BP Solarex MST 50 MV

bpoint

I have four of these panels and would like to do a grid tie setup. I am not sure what inverter would work best, though. I attached the spec sheet from the back of one of the panels. When I checked the voltage from this panel it came back at 98 volts. I will hook them up in parallel. So, again, my question is what grid tie inverter would work best at this voltage?

BB.

Re: BP Solarex MST 50 MV

4x 50 watt panels = 200 watts...

That is a pretty small solar array for grid tied. And these are high voltage panels at Voc~100 volts.

I am not sure there is any practical GT solar inverter out there that will match the specifications of those panels.

About the only one I am aware of that may work is a SMA Sunny Boy 700 (~500 watt) GT inverter for $1,500. There is a "150 vdc" version that could work (Vmp-77 volts minimum?).

Personally, I would not use these panels and get current production panels that match a Enphase micro inverter or similar input requirements. Much more practical cost wise.

The other issue is the requirement for building department and utility permits/approval that would, typically, make it financially difficult to justify (could cost you 100's to 1,000's of dollars to meet the installations/paperwork requirements).

It is not legal to connect a GT inverter to your home's/business' wiring without approvals (and not all utilities will allow GT connections anyway).

Last issue, besides the right of a utility or building inspector to red tag/disconnect power to your home if they discover the installation--Many of the newer utility meters will not "turn backwards" if you pump excess power to the utility, may be reported for turning backwards by meter readers, or actually turn forward if you pump power back to the utility (charge you for pushing power back to the utility).

Obviously, if you use a lot of power, the meter will never turn backwards.

Your only other option with those 200 watts of solar panels is to purchase a "smaller" MPPT solar charge controllers (like this one) and charge a 12-48 volt battery bank. Use the DC power for emergency power/experimentation, or setup a small off grid AC inverter to power some AC loads. Not cheap either.

Morningstar TriStar 45 amp MPPT solar charge controller

Problem with those high voltage panels--if you want to add more panels later you will have to mix and match the Vmp/Imp voltage of those Voc~100 volts with more panels (such as ~Voc~33 volts; 3x panels in series) to add in with those existing panels. Could probably be done--but is even more difficult with odd-ball rated, out of production, solar panels.

-Bill

bpoint

Re: BP Solarex MST 50 MV

Thanks for the reply. I would like to expand this system at some point. For arguments sake, say I bought a larger inverter, one that would allow for future expansion. Could I put a charge controller like the Xantrex C40 on these panels to step them down to 12, 24, or 48 V and then feed them into an inverter that had another bank of newer, lower voltage panels?

icarus

Re: BP Solarex MST 50 MV

First, I don't think the C40 is a MPPT type controller, and therefore can't down convert. Second, you can't use a charge controller without a battery .

Tony

bpoint

Re: BP Solarex MST 50 MV

I looked on the spec sheet for the C40 and it said it would take up to 125 VDC. Maybe I am misunderstanding.

Yes, then a battery bank in between the controller and the inverter. I guess what would be easier is a voltage converter, but I haven't seen one that would step down from 100V to the 12, 24, 48 range.

Cariboocoot

Re: BP Solarex MST 50 MV

bpoint wrote: »

I looked on the spec sheet for the C40 and it said it would take up to 125 VDC. Maybe I am misunderstanding.

Yes, you are. The C40 is a PWM controller. The 125 VDC input max is a Voc rating, not Vmp. In other words, if you have a "48 Volt" nominal array where Vmp is 70 Volts Voc might be 80-90 Volts normally and could spike to 125 under certain conditions. It will not "down convert" the way an MPPT controller can.

Yes, then a battery bank in between the controller and the inverter. I guess what would be easier is a voltage converter, but I haven't seen one that would step down from 100V to the 12, 24, 48 range.

Actually buying an MPPT controller would be better, as it would adjust Voltage and regulate charge.

BB.

