Michael Qulek

I don't even pay attention to it.  I purchase all my panels used on Craigslist, and my single most important criteria is watts/$.  BTW, don't shy away from used panels because they are used.  I've gotten better performance from used panels I got off Craigslist then the brand new panels I paid retail for.  Depending on your location, expect a good deal to be in the range of 3-5W/$.  Don't order your panels on the internet with shipping.  Cash and carry local purchases will be the best deals.

I do bring a voltmeter with me when purchasing to make sure one panel doesn't turn out to be a lemon.  Don't buy a panel that has a Voc more than 10% lower that what the sticker spec states.  So, if a panel sticker says the Voc is 37.5V, don't buy a panel putting out less than ~34Voc.

John C Daley wrote:Talking of fridges, I am off grid in Australia and had trouble with the fridge draining my small battery system.
I found the most efficient fridge made, Hisense, it was resonably priced for Australia $A1200 is about 315 L capacity and uses 25% of the power of other fridges.

What exactly is the size of your battery bank?  Is it being fully charged each and every day, even in June?

High-voltage residential panels are getting so cheap now that the single cheapest upgrade you can make to your system is more solar.  If my batteries are fully charged by 9-10am, my arrays are supplying 100% of my power needs for the rest of the daylight hours, with zero battery depletion.  That way I'm operating normally with a far less expensive standard AC frig/freezer.

Here in California, I used 3/4" plastic pipe designed for flamable gas.  I would suspect that would be far cheaper than 500 feet of copper.  I got it and all the proper fittings from Home Depot.  I do notice though that it takes quite a while for the stove's oven to warm up to 350F, and I think that 1" might have been a better choice.

Ram pumps work, by utilizing the mass of the moving water, to temperarily raise the pressure to the point where water can be pumped uphill.  But, the efficiency is only a few percent, meaning only a few percent of water flowing downhill is actually pumped back uphill.  Basically, a very LARGE volume of water falling downhill can push a very small amount of water back uphill.  A closed loop system would run for a little while until the water in the upper tank is drained, and then it will simply grind to a halt.

Your implication is that it would be an engine that could somehow be applied to producing useful work.  You simply can't get something for nothing. The laws of physics is not on your side.

In making solar power, one important concept to understand is what's called a "peak sunhour" (sh), which is basically the amount of "FULL" sun you get per day.  You multiply your solar panel size by the sunhours to get the total amount of power you can make in a day.  For London, at 51 degrees North, I think you'll get approximately 1.5-2.0 sh per day in December, and 4.0 sh in June, in full sun.  On cloudy/rainy days however, the sh is likely to drop down to ~0.5sh.

These numbers become centrally important with a whole-home solar system, where you're counting on the system to make ALL your power.  I'm working with neighbors down the hill from me right now because they can't understand the idea that there are less sunhours in December, and they have to deal with completed dead batteries right now.

A second factor to consider is that the rating of your solar panel is measured in a controlled temperature chamber with artificial sunlight scaled at exactly 1000W/square meter.  Your real-world solar output is almost always somewhat lower, because of dust in the air, less than optimal angle to the sun, and how hot the panel is.  So, for real-world output, I usually recommend 85% of what name-plate production is.  That means that your 10W panel is likely at best to make only ~8.5-9.0W.  On a cloudy day, maybe just 1W.

When you want to power anything with an electric motor, you also have to contend with something called "starting surge", or "inrush current".  For something like a free-spinning window fan, the starting surge might only be 1.1X the running power, but for motors starting under load, the starting surge might be 3-4X the running power, for maybe 500-1000 miliseconds.  I'd consider a blender an appliance that would have a significant starting surge.  With too small an inverter, and too small a battery, that starting surge might drive the inverter into low-voltage shutdown.

What that means in the real-world is that people are always overestimating how much power they can make, and underestimate how much power they are consuming.  With what you are describing, I'd recommend you'll more likely be served with a 200W panel, charging a 100Ah battery.  Because an inverter is also a power drain on your system, look into powering all your needs with DC-only appliances that can bypass needing to make AC power.

R Scott wrote:There is higher efficiency when the inverter can convert directly from solar instead of charging the batteries and then pulling the power out for the inverter. Choose the string that gets direct light when you use the most power

I don't think this statement is correct.  As far as my understanding goes, ALL solar power passes through the controller into the batteries, and then All power comes out of the batteries to fuel the inverter.

What you might be thinking about is system potential, instead of battery voltage?  When sitting idle at night time, with no power coming in, the system potential is the voltage of the battery.  In daylight however, the system potential is the battery voltage, plus the charging voltage.  So, for example, a fully charged 24V battery bank at 8pm might be 25.4V, but the system potential would be ~28-29V towards the end of the absorption phase during the day.

The system potential becomes very important when you're trying to run a very big load, such as a 240V well-pump.  A BIG load like the well-pump could cause so much voltage drop that the inverter shuts off from a low-voltage warning.  While charging, the higher system potential prevents inverter shutdown because the battery has to first drop from a higher potential, and because power is coming into the batteries, the voltage sag will not be as great.

What's the brand/model of your All in One inverter?  With some brands, they make more than one model of either inverter or a stand alone MPPT charger.  Some brands are designed so that they can communicate with each other via a serial connection, and if your brand supports that, it might be able to slave a second controller to the AiO?  Some controllers, such as my Midnite 200, have this function, and controllers can be placed in parallel, but without knowing your brand/model, that's just guessing.

