3kW, 4kW, 4.5kW?

[Garald]

I think I'll have solar panels installed after all. (For anybody who has not been following: I'm finishing renovating a very non-flat flat that is most of a smallish house in the Paris area; I have a heat pump; the roof has SES and NWN exposure)

 

I've got two quotes and will get more. Questions:

(a) I take it is in fact better to have a separate controller for each panel?

(b) Different installers suggest different installation sizes. What is better for me: 3kW, 4kW or 4.5kW?

 

My energy consumption for the last three months: 374 kWh in February, 168kWh in March (I was away a bit), 292kWh in April (I was also away a bit but I have two AirBnB guests). November was 809kWh and December was 709kWh, but that was when I was having the heat pump heat water at 45C rather than let it choose its own operating temperature. (January was an anomaly that I am trying to get sorted out.) Most of that was the heat-pump. Looking further back: my August and September consumption last year was 233kWh and 216kWh.

 

I can sell the electricity I don't consume myself back to the energy company, but the rate is not fantastic (0.13eur/kWh or so).

 

(On something else - the offer from IKEA is not the lowest one. Do they have a good reputation in this business?)

 

 

[JohnMo]

a) depends on shading and even then you can just fit optimisers. I like a single inverter.

 

More the better for kW. Winter can be rubbish, no matter how much you have.

[SteamyTea]

Check out the prediction with PVGIS.

 

Micro inverters and optimisers are really only installed to cover shading problems, and were often oversold.

Hard to tell if they are needed without seeing the proposed location.  Normal PV modules have bypass diodes in them anyway.  Those diodes cut out any shaded cells and then the inverters maximum power point tracking can deal with the rest.

[MikeSharp01]

2 hours ago, SteamyTea said:

Normal PV modules have bypass diodes in them anyway.  Those diodes cut out any shaded cells and then the inverters maximum power point tracking can deal with the rest.

Yes but the losses may or may not be significant depending on the nature of the setup, personal views on the value / scale of the lost percentage. Solaredge have a couple of briefing papers on it and the use of module level MPP (Maximum Power Point) trackers to wring the last few percent from an array with some shading likely. https://knowledge-center.solaredge.com/sites/kc/files/se_technical_bypass_diode_effect_in_shading.pdf  and the theory of module level MPP trackers https://knowledge-center.solaredge.com/sites/kc/files/moving_forward_to_module_level_power_optimization.pdf

[Garald]

18 hours ago, SteamyTea said:

Check out the prediction with PVGIS.

 

 

 

 

 

This is what I get from PVGIS for a system with 4.5 kW peak:

Is this too much? Roughly right? My consumption should stay beneath what is portrayed here except for December and January.

 

I don't expect much shading. This is my place - or that this is what it looked like from above, before I put in a fair number of additional skylights, postly on the NWN side:

I mean the red brick house. (The garden is not mine).

 

Edited April 30 by Garald

[Garald]

Sorry, I meant: My consumption should stay beneath what is portrayed here between March and October 

[Dillsue]

Your azimuth figure should be -30 for a SES facing roof but that's not going to make a huge difference.

 

Remember that to use PV, without batteries, you need to use it when the sun is out and generating. If you or your guests are out during the day and back in the evening to cook/wash etc then you'll be exporting lots of surplus PV during the day and importing in the evening.

 

The only way to more accurately compare your usage with forecast generation is to use hourly figures. 

[Garald]

11 hours ago, Dillsue said:

Your azimuth figure should be -30 for a SES facing roof but that's not going to make a huge difference.

 

Ah sorry. Yes, it makes next to no difference.

 

 

11 hours ago, Dillsue said:

 

Remember that to use PV, without batteries, you need to use it when the sun is out and generating. If you or your guests are out during the day and back in the evening to cook/wash etc then you'll be exporting lots of surplus PV during the day and importing in the evening.

 

Excellent point, though a hot water tank is a battery of sorts. Presumably things can be set up so that water in the tank is heated mainly when the sun is out.

 

I understand batteries of the more conventional kind have become much more efficient as of late. I.imagine some folks with PVs here have batteries? What is their experience?

[SteamyTea]

15 minutes ago, Garald said:

I.imagine some folks with PVs here have batteries? What is their experience?

People that have paid quite a bit for batteries tend to do a lot of post purchase rationalisation.

[Dillsue]

4 hours ago, Garald said:

Excellent point, though a hot water tank is a battery of sorts. Presumably things can be set up so that water in the tank is heated mainly when the sun is out.

Yep. A PV diverter will do that for you. Ideally you want 2 immersions in your tank and a diverter that will heat the top of the tank first and switch to the bottom immersion when the stat in the top one switches off.

[Garald]

1 hour ago, Dillsue said:

Yep. A PV diverter will do that for you. Ideally you want 2 immersions in your tank and a diverter that will heat the top of the tank first and switch to the bottom immersion when the stat in the top one switches off.

 

Hm, but that's direct electric heating, no? (I have a heat pump.)

[MikeSharp01]

7 hours ago, Garald said:

but that's direct electric heating, no? (I have a heat pump.)

The problem with using the heatpump (HP) to heat the water via PV is that a HP needs to run for long periods. So you may get long periods of sun but you may get a cloudy day and the PV generation is going up and down so causing intermittent availability for the HP which you don't want to be turning on and off all the time so you will end up importing.