I got this idea of getting some solar panels, there are some great deals on Amazon at way below $1/watt, and not doing the tradition DC to AC and tying that to the house grid, but rather using that DC power directly to power some DC appliances.

Say I have some 24/7 computers and equipment that run on various voltages from 12V to 20V DC using AC to DC power supplies. I'd like to feed the power from solar, if there is sun energy being captured, into the output of these power supplies.

What would be the easiest way to accomplish this? Or maybe not the easiest but most efficient? This is not a money saving exercise, but rather something to tinker with, have fun, and learn things along the way.

 

Get a battery and an MPPT controller to charge it from the solar panel.
$1/watt doesn’t seem that cheap, as I am paying £1 for 10W, but I don’t have tariffs to pay.
Watch out for any deals which claim “peak power” of about four times the average. The sun doesn't do peaks.

 

Get a battery and an MPPT controller to charge it from the solar panel.

I already have a UPS with a large lead acid battery. I could do that. But I thought there would be a more electrically efficient way than bringing down say 60V to 12V, then 12V to say 20V.

$1/watt doesn’t seem that cheap, as I am paying for 10W, but I don’t have tariffs to pay.

Sure you do. It's called the VAT.

https://www.amazon.com/dp/B07GTH79JP

Here is a reputable brand 50W panel for $33.99 + 6% sales tax + free shipping = $36.03 = £27.30

How much would a 50W panel cost you delivered to your door? £5?

 

I got this idea of getting some solar panels, there are some great deals on Amazon at way below $1/watt, and not doing the tradition DC to AC and tying that to the house grid, but rather using that DC power directly to power some DC appliances.

Say I have some 24/7 computers and equipment that run on various voltages from 12V to 20V DC using AC to DC power supplies. I'd like to feed the power from solar, if there is sun energy being captured, into the output of these power supplies.

What would be the easiest way to accomplish this? Or maybe not the easiest but most efficient? This is not a money saving exercise, but rather something to tinker with, have fun, and learn things along the way.

Hi there,

A lot of people use diodes to create a logical OR gate to allow two sources to power one load. It seems to work because a lot of people do it that way.
Because the solar panel will probably be one voltage only, you would also use buck circuits to step down the voltage to whatever you need. You then use diode logic to OR them with the main supply.
If the solar panel has a battery associated with it, you can charge the battery and then you have at least some free power even when there is no sun. Depending on the battery and the solar panel this may work nice or not be worth it at all. The battery has to be large enough, and the panel has to put out enough current at full sunlight to make this practical.
Positioning the panel is also an interest when it comes to these solar panels. You can determine what the best angle is by setting it up temporarily and see how the sun hits it, then adjust a little if needed. You might have to rotate it a little and adjust the slant so you get the most out of it. You might even have to put it in a different place if you find it's in the shade sometimes during the day.

I actually did this with a car I had, to keep the battery full even when not using the car. I found I did not need a max power tracker, just let it charge the battery with the current from the panel.
You should be able to get to 12v rather easy, and above that, but getting to 20v may be tricky unless you get a panel that can go a bit above that. 21v for example probably won't be good enough. That's unless you don't mind incorporating a boost circuit to boost the voltage up to a higher level like 25 volts or something. You have to keep an eye on how much current you draw from the panel though or the voltage may fall too low. If you are charging a battery it gets a little easier though.

It's tricky getting a max power tracker to work with set voltages because the voltage at max power may not match the set voltage anyway. That's again unless you don't mind incorporating a buck or boost circuit to accommodate the max power.

See what you think about all this and we can go from there if you wish.

 

As Ian has said, the simplest solution would be to charge batteries.
DC to DC converters are very efficient.

 

I got this idea of getting some solar panels, there are some great deals on Amazon at way below $1/watt, and not doing the tradition DC to AC and tying that to the house grid, but rather using that DC power directly to power some DC appliances.

Say I have some 24/7 computers and equipment that run on various voltages from 12V to 20V DC using AC to DC power supplies. I'd like to feed the power from solar, if there is sun energy being captured, into the output of these power supplies.

