# Inverter Current COnsumption?

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Hello,

I'm new to this forum and find it really interesting because of the technical topics and discussions which

Anyway, I have a small system which consist of the following PV components.

1 - 65 Kyocera Panel
1 - Steca 12V/5A Charge Controller
1 - 125 AH Energizer Deep Cycle Battery
1 - 1000 watts continous Go Power Inverter
1 - Go Power Class T Fuse Block (Rated 110A) between inverter and Battery

Reason why I purchased these components is to try what the outcome will be based on my
technical readings. Im quite happy with the systems performance as far as powering my
Car Stereo, Charging my Portable DVD, Cell phones and other small electronic devices.
I already got the power output per day given by the system which is 350 watts per day.
Takes 4 to 4.5 days to fully charged my 125AH Deep cycle battery. By the way only the Car
Stereo is the one connected to the DC load from the charge controller. The rest are plugged
to my Go Power Inverter.

Quite confuse on how much power eat by inverter given the load connected to it.

My QUESTION is
1. How much power does the inverter get from the battery if for example I plug in my
100watt TV?
2. Can anybody give me a computation for this?

Thanks in advance and more power.

Francis...

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Re: Inverter Current COnsumption?

Power (in Watts) = Volts x Amps = 120volts x 1amp = 120 watts = 12 volts x 10 amps = 120 watts

The inverter will cost you somewhere around 20% losses / 80% efficiency (guess as starting point):

Power from Battery = Watts/Efficiency = 100 watts / 0.80 = 125 watts (100 watt TV needs 125 watts from battery)

Remember the battery will drop from 13 volts to near 10.5 volts under load. So, current from the battery will increase as voltage drops (inverter/TV are basically a constant power device).

Also, make sure that you don't use much more than 50% of the battery's capacity (AMP Hours or Watt Hours) or you will damage its ability to take and hold a charge.

The 1,000 watt inverter is probably way overkill for one 125 amp hour battery (the inverter will pull close to 100 amps at full load--and the battery will be flat in an hour or less (batteries are not perfect--at higher currents they provide less power/capacity overall). At best, you can get about 20-30 minutes of full power (1,000 watts) before the battery is damaged.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: Inverter Current COnsumption?

Thanks BB for the informations and advise.

I do not pushed the battery to the limit ( below 50%) which causing short life for the battery
as you stated.

Does it mean that I need to add battery in case I will increase my AC load using my 1000watt inverter?

Again thanks.

Francis...

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Re: Inverter Current COnsumption?

Well, you have to understand how much, how long, and what types of loads you are planning on using.... I don't know where you live, but if it is in a northern latitude / desert type area... You are looking at 2-6 kWhrs per day per sq.meter. Or, roughly 2-6 hours of full sun equivalent.

Your 65 watt array, will max out (in cool weather) typically somewhere around 57 watts max. Assuming 80% efficiency on charging and 80% efficiency on inverter and 2-6 hours a day of typical sun (winter/summer), you will be able to run a 1,000 watt inverter load for xx per day:

Inverter@1,000 watts = 57 watts * 2 hours * 0.8 * 0.8 / 1,000 watts per hour = 0.073 hours or 4.3 minutes per day (winter)
Inverter@1,000 watts = 57 watts * 6 hours * 0.8 * 0.8 / 1,000 watts per hour = 0.219 hours or 13 minutes per day (summer)

A 100-125 amp*hour 12 volt battery will probably only supply about 10-20 minutes of power before damage occurs.

A bank of batteries (probably 20-40x the capacity of the single 100 amp*hour battery will probably run not 20-40x longer, but 40-80x longer because the batteries are more efficient at delivering power at a 20 hour rate than a 1 hour rate.

And, lastly, the type of load may define the type of inverter you can use--a modified sine wave inverter is cheap, but generates close to a square wave rich in harmonics which will cause overheating in many motors and appliances. A sine wave inverter (at 5+ x the cost and usually heavier) will do a much better job of running reactive and non-linear loads (motors and electronic loads would work better on a sine wave type inverter).

What do you need in terms of batteries (and solar panels), depends on how much power you need and where you are at--and can you use a generator when the sun doesn't shine?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: Inverter Current COnsumption?

Thank you so much BB.

Im living here in L.A. California where peak sun is 5 hours.

Please correct me if my understanding is correct or no... Assuming at 1000w/m2 irridiance or full sun,
using my 65watts panel, charge controller and directly connected to my 1000watts Modified sine wave,
My understanding is that my system will only produced 65watts output even if I used a 1000 watt inverter.

Francis...
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Re: Inverter Current COnsumption?

Solar Fanatic,

Solar panels only generate electricity when sun is shining on them... The 57 watt rating I gave you is an estimate of the power generated on a cool day with a bit of wind near high noon on a clear summer day--it is the number that California uses for calculating rebates as the manufacturer's numbers are way higher than anyone would typically find (except in cold/subzero conditions)...

