Supplemental System Design Help?

[ColdSun]

Please forgive my novice vocabulary.

I want to design and install for my house a solar powered battery bank that will supply:

Two 120V 15A outlets simultaneously. (Think high demand devices like a small window AC unit and a chest freezer.)

For back up only, not needed to supply all day usage.

A setup I could deconstruct and take with me if necessary to a new home.

I’m thinking component-built instead of all-in-one so I can learn about solar, but I’d also like to keep it simple as possible, as this is my first rodeo. I don’t even really know what an inverter is (but I can hook one up if I can find out how). I have extensive experience in construction. (I’ve installed outlets, pump wiring, boat rigging, etc.)

What would your most simple design be for a system like this—can run two 120V outlets at the same time?

 

[krby]

Please forgive my novice vocabulary.

No problem, that's why people post here, to learn!


A few questions:
* Does it need to be portable? Or just not permanent install?
* Do you want to power existing outlets in your home? Or is it ok if the "box" you build has it's own outlets (like a portable gasoline generator does).
* Do you need to automatically "turn on" when the grid AC goes away, or is this a thing you'll wheel into the house, turn on, and use as needed?


I'll try and help with some basic component definitions.
Most systems break down into sort of three rough areas:
* Storage: A battery bank (a way to store power for later, sort of like a gas tank)
* Charging: One or more ways to the battery bank (solar panels, a gas generator, AC power from the power company.
* Load: Some way to use the power from the battery. Since batteries provide DC power and most folks want to use AC appliances, you need to convert DC to AC. You asked what an inverter is, that's what it does. An inverter converts DC power into AC. In the US, typically 120V AC.

There is a bunch of gear and jargon in each of those three areas, but that's how I tend to break things down, charging, storage, and load.

One thing to note about portable vs powering two 120V 15A circuits. Each of those is 1800W, so if you really need 2x1800W you're going to be burning thru quite a bit of power very quickly. That means a bigger battery bank (aka a bigger gas tank) which will be heavier. Since battery capacity is expensive and heavy, folks tend to get really careful about the actual power needs. It would be useful for you to check the exact window AC unit and see what the power draw is. It may pull 13A for a second on startup, but then settle down to something smaller. The cooler is another example of "needs a lot of current when the compressor kicks on, but it doesn't run all the time". As an example, I measured my home fridge and it needs about 500W for really small period. If I average it out over 24hrs, it the same as running a 65W lightbulb for 24hrs. My point is measuring actual power needs is important because more power means more cost and weight in the entire system.

 

[ColdSun]

Thank you

* Does it need to be portable? Or just not permanent install?
[not "portable." Just possible to break down and take in one or two trips in my cargo van to put elsewhere. Modular. For sure not part of the house if I sell the house. Panels in the yard, not on roof, etc. Fortunately I have enough space.]

* Do you want to power existing outlets in your home? Or is it ok if the "box" you build has it's own outlets (like a portable gasoline generator does).
[Definitely a box, maybe the outlets of the box on a heavy guage cord I can move around. ]

* Do you need to automatically "turn on" when the grid AC goes away, or is this a thing you'll wheel into the house, turn on, and use as needed?
[Turn on as needed.]

I'm thinking panels outside, with protected wiring running to the garage with battery bank and electronics, and a heavy gauge cord with a couple outlets in a box I can drag around 15-20' away from the battery bank.

I plan to err on the side of extra weight and expense, until I get some input on what exactly that means. Worst case scenario is that I use it more often for heating and cooling to save on my bill and have a powerful backup system in case of emergency (a simple splitter running multiple items).

But once I have some input I may realize I'm thinking too heavy and expensive.

I'll apologize just once more for the dumb questions I know I'll be asking. Really rudimentary stuff I don't know about electricity.

 

[ColdSun]

3500 - $4000 budget

 

[krby]

It feels like like you might be happy with a DIY "portable power station" or "solar generator" (use the forum search to find examples, Will has some recommendations too) except you don't really need the portable part. The basic components you're going to be shopping for are:
* Solar panels
* A solar charge controller (takes the power from the panels and uses it to charge your batteries)
* A battery bank
* An inverter to convert power from the batteries into 120V AC power.

