I'm one of those newbies who suddenly realised how much electricity was going to cost...

[ApertureMountain]

Hey members!

My name is Dan, I'm from Worcestershire in the UK. I work as a programmer for a manufacturing company and work 3 days a week at home.

After putting a UPS in my office, and another in my wife's office I was able to start tracking actually how much power I was using when we work. My wife averages at 50W and myself at 120W.

I thought I could get a couple of 100W panels and attach this to a couple of batteries and job well done to me.

After getting 1 panel, 2 controllers (because the first one had no comms) and 2 batteries, oh how wrong I was.

I've joined here to learn more about how to get the best out of my system, but at the same time not tying directly into my meter. My plan is to run a cable from the batteries into the house and power our offices off that. When the batteries are low, then switch to grid.

I've since realised my controller is not fit for purpose, but hey.. thats all about learning from your mistakes, right?

Thanks to all in advance, and I look forward to learning a lot from you all

Dan

 

[Rednecktek]

Welcome to the forum, and prepare to have your head overstuffed with info. Yeah, math rears it's ugly head pretty quick and geography is really unforgiving. My weather at home is pretty similar to yours and I have to multiply by 10 whenever I math out my systems as even a 300w setup can't provide 120Wh of power a day for half the year.

 

[Supervstech]

Hey members!

My name is Dan, I'm from Worcestershire in the UK. I work as a programmer for a manufacturing company and work 3 days a week at home.

After putting a UPS in my office, and another in my wife's office I was able to start tracking actually how much power I was using when we work. My wife averages at 50W and myself at 120W.

I thought I could get a couple of 100W panels and attach this to a couple of batteries and job well done to me.

After getting 1 panel, 2 controllers (because the first one had no comms) and 2 batteries, oh how wrong I was.

I've joined here to learn more about how to get the best out of my system, but at the same time not tying directly into my meter. My plan is to run a cable from the batteries into the house and power our offices off that. When the batteries are low, then switch to grid.

I've since realised my controller is not fit for purpose, but hey.. thats all about learning from your mistakes, right?

Thanks to all in advance, and I look forward to learning a lot from you all

Dan

I am guessing you loads are 170W combined, for how long? Say 8 hours... that's 1360Wh
Is the 170W over 24H? That would be 4080Wh
Now divide by the solar hours in your area 1 to 5 depending on time of year and weather... and that's the amount of solar you need...

 

[Rednecktek]

I've joined here to learn more about how to get the best out of my system, but at the same time not tying directly into my meter. My plan is to run a cable from the batteries into the house and power our offices off that. When the batteries are low, then switch to grid.

It sounds like a perfect use case for one of the hybrid AIO's. Even a little 1Kw MPP would run on batteries and panels until the weather kicked in then it would jump over to the utility/grid power and there's GOTTA be something similar for 230v EU power.

@ApertureMountain : Now that my slow ass internet has loaded your stuff I've got a couple observations:

The panel isn't going to last long most likely. Unless you're in a weird place where you NEED your panel to flex, the flexible panels are notoriously short lived. When you go to kick up this system, ready yourself to have that die on you.

The SCC is a nice little controller and at 20a will handle 240w of panel, although considering your location 300w wouldn't be a stretch at all.

The batteries are a great way to save up-front money but they do have 1 major drawback and that is capacity. All the Lead Acid (FLA, AGM, GEL) batteries are only good for around 50% depth of discharge (DoD) before you start damaging them. In your case, since you have 2 of them that's going to be 110Ah @ 12v = 1320Wh. In a perfect world that would power your computers (is that wattage load counting the monitors and speakers?) for 1320Wh / 170W = 7Hr 45Min or not quite a full "normal" work day. With inverter inefficiencies that's going to be less. If you work during daylight hours you could probably make it all day but your system would need to be fully recharged at night via grid power every night since the sun is down.

Obviously flip that if you're both night owls.

To top that off in a day, assuming you can get the average 4 hours of sun a day would be 1320Wh / 4Hr = 330w of panel and a 40a MPPT controller. Considering where you live, that's going to get MUCH larger quickly.

Mind you, this is all Rough Napkin Math before everyone jumps in with calculations down to the 0.000000001w and charts and tables and Colum effects and such. You know who you are ?

Sadly Solar is pretty much the MOST expensive way to get electricity. Paying retail for everything tends to settle out at about $3USD/watt by the time you've got all the batteries and cables and fuses and shunts and and and and Having krappy weather makes the ROI time painfully long, but you get the satisfaction of PWNING N00BS when the power is out.

 

[12VoltInstalls]

Rough Napkin Math

Wildhat Guess here: two more panels and two more identical batteries might make that livable imho. Guessing.

