Configuring the Correct Size System For Our Needs

[RiverBreezeRanch]

Good Morning,

My wife and I have a farm where we raise beef cattle, hogs and dairy goats. We have many freezers that we store our meats in and are hoping to set up a solar system that can power these freezers and a mini-split that we would like to add to keep the freezers in a temperature controlled environment(we live in South Florida). Based on our calculations we need a system that can produce 4000 watts a day and 32 kwh of battery in the evening. Is there a system that would have an option to plug into a home electrical outlet as a backup power source in the event the batteries do not get enough charge on a cloudy day etc? Any other suggestions for our setup needs?

Thank you, Jeff
*Here's a few pics of our goats*

 

[Lawrence_SoCal]

Uh, be careful of terminology
Watts is a point in time measurement (like speed). kWh hours is like volume (or distance, ie miles).
4000 watts a day - not a valid statement.
if that was 4kW system, that would be about half of my system size, and no where near enough to provide 32kWh of energy overnight (you'd obviously be importing most of your energy from the grid). Also beware panel ratings (lab measured) vs expected actual peak output (a lower number [think engine HP, and HP at rear wheel]) and then there is PV production ability based on panel placement (orientation towards sun, angle, etc). In other words, same panels as on my roof would produce different output on my next door neighbors house as roof is oriented differently (also curved road)

And beware Summer vs winter PV production variances. Ideally you need more kWh in summer than winter?

As for basic question... assuming using your existing freezers and HVAC, then you are talking about A/C powered devices, so DC from panels straight into battery does you no good. You have to have something to convert DC in battery to AC for your devices, an Inverter. And if you spec your inverter/system properly, yes it can charge from house outlet (grid)

Issues you need to consider/decide/answer
- where are panels to be mounted? ground mount tends to be desirable, but often not practical (depends). If roof mounting, consider lifespan of panels (often 25+ years) vs roof itself (ie don't put panels on roof that needs re-doing in near term).
- is shade on panels a consideration? some circumstances appear to be able to benefit from micro-inverters, also sometimes more cost-effective in certain smaller systems
- The energy draw of what your Inverter needs to support? ie all the loads you plan to have... have you measured the circuit usage already? identified peak draw?

As PV production drops off significantly as dusk at dawn, and *if* you want to minimize grid importing, I'm going to guess something closer to 40kWh in battery will be target. Then for your geographic location, panel orientation, panel area to work with, etc determine panel layout & quantity, with associated PV production estimates. Assuming you need to produce 32kWh per day (in peak summer, lower for rest of year), then you are targeting 32kWh of PV production on a sunny summer day. I'm guessing a 8kW PV system or larger (that peak production value is only for 1-2 hours a day).

then, if you want to avoid grid-importing during cloudy/rainy days, etc, then you need even more battery (hence my guestimate to start at 40kWh or thereabouts)... but the common adage is the cheapest energy to generate is the one you don't need in the first place (ie, sometimes (MUCH) cheaper to get more efficient lighting, HVAC, cooler units, than getting more solar PV capacity .. ymmv)

And, then you need to consider what happens with battery runs out... you ok with everything powering off? if not, then you'll be 'grid-tied' and all that implies (biggest issue tends to be cost for UL certified gear). You can go for a non-exporting 'off-grid' system, like the EG4 6000XP or 12000XP depending on inverter output requirements (ie your local load)

 

[RiverBreezeRanch]

Uh, be careful of terminology
Watts is a point in time measurement (like speed). kWh hours is like volume (or distance, ie miles).
4000 watts a day - not a valid statement.
if that was 4kW system, that would be about half of my system size, and no where near enough to provide 32kWh of energy overnight (you'd obviously be importing most of your energy from the grid). Also beware panel ratings (lab measured) vs expected actual peak output (a lower number [think engine HP, and HP at rear wheel]) and then there is PV production ability based on panel placement (orientation towards sun, angle, etc). In other words, same panels as on my roof would produce different output on my next door neighbors house as roof is oriented differently (also curved road)

And beware Summer vs winter PV production variances. Ideally you need more kWh in summer than winter?

As for basic question... assuming using your existing freezers and HVAC, then you are talking about A/C powered devices, so DC from panels straight into battery does you no good. You have to have something to convert DC in battery to AC for your devices, an Inverter. And if you spec your inverter/system properly, yes it can charge from house outlet (grid)

Issues you need to consider/decide/answer
- where are panels to be mounted? ground mount tends to be desirable, but often not practical (depends). If roof mounting, consider lifespan of panels (often 25+ years) vs roof itself (ie don't put panels on roof that needs re-doing in near term).
- is shade on panels a consideration? some circumstances appear to be able to benefit from micro-inverters, also sometimes more cost-effective in certain smaller systems
- The energy draw of what your Inverter needs to support? ie all the loads you plan to have... have you measured the circuit usage already? identified peak draw?

As PV production drops off significantly as dusk at dawn, and *if* you want to minimize grid importing, I'm going to guess something closer to 40kWh in battery will be target. Then for your geographic location, panel orientation, panel area to work with, etc determine panel layout & quantity, with associated PV production estimates. Assuming you need to produce 32kWh per day (in peak summer, lower for rest of year), then you are targeting 32kWh of PV production on a sunny summer day. I'm guessing a 8kW PV system or larger (that peak production value is only for 1-2 hours a day).

then, if you want to avoid grid-importing during cloudy/rainy days, etc, then you need even more battery (hence my guestimate to start at 40kWh or thereabouts)... but the common adage is the cheapest energy to generate is the one you don't need in the first place (ie, sometimes (MUCH) cheaper to get more efficient lighting, HVAC, cooler units, than getting more solar PV capacity .. ymmv)

And, then you need to consider what happens with battery runs out... you ok with everything powering off? if not, then you'll be 'grid-tied' and all that implies (biggest issue tends to be cost for UL certified gear). You can go for a non-exporting 'off-grid' system, like the EG4 6000XP or 12000XP depending on inverter output requirements (ie your local load)

Thank you very much for all of this information, it is greatly appreciated.

Jeff

 

[wpns]

Based on our calculations we need a system that can produce 4000 watts a day and 32 kwh of battery in the evening.

Welcome Jeff!

Normally I would say that the first thing you need is an energy audit so you can properly size your system, but you seem to have done that already. Can you share the inputs to that calculation, just so we can confirm you’re looking for the right size system?

 

[Offgrid Jungle]

First - what is your goal? I gather that you are looking for a power reliability system rather than an off-grid or sell-back system.

If your running loads are 4000 watts during the day and you have utility grid power available, then the 6000XP is your answer. Or jump up to the 12000XP for more capacity.

1. The first thing I size is the battery by determining the load from 4PM to 8AM. These 16 hours are when the battery needs to carry the load when the sun is down. If your load is 4000 watts 24/7, then 4000w x16 hrs = 64 kwh (exactly double what you posted)

For example: a 12000XP, pull box, and two weather proof EG4 batteries would be the minimum set up. (you will buy power at night)​

​

2. Now that you have your inverter and battery sized up , you can work on the solar panel calcs. Fill the MPPT inputs if you have the room for that many solar panels. Put in as many as you can fit in the area allowed, at least two strings that max out the two MPPT capacities.

This is an example of how DIY friendly the EG4 system is for the 6000XP, 12000XP, or the 18kpv shown here.



By the way, you're in Florida so don't mess around - get a generator if you don't have one already.