Start looking at Will's recommended systems like this one:

RV Solar Power Blue Prints

Building a vehicle mounted solar power system? Let me help.

www.mobile-solarpower.com

Read through that one and others to get familiar with the names of things and how they connect.
This is also a good starting point.

FAQ

The Basics: Solar Panels: Batteries: Charge Controllers: Inverters: Converters: Wiring: [/LIST] Grounding (Shorts): Breaking (Over-current): Clamping (Surges): Putting it all together: Safety and Troubleshooting: Other Good References:

diysolarforum.com

For the basics on electricity as it applies to these systems, try this: https://diysolarforum.com/ewr-carta/needtoknow/

IMO, where you need to start if figure out how much power you actually need, and how much capacity. It might be helpful to think of power (watts) like gasoline and capacity (amp-hours, or watt-hours) like the size of a gasoline tank. Example:
If you need one gallon to run an engine for an hour and you have a four gallon tank, you can run the engine for four hours. Back to electricty. If need to run an 1000 watt appliance for 4 hours, you need 4000 watt-hours of battery capacity. The reason it's important to figure out your power and capacity needs first is that everything you buy is determined by this.

If you just decide "two 120V 15A circuits", you'll be probably be over buying for everything, but it will work. Here's an example of how using more careful power needs can help.
Your example is 2 outlets, each 120 volts x 12 amps (15A circuits in a house are usually rated for 12A continuous) = 1440 watts. Two of those is 2880W of output. Let's want you need to run full out for 24 hours. 24hrs x 2800W = 69120 watt-hours. This is usually given in kilowatt-hours instead, so 69.120kWh. So your system needs to provide about 3000W of power and you need a little over 69kWh of usable capacity. When you start pricing things, you'll see that is a lot of battery capacity for a starter system.

Instead, maybe you look for specs on the fridge and the window ac unit (often on stickers, the back panel, or a website) and decide that while you may need about 3000W peak, but averaged over a day, you really only need 300W. That's 7200 watt-hours, or 7.2kWh. That's a lot smaller system. A REALLY helpful tool to figure out your exact load is a kill-a-watt or something similar. You can record total usage (kilowatt-hours or kWh) for an day.

Once you know both your power (watts) and capacity (kWh) needs, that will let you know how big an inverter you need and how much battery capacity you need. With that you can then start to decide how much power you need from solar (how fast do you want to recharge this?).

If all this is overwhelming, one place you could simplify is to buy an all-in-one solar system, that one piece of gear will be the "hub" the panels, the battery, and the load (the 120V AC outlets) will connect to. You still need to estimate your power and capacity needs.

One last thing to an already too long post You'll come across this choice of 12, 24, or 48V (volts) system. Roughly speaking, the more power you need (3000W is my guess where you'll end up), the higher voltage system you want. This is because watts = volts x amps. Getting 3000W from a 12V system is 250A, getting the same 3000W from a 48V system is 62.5A. Why does that matter? Lower amps means smaller gauge wire and generally less power loss to heat. It's the same thing with electrical extension cords. Why is it bad to run a circular saw (~1500W) over a very long and very small extension cord? Because (simplifying a bit) a lot of amps running down the cord heats it up and that can be dangerous. larger diameter (bigger gauge) cord have less resistance so heat up less for the same number of amps. This is also why some appliances are 240V vs 120V.

 

[ColdSun]

This is super helpful. Thank you. I guess where I'm wanting to splurge is in the components where I can grow the system LATER if I want more power. So--charge controller and inverter, right? So I'd like to "oversize" those components, even if I start out with fewer panels and smaller battery; where I could start out with a 3000W system, but maybe later grow it to a bigger off grid system without replacing those components. (Am I saying that right?)

I'm following a couple of the other beginner threads now. Thank you. What a resource!

