Solar question

[nap61]

I am meeting with a solar salesman Friday to discuss a solar attic vent. I am also thinking about using solar on my well shed, which is on a secondary power line, as a backup (or as primary power). The well pump is 220 V.
What questions should I ask and what problems should I avoid.

Norm

 

[Carl_NH]

Norm,

Where are you located - it would seem the southwest for an attic vent? Does it freeze there?

Whats the orientation of your property - full sun? WHat is the HP of your pump? What is a secondary power line? Either you need water from the well or you have this as backup to city water?

Submersible pumps require at least 5KW or 5000 watts (for a 1/2 HP) and much more to run on a generator. Above ground pumps are usually 1/2HP also. Water pumps will require a large bank of cells and batteries to run IMO.

So provide some more detail like 1) depth of well, 2) is this a primary source of water 3) what is the existing system HP and depth. 3) what is your goal (probably the most important).

This will enable a more active and informed reply..

Carl

 

[AndyMA]

I am meeting with a solar salesman Friday to discuss a solar attic vent. I am also thinking about using solar on my well shed, which is on a secondary power line, as a backup (or as primary power). The well pump is 220 V.
What questions should I ask and what problems should I avoid.

Norm

There is a big difference between a grid connected system and a "off grid" system. In a grid connected system, you do not use batteries and output of the DC panels which is fed through an Inverter which converts the DC to AC has it's output voltage and frequency controlled by the voltage, frequency and phasing of the grid. Usually no batteries are involved.

In an off-grid system, the output of the panels which if you want AC is still fed through an inverter, but in that case, a charge controller and a bank of batteries are present.

An off grid system is quite a bit more expensive. I'm not sure how large your shed is but you may be surprised how many panels ($) are required to generate the power required to run the pump.

Calculate the power required by the pump by looking at it's name plate. P (watts) = V*I or using 746 watts per HP and then increasing watts needed by about 15% to cover efficiency losses. Also don't forget that being a motor there will be a substantial additional start up surge current required.

In an off-grid system, you also need to be concerned about power for days / times when the sun is not out and must size your battery storage system appropriately.

This is just a few of the points to consider when making the decision. of which way to go.

Also ask about state & federal rebates / incentives that might apply.

If you have any additional questions don't hesitate to ask.

Andy

 

[KTurner]

I am meeting with a solar salesman Friday to discuss a solar attic vent. I am also thinking about using solar on my well shed, which is on a secondary power line, as a backup (or as primary power). The well pump is 220 V.
What questions should I ask and what problems should I avoid.

Norm

I'm doing some research into it myself. I've not looked at the attic vents closely, but I've seen them around. I had the impression they were a self contained attic vent that needed no wires. just cut a hole and install it, but maybe there's more to it.

I'd be surprised if it was feasible to do anything with your well. You'd need a battery bank to store the energy. And either a pump that runs straight off your battery bank voltage (DC) or an inverter. If you want electric or solar, you'll need some sort of mechanism to switch between the two. If you're going through all that, why stop at just your well pump - do it to your house instead.

I'll probably start with a solar water heating system to replace the electric water heater we currently have, while leaving the current heater as a backup. If you're looking to save on your electric bills, you may want to look into these. I understand they have the best bang for your buck when looking to use solar to cut your electric bill. And there's no fancy electronics involved. Some people build the whole things themselves - the simple ones are really just plumbing.

Keith

 

[tommu56]

For the well pump the standard pumps with a current in rush on start is the killer!

Off grid usually use an more expensive pump with an AC drive in the pump to ramp it up slowly.

My grundfus pump was almost 2x the price of a standard pump its off grid not counting the battery's and inverter and panels. on grid will be cheaper in the long run (that is just my opinion).

 

[tcartwri]

You have to take into consideration the duty cycle of the pump. How many days you expect to be without power, and under what circumstaces. If you have to water livestock for example, the system would need to be fairly large. If it's just to flush toilets, and have drinking water, you really don't need very much at all.

