Developing first off-grid/emergency solar system

[jediaelthewise]

Greetings,

I am a bit new to the solar power world here but I am picking things up pretty quickly. I am working on brainstorming a backup/emergency power system to build into my Chevy Express 2500 van that can be used both for off grid power and essentially treat my van as an emergency 'generator' for my house in a no power situation.

Here are the needs/requirements I am aiming for:
1. Capable of powering something as large as a home refrigerator
2. Capable of handling an output peak load for larger appliances such as a blender, drill, or microwave (intermittant use)
3. Solar panels mounted in top of van (limited space)
4. Expandable - I know that I may not be able to afford or get the ideal end system all at once but if I can start as a smaller system and scale up that would be ideal
5. Alternator powered - I would like my van running to also be able to charge the system. If it is possible to send power in reverse to jumps tart my own van battery that would be even better.

I am considering the following setup, but am open to suggestions:

1. Solar Panels - Renolgy Eclipse Panels - I have read these are a bit more efficient but I am open to suggestions if the difference is marginal. These will be mounted on the top of my van. I can likely fit at most 4-6 on top.
2. Mounting - I will need good suggestions here on how I could mount these, if I should consider angling options, and also road/weather safety
3. Battery - There are a number of options I am considering here. I know that LiFePO4 batteries are more expensive up front but last longer. I may go with a Renolgy gel hybrid to start for budget constraints then upgrade later. (I also know not to mix them down the line so I will repurpose the gel into a seperate system later if I upgrade)
4. Controller - Renogy DCC50S For what I'm going for this system seems to be a best all in one controller that I should use between everything
5. Invertor - For my usage I believe I will need at least a 2000 Watt pure sin wave invertor. Open to suggestions on model and kind or if I should consider a larger one

Thanks!

 

[DerekH]

The Chevy 2500 Express Van has about 120 sq. ft. of roof surface which gives you a ~2.5kW theoretical maximum solar output, so squeezing 1.5kW of solar up there should be doable. That's plenty of roof to satisfy requirements 1-3 if you're willing to sacrifice the space inside the van for the batteries and other components. Depending on how your engineering skills are, there's probably a way to mount the batteries under the van which would save you the interior space and probably even improve the vehicle's handling characteristics, but that would add significant time, money, and difficulty to the project.

Requirement 4 is always possible if you try hard enough. ?

Requirement 5 is where the real challenge is. The first challenge is running the wires. I'm not familiar with the engine compartment of that particular Chevy Model, but they're often pretty tightly packed and the alternator is not always easy to access. Running the wires to connect your auxiliary system to the alternator/primary battery might be tricky to do without crossing the path of something that's moving or too hot for the wires.

The next consideration is the electrical impact of drawing power from the alternator. I'd be concerned that drawing load for charging your new auxiliary battery system would negatively impact the charging of the van's primary battery. You'd probably want to consider installing a component to monitor the state of charge (SOC) of your primary battery and only direct power to the auxiliary system when the primary battery is at full SOC.

Regarding component selection, this seems like an application where flexible panels (which are thinner and lighter, but more expensive) might be worth the lower drag and easy installation. Renogy's flexible panels come with an adhesive back peel-and-stick type of installation which seems convenient. Also, the MPP Solar all-in-one controllers are definitely worth looking into. The MPP systems have both the charge control and the inverter all together in one neat package, and there are plenty of system size choices that seem to fit your needs. MPP controllers even have an AC input that you could wire your alternator to. Check out this video if you're interested in learning more about the MPP Solar All-in-one units:

Hope that helps.

 

[jediaelthewise]

This is really helpful thank you!

 

[DerekH]

After looking at this again now it didn't look right so I double-checked. In my first calculation, I used the wrong conversion factor. The 120 sq. ft. of van space actually yields a theoretical maximum of about 1.1 kW. This number depends on your location and the time of year. That means you should be able to get at least 500W of solar productivity up there, which should still be plenty. Energy-efficient modern fridges operate in the 200W ballpark.

 

[alfaeric]

So in terms of your refrigerator- you must get a pure sine wave inverter.

The size- that's one thing I can't seem to get a straight answer- I even asked the maker of my fridge, and they just pointed me to the spec sheet.

One inverter company suggests 4-6x the rated power of the fridge (the rated power is on the boiler plate in side- that says how much current at 120V). But is that 4-6x at for the surge or nominal? I ended up getting 3000w with 6000w peak, and we will see when it's done.

Anyway, I look forward to seeing some of the replies to size an inverter for a fridge.

WRT using your alternator- you may want to look into a higher output alternator conversion. Using more of the engine to generate power is actually more efficient on the van. Not much, but every thing helps.

 

[DerekH]

But is that 4-6x at for the surge or nominal?

They're likely referring to 4x-6x the nominal operating wattage so that your inverter is capable of handling the surge of power consumption needed for compressor startup. Compressor startup usually draws 4x-6x the nominal operating current and can usually be founded listed as Locked Rotor Amperage (LRA) in the spec table. You can find the peak power consumption by multiplying the LRA by 120V; should be in the 400W-700W range for most modern fridges. IMO, a 1kW inverter should be plenty if the only electric load you're anticipating is a fridge.

 

[jediaelthewise]

This is all really helpful thank you!

 

[Santa Fe Big Sky]

The fridge draw will vary based on the ambient temperatures, how often you open the door and if you add new items which are not cold already. You start with the power draw running and then try to measure or guess the % of running time. You could slap,a meter on it for a couple of days but a forked stick might give better results.