Solar panels are "solar batteries" and only, at full sun (near noon with clean and cool weather) will output their rated voltage and current. Anything else will typically reduce their output dramatically. Typically, solar panels are only used in these types of applications:

1. Solar Panel charges a rechargeable battery during the day. The rechargeable battery supplies power at other times (either directly or through inverters, or a combination).
2. Solar Panel connects to Grid (AC utility power for home/office). If sun is up, panel/inverter "injects power" into the power lines (and can spin utility meter backwards.
3. Direct Solar Panel to load. Typically water pumps (from well/lake into tank, or circulating hot water to storage tanks, running swamp coolers, etc.). Useful when power is only need when sun shines or if other storage device for non-sun periods.

For your application... The solar panel supplies power from the sun. The "inverter" just takes the power available (say 12 volts at 10 amps DC) and converts it to another voltage/current (say 120 volts at 1 amp). The inverter (think of it like an "electronic" transformer) cannot create power, only the solar panel (or battery) can do that.

And, yes, as you describe, the inverter would only be able to take 80% of the panel's peak power (say 57 watts * 80% or 45 watts) and be able to output 45 watts of 120 volts AC (at 0.37 amps). That is the "ideal or theoretical" inverter. In practice, the only widely available inverters that run directly from solar panels are those for Grid Tied power applications (there are a few other specialized types used for water pumping--but no need to confuse the issue more here)... You will not really find any commercial Solar Panel/Inverter combination (other than Grid-Tied) that you would plug a household appliance into. If you tried this with your current solar panel/inverter you would probably find it would not work at all--The small solar panel would probably not even be able to start up the inverter--or as soon as you placed any load on the inverter, the inverter would shutdown because the solar panel cannot supply enough energy.

There is also another issue, the typical inverter cannot handle the wide voltage range available from a solar panel (a 12 volt panel can actually output between 17-23 VDC or so--probably high enough voltage to damage the inverter).

The reason nobody makes a solar panel / inverter combination for home use? Think of it this way... The solar panel cannot store energy and neither can the inverter or the typical electro/mechanical load (blender, light, TV, etc.). So, to optimize the system, you connect the solar panel (through a charge controller) to a battery. The battery can take any power from the solar panel to charge (typically morning/evening a little power; mid-day near full panel rating) into the battery. Now, you have a rechargeable battery that can supply the power required by the load (day or night). Either a little at a time for a long time (lights/radio in evening/night/morning) or a lot of power for a short time (microwave oven, electric drill/pump, blender, etc.).

The Grid Tied inverter is a special case--basically, you are using the Electrical Utility like a giant battery for your home or office... Here the Solar Panels (typically lots of them) supply power to a special inverter that can take any power (within reason) from the solar panels and use it to "push" AC power back into the powerlines ("recharging the electric utility) and out onto the utility grid (to be used/shared by your neighbors).

I will stop here--I am running the risk of typing too much and not really answering the "simple" question you asked (your question is not really simple--there are many dependencies and while the answer is no for your question as asked, there are ways it can be done and make sense to do it--but it only for specialized uses).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: Inverter Current COnsumption?

Hi Bill,

I do appreciate all informations that you gave.

Now I'm getting more involve and very interested with the PV system.

I think I have to upgrade my system based on your infos and the power that I need
to supply my AC loads that I need to be run.

I thought my experienced and Knowledged in Electronics are enought for me to
build my PV system confidently, but its not after I hear your genius advise. I
even bought a book from SEI "Photovoltaics Design and Installation Manual" and even
download e-books to support my PV system, which I'm still doing up to this time.

One more thing, my 65watt panel w/c connected to the Charge controller( w/o the battery,
just to regulate the voltage that will be going to the inverter) and lastly to the inverter.
My panel were able to power the inverter but can only power small electronics. Plugging
my Dell Desktop with the Flat screen wont run due to power requirement issue. The Inverter
do alarm whenever I plug high wattage (greater than 65 watts) devices.

I'm planning to buy additional panels to continously power my 1000 watt inverter during
daytime. As per SEI book I bought, I need to add at least 10% power from the panels to be
safe or continously supply the power to the Inverter. Does it mean that I will be needing
1,100 watt panel (10 * 110 watt panel)?

Thanks.
Francis...
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Re: Inverter Current COnsumption?

Francis,

What a cool idea to connect a solar panel to a solar controller to an inverter (without the battery)... It is very interesting that it works for you at all.

There are many types and manufacturers of inverters and solar chargers and I would not count on it working in all conditions/combination.

Another question I would have for you is why would you want to connect this to a desktop computer system? If the sun went behind a could or a big bird landed on your panels, your computer would loose power and crash...

If you took your system (solar panels, charge controller, and inverter) and simply add a storage battery (or several), you would have a standard solar system (storage batteries are not that expensive) with UPS backup.

But, my questions still remains... Do you have utility power (conEd, PG&E or something similar). Why are you doing this, to save money, to go green, to create a portable workstation, a computer system for a remote location, or something else? Is money not a problem? Is maintenance an issue? What about winter operations and cloudy weather, etc...