Re: BP Solarex MST 50 MV

A Vmp=88 volt panel on a 12 volt battery bank will only be about 12% efficient--the other energy would be lost with a C40 type PWM battery charge controller.

Lets backup a second... You are talking about wildly different "things" in these posts.

What is it that you would like to do--Such as:

• Have some solar panels and battery bank to run lights, small computer, and radio in emergency. With 12 VDC and 120 VAC
• Run a weekend cabin and a well pump on 120 VAC
• Emergency AC Power for my home.
• Emergency AC Power for my home + Turn my meter backwards.
• Reduce my electric bill because it is getting too expensive and not worry about black outs since they are so rare in my area (perhaps use a backup genset).

Each of the above is really a different solution--and each solution can be addressed in different ways.

-Bill

bpoint

Re: BP Solarex MST 50 MV

Oh, I see, Cariboocoot. Thanks for your reply. I really didn't want to have to deal with batteries at all, which is why I made the comment about the converter. I would rather just step the voltage down and feed it directly into the inverter, independently, so that if I wanted to expand it in the future it wouldn't be as challenging. I am obviously just cutting my teeth, and am trying to get some experience working with what I have, without throwing a ton of money at it.

BB

Reduce my electric bill because it is getting too expensive and not worry about black outs since they are so rare in my area (perhaps use a backup genset).

That is really all I want to do (reduce my bill a little, albeit only a few bucks) at this point. I have these four panels, and wanted to get a little experience with solar, ideally without batteries. Not sure I will be able to afford a big system. My home and office are connected, and have separate meters. I spend roughly $400-500/month right now between the two. I live in NH.
I know my return on investment won't be that great at this point, but it is zero on so many other things right now (e.g. cars, houses , xbox etc.) I currently have one of those SWEA inverters, but it only takes up to 52 volts, so didn't think I would be able to use it. I was hoping for a solution that wouldn't burn down my house, was relatively inexpensive, and have some flexibility for the future (the latter if I end up having to pony up for a new inverter, or some other setup).

Cariboocoot

Re: BP Solarex MST 50 MV

bpoint wrote: »

Oh, I see, Cariboocoot. Thanks for your reply. I really didn't want to have to deal with batteries at all, which is why I made the comment about the converter. I would rather just step the voltage down and feed it directly into the inverter, independently, so that if I wanted to expand it in the future it wouldn't be as challenging. I am obviously just cutting my teeth, and am trying to get some experience working with what I have, without throwing a ton of money at it.

"Throwing a ton of money at it" is pretty much the definition of solar. :roll:
Grid-tie inverters don't run on 12-24-48 Volts as a rule. The exceptions are the micro-inverter style (one panel, one inverter) or the hybrid type like the Xantrex XW series. The last one has to have a battery bank and charge controller et cetera. Normally you'd expect the panel Voltage to be 250-500 Volts for a GT unit.

You can reduce your electric bill with solar, but that doesn't mean you'll be saving money. In most cases it costs significantly more to produce a kW hour from solar panels than what you can buy it for from the grid. The money is better spent on conservation to begin with.

BB.

Re: BP Solarex MST 50 MV

Conservation will be your first goal... Get a Kill-a-Watt meter and/or a whole house meter for the larger equipment (AC, well pump, etc.).

If you have not done any conservation work before--it is possible you could save upwards of 1/2 your bill or more... It is probably not the big things (microwave, well pump, and such) that is costing you money--It may be the AC, TV, Lights, Refrigerators, computers and things that run 24x7 that are hurting you more.

