Help a noob for setting up my solar system

zlw5009

Hello everyone, I’m Zach and I’m new here.

I’ve been researching solar systems but it still seems very foreign to me.

I’m converting a cargo van into an RV in a couple months and trying to work out the specifics for our solar system. We intend to run a 12v refrigerator, 12v freezer, cell phone booster all full time and will have several other items running for various periods of time from an LED tv, charging electronics (cell phone, laptop, speaker), dual induction stove top, fan, LED lights, and maybe a conventional oven.

My initial plan was to run 4 6v agm batteries (2 in series, each pair in parallel for a 12v battery bank) Aside from that, I’m sort of lost in terms of investors, MPPT charger controller and which panels to use.

My goal would be to run at least 720 watts of solar panels and not allow my batteries below 50%. I’m going to custom fabricate out rack for mounting the solar panels so we can adjust the angles depending on positioning. We anticipate an expense between $3,500-4,500 for the setup.

My question(s): how do I determine the ideal setup for our needs?

I would prefer having enough energy to maximize our use of appliances, electronics, etc. as I run a digital marketing agency and my wife is a psychologist so we will be working many hours in our van.

Any guidance, recommendations, and resources provided would be greatly appreciated.

* note - I do have a friend who is an electrician who has agreed to help me with installation.

mcgivor

WEl come to the forum 
Given the proposed setup is mobile a serious rethink about loads is critical, cook with gas for starters, anything that heats or cools are major consumers, there are some good DC refrigerators/freezer  but they come at a premium, running two separate units would be too much given the roof area, in fact even one would be a challenge. My suggestion would be to whittle the loads down to a bare minimum before design starts, this is the best approach to get an idea of what equipment is required, there is little point suggesting batteries, controller etcetera without hare figures, don't buy anything hardware wise before doing an inventory. My opinion others may differ.

Photowhit

Pretty much what @mcgivor said. Don't buy anything yet, get a handle on your loads. A fridge and freezer may well be over 1500 watt hours per day. Particularly if they are in a hot environment. Do you plan on air conditioning?

Will you have alternate means of charging, a generator and from the vehicle?

Look at the watts used and the hours you will use them, You want to stay in the top 50% of 4 golf cart batteries? That's about 2500 watt hours, and generally 720 watt array will fail to recharge in a typical day. Average day is about 4 hours of direct sun (less in winter) and you will generally only receive about 75% of the panel rating and charging the batteries is another 15-20% loss.

Lots to think about...

I would write down what you intend to use on a daily basis and the expected load on your system. Then work from the load you want to run... 

BB.

As said above--Solar Electric power is expensive and requires space for solar panels and battery bank to support the loads. Conservation is usually key to a successful installation--Particularly so for an RV where weight and space is at a premium.

I understand the reluctance to use fuel for cooking (as an example). If you are concern about fire--Using alcohol stove (common in marine environments) can be an interesting solution (alcohol fires can be put out with water very easily).

Anyway, just to give you an idea. Location is critical for solar harvest estimates. With an RV, camping down south in the winter and up north in the summer can increase the amount of energy you will harvest--You can use a solar calculator and a bit of math to see how much energy you can harvest. For example, a flat mounted solar array in Little Rock AK:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Little Rock
Average Solar Insolation figures

Measured in kWh/m2/day onto a horizontal surface:

Jan	Feb	Mar	Apr	May	Jun
2.39	3.03	4.01	5.19	5.51	5.91
Jul	Aug	Sep	Oct	Nov	Dec
6.02	5.52	4.74	3.71	2.60	2.15

A 720 Watt solar array mounted flat (tilting the array, especially farther north and in winter can increase the harvest):

• 720 Watt array * 0.52 off grid AC system eff * 3.03 hours of sun (February "break even") = 1,134 Watt*Hours per day
• 1,134 WH per day * 1/13.6 Volts battery bus = ~83 AH @ 12 volts for typical February day

That would be (roughly) enough power for a couple small/efficient RV fridge/freezers (at best). And, nominally, for a "base load", you should plan on using ~65% to 75% of predicted harvest (sometimes the skies are clear, sometimes a bit of haze/clouds even in the best of weather conditions). (note RV fridge energy requirements are purely a guess at this point--Need to pick the equipment and obtain the actual energy ratings to be sure)

Getting a small propane RV refrigerator+freezer--Perhaps 1/2 to 1.0 lbs of propane per day. A 20 lbs BBQ tank would last you ~20-40 days and reduce your solar energy requirements a lot.

Another issue is the peak power requirements. Batteries can supply a pretty surprising amount of current, but when operated (for example) at 12 volts--The actual wattage is not that high. Flooded cell are cheap and pretty rugged. AGMs are cleaner (no water to add, no gassing--except at end of life and/or if over charged--But 2x the costs of flooded cell).

For a typical Flooded cell battery, A discharge rate at C/8 is a comfortable maximum. For AGM, depending on brand/model, you can even go as high as C*4 discharge rate (kill the battery in 15 minutes or less)--But for sake of argument, lets say C/2.5 is our aim point.

Say 6 volts @ 200 AH batteries (golf cart type). 4 batteries would be 12 volts @ 400 AH (series parallel connected). The maximum continuous power (say for cooking):

• 12 volts * 400 AH * 1/8 hour discharge rate for flooded cell * 0.85 ac inverter eff = 510 Watt continuous load
  
• 12 volts * 400 AH * 1/2.5 hour discharge rate for flooded cell * 0.85 ac inverter eff =1,632 Watt continuous load

And the maximum current for 1,632 Watt load would be:

• 1,632 Watt load * 1/0.85 AC inverter eff * 1/10.5 volts battery cutoff = ~183 Amp @ 12 volt battery bus current
  

That is a good amount of current... Very heavy copper wiring and a 230 amp+ fuse or circuit breaker.

If size and peak current load are important, there are LiFePO4 (Lithium Ion battery chemistry) that are becoming popular in the RV world. Not cheap batteries, but can be very nice for these applications.

-Bill

littleharbor2

Keep in mind, You want your solar panels in clear, unobstructed sun as long as possible to get full power harvest potential. If the panels are mounted on the roof of your cargo van, it will be in the sun all day. The interior of this van IS going to get hot. The hotter it is the harder your fridge/freezer is going to have to work to maintain temp settings. A vicious circle for sure. You really should consider propane powered  refrigeration. That will dramatically decrease your solar needs.