Sizing a Solar set up to meet the demand of a device?

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claybcook
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Sizing a Solar set up to meet the demand of a device?

Post by claybcook » Tue Mar 13, 2018 2:37 pm

If I'm trying to power a specific device, rather than just attempt to keep batteries charged, how would I do this? My camp needs a pump to get the grey water from the evap pool to the grey water tank. I'm looking at one of various sump pumps at HD. All of them specify amps drawn, etc. How would I take the needs of the pump to size the solar system to power it? Same question if I were to try to power a refrigerator: begin at the need and build back to meet that demand. How?
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Captain Goddammit
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Re: Sizing a Solar set up to meet the demand of a device?

Post by Captain Goddammit » Tue Mar 13, 2018 3:30 pm

You’re not quite making sense, generally batteries run the device and the solar panels keep the batteries charged.
Skipping the batteries is a crummy plan, especially for a must-not-fail system like your evap cesspool (another bad idea).

I take it you’re not a solar hobbyist, which is normally the only good reason to run solar at Burning Man. Just practically speaking, solar isn’t a good way to run temporary power. It’s more money and hassle than it’s worth.
In a semi-permanent installation things are different.
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Token
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Re: Sizing a Solar set up to meet the demand of a device?

Post by Token » Tue Mar 13, 2018 3:48 pm

Super easy.

Find someone in camp that understands AC and DC electricity, Amps, Volts, Watts, and the likes, then delegate.

For grey water transfer, these are awesome and powered by BPR or Whiskey!

Image

For running a fridge, look at the Volts and Maximum Amps, multiply them to get the Watts. This is very important and used everywhere.

Take that Watts number and multiply by 1.5 and that is the size of inverter needed.

Next you need to estimate the duty cycle of the fridge - I.e. how long the motor actually runs during an hour, on average over a 24 hour period. Take that runtime per hour average and multiply by 24 hours. Write that down as it is used to figure thhe size of batteries and solar panels.

Now, them Watts we figured earlier, multiply that with the duty cycle for the 24 hour period we just figured - that is how much energy you need to generate and store in the batteries over that 24 hour period. It will be expressed as Watt-hours. Or more likely KiloWatt-hours.

Now the tricky part; batteries usually are 12V and have a rating of Amp-Hours. So we gotta covert that into Watt-hours so we can have apples and apples. Take your battery Amp-Hours, multiply by the battery voltage of 12V and divide by 2 because batteries should never discharge below 50% capacity or they get ruined.

Now you can figure out how many batteries you need. Take the Fridge Watt-hours number and divide by the battery Watt-hours and round up.

Are you sure you don’t want to delegate to someone ... the solar panel one is even worse as we need to deal with the sun moving across the sky, inclination, azimuth etc ...

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Re: Sizing a Solar set up to meet the demand of a device?

Post by Popeye » Tue Mar 13, 2018 5:38 pm

Thank you Token. Very well put. If you don't mind I might copy that.

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Re: Sizing a Solar set up to meet the demand of a device?

Post by claybcook » Tue Mar 13, 2018 7:42 pm

Unnecessarily judgemental guys. Any post that begins, "You don't know enough to..." should disqualify the poster. If this isn't the place to ask questions, where should I go?

Given the vast range of panels and inverters and devices contemplated, it seemed easier to cut to the chase and ask the fundamental question rather than wait for the specifics to materialize before any question could be asked.
A device will use power at a certain advertised rate.
A battery can store a certain quantity of power.
A solar panel can recharge that battery at a given rate.
The inverter can process the DC into AC at an advertised rate.

I know there is a fundamental equation here; I just don't know it. Hence; asking for help.

Thumper's Rule still applies.
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Re: Sizing a Solar set up to meet the demand of a device?

Post by Captain Goddammit » Tue Mar 13, 2018 8:41 pm

All of that is false. Literally all of it.

So clarify... are you trying to skip having a battery in the system?
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Re: Sizing a Solar set up to meet the demand of a device?