 

[krby]

You are saying it right, yes.
Ok, if you think you're at about 3000W of output now and you think you might want to grow, I suggest looking only at 48V systems. The system voltage is the thing that's hard to change later. That means a 48V charge controller, 48V battery bank, 48V inverter.
Sizing the inverter is kind of a simple, problem. If you think you want 3000W output at once, round up and go a little higher. Also, buying a charge controller separate from the inverter vs an all-in-one would let you upgrade those separately later if needed.

Adding batteries later to an existing bank is not as straightforward. The general advice to to use the same capacity, age, and manufacturer in a single battery bank. It can be done, it's generally possible with LFE (LiFePO4) batteries but not really with SLA (lead acid) batteries. But requires some planning and care.

 

[Rednecktek]

If all this is overwhelming, one place you could simplify is to buy an all-in-one solar system, that one piece of gear will be the "hub" the panels, the battery, and the load (the 120V AC outlets) will connect to. You still need to estimate your power and capacity needs.

This is especially useful if you're working with a tighter budget as you can't buy the 48v inverter, 48v SCC, transfer switch, and AC charger for near the lower cost of the All-In-Ones. Since you're looking at a huge battery bank and that's going to be the most expensive part of it, saving quite a bit on the parts and wires and fuses that will be required for a component system adds up quick.

Heating is going to be the real killer. To put it in perspective, your bog standard electric heater wants 1500w and your bog standard 100Ah 48v battery (at near 100lb) will run that for about 3 hours. Air conditioners can be quite a bit better if you spend more up front for the inverter heat-pump style units that can also provide heating. Since you're wanting to be able to take this system with you, you'll be looking at window or free standing dual hose systems. Madea makes a few good ones that you'll want to look at for this project. The saying for heat is "Anything But Solar" because it requires a LOT of power for a LONG time which requires a LOT of battery.

Somewhere in the Resources section is an Excel sheet for doing a Power Audit. Start plugging in the numbers from your units (fridge, heater, lights, etc) and tell it you want a 48v system (just go to 48v right out the gate, it makes upgrades in the future MUCH easier) and it'll automagically calculate how big your inverter needs to be, how much battery capacity, and how big the solar array needs to be. You'll be running through that sheet at least 3 times.

First run: Put in everything you could ever want. Heaters? Sure. Jacuzzi? Go for it. Margarita-Master-9000? Why not! This'll get you used to how the form works and show you how things all work together.

Second run: Put in only what you absolutely need like the beer fridge and a couple light bulbs. This'll show you just how much your other systems affect the sizing and config of the system.

Third run: Now that you kinda see how the watts and amps and watt-hours all work with each other, put in what you ACTUALLY want it to do. This is where you'll see just how big your battery bank adds up and how much yard space you're going to need for all those panels.

As you get more used to how everything works, you can start tweaking loads here and there to get something that you can actually afford that will still do the job, or find better ways of accomplishing the same job (may be time to replace those Halogen lights with LED for example).

As for the portability, mounting the component guts on a hand truck you can just stand up in the corner of the garage makes everything more portable and gives you a good flat board to screw everything to at the same time. Adding and disconnecting batteries is much easier when they're just stacked in a corner and you can tackle them one at a time since the batteries are going to be HEAVY after the first couple. People like me who build their batteries with the really high capacity cells do it with the understanding that we're not going to have to move them very often so we can get away with building batteries that are 3x as heavy, but even then things like my camp battery ended up being 5 boxes and assembled on site because there was no way my old broken as was lifting that thing once assembled. ?

So, step 1: Go grab the Power Audit form from the Resources section.
Step 2: Start grabbing the amps and watts numbers from the things you want to run. A Kil-A-Watt can be really REALLY handy for that, just be prepared to let it run for a week or so on each device so you can get a more accurate picture of usage over time. As cheap as they are you can always get 2 or 3 or more and let them all plug along at the same time. Throw one on an electric heater if you want to cry yourself to sleep at night.
Step 3: Start throwing numbers from the devices into the Power Audit form and see what it comes up with.
Step 4: Keep us up to date as you go along so we can help fine tune things as you go.
Step 5: Post pics! We love that kind of thing here. ?