Predicting Solar Needs

[puntloos]

Just some random thoughts here:

 

My current home is fairly energy hungry. I guess because I'm somewhat of an IT nerd I have a permanently running server - say 60-ish watts, a bunch of smart displays (10 each, maybe), electric car just a large amount of devices overall that somewhat add up to an average wattage of about 700W (6500Kwh per year) but if I add the upcoming ASHP to my estimated future usage I'll probably hit 1000W average (8000Kwh/year)

 

How do I figure out a reasonable amount of panels and batteries..

 

I think as a rule of thumb, an 1000W array could optimistically create 1000kWh in the UK, if it's pointed exactly the right way. Less nice angles will drop that somewhat. The maximum amount of panels I can 'probably' do is 30, which would be 30*400=12000W which seems like the right ballpark to aim for. How much battery space would one recommend to go with that?

 

[joth]

 

Why predict when you can measure! (If your existing smart meter is on DCC)

 

[billt]

This tool will give you a good idea of how much you can generate. https://re.jrc.ec.europa.eu/pvg_tools/en/ 

 

Battery size is usually calculated by working out how long you want autonomy for. If you use 8kWh a day and you want 1 day autonomy you need about 8.5kWh of storage which would be about 170Ah for a 48V battery.

 

Note that solar production is very variable and you'll get very little in the winter when you're running the ASHP most.

 

My system has about 15000W of panels and averaged about 4kWh per day last December but 44kWh per day in May. Being further south and probably having a better site you may get less variation than that but it's still going to be large.

[JamesPa]

If you haven't already You might want to read this thread in Energy Storage ' 

There is a fair amount of discussion on whether battery storage  makes financial sense and the answer, in many cases, is no, particularly if you have or can get a reasonable export rate.  Unless that is unless you have a source of dirt cheap batteries.

 

Of course if the objective is autonomy that's a different consideration.  

 

I don't think there is an environmental case for battery storage, unless someone can make an argument to the contrary.

[SteamyTea]

35 minutes ago, JamesPa said:

don't think there is an environmental case for battery storage, unless someone can make an argument to the contrary

Well you could charge batteries when the grid has excess low carbon generation.

Should be easy enough to grab the 5 minute data from Templar Gridwatch and switch the charger on.

I think last week most of my usage (22 kWh) was when low carbon generation was over 50% of total generation. 

[Dillsue]

32 minutes ago, SteamyTea said:

Well you could charge batteries when the grid has excess low carbon generation.

Should be easy enough to grab the 5 minute data from Templar Gridwatch and switch the charger on.

I think last week most of my usage (22 kWh) was when low carbon generation was over 50% of total generation. 

Appreciate charging a single battery wont make any difference but if that principle was adopted by lots of battery owners then a gas turbine will ramp up to serve the additional load. 

[SteamyTea]

8 minutes ago, Dillsue said:

Appreciate charging a single battery wont make any difference but if that principle was adopted by lots of battery owners then a gas turbine will ramp up to serve the additional load. 

Yes, it is the same problem as ToU billing.

[JamesPa]

Well fair enough in principle, but doing this at grid scale where you have the right data makes more sense.  So I think I will stick with the conclusion that there is no environmental case for local battery storage (other than in a car of course where the environmental argument is about air quality and reduced carbon overall).

[SteamyTea]

2 minutes ago, JamesPa said:

other than in a car of course where the environmental argument is about air quality and reduced carbon overall

V2G will probably become more useful in the next decade. Really want Vehicle to My House for a bit more control.

[puntloos]

23 hours ago, SteamyTea said:

V2G will probably become more useful in the next decade. Really want Vehicle to My House for a bit more control.

I was thinking this, but my understanding is that "V2G(rid)" really means "V2H(ouse)" in most cases? And indeed a Nissan Leaf has a 60kWh battery. Of course you wouldn't want to use it up completely (still want some range for emergency drives to e.g. the hospital etc) but with my 1000W house I should be able to easily last 2 days and have 12kWh left (48 miles or so) ..

 

 

[JamesPa]

Presumably V2House only works when the grid is 'on' to protect against shocking people working on grid faults.  So I'm guessing it does not serve as a means to deal with power cuts.  Just a guess I admit.

[TonyT]

It’s vehicle to load isn’t it?