diy solar

diy solar

Spreadsheet for sizing battery and solar array

hclarkx

New Member
Joined
Aug 5, 2020
Messages
53
Location
Granite Bay, CA
I've assembled a spreadsheet to size my RV solar/battery system. I didn't find anything like it on the internet so did the DIY thing.

I'm now on my second system upgrade planned using this spreadsheet. I don't like running my generator so used the spreadsheet to size my battery and solar array to eliminate generator run events where and when I camp. It has worked well as I've come close to needing the generator (inclement weather) and have seen my battery hit 20%, but so far the generator has not run in several years. My current upgrade covers a mini split A/C.

While the spreadsheet is designed for RVing, it should work fine for residential off-grid or cabin situations. Maybe marine as well.

Currently the spreadsheet is in Excel but users I've shared it with have used other spreadsheet programs that can import a *.XLSM Excel file, including Google Sheets.

There is no charge. The spreadsheet is in the public domain.

I am not able to make the spreadsheet file available via DIYSolarForum.com because it is a *.XLSM file which is not supported. So, for now, if you would like a copy, PM your email address to me and I'll send it to you.

Overview .......
Extensive documentation (yes, I have a writing problem)
A day/night load calculation worksheet (you can enter totals directly)
Paste-in of representative yearly hourly solar data from PVWatts
Simulation of day to day evening and morning battery SOC
Supports two mini-split or heatpump A/C units and electric fridge
Designed for LiFePo4 batteries (user can approximate AGM with some effort)

Results include ......
Evening generator run events (solar and/or battery falls short)
Daytime generator run events (solar and/or battery falls very short)
Generator Ah use at each generator run event
Evening battery SOC (sundown)
Morning battery SOC

Data Required ...... (enter for each month)
Day and night load data by season (summer & winter)
Refrigerator energy use at 70F (amps and duty cycle) (12V or Residential)
Space heater amps and duty cycle
A/C 1 rated Watts plus day and night duty cycle
A/C 2 rated Watts plus day and night duty cycle
Minimum battery morning SOC in percent

What-if analysis ........
Enter PVWatts for a location
Enter trial battery and solar array sizes
See annual generator run events
Adjust battery and solar array sizes for tolerable generator run events

The main focus of the spreadsheet is to size the battery and solar array for the number of generator run events you can tolerate. If you see more generator run events in the months and locations you will camp or be at your cabin, you will need more battery (mostly) and possibly more solar (second order effect). If you can tolerate more generator run events, you can reduce system size. Once you are close, you can look at the trade-off between battery and solar capacities. Costs suggest more solar and less battery, though there are definite constraints on minimum battery size.

Future Upgrades: ... The solar data that comes from PVWatts includes hourly temperature. At some point in time I expect to adjust A/C duty cycle based on temperature.
 
Not on the Internet?

Link #1 in my signature. Was posted in 5/2020.

Recommend you review it and refine yours as needed. If it's a notable improvement and retains user-friendliness, it might be appropriate as an addition to Resources.

Want to avoid something so complex and unwieldy that makes it difficult for a novice user.

Can ZIP and attach to post without issue.
 
Not on the Internet?

Link #1 in my signature. Was posted in 5/2020.

Recommend you review it and refine yours as needed. If it's a notable improvement and retains user-friendliness, it might be appropriate as an addition to Resources.

Want to avoid something so complex and unwieldy that makes it difficult for a novice user.

Can ZIP and attach to post without issue.

I'm on the internet but mostly only at home. We mostly camp in out-of-the-way places without cell service.

I saw your link. My spreadsheet has a load data builder page, but one can enter already known load data based on experience or data from your sheet. The focus of the sheet is modelling the day to day battery level as it changes based on weather and resulting solar availability. It steps through a representative year, day by day, for a specific location, and indicates when the battery or solar is not sufficient and a generator must be run.

Yes, it's fairly complex but is well documented. A number of users on iRV2.com and ForestRiverFourms.com are using it successfully. But, I should have noted in my description that it's not for the feint of heart or those that don't at least know what a spreadsheet looks like and have access to one.

Please take a look at it. If you think it's overkill or too complex for folks here, I'll take it down.

Attached is a zip file containing the spreadsheet.
 

Attachments

  • Solar Planning Spreadsheet V52.zip
    878.8 KB · Views: 80
OOPS!! I just noticed that locking the formula cells on the Analysis page to keep users from accidentally wiping out a formula also blocks access to the embedded documentation. Here is an update with the analysis page not protected. So, be careful not to overwrite a formula cell (they are the darker colored cells).

For anyone wishing to unlock other sheets, the unlock key is wrxwrx.
 

Attachments

  • Solar Planning Spreadsheet V52-3.zip
    887.2 KB · Views: 64
Very interesting. Definitely a purpose built tool with fine granularity. Speaking as someone who routinely advises complete newbs on the subject, it is not at all beginner-friendly. I wouldn't recommend it for someone unless they voiced so specific a need, already had a grasp of the concept, and was likely capable of eventually developing the tool themselves.

Most folks just want a straightforward simple way they can design a system. Link #1 reliably specifies a system that meets the design criteria well... perhaps a little over-built and a little more costly, but most people don't complain of having too much solar or too much battery.

IMHO, it's worth putting in resources as an "Advanced" tool with the more detailed end-goals. For someone with a good fundamental understanding of the concepts and wanting to take it to the n-th degree, it has serious potential.
 
I agree. It's for those who want to be sure they have enough battery and solar to ride through inclement weather. The use of representative location-specific weather data from NREL is, I think, what really makes it interesting. Those who have had some exposure to spreadsheets are more likely to dive in.
 
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