New from Europe

[jnbspace]

Hi people,


Astrophysicist and tinkerer who wants enough off grid solar to run the freezers when the power goes down over winter.

I'm new to this forum and almost completely new to building solar systems. So far I've built and wired from scratch my workshop and my wife's studio which are both on grid for the moment. I've built a tiny solar lighting system for the workshop and a larger offgrid system which can power some of my workshop tools and charge up the battery ones. So I have enough experience to know how little I know.

Now I'm looking to build something bigger. My current system uses 240W of solar panels charging 1.3kWh of battery running into an inverter which can nominally put out 2kW (not that I would trust it to do that). What I want is enough power that when Britain gets to its expected winter power cuts I can keep the freezers and computers going.

 

[SeaGal]

I didn't think we're in Europe any more .

Welcome!

Technically a simple calculation....

a) What is kW usage of your freezers and computer use * how many hours of power cut is expected = kWh required
b) * 1.2 as battery will only do approx 85% DoD
c) How much sun available in Dec / Jan between anticipated power cuts to determine PV panel capacity to charge to 100% between power cuts.

Think a) and b) are easy to calculate... c) less so ?️?️?️

A rough guide would be 10% of kWp in daylight cloud; so 4kW of panels may generate 400W for 6 hours on a winter's day if dull and no sun?

 

[jnbspace]

I didn't think we're in Europe any more .

Welcome!

Technically a simple calculation....

a) What is kW usage of your freezers and computer use * how many hours of power cut is expected = kWh required
b) * 1.2 as battery will only do approx 85% DoD
c) How much sun available in Dec / Jan between anticipated power cuts to determine PV panel capacity to charge to 100% between power cuts.

Think a) and b) are easy to calculate... c) less so ?️?️?️

A rough guide would be 10% of kWp in daylight cloud; so 4kW of panels may generate 400W for 6 hours on a winter's day if dull and no sun?

The kW usage of freezers is quite easy to measure (or at least should be as soon as I can find my meters which I have obviously put somewhere really safe) Online I have seen figures or 50W quoted as typical but that seems wrong because with four fridges and freezers that equates to half my electricity being spent on just refrigeration. PIcking 100W which is either modern efficient freezers or rationalising it to two freezers when the power goes down means 2.4 kWh for a full day. Adding in one computer and the routers / WAP adds maybe 600 Wh. So lets say 3 kWh per day (better figures are pending)

Length of power cut is undetermined. Last time we had a long power cut it lasted five days but that was exceptional. More realistic is that without reliable power from Europe rolling power cuts have been mooted as a planned option. (actually those plans have always been in place its just more likely now) so allow for 12-24 hours. So being really lazy with the calculations that means 3kWh of reserve.

allowing for DoD that means about 3.6 kWh of battery.

Available sun in Dec/Jan is actually surprisingly easy to find. Long term winter average for northern Europe is about 2 hours per day. Obviously that could be 2 days of cloud and 1 sunny day but we don’t tend to have extended long periods of grey weather. So a 1kW array of panels would sit idle for 2 days and then fully charge the batteries if line up perfectly in about 4 hours. So the plan is;

1kw panel array. Probably 8 x 120W panels
run the system at 24V
That runs into a 60A charge controller
4 batteries (probably 110 Ah 12V)
And run that into a 3000W inverter

at the moment what I have is
2 x 120W panels
A really nasty cheap charge controller
1 110 Ah 12V battery
A 2000W inverter that I really wouldn’t trust
and a learning curve

That ignores the charging from overcast days but if I include charging at the 10% rate you suggest then such a system could run for two days even over winter.

of course my learning curve may show all of the above to be wrong ;-)

 

[Danke]

For power outages, cheapest and reliable way is with a generator.

If you don’t want it to run constantly, you can also have it charge batteries.

 

[mrzed001]

Use the EU simulator
It has an off-grid option. So it will tell how many kWp PV, how many kWh battery, with how many daily kWh use will be enough.

JRC Photovoltaic Geographical Information System (PVGIS) - European Commission

Photovoltaic Geographical Information System (PVGIS)

re.jrc.ec.europa.eu

Generator is cheap but not an UPS. Needs time to start.
Also very loud. If you start it at night you neighbours get maybe a bit irritated :D

And do not forget the inrush. The PC power supplies, the electric motors have it.

I would go with an All-in-one inverter like MPP Solar.
Everything is built in.
Just connect it, and you have a solar UPS system :D

 

[jnbspace]

Use the EU simulator
It has an off-grid option. So it will tell how many kWp PV, how many kWh battery, with how many daily kWh use will be enough.

JRC Photovoltaic Geographical Information System (PVGIS) - European Commission

Photovoltaic Geographical Information System (PVGIS)

re.jrc.ec.europa.eu

Generator is cheap but not an UPS. Needs time to start.
Also very loud. If you start it at night you neighbours get maybe a bit irritated :D

And do not forget the inrush. The PC power supplies, the electric motors have it.

I would go with an All-in-one inverter like MPP Solar.
Everything is built in.
Just connect it, and you have a solar UPS system :D

An EU simulator would be a lifeline for the UK right now ;-) Nice simulator. Interestingly it shows something I had thought before which is that if you are not worried about summer performance then you are almost better off putting these things as upright as possible. 74° optimises winter performance here but is so close to upright that you might as well bolt them to a wall.

I've not seen the MPP range before. It seems surprisingly cheap but the only suppliers I can see are in china or ebay. They don't seem to have an EU supply chain. What is their warranty / support / reputation like?

 

[mrzed001]

An EU simulator would be a lifeline for the UK right now ;-)

?

Nice simulator. Interestingly it shows something I had thought before which is that if you are not worried about summer performance then you are almost better off putting these things as upright as possible. 74° optimises winter performance here but is so close to upright that you might as well bolt them to a wall.

Exactly. Many use them in Germany on the walls and balkon. Balkonkraftwerk

I've not seen the MPP range before. It seems surprisingly cheap but the only suppliers I can see are in china or ebay. They don't seem to have an EU supply chain. What is their warranty / support / reputation like?

MPP Solar (same as Voltronic Axpert) inverters can be bought from Taiwan. 5kW MGX is one of the best sellers with the 500Voc MPPT.
And it can do that the grid consumption is lowered by the current PV production

MPP Solar Inc » PIP-MGX Series

www.mppsolar.com

Or you can buy it from Italy:

Inverter – SolarPower24

www.solarpower24.it