Two approaches to solar install. Thoughts appreciated!

[Everest]

Pretty sure my installer has suggested we'll be limited to 5kw export when it's done

I'm pretty sure he's correct.... as he's installing a 5kW inverter

 

[MattyS]

I'm pretty sure he's correct.... as he's installing a 5kW inverter

There was me thinking that means per day not per hour.

 

[Everest]

DNO's only limit export power, not energy as such.

Watts or kiloWatts (kW) is a measure of (instantaneous) power; Watts = Volts x Amps.

Joules, Watt-hours or, more commonly, kilo-Watt-hours (kWh) is a measure of energy. Energy = Power x time.

They are related, but totally different measurements - similar to the relationship between, say, distance (miles) and speed (miles-per-hour).

And, for completeness... units that are derived from a person's name are usually capitalized. The SI unit for Watts is W, not w (as it derives from James Watt). So, it's kW rather than kw. And definitely not KW which would imply Kelvin-Watts!

 

[MattyS]

I consider myself told

 

[johnb80]

DNO's only limit export power, not energy as such.

Watts or kiloWatts (kW) is a measure of (instantaneous) power; Watts = Volts x Amps.

Joules, Watt-hours or, more commonly, kilo-Watt-hours (kWh) is a measure of energy. Energy = Power x time.

They are related, but totally different measurements - similar to the relationship between, say, distance (miles) and speed (miles-per-hour).

And, for completeness... units that are derived from a person's name are usually capitalized. The SI unit for Watts is W, not w (as it derives from James Watt). So, it's kW rather than kw. And definitely not KW which would imply Kelvin-Watts!

- Every day a school day

I like the speed analogy, I've not heard that one before.

 

[JohnV6]

Yes i like the speed analogy

 

[wattmatters]

The water tank analogy is a bit more akin to battery storage (be it a car or home battery):

Tank capacity (e.g. litres, gallons etc) is analogous to battery energy storage capacity (kWh)

and

Water flow rate into or out of the tank (e.g. litres per minute, gallons per hour) is analogous to charging/discharging power to/from a battery (kW).

In both cases (distance/speed and volume/flow rate) they express a quantity and a rate of change of that quantity.

 

[unbornidentity]

If it was me I’d go for the bigger system but ask them to adjust it so you can charge from solar. Even if your DNO won’t allow you to have a 5 kW inverter it’s better to over spec the panels provided the inverter can cope with it. The panels are the cheapest part of the system and whilst you will have days when the output is clipped you’d get more out of it when it’s not and benefit from it.

You don’t have to have a particularly fancy EV charger to make it work so long as you can change the charge rate via the car at least. My EV charger will draw as much power as it can give but I can tell the car to only draw 1.8 kW. Not that I’ve ever actually done it. There are chargers that are more dynamic with solar integration but normally require other compatible components; like Zappi.

At the moment it makes no financial sense to charge from solar but that will probably change over time. The advice you’ve been given by an installer about changing the car is correct now though.

Definitely get as many panels as you can fit; the inverter should ideally match the output of the panels or battery but if your DNO won’t allow it then over spec panels are still a good idea. It doesn’t matter if you occasionally draw from the grid to boil the kettle with the tumble dryer on if you’re not doing it regularly vs the cost of being able to.

As for the battery; that depends on your future demands as much as current ones (it’s also the most expensive part, other than installation). If you’re going to get a heat pump go for 20 kWh now and save yourself the expense of upgrading later. If not then 10 should be plenty if you don’t regularly use more. It will also help act as a buffer if you do want to charge from solar in the future without a compatible charger. I went with a 5kWh battery and although it’s working for me now, it’s the most likely thing I’ll need to upgrade!

 

[Bam Bam]

And, for completeness... units that are derived from a person's name are usually capitalized. The SI unit for Watts is W, not w (as it derives from James Watt). So, it's kW rather than kw. And definitely not KW which would imply Kelvin-Watts!

On the other hand, I was corrected for using mW today, being told that this mean Milli-Watts whereas I meant Mega-Watts so the M should have been capitalised. despite not being a name

Every day is a school day.

 

[Coulomb]

so the M should have been capitalised.

Yes, the M is a multiplier, not a unit. All the big (>1) multipliers are capitalised, M, G, T, E etc, except for 'k' for kilo. All the small (<1) multipliers (m, μ, p etc) are lower case.

 

[MattyS]

Thank you everyone for the advice and help. I've just put in the order for the 15 panel array and the Fox EVO 10kWh battery, and I'll be asking them to ensure that I can charge via solar if I would like to do so to make sure it's future proof and flexible to my wants and needs.

For context, I live in a Mid Terraced 80's built house with a conservatory. There's no room for more batteries or a heat pump, so I'm trying to go as big as I can straight away, hence I am trying to be as particular as possible.

 

[johnb80]

Thank you everyone for the advice and help. I've just put in the order for the 15 panel array and the Fox EVO 10kWh battery, and I'll be asking them to ensure that I can charge via solar if I would like to do so to make sure its future proof and flexible to my wants and needs.

For context, I live in a Mid Terraced 80's built house with a conservatory. Theres no room for more batteries or a heat pump, So I'm trying to go as big as I can straight away hence why I am trying to be as particular as possible.

Just make sure that the Zappi is fed before the CT's for the solar / battery, and you will be able to do anything you wish with regards to charging.

 

[Bam Bam]

Thank you everyone for the advice and help. I've just put in the order for the 15 panel array and the Fox EVO 10kWh battery, and I'll be asking them to ensure that I can charge via solar if I would like to do so to make sure its future proof and flexible to my wants and needs.

Sound! Good luck with the install.

For context, I live in a Mid Terraced 80's built house with a conservatory.