What would be the easiest way to accomplish this? Or maybe not the easiest but most efficient? This is not a money saving exercise, but rather something to tinker with, have fun, and learn things along the way.

Been there, done that.

You will need at least 200W of panels for it to useful for DC power applications, so don't buy 50W panels. Even at those power levels 12vdc becomes inefficient and really impractical due to wiring requirements to keep losses low as power levels increase.

 

The trick to my battery is that is connected to a UPS. So the battery is not being used for power unless there is a power outage. So if I charge it with solar, I would need to boost it up for 20V devices. So the voltage would need to be stepped down from solar, then back up. Two steps. I thought stepping down once to 20V would be more efficient.

A lot of people use diodes to create a logical OR gate to allow two sources to power one load. It seems to work because a lot of people do it that way.

The diode method is what I was thinking about initially, but that sounded too primitive. I thought maybe there are more elegant and efficient solutions.

Even at those power levels 12vdc becomes inefficient and really impractical due to wiring requirements to keep losses low as power levels increase.

With panels, the ones I was looking at are 19V under load under full sun. So if I run 3 in series that would be roughly 60-65V peak, and probably much lower under load. Series connection should help with wire losses too.

 

Sure you do. It's called the VAT.

Renewable energy products are exempt.
(And import duty and sales tax are not the same thing)

 

Renewable energy products are exempt.
(And import duty and sales tax are not the same thing)

Exempt for professional installation costing >10,000 or for retail purchase in small quantities?

I'm honestly intrigued if you could buy a single or a few panels like I mentioned at a lower cost delivered to your door in UK than in US. If you can provide some link that would show a delivered to the door price I'll gladly change my mind about European over-regulation.

 

The trick to my battery is that is connected to a UPS. So the battery is not being used for power unless there is a power outage. So if I charge it with solar, I would need to boost it up for 20V devices. So the voltage would need to be stepped down from solar, then back up. Two steps. I thought stepping down once to 20V would be more efficient.



The diode method is what I was thinking about initially, but that sounded too primitive. I thought maybe there are more elegant and efficient solutions.



With panels, the ones I was looking at are 19V under load under full sun. So if I run 3 in series that would be roughly 60-65V peak, and probably much lower under load. Series connection should help with wire losses too.

Take a look at this thread: https://forum.allaboutcircuits.com/...rge-controller-datalogger.194146/post-1825897

Lots of tinkering with small panels in various ways. Optimize your central power bank with something higher than 12VDC.

I tinkered with DC distribution with earlier systems, It's a dead-end IMO. I also used diode isolation between batteries.
https://forum.allaboutcircuits.com/...ic-controlled-battery-array.32879/post-204585

 

Make some little surgery to bring out of your UPS box its internal battery terminals to access charging it from solar panels using a $10 charger gadget or voltage regulator, and use it. You already have it.
If want to go beyond, add DC wiring to your dwelling with proper DC wall jacks/switches to feed your DC compfusers, lights, equipment.

I wish to do the same with 12VDC at chosen locations of the house; but my solar array puts 400VDC to the inverter in the basement and tapping that down to 12V can be not simple.
Anyone suggesting how DC to DC converter 400 to 12 perhaps 30 Amperes?

 

Exempt for professional installation costing >10,000 or for retail purchase in small quantities?

I'm honestly intrigued if you could buy a single or a few panels like I mentioned at a lower cost delivered to your door in UK than in US. If you can provide some link that would show a delivered to the door price I'll gladly change my mind about European over-regulation.

I don't mind a bit of regulation if it means safe electrical products, food that's safe to eat and not getting shot.

https://www.bimblesolar.com/solar/large-panels/SUN-405?sort=p.price&order=ASC
The VAT situation is complicated. You would pay VAT if you just want to buy some panels, but if you have them installed you don't. You also don't pay VAT on the labour costs not any other costs involved. For example, when I had panels fitted to the house roof, I paid no VAT on the £900 of scaffolding costs.

