Winter is coming here in oz and no doubt where I am the 40oC temps will soon be replaced by 4oC
I'm thinking / planning a few options for heating and power generation and would like to get some feedback on things I may not have thought of and maybe give others some ideas as well.
My home is 20 Yo and all electric. The insulation is not bad but due to the style of the house, there are a LOT of windows and Doors. Something like 16 SETS of windows ( all being 2-3 pane/ openings) and 7 Doors, 5 of them doubles and at least half glass. Not great for insulation. No gas in the area, no wood heating etc. All out heating and cooling is from a big 3 phase AC unit.
I have 20Kw of solar on the roof and adding a bit more but it's a case of very diminishing returns. I have about 10KW on the optimal north side and the rest is on the west and a bit on the south. While the south is the complete " wrong" side, because that is on the shed with only a 5o Tilt ( 34 optimal here) it actually produces pretty good power. The panels were only leftovers I had anyway so put them up to make some use of them and have been surprised how well they do..... in summer at least. Winter is pretty useless but then again the west ones fall off badly in winter too but crack along in summer.
The problem with more panels is I only need the power in winter where the solar radiation falls through the floor. In summer I have been running about half my present capacity and making more power than I know what to do with literally and don't get anything for feedback. In winter I can't make enough and one of my smaller arrays in summer will make more power than all the systems put together in winter.
They don't really tell you about this fall off in the solar marketing hype and it must catch a lot of people out.
I have 3 phase power and feed back to 2 Phases that have old spinny meters so I can use the grid as a battery. The 3rd phase is an electronic meter that registers input or use as a consumption. Unfortunately the only thing that uses the 3rd phase is the AC which is all our cooling and heating and even on one phase, is expensive to run.
To compensate for the 3rd leg usage I have an inverter hooked up to about 4 Kw of panels but only to one tracker to limit the output to that of close to what the AC uses. I put a relay in the AC unit that is activated off the compressor. When the AC Kicks in the power from the inverter compensates that phase. Being a DPDT relay, when the compressor is not running or the AC is off, the relay divers power to another phase to wind back some credit on the meters.
This way I can run the AC all day and only use 1-2 KWh of power on that phase instead of 14-16Kwh.
Don't work so well at night though!
last winter my solar couldn't keep up with demand on the 2 phases Due to 1 thing.
Heating. That was for both the AC and the hot water. I worked out that just the winter temp drop of the incoming water between summer and winter would use 3-4 Kw a day more energy in winter than the warmer start temps of the water in summer. It adds up.
I have a few ideas to heat the house cheaply and with some independence of DIY thrown in.
First is the 100KW gas spa heater I have which I am going to convert to waste oil. Simply remove the gas burners and replace with a DIY oil burner.
I'll circulate the heater water through a car radiator probably located in a back window in a housing and use the fans to pull air in or could just have it recirculating air in the house. Obviously way overkill output wise but I can limit the burner output and will need to be run with someone at home and awake although I will see what over temps and controls I can put on it. The thing should be very stable, I have run hundreds of hours on the things but I'll locate it away from the house so it the thing does go up in flames, it won't matter anyway. One reason I want to use hot water as the energy transfer medium and not just go direct air heating which would create a path for fire into the home.
I will be using metered ( Pumped ) fueling as gravity feed despite the simplicity everyone loves, is pathetically inconsistent for this application. Pumping the oil with the tank lower than the pump and burner means no chance of run away or the fuel flow getting smaller as the tank drains and thee is less head pressure.
The base controls will be a thermostat that change fueling and air from the blower from Idle to heat as the temp of the water requires. I'll put in some various over temp cutoffs as well as a fuel cut as well.
2nd thought for heating was a used, 400L hot water heater to take advantage of the excess power I make. Due to several factors including poor grid voltage regulation, I have a high voltage problem which trips the inverters out. It's actually better in summer despite much higher solar outputs because the grid voltage is a LOT lower I suspect due to everyone running their AC and maybe pool pumps etc. To stop the inverters re booting and turning off again all day, the procedure of which takes a couple of minutes, I have a voltage monitoring relay switch in dummy loads like a fan heater when the voltage gets high and the domestic hot water is already up to temp.
The thought with this 2nd heater which would be stand alone was I could use the excess power to heat the tank then circulate the water same as the oil heater to put warmth back in the house at night.
400L of water taken from 90c to 20C has 32Kwh of energy! Quite a good amount. I then recalled that there is no way I'm going to have 32 Kwh of power to spare, not in winter anyway and I'ld probably want closer to 35 Kwh generated with losses to heat it. That heat would be good to have at night and in the mornings though.
Follow on thought was to use the oil burner to heat the water that first heats the tank then goes to the radiator so the tank always has the best storage capacity possible when shut down.
50Kw of output on the oil heater will be a walk in the park. That should give me enough to heat the house and the tank at the same time and finish with a tank full of hot water for later on. I'm more concerned about limiting the heat output of the burner than I am getting enough heat and with 100Kw potential, more than I'll need by far.
3rd option will be using a waste oil powered diesel engine to drive a 12 Kw Induction motor to backfeed the grid and just use my AC or resistance heaters.
