Solar Cottage on an Island

Hello all.
I'm about 75% complete in the construction of a 1200 SQFT cottage on an Island. Solar is my only practical power solution and I am getting ready to make some purchasing decisions.
I have calculated my power requirements to be approximately 3000Wh per day (not including HVAC). This is completely feasible to be 100% solar with a generator backup.
However, I want to install a mini-split system which will consume 1300W of energy (230VAC) by itself. I have settled on the Fujitsu mini-split systems since they seem to have the highest efficiency on the market (29-33 SEER, depending on the unit).
The first solar reseller I spoke with recommended I run the HVAC completely from the generator (starting the generator only when the HVAC is calling for it). However, this is not possible according to Fujitsu since their compressor unit powers the wall unit (there is no way to divorce the control power from the main power from what I can see in their schematics).
It seems like the best method would be to tie the HVAC into my off-grid solar inverter. The HVAC controller does have a contact to which activates when the system is running. I could use this to tell the generator to start. Ideally, the inverter could then use this opportunity to charge batteries while the generator handles the load for the duration of the call for HVAC. When the HVAC shuts off, the generator shuts off and the system returns to battery-only mode.
Does anyone here have any advice on how to accomplish this? Or a better way to accomplish this?
Gary
I'm about 75% complete in the construction of a 1200 SQFT cottage on an Island. Solar is my only practical power solution and I am getting ready to make some purchasing decisions.
I have calculated my power requirements to be approximately 3000Wh per day (not including HVAC). This is completely feasible to be 100% solar with a generator backup.
However, I want to install a mini-split system which will consume 1300W of energy (230VAC) by itself. I have settled on the Fujitsu mini-split systems since they seem to have the highest efficiency on the market (29-33 SEER, depending on the unit).
The first solar reseller I spoke with recommended I run the HVAC completely from the generator (starting the generator only when the HVAC is calling for it). However, this is not possible according to Fujitsu since their compressor unit powers the wall unit (there is no way to divorce the control power from the main power from what I can see in their schematics).
It seems like the best method would be to tie the HVAC into my off-grid solar inverter. The HVAC controller does have a contact to which activates when the system is running. I could use this to tell the generator to start. Ideally, the inverter could then use this opportunity to charge batteries while the generator handles the load for the duration of the call for HVAC. When the HVAC shuts off, the generator shuts off and the system returns to battery-only mode.
Does anyone here have any advice on how to accomplish this? Or a better way to accomplish this?
Gary
Comments
KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
Sequence of operation:
1) Mini-split HVAC system is tied to inverter system drawing minimal power while it monitors room temperature and occupancy.
2) Mini-split HVAC system calls for cooling and commands the compressor to activate, drawing as much as 1300W. This event causes a contact closure on the HVAC.
3) Contact closure tells generator to start.
4) Generator takes over power delivery to the large HVAC load (and charges batteries).
5) Mini-split satisfies temperature requirement, shuts off compressor and contact closure opens.
6) Generator turns off and power is restored to battery-only mode.
The HVAC will draw between 500W and 1300W when active, and I don't plan to run this off of the batteries for more than a few seconds while the generator activates.
I appreciate any help that anyone can offer!
KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
Have you seen this Thread on this Forum?:
http://forum.solar-electric.com/forum/solar-electric-power-wind-power-balance-of-system/energy-use-conservation/23007-mini-split-update-for-offgrid
IMO, due to the way that Min-Split systems operate, looking to Generator Support for this function may not work well, because, generally the compressor can run for extended periods, but at fairly light loading. All depends on your situation. FWIW, Vic
That's a great thread. Read the whole thing after you linked me. Some interesting stuff there on WIFI control features now offered by some of the manufacturers (in addition to a great supplier with some excellent pricing).
I'm going to have to look into this "Generator Support" function that westbranch mentioned. From discussing more with some of the solar suppliers, it sounds like the "normal" mode of off-grid option will have the inverter automatically moving over to generator supply as soon as it sees load on the generator terminals (Magnum inverters), simultaneously allowing the inverter to go into charge mode to fill the batteries while the generator runs (this is what I want).
However, the solar charge controller will probably sense this high voltage at the battery terminals and go into maintenance mode, essentially throwing away any power being generated by the array during that time.
Despite the fact that it sounds like my approach will work, it still feels like there may be a more efficient way to run this system. I will put a post into that thread and see how others are driving their HVAC system.
