Reducing the grid load with solar...

[Doktor Jones]

I have a friend who lives in a (somewhat permissive) apartment complex... he's looking at a DIY solar option to help cut his electricity bill. He's looking at starting out with a 1KW system to power some of his electronics that he has running. He doesn't intend to go entirely off-grid, but would like a solar array to power some of his electronics (and ideally charge some deep-cycle batteries) while the sun is out, then when the sun goes away the batteries continue to feed the system for a while. Finally, if his power requirements drain the batteries before the sun is available again, he would need the system to switch back onto the grid (without interrupting power to the devices).

Is building this sort of system plausible? If so, where would he get started, and what sort of components would he need? He was looking at a set of five 12V 200W cells... to minimize the necessary size of the transmission line, I was wondering if it'd be possible to run the cells (and therefore batteries) in series, for 60V @ ~17A max -- how feasible/practical would this be?

Attached is a diagram of what sort of setup he'd like to accomplish, in case my description wasn't terribly clear

 

[nsaspook]

Your friend would need a MPPT charge controller to convert the ~60V PV to something a battery bank could use. In the US a (legal) grid-tie system in a apartment would be almost impossible in most locations but a off-grid secondary power system is possible but not very cost effective. The best way to save money is with conservation, efficient appliances/devices and knowing what your loads are. The first thing to do is buy a KillAWatt meter to see how much power each device uses. Use this data to make a plan on what needs to be replaced or not used.

I'm not saying don't do it but the breakeven point on a small system vs the utility cost of power is something you have to take a serious look at.

 

[Doktor Jones]

Yes, he'd initially looked at a GTI, but that's not feasible since the landlord draws the line at molesting the building (or its wiring) directly

Would something like this work? I'm thinking he could start with that, and only four solar cells (48V, 800W)... and charge a 48V battery bank. If that works, then he would need a 48V inverter, and the switching system. Any suggestions on that?

Cost effectiveness isn't too much of an issue at this point, he's currently just trying to turn theory into practice, and if it works is contemplating a larger-scale investment that will provide much better ROI. As far as conservation, he has a lot of computer equipment that he can't turn off (servers, data processing, etc), which is why he's looking to cut back on his grid usage; it's as much for environmental purposes as anything else

 

[nsaspook]

That controller (morningstar) would work but you will also need a utility charger to top off your batteries or keep them charged when there is little sun, you can buy a combined inverter/charger for this. Because this is indoors, flooded lead acid batteries are out, AGM/Gell batteries rated for RE use would be a good choice for the bank. **broken link removed**
A inverter with a utility transfer switch can handle the switching needs. https://www.electro-tech-online.com/custompdfs/2011/11/Spec_Sheet_ST2000-148.pdf

You can run the calculations but in this case I don't see a need for a 48 volt DC system unless you need 2kW+. The morningstar controller can down-convert up to 150 volts DC to a lower battery voltage of 12-24-48.

I have an on going DIY R&D solar off-grid project that I plan to build into a retirement home in a few years at the 4 to 5 Kw power level.

http://www.flickr.com//photos/nsaspook/sets/72157622934371746/show/
http://code.google.com/p/solar-monitor/

 

[tcmtech]

The most practical solution is to do a honest cost Vs savings over a realistic time frame analysis.

If your energy saving system cost more than what the electricity costs over the realistic life time of the the components plus their related maintenance costs over their expected life time it should be obvious that its not practical or remotely realistic!

Now if you have money to burn along with the time and reasons to want to experiment with the concept then you can spend what you want and do as you please despite the more than likely reality of it never paying for itself in any rational cost avoidance savings over what would get put into it.

 

[nsaspook]

Grid-tie is the only method that will have a breakeven point under 10 years. Practical systems can convert PV power directly to grid power at >90%. The losses in conversion to chemical energy and back to electrical energy with a battery based system means that you're lucky to be at >60% when all factors are accounted for.
It is pretty cool to be able to run an air conditioner, tv, etc... directly from solar and have some electrical power if nature attacks like what happened in Conn. this October with people without power for 10 days and no gas for generators after a few days.

 

[Doktor Jones]

Now if you have money to burn along with the time and reasons to want to experiment with the concept then you can spend what you want and do as you please despite the more than likely reality of it never paying for itself in any rational cost avoidance savings over what would get put into it.

This, mostly

 

[bryan1]

Well where you talk about a 48 volt array and everything that goes with that said array probably the best one could do is move out of that apartment block and get out in the real world then not only a better lifestyle but one will find where they thought they need 15Kwhours a day just to live was way over the top.

Sheesh on a hot summers day when the power goes out we get friends around with young kids as when the sun is full on and it's a tad windy I'm making that much power I just dump it into an aircon. When it is 45C in the shade with less than 10% humidity it can be a killer for the poor grid dwellers and yet 10 years ago the same crowd were asking if we lived in a cave as we are off the grid....

