solar help

[bobhenry]

OK I need help !


I am in the advanced planning and construction mode of the tiny house and need a lesson on electrical capabilities.

A little background...

I intend to purchase two harbor freight 45 watt solar systems. I know you are gonna beat me up about the HF junk but it is a place to start for folks of very limited income. I checked the electical stats on the mini fridge and mini freezer and they are 1.6 and 1.5 amp draw. It appears there is also a 6 amp startup draw. I intend to dedicate one appliance to each seperate setup. The panels will also be utilized to run 12 volt led lighting a lap top/tv and some 12 volt water pumping equipment. Each system will have a seperate bank of 2 batteries (size and capacity to be determined with some kind help). My head tells me this may be a bit much to ask of these units but I hope I am just being pesimistic without cause. Can a few of you guide me thru the math on this matter. Thanks in advance !!!

[bobhenry]

One thing I forgot to mention is the duty cycle the units have been running for 3 days with food stocks in them in the house and they run approx 5 minutes about every 1/2 hour. Perhaps I need to monitor this more closely to get a better study of the actual draw utilized

[8ball_99]

I would not bother with that setup from harbor freight.. The market for solar is in a bit of a hard spot because of the tarriff that went in effect a couple weeks ago.. But for example I purchased two 80 watt panels for 108 a piece before the tarriff took hold.. They are much better panels then the harbor freight ones.. Yes I still had to buy a controller which was around 90 for a good one. The harbor freight stuff is really not worth the price.. FWIW this is coming from someone who already has 4 panels and a controller I bought from northern tools a few years back.. Its the exact same panels and controller harbor freight sells now..

[Shadow Catcher]

The deciding factor is cost per watt, and HF does not do the job. I sat with a calculator and looked at panels on Ebay (my math skills are nonexistent).
My suggestion is to start with Handy Bob http://handybobsolar.wordpress.com and just wade through it all. I made a bunch of mistakes that have worked out well i.e. high voltage panels, MPPT controller because I bought high voltage panels...
Another resource is http://www.wind-sun.com/ForumVB/index.php a couple of us are on the forum.
This one place you really really want to do your homework, particularly if you are going to be off grid.

[bdosborn]

I checked the electical stats on the mini fridge and mini freezer and they are 1.6 and 1.5 amp draw. It appears there is also a 6 amp startup draw.

Sorry Bob, I forgot about you!

I assume these are 120V? 1.5 amps at 120V is 15 amps at 12V through an inverter.

Lets figure the energy usage of one of the fridges:
15 amps-hr *(10 minutes running/60 minutes)=2.5 amp-hrs on average at 12V.

2.5 amp-hrs * 24 hours per day is 60 amp hrs per day just to keep up with the usage. BUT, we have to add in some inefficiencies for controller losses, less than ideal battery charging, wire losses, etc. Say 77 amp-hrs per day to keep up. So you're going to need two batteries per fridge and it would be better to have four for longer battery life.

If we assume that the your PV panels are at full output for 5 hours a day (average for where I live in the summer time), you would need around 200 watts of solar panel to replace the daily usage. Multiply that by however many days of cloudy conditions you want to ride through (most people plan on 3 days ). 600 watts would be a robust design goal.

Running a 120V appliance off a PV panel is tough, it requires a much bigger battery and PV panel than most people expect. That's why most people use a propane fridge in their RVs.

Bruce