It's easy to upgrade to Frontline's Analytic Solver products, which have much higher limits on both decision variables and constraints -- your Excel Solver model can be used as-is, with no changes. (Analytic Solver has all of our former Premium Solver capabilities, plus much more.) Before you reach the standard Solver's size limits, you may find that the solution process takes a long time. Click on this topic to learn about steps you can take to speed up the solution process. You can usually obtain much faster solutions with Frontline's Analytic Solver products.
The standard Microsoft Excel Solver has a limit of 200 decision variables, for both linear and nonlinear problems. The only way around this limit is to change your model so that some of the cells you have chosen as decision variables are removed from the By Changing Cells reference, and are held constant in the optimization process. To explore the consequences of varying the cells which are no longer determined by the Solver, you'll have to employ what-if analysis or other methods.
Frontline's Analytic Solver Upgrade product has a limit of 2,000 decision variables for linear problems, and 500 variables for nonlinear problems -- and it solves problems of this size in much less time. Analytic Solver Optimization (more info here) handles linear and quadratic problems of up to 8,000 variables, and Solver engines for Analytic Solver Optimization can handle problems of virtually unlimited size.