OK go price up for a 48 volt array

solar panels say 15-20K
48 volt inverter 10+K
decent charge controller say 2-3K
sparkie to come and install it all -- your grandkids

As you can see being on the grid and wanting to 'be green' isn't that glossy when the real facts come in. People over went on mass to put solar panels on their roof's at great expense due to a so called govt rebate( which brought out all the scum to cash in). now we have a carbon tax coming the govt has said the solar rebate scheme will end. so how many 10,000's of people have gone into debt but still have a contract to supply power......

Solar is great for off grid array's but if folks think solar is great for on grid do the sums and you will find the breakeven point is long after the solar panels life span.

GO GREEN AND PUT IN GRIDTIE SOLAR............ THE BIGGEST SCAM IN MODERN TIMES

 

[Doktor Jones]

Well where you talk about a 48 volt array and everything that goes with that said array probably the best one could do is move out of that apartment block and get out in the real world then not only a better lifestyle but one will find where they thought they need 15Kwhours a day just to live was way over the top.

You don't know what San Francisco is like, do you ? Apartments are all there are, pretty much, unless you're pulling in a mid-six-figure income. Technology is my friend's life, and his job, friends, and hobbies are all in SF, so leaving SF is not an option.

Solar is great for off grid array's but if folks think solar is great for on grid do the sums and you will find the breakeven point is long after the solar panels life span.

GO GREEN AND PUT IN GRIDTIE SOLAR............ THE BIGGEST SCAM IN MODERN TIMES

Perhaps you missed the part where I said he DOESN'T want to tie into the grid? Or the part where I said he's not doing this for the cost savings?

 

[Nigel Goodwin]

Perhaps you missed the part where I said he DOESN'T want to tie into the grid? Or the part where I said he's not doing this for the cost savings?

Unfortunately tying in to the grid is by FAR the most sensible and best method, you don't need masses of expensive and short lived batteries to try and store the energy.

 

[Sceadwian]

Or the part where I said he's not doing this for the cost savings?

What's the point then? On this kind of scale it would be difficult if not impossible to measure the environmental impact the reduced draw on the grid would take. I'm with Bryan1, if he's honestly hot about making a difference then the solution is simple, use less! Do without! Change the habits. It's the only way realize any true lessening of environmental impact.

 

[bryan1]

G'day Dr Jones,
Well you say ya mate lives in an apartment which I would imagine it would be in a multi level building. Now where would be the space to mount the PV panels externally to get the maximum exposure on a southerly direction. A 48 volt array is generally used for large off grid installations and the cost is way up there. OK if your mate does want a off grid array then a 24 volt array would make sense. All of those big pv panels are rated at 24 volts so by say getting 2 0ff 175 watt ones and mounting them in parrallel, then say get some decent deep cycle batteries to make up 250AH array ( at a min). Then all that will be needed is a charge controller to stop the batteries being over charged. 24 volt inverters are a heap cheaper but even with a 250 ah array and only 350 watts of PV a ongrid charger will be be needed to ensure the batteries are charged properly.

I'll explain our setup which has been going on now for close to a decade.

14 off of those 90 watt Kaneka high voltage panels all mounted in parrallel going into a Outback FM60 MTTP controller
2 off 175 watt 24 volt panels directly mounted to the batterybank.
12 off 600AH sonnenschein 2 volt deep cycle batteries in series.
SA32 Selectronics Pure sinewave inverter
80 amp ultra smart traction batterycharger ( think souped up forklift charger)

That array cost us 17K back in 2002 and the only problem I had was the original MPPT died so we got the FM60 under insurance.

Fridges working off inverters can be a big killer for batterybanks so if the grid is around it does make sense to leave fridges connected. most other appliances will work fine but it all comes down to how the array is setup. What if one doesn't get any sun for a week or so, if batteries are left to drain to a real deep cycle they won't last long at all.

My advise would be start small and learn but have that said small array capable of being upgraded with more solar and more batteries. So that would mean buying a decent 24 volt inverter and always check on the idle current power draw.( Both of my 24 volt inverters have less than a 6 watt power drain). If one does want to use a MPPT then by putting the panels in series and programming the MPPT to suit the array is the way to go.

Like I said above deep cycle batteries will last a long time if looked after and for a 24 volt array the cutoff should be set at 23 volts min. Keeping the battery specs for charging is also needed so have a real good read about deep cycle batteries and learn what they do require.

I do apologize if I came over rough in my first post, but wanting to be grid independent is a disease and only gets worse over time so getting it right first time can bring a lot of enjoyment that can last a long time or it can all go wrong and leave the wallet empty......

Cheers Bryan

 

[SirSparks]

Unfortunately tying in to the grid is by FAR the most sensible and best method, you don't need masses of expensive and short lived batteries to try and store the energy.

12 Kwhr of Trojan deep cycle batteries for $900 and a life span of nearly 3,000 daily cycles (at 25% discharge ) or 8 years, is NOT what I call short lived expensive. That's what I have and my system rocks!