Theres no room for more batteries or a heat pump,

Are you sure? Where there is a will there is a way with heat pumps. Might need some digging or something awkward and expensive though.

Friends have got a heat pump in their terrace garden though no conservatory (just a big long extension).

Then there are air-to-air heat pumps which can be hung on a wall or something.

 

[MattyS]

Sound! Good luck with the install.


Are you sure? Where there is a will there is a way with heat pumps. Might need some digging or something awkward and expensive though.

Friends have got a heat pump in their terrace garden though no conservatory (just a big long extension).

Then there are air-to-air heat pumps which can be hung on a wall or something.

Unfortunately the WAF (Wife Approval Factor) turns to zero when discussing a heat pump in the garden which is the only realistic place it'll fit.

 

[KnightRider]

Ooh lots of amazing advice.
I have to agree - go as big as you can.
We got ours done on the Eco4 grant.
We had the ASHP and 5.2kW of panels. For free.
We bought the Tesla Powerwall 3 (13.5kWh, charges up at 5kW and can output 7kW)
So far excellent.
I wouldn't worry about involving solar and the car.
With up to 100kWh to fill, solar just won't do it.
I may use excess solar once the house battery is fully charged in Summer, rather than export it at the new and pathetic 12p/unit (a reduction of 20%!)
We just charge the car overnight at 8.5p/kWh, it puts 35% in.
We also got the grid to allow us up to 7kW output.
Last year was a good solar year.
We hardly bothered the grid for import at all.
The biggest % was the standing charge!

 

[MattyS]

Ooh lots of amazing advice.
I have to agree - go as big as you can.
We got ours done on the Eco4 grant.
We had the ASHP and 5.2kW of panels. For free.
We bought the Tesla Powerwall 3 (13.5kWh, charges up at 5kW and can output 7kW)
So far excellent.
I wouldn't worry about involving solar and the car.
With up to 100kWh to fill, solar just won't do it.
I may use excess solar once the house battery is fully charged in Summer, rather than export it at the new and pathetic 12p/unit (a reduction of 20%!)
We just charge the car overnight at 8.5p/kWh, it puts 35% in.
We also got the grid to allow us up to 7kW output.
Last year was a good solar year.
We hardly bothered the grid for import at all.
The biggest % was the standing charge!

Can I ask what your yearly usage is like for electricity with and without your car?

 

[johnb80]

We bought the Tesla Powerwall 3 (13.5kWh, charges up at 5kW and can output 7kW)

Hideously expensive compared to the rest of the market but definitely a nice piece of kit.

I wouldn't worry about involving solar and the car.
With up to 100kWh to fill, solar just won't do it.

Very few EV's have 100 kWh and above. It's really not the right approach to consider full charge from empty, you really need to consider replenishing the charge you use on a daily basis.

I may use excess solar once the house battery is fully charged in Summer, rather than export it at the new and pathetic 12p/unit (a reduction of 20%!)

It's the way of the world at the moment and I fear it could get worse.

We just charge the car overnight at 8.5p/kWh, it puts 35% in.

Change to Intelligent Octopus GO at 7p kWh for 6 hours.
Only 35% overnight, just how big is your battery or, how slow is your charger?

We also got the grid to allow us up to 7kW output.

Is that all of what you requested or a limit they imposed?

Last year was a good solar year.
We hardly bothered the grid for import at all.

You did well, I can get close to zero import when the weather is perfect but with 2 x EV and several heat pumps we have to import during off peak. That said, over the last 12 months only 3% of our electricity has been at peak price.

The biggest % was the standing charge!

Having just renewed, ours has gone up from 56p to 66p which is madness in my book, then again I received some quotes for my business energy where the standing charge was £8.56 per day!

 

[Bam Bam]

Unfortunately the WAF (Wife Approval Factor) turns to zero when discussing a heat pump in the garden which is the only realistic place it'll fit.

Pebbles wasn't keen on losing space on our deck too and described herself as a 'victim of climate change.'

In the grand scheme of things it seems like a small sacrifice to me, but I realise your partner might need some convincing!

It was hung off the side of the building in the end as well so as not to interfere with the decking.

 

[Everest]

Definitely get as many panels as you can fit;

re ^^^^.

But I disagree with these two...

Even if your DNO won’t allow you to have a 5 kW inverter it’s better to over spec the panels provided the inverter can cope with it.

For any grid-tied inverter than can output more than 16A at the nominal 230V (i.e. 3680W), G99 approval is required from the DNO prior to installation. Depending on your local supply wiring and existing micro-generation taking place locally, the DNO can & will specify a maximum export power for your new installation. However, the vast majority of UK approved ENA type-tested inverters will also support the engineering standard G100, used for limited export power.

Hence, the best solution is to still have a larger inverter - to supply the maximum typical house loads - but simply configure it with its G100 export power limitation feature to the limit that the DNO specify.

the inverter should ideally match the output of the panels or battery but if your DNO won’t allow it then over spec panels are still a good idea. It doesn’t matter if you occasionally draw from the grid to boil the kettle with the tumble dryer on if you’re not doing it regularly vs the cost of being able to.

I disagree that the inverter should match the output of the panels. IME, 'overpannelling' is preferable than not, especially with UK weather. With the low cost of panels these days and, assuming sufficient physical space, it makes sense to install more kWp of panels than AC output capacity of the inverter, for the reasons I mentioned in posts #9 and #14 and @Bam Bam expanded on in post #20.

 

[T1 Terry]

Unfortunately the WAF (Wife Approval Factor) turns to zero when discussing a heat pump in the garden which is the only realistic place it'll fit.

Could you mount it on the roof? Popular in big coaches converted to motorhomes

T1 Terry