What makes an effecient build?

[Bossrox]

Input on putting together a well balanced system

Here is the place where you ponder the ?'s of how much of what you need in system components to accomplish your desired goal, so ask your ?'s or if you know some of the answers, tell us what you know.

My 1st ? would be for instance, it's my understanding that it takes more energy to recharge batteries than what gets drawn off them. If that's true then let's say i draw 2 kw from my batteries, how much more than 2 kw will I need to produce to replace that 2kw. then once I know that, I have to take into account how much panel power will I need to service my typical demand with enough excess to deliver what the batteries need to recover & keep them topped off.

I'm pretty sure that the condition of the battery has a lot to do with it. Older batteries will likely be more resistant taking a charge than newer 1's. This might be only figured out thru trial & error but I'm wondering if there's a formula of averages as a guideline. It wouldn't be too hard to figure out if everything was 100% efficient but that's never the case, there's many variables.

Update: Now that I'm well into testing my current set up with 4000 watts of panels, 550 amp/hrs battery bank, 100 amp charge controller & a 4000 watt sine wave inverter..... In a perfect world of 100% sunshine everyday, I should have enough power generating ability to make & use at least 20 kw a day however in my 1st month of documenting my real world stats, they were 250kw generated & used from solar for the month & 200kw from the utility company which averages 15.5 kw total use per day so with an abundance of cloudy weather issues & inefficiency of power in vs. power out with batteries, a system that would seem more than adequate to do the job, wasn't enough to even get close.

My estimation to get close to energy independence from what I've seen so far is I'll need another 6 solar panels, a 2nd 100 amp charge controller & about 350 amp/hrs more added to the battery bank, so there's another 3 1/2 grand worth of stuff, not including the 5kw inverter for a grand I really want to get, so my advice is if you jump into this with over optimism like I have & what you got & think should be adequate to reach your energy production goal, I'm finding you'll ultimately be disappointed but if you got the bux you're willing to throw into it & in it for the thrill of achieving victory like me, it's a rather challenging, addictive & expensive hobby for sure!

[Bossrox]

Is panel wattage the same as house wattage?

As far as I can determine, watts is watts no matter whether it's dc/ac or 12 volts/ 120 volts I haven't found anything that would conflict on that principal. Do you electrical experts have any other input?

[Bossrox]

My rudimentary estimate for designing a balanced system

This system design is based on my own needs but the parameters I'll use for it should be helpful for your own planning.

I started this off as a hobby project & was only aiming to trim some off my utility electric use but has grown into building it wit the goal to have very little need for utility power, so here's the planning that's got me where I'm at now.

I'm assuming most utility services nowadays have your usage stats available on their site in graphs so you can see what your usage looks like.

For me, I'm using an average of .5 to 1.5kw p/hr with the house just on idle, not counting when the water heater, various winter heaters, 2 A/C's, the washer or dryer is active, so let's just average that to 1kw p/hr for 24 hrs for 24kw as a baseline.

So if I wanted to create 24kw of solar power a day, what will I need to cover that?

So far, I put together a 4 kw solar panel array tied into a 4kw inverter so if I have full sun in a day, about 4 hours is peak output which amounts to about 16kw, then 2 hours before & after peak I'll guess that 2kw should be about right so add another 8kw for 24 kw total.

So It looks like I can generate enough power to supply every bit of my typical daylight use & have plenty left over to charge the batteries & get me thru the night providing I have a big enough battery bank. Theoretically I should be able to cover my typical use & finding that I am but haven't fired up the 2 a/c's yet so it looks like I might be a bit short of my capacity needs or darn close.

Side note: After much testing, about 18kw is the best I've been getting.

Being my system has been up & running for the past month here in the spring, I can tell you that on a full sun day, I can run all day with less than 1 kw a day help from the power company so my estimate is working out pretty close right now but will likely change once the a/c's get fired up.

1 of the things you have to take into account is losses of inefficiency of the batteries & inverter. Since I'm using flooded & just recently added some AGM batteries, from my understanding, it takes around 30% more energy to restore them to full charge than what you draw out. Then inverter loss in most cases is about 10%.

