Planning out an off-grid shed

[skuzuker28]

Finally got my shed installed, and the plan from the beginning was to have its own self-contained electrical system for a couple reasons, one of which is: it seems like it would be fun! Where I especially am looking for guidance is in regard to sizing of the panels and batteries. One idea I had was to have a large chest freezer out in this shed not only for additional food storage (so we can buy more in bulk and such) but also give us a contingency plan for keeping our food safe during a power outage. With that I'm estimating about 1kWh per day on average. Using alt-e's calculator to get some ballpark figures, it's saying I need 300ah of battery at 12v for two days "without sunlight" and 750w worth of panels.

Batteries are obviously a big cost, and 3600wh of battery is going to be expensive no matter how you slice it. How much can I reduce my battery needs with more panels? Big concern is the winter time, as it is almost constantly overcast in my area and in December it seems we only get 64 sun hours in the month on average. If I could manage to put together 1800w worth of panels, how much less battery would I need in that case?

I also need to plan out the rest of the system, but this is the driving question. If I decide that it's not practical to have the freezer then my power needs will go down considerably and so will the size of the inverter, SCC, etc.

 

[Bluedog225]

Welcome!

Lots to learn here. Best I can give you in the few minutes I have is don’t buy anything yet.

Once your system is planned, you will save a lot of money avoiding mistakes.

 

[skuzuker28]

Only thing purchased is the shed, just put together yesterday! Definitely looking to make sure I plan ahead and only buy once.

 

[skuzuker28]

Edit: double-post somehow.

 

[OffGridInTheCity]

Finally got my shed installed, and the plan from the beginning was to have its own self-contained electrical system for a couple reasons, one of which is: it seems like it would be fun! Where I especially am looking for guidance is in regard to sizing of the panels and batteries. One idea I had was to have a large chest freezer out in this shed not only for additional food storage (so we can buy more in bulk and such) but also give us a contingency plan for keeping our food safe during a power outage. With that I'm estimating about 1kWh per day on average. Using alt-e's calculator to get some ballpark figures, it's saying I need 300ah of battery at 12v for two days "without sunlight" and 750w worth of panels.

At 1kwh/day load and 750w of panels a pvwatts ( https://pvwatts.nrel.gov/pvwatts.php ) for my location shows I'd be in the ballpark. The 38kwh/month (low) would 'technically' be enough. *Suggest you try pvwatts for your location.


However, the reality of my location is that I went 6 days with basically NO PV last December. Heavy, heavy, heavy clouds/rain. It was the worst in 3 years of operation. So battery for 6 days is more realistic OR allow for contingencies - e.g. grid assist or let the freezer stay unpowered for 5 days in the winter OR .... this would be up to your situation.

Finally - I happen to be building 10 x 13ft shed myself and one issue is climate control. I'm in zone 4 (milder temp ranges) and most of the time I could get by within heat/cool specs of lithium batteries - but not all the time. SO... I need climate control. Thinking of an RV style maxxfan to keep heat <90F and perhaps some heating pads for batteries. A full on mini-split is likely overkill and would require an order of magnitude more power than a maxxfan and heat pads But it's an issue to think about.

 

[skuzuker28]

I'm in Salem, OR so it's a bit worse for me. PVwatts gives me a total of 876kWh, with a low of 29 in December with 750w array. A larger 1.6kw array pulls the low up to 63kWh, However, as you alluded to WHEN those watts are generated is a big problem. I'd imagine the freezer could go unpowered for a day or so, ambient temperatures would be low after all. I could also supplement the storage with my Bluetti AC200Max if there are a bad run of days. I'd want to have some sort of remote monitoring/alerts set up for that though just in case. I'm sure there is something that integrates with Home Assistant for that.

 

[skuzuker28]

So, related question: my roof is 75 inches tall 160 inches wide. There are used panels available locally that are stated to be 65 inches tall and 39 inches wide. THEORETICALLY 4 could fit in a portrait orientation, but I know mounting hardware would take up some space. Would the 4 inches of wiggle room be enough?

 

[OffGridInTheCity]

So, related question: my roof is 75 inches tall 160 inches wide. There are used panels available locally that are stated to be 65 inches tall and 39 inches wide. THEORETICALLY 4 could fit in a portrait orientation, but I know mounting hardware would take up some space. Would the 4 inches of wiggle room be enough?

From my experience - yes. For example, you can run the rails vertically and fasten top/bottom and have the panels with no gap along the vertical edges. That would be 1" on top, 1" on bottom and 1/4" between = 65" + 2 1/4" = 67 1/4" total = OK.

It might just barely fit running the rails horizontally with 1" left edge, 1" right edge and 3 x 1/4" bolts inbetween = 2 3/4" + panel width = 156" + 2 3/4" = 158 3/4" = OK.

A shed is likely OK but a house might have local codes that require fireman walkway along the edges - and so it wouldn't work for code reasons. If you think local codes apply, you might want to check.

