I'm not using my solar panel effectively -- advice appreciated

Hi there,

I've had a solar panel for a number of years. It's very similar to this 100-watt solar panel system from Harbor Freight, with a second inverter attached to the battery so I can plug in a normal, 3-prong plug. Right now, it's reading 14.4 volts, and nothing is plugged into it.

I can run a bread maker on it, or a food processor. I can run a crock pot on 'low' for a while, though it kicks the fan on in the inverter and runs down the battery after a couple hours. And we charge our phones on it, and other battey-powered devices.

The problem is that the panels are always trapping more energy than we're using from them, and I have never figured out a way to use the energy. I don't think I want to run extension cords all over the house --- though I could run one from the kitchen down to the laundry room. But even then, I don't know what I would run down there.

It seems like I need a way to passively consume solar energy when it's available, and standard power company power when it's not. I'm curious to know how you consume solar power the most effectively.

You have a pretty basic system. The most straightforward  approach I can think of is to add more batteries to store the energy.

Thanks for the reply. I thought about doing this, but then I just have that much more stored energy that I'm not using. I do have a friend who's an electrician, so maybe I need to talk to him about getting the solar power into the wall somehow. Maybe I mark some wall outlets in green, and somehow run power from the panel to just those outlets. I'm not sure how feasible that is, though.

Hi Morgan;  Big Welcome to Permies!

A little more information about your system would help.
You mention 2 inverters?  Why two?  
Do you have any charge control hooked up to protect the battery?
What type and size battery are you using? How are you monitoring it? Just a voltage reading? Do you check the battery itself? Water level, specific gravity of the cells?  

As you discovered, any electric heating device will run down your battery.  
Bigger or more battery's would delay that. But a heating element is a hard draw and should only be used sparingly.

Sounds like you are wanting to create and use your solar energy when you can and use utility power when the sun is not shining?
A 100 watt system just can not do very many things.  
500-1000 -2000 watt systems can run bunches more things, but it comes at a cost.  
Bigger better battery's, large charge control, pure sine wave inverter's ... the list goes on.

To use what you have, turn on more things when the sun shines.  
Lights, stereo, fans, TV ...
Just monitor the battery and turn them off when your using too much power.

I'm not a solar installer, but to me this sounds like a job for a grid-tie inverter.

I don't know what your local laws are for "selling back" to the power grid, but with that small a panel it probably won't ever come to that.  Instead, the idea behind the grid-tie-ness is that it "adds" power back into the AC that your house is already using.

For instance (with totally made up numbers), say your house is using 1,000 watts from the grid, your panel ties in an additional 100 watts... so now you are only drawing 900 watts from the grid.  That kind of thing.

I agree with Thomas 100 watts is just not very big. Storage would be the answer in my opinion. Longer runs (extension cords) can have an efficiency drop.  Bank the excess for use when you need it. Nobody can eat all their zuchinni's, store it so it's available when your needs are higher. I use the Harbor freight panels to run fans and pumps in my greenhouse, and they have been trouble free.

Hi there,

thomas rubino wrote:
You mention 2 inverters?  Why two?

The main inverter only has usb and simple wire outlets. So one pair of clamps connect to this, and the panel. Then I have a second pair of clamps running to an older inverter I already had. This one has 3-prong outlets, so I can run normal appliances on it.

thomas rubino wrote:
Do you have any charge control hooked up to protect the battery?

I recently bought a new solar inverter with a regulator that will shut itself off when the charge gets too low. My old one didn't do this, and it eventually ruined the battery. My second inverter just sounds an alarm when the battery is too low, but I don't usually leave this one running passively. I know the new inverter also has some kind of surge protection. This is the unit.

thomas rubino wrote:
What type and size battery are you using? How are you monitoring it? Just a voltage reading? Do you check the battery itself? Water level, specific gravity of the cells?  

This is the battery. I monitor it using the solar inverter. It has an LED voltage reading. It's a pretty new battery and I've never checked the water levels.

thomas rubino wrote:

To use what you have, turn on more things when the sun shines.  
Lights, stereo, fans, TV ...

Yeah, and I think there are only four options here, that I can think of:

Figure out a way to get solar power into some of the wall outlets. This seems difficult.

Figure out a strategic way to run extension cords to different parts of the house.

Get more mobile power sources, charge those off the panel, then move them to different parts of the house and run things off of them.

