Solar Van with micro inverters

[Brad Taylor]

Hi - I'm putting together a solar system for my new 1995 VW camper van (well- new to me I'd appreciate any comments on the sizing and components below. Any links to existing posts, kits and suggested vendors/models would be great. Since Eurovan camper already has a RV electric system, I'm also interested in how to add solar using the existing camper infrastructure.

Usage
o Plan to vacation in my new 1995 VW camper van to store about 1 kWh
o expect to use about 50 W for lighting and computers 4 hours / night (200 Wh/day)
o wish to use 750W microwave up to 30 min/day (375 Wh/day)
o electric teapot 1000W up to 15 min/day (250 Wh/day)
o electric fridge 30W * 24 H * 30% on = (300 wH/day)
o hope to size solar for cloudy days (1.2 kWh/day = 400 W * 3 h/day)

System sizing
o 4 x Solar Panels (400W?)
o Solar battery charger (20A? MPPT)
o Land line battery charger (20A?)
o Charger/switch from auto generator (?)
o Inverter (1800W?)
o Meter/Display/Master controller
o Battery (1X 12V 130 AH? AGM?)
o 14L"x6.5W"x10H" compartment available

Ideally I'd like to find a single electronics component to manage all charging sources and and the inverter. I was also considering using micro inverters on the panels with and AC charger and UPS, but that may be impractical.

Thanks, Brad

[Wy_White_Wolf]

Hi - I'm putting together a solar system for my new 1995 VW camper van (well- new to me I'd appreciate any comments on the sizing and components below. Any links to existing posts, kits and suggested vendors/models would be great. Since Eurovan camper already has a RV electric system, I'm also interested in how to add solar using the existing camper infrastructure.

Usage
o Plan to vacation in my new 1995 VW camper van to store about 1 kWh
o expect to use about 50 W for lighting and computers 4 hours / night (200 Wh/day)
o wish to use 750W microwave up to 30 min/day (375 Wh/day)
o electric teapot 1000W up to 15 min/day (250 Wh/day)
o electric fridge 30W * 24 H * 30% on = (300 wH/day)
o hope to size solar for cloudy days (1.2 kWh/day = 400 W * 3 h/day)

System sizing
o 4 x Solar Panels (400W?) Not enough. Since your panels will be mounted flat instead of aimed at the sun. Also with 3hrs that doesn't figure in system ineffeciencies. Look at the off grid stickes or plan on running the engine daily to makeup the difference.
o Solar battery charger (20A? MPPT) 400W/12V=33.3A. 20A is not big enough
o Land line battery charger (20A?)
o Charger/switch from auto generator (?) Called a battery isolator
o Inverter (1800W?) on the large side for array and battery
o Meter/Display/Master controller
o Battery (1X 12V 130 AH? AGM?) Way to small for 1200WH daily. You should never use more than 20% daily. 1200WH/12V*5 = 500AH
o 14L"x6.5W"x10H" compartment available

Ideally I'd like to find a single electronics component to manage all charging sources and and the inverter. I was also considering using micro inverters on the panels with and AC charger and UPS, but that may be impractical. Micro inverters do noy work in off-grid situations.

Thanks, Brad

see above

WWW

[Brad Taylor]

more on microinverters

Hi WWW:
Thanks for the quick reply. I'm limited for now by battery cost, weight and area. So I may have to get by with the largest battery I can afford, which still fits in the Eurovan battery compartment. This means I will need to look at 80% discharge. I understand that discharging to 80% will reduce battery life, but I may not have any other options. Of course we can always reduce our usage to match our available power. One option is to pony up for a Lithium battery, but this complicates design and as far as I can tell the technology is still evolving.

I spent the better part of the day evaluating microinverters. I Found a good link here describing the issues for residential systems. It sounds like you can make it work, but its not turnkey. The primary advantage is using micro inverters is that during the day, any used AC power just goes through one conversion (PV->AC) , rather than 2 stages (PV->DC -> AC) improving efficiency. The primary disadvantage is that the microinverters are current sources which don't have a shutdown mode. Therefore if the sun is shining, the batteries are full and house power is not used, the microinverters either need to be disconnected, or the excess power needs to be dumped into a dummy load. This is harder to do than it sounds.

http://solarprofessional.com/articles/products-equipment/inverters/ac-coupling-in-utility-interactive-and-stand-alone

[Sunking]

You cannot use Micro Inverters on battery systems. End of story. Micro Inverters are used in Grid Tied Systems, not battery. You charge batteries with DC, Inverters make AC.

[Sunking]

One option is to pony up for a Lithium battery, but this complicates design and as far as I can tell the technology is still evolving.

Lithium is doable technically, but if you cannot afford to do it right with lead acid, there is no way you can afford lithium. To use Lithium requires a great deal of knowledge and cash to operate, and judging from your questions and statements you do not have the knowledge or cash.

[Brad Taylor]

Lithium is doable technically, but if you cannot afford to do it right with lead acid, there is no way you can afford lithium. To use Lithium requires a great deal of knowledge and cash to operate, and judging from your questions and statements you do not have the knowledge or cash.

