Trying to understand some basic numbers

[fredoliver57]

Hi everyone. Brand new here. I wish to understand if I have my understanding right. If I have five 100w panels each potentially producing up to 500w per sunny day, that gives me 2,500 watts of power for the day. Is this the same as saying that I'm generating 2.5 Kw daily? Does this also mean that I would have a 2.5 kw solar power system? If, what size/power of inverter could I use, a 3,000-watt or 2,000-watt inverter? Last, how many 100 ah batteries for such a system? I'm about to buy everything in a few days. Thanks.

 

[FilterGuy]

Hi everyone. Brand new here. I wish to understand if I have my understanding right. If I have five 100w panels each potentially producing up to 500w per sunny day, that gives me 2,500 watts of power for the day. Is this the same as saying that I'm generating 2.5 Kw daily?

If you have five 500W panels they will produce 2500W when in Standard Test Conditions (More on STC later). Note: Watts is an instantaneous measure of power.

Next, you have to know the Insolation number. This is the number of full-sun equivalent hours per day. A typical Insolation number is 5, but this will vary with weather and time of year. (Lower in the winter) there are various irradiance maps on the web that can give you this info for your location. It is usually listed per month.

Assuming your Insolation number is 5hr/day, you would get 5hr x 2500W = 12,500Wh/day at standard test conditions.
Note: What hours is a measure of energy

Note: Standard test conditions assume a certain irradiance and a certain temperature as well as a few other defined parameters. Has the panel gets hotter, the production will go down. If the panels are at the wrong angle they won't get as much sun and the production will go down.
This is all to say that it is likely that any given installation would probably produce less than the number would imply. Some people see nearly 100% of the rating but it is not unusual to see 20% less.

Does this also mean that I would have a 2.5 kw solar power system?

Yes.... the traditional system sizing is based on the solar array. This made sense when we just had panels tieing directly into an inverter and then the grid. However, when you add batteries, there are a lot of other factors such as battery capacity and inverter power that become important and the array size is not necessarily a good description of the system.

If, what size/power of inverter could I use, a 3,000-watt or 2,000-watt inverter?

The array size on a battery-based system does not typically define the inverter size. You should do an energy audit to start getting a feel of the size system you need.

System Energy Audit and Sizing Spread Sheet

To get the spreadsheet, click on the orange button at the top of this page. This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;) Notes...

diysolarforum.com

Last, how many 100 ah batteries for such a system? I'm about to buy everything in a few days.

Again, the array size does not define the battery capacity. You need to do an energy audit.

I'm about to buy everything in a few days.

Woh Partner..... you may want to slow down a bit. There is a lot to learn before things are purchased. Based on the questions, there is a good possibility the wrong equipment will be purchased.

 

[BenQ]

Yeah what he said, but since you only have 100 watt panels you’re initially correct that you’ll have the potential to harvest 2.5 kW of energy per day assuming you get 5 hours of insolation. These numbers have less to do with your inverter and more to do with your charge controller (CC). If you plan on getting an “All-in-one” (AIO) unit then your CC comes with your inverter. Going off of what you said, most 100 watt panels are 12v architecture so you’ll want a CC or AIO that works with that voltage. Since you have the potential of making 500 watts at 12 volts with perfect conditions you’ll want a CC that can handle 500/12 = 42 amps most CCs come in 10,20,40,60,80 or 100 amps so you’re looking at getting a CC or AIO that is rated for 60 amps at 12 volts which will be more than you can produce so you’ll be covered just fine. Finally come the batteries, you can make 2.5kw a day in perfect conditions so it might be a good idea to be able to capture all of that. Batteries are usually advertised in Amp hours so 2,500 watts / 12 volts = 208 amps you’re looking for a 200ah 12v battery. If you’re not worried about wasting money and want to use the panels you’ve got then this is a great start. If you do an energy audit and it looks like you consume 30 kW hours of power per day (this is the average I get when I Google it) then your 5 x 100 watt solar panels will cut your consumption by 1/12 good luck buddy!

 

[DIYrich]

Hi everyone. Brand new here. I wish to understand if I have my understanding right. If I have five 100w panels each potentially producing up to 500w per sunny day, that gives me 2,500 watts of power for the day. Is this the same as saying that I'm generating 2.5 Kw daily? Does this also mean that I would have a 2.5 kw solar power system? If, what size/power of inverter could I use, a 3,000-watt or 2,000-watt inverter? Last, how many 100 ah batteries for such a system? I'm about to buy everything in a few days. Thanks.

I thought the "power system" is based on panels, so you have a 0.5kW system capable of producing 2.5kWh per day. I need a 10kW system for my 35kWh average per day needs.

 

[Mattb4]

Hi everyone. Brand new here. I wish to understand if I have my understanding right. ...

Other posters have covered some of the problem areas. Just a few things I can add.
Watts = Volts X Amps Watts over time is calculated by watts demanded by a load over a hours time, or watt-hours, abbreviated wh

Panels do not push watts, loads demand watts in order to operate. If you have no loads your panels just sit there doing nothing.
Inverter sizing has to be sufficient to power any loads you intend to run with it. This is not only the running wattage but also startup current demands which are much higher for items such as motors.