-Bill

bpoint

Re: BP Solarex MST 50 MV

Bill and Cariboocoot,
I have done a fair bit with conservation, but I do live in an 1880 Victorian. I could replace all 40+ of the windows for $50K. I insulated the attic as best I could, but the walls and foundation could be improved. I put in a mod/con natural gas boiler at 90+efficiency two years ago. The AC could be improved, but I am spending around $400 on electricity without it. Honestly, the solar project was just supposed to be a fun diversion. We have had brain, heart and shoulder surgeries in my household in the past six months, and my mother moved in with us. We are through the worst of it all, knock on wood, and I was just looking for a little fun. Something new I could learn about. I had these panels that I picked up used 5 years ago, and just never got around to doing anything with them. Thought it made more sense to put them outside than keep them in the barn, but now that I have done that, it seems the options are limited. Yes, I could have thought this out better, but see above. Anyway, thanks for taking the time to reply.

BB.

Re: BP Solarex MST 50 MV

I have a ~70 year old salt box home that had virtually no insulation and single pane windows.

Insulated the walls and ceilings. And ours were simple double hung windows that I could replace from either the outside or inside of the home with a little wood work (and I am no carpenter) with standard double hung vinyl units.

Made a huge difference for our home (also put in some operating skylights in our home with double pane low E glass too to brighten up a couple dark areas and provide more ventilation). There is no wind through our home now-at all... And even though we have some warmer summer days with usually cooler nights--the home which used to always be too hot during the day can now be too cool at times (takes several hot days to warm up).

Our region does not usually use A/C--so we will live through a week or two of too hot weather a year.

We changed out about 19 windows and one set of double doors (I even did the garage windows too and insulated the garage).

The best bet for your setup--Possibly a 48 volt battery bank with the C40 and powering whatever smallish 48 Volt inverter or DC loads you can figure out.

Or get a good quality 45 Amp MPPT controller like the MorningStar version and you can then use a 12 volt battery bank and power DC loads directly and/or get a small 300 watt TSW inverter (this is a very nice one for these applications).

Here is a thread that talks about building a small emergency power system:

Emergency Power

The systems can be pretty simple, but using proper gauge wiring and fusing/breakers is important... Both to reduce the risk of fire and to keep voltage drop low (12 volt systems can only have about 1.0 volt drop maximum through wiring and fuses--need short/heavy copper wire to achieve that).

Sorry for your family's health issues... I understand the need for some sort of productive distractions.

Unfortunately, solar done right, is not usually very cheap. But it can be very reliable if done correctly and you have the correct expectations.

I will push the insulation bit again--That is usually about the best place to invest your money... Reduces your power bills forever more with no additional maintenance costs, reduces outside noise and dust, make the home much more livable, plus can actually add to the value of the home--unlike most solar projects which do not usually add to the value of home (or at best, a fraction of the installation costs).

-Bill

bpoint

Re: BP Solarex MST 50 MV

I have heard mixed results from people who have had their walls done here in NH. Many don't notice much difference in comfort or savings. If I was to do it, I think my best bet would be to do it from the outside with rigid foam insulation and re-clapboard. This is a serious investment, though, especially if I don't do it myself. The house is big, more than I would like to take on at this point. The windows, excepting a few, are all larger than standard and, therefore, more expensive, and not available off the shelf at Home Depot or otherwise. I have one area of flooring that is over a crawlspace that really should be insulated with closed-cell spray foam, but that would probably cost around $2-4K. I am spending about $3K on heat/year (natural gas) for around 5000 sq/ft. I have already piled tons into this place, (new roof, heating system etc). It's endless. The idea of making a profit at sale anytime in the next decade is not likely. We moved out here from SF in '99 and the thing that gets to me most is the heating expense. Oh, and I miss the restaurants.
Thanks for the excellent suggestions.

Sean

bpoint

Re: BP Solarex MST 50 MV

One thing I forgot to ask was that on the spec sheet, attached, for these Solarex panels it says nominal voltage (battery charging) 48V. What does that mean exactly?

BB.

Re: BP Solarex MST 50 MV

Panels with Vmp~70 volts are the proper voltage for charging a battery bank with a PWM charge controller (basically, hot panels will have their Vmp voltage fall, plus there is wiring and controller voltage drops too).

