Setup camper van

toddy · October 2017

Solar panel 2x 36V, 20A parallel 1440W measured by the meter.

Plan connect with:

Controller 36V 60A. 20A reserve for future solar panel.

Deep cycle marine battery 2x or 3x 12V 400A series

Inverter 24V 2000W continuous, 3000W peak

Will system work and supply maximum efficiency of output power?

In desert like area of California.

Use for continuous operation of 200W compact frig, 400W computer, 15W misc. and alternative running of 400W air conditioner or 700W microwave [2.8kw peak] or 1000W tools.

Please QC and correct me if I miscalculate anything. I never used or did this before. Unsure 24V or 36V controller? Unsure 38V read solar is regarded as 24V or 36V? Many thanks.

mcgivor · October 2017

You need to start with loads, with limited real estate on a mobile application, the loads would have to be kept to a bare minimum, a refrigerator alone is a major load, forget air conditioning, tough in a desert I know, but one has to be realistic, 400w for a computer is extremely high, consider a tablet or laptop at very least, microwaves although a large load it is for short durations so not really huge consumers.

Once the loads are narrowed down, then the design can begin, to answer briefly the question of voltage, 36V is not something common, you would either choose 12, 24 or 48V as a nominal voltage, the choice of which is largely dependant on loads, hense loads first, battery next then array. Hope you haven't bought any hardware yet, because it's extremely difficult to work backwards. For now forget the hardware and concentrate on establishing loads, with a set figure, the process can begin. To establish loads watts alone mean little, a time of use has to be included, for example a 100W load for 6 hours is 600Wh, or 0.6Kwh. Checking consumption with a kill-a-watt meter using grid power for each device is invaluable information to establish a figure.

littleharbor2 · October 2017

24 volt inverter will require 2 or 4 of those 12 marine RV batteries. 3 batteries cant be configured into a 24 volt bank. Better option would be 6 volt deep cycle batteries. 6 volt golf cart batteries work well for a starter set. They are very reasonably priced. Check Costco or Walmart.

We need a clearer description of your panels. 36 volt could be open circuit voltage, Voc,, which would equate to 60 cell panels. 36 Vmp. would equate to 72 cell (24 volt nominal) panels. This info is needed to configure your array and choose a charge controller.

mcgivor · October 2017

Again loads before hardware, no point in discussing battery requiments or voltage, array size, or the array voltage, without addressing loads first, loads are what determine the ballance of system, it's as simple as that, no offense implied.

littleharbor2 · October 2017

mcgivor said:

Again loads before hardware, no point in discussing battery requiments or voltage, array size, or the array voltage, without addressing loads first, loads are what determine the ballance of system, it's as simple as that, no offense implied.

Totally agree, none taken. Just putting a few thoughts out there. The lack of details and confusion of what a 24 volt panel is seems to be a common denominator with the "I've never done this before" crowd. From the op's posting it sounds like he fits that description pretty well. I'm not jumping in to help design his system. Probably shouldn't have used the term "We"

Estragon · October 2017

+1 on getting a better handle on loads. In addition to getting numbers for daily watt-hour consumption and peak consumption in watts, it would help to know if the van will have rv type DC loads (eg water pressure or lighting).

As you appear to have panels already, it would help to post specs from the sticker on the back - ie; Voc, Vmp, Isc, and Imp.

Will you have a separate generator and charger, or will you run the van engine for charging in bad weather and/or heavier use of loads?

toddy · October 2017

Already had solar which have no label/sticker. Will check with factory and post Voc, Vmp…

Presently I use alternator, small inverters 12V 700-1000W and many old junk batteries, smart charger, to run tools few hours.

Frig: 200W, .4Kw peak, load 2Kwh

A/C: 450W, .8Kw pk, load 3.6Kwh

Microwave: 700W, 2.8Kw pk, load .7Kwh

Alternative DC stove 200W, .2Kw pk, load .2Kwh

And 3 cups rice cooker, 200W, .25Kw pk, load .2Kwh

Or freeze dried foods.

Misc 50W, .05Kw pk, load .5Kwh

Drop computer, no heat water or pumps.

Total: 1.7-4.05Kw peak, load is 6.8-6.9Kwh

[1.7Kw peak for stove and rice cooker, 4.05Kw peak for microwave]

Without A/C: .9-3.25Kw peak, load is 3.2-3.3Kwh

toddy · October 2017

The panel has 72 cells. It is no-load measurement, so probably it is 38Voc and 20Isc. I use Flute meter and another brand to measure. I was very surprised at first too, but it is possible.

Estragon · October 2017

Even without A/C, I'd suggest adding a generator. You would use the generator to bulk charge the batteries up to around 70% full in the morning, and to run A/C if needed after that. The panels could then finish charging in the mid-day sun.

