Re: energy in UK

On 4/17/25 2:28 AM, Don Y wrote:

On 4/16/2025 6:55 PM, KevinJ93 wrote:

On 4/16/25 3:49 PM, Don Y wrote:
 > On 4/16/2025 3:11 AM, Martin Brown wrote:
<...>
 > Here, the issue is the high PEAK demands that the ACbrrs place on
 > individual
 > subscribers.  We could probably get by on a 3-5KW plant -- but, only if
 > we could store and deliver for large loads (I think the ACbrr is ~14KW).
>
That's a very large residential A/C. Our 4-Ton unit (48kBTU/Hr) takes about 5kW and suffices a 2,900 sq ft house in northern California. (Don't you like all these antiquated units!)

 That's the startup load.  An inverter for a (pure) solar solution would
have to tolerate that for some large fraction of a second/seconds.  I.e.,
you would NEED to be grid-tied in order to support such large loads,
even temporarily.
>

14kW startup is about 60A LRA (locked Rotor Amperage). A single Tesla Powerwall 3 battery is rated for 185A LRA and it is very common to have two or more Powerwalls in a system which increases the available short term power. Our A/C has a 104A LRA spec.

By contrast, using minisplits -- and staggering their actions -- we could
get by with something considerably smaller.
>

Yes, I like the minisplit approach - we have an 18,000BTU/Hr one for a separate room and it extremely quiet and efficient. It normally only takes 200-300W with very low inrush.

<...>
 >>
 >> There are incentives to install solar PV but none for solar hot water.
 >
 > You could, of course, use (PV) electrically heated water.  There are
 > myriad schemes to make better use of the energy available but few
 > see widespread use.
>
California encourages (and will soon require) heat pumps for domestic hot water, that gives you a threefold improvement in efficiency if running from solar generated electricity.  They are pretty common.

 We could easily use true solar water heaters (e.g., evacuated collectors).
Many people use solar to heat their swimming pools -- something that would
be prohibitively expensive to use electric or gas.
 (though I have a friend in Chicago who does exactly that -- but his pool
is indoors)
 The technologies used are often cheap and low efficiency (e.g., a shitload
of coiled black pipe on the roof).  Some similar uses for domestic hot water,
but less common.  Heating water with natural gas is relatively inexpensive.
 

<...>
 >>
 >> UK allows up to 4kW solar generation on any domestic premises. More
 >> than that
 >
 > I don't think the *city* places limits on size of plant.  But, requires it
 > to reside on rooftops to avoid permitting, architects, etc. (of course).
>
Here in PG&E land around the SF bay we're allowed up to 10kW of solar generation without significant additional requirements.

 It's the *mounting* that causes the additional requirements.  You have
to be able to certify that the STRUCTURE that you use (or create)
can bear the load under high winds, etc.

Yes, we had to get the city to give their permit that involves what you mention plus features for emergency responders such as adequate access to the roof and approved means of disabling the panels and batteries with suitable signage.

E.g., I am hoping to mount a dozen panels on the south wall of
the house (sloping down OVER the south lawn).  This would give
me the desired south-facing orientation.  It would also place the
mass of the house between the panels and the microbursts that
we frequently encounter FROM the north.  (i.e., locate the tops
of the panels at or below the top of the southern wall)
 This also makes it convenient to route to the intended destination.
 AND, keeps all that crap off the roof so roof maintenance doesn't
hinder energy collection.
 (Roofs here are pretty flimsy as we have no snow loads, earthquakes,
etc.  There have been homes where a microburst will lift the solar
panels and rip the roof off.  Microbursts often fell 75 ft trees
and rip smaller ones right out of the ground!)

<...>
>
kw