Sunking - Agreed, this exactly why I'm asking this forum for guidance. I don't expect to be knowledge free forever though

[inetdog]

Sunking - Agreed, this exactly why I'm asking this forum for guidance. I don't expect to be knowledge free forever though

Step one: For a mobile system like the one you propose, it does not make much sense to spend the money and carry the weight to provide a grid tied or hybrid system.
You will be best served by making use of your vehicle alternator whenever possible and going with a pure off grid inverter.
You can still use so called grid tie panels (high Voc) in combination with an MPPT CC though.
There is a small chance that a system using solar optimizers on each panel would work for you, but the Solar Edge works only with their own grid tie inverter.

Some pure off-grid inverters are listed on their (Chinese) sales site as "microinverters" just because they are small, so do not get confused. (Most of them are not safe and not worth the price compared to a reputable brand.)

[Sunking]

Brad what you asking for is a Off-Grid System.

Use Grid Tied Panels because they are much less expensive than Low voltage battery panels, but you must use a MPPT Charge Controller to charge the batteries. As long as you are going 200 watts or more on panels, a MPPT system is less expensive. It takes a 300 watt PWM system to equal a 200 watt PWM system. A 200 Watt MPPT system ccost around $100 less than a 300 watt PWM system.

If you need AC power which you shouldn't in a mobile application, use one only large enough to meet you needs. Otherwise run every thing directly off 12 volts DC and eliminate the inverter.

But before you buy one single panel, get a Electronic Battery Isolator so you can use your vehicle alternator to charge the batteries. If you drive an hour daily you will not need panels as your alternator can generate more power in a hour than a van full of panels can generate in 2 or 3 days. A $50 Electronic Isolator does more work in an hour than a $1000 worth of panels can do in a day. Smart Money.

[Brad Taylor]

But before you buy one single panel, get a Electronic Battery Isolator so you can use your vehicle alternator to charge the batteries. .

Seems like good advise to get started. As always I have a few questions:
I notice there are several different types of isolators, any advantage to the electronic types? The relay based ones seem to offer lower drop. Will they automatically connect when the engine starts up and isolate when the RV battery is charging from PV or AC? Or should I just put these on a manual switch? Any particular models that work well? Thanks in advance

[donald]

You are trying to do far to much with electricity in a small vehicle with limit weight carrying capacity. You will need to do most cooking with fuel, unless you have a very large budget. Like a budget for electric in a racing yacht.
The way to get by without a generator in an RV is a large battery system than can be charged from a lot of panels, and a quality alternator connection. Even this only works if you drive most days to charge the battery. I don't see how you have anywhere near the space weight carrying capacity to do that kind of systems.
I do less electric in my camper and I have 450lbs of battery.
The place to start is to talk to others with your vehicle size. Don't focus on equipment first, but solving problems. You will struggle to be able to run an electric refrigerator overnight, much less cook. The "standard way" people travel and camp in your vehicle will be the right way. You simply don't have a big enough RV to reinvent the wheel with electricity.

Note the price, weight and performance of the device below compared to your solution:

http://www.webstaurantstore.com/portable-gas-stove-butane-burner-with-1-range/472E10SL.html

[Brad Taylor]

Donald - I get your point. I have 5KW of solar on my home roof and it works well, but translating that to an RV battery system, well I suppose I'm trying to do the impossible. I'm not quite ready to give up as I really want to spend significant time camping comfortably off grid. In that case I really want a small working solar fridge without running the RV for my veggies and cheese. As you suggest I can focus on reducing the power I use until it is practical. Going to look at some ultra insulated refrigeration now.

[donald]

To work overnight on one house battery the cooler will need to be compressor based, like Engle. The cheaper 12v technology uses too much power, and is designed to be used with the engine running.
I have a large Engle. It is very nice, but somewhat pricey. I mostly use it as a freezer.

[Wy_White_Wolf]

...This means I will need to look at 80% discharge. I understand that discharging to 80% will reduce battery life, but I may not have any other options. Of course we can always reduce our usage to match our available power. One option is to pony up for a Lithium battery, but this complicates design and as far as I can tell the technology is still evolving. ....

But you have a problem with the 1000W load on a single battery. That would be a C/1.2 (1000W/12V=83.3A) discharge rate for a 100AH battery. Not even AGMs can handle that high of a discharge rate. You need a bigger battery. AGMs would be a maximum discharge rate of about C/4 and flooded batteries about C/8.

WWW

[inetdog]

But you have a problem with the 1000W load on a single battery. That would be a C/1.2 (1000W/12V=83.3A) discharge rate for a 100AH battery. Not even AGMs can handle that high of a discharge rate. You need a bigger battery. AGMs would be a maximum discharge rate of about C/4 and flooded batteries about C/8.

WWW

An AGM cranking battery could easily handle C/1, but the cycle life might not be very good.

[Sunking]

Seems like good advise to get started. As always I have a few questions:
I notice there are several different types of isolators, any advantage to the electronic types?

Huge advantages. To start no welded contacts first time you discharge your battery deeply. The big advantage if you use good ones like Sure Power you will note they are made for vehicle manufacture specific like Ford, GM, Dodge, Toyota etc. They are wired into the Vehicle Alternator taking voltage regulation to the Isolator so each battery port receives the proper voltage and current. Something a relay and most Isolators cannot do.