 

[12VoltInstalls]

•

 

[Rednecktek]

Could someone throw up the PWatts and JRC Solar Calculator info for Worcestershire, UK please? For some reason our firewall doesn't let me go there.

But I can get to Pornhub...

I guess they really DO know sailors. ?

 

[ApertureMountain]

Thanks for this AMAZING advice, it really really does help, thank you!

@Rednecktek
Regarding the batteries, they're both 110Ah, so would I be correct in thinking that would make 220Ah so 2640Wh at 12V?

The reason I went for a flexible one is that the idea is this was more of a 'test' panel, and it will end up ontop of a rooftent for my vehicle longer term. I want to prove to the financial director (read: my wife) that solar makes sense for the investment..hoping it is the case!

RE the controller, I realised after I got it that it had this specification:
Max Input Power:12V @ 260W | 24V @ 520W
Does this mean that I could only ever get max 260W (at 12V)?

@12VoltInstalls
I sort of think the same as you, if I get another couple of panels (on the roof I'm putting them on, I could fit around 6) then double the batteries it might make it (5280Wh I would think? Or have I calculated it wrong at 440Ah)

@Supervstech
Thanks for the really consise breakdown of what I need, this really helped easily work out what I'll need. Thank you.

 

[Rednecktek]

Thanks for this AMAZING advice, it really really does help, thank you!

@Rednecktek
Regarding the batteries, they're both 110Ah, so would I be correct in thinking that would make 220Ah so 2640Wh at 12V?

You would think so but as I mentioned lead acids start getting damaged if you drain them below about 50% so your 220Ah is only half usable, or 110Ah @ 12v = 1320wh of usable capacity. That's one of the reasons people love the Lithium flavors as they can be drained to 100% and not be damaged, but you gotta be willing to pay for it. Personally I use a LOT of similar batteries to yours because if I damage one with my krappy weather it's only a 15 min drive and $100USD to replace it.

The reason I went for a flexible one is that the idea is this was more of a 'test' panel, and it will end up ontop of a rooftent for my vehicle longer term. I want to prove to the financial director (read: my wife) that solar makes sense for the investment..hoping it is the case!

Aaahh, one trick I've seen to help keep them from overheating is to grab the corrugated plastic sheets from your local craft store and put that behind the panel to allow airflow behind it. The biggest issues those tend to have is overheating because there's no airflow on the back side.

RE the controller, I realised after I got it that it had this specification:
Max Input Power:12V @ 260W | 24V @ 520W
Does this mean that I could only ever get max 260W (at 12V)?

Yup, that's the max the controller can do before it cooks itself. In your weather you could probably over-panel that to 300w since the odds of you ever getting perfect conditions is next to nil or less.

@12VoltInstalls
I sort of think the same as you, if I get another couple of panels (on the roof I'm putting them on, I could fit around 6) then double the batteries it might make it (5280Wh I would think? Or have I calculated it wrong at 440Ah)

See calculations above on Lead Acid and DoD. If you've got space then you should look at a single higher wattage panel rather than multiple smaller panels. The cost per watt is usually better as you scale up.

 

[madmax]

170w consumption. 100w production.
If grid tie is allowed, id just do that. Power would never make it to the grid anyhow., And best you can do is offset, you still need 70w from the grid.

 

[ApertureMountain]

You would think so but as I mentioned lead acids start getting damaged if you drain them below about 50% so your 220Ah is only half usable, or 110Ah @ 12v = 1320wh of usable capacity. That's one of the reasons people love the Lithium flavors as they can be drained to 100% and not be damaged, but you gotta be willing to pay for it. Personally I use a LOT of similar batteries to yours because if I damage one with my krappy weather it's only a 15 min drive and $100USD to replace it.

Ah, I should of assumed I misread than the other way round thanks for clearing that up. Long term lithium does make sense. I think I'll end up putting the 2 batteries I have in the car as well as the flexi-solar on the roof as less of a requirement to always work etc. Thanks for explaining that.

Aaahh, one trick I've seen to help keep them from overheating is to grab the corrugated plastic sheets from your local craft store and put that behind the panel to allow airflow behind it. The biggest issues those tend to have is overheating because there's no airflow on the back side.

Ahha! Well thats exactly what is holding the panel at the moment. My house is North facing but I've put a lean-to on the side with corrugated sheets as the roof, hoping this'll suffice and hold the panels (ignore the network cables..I will tidy I promise):


I'm aware the foilage is ruining my peak output, but as mentioned this is just a test panel and gives me the most cable to work with. Long term the panels will start from the far side I promise!
But thanks regarding the overheating, hoping the fact it's currently as it is, that should help the lifespan.

Yup, that's the max the controller can do before it cooks itself. In your weather you could probably over-panel that to 300w since the odds of you ever getting perfect conditions is next to nil or less.