So--Yes, if you want to have a 48 volt battery bank and use a C40 charge controller--that is a valid and functional configuration.

Then you need to pick a 48 volt input inverter to go with your setup (if you want 120 VAC).

Remember that 200 watts of solar panels will not provide that much power (especially during periods of low amounts of sun)... A generic amount of power assuming 4 hours of full noon time equivalent sun per day minimum:

• 200 watts * 4 hours of sun * 0.52 over all system efficiency = 416 WH per day

The amount of charging current for a battery bank rule of thumb is around 5-13% of the battery's 20 Hour Amp*Hour capacity:

• 200 watts * 1/59 volts charging * 1/0.13 rate of charge * 0.77 solar panel derating = 20 AH @ 48 volts
• 200 watts * 1/59 volts charging * 1/0.05 rate of charge * 0.77 solar panel derating = 52 AH @ 48 volts

You could use larger than 54 AH battery bank, but you would then need to use Grid Power or a backup generator + AC battery charger to keep the bank properly charged.

Don't put a huge AC inverter on the system... Work out what loads you would like to run and then size the inverter for that...

For example a 30 watt laptop computer plus 11 watt lamp would run around:

• 416 WH per day * 0.85 eff inverter * 1/(30 + 11)watts = 10.2 hours per day

On a sunny summer day... During winter, you probably would get 1/2 to 1/4 that amount of time from the solar panels.

-Bill

bpoint

Re: BP Solarex MST 50 MV

I am now thinking of setting this up as a battery backup for my boiler. I already have a portable generator that has a line running from it to a Gentran transfer switch. The ideal would be to run power from whatever inverter I get through the same line from the generator to the switch. The plug to the generator is 4 prong. Is there a conversion from the three prong outlets, like on most inverters, to a 4 prong generator plug (three prong male to 4 prong female). I am not sure what the draw is on my boiler+pumps yet, so have to figure out if that will make it worth doing.

The other thing I was thinking was just getting a DC/DC converter like in the attached PDF and run it to the SWEA grid tie inverter that I have. Not sure that would work though/be worth it either. The first scenario would likely give more utility, I could also use it to keep car batteries charged. Or I could just give these panels to my friend that has six of the same ones. Then at least one of us would have something more functional.

BB.

Re: BP Solarex MST 50 MV

I would not bother with the DC/DC and SWEA setup--You are going to have a lot of losses with all the conversions (and the expenses of the hardware). You probably would never even break even on your power bill.

Guessing--it is possible that you are looking at a 120/240 VAC generator outlet?

Usually they also have 120 VAC outlets too.

If the genset is a 208/240 VAC 3 phase output--that is a different kettle of fish.

-Bill

bpoint

Re: BP Solarex MST 50 MV

I ended up getting the MorningStar 60 Amp MPPT controller. I think I will probably end up getting six more of these same panels from my friend. I am thinking maybe I should have gone with the SMA Sunny Boy 700 (~500 watt) GT inverter, but am committed now with the MPPT controller. Now trying to figure out what batteries to get etc. Have been reading through the Emergency Power link you gave, Bill. I wish I could set it up to charge a set of batteries and divert excess to the SWEA grid tie inverter that I have. I am guessing there is no easy way to do that? It wouldn't get me very far anyway since it only handles 250W.

I was going to use this wire to run from the panels to the charge controller. Still trying to figure out the batteries. and inverter.

raydias

Re: BP Solarex MST 50 MV

depending on how handy you are you could reduce your heating costs with solar space heating and hot water.

http://www.mobilehomerepair.com/article17solar.php

http://www.byexample.com/projects/current/batch_collector/

http://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm

would be more cost effective along with efficiency improvements.

bpoint

Re: BP Solarex MST 50 MV

Thanks, Ray. This one looks interesting: http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm
I don't have a lot of options for positioning something like this, though, at least in terms of its relation to my forced hot water heating system. Anyway, one project at a time