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.