Hey richwill, great question. There are a lot of details, but I'll take a shot at an overview.
You will need your solar panels, batteries, a solar charge controller, an inverter (if you want "household" voltage), and in my case, I also used a small breaker box to connect everything.
Solar panels: I have two Renogy 100-watt flexible panels adhered to my roof with Sikaflex, and then their perimeters sealed with Dicor sealant. Even though they are more expensive, I like the flexible panels because they bend to the curve of your roof and you can barely see or notice them. Very stealthy. The Renogy flexible panels are off the market and being redesigned right now, but several other brands have similar panels (I got mine on Amazon). $200 USD each
Batteries: I have 2 100-amp hour VMAX tanks batteries. They are highly rated and have functioned well, but I honestly can't tell you which brand is the best. My 2 batteries were $250 USD each.
Charge Controller: You will get a lot further with an MPPT controller rather than the cheaper PWM controllers. Both of them monitor incoming solar voltage and battery voltage and drop incoming voltage to what the battery needs in real-time, except the MPPT controllers do it about 30% more efficiently (they are also better in low-light conditions, which would help you out in winter). Mine is a Morningstar MPPT-45 which is way overkill (I liked the quality/data logging), but you could try one the Renogy MPPT 20-amp models to do the trick.
Inverter: I have a small 300-watt Pure Sine Inverter from Go Power. About $175 USD. You may already know, but this will boost your 12-volt DC battery power to 110 or 230 volt AC power. These lose about 15% of the power when converting, so I just use it for my desktop computer. Everything else is 12 volts for efficiency reasons. I wouldn't waste time with a Modified Sine inverter, as it will destroy your delicate electronics. Pure Sine will work for everything.
Breaker box: The most "controversial" part of my system, as it seems like overkill for a van. But once you see how many fuses and cutoff switches you need, this box makes everything really compact. Plus you can use DC solar breakers in it, which are a fuse and switch in one, helping to simplify things. I used the MidNite Solar MNDC-125 Mini DC Disconnect. About 175 USD. You could leave this out and just not have as many cutoff points, but you will still need a bit of wall space to mount switches and fuses.
One last item. I used a small fuse block to power up my 12-volt branch circuits around the van. I used a 12-circuit fuse block from Blue Sea Systems (made for boats). It's really high quality. My batteries connect to this fuse block and that in turn powers up all of my 12-volt outlets and LED lights around the van.
As kryten said, you could use a battery isolator in your engine compartment to send power back to your batteries when your engine is running. I don't have one of these, but for about 80 USD, you could cut down on the number of solar panels. Like you though, I wanted to be able to park for weeks and not worry about driving around to keep my batteries charged. You could also use this in combo with your solar panels.
All together, my setup, with wire, connectors, etcetera, was about 1700-1800 USD. I could have cut this down with a cheaper charge controller, maybe to $1500 USD. This is by far the most expensive part of your conversion.
I hope this answers your question!
Ross
You will need your solar panels, batteries, a solar charge controller, an inverter (if you want "household" voltage), and in my case, I also used a small breaker box to connect everything.
Solar panels: I have two Renogy 100-watt flexible panels adhered to my roof with Sikaflex, and then their perimeters sealed with Dicor sealant. Even though they are more expensive, I like the flexible panels because they bend to the curve of your roof and you can barely see or notice them. Very stealthy. The Renogy flexible panels are off the market and being redesigned right now, but several other brands have similar panels (I got mine on Amazon). $200 USD each
Batteries: I have 2 100-amp hour VMAX tanks batteries. They are highly rated and have functioned well, but I honestly can't tell you which brand is the best. My 2 batteries were $250 USD each.
Charge Controller: You will get a lot further with an MPPT controller rather than the cheaper PWM controllers. Both of them monitor incoming solar voltage and battery voltage and drop incoming voltage to what the battery needs in real-time, except the MPPT controllers do it about 30% more efficiently (they are also better in low-light conditions, which would help you out in winter). Mine is a Morningstar MPPT-45 which is way overkill (I liked the quality/data logging), but you could try one the Renogy MPPT 20-amp models to do the trick.
Inverter: I have a small 300-watt Pure Sine Inverter from Go Power. About $175 USD. You may already know, but this will boost your 12-volt DC battery power to 110 or 230 volt AC power. These lose about 15% of the power when converting, so I just use it for my desktop computer. Everything else is 12 volts for efficiency reasons. I wouldn't waste time with a Modified Sine inverter, as it will destroy your delicate electronics. Pure Sine will work for everything.
Breaker box: The most "controversial" part of my system, as it seems like overkill for a van. But once you see how many fuses and cutoff switches you need, this box makes everything really compact. Plus you can use DC solar breakers in it, which are a fuse and switch in one, helping to simplify things. I used the MidNite Solar MNDC-125 Mini DC Disconnect. About 175 USD. You could leave this out and just not have as many cutoff points, but you will still need a bit of wall space to mount switches and fuses.
One last item. I used a small fuse block to power up my 12-volt branch circuits around the van. I used a 12-circuit fuse block from Blue Sea Systems (made for boats). It's really high quality. My batteries connect to this fuse block and that in turn powers up all of my 12-volt outlets and LED lights around the van.
As kryten said, you could use a battery isolator in your engine compartment to send power back to your batteries when your engine is running. I don't have one of these, but for about 80 USD, you could cut down on the number of solar panels. Like you though, I wanted to be able to park for weeks and not worry about driving around to keep my batteries charged. You could also use this in combo with your solar panels.
All together, my setup, with wire, connectors, etcetera, was about 1700-1800 USD. I could have cut this down with a cheaper charge controller, maybe to $1500 USD. This is by far the most expensive part of your conversion.
I hope this answers your question!
Ross