Hi,
I'm still messing about with opportunity diversion loads and dump loads. Our current system consists of 3.2 kW of PV, and our 15' axial. I had previously configured an opportunity diversion to a water pre-heat tank using the aux diversion setting on the PV controller, an OB MX60. This is to a Marathon 40 gallon tank with 2- 1,250w 48VDC elements via SS relays. Aside from wishing the tank was a bit larger, this arrangement has worked very well for several years now.
When we got the turbine up and running, I added another pair of control wires from one of the non-PWM aux outputs from the Classic. Currently this is set for “PV High – Onâ€. Above a set voltage - about the point that our second controller starts to see load - we add some load to the bank in similar fashion to the PV set-up. But wind is fickle, as we all know, and I've been wanting to increase the available diversion load particularly when the winds are gusty. So, I recently reconfigured the water heater control such that:
1) when the PV is diverting nothing is change, the elements are interlocked (max load 1x 1250w, ~22A)
2) when the WIND is diverting both elements are firing, assuming they are calling for heat (max load 2x 1,250w, ~45A)
The logic was that often the wind is sporadic, though shorter in duration, and the added available load would help keep the voltage moderated while doing something useful. I'm further looking to move this to the PWM output of the second controller (there are two for the turbine), so it can be a bit smoother.
I should mention that the above arrangement is separate from our 3-phase load bank, or home-made ‘clipper,' used for protection of the wind system. There, we close in on a resistor bank above a higher preset voltage, adding the equivalent of about 4+ kW of load on the 3-ph input to managed input voltage.
What I'm trying to figure out is how best to manage things when the ‘opportunity' is not there. I could add another air heater for when the water heater is satisfied and the wind resource is still high. I've also considered setting the dump/clipper to engage once float is reached, or alternatively automate the manual furling (with an actuator).
Generally we want to (in descending priority):
1) protect things
2) recharge the battery bank
3) leverage opportunity loads that are useful, but not have unnecessary were and tear
Up until now I've been managing with a bit of manual intervention; close down the turbine on a sunny day when we're away at work. Opening it back up when we get home. Predicting the weather some days is a challenge.
Ideas & cold beer welcome. ~ks