 

[skuzuker28]

OK, so have an update: purchased the panels. They are Trina SS250P-60 panels with the following specs:

Max Power	Watts	250​
Open-Circuit Voltage	Volts	37.6​
Voltage at Pmax	Volts	30.3​
Short-Circuit Current	Amps	8.85​
Current at Pmax	Amps	8.27​
Max System Voltage	Volts	600​
Fuse Rating	Amps	15​

These will all be facing west on the roof. If I wire them in 2S2P it looks like it should fall right into the specs for this All-in-one:

HYBRID LV2424 – 24V 2.4kW, 120V Output, 2kW Solar Input 80A Mppt (Grid Feedback Optional) – Watts247 Wholesale

watts247.com

I'm giving up on the idea of running a large freezer in the shed, just isn't practical. Honestly, this will have more power than I need for what I'll probably end up using it for, but it will be good practice. The simplicity on an All-in-one is appealing, since all I'd need to get is a battery (thinking the Amperetime 100ah 24v to keep things simple). Any other thoughts?

 

[skuzuker28]

So the wiring of the shed is going slowly but surely. Starting to have second thoughts about that all-in-one in my previous post, as it seems that it idles at about 60w! That's 1.4kWh a day just to run the inverter, much less actually power anything. I see that it has a standby mode, how well does that work? The user manual doesn't say much other than it turns the inverter portion off when loads are "pretty low or not detected".

 

[OffGridInTheCity]

So the wiring of the shed is going slowly but surely. Starting to have second thoughts about that all-in-one in my previous post, as it seems that it idles at about 60w! That's 1.4kWh a day just to run the inverter, much less actually power anything. I see that it has a standby mode, how well does that work? The user manual doesn't say much other than it turns the inverter portion off when loads are "pretty low or not detected".

60w is not bad overall. You can spend $ and get lower... I read that some Victron equipment can be lower but I'm not a Victron expert. I suspect you'll get info/comments on this.

However - from someone 4 years 'on the other side' - there is such a thing as SOCD Solar Obsessive Compulsion Disorder. I won't fault you because I've been fighting it since I first realized I was loosing so much. But I can try to share some balance. For example, my overall system has ~19% losses. YIKES!!! 19% wasted every day! In my case, it's at least 3,000kwh/year.

So you break it down...
- Panels don't produce 100% that you might plan for due to sun angle, heat, many factors.
- 2% is wiring (several hundred feet in my case).
- 1-2% is Battery charge/discharge inefficiencies (e.g. lithium ion is good but you don't get back 100% of what you put in).
- MPPT charge controllers are 1-2% losses.
- My inverters are around 14% loss leaders and they have a 200w+ draw for each one - e.g. 400w+ in my case.
- I need UPSs since I'm off-grid w/grid assist, and my total is ~120w/hour APC idle consumption.

My point is, it's OK to burn 60w/hour - it's not bad considering you also have a UPS built-in. And there are other issues besides this 60w as I've listed above.

On the other hand, its also OK to obsess. You're response might be to spend $ on different equipment w/different features OR oversize you're array to account for losses OR add sun angle tracking for your panels to address panel losses OR ... many things. Overall, it's a formula of $ and solar expectations and DIY expertise.

And after all that - the clouds might just destroy solar production anyway. And where I live wildfire smoke is as bad as clouds. Solar works, and to me works really really well - but it's messy.

Just trying to share some perspective.

 

[skuzuker28]

I appreciate the perspective! I’m just running the numbers and with the 1000w of panels I can fit on the roof of the shed I’d likely run out of battery and times during December and January just having the inverter on unless I buy more battery. My understanding is that the stand-alone inverters are significantly more efficient at idle, so while it might cost a little more to buy and wire together a separate inverter and MPPT charge controller, it would be cheaper than buying more battery.

 

[OffGridInTheCity]

I appreciate the perspective! I’m just running the numbers and with the 1000w of panels I can fit on the roof of the shed I’d likely run out of battery and times during December and January just having the inverter on unless I buy more battery. My understanding is that the stand-alone inverters are significantly more efficient at idle, so while it might cost a little more to buy and wire together a separate inverter and MPPT charge controller, it would be cheaper than buying more battery.

I'll be interested in what you settle on if you care to post

 

[skuzuker28]

I'll be interested in what you settle on if you care to post

I’ll definitely be getting feedback before buying anything, I’m grateful that there is such a wealth of knowledge here!

While I think about what direction to go with on the electrical side of things, I’d appreciate some input on panel mounting. The used panels I purchased came with some new z-brackets but they seem pretty light weight for full-size panels. Are these going to be okay?

 

[OffGridInTheCity]

I’ll definitely be getting feedback before buying anything, I’m grateful that there is such a wealth of knowledge here!

While I think about what direction to go with on the electrical side of things, I’d appreciate some input on panel mounting. The used panels I purchased came with some new z-brackets but they seem pretty light weight for full-size panels. Are these going to be okay?

You mean brackets like this - https://www.amazon.com/Renogy-Light...ruction-Installation/dp/B00BR3KFKE/ref=sr_1_1

I have 1 panel using 4 of these, wood screwed into pressure treated lumber - and it won't tear off but not sure how long screws -> wood will stand up to rain before rotting loose.

The rest of mine are all Ironridge rail + bolts and the ground array is universal strut (rail) + bolts. I like rails - e.g. separation of labor in that you afix the rails to the roof and then bolt the panels to the rails.

What are you planning?