Next door neighbour has shown me his bach 'system' which consists of six 270W panels in series, a 10A mcb and directly fed to his 3kW HWC element. I've had a poke and prod with my meter and in the hot bright sun, there is 216v DC at the cylinder with 8.35A flowing.
His comment was why did he need any control gear or inverters to run this. I'm stumped for a reply. Theoretically, if the cylinder gets up to temp, the thermostat will open - dunno if solar panels can run open circuit?? But I can't really see any risks..... can anyone else? I guess if the panels did get above 230v in series total, things might smoke? Interesting idea.
Direct coupled solar panels
Re: Direct coupled solar panels
Not really relating to electric vehicles...
Using d.c from PV to heat water is not new; but there are several fish-hooks.
The load is just a resistance (around 18 ohms), so the variable voltage from unregulated PV will simply result in varying current / power.
So as long as the resistance is selected to match the array max output (or vice versa), unlikely to let any smoke out.
The array is required to comply with ""5033"; and being above ELV (open-circuit voltage) installing the system is (high risk) PEW.
NOT within "homeowner" provisions.
A standard w/h t'stat isn't rated for switching d.c.
The mcb may have the same issue.
How is fault protection being provided?
What happens when the element sheath corrodes, and the water comes into contact with LV d.c.?
All circuits must have overcurrent protection, and unless one side is earthed must be provided in both.
PV is inherently current-limiting; so a single string as described can't produce huge current even into a short circuit.
In this config; a normal mcb isn't really doing anything - the array will never be able to produce enough current to operate it
- which has to be carefully selected so as to actually operate on the available short-circuit current.
We need special fuses for this, not the types of fuse / mcb we'd use on a normal LV a.c. circuit.
Overload protection can be done anywhere in the circuit (and isn't really needed here anyway);
but short circuit protection has to be at source end.
if a short develops in the array downlead; the resulting arc, constantly fed by the PV, could easily result in fire.
Other array configurations can have issues with circulating currents under fault conditions, requiring string protection
And if feeding into a battery, we need protection against battery-fed short circuits.
Using d.c from PV to heat water is not new; but there are several fish-hooks.
The load is just a resistance (around 18 ohms), so the variable voltage from unregulated PV will simply result in varying current / power.
So as long as the resistance is selected to match the array max output (or vice versa), unlikely to let any smoke out.
The array is required to comply with ""5033"; and being above ELV (open-circuit voltage) installing the system is (high risk) PEW.
NOT within "homeowner" provisions.
A standard w/h t'stat isn't rated for switching d.c.
The mcb may have the same issue.
How is fault protection being provided?
What happens when the element sheath corrodes, and the water comes into contact with LV d.c.?
All circuits must have overcurrent protection, and unless one side is earthed must be provided in both.
PV is inherently current-limiting; so a single string as described can't produce huge current even into a short circuit.
In this config; a normal mcb isn't really doing anything - the array will never be able to produce enough current to operate it
- which has to be carefully selected so as to actually operate on the available short-circuit current.
We need special fuses for this, not the types of fuse / mcb we'd use on a normal LV a.c. circuit.
Overload protection can be done anywhere in the circuit (and isn't really needed here anyway);
but short circuit protection has to be at source end.
if a short develops in the array downlead; the resulting arc, constantly fed by the PV, could easily result in fire.
Other array configurations can have issues with circulating currents under fault conditions, requiring string protection
And if feeding into a battery, we need protection against battery-fed short circuits.
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