40% estimate of loss in my real life usage experience being it's spring & not requiring a/c at night yet, I'm only using about 3kw overnight & if I don't use the a/c during the day, my batteries will be fully charged around 1 pm but if I do use the a/c during the day, it takes til the end of the day for the batteries to get a full charge so it appears those loss figures could be realistic just from my cycling time observations.

2nd thing is matching your charge controller to your panel capacity. I started out with an 80 amp charger but my panels can crank out 100 amps so I wasn't utilizing its full potential, Now I have a 100 amp charger & finding I can produce more than I can use or store so more batteries are needed to store the unused potential & squeeze every drop of energy I can create.

I got lucky & without knowing or planning for it, my charger & panels are a perfect match for each other. 100 amps panel output & 100 amp charger, a totally efficient companionship. If I later decide for more panel power, I'll have to add another charger since the current is maxed out or switch to a 48 volt system that will double the chargers output

If you get bitten with the bug like I did, you just wanna go bigger so I'd recommend getting a bigger charger than what your panels can generate, that way you can add more panels without having to upgrade or add another charger.

3rd thing to plan for is your battery bank size. When the sun is gone & you're totally on battery power, draining the batteries past 50% consistently will shorten their lifespan considerably & as expensive as they are you' best make your drain target more like 25% or less, you sure don't want the expense of replacing batteries very often.

You'll get 1kw of power for every 83 amps of battery power but that's if you fully discharge it which you definitely want to avoid, if you want the battery to last, half a kw or a 50% discharge is the most you should allow for & 50% isn't a good goal to shoot for.

If you want to get a good long lifespan from your bank, a target of 25-30% discharge will just about double their life. There are some batteries that can tolerate deep discharges & still have a long lifespan but they're more expensive than than most can shell out for.

Now in my case, if I want to run entirely on battery power from sundown to sun up, I'll need to generate about 5-6 kw overnight if the ac's are in use so I would need at least 540 amp/hrs to get there. In my case I have 550 so I'm about right on but that's pushing my comfort zone on battery drainage to undesirable. I don't want to stay at 50% discharge very long & as soon as I run across a good battery deal will add at least another 250 amp/hrs with a goal to get up to an ideal 1000 amp/hrs.

Last but not least is inverter power. I have a sine wave 4000 watt inverter with 12000 peak & it has hung up & shut down trying to start my 120 volt well pump which draws an enormous amount of power on start up so I had to switch it permanently to utility power, but along with all the normal electronics, a frig, freezer, toaster & 2 window a/c's as long as none of them start up at the same time, is plenty of power to handle my typical usage but anything smaller would be a pretty good strain so 4 kw is the least I'd go with if you're dealing with a similar demand. I'd really like to upgrade to a 8kw tho.

That's all I can think of for now, hope this info helps out in your system planning.

Update: The previous, I wrote quite awhile back. Since then I've found my adequacy conclusions are ok for ideal solar conditions but sometimes there'll be extended lack of it. We're going thru a 5 day run of total overcast as I write this & I've doubled my panels since the previous post.

With 24 panels, I've averaged 3.5kw's production per day during this extended overcast spell which is severely short of meeting demand & in scenarios like this has shown me that it would take at least doubling my panels to 48 & adding 1600 amp/hrs more in batteries to come close to meeting the demand of a long term low solar event like this.

[Bossrox]

Energy guzzlers you want to avoid while on battery power!

I recently discovered my frig went into it's defrost cycle after sundown which draws about 700 watts for about 15 minutes. Yours could be more or less but not what I want happening when running off batteries if it can be avoided. As I've now discovered, the frig goes into defrost twice a day, yours might be different.

If I was really ambitious, I could dig into the frig wiring & tie in a manual defrost switch but then I'd likely forget to run it sometimes & that can cause problems. So assuming the defrost cycle is in a regular cycle, I unplugged the frig for a short period, many multiple times to target when it kicks in til I got the timing so it engages during sunlight hours.

Unless you have adequate battery power to handle this, it's something you'll need to find a way to deal with.