The winter fall off in generation is severe so although I shut down some of my solar in summer because I have more power than even running the AC 9-10 Hour a day can burn, in winter I come up short using the AC as minimally as I can for heating. The idea will be to fire up the induction motor, particularly on overcast days when the solar isn't doing anything significant and pump back some power to spin the meters backwards and make up for what I have used and maybe a bit of credit till the next read. I then have to let the meters advance a bit and pay something as the price of being able to use the grid as a battery.
I only have 2 phases going to the garage which I want to upgrade to 3 phase but probably won't happen in time for winter as there are other renos planned and it will all be done at the same time along with some new high capacity circuits for the solar. The engine times might be a bit limited due to noise and running with the solar will again no doubt case the high voltage problem and trip the inverters out. Even in winter the grid voltages are well out of spec even at night so they can't blame too much solar input for that. There have been complaints made about the high voltage but so far, the power co's just make excuses it's intermittent and nothing they can do. Installing some autotapping transformers that were made this century might be a start but anyway.
If I set the Motor up in a C2C configuration which combines all 3 phases into a single phase I will have 12KW potential, probably 9-10 practical output. This is never 100% efficent. in any case, too much for the wiring I have by far and probably more than I would have upgraded to anyway for any single phase. I can educe output by slowing the motor however as with an IMAG speed is very directly coupled to output.
If I run each phase individually, I'll have 4KW potential, probably 3 Kw Practical. A little lower than I'd like. I don't know if it's possible to combine just 2 phases into a single. Probably might be with a capacitor across the motor terminals like a C2C but this would only be 2 C or 1C. More reading up, learning and testing required.
In any case, 3Kw input to 2 phases on an overcast on wet day is a lot better than nothing. The run times to compensate the shortfall in solar is something I'll have to see about.
4th Idea is to use a 2nd hot water heater for the domestic supply as a pre heater for the main tank.
I have a 125L gas water heater I have set up several times with an burner to heat the water. Once up to temp, the burner will maintain hot water in the tank is if is being used constantly. Set it up once at home and the whole family had the longest showers ever with the water never dropping off and costing nothing at all to heat.
If I can heat the tank once a day and have it feeding into the main tank, that could easily save me up to 12 Kwh a day that we used on average last winter.
This alone might be enough to get me to near break even on the power consumption even with no other changes. I could also use this as the heater for the house but I prefer the additional capacity of the spa heater and the better and more presentable packaging there of.
I want to do something to save costs but I don't want to turn the place into something that looks like the set of a mad max movie. Presentation counts too.
This is also another possibility which will need investigating.
Mrs wants an outside Spa. Mate has one he wants to give away. She sees relaxing soaks. I see 3000L of thermal storage right at the back door.
This thing is electric only but an oil fired heater would be the perfect match. With that much storage even if the water was only taken to 50C ( don't know that the materials will take on those) that's over 100Kwh of heat! Good enough for 2-3 days at least.
Not sure about this, Trouble is if I get it, it's a heap of work to set up an area and landscape it. Then again, could be a true asset for energy storage as well.
I'm thinking at this stage to try and work on all all these initiatives and then see which one is best or combination of a couple.
All have drawbacks. The oil heater I probably would not want to leave going over night. I'll have to get oil and process it and, the biggest thing, it's hardest to set it up and blend in with the look of the house without detracting from the look and standing out like a sore thumb.
The generator WIll be noisy and also somewhat limited when I can and want to run the thing. Spose I could set up up a remote shutdown at least so I don't have to go out in the cold to turn it off or put it on a timer. Have radio switches already that would do the job.
Unfortunately there is no opportunity to co gen with my water cooled lister and use the heat from the coolant. There is a place I could locate it at the end of the house but it would be very close to the neighbors and I can see that would quickly become a point of contention. I don't think I could enclose it in a small enough building to fit where I'd want to put it. There are plans for an outdoor bathroom in that area and the engine would make it congested there and limit the open feel I want to get with the tropical feel bathroom. There is still the thing of running pipes to where the heat would be most wanted which is at the other end of the house.
In any case I don't think the heat output would be adequate but if it was turning a 3 phase genny, could supplement the AC. Might be able to trailer mount it all and make it mobile so it could be set in place in winter and removed in summer. Spose if it was all built onto a trailer it could be sound proofed but it would weight about 3/4 ton all up with engine, alternator, trailer etc. A lot for the Ride on mower to move as that's all that would fit round there, barely.
I think pretty much any of these would allow me to catch up on the power I use. That said, I was pretty frugal with the heating last winter and not always as comfortable as could have been. The big oil fired heater would make sure the place could be toasty warm all the time. Which is really what I want. Too old and tired to be trying to save power/ energy now or running round with 3 jumpers on. I want to be comfortable first and foremost.
the other thing here is it gets cold enough so the AC is pretty useless at the real cold times anyway. Falls off the curve and makes bugger all heat.
Oil is the way to go be it burned direct or in an engine as its reliable and can supply as much heat as I want.
None the less I do have some more panels to put up to hedge my bets but with winter fall off and orientation of the space left, I'm probably realistically going to be putting up 4 Kw of panels to get a Kw of generation back. Cost isn't the issue, I buy them used very cheap it's just the fact one is chasing ones tail with them in reality and then they are completely overkill in summer.
Wish I could find something to do with the excess power. Spa might be an idea for that reason alone.
Interested to hear what other people do to offset their winter power use and heat their homes as well as any thoughts or heads up on what I am thinking.