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Total beginner question on Solar


Justin_A

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I agree Jay. I am thinking of doing the following now:

1. Split DB and put stove and oven on Eskom only.

2. Add pugs feeding 2 x heat pumps and pool pump, tumble dryer, washing machine and microwave to the external contactor as DownTime suggested. (Will only be available when Eskom power is  available, but cannot run if Eskom is down and inverters are running off batteries)

3. The rest gets connected directly to inverters and will be available at all times, even in the event of a power failure.

Does that make sense?

 

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Also perhaps add a delay-device of some sort to the contactors so that a short dip in supply on the eskom side doesn't translate to the output side. I suppose it depends on how bad the power is that side, if not too bad this might not be necessary.

Depending on type of washing machine it might not matter too much. Top loaders use maybe 500W when spinning and I had no problem running my old top-loader from my small 1600VA inverter. Front loader is only a problem when it is heating water, which doesn't take all that long. But Tumble dryer, pool pump and microwave.... that sounds about right :-)

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@Don your idea will work, depending on how the DB circuits are wired there might be a speed bump or two.  Check which other appliances work on the same plug circuit, usually the plugs for the microwave, washing machine and tumble dryer are all on the same circuit as the fridge/freezer (as well as toaster and kettle).  If you want to cut the power to those appliances you will also lose power to the fridge/freezer unless you install a separate plug circuit for it. 

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DownTime, yes, I realise that most of the plugs will be on the same line as you said, including the fridges. I will have to pull in some extra wires to cater for that. 

What is the correct name for this external contactor on how big is it? When I go to the electrical shop, I want to buy the correct item first time round. I don't want to come home with a 10kg coil and everyone laughs at me for buying the wrong thing, haha.

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3 hours ago, subok01 said:

stove/oven with gas

I disagree. Gas is not cheaper than electricity. Might as well leave it on the Eskom side.

With that bombshell out of the way: I do recommend that people install gas stoves but for different reasons, those reasons being that it is very nice to cook on gas, you can cook when the power is out, and the carbon foot print of burning LPG is lower compared to coal plus all the transmission losses. But it is not cheaper, which means there is no ROI, it is strictly a luxury thing.

The reason why it is not cheaper is because a kg of lpg has 53.6MJ of energy per kg, which is just short of 15kwh (divide by 3600, a watt is a joule per second), so a 9kg bottle contains the equivalent of 130kwh of electricity. It costs around R190 to refill a 9kg, so the per-unit cost is around R1.46 per kwh. On the face of it that looks good (it is significantly less than CoCT rates for example), but keep in mind that the efficiency (how much makes it into the food you're cooking) is significantly less than for an electrical heating element (assuming a flat utensil of the right size and all that), so the true cost of LPG is actually slightly more than for electricity (when cooking).

It isn't so much that people notice though, in fact it is so close that most people believe it is cheaper.

So I would not convert to gas unless I had the money for the luxury or frequent power failures. Barring those, I'd just move it to the Eskom side.

This is an opinion though, let me just stress that. Gas is an important part of the overall strategy, but not a prerequisite :-)

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9 hours ago, plonkster said:

I disagree. Gas is not cheaper than electricity. Might as well leave it on the Eskom side.

With that bombshell out of the way: I do recommend that people install gas stoves but for different reasons, those reasons being that it is very nice to cook on gas, you can cook when the power is out, and the carbon foot print of burning LPG is lower compared to coal plus all the transmission losses. But it is not cheaper, which means there is no ROI, it is strictly a luxury thing.

The reason why it is not cheaper is because a kg of lpg has 53.6MJ of energy per kg, which is just short of 15kwh (divide by 3600, a watt is a joule per second), so a 9kg bottle contains the equivalent of 130kwh of electricity. It costs around R190 to refill a 9kg, so the per-unit cost is around R1.46 per kwh. On the face of it that looks good (it is significantly less than CoCT rates for example), but keep in mind that the efficiency (how much makes it into the food you're cooking) is significantly less than for an electrical heating element (assuming a flat utensil of the right size and all that), so the true cost of LPG is actually slightly more than for electricity (when cooking).

