost $10,000. I'm starting to see the light here...