Beginner Queries. How to match solar setup.

[solarnoob83]

Hello All,

I am a complete newbie to solar and all the numbers. Sorry for any silly questions.

I have a solar grid that has 12 panels x 550W = 6600W or 6.6kW (that's one number I figured out).

My question is, I want to pair this with a battery and inverter. What would be the most optimal options?

My current usage is not much, but this will be used for a small house that is being built. It's completely off-grid. More panels may be added later if the need arises. For now, I want the most optimal and maximum possible battery and inverter options.

I have the below options from a seller:

5.5 kW inverter + 51.2v, 200Ah Lithium Battery pack = 10.2 kW Battery and 5.5 kW inverter. Is it okay to use a lower inverter and more battery storage? Or should it be a higher inverter and lower battery? Or should I use a 10kW inverter and 10 kW battery pack? Since this is higher than my solar panels, what would be the downside? Slow charging? Would this be future-proof if I add panels later?

Another option is 5kW and 51.2v, 100Ah = approximately 5 kW battery and 5 kW inverter.

Or are there any other options recommended?

Another question is, what if my battery usage is minimal for now as the house is not done yet and the only connected things, for now, will be a pump for irrigation (2.2kW will be used with solar directly, and if no sun will use battery, watering will be for a total of 30 - 40 minutes max a day), CCTV cameras, wifi routers, and long-range wifi extenders, since this is Lithium batteries and there is no discharging as there is no usage, it would be ok right? The inverter will be protecting the battery correct? Will it in any way affect the life of the battery?

Thank you.

 

[solarnoob83]

An add-on question to this, since my solar array is 6.6 kW, if there is full sun, does it mean it can fully charge a 6.6 kW battery in an hour?

 

[Q-Dog]

An add-on question to this, since my solar array is 6.6 kW, if there is full sun, does it mean it can fully charge a 6.6 kW battery in an hour?

The panels may not output their full rating, and some charge controllers are more efficient than others, and batteries are not 100% efficient either, and it may not be a good idea to charge a battery at that rate. But yes, if the panels can output 6.6 kW in one hour you would make 6.6 kWh of power.

 

[shadowmaker]

I'm not the best one to answer this as I'm still a noob myself and grid tied, but here we go. Inverter needs to take care of your peak loads so you size it accordingly. You need to calculate your max possible usage when everything is on at same time. (irrigation pump, AC, heating?, stove, lights, micro, fridge, water heater, etc.). Also need to keep in mind that electric motors can take 5x more at startup so inverter needs to be able to cope with surge or you might need to install easystart devices to your motors. I'm grid tied so I don't need to worry about these at all.

You size your battery with days you want to get through without decent solar generation. If your average daily consumption is 5kWh, you need at least 25kWh battery to get through five days without solar. If you have a generator, you can get by with less battery, if not it's better to be safe than sorry.

For panels it's hard for me to tell how much would be adequate for your needs even if I knew your consumption figures as it depends on your location, daily variation (sunny, cloudy, rain, big storms), is your array shadow free, etc. For my setup I just decided to get two pallets of panels and it seems to cover my yearly consumption 100%, but there's no chance to go off-grid with it as biggest production is when my consumption is at its lowest. Winter here is no joke and it can be weeks/even month without sun. You should try PVWatts to get some estimate of your monthly production. It seems to work quite well with my setup. Just keep in mind that those are estimates and can easily have 30-50% monthly variation. Yearly estimates can vary some 10-20%. Panels are usually the cheapest part of any system so I'd overpanel to get decent production even when conditions are far from ideal.

Lifepo batteries don't mind being full or close to empty (not totally empty). They hate cold or heat though. Around +20C they are fine for years.

You should start by doing Energy Audit.

 

[Rednecktek]

Blurb time!

Well, I'll start the default answer to these questions and we can work from there. Here's you To-Do list:

1: Power audit! This will give you some important information on how big your inverter needs to be as well as how much battery capacity you'll need. There is a link in the FAQ section (I think, or someone here will post it shortly) so fill in the blanks and see what it comes up with. You'll probably need some sort of Kill-A-Watt to get accurate measurements. Are you going to be running a 12v system? 24v system? 48v system? What are the specs on your solar panels? VoC? Vmp? Being as this is a new build, throw together a wish list of what you want and estimate on the high side.

1a: Where do you live? Speccing out a system for Scotland is a LOT different numbers than Arizona due to the amount of light you actually get. Someone here can post the link to the PVwatts.com or JCR Solar Uber-Sun-Hours calculator sites to help figure out how much you'll have to work with. That will be a box in the Power Audit form.

2: Parts list: You don't need a make & model list, just a parts list to start from for reference. You'll need an inverter, a MPPT charge controller, fuses, shunt, buck converter, batteries, wire, etc. Once you have a basic list it can be fine tuned to make & models after that. If you're looking at the All-In-Ones check for correct voltage outputs (120v or 240v Split Phase for North America, 220v Single Phase for European type areas) and make sure it has enough capacity for a little bit of growth and fudge factor.

3: Budget!: Steak is great but doesn't mean anything if your wallet says hamburger. Figure out what you're able to spend now vs what you'll have to cheap out on now and upgrade later.

4: Tape measure! Figure out where you're going to stick all the stuff you'll need. A dozen 3000AH batteries sounds great until you're sleeping on the floor because there's no room left for a bed. Is there a compartment that can house all this stuff? Will the server rack batteries fit? Are you going to have to make space? Physics can be pretty unforgiving.

5: Pencil out what you think you need and throw it at us so we can tell you what you've missed (because we ALL miss stuff the first go-round ) and help figure out which parts and pieces you're going to want to get.

Well that's the thing about solar systems, there is no 1-Size-Fits-All answer. Your system will need to be designed to fit YOUR needs. When you design and built the system, it's not going to be the perfect system for me, or Will or 12vInstall or anyone else, but it Will be the right system for You and that's the goal.

As for where to get started, let me throw my standard blurb in here to help point you in the right direction. There's going to be a lot of math and research involved, but that's going to be a LOT cheaper than just buying parts off of someone's list and finding out that it doesn't do what you need.

Don't panic on the Power Audit, you'll actually be doing that a few times. When you do the first pass put in ALL the Things that you might want. AirCon? Sure. Jacuzzi? Why not. MargaritaMaster-9000? Go for it.

The second pass will be the "I Absolutely Need This To Survive" list that isn't going to have much on there.

The third pass will be the "This is what is realistic" audit that you'll use to design the rest of the system.

The Power Audit is going to tell you 3 primary things: 1: How big does your inverter need to be to power your loads? 2: How much battery bank do you need to last $N number of days with krappy weather? and 3: How much solar panel will I need to install to refill those batteries in a 4 hour day (the average usable sun hours rule-of-thumb).

Once you know what you Want and what you Need and what your budget can Afford there will be somewhere in that Venn diagram where those three things meet.

After that, THEN you can start looking at parts.

Yes, it's a long drawn out process, but it's worth it in the end. Not every house has the exact same floorplan, not every vehicle is the same make & model, and not every solar system is designed the same.