plan/estimated cost

Re: plan/estimated cost

Solar backed up power should be a neat way to do... However, (you know that there would be a however...) there are issues.

1. Solar power only pays for itself if the power it generates 365 days per year is used. If it is only used for 2 weeks per year, the costs "per kWhr" generated are 25x or more.

2. Solar usually needs to be backed up by battery, so you now have the maintenance and losses associated with a battery pack (not cheap).

3. Generators are cheap, and only use fuel when running. If you have a place to store the fuel for the runtime needed, they can be pretty cost effective.

4. Solar, usually needs a backup (three days of stormy weather and you are out of power). You might have a generator anyway.

5. Solar is expensive, so installations tend to be on the smaller side. For example, a 3kW peak GRID TIED system that can generate ~10-20+ kWhr per day (on a sunny day) is going to be somewhere between $20-$30,000 installed (not including batteries). And, you are not going to run much in the way of heavy loads (Airconditioning, electric heat, etc.).

6. A typical grid tied Solar PV panel system usually is connected for higher voltages (180-550 Vdc) than the typical battery backed Solar PV Chargers/Inverter systems (12-60 Vdc). So, it is, currently, difficult to even switch the panels from your main Grid Tied inverter to a small solar/battery backed system (as the main solar buss voltages are so different).

7. A quiet 2kW rated Honda Generator will cost you less than $1,000 and will use ~2-5 gallons (depending on load) of gas per day to power the same loads as a 3kW solar system or more (10-30 kWhr/day) rain or shine. Larger systems and Diesel generators can even be more efficient--less fuel or more kWhrs per gallon.

The least expensive method to install Solar PV panels is to install a Grid Tied inverter system. However, there are no batteries and it cannot run if the utility power is out.

You can install a different inverter system + batteries and get the advantages of a Grid Tied system (saving money by offsetting your utility power) and backup power via batteries/Solar-charging. But it will cost (very roughly) ~20%+ more to install, plus you will need to replace the battery pack every 7-15 years. And, unless you size it really large, it will not support A/C and other heavy electrical loads.

To figure out whether to go Solar and/or generator, you need to identify the minimum amount of power you need to have during the two weeks (or whatever) the power is out. If you need A/C (medical condition, climate), then generator is probably the way to go.

In any case, Solar or generator, conservation is going to be your friend. Changing lights to compact fluorescent fixture, insulation + double pane windows to keep the home comfortable, efficient refrigerator/washer/drier, electric ceiling fans instead of A/C, etc. is going to be a much better place to start spending your money. Usually, it will cost you less to save a kWhr of electricity than to purchase an extra kWhr worth of Solar PV Panels (and batteries, generator capacity/fuel, etc.) to power the "excess load".

-Bill

Re: plan/estimated cost

Hi Neil,

Yes, I agree with what you are saying... I have always assumed (maybe incorrectly) that a full grid-tied system with battery backup that could also sell power on the grid would be way-overkill, both in costs and complexity for somebody living in the city with pretty reliable power.

I was hoping to find a smallish high voltage compatible solar charger that I could use as a simple manual backup.

Use the Grid Tied inverter for the day in and day out usage... And a small charger controller (like an Outback MPPT 60 amp charger tied to a 320 Vdc nominal 10 amp set of panels) with a few storage batteries + inverter that can handle lights and maybe a refrigerator on a sunny day--less need for the generator. The backup system would have not be too expensive (or large or even particularly efficient) and I would have the efficiency of the larger Grid Tied inverter for the rest of the time.

I would just float the batteries with utility power for 99.9% of the time, and throw a DPST switch on the DC Panels when the power goes out.

For my area, the power is probably more likely to go out in nice sunny weather (like we did in 2000) or an earthquake (which is not weather related). So far--knock on wood--I know of only one time when we lost power for more than a a few hours due to weather--and that was ~50+ years ago (4-5 days--before I was born).

-Bill