It isn't so much that people notice though, in fact it is so close that most people believe it is cheaper.

So I would not convert to gas unless I had the money for the luxury or frequent power failures. Barring those, I'd just move it to the Eskom side.

This is an opinion though, let me just stress that. Gas is an important part of the overall strategy, but not a prerequisite :-)

Areed. The 3 closes gas resellers to us generally sell (and compete) for about R220/bottle. R200 is a bargain ;)

 

 

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Of course for space heating the picture changes. Now the efficiency is significantly better and at the calculated cost it is cheaper to use gas than an electrical heater. But when you get to heating, you can use an air conditioner (aka heat pump) and then gas loses again. Where gas wins (for heating) is in the capacity to heat, when you turn on all three little "plates" on the gas heater the rate at which it heats beats out anything else (but it also eats gas, so it costs lots of money when you do that). The other difference is that water vapour is a side product of combusting LPG so a gas heater tends to push up the humidity, whereas a heat pump (aka air conditioner) brings down the relative humidity (which some people find uncomfortable). So multiple aspects to that.

Water heating? I am inclined to believe gas will win over electricity, but lose to the heat pump.

Of course this assumes LPG per bottle. If you have the luxury of natural gas delivered from the street (eg if you live with the larnies in South Down Estate in Centurion), the picture changes yet again.

I once tried to do all this math for wood vs electricity too. Now try and get a number of calories or joules for wood by the kilogram... not to mention, that depends on what kind of wood is used too! It would seem to me that if you use a closed-combustion stove/heater and that thing can also heat water, then the combined process might make it worth to heat water using wood, but I don't have hard numbers for this.

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5 hours ago, plonkster said:

Of course for space heating the picture changes. Now the efficiency is significantly better and at the calculated cost it is cheaper to use gas than an electrical heater. But when you get to heating, you can use an air conditioner (aka heat pump) and then gas loses again. Where gas wins (for heating) is in the capacity to heat, when you turn on all three little "plates" on the gas heater the rate at which it heats beats out anything else (but it also eats gas, so it costs lots of money when you do that).

I wonder how this applies to induction plates? Our induction plates boil water at the same rate of one of these new kettles with the element in it's own "pocket" under the water - i.e. not inside the water. Heat is instant so there's little losses. IF I had a gas stove / cooker, and some way to accurately measure the gas consumption, I could have compared the two to see how long it takes to boil 2L water, and how much gas was used. 

 

5 hours ago, plonkster said:

I once tried to do all this math for wood vs electricity too. Now try and get a number of calories or joules for wood by the kilogram... not to mention, that depends on what kind of wood is used too! It would seem to me that if you use a closed-combustion stove/heater and that thing can also heat water, then the combined process might make it worth to heat water using wood, but I don't have hard numbers for this.

There's definitely some cost effective ways to heatup water and the house with some fancy burner designs. But most people don't want to "stook die donkie" every few days. 

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41 minutes ago, SilverNodashi said:

I wonder how this applies to induction plates?

The numbers I have is that the efficiency for gas is around 35%, for a normal electric element 70%, and for induction its 80%. Those numbers are too round to be exact, just ballpark numbers I got from various places on the interwebz. Most of the research was done in the states with natural gas for heating water.

So I would expect induction to be slightly better than a normal electrical stove.

Nothing beats a good old electrical kettle (with the element in the water) for boiling water. Usually you lose efficiency because things get hot while you're trying to do other things, but in this case you actually WANT heat. As a result, a kettle is darn near 100% efficient. Same for the geyser.

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Just now, plonkster said:

Nothing beats a good old electrical kettle (with the element in the water) for boiling water. Usually you lose efficiency because things get hot while you're trying to do other things, but in this case you actually WANT heat. As a result, a kettle is darn near 100% efficient. Same for the geyser.

