System sizing

TrashPanda10k

New Member
Hi, I'm in the process of setting up my first system. I've got 8 3.2v 78ah LFP batteries at the moment (so about 2000 watts/hr), but that's it, everything else is in flux.
My power needs are:
2 gal electric water heater- kill-a-watt says this uses 0.55 kwh per 2 gal heating cycle. Planned use is 3-5 cycles a day.
Microwave- 700 watts- not used every day, but handy to have for meals. So, on average used like 1 hour a day for easier math.
Water pump- 35 watts @ 12v. Used say, 1 hour over the course of a day, again, for easy math.
Lights- when everything is on, 30 watts

That's about it, it's a small travel trailer. I'm thinking 600 watts solar, (400 watts is about as low as I would want to go) to account for panels not working at full puff, system losses, bad math, etc.

Thoughts?
 

OffGridInTheCity

Solar Enthusiast
5 * .55kwh = 2.75kwh / day (water heater)
1 * 700w = 0.7kwh /day (microwave)
1 * 35w = 0.35kwh / day (water pump)
----------------------------------------
Total = 3.8kwh/day.

I have 4 x 300w panels on my 7 x 14 cargo trailer -> camper conversion. They are 'flat' and I get aprox 3kwh/day in full sun summer time. In winter, that would be on the order of 750wh/day.
1623510753341.png

More panels are better! and tilt helps somewhat but beyond that - the water heater use would be the biggest issue I see - maybe cut down to 1 cycle a day?. One thing we put in was one of those small instant hot water "InSinkErator"(s) - https://www.amazon.com/gp/product/B00ZC5QRCI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 - they use a lot less than a water heater. We only use the water heater for showers (less than once a day :) )
 
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OffGridInTheCity

Solar Enthusiast

snoobler

Solar Honey Badger
Microwaves use 50-60% more power than their output rating, so a 700W microwave is going to use 1100W.
 

snoobler

Solar Honey Badger
Per the other thread, yep, you need at least 2X of those batteries to conveniently meet your needs and have some reserve capacity.

Best to have two separate batteries, each with their own BMS.
 

TrashPanda10k

New Member
5 * .55kwh = 2.75kwh / day (water heater)
1 * 700w = 0.7kwh /day (microwave)
1 * 35w = 0.35kwh / day (water pump)
----------------------------------------
Total = 3.8kwh/day.

I have 4 x 300w panels on my 7 x 14 cargo trailer -> camper conversion. They are 'flat' and I get aprox 3kwh/day in full sun summer time. In winter, that would be on the order of 750wh/day.
View attachment 52560

More panels are better! and tilt helps somewhat but beyond that - the water heater use would be the biggest issue I see - maybe cut down to 1 cycle a day?. One thing we put in was one of those small instant hot water "InSinkErator"(s) - https://www.amazon.com/gp/product/B00ZC5QRCI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1 - they use a lot less than a water heater. We only use the water heater for showers (less than once a day :) )
Cool! So, it looks like mine uses about double that instant one. But, I've plumbed it in to the existing system so now the sink and shower both have hot water. Here's what I'm using:
 
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