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OtleyLad

Spec for my shed - what do you think?

I've got a provisional spec for my shed electric system for under £1000:

250w PV panel £359 here
Charger/Controller MPPT 600W at 12 or 24V here £199
2 110ah batterries here £232
Inverter 1500w pure sine 12v->240v here £159

The logic is that I can get more solar panels later and maybe switch to 24v operation by getting a new inverter.
I hope to run:

PC 200watts 5 hrs 5 days a week
Lights 50watts 3 hrs 5 days a week

It would be nice to run the freezer too:
Freezer (65watts) on all the time - but this may not happen
until I get another PV panel.

I imagine that this will run out of juice in winter, but then as I add new panels it will get nearer to meeting my needs.

Any comments would be welcome....
marigold

A thousand quid just for the shed electrics? Shocked Some shed!
Jb

Is your freezer really on all the time? My freezer uses about 80 - 85 W but only about half the time.
OtleyLad

A thousand quid just for the shed electrics? Shocked Some shed!


I work from home and its my office so i'm in it every day.
OtleyLad

Is your freezer really on all the time? My freezer uses about 80 - 85 W but only about half the time.


Well it rated at 65watts (checked it with the manufacturers). As its in an open car port I am sure it doesn't have to work too hard most ofthe year.
marigold

A thousand quid just for the shed electrics? Shocked Some shed!

I work from home and its my office so i'm in it every day.

I see Very Happy
RichardW

With that level of usage you are going to be running those 2 bats very very hard. Cycling to 50% DOD every day will soon kill them.
(I have ignored the fact that a lot of your loads will actually be provided directly from the PV & not the battery at all, better to calc worse case I always think)

You need to think about doubling the battery bank size.

What about dull days? How long do you want to run on the bats before having to go back onto the mains? Even in summer you can get up to 5 bad days in a row.

One good thing is every 5 days they will get a rest so can be fully fully charged with no loads.

Your usage is about 1/3rd of ours. Our battery bank is over 4000ah @ 12v.

A 250watt panel will give about 1.5kwh per good day in summer (you are using 1.15kWh) so that is also a little tight allowing for UK weather. Out side of summer you dont have a hope in hell of powering those loads from one panel & with the small battery bank you cant carry the power over from 7 days to power the 5 days as you only start the week with one days power in the bank.


What about THIS inverter? I think its almost the same one.

Just check the temp calcs on the panels as the 60v OCV could be nearly at the controllers max input of 75v in very cold weather.

Roughly

panel spec temp 45c + -2c
tolerance 3%
voltage increase per 1c drop in temp 0.34%
coldest winter -15c (its been colder)
total temp range 50c
50 x 0.34% = 18.7% + 3% = 21.7%
(plus compounding but I cant be bothered)
21.7% of 60.7v = 13.17

60.7v + 13.17v = 73.87v

That is far far to close for comfort, never mind the lack of compounding.


If you are thinking of going for a 24v system do it from the start. Each unit should cost about the same any way.
OtleyLad

Richard
Thanks very much for the detailed info.

Is your Inverter recommendation just on the price difference (about £8 after postage)?

I see that I need to find another charger/controller that can handle a higher input voltage - like this one?
Has max input voltage of 150. So this would be ok for 2 or more 250w panels in parallel?

Can't find a similar priced 250w PV panel config (like 2 x 120watt) that comes close to the single 250watt price though.
Thats the reason for starting at 12v.

See what you mean about the batteries.
I'd would start off running just the lights, adding more panels/batteries before powering the PC.
Finally getting to running the fridge too (Before spreading to the house).
RichardW

Richard


So this would be ok for 2 or more 250w panels in parallel?

Can't find a similar priced 250w PV panel config (like 2 x 120watt) that comes close to the single 250watt price though.
Thats the reason for starting at 12v.



Not a recommendation re inverter just "putting it out there" Personally I think the extra £8 is worth paying to get local support.

That controller looks good & is fully configurable via a PC. You could have 2 panels in series & more in parallel up to 60amps of charge current. So thats 840 watts at 12v or 1680 watts at 24v (another reason to go 24v).
Looks a cheap price for what it offers.
(ah just spotted its not a BIN so will go much higher)

Those panels are suitable for a 24V system even if using one panel as the MPP (Vmpp) is 50v. You could also go for 36v but parts are harder to find. 50v is not enough for a 48v system.
OtleyLad



That controller looks good & is fully configurable via a PC. You could have 2 panels in series & more in parallel up to 60amps of charge current. So thats 840 watts at 12v or 1680 watts at 24v (another reason to go 24v).
Looks a cheap price for what it offers.
(ah just spotted its not a BIN so will go much higher)

Those panels are suitable for a 24V system even if using one panel as the MPP (Vmpp) is 50v. You could also go for 36v but parts are harder to find. 50v is not enough for a 48v system.


So I could run at 24v with the one panel - as long as I get a 24v version of the inverter above. So I wire my 2 batteries in series (and then 2 (serial) pairs in parallel etc).

Its very reassuring to have your feedback - I have the 2011 Solar Electric Handbook but its not the same.

Thanks again.
RichardW

Yep you got it.

Try to keep the number of strings (the parallel lines) down to a minimum (under 6 pairs under 4 pairs is better) so if you want more storage you need larger individual bats to start with.

When you are ready I will go over the actual wiring connections & where to put them cos a small difference will make a huge performance & life difference to the bank.
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