The second option, already suggested, is to just wire in a second MPPT controller in parallel, with the bulk/absorb/float setting identical to those of the AiO.  That is likely to be good enough.

Dominic Frasca wrote:Please know I am ignorant about making power for my home but I’m interested in learning more for the hopes to eventually build a system for my wife and myself.

My hopes are to use an alternator run by a lawn mower type engine, an inverter, and battery’s for storage.

Why an alternator?  Solar is now cheap as dirt, quiet, and reliable if in the right climate.  Where are you located?

Dominic Frasca wrote:
My first question is wouldn’t a 24 volt alternator be more efficient than a 12 volt alternator?

The reason why 24V is more efficient is because of voltage drop.  Amps flowing through a wire creates heat, causing voltage drop and the proportional power loss.  Raising the voltage usually means dropping the amps for the same amount of watts, so that's where the efficiency lays.  With today's solar, you can wire panels in series to transport the power hundreds of feet, then drop it down to battery voltage at the MPPT controller.

Dominic Frasca wrote:
How would I figure out how much battery storage would be required to comfortably rely on this to power my energy needs?

Make an itemized list of all the loads you want to power, including the watts, and the total watthours.  Include the consumption of the inverter itself if you want standard AC power.  For my own cabin with lights, TV, and the refrigerator running my total consumption per day is 3.5kWh (3500Wh).  Decide how many days of cloudy weather you need to get through before draining the battery. Multiply by your battery chemistry number, which should be 2X for lead-acid, or 1.5X for Lithium.  So, say for three days of cloudy weather, the math would be (Total watthours (Wh or kWh)) X number of days of autonomy, X 2 for a lead-acid battery)
3500Wh X 3 days X 2for lead-acid = 21,000 Wh or 21kWh.

Most batteries don't list their watthours, but instead list amphours, over the course of 20hr.  It's called the 20hr rate.  You multiply your 20hr rate X the battery system voltage.  For my 48V cabin system, with 568Ah at 48V, that gives me 568Ah X 48V = 27,264 Wh (27kWh) of power.

Dominic Frasca wrote:
From what I’ve read an EFI engine would be a better choice as it would produce energy at a lower RPM than a carburetored engine, is this correct?

Standard RPM of both types is usually 3600RPM, so it's irrelevent.  Fuel injection though likely means the engine itself produces a bit more power for the same amount of gasoline.

Dominic Frasca wrote:
Also (and I have serious doubts about this question) but would a hybrid battery from a Prius work for energy storage?

I believe that a Prius battery runs at 48V, so you would need a 48V system.  Interfacing with the battery's "battery management system" (BMS) would be critical to make it safe.  Remember there have been many disastrous fires that have occurred involving Li-ion batteries.

Well, remember what Thoreau said, "wood heats you twice, once when you cut it and secondly when you burn it".  For some, I guess it's up to seven times.

For me it's...

cut
haul
split
stack
wait two years
relocate into the cabin
burn

Diane Frenser wrote:
To prevent this from happening or lower risk of running out of energy is to add more batteries. What is the limit on batteries I can hook up?

In the real-world, I have found this mentality to be a complete mistake.  If you have a system that can not keep it's batteries charged, adding more batteries just makes the situation worse.

The root cause of why the batteries aren't charged is too little sun in the winter, coupled with too much power demand.  So, instead of adding more batteries, you should instead be adding more solar.

Really, 400W of solar is very small for a cabin.  One concept to understand is a number called a "Sunhour" (sh).  It's NOT the number of hours of daylight, but the number of hours of FULL sunlight that panels can make.  At my location at 35 degrees North, I'm getting about 3sh in December, and about 6sh in June.  To calculate how much power you can make in a day, you multiply your sunhour value by the watts of panels you have.  So, at my location, on a sunny day, 400W of panels could make 400W X 3sh =1,200Wh of power, or 1.2 kWh.

The problem that happens though is you don't get 3sh on cloudy days.  In the middle of winter with cloudy weather, you're more likely to get ~0.5sh instead of 3.  So, multiplying 400W X 0.5sh = 200Wh of power, not enough to keep the batteries charged.  So, to make on a cloudy day what you would have made on a sunny day is 1,200Wh/0.5sh = 2,400W of panels.  Honestly, that is a LOT of panels for a 12V system, but realistic for what you would actually need to keep up with rainy weather.

Sticking with 12V is also a mistake for something the size of a cabin, and I myself abandoned 12V back in 2016.  I upgraded to a 48V system for my cabin, and a 24V system for my workshop.  For my 24V system, which keeps my freezer running, I find that 2000W of panels keeps the system fully charged in the worst weather, with it consuming about 2.5kWh/day.  I do have a BIG 568Ah battery at 24V, so I can sail though a low production day with no issues.  Those 8 residential grid-tie panels are paired to an MPPT charge controller.  I have them wired 4S2P, meaning I have two parallel strings of four panels wired in series.  The raw 120VDC from the panels gets transformed down to ~25-28VDC to charge the batteries, with the extra volts transformed into extra charging amps.

So, bottum line, upgrade your solar first, BEFORE adding more batteries.  The best deals on panels are with local cash and carry purchases.  Look on Craigslist to find the best deals.  Look for getting 5-6W/$ with high-voltage residential grid-tie panels, which are easy to blend into an off-grid system with a MPPT charge controller.