Here is more info to give you a better picture:
My household consumption for a month is about 350KWh. Say about 12KWh per day. My absorption freezer consumes 4KWh/d. Needles to say I will get rid of that so that leaves me with around 8KWh/d. I'm installing solar water heating which could save up to 50% but lets rather work on around 30%. So 8KWh - 30% = 5.6KWh/d. We get an average of 7h sunlight each day. With a 1Kwp array running at say 50% output I'll get 3.5KWh/d. I'm planning on changing over to LED lights running from a different 250Wp circuit which will obviously tip the scales in the positive direction w.r.t. the 1KW production vs consumption.
Changing the efficiency of the solar water heater to 45% and the array output to 65% I'm already producing more than I need (4.4 Cons vs 4.55 production). If I were to use batteries for the 1KW system that would drop my overall efficiency quite a bit so I want to stay away from that as far as possible. My main consumers at night are lights/TV/cellphone chargers - this will hopefully run on the 250W system.
I don't have AC, the freezer will be on timer/load management to run during sunlight hours, washing is done during the day, fridge is a bit of a problem so will have to see how it will pan out.
Electricity costs p.a is around $600. A 1.25KW solar array + mounting is around $1300 + $500 for charge controller + $400 for inverter = $2200 so around 3.6 years to pay back the system. If I were to add batteries, things would change quite a bit. Therefore I want to reduce my reliance on batteries and rather get a few (free) old golf cart batteries and do proper load management. Grid tie is an option to get FIT and reduce storage requirements but again a huge cost (Around $2800) and if the grid is off, which happens a lot, you're stranded.
Your input and comments are welcome.
Edit: I see there were some replies whilst I was typing. Confirms what I just calculated. I would prefer/enjoy to design the system myself but thanks for the offer.
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Thanks Mike I'll look into that. Problem is still that I can't manage the load, it's either all or nothing with a controller activated relay. Either way I'll look into it.Leave a comment:
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The Midnight controller has a "Waste Not" feature, where it can activate a relay when the batteries are in float, if voltage drops too low, it cuts off. Check it out. I've not used that featureLeave a comment:
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Not manual, must be automatic and off grid so Hybrid is not an option. Array will be around 1KW, consumption at night will be a few hundred watts at most; TV, DVD, LED lights, cell phone charger, PCLeave a comment:
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hi, Sir, I guess it is a manual control system, you switch power distribute by yourself, right?
If so, it is simple, don't need monitor current, there will be indication on battery full charge or over discharge.
If you need a automatic control system, hybrid inverter is suitable for you, it will control charging battery, operating loads intelligently and automaticly.
What is capacity of solar power system? What is electricity consumption at night?Leave a comment:
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Solar Load shedding/load managment of excess production
Hi Guys,
I've seen this question asked before but none with a very conclusive answer so I'll try and make my objectives clear and hopefully get some answers.
I want to install an Off grid PV array with a Morningstar MMPT 60A and a small battery bank. The idea is to charge the batteries first thing in the morning, then after they are full run a AC inverter and run loads like the chest freezer/ fridge, washing machine directly from the array (through the MPPT of course) without discharging the battery. If the loads are done then switch on the water heater and store more energy there. At night the battery will be used for LED lights and small loads.
The purpose of this is to rather invest money in PV than batteries and manage the loads better. I've looked into battery voltage monitoring but this is very crude and not ideal. After reading the MorningStar Tristar 60A MPPT manual it seems the answer might lie in the communications with the controller. The webpage interface shows a "Battery power" and a "Sweep Pmax" values. From a youtube vid (https://www.youtube.com/watch?v=X2XBguHAK_w) at around 1:06 I saw some values of 131W for battery power and 172W for Sweep Pmax. So an excess of 41W, so if I were to control my loads to use say 40W I can increase/decrease depending on the excess. The 1W is left as an indication that the battery gets its fair share, if it becomes zero the load is throttled back and vice versa. I'm thinking X10 control for the loads and phase control for the water heater. Micro-controller does the calculation/ Load priority matrix management.
I've asked the Morningstar tech help if this will work as there are also some other/similar MODBUS variables that can be monitored but I'm still awaiting a reply. The beauty of this is that there is no need for current shunts and it can be done over the network some distance form the MPPT and could also be implemented on other brands of controllers featuring comms and readable variables.
Has anyone looked into using these variables like this? Has anyone gone the current shunt route and done load management doing this. Is this even possible with a MPPT? The only other method I can think of is to monitor current into battery and total current drawn from MPPT but this leaves the question: how much power is really available and how much does the battery want?
Your comments and thoughts are welcome!
Thanks in advance
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