Two General Solar Questions

[steveap]

Hi, new to solar but I'm learning.
I have a 900 watt DC device I would like to power directly by solar. It's not picky about voltages or current and can handle some over-powering.
First question, what two panels would you recommend (manufacturer and model) that would give me a real 850 to 900 watts of power? I'm thinking perhaps two 425 to 450 watt N-type bifacial panels wired in series. Economical as the device is used only occasionally, mostly in winter, and low-light production (as in early mornings/evenings and partly cloudy days) is very important.
Second question will depend on the actual panels recommended.
Thank you all for your help and recommendations.

 

[Brucey]

Hi, new to solar but I'm learning.
I have a 900 watt DC device I would like to power directly by solar. It's not picky about voltages or current and can handle some over-powering.
First question, what two panels would you recommend (manufacturer and model) that would give me a real 850 to 900 watts of power? I'm thinking perhaps two 425 to 450 watt N-type bifacial panels wired in series. Economical as the device is used only occasionally, mostly in winter, and low-light production (as in early mornings/evenings and partly cloudy days) is very important.
Second question will depend on the actual panels recommended.
Thank you all for your help and recommendations.

You'll be better of expecting 70% of nameplate values. Four panels would be a more realistic choice. Winter time with low ambient light may not be enough.

 

[BaylentheSky]

You'll be better of expecting 70% of nameplate values. Four panels would be a more realistic choice. Winter time with low ambient light may not be enough.

Agreed! 4 panels in 2S2P configuration if your device can't take 4 in series. You can probably get 4 280W used panels for under $30/each, going the secondhand route is probably the most economical.

 

[eppich8479]

I have 4x 400w in 2s2p and i peak at like 800w. They are not ideal angles. But most of the day i make 200-300w

 

[steveap]

I have 4x 400w in 2s2p and i peak at like 800w. They are not ideal angles. But most of the day i make 200-300w

Interesting . . . so I should seriously consider much bigger or more powerful panels. I live in a small, old all-electric house. Eventually I would like to get a professional solar system and battery stack. But until then, at least especially this winter, I would like to supplement my electric heat with what I understand to be a 900 watt heating element / space heater, that works with either DC or AC. I don't want to burn the heater out on a day like today - very sunny but very cold. But it's unknown what it's burn-out threshold is. But two panels in series I would assume is ok as their open circuit voltage is most likely somewhere between 45 and 50v each. And it would seem, (I would guesstimate) four panels total would provide enough current to get that space heater element hot. The heat output is only regulated by the power going in. And these 4 panels will have no other function than to power this space heater during the day. So what are your recommendations/opinions on the rated power of the four panels I should use?

 

[eppich8479]

So a delta pro is 4kwh which means you could run that heater for 4h (if 100% efficient) i have a similar 4kwh all in one and i charge maybe 50% right now, winter, with 4x 400w 2s2p. Im going to upgrade to a 3s3p soon, so 3600 watts of panels. That would probably be more realist for running a heater 16 hrs a day. I say 16 because once the sun goes down you are on the clock.

Its really like a $8-10k investment just to run that heater all day

 

[steveap]

So a delta pro is 4kwh which means you could run that heater for 4h (if 100% efficient) i have a similar 4kwh all in one and i charge maybe 50% right now, winter, with 4x 400w 2s2p. Im going to upgrade to a 3s3p soon, so 3600 watts of panels. That would probably be more realist for running a heater 16 hrs a day. I say 16 because once the sun goes down you are on the clock.

Its really like a $8-10k investment just to run that heater all day

At the moment I'm grid-tied so my home heater (and everything else) is running 24/7 from the grid. I would like to just supplement the heat during the day with a solar powered heater system so at least for a few hours each day my grid space heater need not be running. I know and I'm planning on getting a complete solar system, panels, inverters, batteries, etc and I know that will cost me a lot of $$$ even with me doing much of the work. But this little independent heater system will always be independent of the main solar and/or grid system and will only supplement day-time heating. So I want it to be as economical as possdible but still work well . . . when the sun is shining.

 

[Backyard]

I'm going to assume your trying to power an electric heating element that originally ran on 120 volts AC at 7.5 amps and thus 900 watts

If you use two panels rated at say 450 watts each and 50 volts. That's only going to run the element at 100 volts maximum. But since we are putting a load on the panels the voltage will be less. Say maybe 80 volts total. That will be a about 400 watts at the element

You need to match the voltage and current of the panels to the resistance of the element

Say the element is 16 ohms. You might actually need three of these panels to get the needed voltage to run the element at 900 watts. You'll need to look at the voltage to current load chart of the panels to see where your current will be at what particular voltage so you can run the panels at the rated wattage. Sort of like how MPPT does it. Except your going to have a fixed load so there will be times when the panels won't be at their maximum power point and thus not running the element at full wattage.

If your element is a different voltage then the assumption above then adjust accordingly

 

[BaylentheSky]

I think he said his heater is DC, which means he's going to be able to use solar panels to power its heating element directly.

I have 4x 400w in 2s2p and i peak at like 800w. They are not ideal angles. But most of the day i make 200-300w

How are you only getting 2-300W out of a 1.6kW worth of solar panels?????

