diy solar

diy solar

Day use only, dont need to store power in a battery

alborosillica

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Jun 19, 2021
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Am converting a van for full time living, new to solar tech. I gather that the conventional approach is to get a total watt-hour expectation of my daily needs; then configure a battery bank based on this expectation. Panels, controller, and inverter come next. Would I be on the wrong path if I planned to build a solar system thinking my two 350 watt (voc) panels will power all my needs during daylight hours only? Aside from phone, laptop, chest fridge, and possibly a shower water pump, I have some milwaukee power tool batteries (m18 series) that are interchangeable with many tools including an LED lamp. Other than for surge buffering perposes, I'm not sure why I should include a battery bank in system. I dont think I have need to store power for a rainy day. I bet I sound so newb, thanks for any help,
-Alan
 
Most solar controllers expect to have a battery connected in order to function. Certainly possible to go with a minimum sized battery as long as the limitations are understood. Worst case you could always add more battery only if needed.
 
Am converting a van for full time living, new to solar tech. I gather that the conventional approach is to get a total watt-hour expectation of my daily needs; then configure a battery bank based on this expectation. Panels, controller, and inverter come next. Would I be on the wrong path if I planned to build a solar system thinking my two 350 watt (voc) panels will power all my needs during daylight hours only? Aside from phone, laptop, chest fridge, and possibly a shower water pump, I have some milwaukee power tool batteries (m18 series) that are interchangeable with many tools including an LED lamp. Other than for surge buffering perposes, I'm not sure why I should include a battery bank in system. I dont think I have need to store power for a rainy day. I bet I sound so newb, thanks for any help,
-Alan
Inverters need a battery to handle surges that the solar cannot supply for your fridge, water pump, and power tools.
 
watt-hour expectation of my daily needs; then configure a battery bank based on this expectation.
Some watt hours can be covered while the sun is shining. The battery for the most part needs to be sized for providing power when the sun isn't shining at maximum (19 hours a day). If you can charge your toys during peak solar you won't need to count for this with batteries.
One thing for sure is that your panels will need to produce more than your daily usage.

Get your daily usage figured out a get an array to cover these needs. Then determine your needs when sun isn't shining. Get batteries to store power for this amount. An SCC needs to work with your array and convert power and charge your batteries in the quantity you use.

Get your numbers worked out and we can figure out a lot of this with you.
 
what is going to keep your food cold at night or on a rainy day
I think the residual cold will be sufficient, then the fridge can turn on at, say, 9am using a timer. I can buy ice for a rainy day, thats what i I hope anyway.
 
I prefer the idea of PV direct, because batteries cost 2x to 20x what PV does (on a per kWh of lifespan basis, or over 10 years, whichever comes first.)

Most loads draw whatever power they want. Heating elements and incandescent bulbs draw less at lower voltage, as do brush-type motors. Switching power supplies and many motors draw more current at reduced voltage.
None of those fit PV direct well.

About the only things optimized for PV direct are MPPT battery chargers, grid-tie inverters, and PV direct pumps.

Most practical implementation is probably to use a small battery, and enable/disable loads according to battery voltage.
Inverter drive motors (found in some refrigerators and mini-split A/C) have no starting surge, but most others require 5x current to start. That means you would need 5x PV to get them running. A small battery can take care of the surge.

It can be done for home backup (6kW GT PV inverter with 2kW convenience outlet to use during grid failures.) But for a van, you want to make use of all the panels you've got.
 
I started out living and working from my Honda Element. 200 watts of panels and the largest marine deep cycle/ starting battery I could cram under the hood. Its not an ideal solution but it got me through the start up surges and such until I got my off grid shop/home built.
 
Direct use tends to be an ignored section of solar because it is fairly complex. I run mu fridge only during the day by sensing the battery voltage is at least 13.4V before it will start and running for a timed period. This insures the battery will never be drawn down and vehicle will always start. Cold is stored in mass liquids for overnight. With those two panels you should also be able to make hot water. Days without sun can still be a problem with that few a panels. But, the fridge will still run and keep things relatively cool and a bag of ice will last a lot longer.
 
I read into this you’re trying to limit your spending on this project. I’ve been 100% off grid and no generator for 3+ years (other than winters ~4 frozen months which i rent a room or small short-term :))
My first purchase was a windyNation 200W kit and a Giandel 1200W pure sine inverter. I used two big lead acid deep cycle batteries.

Take my advice: just get a battery or two. Sure, they add convenience, but not thinking about power is peace of mind AND your solar panels need/want the buffer of batteries, ANYWAY.

Did I miss what fridge you have?
200W can run a fridge, but not a lot of resistance refrigerators- power consumption will be too high. Even some ‘electric coolers.’
I’ve experimented with four different refrigerators and the RV ammonia fridge used a ton of power. 200W wouldn’t keep up even on sunny days is what I found.
200W ‘will’ run 1/2-size mini fridges and even an old coil-type cube dorm fridge which I got used to test and (now) regret selling (cuz you can add insulation to those).

Put it this way: compared to rent $$, your off-grid van solar will be paid for in one month or less. Then it’s free.
 
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