I guess this is why I need to look at the hybrid MPP idea you mentioned originally. It makes sense rather than me building in a transfer switch or similar, if a controller can do the whole thing anyway!

See calculations above on Lead Acid and DoD. If you've got space then you should look at a single higher wattage panel rather than multiple smaller panels. The cost per watt is usually better as you scale up.

Ooo..that i didn't know.. I'll have a look into that. I am limited height wise, but nothing prevents me mounting the solar panels lengthways right?

Thanks to everyone once again, this has been my best experience yet of talking to the community about my terrible set up haha, so thank you

 

[ApertureMountain]

170w consumption. 100w production.
If grid tie is allowed, id just do that. Power would never make it to the grid anyhow., And best you can do is offset, you still need 70w from the grid.

Thanks for this - I do plan to have around 600W total at some point but for now I just wanted to test that the concept works. As you mention a grid tie would make sense, I'm looking at a backward-UPS idea, so it'll pull from the battery (powered by solar) until battery is low, then pull from grid (I think this is what the hybrid system @Rednecktek mentioned is), so thank you for explaining

 

[Rednecktek]

Ooo..that i didn't know.. I'll have a look into that. I am limited height wise, but nothing prevents me mounting the solar panels lengthways right?

Nope, you could mount them diagonally for all they care, as long as they get direct sunlight they're happy.

The corrugated in the back should work perfectly.

Long term, and barring environmental considerations, LFP is the Bee's Knees if you can afford it. I have 4 cats and a wife to feed along with environmental concerns so LFP is a non-starter for me. As a "Proof-Of-Concept" system, it's easier to swallow destroying a leisure battery than a LFP.

 

[Rednecktek]

I guess this is why I need to look at the hybrid MPP idea you mentioned originally. It makes sense rather than me building in a transfer switch or similar, if a controller can do the whole thing anyway!

It's also going to be cheaper than buying all the components individually. I would recommend jumping to a 2-3KW system and 24v batteries right out the gate if you can pass it by the CFO as it will give you more overhead (when you ramp up the load on the computer the wattage goes up) and room to grow (2000w of panel support) and since you already have 24v batteries (ya know, 2 of the 12v hooked up in series) it's not a huge change-up.

 

[DerpsyDoodler]

Thanks for this - I do plan to have around 600W total at some point but for now I just wanted to test that the concept works. As you mention a grid tie would make sense, I'm looking at a backward-UPS idea, so it'll pull from the battery (powered by solar) until battery is low, then pull from grid (I think this is what the hybrid system @Rednecktek mentioned is), so thank you for explaining

What respondent described is unsafe. If grid is down, you would be backfeeding. It could potentially hurt or kill someone expecting those lines to be dead. Best to do it right. You can get inverter/chargers. They take ac in from the grid, and pass it through. They have built-in auto-transfer switches that are usually configurable. It's simple and most importantly safe.

 

[Rednecktek]

And they can be configured to draw off the solar/ batteries first OR the grid first making it an over glorified UPS.

Something like the MPP 3Kw 24v would be a pretty sweet spot.

 

[Supervstech]

170w consumption. 100w production.
If grid tie is allowed, id just do that. Power would never make it to the grid anyhow., And best you can do is offset, you still need 70w from the grid.

That assumes the panels will come close to 100W, and the load is only during peak sun hours.
In reality it's more like 60W during peak sun, and 10 or so the remainder of sun...
And the load is constant the entire workday, often into the night, so...

 

[madmax]

Thanks for this - I do plan to have around 600W total at some point but for now I just wanted to test that the concept works. As you mention a grid tie would make sense, I'm looking at a backward-UPS idea, so it'll pull from the battery (powered by solar) until battery is low, then pull from grid (I think this is what the hybrid system @Rednecktek mentioned is), so thank you for explaining

The mppt type systems are probably your easiest solution. If you stay under 1kw it will not be that expensive. 600w may seem like a lot, but unless you have optimal panel installations, expect something significantly less. Shade, angles, etc, and clouds all change things.

If you break 1kw production a day, your doing pretty good . Except your using 170w/hr.
You can actually split your systems. Add a grid tie with about 300w... And then when you have enough funds/needs add 600w and a all in one type unit.
Keep the grid tie on the inverter side of things so it's isolated from the main grid. Then have the all in one set to "always use from battery/solar" unless the voltage drops from the battery below a set voltage. Then it switches to grid.

That assumes the panels will come close to 100W, and the load is only during peak sun hours.
In reality it's more like 60W during peak sun, and 10 or so the remainder of sun...
And the load is constant the entire workday, often into the night, so...

Agreed. Which is why grid tie is the easiest way without a high overhead cost of batteries. Its such a low production he would use it up before it even made it to the battery.