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diy solar

I want to build a "hurricane ready backup"

ereams65

Solar Enthusiast
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Feb 10, 2021
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The ultimate goal is to be able to replace my gas powered generator that is only for storm-caused power outages. Now that I have built myself 48v li-ion batteries for my golf cart, and happen to have about 4.5kWh "extra", plus the battery I just built for the cart from the Samsung SDI 94Ah cells, I think it's time to invest in an all-in-one solar charger inverter and some panels. From everything I've read, the ideal is to find used panels locally, so I'm starting to scour CL and Marketplace, but I'm not sure exactly what I will need in term of how many panels. My thoughts are to build a system that will power my workshop, as now Its run solely off a 50' extension cord. I'm in Florida, so there's plenty sun melting everything else, why not harness some of that power?

I've found a crazy range of prices on Amazon for all-in-ones, any I should stay away from? For example, is this horrible because it's cheap?


I haven't even considered doing an energy audit yet, so bear with me. The generator has been getting us through and it's a 3500w unit, which is why I was drawn to the 3500w inverters. We normally only plug in the Fridge so the food won't spoil, the TV to keep updated on the weather and then a small 5k BTU window ac so we don't die in our sleep from the heat. I'm thinking I want to build a rack so the panels will be off the ground and at the appropriate angle. I thought about on the roof of the shop itself, but there's a lot of tree cover shade that I can't really do anything about. I have zero intention of going off-grid, and quite frankly, prior to the golf cart builds, it never entered my mind to go solar for the back up, but I've learned quite a bit and am continuing to see the value is "using what I got", so-to-speak. Any thoughts or ideas would be greatly appreciated. I've spoken to the folks at Santan Solar that someone here recommended and they're getting a facility in Savannah. They have used panels at a pretty good value, it seems, ($50.00 each for 250w?) but the shipping of course would double that cost for 4. Which is what I would start with unless you guys say that's not smart. I may even work it out where I just drive to Savannah and pick up more to save the shipping? Thanks in advance.
 
I wouldn't consider buying anything until I understood what my needs/objectives were as most of the cheap all-in-ones can't be paralleled (e.g., if you buy 500 watts too small you have to sell it on eBay at a loss and start over). Generally, an energy audit is the place to start.

The typical answer for no-worry scalability is microinverters, but they're not a good fit for hurricane-induced power outages as they turn off when the grid is off and to get power from them when the grid is down requires AC coupling (e.g., Skybox) or smart AC batteries (e.g., Powerwall or Encharge) to manage them. The economics and products will probably change in the near future, but I don't think it's here yet.

Will just reviewed some Santan panels and was disappointed by their performance, so caveat emptor.
 
I think I can get by on 5kWh a day. That's using a window ac, couple of ceiling fans, the fridge, limited TV usage, the router and still be able to make a pot of coffee. Somehow, we make it through with just the gas generator now. In essence, I guess I'm asking what kind of panels do I need to build a 48v solar generator.
 
5kWh is likely not enough battery if you want to run air conditioning, unless you supplement with something. If you have enough panels you can run the A/C while the sun is shining, but 5kWh of battery might only last about 5 or 6 hours for your small A/C, maybe a little more depending on how efficient it is. Get a Kill-a-watt device and measure your appliances. Or maybe look at your power bills for some enlightenment.

I used the Kill-a-watt, then confirmed with my power bills. My refrigerator uses 1.2 kWh per day. My window A/C uses 950-1000 Wh at high speed, that is nearly 1kWh per hour, or approximately 24 kWh per day. And my power bill shows that on a day when I ran the fridge and window A/C I used 25 kWh from the grid. With that info I know I would use up 25 kWh of battery in a day with no charging at all. If the grid is down, that window A/C compressor will never cycle off as the unit is way too small to cool the entire house. But, it does take the edge off and makes the house tolerable when it is 95º and humid outside.

Now, if you want to fully charge 25kWh battery from solar you would need enough panels to fully recharge the battery while the sun is shining (5 or 6 hours), plus run the loads while charging, else the battery would never get full. It is just simple math once you know how much energy your appliances need.

I have enough battery and solar to run the refrigerator full time off of my backup system. Add the computer network and phone stuff and a few lights and my panels can't keep up. During extended power outages I supplement with the generator. I plan to add more battery capacity so I can run longer without starting the generator. I can run the window Air Conditioner while the generator is charging the battery.
 
I have 9kWh of battery. The generator is never on more than 3-4 hours as rhe 5k btu AC is only in the smallest bedroom with the door closed and it’s only run for a few hours to keep it below 90 inside to sleep. We’ve been very lucky on the Nature Coast and never lost power for more than 36 hours. I have my generator set up to back feed into the panel if I ever truly needed it and it’s not going anywhere it’s just a pain to operate. End of the day I think I just want enough solar to keep the batteries charged should the proverbial “crap” hit the fan. It’s kinda like the 4 cases of water, 8 flashlights, 2 portable radios and cans of food we would usually never eat.....just in case, lol.
 
Just do a proper energy audit. As has been pointed out a 3.5k genny can make a lot of kWh in 24 hours. Just guessing is a sure fire way to be either disappointed or spend way too much money. It should only take an hour or two and will ensure that your system is up to what you need it to do.
 
It is a way of thinking and adjusting your lifestyle. At my summer home for four months I have a a fridge, hot water, dishwasher, clothes washer and all the other peripheral stuff, even something to keep me alive. I only have a car battery. I think I live pretty well. Certainly some could make allowances for a disaster.
 
please consider to get a kill-a-watt kWh wall plug meter and write down time at zero and time+kWh after at least one day prefer two three. if you can collect that data (it’s kinda inconvenient to unplug stuff, shutting down computer) and share here, that would give us strong information to give really good advice to encourage good outcome

optional homework: major 120V appliances: divide kWh by time since plugged into reset kill-a-watt meter, post for as many appliances as comfortable to ?
 
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