Batteries are energy storage and they most often are rated in amp hours (ah). It is important to keep in mind that they are a load for your PV system except when fully charged. Batteries must be sized at minimum to power the inverter. Both in max amps draw but also in sufficient capacity to handle voltage droop under max inverter loading.

 

[fredoliver57]

If you have five 500W panels they will produce 2500W when in Standard Test Conditions (More on STC later). Note: Watts is an instantaneous measure of power.

Next, you have to know the Insolation number. This is the number of full-sun equivalent hours per day. A typical Insolation number is 5, but this will vary with weather and time of year. (Lower in the winter) there are various irradiance maps on the web that can give you this info for your location. It is usually listed per month.

Assuming your Insolation number is 5hr/day, you would get 5hr x 2500W = 12,500Wh/day at standard test conditions.
Note: What hours is a measure of energy

Note: Standard test conditions assume a certain irradiance and a certain temperature as well as a few other defined parameters. Has the panel gets hotter, the production will go down. If the panels are at the wrong angle they won't get as much sun and the production will go down.
This is all to say that it is likely that any given installation would probably produce less than the number would imply. Some people see nearly 100% of the rating but it is not unusual to see 20% less.

Yes.... the traditional system sizing is based on the solar array. This made sense when we just had panels tieing directly into an inverter and then the grid. However, when you add batteries, there are a lot of other factors such as battery capacity and inverter power that become important and the array size is not necessarily a good description of the system.


The array size on a battery-based system does not typically define the inverter size. You should do an energy audit to start getting a feel of the size system you need.

System Energy Audit and Sizing Spread Sheet

To get the spreadsheet, click on the orange button at the top of this page. This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;) Notes...

diysolarforum.com

Again, the array size does not define the battery capacity. You need to do an energy audit.


Woh Partner..... you may want to slow down a bit. There is a lot to learn before things are purchased. Based on the questions, there is a good possibility the wrong equipment will be purchased.

Thank you, I'll do the audit spreadsheet. Great info!

 

[fredoliver57]

Thanks for all the answers here. What do you all think of the flexible solar panels vs the regular glass and frame types? Which is more efficient? I am in favor of the flex ones because we get a lot of thunderstorms in Florida and I'm thinking that the flex panels are lighter and more sturdier when it comes to wind, debris and especially hail; I'm really concerned about hail destroying my panels. Fred

 

[BenQ]

Glass is generally more efficient and with companies like Santan Solar they’re cheap and easily replaced.

 

[fredoliver57]

Glass is generally more efficient and with companies like Santan Solar they’re cheap and easily replaced.

What about hail, wouldn't glass break under hail?

 

[fredoliver57]

If you have five 500W panels they will produce 2500W when in Standard Test Conditions (More on STC later). Note: Watts is an instantaneous measure of power.

Next, you have to know the Insolation number. This is the number of full-sun equivalent hours per day. A typical Insolation number is 5, but this will vary with weather and time of year. (Lower in the winter) there are various irradiance maps on the web that can give you this info for your location. It is usually listed per month.

Assuming your Insolation number is 5hr/day, you would get 5hr x 2500W = 12,500Wh/day at standard test conditions.
Note: What hours is a measure of energy

Note: Standard test conditions assume a certain irradiance and a certain temperature as well as a few other defined parameters. Has the panel gets hotter, the production will go down. If the panels are at the wrong angle they won't get as much sun and the production will go down.
This is all to say that it is likely that any given installation would probably produce less than the number would imply. Some people see nearly 100% of the rating but it is not unusual to see 20% less.

Yes.... the traditional system sizing is based on the solar array. This made sense when we just had panels tieing directly into an inverter and then the grid. However, when you add batteries, there are a lot of other factors such as battery capacity and inverter power that become important and the array size is not necessarily a good description of the system.


The array size on a battery-based system does not typically define the inverter size. You should do an energy audit to start getting a feel of the size system you need.

System Energy Audit and Sizing Spread Sheet

To get the spreadsheet, click on the orange button at the top of this page. This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;) Notes...

diysolarforum.com

Again, the array size does not define the battery capacity. You need to do an energy audit.


Woh Partner..... you may want to slow down a bit. There is a lot to learn before things are purchased. Based on the questions, there is a good possibility the wrong equipment will be purchased.

Thanks for all of this.
I'm trying to understand the energy audit. Just to run my full size refrigerator that uses 6.5 amps at 115 volts I calculate 747 watts per running hour at about 17,928 per day. I just ran the audit for the fridge only. Based on the results (see image), how many 100w panels and how many 100ah batteries I need to keep up with just my fridge? Can I get help interpreting what the audit (pic) says?

 

[timselectric]

Hail isn't usually a problem until it gets to baseball size.

 

[TomC4306]

Better to actually measure the appliances rather than just use spec sheet data.
Get a Kill-a-watt meter, plug in, plug the fridge in to the meter and come back 24 hours later to see what it actually consumes. Use this process with all the major appliances you wish to power with your solar system. Also, use this data to accomplish the audit spreadsheet.