It probably also depends how the element in the kettle makes contact with the bottom of the kettle. An element submerged in water tends to have poorer efficiency over time, as scale builds up, but you already knew this ;)

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On 06 January 2017 at 9:39 AM, Don said:

I agree Jay. I am thinking of doing the following now:

1. Split DB and put stove and oven on Eskom only.

2. Add pugs feeding 2 x heat pumps and pool pump, tumble dryer, washing machine and microwave to the external contactor as DownTime suggested. (Will only be available when Eskom power is  available, but cannot run if Eskom is down and inverters are running off batteries)

3. The rest gets connected directly to inverters and will be available at all times, even in the event of a power failure.

Does that make sense?

 

Thats exactly what I did ;)

The geyser and stove are on eskom power only.

The sockets feeding power to my fridges is controlled via a mains failure contactor so during the day when the sun is shining and eskom is present, I generate PV power which is pumped into the lights, TV AND the fridges.

In the event of a power failure the contactor feeding my fidges opens and they are disconnected form the inverter but my light and TV will stay on.

This way my battery bank didn't need to be massive but during day light hours my solar panels are supplying power to my fridges;) 

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34 minutes ago, Noobie said:

the contactor feeding my fridges opens

I replaced my fridge and freezer so that I don't have to worry about that. The replacements need only 90W to run.

Of course that cost me a lot more than just the price of a contactor!

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18 hours ago, plonkster said:

I replaced my fridge and freezer so that I don't have to worry about that. The replacements need only 90W to run.

Of course that cost me a lot more than just the price of a contactor!

Now you have to share....

How did you manage to get that right?

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What I did few years back was to add separate circuits for all I want to power using solar.

Brought plug points down in corners, when wire was still a bit cheaper. What I should have added was the red/black/blue plugs, but that got too much.

It was a shleph but in the end it worked out perfectly. All Tv's, DSTV, Network devices, alarm, computers, lights and fridge/freezer are "off-grid" on a separate circuit to the rest of the house ... with Eskom as backup. I balanced the load winter and summer to the panels, adding more in summer, taking off in winter for Cpt winters have little sun and lots of cloud, not like in Tvl where you have less sun with cold days assisting better production.

And because of Plonkster's 90w fridge, Bosch, I went out and bought one as well as a lower wattage Defy freezer. They are running off solar 24/7, has never even been on Eskom.

One of the expenses with solar is the cost of replacing high wattage with lower wattage devices - or just add more panels and bigger inverter. I chose to go as small as I can to remove the base load off Eskom where I can.

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1 hour ago, Noobie said:

How did you manage to get that right?

 

26 minutes ago, The Terrible Triplett said:

And because of Plonkster's 90w fridge, Bosch, I went out and bought one as well as a lower wattage Defy freezer. They are running off solar 24/7, has never even been on Eskom.

What TTT said, that is how I did it. Well, I have the advantage that my parents had solar power back in the 80s before it was cool (before PV panels had the capability to pay back their manufacturing costs even). One of the first things my father did was spend a truckload of money on decent cooling appliances. What you have to keep in mind is that back then the competing tech was either paraffin or the Minus-40 cooling-bank freezers. So round about 1989 he bought an AEG freezer with a 110W compressor for just over 6k. Remember that back then a good car was around 25k. I always remembered this part of the implementation.

So that was one of the first things I measured and replaced. My old cheapie KIC/Fridgemaster jobbies used about 3kwh each per day. The Bosch was rumoured to use less than 1kwh per day. Then one day I walked into Dion Wired and it was on special for 7.5k (normally closer to 9k, this was in 2013). Bought it on the spot. The Defy freezer was slightly more of a gamble. It's a smaller 210 liter unit and it is A-rated (The fridge is A++). Due to the small size (for a freezer) though, that still works out around 1kwh a day. I paid R1999 for it (it is now closer to R2999). 2kwh a day saving at rouglhy R1.50 per kwh is R3 a day, so 2000/3 is roughly 700 days. So ROI just under two years. Plus I sold the old one for a couple hundred bucks, so it was closer to 18 months.

