On 9 Oct 2017 at 14:41, RussellMc wrote:

> Some of the mhe main advantages of direct PV to water heater are that
>=20
> - The controller / "converter" is low cost (panel cap, PWM switch,
> control) Higher PWM frequency allows lower panel cap uF but more expensiv=
e
> switch (FET, IGBT). Lower PWM frequency needs larger cap uF.
>=20
> - If you use hot water regularly and if PV daily energy is <=3D daily hot
> water energy use then the water heater is about as low cost and durable a=
n
> energy storage "battery" as you can get.
>=20
> - No need for mains, "proper inverters", grid tie, ...
>=20
> - If at ELV-DC, no regulatory issues.
>=20
> - Microinverters may be run on selected panels if desired - either instea=
d
> of water heating or if water heating requirement met or ... .

I like your ideas. I've seen the "variable output voltage" inverters that d=
o it the hard=20
(proper?) way... AC input from existing solar PV, CT to monitor household=20
import/export, 0-240VAC output to direct surplus generation to existing wat=
er heater=20
element & thermostat... quite expensive.

I have instant gas hot water, and toyed with the idea of adding a water cyl=
inder on=20
the inlet side and pre-heating with surplus PV generation. But in rough ter=
ms gas=20
costs me 7c per kWh (on top of fixed charges etc), and exported electricity=
 I sell for=20
8c per kWh. Decided to save myself some work, and ~1c per unit, buy not cha=
nging=20
anything ;-)



--=20
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