How much has been spent, year by year starting in 1970, by both the private 
sector and the US government on alternative energy research?

I think I may have found the information you're looking for.  Someone at the US 
Department of Energy pointed me toward a table which breaks down the Research 
and Development budget for fiscal years 1978-1999.  (The Department of Energy 
was created in October 1977).  These tables list R&D expenditures for each 
year, and also show the numbers for research into different types of energy.

Here is the first part of the table, covering the R&D budget for FY 1978 - 1988:
http://www.eia.doe.gov/cneaf/solar.renewables/rea_issues/reatabp1.html

This is the second part of the page, covering FY 1989 - 1999 (you can also see 
this one by clicking the "next page" link from the first part of the chart):
http://www.eia.doe.gov/cneaf/solar.renewables/rea_issues/reatabp2.html

If you want information on the more recent budgets, you can look here 
(the "budget highlights" document has renewable energy figures for 2001-2003):
http://www.eren.doe.gov/budget/

Unfortunately, I haven't been able to find information prior to 1978.  During 
the early part of the 1970's, energy research was being consolidated from a 
number of smaller regional agencies, first under the Atomic Energy Commission 
and then the short lived Energy Research and Development Administration (1974-
1977) which was the predecessor to the Department of Energy.  Because the 
research was not as centralized, and because the organizations which began to 
oversee it no longer exist, the budget data is very difficult to find.

Finally, although data on private sector energy R&D expenditures is difficult 
to find, I did find an analysis of US energy R&D programs.  Partway down the 
page is a graph showing both public and private investment in energy R&D since 
1974.  Unfortunately, the document doesn't specifically tell you how much of 
the R&D was in renewable and alternative energy sources, but it does illustrate 
the trend in energy research.

Here is the US energy R&D analysis:
http://energytrends.pnl.gov/usa/us005.htm

I hope this information is helpful!

Nice job.  While it doesn't go back as far as I'd hoped, the information that 
dscotton found is excellent and s/he deserves full marks.  Thank you!

Could you please clarify what you mean by alternative energy?  i.e., solar, 
wind, hydro-electric, all or none of the aforementioned?  Nuclear?  Thank you!

Although this does not answer your question, you may find it interesting. This 
page does a comparative review of alternative energies:
http://zebu.uoregon.edu/1996/ph162/review.html

Clarification: any source of energy except for fossil fuels.  So this would 
include the ones you mentioned (solar, wind, hydro); it would also include 
fusion.  It would not include natural gas.

-markm