balance in W between pv array and inverter

robocop · May 2017

Have read should the pv array in watt be more than the inverter?

should be a ratio between them?

could somebody explain

thnks in advance

bob

Photowhit · May 2017

You can make a ratio between the inverter and array, but more important would be inverter to battery size and type and application and location!

You should think more toward planning out a system.

Lead Acid batteries are rated according to their discharge rate, normally over 20 hours. So if you have a 12 volt 100 amp battery it is rated to deliver 5 amps an hour for 20 hours. If you discharge the battery faster than 5 amps an hour the effect is that you lose more than 5 amps from the battery bank's remaining capacity. This is NOT to say a higher load isn't normal. It's just important to keep in mind.

Example if you have a desert location and the systems sole use will be to microwave soil samples for a 1minute every other day you could have a small 400watt array feeding a 2-4 GC battery bank and a 1500 watt inverter to deal with the microwave. An extreme example. Something I've done, with a 1000 watt array but a 1400 watt inverter to start and run a window air conditioner due to the starting wattage needed, but running wattage around 440 watts.

You might also have alternate means of charging the battery bank trying to 'grow' a system with a smaller array with generator support, because you understand that to add batteries later would be difficult, but you could add panels.

I'd say not having an array wattage smaller than your inverter wattage isn't a bad thought, but not a hard and fast rule.

I like having a battery bank large enough that your major normal load longer than 1 hour doesn't draw more than 1/20th of your capacity, but I violated that with the 'window air' example above, and violate it 'sort of' now often running a 1000 watt+ load running a water heater during the day. (I say 'sort of' since this load is on the array and not the battery)

robocop · May 2017

thnks for your time friend

It will be a 48v/400ah battery bank as this is for a couple of houres a day about 3600-400 continuous inverter and have in mind 315w panel load is about 2800 wh inverter airconditioning

Will this give you a better idea so you can help me better?

mcgivor · May 2017

robocop said:

Have read should the pv array in watt be more than the inverter?
should be a ratio between them?
could somebody explain
thnks in advance
bob

You are asking a very complex question which involves loads, battery capacity and solar availability. There is no simple answer without details about what it is you are trying to achieve, if one was to simply give a ratio without knowing all the details, my belief is that such information would be misleading. For example if there are daytime loads which exceed the array output, there would be a need to have a larger array to satisfy both the load and the battery charging requirements. The ratio would be based on the difference between the two, without information, there is only speculation, my opinions, others may disagree.

Raj174 · May 2017

Hi robocop,
Although the power of the inverter and the array are often similar, they are not arrived at that way. First the battery size is based on the loads and then the PV array is sized to charged the batteries. The inverter is sized based on both surge and continuous power requirements of the load.
Rick

jonr · May 2017

As others have said, size your inverter according to your peak load (often starting a motor). Size your batteries, charge controller and panels relating to wh/day (and other things). You need 2800 wh/day? If so, 315w of panel isn't enough.

robocop · May 2017

thnks JONR I need 2800w for about 4 hours a day have a 48v 400ah battery bank need to know how many panels 315w needed if on panel only or just to charge the battery bank.Or a combination of the 2. A 4000w hybrid puwrese inverter is enough so I can use more panel in the future? plse explain thnks

jonr · May 2017

So you need 11200 wh/day (2800x4). Or 11.2 Kwh/day, during the day (I assume). Others know better, maybe 15 or 16 panels (don't use this number) which is roughly enough to power your load and bring the battery up from 50% SOC. Where is your location? You can use a generator sometimes?

robocop · May 2017

I learn volt x amp = watt thus 48v x 400ah =19200 wh I ythink I have a battery bank of 19200 w?? somore that the 11200?? I am in curacao in the tropics like sure 6.50 hrs per day sun its summer the whole year

Photowhit · May 2017

robocop said:

thnks JONR I need 2800w for about 4 hours a day have a 48v 400ah battery bank need to know how many panels 315w needed if on panel only or just to charge the battery bank.Or a combination of the 2. A 4000w hybrid puwrese inverter is enough so I can use more panel in the future? plse explain thnks

I think we went through this in another thread. I don't know if we ever established when your loads are? I think it was just an air conditioner. But of course an air conditioner doesn't run at the same wattage all the time, it uses far more electric when the compressor is running. If you want to run the air conditioner when the sun is shining and the batteries are full, much of the load won't come from the batteries.

