Energy Audit and System Sizing Spreadsheet

[FilterGuy]

EDIT: The Audit & Sizing spreadsheet can now be found in the "Resource" section of the fourm:

https://diysolarforum.com/resources/system-energy-audit-and-sizing-spread-sheet.12/

In order to avoid any confusion, I will change the links in this thread to point to the resource rather than the google doc.



Folks, this is a link to google sheets where I have placed a simple Energy Audit and System Sizing spreadsheet.
https://diysolarforum.com/resources/system-energy-audit-and-sizing-spread-sheet.12/
PLEASE DOWNLOAD FIRST. (Don't modify what is on the server).

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

When entering the wattage of your various loads, it is best to actually measure them. If you use what it says on the back of the device, the estimates will be high.

 

[bladetoyshop]

Very useful tool, especially for designing a system like the one I want to build.

 

[FilterGuy]

A few comments about the spreadsheet.

• One of the best uses of the sheet is to help you identify where to reduce/conserve. (Energy not used is the cheapest)
• To get the best sizing, use measured values of wattage for the load calculations. If you use the values shown on the back of the device, it will almost always be higher than actual. The higher-than-actual number then gets fed into the system sizing and the difference can get amplified.
• For things like refrigerators that cycle on and off, it is sometimes hard to come up with an hours-of-use for them. If you can stick a Kill-a-Watt on it, you can get a good measure of the Watt-hr usage.
• The sheet does not attempt to account for turn-on surges. Anything with a motor will have a turn-on surge that can momentarily peak at 3 or more times the normal current. The surge is short enough that it does not really matter for your solar sizing and storage capacity, but it could impact what you need for an inverter and peak amps out of your battery.

 

[nosys70]

for 10 to 50$ you can get a watt recorder

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if you plan to spend several thousands of dollars into an off-grid system, you can probably afford it.

 

[FilterGuy]

for 45$ you can get a watt recorder

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if you plan to spend several thousands of dollars into an off-grid system, you can probably afford it.

Yup, that is a fancy version of a Kill-a-watt.

You are right about getting one. If you are going to be installing this kind of stuff (even once). You should get something like this and you should get a clamp-on DC ammeter.

 

[nosys70]

yes, they are nice for device like a fridge where the sticker info is not really usefull.
choose a model that displays the max power so you now the inrush power when motor start.
you can also use it for for device you do not control the use (like a TV set in the kid's room).

 

[FilterGuy]

Figuring out hours of use to put in the spreadsheet:

For things like refrigerators that turn on and off by themselves, I have put a Kill-o-watt on it and measure the whr consumed over a set period of time.
I can then calculate the duty cycle.

Example with random numbers:
Watts used while on: 6
Watt-hours over a 6 hour period: 18
Watt-hours/day = 18 Hrs* (24Hr/day/6hr) = 72Whr/day
Hours on/day = 72Whr/day/6watts = 12 hrs/day


For things like lights that you manually turn on and off, it is usually good enough to just watch what you do for a couple days to make a reasonable estimate.

 

[GME]

Folks, this is a link to google sheets where I have placed a simple Energy Audit and System Sizing spreadsheet.
https://docs.google.com/spreadsheets/d/1QahYPTugz3VYL8LPGypeBl3vr04l1cyATUX0n2rQyqE/edit?usp=sharing
PLEASE DOWNLOAD FIRST. (Don't modify what is on the server).

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

When entering the wattage of your various loads, it is best to actually measure them. If you use what it says on the back of the device, the estimates will be high.

This is very useful - thank you for posting it!

 

[Credopower]

Thank you a bunch. So much love the guide

 

[svetz]

WoW! Nice job with the spreadsheet! The reward for great work is, of course, more work. So, a couple of suggestions:

1. Make the spreadsheet read-only so folks can't overwrite it; they have to d/l it.
2. On the example tab, add cell phone chargers and WiFi router.
3. I'd say add an Air conditioner and hot water tank too, but leave hr/d at 0 as the default.
4. Change "hours of Solar Operation" to "Insolation factor", and link the label to the NREL page. People will see 4 and go What? I get 10 hrs sunshine.
5. Add a $/watt, default it to $2/w and in the notes mention that's a DIY value and $3/W is avg installed, and then show an estimated cost. That's just for the solar. You could do the same for the batteries using $/w/cycle to account for lead vs Lithium.
6. Add round-trip battery losses (default to .8 for lead) into the calculations
7. Challenge: Add a cost of electricity inflation factor (default 4%) and then show the payback period based on the costs.

If you're really feeling creative... the next biggest questions asked over and over are:

1. Minor: Add battery fuse sizes
2. Minor: Is grounding needing? Just mark this as YES and make it a read-only field. ?
3. Medium: Add calculation for inverter size that accounts for maximum simultaneous startup loads
4. Medium: MPPT calculations - let them input the panel wattage, voltage, amps, temperature corrections (or even better a drop-down pulling information from the GO database) and MPPT values. Calculate the number of panels in serial/parallel or ERROR if mismatched.
5. Large: Wire size - Have them enter the length underground, length exposed to sun, other length, ambient temperature, and use the values calculated in #1 above to recommend minimum wire gauge/type for each.

 

[FilterGuy]

WoW! Nice job with the spreadsheet! The reward for great work is, of course, more work. So, a couple of suggestions:

1. Make the spreadsheet read-only so folks can't overwrite it; they have to d/l it.
2. On the example tab, add cell phone chargers and WiFi router.
3. I'd say add an Air conditioner and hot water tank too, but leave hr/d at 0 as the default.
4. Change "hours of Solar Operation" to "Insolation factor", and link the label to the NREL page. People will see 4 and go What? I get 10 hrs sunshine.
5. Add a $/watt, default it to $2/w and in the notes mention that's a DIY value and $3/W is avg installed, and then show an estimated cost. That's just for the solar. You could do the same for the batteries using $/w/cycle to account for lead vs Lithium.
6. Add round-trip battery losses (default to .8 for lead) into the calculations
7. Challenge: Add a cost of electricity inflation factor (default 4%) and then show the payback period based on the costs.

If you're really feeling creative... the next biggest questions asked over and over are:

1. Minor: Add battery fuse sizes
2. Minor: Is grounding needing? Just mark this as YES and make it a read-only field. ?
3. Medium: Add calculation for inverter size that accounts for maximum simultaneous startup loads
4. Medium: MPPT calculations - let them input the panel wattage, voltage, amps, temperature corrections (or even better a drop-down pulling information from the GO database) and MPPT values. Calculate the number of panels in serial/parallel or ERROR if mismatched.
5. Large: Wire size - Have them enter the length underground, length exposed to sun, other length, ambient temperature, and use the values calculated in #1 above to recommend minimum wire gauge/type for each.

Great suggestions! I'll work on them sometime, but probably won't do all of them. One thing I want to be careful of is making it appear too complicated. I don't want to scare people off.

One idea I have had is to add a forum section on system planning and design tools. This and my fuse sizing & placement thread could go there. @upnorthandpersonal has a max panel voltage tool that could go there and links to other usefull tools on the 'net could go there.