I am not sure that I am being quite helpful here yet to you.

But, as that has never slowed me down before, , I will recommend several more things. One is to purchase a kill-a-watt meter for \$25-\$35 or so... Name plate rattings just don't supply the information needed to optimally design a solar power system where solar is expensive electricity and you can usually save a whole bunch of power through conservation and choosing appropriate appliances for your needs:

http://www.amazon.com/P3-International-Kill-Electricity-Monitor/dp/B00009MDBU

Next, do you really need a desktop system? Typically, laptops, because they are already designed to run on battery power are a good choice to use with solar. I can use my desktop system which uses 400 watts or my (now old) laptop that runs at 20-30 watts (and 1-2 watts in standby) and already has a built in UPS (the laptop battery). If you need, for example, a large screen, connecting one to a laptop is probably still a better idea (in terms of power management).

Again, if you have utility power, and that is all you need look into conservation (to reduce your power needs) and into Grid Tied inverters with solar panels... Grid Tie will not give you battery backup (without spending a bunch more money) but they are by far and away the best bang for the buck for going green--and they don't have the maintenance issues of battery banks (and battery replacement every 7-15 years or so).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: Inverter Current COnsumption?

Thanks again Bill.

That system really work on me and I was amazed also by the result which trigger me
to upgrade my system in the future.

I connected the desktop to my system without the battery just to try if the system can
power it up, but its not. I know it will crash my computer once the light is interrupted
since I dont have a backup battery or UPS.

We have a utility power here which is the Edison. I want to build a 1Kw system to
save with electricity bills. And I'm thinking what will be the best approach or design
or the cheapest(with good quality) way I can do this...

Also I have a plan also to purchase 2pcs. 10watt panel which can produced 1.2 Ampheres
just enough to power up my Laptop and at the same time charging the incorporated
battery on it. What do you think?

I think I need to buy that Kill-a-watt device to measure my electric consumption.

Thanks,
Francis...
• Solar Expert Posts: 10,300 ✭✭✭✭
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Re: Inverter Current COnsumption?

it will work, but i consider this a waste just to save on the cost of a battery and i can't think of too many uses for it with it's 'use it while it's there' form. a solar fan that is 110vac is one such application that would come to mind. i can't see the practicallity of you skipping the battery as your pc would drop out as a cloud passes. it is one way of only using what is produced though, but it is too erratic to really be practical.
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Re: Inverter Current COnsumption?

Francis,

Personally, don't waste the time and money on 20 watts of solar panels for a laptop that is used around home, car, or other places with power available. Just to keep up with the PC, you would need about 2x the power in panels to account for all of the inefficiencies and stuff...

What you need to do is:

1) Conserve. Look at your current monthly power bill... If don't use AC, have natural gas for heating/cooking, then compare your bill against the averages for your area. I can easily keep my home's usage in the 200-250 kWhrs per month (near SF CA) just by using CPF Lights, newer fridge, hand washing dishes, laptop instead of desktop, turning off/unplugging wall transformers/digital TV receivers/TV sets when not needed, using natural light, insulating walls and vinyl double pane windows, etc. for my home with 4 people occupied 24x7 for work and schooling.

2) After conserving, look at Grid Tied Solar. The Grid Tie inverter is not a very expensive unit. Where you will spend the most money is for the solar panels and installation. And, it will only work if you have good southern exposure with full sun from roughly 9am-3pm. If your lot/home does not have this, Solar is not really going to work well for you. California still has good rebates and the 1 year net metering (using the utility as your unlimited storage battery for a \$6 per month minimum connection charge is a great deal too).

3) Look at your other energy usages... Natural Gas is getting pretty expensive--solar hot water and solar hot air heating is not a bad thing to consider... You don't need nearly as much roof space, the panels are much more shade tolerant than Solar PV, and, to save the same amount of money, solar heating is generally much cheaper to install (altough solar heating probably has more maintenace requirements than grid tied solar PV).

Anyway... Have fun!

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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Re: Inverter Current COnsumption?

I think it's great that you are interested in solar energy and hope you keep at it and that it all works out for you.
That said, I fear you are barking up the wrong tree with some of the ideas you are working on and that the result will be wasted money; dissatisfaction; dissapointment and a turning away from "useless" solar. I believe seriously that you really do need to listen to these guys who are trying to offer a helping hand. Believe me, they really do know what they are talking about, they've been around the block with solar and it works for them and it works for me.
Cheers
Wayne
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Re: Inverter Current COnsumption?

Thanks guys. You really educate me and I appreciate that.

Our average monthly power consumption is 150Kw.

Can you give me an advise on what PV system appropriate for me.
We are getting a full sun here most of the time in Southern CA.. We are
near the valley so its prety hot especially during summer time.

The reason I want to pursue with the 20Watt panel is that I will only be
using that during emergencies when Im not at home, also to promote
solar power to my friends.

Thanks,
Francis...