Post by motskyroonmatick » Tue Mar 13, 2018 9:32 pm

Here's a real world scenario for you. I ran an evaporator for a camp of 3 having minimal showers off of a Harbor Freight Solar panel setup. The only thing ran was a low amperage 12 volt DC bilge pump lifting water 4' to the top of the evaporator. It worked perfectly and the battery did not run out of charge in the night.

They key to continuous power was a power draw(consumption rate) that did not drain the battery(big enough capacity) during the non charging period(overnight). A charging system that simultaneously could charge the battery to max capacity and power the system during the charging hours(direct sun). Regular maintenance to make sure panels were relatively clear of dust and oriented to the sun.

BUT

The solar set up cost about 150 bucks at the time

I bought different charge controller for about 25 bucks

The battery cost me 150 bucks (It was a really nice battery)

Were already at 325 bucks here and all I really got was in-between 1 and 2 amps of power use 24 hours a day for 5 or 6 days. I might have spent as much on the project as I spent on my Burning Man ticket that year.

It was a neat little project that worked well and at the time I had money to spare but it is pretty ridiculous to spend that kind of money for so little power. I think alot of solar power things end up this way on the Playa.

Research 12 volt DC bilge pumps. They are much more conducive to using with solar power than 120v AC motor powered sump pumps. Some come with float switches which can be super handy.
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Token
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Re: Sizing a Solar set up to meet the demand of a device?

Post by Token » Tue Mar 13, 2018 10:10 pm

I just love it when someone asks a vague question then complains about the provided solutions or advice.

It is impractical to design a solar solution that does not have some form of energy storage.

There are rare scenarios where this is done - solar attic vents, small gadgets like calculators.

Why is it impractical? Because solar panels are big, bulky, expensive plus don’t produce constant energy and very few devices run 100% duty cycle or can tolerate variable power input based on light availability and efficiency.

So, the whole pump thing can be done with a battery and say a 50W panel or no battery and a 400W panel for the 30 minutes you run the pump per day.

Similar for the Fridge question. It will be big, heavy, bulky, expensive.

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Re: Sizing a Solar set up to meet the demand of a device?

Post by FlyingMonkey » Wed Mar 14, 2018 10:09 am

You will need to "no-shit" evaluate your power requirements and scale your system from there. If all you are doing is using a solar panel to pump grey water then you can probably get by somewhat cheaply. If you want to start out small & grow your system over the years then you can spread the cost out.

What pumps are you looking at? I would recommend using an RV or boat pump rather than something from HD. Your requirements will be much less than a house sump pump.

Things to keep in mind......

It sounds like you have essentially zero experience with solar power. This is not a big deal because everyone starts at zero. I would recommend doing a lot of reading and get smart enough to be dangerous. It's not rocket science but you want to be safe & not ruin expensive equipment. Here's a good start: https://www.homepower.com/solar-electricity

Something to consider since it seems that you wanted to go battery free, most systems use a charge controller to charge batteries & distribute power. Many charge controllers do not work if they don't detect a battery. That's really good to know before you set up on the Playa.

Things go wrong, charge controllers burn up, if it can break it will. Have a back-up plan. The bilge pump that token posted a pic of is actually a good idea. Consider having some spare components. I always have a spare charge controller.

Once you get everything built test it at home to make sure it works.

I think you can do this with a small bilge pump and may or may not need a battery.

Running a fridge is a different matter. I honestly don't think it's worth building a solar power system that is capable of powering a fridge. Consider an using an RV fridge (maybe LP) or just use good old fashioned ice & coolers. When you start powering big appliances like a fridge you will obviously need to incorporate deep cycle batteries. Those batteries weigh 60-80 pounds & usually cost over $100. Typically you will need more than 1 battery. So, as you can see, when you start increasing your requirements you will need to go "all in" & get smart about Solar power, purchase expensive equipment, & haul all that heavy equipment out to the Playa. People do it but only you can decide if it's worth the effort & expense when a big cooler & ice can accomplish the same thing.

If all your doing is running lights, charging phones, & pumping gray water then yeah, that's easy.