It's all a big math problem, to solve it you try to have all the factors.

Will there be an alternate source of energy? which branches to< If you will how much do you want to exclude running it, if not, what is the least amount of charging and can you do with out to save your battery? If you need it then What is the shortest amount of sunlight you can expect during the time of year you have the load? How many days will the sun not shine due to weather?

We can solve for straight battery use, and % of battery capacity. If you have 2800 watt load for 4 hours and have a 48v 400 ah battery, you have a battery with a capacity of roughly 48x400= 19Kwhs, If you have a load of 2800 watts (including the inverter) That is roughly 1/8th of the battery bank capacity so you will effectively drain roughly 3500 watt hour every hour or @73 amps, after 4 hours with no supplemental charging your voltage will likely sag and have the inverter shut down.

We can likely have better results if we had better numbers, perhaps 2800 is watt hours total?

robocop · May 2017

2800 w is the total of watts the the inverter aircon use .

y question was in the beginning that my total panel wattage should be more than the wattage of the inverter?

Can I use a combination of the panels and battery bank?

jonr · May 2017

Yes, you want the panel wh/day to be more than the AC wh/day. Because the previous day may have been cloudy and the battery was discharged. So you need extra wh/day to charge it. There are also losses, so you need extra wh/day for this too.

Photowhit · May 2017

robocop said:

2800 w is the total of watts the the inverter aircon use .

y question was in the beginning that my total panel wattage should be more than the wattage of the inverter?
Can I use a combination of the panels and battery bank?

The total it uses in an hour?

If it is the total over a 4 hour period, you should use the term 2800 watt hours.

Example, my window air conditioner uses 500 watts, I need to run it for 4 hours, so I will use 2000 watt hours of energy.

robocop · May 2017

ok mine uses 2800w hours of energy run 4 hrs will be 11200 watt hours

Photowhit · May 2017

robocop said:

ok mine uses 2800w hours of energy run 4 hrs will be 11200 watt hours

Is it likely that they would reach a thermostatically set temperature during that time and have the compressor turn off?

Most of the energy used by an air conditioner is used by the compressor. It would be good to get a handle on the actual use before trying your system, if it doesn't use less energy, go back and read my reply #10!

Raj174 · May 2017

Hi Bob,
As I remember from a previous post, the charge controller is rated at 60 amps, so keeping that in mind and that most AGM batteries take up to about a 20% charge rate, I would say that 10 or 12 panels would be required for this system. Check the specs and charging recommendations for the AGM batteries you have chosen. If it is specified that they need an equalization charge, some do, then the 315 watt panels will not provide adequate voltage to do this. If an EQ is not required, then 2 panels in series and 5 or 6 strings in parallel will charge your batteries. If the batteries require an EQ then a 60 cell panel is needed. They usually range from 240 to 285 watts and these need to be 3 in series. If you can find these panels it might be better to use them and be assured no charging problems.

If the inverter A/C units have been sized correctly, they will not require 2800 watts continuously. They will run at 100% until the thermostat setting has been reached and then reduce speed/power requirement, to maintain the temperature setting. If you are sure that hey have been sized correctly then I recommend 10 panels. If they are undersized then 12 panels or their equivalent in 60 cell panels.

Rick

robocop · May 2017

Hi rick glad to hear from you. Will use gel batteries. will send you the specs thx

Raj174 · May 2017

Gel batteries are not usually a good choice for solar power systems. The charge rate is limited to about 5 percent. Slow to recharge and fewer panels to support loads.

Rick

balance in W between pv array and inverter

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