 

[steveap]

Thank you for your replies. I think I'll just start with two panels, take readings, watch how the heater reacts to full sunlight power and add panels as necessary with the understanding I may need as many as 4 panels.
But now for the second question.
I'm looking for the DC equivalent of the picture added here. I want the switch to be made for DC and I want a DC plug and socket where I can just unplug and remove the appliance when not in use. I still want something as small and compact and good-looking as possible as the unit will be installed on the wall inside the house. Where would I source such a thing? I'm not even sure what a DC plug and socket like this looks like. Your help is appreciated.

 

[Backyard]

Thank you for your replies. I think I'll just start with two panels, take readings, watch how the heater reacts to full sunlight power and add panels as necessary with the understanding I may need as many as 4 panels.
But now for the second question.
I'm looking for the DC equivalent of the picture added here. I want the switch to be made for DC and I want a DC plug and socket where I can just unplug and remove the appliance when not in use. I still want something as small and compact and good-looking as possible as the unit will be installed on the wall inside the house. Where would I source such a thing? I'm not even sure what a DC plug and socket like this looks like. Your help is appreciated.

You'll need to tell us what voltage and amp rating you'll need

What voltage is your system and how much current are you planning on switching or supplying from your outlets?

 

[steveap]

You'll need to tell us what voltage and amp rating you'll need

What voltage is your system and how much current are you planning on switching or supplying from your outlets?

I'm not exactly sure based on the comments above. But my target is 900 watts and voltage I doubt will be more than three panels in series or 4 in series/parallel. Probably safest to shoot for the highest possability - 3 panels in series or 4 in s/p. If it takes more than 4 panels to produce good heat, I'm not going to do this.

 

[BaylentheSky]

Thank you for your replies. I think I'll just start with two panels, take readings, watch how the heater reacts to full sunlight power and add panels as necessary with the understanding I may need as many as 4 panels.
But now for the second question.
I'm looking for the DC equivalent of the picture added here. I want the switch to be made for DC and I want a DC plug and socket where I can just unplug and remove the appliance when not in use. I still want something as small and compact and good-looking as possible as the unit will be installed on the wall inside the house. Where would I source such a thing? I'm not even sure what a DC plug and socket like this looks like. Your help is appreciated.

If it's a DC breaker that you need, it should be a simple purchase. If you need a receptacle, now that's..... it's going not going to be hard to jerry rig something like that yourself. There is what is called an Anderson plug/receptacle that you can buy to wire your DC input and output wires to. But the end result is, depending on your handiness, not going to be as clean as an AC receptacle, especially if you want it inside the wall.

 

[BaylentheSky]

Don't mind my Paint skill, here's an example of what I mean.
For a clean set up, you can buy those AC receptacles and run DC wires through them, and through the AC plug. However I'm not sure if I want to recommend this, as someone might one day try plugging into that DC receptacle with an AC plug and potentially ruin their device.

 

[steveap]

Don't mind my Paint skill, here's an example of what I mean.
For a clean set up, you can buy those AC receptacles and run DC wires through them, and through the AC plug. However I'm not sure if I want to recommend this, as someone might one day try plugging into that DC receptacle with an AC plug and potentially ruin their device.

Yes, something like that may work ok. If I could put that breaker and Anderson connector in a small box of some kind at the baseboard it would not stand out too much. And just open the cover whenever I wanted to plug and unplug the device, or turn the power on or off. And that's better than putting the breaker outside with the solar panels like I was thinking of doing. Thank you.

 

[BaylentheSky]

Yes, something like that may work ok. If I could put that breaker and Anderson connector in a small box of some kind at the baseboard it would not stand out too much. And just open the cover whenever I wanted to plug and unplug the device, or turn the power on or off. And that's better than putting the breaker outside with the solar panels like I was thinking of doing. Thank you.

Make sure you size your DC breaker and the Anderson connector, as well as all the wirings, with the right amperage. If you're doing 4 in series, then the current will likely be below 10 amps, so buy a 15 amp breaker. Double that for 2s2p.

 

[steveap]

Make sure you size your DC breaker and the Anderson connector, as well as all the wirings, with the right amperage. If you're doing 4 in series, then the current will likely be below 10 amps, so buy a 15 amp breaker. Double that for 2s2p.

Thank you. As a self-taught DIYer I tend to be very conservative when it comes to electrical. For example when I first moved into this 90 year old house I noticed most of the electrical outlets were on 20 amp breakers. Perhaps the wiring was made for 20 amps, but I doubt it due to the age of everything. So I replaced those 20 amp breakers with 15 amp breakers and never had an electrical problem. I've just never worked with DC before, other than small car and truck things.

 

[BaylentheSky]

If you don't notice the inconvenience of it tripping more often than you'd like, then that's ok! Sometimes my wife would use her hair dryer while running the space heater in the bathroom, while I'm running another space heater in our bedroom, and the 20 amp breaker would trip since they're all on the same circuit. She since learned to turn off the space heater then use her hair dryer with no issues

 

[steveap]

If you don't notice the inconvenience of it tripping more often than you'd like, then that's ok! Sometimes my wife would use her hair dryer while running the space heater in the bathroom, while I'm running another space heater in our bedroom, and the 20 amp breaker would trip since they're all on the same circuit. She since learned to turn off the space heater then use her hair dryer with no issues

I've never had one trip on me, but one of the outlets I replaced was very burned and black.

Until I purchase things next week, I'm still very open and look forward to any other suggestions or insights anyone else may have.