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Token
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Re: Sizing a Solar set up to meet the demand of a device?

Post by Token » Wed Mar 14, 2018 5:36 pm

BTW, here is the requested equation:

E=mc2

Unless you’re a black hole that is.

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FlyingMonkey
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Re: Sizing a Solar set up to meet the demand of a device?

Post by FlyingMonkey » Thu Mar 15, 2018 7:58 am

Token wrote:BTW, here is the requested equation:

E=mc2

Unless you’re a black hole that is.
And that's exactly the kind of thing a Burner (Old school non-Frat Boy or tourist) would do. Make a small nuclear reactor to pump grey water. :mrgreen:

However, I think Ohm's Law would be more appropriate in this case. But I'm not opposed to someone splitting a few atoms on Playa as long as it's quiet & not moopy.
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FlyingMonkey
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Re: Sizing a Solar set up to meet the demand of a device?

Post by FlyingMonkey » Thu Mar 15, 2018 8:10 am

And there is this.

https://www.theplayalabs.com/home/labs/solar-home

That'l pump yer sump.
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some seeing eye
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Re: Sizing a Solar set up to meet the demand of a device?

Post by some seeing eye » Thu Mar 15, 2018 9:07 am

A search of ePlaya for Ah Wh Watts produces

viewtopic.php?f=277&t=81177&p=1138388&h ... s#p1138388

and

viewtopic.php?f=278&t=80397&p=1137228&h ... s#p1137228.

Most cities will have solar hobbyists and maker spaces. Visit the Alternative Energy Zone (village) the year in advance of your need.

A current new solar panel at $1 a Watt, charge controller, deep cycle battery and inverter have use around the house for power outages and disasters. They are a better investment than Harbor Freight, G**l Zero play systems or janky CL panels priced above $.10/Watt.
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Luigi
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Re: Sizing a Solar set up to meet the demand of a device?

Post by Luigi » Thu Mar 15, 2018 11:53 am

Hi Clay

Sounds like you need:
12 volt bilge pump with a float switch (so it only turns on when the float says it is needed)
Deep cycle 12 volt battery
Charge controller (to avoid over charge of battery)
Solar panel

The key to your question is the size of your pump and how long it will run (how many gallons will be pumped)

When you have that key, the rest is math.

Cheers, Luigi
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Re: Sizing a Solar set up to meet the demand of a device?

Post by BBadger » Sat Mar 17, 2018 10:35 pm

Claybcook,

It looks like you have all the component specifications listed in terms of rates and capacities. The equations essentially fall out by themselves with only a few additional other unit conversion formulas, and maybe additional margins and factors to keep things safe.

The fundamental equation here, as with all equations, is:

Inputs = Outputs

You'll be working in terms of energy. Power (Watts) = Volts * Amps; Energy (Joules) = Watts * Time

- Battery specifications: Energy capacity = Volts * Amp*Hours ; (only discharge to 50% so use only half the rating)
- Solar Panel: Output power = volts * current generation = watts; energy production = power * time
- Load (like a refrigerator): input power = watts; energy consumption = watts * time

You will have two phases: day-time and night-time. These affect whether something, such as a battery, is a sink (output) or a source (input). It'll also affect whether sources such as solar panels produce anything at all.

Day:

inputs = solar_panel(W/panel) * solar_radiation(kWh / day / 1kW/panel)
outputs = battery(0.5 * volts * amps * hours) + load(W) * day_time(seconds)

Night:

inputs = battery
outputs = load(W) * night_time(seconds)

Solve for battery capacity and solar panel rating using the two equations.

The factor of 0.5 on battery is so you only have 50% discharge.

You can easily figure out battery capacity, and then plug the rest into your equations. Solar radiation is like 4.3kWh/day/kW/panel in Nevada under perfectly ideal conditions. Then add margins, etc. so you don't burn out your stuff, can deal with inefficiencies, and can compensate for problems such as lack of strong sunlight, bad panel angle, etc.

Token already went through this process, just without the explicit equations.
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