Solar System Sizing - Capacity Factor

fordtrucksforever said:

Are you trying to cover most of the conveniences that electricity offers? When power is down, you cut back on anything that is not necessary to get thru the day.

A larger bank is good to focus on. This way it covers night time and the off days when sun is not producing.

You can add panels until at a comfortable level of power to recharge. Securing alternative heating sources would seem to be paramount that far north.

Coffee maker and microwave should be considered luxuries when grid is down. Focus on keeping food from going bad and learn to see in the dark. Re-learn how to read real books to pass your time if everything else is under control.

After that last arctic blast before Christmas, I had enough of relying on propane to keep warm. It gets expensive fast. I finally installed a pot belly stove and worked a way to have quasi central heating so the upstairs and downstairs is relatively at the same temperature.

All of my lighting is LED and most of the standard bulbs only draw 4 watts. I carefully watch what is drawing current later in the afternoon until I loose all sunlight for panels. During the day, not so much. The batteries need some load so they get a full charge, instead of in float.

During milder weather and longer days, I might not draw enough from battery bank to take the control charger out of float. Sometimes this has been a inconvenience at night if I dont want to let the voltage drop too much.

There are enough things from your list that will be a constant drain on your battery bank. So at night, your batteries have to be in full charge or you drop below a save margin for longevity.

Hopefully you are not in a large populated area or inner city. Having some acreage or at least access to wood to burn if necessary sometimes. At least some deadfall during emergencies.

My solar array is fairly small, but runs everything I need for now. I have south and west facing panels on the roof. Around 3 pm during the winter months, my panel output drops off substantially for a half hour as the sun transitions between the two rood angles.

It took me a while to even figure this out. During the summer months, not even noticeable. Even with the leaves blocking a lot of the panels. But the winter angle of sun really cuts down on output. It does not take too many branches or limps to block a few cells to drop voltage down a bunch.

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Thanks to all who responded so far.

I spent the day at my friend's house looking at his set up and a few hours with a colleague who does solar installs. Of course the solar guy wanted to sell me a system, but he realized quickly I am no where near what his typical customer wants to spend. He does everything from 5KW arrays to 35KW arrays, off grid, hybrid, grid tied and big battery storage systems. He uses higher end stuff (see Sol Ark inverter/charge controllers). He was able to access the inverter/charge controllers and show me the production day to day and month to month for a number of his clients. He has access so he could troubleshoot or answer questions when they call.

Anyway, I learned a lot about solar.....everything from panels with micro-inverters for 2 leg-240vAC grid tied systems, to what I want to do - simple/basic battery back up, not grid tied, for critical loads (power to outlets, fridge, freezer, and lighting for when we lose power).

The major take away is that for my AO, for the worst "sun-hour" months (November-February), I would need about 5000-6000 watts of solar to be able to provide the energy for the loads. That isn't gonna happen right now.

But I can get an inverter/charge controller unit that is big enough for my loads and can handle 5K watts solar for the final build out, if I go there. They are from reputable companies with a good warranty, serviced in the USA, have replacement components available, and aren't much more than cobbling together parts from amazon.

The inverter/charger units can take power from solar panels and from normal grid power for charging the batteries. So if my panels don't produce enough, I can top off batteries overnight via normal grid power. I'll put the charger on a timer.

The most important thing is battery back up tied to an inverter/charger that can handle the critical loads for about 3 days. This assumes having 800-1200 watts of panels producing about 30% due to cloudy conditions for the three days in a row. And during "good" months (June-September) we should get about 5-6 sun hours per day, so it might be able to provide the necessary power.

I'll probably go with a set up from EG4. Their EG4 3000 watt inverter/charger and three EG4 Lifepower 48V batteries.

Notes for people's replies.....correct, NW PA it not a very good place for solar compared to out west like New Mexico. But I like the no noise aspect. If SHTF I can take the stuff to the BoL. and not draw attention when I'm using. (of course light discipline will be used at nighttime).