Maybe there are other solutions. Surely, those of you who are totally off-grid had some point when you were inbetween solar and conventional power. I'm having a hard time committing to more solar when I can't seem to make it work with the solar I have.

https://super-solar-power.com/100-watt-solar-panel/

Realistic expectations on what you can do with 100 watts and storage. A big battery bank can store the energy but depending on usage how long will it take to top the batteries off with 100 watts.
What do you want to run would be the starting point in determining just how much or how big your system needs to be.
I run 1000 watts on my bus and it is way more than I need but with that 1000 watts I have never needed to run my gen set.
I plan to install 1000 watts on my house this summer with a way to piggy back the 1000 watts from my parked my bus to the house storage. That additional 1000 watts giving my house system 2000 watts and the added battery bank of 4 T105's for storage will be a huge boost, and still give me a portable 1000 watts when we use the bus.

I agree that you need more storage. The general rule that I was taught was that you want your solar set up to be sized so that when you use it as  much as you want you keep your batteries between 50% and 90%.

It sounds like your current system hangs out between  0% and 110%, so clearly not ideal.

The way I see it you've got a few options;
1. Add more batteries, enough that you can run the stuff in your kitchen as much as you want without running down the battery. This might just be one more battery.
2. Scale up the whole system  more so that it can run all/most of your home needs.
3. Accept that your current system has its limitations and use it for what it is while taking the opportunity to consider what your total energy needs are and what it would look like to acquire it all by solar.

Your mobile power storage idea might be right for you but it is ultimately just buying more batteries except that you have to buy very expensive batteries so that they are mobile. I would go with option 1 if I were in your shoes

Thanks for the replies. I can see how one would run a bus off of solar panels. For those of you who live in a house, how do / did you get solar panel around the house? Do you connect it to your breaker somehow? How do you spread the solar power around the home?

Instead of simply switching off the feed from the panel, some charge controllers have the ability to shunt the surplus wattage to a secondary load, such as a 12 VDC water heater element or motor.

This could preheat a small amount of water for washing hands, for example. Or stir up the air strata in a greenhouse. Or maybe run a tiny pump to aerate water in a fish pond. Or run a music system. Or power an old laptop with a weak battery. Or a LED grow light.

On straight 12V, a mechanical bathroom fan timer could be useful to ensure you don't run down your battery to a damaging level.

While it's more wasteful, you could run the inverter and a timer to power an old crockpot for hot water or maybe even incubating eggs.

The possibilities seem endless.

Hi Morgan;
First let me tell you that I have been 100% off grid since 1983...
I've seen many changes over the last 37 years.

Your System)  100 watt panel, a 35 amp hour AGM sealed battery (you can not check water in these) and your new charge controller. I assume you bought the 10 amp?
You mention an older inverter?  How old ? Many older style inverters use a fair amount of power just to be turned on!
Another bit of information you may not know. Is that a pure sine wave inverter , or a modified sine wave?  Big difference to sensitive electronics.

Right now you have a very basic stand alone system.
For things within its capability's it is perfectly fine.
To ask it to run more will require upgrades...  

Your question) For a stand alone system(not grid intertie)  Your solar panels or any alternate DC power source are run to a battery bank. This bank must be sized as mentioned earlier to your total needs.
These battery's are in a location where you also locate your large pure sine wave inverter.  
The A/C output from that inverter is then run into your homes breaker box.
Your home is 100% normal household wiring.  The magic takes place in the power room!

I hate to be the economist in this discussion* ...but here we go.  This is a mental exercise, not a slam...

"So What?"

Yes, you're not using 100% of the energy a small system is generating - but what is the impact?  Oh no, some sunlight is "wasted"? Your present watts are very cheap - or maybe the generating equipment is a sunk cost so the watts are "free" so the cost of not using them is ... zero.  Ok, maybe the panels are shading a tree or a patch of grass and it makes a marginal difference in its productivity, so there is some cost.  Or maybe the panels shade the roof and make it cooler - in which case the panel is already making a contribution and the watts are a by-product.

So let's flip this ... if there are other electrical needs that are currently using expensive watts:
a) how many extra free watts do you have?
b) how expensive will it be to get those watts to some appliance and substitute for the expensive watts?
c) what is the new cost per watt?

I'm always shocked at how expensive it is for these ideas of mine!  And to add insult to injury ... 100w panel is, generously, about 1200w/hr per day.  That's 1.2 kw/hr.  That's what, 14 cents?  maybe 20 cents?  If your current consumption is half of that, then you're looking at trying to "save" like ten cents a day of electricity.

