To what extend, exactly?
In the past years the price for solar panels have come down considerably. At present day the numbers are promising a highly lucrative return.

( Wikipedia is the source)

I have been interested in renewable energy technologies from a youth and to this day have experimented with solar panels and models that could see( not their yet) a suburb or town completely running on renewables without changing habits.

So far I have gone from a "spinning wheels" concept to a heated salt that has an extreme ability to retain heat, while being inexpensive. Currently this salt is used at, Solar farms where the heat of sunlight is concentrated on a single spot. Like so...

This is PS20 and PS10( Wikipedia is the source)

Obviously is this not the thing you want in your backyard. It's kinda big. What I'm referring to is photovoltaic solar cells. These are expensive in comparison however in recent years have become more... lucrative...

Let me explain. Via my Country South-Africa as an use case.
Facts to be noted.

1. South-Africa is a sunlight rich country.
2. Our Currency ZAR is subject to change( often) Currently hovering at R13.4 for each 1USD
3. We are an coal rich nation and use coal as our main resource to generate electricity.
4. Our Electricity bills are on a scale like income tax...
5. We largely import photovoltaic cells from abroad. And yes it is a long ride.(South-Africa)

Currently this is the numbers, should I wish to install a 3Kw/h solution.
An 1unit or 1kw/h measured is currently just shy of R2 or 0.15USD
My store I tend to look at.
http://www.gwstore.co.za/product/solar-kit-1-3kw-grid-tied-system/
12 x Renesola 250wp Premium Grade Solar Modules **see notes
1 x Solar World Sunplug 3.0 – 3kW Grid Tied Inverter ** see notes
1 x GW High Voltage Single String Combiner Box
1 x Set roof mounts ** see notes
1 x Set MC4 connectors
1 x 50m x 4mm Suncable
1 x 20Amp AC Circuit Breaker and mini DB box
Notes – all components denoted with ** see notes, are interchangeable for either higher quality units, different brands or 3 phase instead of single. In the case of roof mounts, the selection is based around using galvanized hot dipped rails or aluminum sun rails. A grid limiter is also available for users with prepaid meters.

All of this for R58,149.31 or 4339 USD. Excluding labour this could be another R10000(746USD) depending on transport location etc and I'm over exaggerating with labour. I guess this could change a lot based your country.

So for a total of R68,148.31(est) or 5085 USD you could be the new owner of 3Kw/h when the sun shines. Also I chose the grid tied version. This allows your local electrical provider to provide electricity during night times etc.

So lets do the "Investment grade math"
First we need to assume an daily sunshine hours.
So In South-Africa we could easily assume 11 avg throughout the year.
Now for the math:
311365.25=12053.25Kw
The value of these units at 1.8( to make sure it's profit) is R21,695.85 or 1619.09 USD...

This equates to an annual return of 31.8%!

Now something the remember. This is a saving only if you use on avg 3Kw or more continuously during Daylight, should you use less you would save less...

This is excellent for Companies and those resorts that need's some "Going green" status while making it worth their while. What stock or broker could undeniably give you an 30% annual return on investment?

So who is buying solar panels tomorrow? Just remember to do your homework and take into account where you live(Obviously the arctic circle might not be ideal...)