Since the HVAC will be all electric, the house will get a 500 gallon propane tank for heat back up. I already have a ProComm vent less propane fireplace to install. The house will also get an antique wood burning parlor stove. That's why on my list in the OP I have box fans. I figure I'd have to move that heat around in a power outage.

I have a couple 4k gasoline generators that can tie into a transfer panel if we lose power for longer than the batteries can supply. Or just use the genny to charge the batteries.

And if we lose power, managing power usage from the batteries will be priority.....No microwave popcorn at that point! But coffee is a must.

Thank you colorado and lasers...you gave the real time info and lit a fire for me to go seek more.

hoplite59 said:

Pardon my ignorance but as I understand solar, it will store the energy it collects on a sunny day and be ready for use after the fact ?

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Not really. the term "solar" is a very broad brush stroke. There are different types of solar systems.

Solar panels themselves can not store it. They only convert available light to DC (direct current) electricity. No sunlight..no power.

Batteries store it.

The basic three types of solar systems are:

Grid Tied - usually bigger solar panel array that makes DC power. The DC power goes to an inverter. The inverter changes DC to AC (alternating current) and connects to your home's electrical system, which is connected to the grid. This is a "two part" system. Panels and Inverter. Obviously it only makes power when there's sunlight. When it's dark you still have grid power. If grid goes down...you have no power. (there's can be more but this is the most simple explanation)

Off Grid - Typically this type of system is for us "preppers". We want to be able to power things when the grid goes down. The amount of panels and the amount of batteries depends on what you want to power. It's a "four part system". You have solar panels which make DC power. The DC power goes to a charge controller. The charge controller "controls " the voltage/power, which will charge the batteries. The batteries supply DC power to an inverter. The inverter changes DC power to AC power. Once inverted we can use it with our "normal" 120VAC things that we plug into our home outlets. The four parts are solar panels, charge controller, batteries and inverter.

Hybrid - combination of the two.

Below is a screen shot from a friend's house. He has 8K of solar panels. It's grid tied (he has no storage). What he makes he uses, and if there's excess it gets fed back to the grid.

This graph is from 28 Jan. The last three days (Jan 29, 30,31) he added another 20 KWH, for a total of 197 KWH for January. He made 226 KWH in December.

I knew the capacity factor of solar was not great, especially in our area (NW PA). I'm a mechanical engineer and I work in power generation. So availability, efficiency, capacity factor are things I am familiar with. But I guess not familiar enough because I'm not a "renewable" guy. I work gas plants.

From the numbers I'm getting from my friend, here on SB, and a colleague, I'm definitely going to need a grid tied charger for batteries. I'm not going to build a solar panel array big enough to keep batteries topped off. Our worst case is 5-7 days with only 25% (avg) being generated of installed capacity.

But again my goal is to use what I can, have back up for power outages lasting a couple/few days and in the event SHTF, I'll have something long after the gas and propane is gone.

I don't plan on having a good return on investment for my system. 1200-1800 watts solar, 15KWH of battery storage and a quality 3k Watt or higher inverter/charge controller. My estimates, based on current cost per KWH, it will break even in 17 years... I'll consider it the same as my food stores, bang stick food, car insurance, life insurance, etc. It's better to have it and not need it, than need it and not have it.

When I started this thread I was looking at "how much do I need?"

That was not only for the size of the solar panel array. I was also calculating the battery back needed up considering we live in a cloudy area and inverter sizing for basic lighting and 120V electrical outlets.

I know I will not put up enough solar to always keep the batteries fully charged. We go 3-5 days in a row where there's cloud cover and the array is only producing 15-20%. The return on investment sucks for solar in NW PA.

The most important element is to have power if the grid goes down. Typically we don't see grid down events often around here. So I figured I need 3 days of battery storage for the basic electrical usage/load. There will be no high load 120V or 240 if grid is down. I am going to go with the EG4 3K inverter tied in to a 30A 10 circuit transfer switch and three EG4 Lifepower 48V -100AH batteries in a nice rack. This should cover essential 120V power for 3 days.

Then I'm at a Power Generation conference in Orlando and see this, and my heart stops..532 KWH of power!!!!!