I'm not saying you shouldn't do this - I think I'm saying that there might be better ways to be good to ourselves and the planet.

I really can't recommend altering house wiring - that's a whole bucket of installation pain AND electrical code pain.
Adding batteries seems like a good idea.
Grid tie is a solution - but not for a 100 watt panel!

And you've bumped into the problem of a "smart grid" or "smart appliances".  It would be great to have an in-house appliance bid system - refrigerator bids for electricity, and the deep freeze.  The AC can wait until electricity is really cheap.



*This is what goes on in my head every time I have a really dreamy idea.  Sometimes it helps me, but its usually annoying.

I agree with Eliot. Small scale solar is great fun to mess around with. But for most, it is very expensive per watt. (This calculation changes if grid supply is a long way away; bringing in lines can be very expensive.)

It's still fun to mess with, encouraging creativity and awareness of energy usage.

But if the goal is to save money (and energy) the expenditures that pay off will focus on reducing consumption, as opposed to increasing generation.

Maybe for storage you want to look at a Goal Zero or similar system that is mobile and you can move around. I poo pooed them until I was able to use them during a very large relay run and ran LED floodlights off of them rather than previous years generators and was impressed with their performance.

A small portable system can be very useful. Ive seen nice garden carts with solar and stereo sound system for the gardeners. Great also for pumping water, charging phones, computers, running tools, running fans, making a cup of tea.......and you could make your portable system as the off-the-shelf unit’s are expensive. A indoor variation could be add on a lightweight folding hand truck and a suitcase from a thrift store. It would have a vertical shape so would not take up much space.
You’re discovering what I discovered. I’m great at building systems but using them efficiently is a whole other challenge. I’m busy looking for another system to build as I really enjoy that part.
One guy I know just runs lots of efficient computer fans for fresh air ventilation with his surplus solar power. He has a 100 watt panel also.

To add to all the great advice above please do not try to convert any of the existing plugs to solar as the small inverters are what is called floating neutral and your house is bonded neutral. Use an extension cord to move power around as the existing outlets are not considered safe to run as floating neutral.

Morgan,

Eliot is exactly correct.  There is never ever going to be a solar electrical system that is 100% efficient.  For that matter, you are never ever going to find any system that is 100% efficient.  There will always be energy losses due to:

1)  Heat
2)  Battery chemistry
3)  On board electrical components
4)  Electrical resistance in the wiring (which becomes heat)
5)  And the list can go on endlessly

Actually I think you have done an awesome job given what you have.  I would not have thought of using a crock pot, but you got it done so congrats.

You can always add more batteries for more storage, but you have a pretty good system as is.

Eric

Thanks for all the replies. I think I'm going to try connecting the inverter to a power strip, then running cords back out of the house and back into adjacent rooms. This way, there are alternative 'wall outlets' in multiple rooms, and I think it would be easier to do this on an exterior wall and have it still look tidy.

I'll let you know the results. Thank you for all the thoughtful responses!

In most states, there is a policy known as “net metering.” This policy asserts that the energy your panels generate that you don’t utilize is transmitted to the grid in exchange for credits on your energy bill. When you get your monthly energy bill, any net metering credits you utilized for that month would be specified, and you won’t have to pay for that energy. The remaining energy you draw from the grid that wasn’t compensated by net metering credits is where you’ll see minimal charges for energy.

Daily Production = Solar Panel x Hours
Daily Production = 100W x 4hrs
Daily Production = 400Whr (about 300Whr in the winter)

There is only so much you can do with 300Whr/day. A toaster uses up 1800Whr in 1hr(60minutes). so 300Whr is about 1/6 of an hour or 10minutes. that is why your toaster stop working after 10minutes+

You use a battery+inverter and that has conversion inefficiencies, so there is even less energy to work with than what is quoted above. Batteries don't like to be discharged more than 50%. They also waste alot of energy and get hot when they try to charge more than 80% so even more of that energy is lost.

But less pretend there is no loss and you want to store more than just a days worth of power you can increase your battery bank. Lets say you wanted 3-4days. You could get a 1200Whr battery bank (12V x 100Amp-Hour). Such a system could technically run your toaster for 2/3 of an hour (1200wh/1800wh). But once the battery dies it is going to take quite a few days of minimal energy usage to refill the battery.

There is only so much you can do with 300Whr/day, I don't think that you can really extract much more out of the system.  At best I could connect a chest fridge to it, They use about 300Whr/day. Some of them can even be connected without the inverter, or even directly powered by the solar panel.