 

Make some little surgery to bring out of your UPS box its internal battery terminals to access charging it from solar panels using a $10 charger gadget or voltage regulator, and use it. You already have it.

I already have an XT60 terminal on my UPS that goes to a large external car battery, BUT, the UPS only charges the battery with a small current. Since I assume it has a small 120v AC →12v DC circuit for charging, and a large 12v DC → 120v AC circuit for on battery operation.

So if I tap into the battery, and the solar panel output + UPS charging circuit can't keep up with the load (not even close) then I'd need to add a ~13.8V power supply to the mix to keep the battery topped off.

 

The diode method is what I was thinking about initially, but that sounded too primitive. I thought maybe there are more elegant and efficient solutions.

There is, use Schottky diodes.
If you want to get fancy, look into MOSFET switching. You'll pay the price though with a lot more complexity unless you can find a ready-made IC or module.

 

You may not need to purchase panels from new. Now that solar has been installed on residential roofs for so long, I can get panels from the local recycling center for almost no cost (maybe < $0.05c / watt) - usually nominal 200W, less the degradation with age. They are perfect for playing around with - I'm looking at powering air con on my shed with a stand-alone system.

 

You may not need to purchase panels from new. Now that solar has been installed on residential roofs for so long, I can get panels from the local recycling center for almost no cost (maybe < $0.05c / watt) - usually nominal 200W, less the degradation with age. They are perfect for playing around with - I'm looking at powering air con on my shed with a stand-alone system.

I live in a pretty densely populated area of the country. Hence the 2nd hand market tends to be a seller's market. There is an identical Renogy 50W panel that I linked at on sale on Craigslist for $2 more than I can get it from Amazon.

Some of the better deals are quite a drive. But none that I can see with anything near 5 cents per watt. Maybe 3-4 times that. But I'll probably get a few smaller 50W panels new since I had this crazy idea of having a fan in my car pulling hot air out in the summer while it's parked. And that's where some of these smaller panels will end up eventually. On the roof of a car. Keeping the battery topped off is really nice too. Especially in the winter.

 

I had this crazy idea of having a fan in my car pulling hot air out in the summer while it's parked.

and putting it through a heat pump to produce domestic hot water?

 

But I'll probably get a few smaller 50W panels new since I had this crazy idea of having a fan in my car pulling hot air out in the summer while it's parked. And that's where some of these smaller panels will end up eventually. On the roof of a car. Keeping the battery topped off is really nice too. Especially in the winter.

Those products already exist and have done for a while. However, if you would like to tinker with it yourself, it is a nice project.

https://www.techgearinsider.com/sol...P-Uw_fNmam0hUrjSh2j7bn1pb07-PpyRoCzdAQAvD_BwE

 

I got this idea of getting some solar panels, there are some great deals on Amazon at way below $1/watt, and not doing the tradition DC to AC and tying that to the house grid, but rather using that DC power directly to power some DC appliances.

Say I have some 24/7 computers and equipment that run on various voltages from 12V to 20V DC using AC to DC power supplies. I'd like to feed the power from solar, if there is sun energy being captured, into the output of these power supplies.

What would be the easiest way to accomplish this? Or maybe not the easiest but most efficient? This is not a money saving exercise, but rather something to tinker with, have fun, and learn things along the way.

Hello again,

With regard to choosing either a buck or a linear, here are two text files you can check out.
One includes entries for all possibilities even when the buck is worse than the linear. The other only includes entries when the buck is better.
The buck is better when the percentage increase PiBL is positive. If it is negative, then the linear is better. If any happen to be zero, then they are both the same.

In the tables, the input voltage range is from 3v to 24v, and output voltage range is from 1.2v to 23v.
Output current ranges from 0.1 to 1.0 amps.

 

With regard to choosing either a buck or a linear

Linear to step down from solar panel voltage to whatever someone needs?

If the panel voltage is highly variable would anyone ever consider linear?