I'm assuming 2x 36v means 2 panels, each with a Vmp around 36v and Imp around 8ish amps for an STC rating of around 300w. Real world will be about 75% of that with reasonable tilt and not scorching hot weather, so around 400w for a pair. I don't know where "1440w measured by the meter" comes from. Is this watt-hours over a day?

toddy · October 2017

Estragon, you are absolute right. I misunderstood solar calculation with measured 36V Voc x 20A Isc x 2 panels = 1440!

So depress to find one of the solar stickers with a note. Barely enough power to run a small frig. and a rice cooker or alike although DC water boiler and stove can run through cigarette lighter.

Will post tomorrow for help of the right controller and batteries.
Thanks.

toddy · October 2017

solar spec:

4.8A Isc 34.4V Voc 600V Max

Rated 4.4A 34V 150W

hand written notes found: 170W (4.4Ax38Vmp)

Local solar radiation is about 6Kwh/m^2/day

Solar power supply estimate 2.46Kwh/day [.15Kw x 1.24 m^2 x 6 rad. x 2 panels]

Load 2.2Kwh and .5Kwp

Will this work?

Mppt 20A 12/24V, 95% efficiency

Battery 2x 12V 100A 2.4Kw

Keep same inverter 900W/1.3Kwp, efficient %?

Estragon · October 2017

I think you may be optimistic on pv production, but time will tell.

If the batteries are true deep cycle (not marine type), you can take them down to about 50% state of charge if recharging daily,;and still get a reasonable service life. If not true deep cycle, they won't last long doing that, as they'll be designed for brief, high current discharges and nearly immediate recharge. Even if you don't care about ruining the battery trying to use 100% of capacity, at low states of charge the voltage will drop off to a point the inverter won't work.

To get 2.4kw usable power with a good deep cycle battery, you need ~200ah@24v. That lets you take the 4.8kw bank to a 50% state of charge. 4x6v golf cart batteries for ~225ah@24v would be a reasonable choice.

Inverter efficiency varies with load. They tend to be reasonable (~85%) when running close to capacity, but can be not efficient at all when lightly loaded (eg running a couple of LED lights). A modified sine wave inverter may be about the same as pure sine wave running a resistive load (eg. rice cooker) but may have trouble running inductive loads (eg fridge) efficiently (or possibly running them at all).

toddy · October 2017

Thanks Estragon. You have plenty good knowledge of setting up camper van with solar. I learnt from you deep cycle 200A 24V to use 50% of battery capacity. Inverter can cut off 100A battery faster.

5 rad instead of 6 at my area from November to Spring.

My mistake again, load is 4.8Kwh for 200W frig [200x24]

With 85% efficiency, I can only use 1/2 day then charge by a generator, unless I can find another smaller frig 100W!!!

Estragon · October 2017

If you have propane on board already for cooking or heating, you might want to consider a propane fridge.

Another option might be to build a very well insulated box, and a Danfoss DC compressor and evaporator. I'm doing this for a dual compartment fridge/freezer at my cabin. Although not cheap, and involves labour to build the box, it should be very efficient. The first compartment more or less completed, uses about 200w/day at fridge temps, and about 350w/day at freezer temps.

toddy · October 2017

My mistake again! But very good news.

Annual maximum load is only 213-325Kwh or .89Kwh/day for a Frigidaire from the factory’s spec, not 200W x24hrs like I thought!

Presently I use compact propane stoves for camping, but solar will save a lot of time and dozens cans. I start making freeze-dry foods at home and plan to build my own machines and will use 3 more solar panels for this. So the frig is for fresh vegetable, fruits, drinks mostly. If I go fishing then I will consider a small freezer which is inexpensive around this area.

Calculate battery size:

890Wh / ( .85 efficiency x 24V battery)

50% state of charge results 87Ah or ~100Ah@24V battery.

I still like 200Ah to store more energy in case it needs and for summer, any disadvantage?

Will gauge 0 jump start cable wires work?

Thanks.

BB. · October 2017

One of the problems with lead acid batteries is they simply need a lot of time under charge--Especially if the batteries are discharged by 50% or more. Generally, there are simply not enough hours in a sunny day to bring a 50% discharged bank back to 100% state of charge on a daily basis. Running 25% discharge per day (2 days to 50% state of charge) will give you a longer battery life (in general).

Placing some panels south west and south east (virtural tracking) will help extend the hours in a day...

-Bill

Estragon · October 2017

I'm not a fan of using jumper clips as connectors. Something like Anderson connectors make for easy connection but safer and more reliable than clips. I would use the heaviest cable that will fit on the inverter, and keep it as short as possible. There needs to be a fuse or breaker on the positive (assuming negative ground) cable from battery to inverter.

toddy · October 2017

Thanks for all value answers that help a lot. Now I can sure at least small Frig up running and hopefully a kettle/cooker on sunny days as well. There are a lot of sun hours here daily.

I have seen few solar power plants from the highway. Voltage was steady in 9 hours with the meter, I think of potential ~3Kwh, not 1 or 2Kwh, if the controller, wire and batteries are ready. And the mystic note of 170W from the plant engineers is 150W panel x (1m long x 1.13m wide) or 169.5W exactly.

Setup camper van

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