Hi all,
Question: Is there any cheap and safe ways to adjust the input power to my 2.4kW heating element and 2 kW mixer motor to match the output of my solar PV system, which is usually between 1kW and 1.2 kW between 10am & 2pm most days?
I have a 1.5 kW solar PV system and no battery storage. Where possible, I try to maximise the use of that PV system to minimise import of electricity from the grid and minimising export of the PV to the grid (as I only get 6c/kWh feed-in tariff). My main driver is similar to that for using biodiesel - to lower my dependence on fossil fuels on a budget.
This involves setting my washing machine and dishwasher to go off via a timer as close to the middle of the day as possible. As it is only a 1.5 kW system and most of the time either side of midday I am lucky to get 1.2 kW out of it, I stagger the appliances. If it is a cloudy day, I try to wait until the sun is out, within reason.
I also apply the same principle to making biodiesel.
The problem is, the electrical demand on my 2 biggest electricity users are nearly double what the PV system can produce at any one point. My oil heater is 10 amp / 2.4 kW and my mixer motor is (if I remember correctly) about 2 kW.
I have sort-of built a thermostatic controller for my oil heater from bits from eBay (I bought the controller and put it in an IP-rated box with Australian GPO and 3-pin flex plug). As much as I don't like to walk away from it, I feel fairly confident living it unattended for up to 2hrs while I'm doing other things at home.
I am not an electrical engineer but understand a bit about motors resistive elements and wiring, but was wondering if there is anyone who knows a bit more who could advise on varying the input power for both the heating element and the motor to more closely match the PV output. The solution would have to have a low capital cost and not damage the equipment to be worthwhile.
Correct me if I'm wrong on any of this, but my understanding is that the resistive load of the heating element is relatively easy to control. Similar to a halogen light dimmer, but it would need to handle a lot bigger load. Since Power = Voltage x Current (amps). Is it just a case of using something like a variac or autotransformer that steps the voltage down? How low can you go?
With the motor, I understand 3-phase motors are easy and safe to control with variable speed drives (VSD) that lower the input frequency to as low as 15 Hz to slow the motor. Going too far will move the impeller speed out of the efficient pump curve and not move any fluid. There are similar motor controllers available for single-phase motors (especially pool pumps), but I'm not sure on how they work, but maybe that lowering of voltage is involved like with a step-down transformer? I have heard there is risk of lowering voltage too far burning the motor out and also slowing it so far as the direct-driven cooling fan on the back cannot provide enough air flow to cool it.
Question: Is there any cheap and safe ways to adjust the input power to my 2.4kW heating element and 2 kW mixer motor to match the output of my solar PV system, which is usually between 1kW and 1.2 kW between 10am & 2pm most days?
I have a 1.5 kW solar PV system and no battery storage. Where possible, I try to maximise the use of that PV system to minimise import of electricity from the grid and minimising export of the PV to the grid (as I only get 6c/kWh feed-in tariff). My main driver is similar to that for using biodiesel - to lower my dependence on fossil fuels on a budget.
This involves setting my washing machine and dishwasher to go off via a timer as close to the middle of the day as possible. As it is only a 1.5 kW system and most of the time either side of midday I am lucky to get 1.2 kW out of it, I stagger the appliances. If it is a cloudy day, I try to wait until the sun is out, within reason.
I also apply the same principle to making biodiesel.
The problem is, the electrical demand on my 2 biggest electricity users are nearly double what the PV system can produce at any one point. My oil heater is 10 amp / 2.4 kW and my mixer motor is (if I remember correctly) about 2 kW.
I have sort-of built a thermostatic controller for my oil heater from bits from eBay (I bought the controller and put it in an IP-rated box with Australian GPO and 3-pin flex plug). As much as I don't like to walk away from it, I feel fairly confident living it unattended for up to 2hrs while I'm doing other things at home.
I am not an electrical engineer but understand a bit about motors resistive elements and wiring, but was wondering if there is anyone who knows a bit more who could advise on varying the input power for both the heating element and the motor to more closely match the PV output. The solution would have to have a low capital cost and not damage the equipment to be worthwhile.
Correct me if I'm wrong on any of this, but my understanding is that the resistive load of the heating element is relatively easy to control. Similar to a halogen light dimmer, but it would need to handle a lot bigger load. Since Power = Voltage x Current (amps). Is it just a case of using something like a variac or autotransformer that steps the voltage down? How low can you go?
With the motor, I understand 3-phase motors are easy and safe to control with variable speed drives (VSD) that lower the input frequency to as low as 15 Hz to slow the motor. Going too far will move the impeller speed out of the efficient pump curve and not move any fluid. There are similar motor controllers available for single-phase motors (especially pool pumps), but I'm not sure on how they work, but maybe that lowering of voltage is involved like with a step-down transformer? I have heard there is risk of lowering voltage too far burning the motor out and also slowing it so far as the direct-driven cooling fan on the back cannot provide enough air flow to cool it.
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