Costing out a small, rural solar panel installation

[Grant H.]

Without derailing the thread too much, what do you think would be the minimum amount of system required to just run a laptop? The system on my van won't do it, but I'm not sure how far off I am.

You have a Lenovo w520 (if memory serves from your laptop thread), right? (I know, I could go search it, but I'm being lazy.)

The power brick that comes with those has a 20VDC @ 8.5A output. That's what your laptop wants to see on it's input. It doesn't need the full 8.5A if you put it to sleep/turn if off and just charge it.

Assuming you have a 12V system in your van, you would need to use a DC to DC converter to get the 20V out. Something like this (tunable output, rated for enough amps) https://www.ebay.com/itm/Boost-DC-DC...gAAOSwBLlU9qKi

With that, you can use a multimeter to measure and set the output, then use it to run your laptop.

Now, the solar side gets a little more tricky for a few reasons:

1. You now how a step up converter (not 100% efficient). This means you have to oversize your system.
I'm sure we can find the efficiency curve for that design somewhere, but I'd just buy one and set it up with a current meter inline on the supply side to know how much to plan for.

2. Your panel is mounted flat, not aimed at the sun.
This gives you losses in what your panel can generate.


What battery setup do you have? That will help us figure out how long you can run your laptop before having to let the batteries recover.

[Grant H.]

Grant really knows his stuff, especially solar specific... I come from a general electrical/electronics engineering background and am not intimately familiar with solar panel and charge controller specs like he is...

at first I was like 9.23A for 12AWG, that's not right... but I realized you're using power transmission spec which is 700 circular mils per amp rule (VERY conservative, to minimize loss)... you're perfectly safe with up to 20A on 90degree C insulation on 12AWG according to NEC (National Electrical Code).. but you will have more loss at higher current with that spec.
That is to say, the choice for 12AWG vs 10AWG in this instance is an economic exercise, not a safety factor.

Of course, whenever you're doing longer runs (than say 50'), you should run a voltage drop calculation to determine if larger conductors are needed to keep voltage drop under 2% in design, in practice (after installation) it should be less than 5%... but this is based on whether or not everything will work, not best efficiency.... you'll find with power transmission spec, you have to get REALLY long runs before this is an issue.

Thanks. You clearly know electrical stuff very well, as well.

I've done a lot of solar over the years, and I enjoy it.

I appreciate you jumping in and adding depth in these conversations.

You are absolutely correct, I do use the power transmission spec. Several of my customers demand that their solar installs abide by it, so I just use it as a general rule of thumb. Overkill? Yes. But they write the checks and make the demands... The original customer to require that wire spec are the ones that we build 15KW installs to support major network backbone tower sites for.

[Irving]

I have a 50w Accopower panel and an 18AH battery. Right now I run my cheapy inverter off the vehicle. I'd like to be able to run it off my panel, but if not, I'll survive.

The nice thing is that my panel spends far more time charging the battery than the battery spends powering anything.

[Justin]

Stupid question:

If we build a system, and then decide at some future date that we'd like to have additional power, how hard is it to add extra battery capacity?

[Irving]

Not difficult, just a matter of wiring them all in and having the space.

[crays]

Seems a lot for the power requirements you listed. If you could DIY, the cost would be a lot less. The set-up is straightforward.

https://www.wholesalesolar.com/


Sent from my iPad using Tapatalk

Wholesale Solar is is running a special on battery banks right now. 50% off select battery banks with purchase of any qualifying off-grid system. (saw it on FB)

OFF GRID SOLAR SALE

Get 50% Off your off-grid battery bank when you purchase a cabin sized package or larger.

No matter how many batteries your chosen system needs—four, eight, sixteen, twenty-four or more—we’ll give your battery bank to you AT 50% OFF

[Grant H.]

Not difficult, just a matter of wiring them all in and having the space.

This.

You can always add batteries. It will just take longer to fully charge, with no change in panels.

Growing a system is generally pretty easy.

[Grant H.]

Wholesale Solar is is running a special on battery banks right now. 50% off select battery banks with purchase of any qualifying off-grid system. (saw it on FB)

I don't mean to sound like I am harping on them, but there is a reason they can offer to sell a battery bank at 50% off.

The offer requires the purchase of a "Cabin" sized system or larger.
The cheapest (smallest) "Cabin" System is 1080 watts, and costs $6620 with no batteries. It does have a very good solar controller (Midnite Classic 200), and a decent quality inverter, so those are good selling points, but it's still 2.5x the cost of a complete diy system.
A comparable battery bank is $1466, and you can save $733 (50% on it)

So, for an extra 180 watts of solar, a better solar controller and inverter, you would be spending a grand total of $7353+shipping.




For comparison:

Taking the $2450 system I laid out earlier:
Add another panel - +$250
Upgrade the controller to the same Midnite Classic 200 - +$400
Upgrade the inverter to the same - +$1300
Add some more batteries - +$400

So now you have:
1200w Solar
High end MPPT Solar Controller
Decent Quality Pure Sine Inverter
860AH of Batteries

For $4800+shipping.

[crays]

Didn't know if it was a good deal or not.
Figured I'd throw it out there.



Sent from somewhere...

[bradbn4]

Interesting; sort of wondering how much shipping adds to the overall bill.
I figure batteries would be best sourced local to cut down on shipping costs.

Add in some supper caps to provide for the high startup surge on some appliances...