Not exactly to your question, directly, but more to the point of how many Mini-Split Inverter-type A/C units operate.
The Inverter allows the amount of cooling required to vary the output of the compressor. This often means that the compressor runs for a long period of time, but at light loading. This means that the power needed to run the A/C can be quite small. It would make little sense to run the generator when the loading is light, and the PV or other RE energy is sufficient for the task.
Later, Vic
KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
Vic -
This is a good point. However, I believe upon arriving at the property the inside will be at a max temperature differential to the outside and both mini-splits will immediately turn on and go to maximum compressor output. This does beg the question for the control scheme. Maybe I need to bring the generator online only for the initial cool-down and then allow the battery system to take it from there. Perhaps I can monitor power to the mini-split and turn the generator on only when the loading exceeds X watts.
I will be using either the 15kW or the 6kW generac propane generator. Primarily because it makes for a nice looking permanent install that will not be as prone to theft and also because I am able to get about $2000 back (approx half the cost) on either of those through an incentive by the Propane council. I'm not a fan of propane, but I need it on site anyway for cooking and instant hot water.
Since this place is going to be unoccupied, I think you need to rethink some of this. Start small, what is the rush? Time can be a big help and providence often steps in and makes the thinking clear.
http://members.sti.net/offgridsolar/
E-mail [email protected]
The H3000 series ,and up, are electric start
KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
The 6kW is rated for lower noise level than the Honda inverter generator of equivalent size. However, although it is rated 10dB louder at full load, the 15kW is also a variable speed unit which idles the engine down at low loads (the 6kW Generac is constant speed). I've been thinking about this for a long time. Problem is, I'm doing my electrical wiring now and decisions must be made for electrical systems before I put up my knotty pine paneling on the interior.
I really don't know why I would do this since the Generac 6kw is rated for the same noise level as the equivalent Honda, is made for off grid applications, looks nice for a pad mounted permanent install, has a huge advantage on oil change intervals and has remote start out of the box. Oh, and with the incentive, it costs half as much.
That is a nice generator. I have a friend with one. Running noise is not objectional as far as generators go. His operates on propane.
If you search here forGenerac, I beleive you will see comments about contiuous use and off grid use are not covered for most of their products...
KID #51B 4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
West Chilcotin, BC, Canada
These ECOGEN products are specifically made for off-grid and they are warranted for that. However, they do NOT want you to use it for primary (continuous) power - only as part of an alternative energy off-grid system like solar or wind.
And that is why the Honda make just keeps running for decades! Change the oil and that is about it.
http://members.sti.net/offgridsolar/
E-mail [email protected]
I think the Honda wants an oil change at 50 hrs which isn't practical in my case at all. I could run enough for an oil change over a 3 day weekend!
Hope that you have the option to add considerably more PV to the system. Also hope that you are considering, carefully, the battery capacity for the system -- it is often difficult to just add some more batteries to a system, without tossing the first set.
It is just a personal taste thing, but, L O N G generator run-times can be very tedious. Realize that humidity may be an issue in your area, but expecting a genset to cycle a number of times per day can create maintenance issues.
Also, even it the 15 KW genset that you are considering is an Inverter model, this is still a large genset, and still seems over-sized, to me. Many inverter-generators are not really Variable Throttle designs, but really Stepped Throttle units, which reduces the of fuel savings.
Propane is not an efficient fuel for engines, but it is convenient, as it ages well, and can be delivered in large quantities ... wonder, on your island, just how the Propane will get into your tank ... does the Propane truck come over on a Ferry ?
Opinions, FWIW, Vic
For example:
http://gens.lccdn.com/generaccorporate/media/library/content/all-products/generators/home-generators/ecogen-series/15kw-6103/0k8466-c-15kw-ecogen-hsb.pdf
15kWatt Generac on Propane:
That is 1.32 Gallons per Hour for 50% to (roughly) 0% load... Can you "consume" ~7.5 kWatts from your genset for hours on end for fuel efficient operation? If you you only need a few kWatts, that is a lot of fuel for little amount of power.
-Bill
Bill:
I've been looking at these specs for some time. Why do you believe that this unit consumes 1.32g/h all the way down to 0% load? The 15kW is a variable RPM generator. I'm not an expert on these, just don't know how you jump to that conclusion.