For a short to moderate interuption of up to a few days, a battery bank and an inverter charger are all you need. No need for solar. To run a 1/2 Hp pump a 2500 Watt inverter should be fine. Unlike a genset, they have pretty huge surge capacity. Finding a split phase 120/240V inverter that's less than 4kW could be a problem though. A 4 kW inverter will run you about $2500.

If you do add solar, you should expect to pay about $2.40~$2.60 per Watt for the panels. An inverter charger, with solar panel inputs, becomes progressively more expensive.

 

[dmccarty]

I would be very curious as to the installed cost per watt.

In the last year or so I went looking for installed system costs per watt. The asking price was $8-10 for a grid tied system. Ya would think with a bad economy the real cost would be lower.

Also ask about total efficiency of the system. I have a Home Power issue some where that went through the pros/cons and costs of a small PV system. I think it was 5KW and grid tied. One thing that really shocked me was that the system was only 60% efficient. Meaning that you only got 60% of the power out of the outlets compared to the number of watts generated on the roof. That really surprised me.

The price for the system shocked me as well but I have been shocked about the system prices for years.

What I keep reading is that if you are grid tied, which is the cheapest way to go, but the power goes out, the PV power is also disconnected. So I would ask about this as well.

Later,
Dan

 

[tcartwri]

What I keep reading is that if you are grid tied, which is the cheapest way to go, but the power goes out, the PV power is also disconnected. So I would ask about this as well.

Later,
Dan

That is correct, and it is code. You can't energize the grid when there might be someone fixing the lines.

 

[dmccarty]

That is correct, and it is code. You can't energize the grid when there might be someone fixing the lines.

Which is perfectly reasonable and RESPONSIBLE. :laughing:

But one of the benefits of having a PV system would be to have at least SOME power if the grid goes down. There has to be a way to disconnect from the grid to allow the use of the PV system. I never see that mentioned when I read these articles.

We have a simple manual switch in the power panels. We can be on grid or we can be powered by the generator. Simple, cheap and effective. :thumbsup:

I would hope there is a way to work around the safety issue of PV power during a grid outage. Preferably a cheap solution. But I bet cheap ain't part of the solution. :laughing:

Since our OP is talking with the vendor today, said OP should ask since this seems to be one reason for his PV system.

Later,
Dan

 

[tcartwri]

There are auto switchers that sense the grid voltage. I think you can even buy them at Home Depot.

Grid tie Inverters have this feature built in. Off grid style do not.

 

[clemsonfor]

I am meeting with a solar salesman Friday to discuss a solar attic vent. I am also thinking about using solar on my well shed, which is on a secondary power line, as a backup (or as primary power). The well pump is 220 V.
What questions should I ask and what problems should I avoid.

Norm

The solar vents are just a fan that installs on your roof or you can get a gable one. But it has a built in fan on the roof version. Cut a hole and install it! No big deal, I think they can be had for around $100. AN easy install, if your paying a roofer to do it id imagine you can be out the door for $300?

Well house, thats different thats gonna take some juice batteries and pannels!

 

[AndyMA]

Which is perfectly reasonable and RESPONSIBLE. :laughing:

But one of the benefits of having a PV system would be to have at least SOME power if the grid goes down. There has to be a way to disconnect from the grid to allow the use of the PV system. I never see that mentioned when I read these articles.

We have a simple manual switch in the power panels. We can be on grid or we can be powered by the generator. Simple, cheap and effective. :thumbsup:

I would hope there is a way to work around the safety issue of PV power during a grid outage. Preferably a cheap solution. But I bet cheap ain't part of the solution. :laughing:



Since our OP is talking with the vendor today, said OP should ask since this seems to be one reason for his PV system.

Later,
Dan

As I said in my previous post Grid Tied systems set both there frequency and voltage by the inverter locking it to the grid it is tied to.

Most of the inverters that I am familiar with (and I have designed some) will not run unless there is a voltage on the grid.

If you want a systems that can run bot on and off grid, you will need to have it designed that way and probably have storage batteries.

Andy