:-)

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Bought my Bosch last year for 7500 - "paid" only R2500 for I sold the existing fridge for R1000 and got rid of a few computers standing around that the wife gave me terms on. :D

The Defy 210l fridge I bought for R2399 Nov 2016 as it was on special. It's price goes up and down all the time - R2999-R2599-R2899-R2399 etc.

All thanks to @plonkster posting what he did here. (thumbs up)

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11 hours ago, The Terrible Triplett said:

What I did few years back was to add separate circuits for all I want to power using solar.

Brought plug points down in corners, when wire was still a bit cheaper. What I should have added was the red/black/blue plugs, but that got too much.

It was a shleph but in the end it worked out perfectly. All Tv's, DSTV, Network devices, alarm, computers, lights and fridge/freezer are "off-grid" on a separate circuit to the rest of the house ... with Eskom as backup. I balanced the load winter and summer to the panels, adding more in summer, taking off in winter for Cpt winters have little sun and lots of cloud, not like in Tvl where you have less sun with cold days assisting better production.

And because of Plonkster's 90w fridge, Bosch, I went out and bought one as well as a lower wattage Defy freezer. They are running off solar 24/7, has never even been on Eskom.

One of the expenses with solar is the cost of replacing high wattage with lower wattage devices - or just add more panels and bigger inverter. I chose to go as small as I can to remove the base load off Eskom where I can.

I dunno why,  but somehow it made more sense to add more panels and a bigger inverter. No need to split the DB (except for the stove). No need to run seperate cables and plugs (which cost money). No need to run a seperate 12V or 24V system (as many people do). No need to worry about explaining the whole system to new buyers in the future. No need to try and explain the whole system to insurance or 3rd party electricians / plumbers, if the need arise. No need to explain the limits, etc al to visitors. BUT: Use the "heavy" stuff when the sun shines ;)

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10 hours ago, SilverNodashi said:

I dunno why, ...

Because when I started panels where just coming down from +-R32.00 a watt.
Solar geysers had nice rebates.
Everyone back then knew rule one for solar is to first reduce the load, which costs a pretty penny by itself, and it takes time.
MPPT controllers where pretty new and if you found one in SA, very expensive.
Only "cheap": part was the Victron Phoenix inverter and Trojan batteries where very "expensive" compared to UPS batteries at +-R600 for a 105AH.
Electricity was cheap.
Axperts did not exist.
Grid tie was something you did not eat.
And switching on SOC - was probably one of the first in the world to use a BMV to change from batteries to Eskom as it was never done before I did it. Believe me, I Google and emailed every single mainstream manufacturer in SA and international at the time asking for it. 

So after having done all the way I did it for dealing with Ekom failures since 2008, solar UPS with Eskom as backup, why change it if I know that I do not want the kitchen hairdryer vacuum cleaner on solar for I know the load that is costing me money?

And you know that in Cpt it is illegal to grid tie unless you spend some more and then it is still geared against you when you do the sums, as we have touched on before.

End result: At times in the day the house uses 40-60w for hours on end, tenants pushes it up to +-250w, which is not my cost.

And as we all know powering stuff at night, Eskom wins if you are wise.

One day when it is just the wife and I, my little system will run us comfortably nearly off-grid with Eskom powering only the larger loads.

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With solar you have three choices:

Option one - a Want: Add panels and inverter to meet your needs.

Option two - a Fun Project: Reduce the load resulting in very low Eskom bill therefor you need much less panels and a smaller inverter whilst still using Eskom for selected limited large loads.

Option three - a Need: If you are on a farm or with no Eskom to your property, go bos for then the cost of solar makes a lot of sense.

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4 hours ago, The Terrible Triplett said:

Because when I started

That makes a rather big difference. When I started I installed the system so my office would run during load-shedding.

Then load shedding stopped and suddenly spending another few thousand to turn it into a self-consumption setup didn't seem so bad. One of the rules of investment: you ignore the historical cost and only look at the present potential (you already paid for the historical cost anyway).

If I had to install it from scratch today, I wonder if I'd do the same. I'd look at the overall investment from a completely different angle, right?

Necessity is the mother of invention as they say.

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