I completely agree that buying the smallest generator would be the intuitive right choice for economy, but the 6kW Generac consumes significantly more propane at 6000W than this one does at 7500W. Having said that, The only time I will need this kind of power is when the battery charger is set to maximum charge level. Otherwise, I could get by with something less than 3000W including the HVAC.
- Other contributing factors to considering the 15kW: 1) It's nice to have the extra capacity when you need it one day. 2) The 15kW comes ready to supply 230V, while the 6kW requires a conversion kit - actually making the 6kW more expensive. 3) The 15kW is a newer design than the 6kW.
Vic-
I am the delivery mechanism for all things island related - including the propane. I will have to bring it over in 100# canisters (they hold about 24g of propane each). There will always be one in use and one on deck. Since I need propane for the stove and instant hot water heater, it seems like the obvious choice for a generator that won't have to run full time.
My usage on the island will be periodic. There for the weekend, gone for the weekdays, typically.
Sadly, even though PV systems are a perfect match for my needs, my 1.25 acre island is heavily wooded. I won't have perfect sunlight for the PV array. I'm even half considering putting my panels out over the water to escape the tree line.
Gary
It is hard for the rest of us to picture all of the details of anyone else's site.
A 15 KW genset is very large, compared to the rest of your system.
As BB Bill mentioned, it is very nice to have several genset options -- believe that was your plan, anyway.
We do not know about the rest of your system, like just what is your inverter, planned battery etc, and therefore the charger and charging needs that the genset will need to supply.
Again, the Inverter gensets that I have looked at are NOT really Variable Throttle -- they are Stepped Throttle, with about four plateaus. This somewhat reduces the fuel savings at partial-load on the genset.
You have the data, and you are the fuel transporter, and the endurer of any generator noise.
Gen Support would drive me NUTSo, but you know your sensitivities, and seems that, given the location/setting of the site, you do not have too many options.
Opinions, FWIW, Good Luck. Vic
http://www.centralmainediesel.com/order/7000-watt-propane-generator.asp?page=P7000
Attachment not found.
I agree your inverter/generator should use less fuel than a fixed RPM unit at lower power usage... Interestingly, at least for the smaller Honda eux000i family, they are probably a bit less efficient at full loads (the wild AC to AC inverter fixed frequency output conversion losses) vs fixed rpm units.
I wonder if Generac will send you a fuel consumption graph/data?
I just try to be very conservative--If the Generac 15kWatt is fuel efficient down to 25% of rating--That would be 3.75 kWatts...if you can maintain that as an average load--Then it may be a good match for you.
In any case is ~0.7 gph hour of propane "OK" for your needs?
-Bill
http://members.sti.net/offgridsolar/
E-mail [email protected]
I do hate the generator noise, however it seems like 53dB (the volume of a quiet conversation) would be tolerable, but I won't really know until I get there.
The solar system being recommended to me is: 12 panel system capable of 3,360W. 48V, 415Ah AGM battery bank and Magnum 4400W inverter which can do 230VAC.
I am in an area with about 4.2 sun hours which will be further reduced by the trees (which I don't want to cut down since they provide privacy and shoreline erosion protection).
The periodic use makes me hesitant to go crazy with a huge battery array (which I know I will have to replace in 5 years). I like the generator because I can start with that (alone) and then add the solar and convert the generator to serve as the backup system when batteries deplete.
Again, I'm here for the advice and other options from people who have done this already. My ideas may be completely misguided!
Bill:
The 6kW Generac is actually FIXED RPM. I'm guessing it follows your curve fairly closely. The 15kW is variable RPM from 2700-3600 RPM.
Generac will not provide ANY data not in their spec sheet. I tried everything - even calling their manufacturing site to speak with a design engineer. Their minions who answer the tech support line simply read the spec sheets back to you which isn't very useful...
If I do as I originally stated and use the generator simply to run the HVAC when it calls for operation, the generator will supply 1300W plus whatever the battery charger wants. My understanding is that the battery chargers will allow you to set a charging level based on the size of generator you have (so I assume I could get faster battery charging from a higher capacity generator).
Since I will have canisters of 24g of propane, 0.7g/h of propane would allow that canister to last for 34 hours of continuous runtime. I can probably live with that (but, of course, will not feel as happy about it when I have to lug another 100# tank onto the boat to replenish it!).
Gary