Edit- I was amazed how little electricity my refrigerator and full size freezer used once already cold. About 2 kwh each for a 24 hour period.

 

[JRH]

Hi everyone. Brand new here. I wish to understand if I have my understanding right. If I have five 100w panels each potentially producing up to 500w per sunny day, that gives me 2,500 watts of power for the day. Is this the same as saying that I'm generating 2.5 Kw daily? Does this also mean that I would have a 2.5 kw solar power system? If, what size/power of inverter could I use, a 3,000-watt or 2,000-watt inverter? Last, how many 100 ah batteries for such a system? I'm about to buy everything in a few days. Thanks.

If you have a lot of cash to blow then charge ahead Lt Col Custer.. and buy alot of stuff..
if your NOT loaded then dont buy anything yet… your not near ready…you will waste a lot of your money and time… and be totally frustrated…don’t end up like me while a giant pile of new great equipment that doesn’t work or fit with the other great stuff I bought Without knowing enough. …. Seriously take the time to learn a bit…

PS… yes I finally got a great system assembled from the pile of stuff I bought…
Thanks to the Forum people….
To justify keeping it im Gona build another whole system out of the left over parts and accessories .
J.

 

[BenQ]

What about hail, wouldn't glass break under hail?

Many panels are rated to withstand hail, each panel is different. “Solar panels can take a beating and keep going. The tempered glass on the surface is typically strong enough that most hailstorms will not damage your panels.”

8 Ways To Protect Your Solar Panels from Hail Storm Damage

Solar panels can withstand most extreme weather, but hail is a unique threat. Protect your solar panels from a hailstorm and safeguard your investment.

blog.ecoflow.com

 

[BenQ]

Thanks for all of this.
I'm trying to understand the energy audit. Just to run my full size refrigerator that uses 6.5 amps at 115 volts I calculate 747 watts per running hour at about 17,928 per day. I just ran the audit for the fridge only. Based on the results (see image), how many 100w panels and how many 100ah batteries I need to keep up with just my fridge? Can I get help interpreting what the audit (pic) says?

These numbers are off. 747 watts must be the start up wattage. As stated earlier by someone else, refrigerators have a different running wattage after they reach the desired temp. Unless you plan to leave the refrigerator open for an hour while cooking, like my wife ? you’ll rarely shell out 747 watts an hour.

 

[BenQ]

These numbers are off. 747 watts must be the start up wattage. As stated earlier by someone else, refrigerators have a different running wattage after they reach the desired temp. Unless you plan to leave the refrigerator open for an hour while cooking, like my wife ? you’ll rarely shell out 747 watts an hour.

Also, after watching this video to see if it would help you it seems as if your fridge is terribly inefficient compared to the one in This video which runs 3 amps at 115v.
Or 300+ watts, but when he put it on a kill-a-watt meter it averaged out to 84 watts per hour.

 

[fredoliver57]

Also, after watching this video to see if it would help you it seems as if your fridge is terribly inefficient compared to the one in This video which runs 3 amps at 115v.
Or 300+ watts, but when he put it on a kill-a-watt meter it averaged out to 84 watts per hour.

It's an 18 yr old fridge, but it works very well. The label (see pic) says 6.5 amps at 115 volts, so = 747 watts "full load". Is "full load" a clue as to what the numbers mean?

 

[BenQ]

It's an 18 yr old fridge, but it works very well. The label (see pic) says 6.5 amps at 115 volts, so = 747 watts "full load". Is "full load" a clue as to what the numbers mean?

No, that’s how much it pulls max, but refrigerators don’t always run at max unless you leave the door open. Unfortunately, refrigerators have become twice as efficient in the last 18 years so it’s your call. Replace the fridge or get more batteries and a bigger inverter. A lot of this depends on your budget. You can also buy a system with the ability to add on and increase inverter power and battery storage as your needs require.

 

[Tomthumb62]

It's an 18 yr old fridge, but it works very well. The label (see pic) says 6.5 amps at 115 volts, so = 747 watts "full load". Is "full load" a clue as to what the numbers mean?

Again, don’t buy a system based on appliance specs. Your fridge likely uses 750W to start up the motor, which takes from 0.5 to 3 seconds. That’s likely the “full load” rating. Then it likely drops down to 100-300W for a while until it cools down to the thermostat setting. Then it probably drops down even lower to maintain temp. Then it will turn off once fully cooled, until it starts up again to maintain that temp.

This is why a killawatt meter can be really helpful. They’re only $15-30.

If you buy stuff based upon the spec label, you’ll be spending a LOT of money that you don’t need to.

Our smallish 7.2CF fridge only uses 800-1300 Wh per day, and only about 45-80W to maintain temp. It’s about 5 years old.

 

[AT1(AW)]

If this will help, I run a 20 cuft refer/freezer in my garage that consumes about 800 watt hours a day in the winter and 1500 watt hours a day in the summer. Remember a the motor/compressor does not run all the time. Mine says 6 Amps at 120v and takes about 100 watts when running, but only runs about 20 minutes every hour. Get a Killawatt and plug you refer into it for 24 hrs. It will tell you every thing you need to know.